啓介 田﨑, 明 中務, and 伸雄 小林, “Morphological Analysis of Bristle-Flowering Cultivars with Narrowed Vase Morphology in R. Macrosepalum Maxim.,” Journal of the Japanese Society for Horticultural Science, vol. 81, no. 1, pp. 72–79, 2012.
doi: 10.2503/jjshs1.81.72.
P. I. Ahmad et al., “Influence of Different Treatments and Techniques on Rooting Behaviour of Rhododendron Arboreum Sm. In Indian Himalayas,” Acta Ecologica Sinica, vol. 41, no. 4, pp. 332–335, Aug. 2021.
doi: 10.1016/j.chnaes.2021.01.001.
Rhododendron arboreum Sm. a wild flowering tree is on the verge of extinction from natural habitat due to overexploitation of its flowers and slow regeneration rate. The objective of this research was to explore the effective method for propagation of this species vegetatively, therefore, to maintain its genetic identity and population. In this context, effectiveness of vegetative propagation methods like FRI-Wire Technique and Air Layering in combination with root promoting hormones such as Indole 3- Butyric Acid (IBA), Indole Acetic Acid (IAA) and Napthelene Acetic Acid (NAA) at concentration of 1000 ppm (ppm), 2500 ppm and 5000 ppm each were evaluated through well designed experiments. Air Layering method failed to produce roots on this species, whereas, FRI-Wire Technique showed a remarkable success for rooting in the month of April with hormones IAA and NAA at 1000 ppm and 2500 ppm concentrations and no response from IBA. Branch sizes of length 45–51 cm, when treated with 2500 ppm IAA concentration performed significantly better and produced 66.66% rooting in comparison to other treatments with the technique.
M. S. Akhalkatsi, N. V. Togonidze, G. G. Arabuli, N. W. Goginashvili, and W. K. Smith, “Birch Forest and Rhododendron on North-Facing Slopes in Central Greater Caucasus,” p. 14.
Subalpine timberline in the Central Greater Caucasus is birch forest on north-facing slopes in 1800-2300 m a.s.l. of the Kazbegi region of Georgia. Subalpine forest is as Betula litwinowii, B. pendula, B. raddeana, and other trees and shrub species. B. litwinowii was occurs only this species of birches and its reaches in treeline at 2300-2550 m and associated with the shrub, Rhododendron caucasicum on north-facing slopes. Recent hypotheses are on climate and soil surface with ECM and ENM fungi. Seeds of B. litwinowii and R. caucasicum were germinated to laboratory. Seed germination was in Petri dishes with determination of temperature. Soil was coming from 1-5 sites of Kazbegi which have these ECM species and B. litwinowii seeds have been germinated on different soils of the 1-5 sites. Seed germination of R. caucasicum needs to determine ENM species with microscope. Seed germination and seedling development were defined as follows: imbibition, germination, growth and seedling. Temperature revealed highest germination. Soils are with ECM to 2254 m and number of species determines of tree height. Seed bank analysis has shown that the number of seeds of birch, rhododendron and other plant species varies significantly in different sites of timberline and treeline. B. litwinowii is tetraploid (2n=56) and it is collected with treeline at 2553 m. Treeline are contacted by shrubs and R. caucasicus are on north scopes. This activation of seed germination is for B. litwinowii with ECM mycorrhizal species. We suppose that seed germination requirements of studied species determine their distribution patter in natural environment.
R. Almeida, S. Gonçalves, and A. Romano, “In Vitro Micropropagation of Endangered Rhododendron Ponticum L. Subsp. Baeticum (Boissier & Reuter) Handel-Mazzetti,” Biodiversity & Conservation, vol. 14, no. 5, pp. 1059–1069, May 2005.
doi: 10.1007/s10531-004-8413-3.
In vitro propagation of Rhododendron ponticum L. subsp. baeticum, an endangered species present in limited and vulnerable populations as a Tertiary relict in the southern Iberian Peninsula, was attained. Several cytokinin:IAA ratios and a range of zeatin concentrations were evaluated for their effect on shoot multiplication from apical shoots and nodal segments. The type of cytokinin and the origin of the explant were the most important factors affecting shoot multiplication. The highest shoot multiplication rate was obtained from single-nodal explants on medium supplemented with zeatin. Increasing zeatin concentration promotes shoot multiplication independently of explant type, although this effect tends to decrease with higher zeatin concentration. Shoot growth was higher in apical shoots and it was not stimulated by the presence of auxin. A number of experiments were conducted to identify suitable procedures for rooting of in vitro produced shoots. The best results in terms of in vitro rooting were obtained with Anderson’s modified medium with macrosalts reduced to one-half, regardless of the auxin or its concentration in the medium. Although rooting frequency rose to 97% by basal immersion of shoots in auxin concentrated solution followed by in vitro culture on an auxin-free medium, the survival of the plants after 6 months of acclimatization was poor (50%). Best results (100% rooting and survival) were observed for ex vitro rooting. The micropropagated plants from this study were successfully reintroduced into their natural habitat (87% of survival after 8 months).
R. M. N. T. Amarasinghe, J.-H. Wang, W.-X. Xie, L.-C. Peng, S.-F. Li, and H. Li, “Seed-Sterilization of Rhododendron Wardii for Micropropagation,” Sri Lanka Journal of Food and Agriculture, vol. 4, no. 1, pp. 9–14, Oct. 2018.
doi: 10.4038/sljfa.v4i1.51.
The Sri Lanka Journal of Food and Agriculture (SLJFA) is a publication of the Sri Lanka Council for Agricultural Research Policy (SLCARP) of the Ministry of Agriculture, Government of Sri Lanka.
F. Belleau and G. Collin, “Composition of the Essential Oil of Ledum Groenlandicum,” Phytochemistry, vol. 33, no. 1, pp. 117–121, Apr. 1993.
doi: 10.1016/0031-9422(93)85406-H.
The composition of the essential oil of Ledum groenlandicum Retzius was investigated. This oil was obtained by steam distillation (hydrodistillatio
T. E. Bilderback, L. Q. Thomasson, and P. R. Fantz, “‘Carolina Spring’ Rhododendron,” HortScience, vol. 27, no. 4, pp. 378–379, Apr. 1992.
doi: 10.21273/HORTSCI.27.4.378.
F. Blazich, S. Warren, J. Acedo, and W. Reece, “Seed Germination of Rhododendron Catawbiense and Rhododendron Maximum: Influence of Light and Temperature,” Journal American Rhododendron Society, vol. 45, no. 3, 1991.
M. H. Brand and R. Kiyomoto, “Redevelopment of Tissue Proliferation Symptoms in Rooted Rhododendron Cuttings,” HortScience, vol. 34, no. 4, pp. 723–726, Jul. 1999.
doi: 10.21273/HORTSCI.34.4.723.
Tissue proliferation (TP) of Rhododendron sp. is characterized by basal tumors that often develop into numerous dwarf shoots. Growers need to know if the TP condition will recur in plants grown from normal-appearing cuttings collected from plants with TP tumors. Stem cuttings of seven cultivars were collected from stock plants with TP [TP(+)] and without TP [TP(–)] and rooted. Plants were grown in containers outdoors for 2 years and were then evaluated for tumor formation and other TP-related morphological symptoms. Shoots of TP(+) plants were either similar in length to shoots of TP(–) plants, or were shorter, as was the case for ‘Boule de Neige’, ‘Catawbiense Album’, and ‘Montego’. Plants grown from TP(+) cuttings of all cultivars had more leaves per growth flush than did plants grown from TP(–) cuttings. ‘Holden’, ‘Montego’, and ‘Scintillation’ TP(+) leaves were narrower than leaves from TP(–) shoots and had greater length: width ratios. Leaves of TP(+) ‘Montego’ and ‘Scintillation’ plants were shorter and smaller than leaves from their TP(–) counterparts. Tumors were not observed on any propagated plants, regardless of the TP status of cutting stock plants. To further test the influence of age and TP status of source plants used for cutting propagation, ‘Montego’ plants were grown from cuttings collected from the following sources: 1) in vitro shoot cultures; 2) 3-year-old plants with TP; 3) 6-year-old plants with TP; and 4) TP(–) plants. Cuttings from TP(+) micropropagated plants less than 3 years old were more likely to develop tumors than were cuttings from older plants. Eighty-three percent of plants from microcuttings and 74% of plants from cuttings of 3-year-old TP(+) plants formed tumors, whereas no plants grown from 6-year-old TP(+) or TP(–) cuttings did so. Large tumors that surrounded half or more of the stem were more likely to develop on plants grown from microcuttings than on plants grown from the next youngest, 3-year-old TP(+), stock plants. Growers must be aware that cuttings from TP(+) plants may produce plants that exhibit morphological and growth abnormalities, possibly even including tumor redevelopment.
B. A. Briggs, S. M. McCulloch, and L. A. Caton, “In Vitro Propagation of Rhododendron,” Acta Horticulturae, no. 364, pp. 21–26, May 1994.
doi: 10.17660/ActaHortic.1994.364.1.
Rhododendron is the most abundant genus in the Ericaceae family, consisting of over 1000 species that are native to North America, Western Europe, and Northern Asia. With certain Rhododendron varieties being desirable due to flower color or bloom time, propagation of these shrubs is of increased interest. Micropropagation is a technique of multiplying small plant explants, or cultures, in a sterile environment. The overall goal of this study was to improve established micropropagation protocols to increase explant survivability and shoot growth of native deciduous Rhododendron in vitro. The specific objectives were: 1) to evaluate fungicide media amendments to increase shoot survivability; 2) to investigate fungal contamination found in micropropagation systems for endophytic associations; and 3) to investigate alternative hormones and container sizes for increasing shoot production. For the first objective, five native deciduous Rhododendron nicknamed varieties were established in fungicide amended media. Shoot survival and bud production in each variety was recorded for all fungicide-amendments over 31 days in culture. Thiophanate-methyl-amended media was shown to significantly increase survivability and bud production in four of these varieties. To address the second objective, 20 fungal isolates were identified and analyzed for potential endophytic associations. Of the 20, two isolates were identified from genera Alternaria and Trichoderma, both known for endophytic activity within Rhododendron. For the third objective, Thidiazuron hormone ratios and container sizes were tested in five Rhododendron varieties. Change in explant weight, shoot proliferation, and shoot elongation was evaluated over a 4 week culture period. Shoot performance was significantly improved with the addition of 4.4-8.8 ppm of TDZ stock solution and larger test tube sizes compared to the control.
I. Bruni et al., “Genetic Variability of Relict Rhododendron Ferrugineum L. Populations in the Northern Apennines with Some Inferences for a Conservation Strategy,” Plant Biosystems - An International Journal Dealing with all Aspects of Plant Biology, vol. 146, no. 1, pp. 24–32, Mar. 2012.
doi: 10.1080/11263504.2011.557093.
In this study, the genetic diversity of three Rhododendron ferrugineum L Apennine populations (AP1, AP2, and AP3) was analyzed and compared to three populations of the Maritime Alps and six populations of Central-Eastern Alps. Genetic variations across microsatellite markers revealed that the Apennine populations show some clonal individuals and the lowest genetic diversity values (AP1 and AP3 A[18] values are 2.46 and 2.31, respectively), as well as heterozygosity deficiency with respect to the Alpine populations. Genetic relationships among populations (Nei’s genetic distance) showed that populations from the Central-Eastern Alps and from the Maritime Alps clustered in two separate groups. Unweighted pair group method with arithmetic averages as well as PCA analysis showed a clear separation of the three Apennine populations according to the high FST values detected (AP1–AP2 = 0.427; AP1–AP3 = 0.446; AP2–AP3 = 0.325). Mantel test revealed a significant correlation between genetic and geographical distance matrices (r = 0.314, P = 0.001, 999 permutations). Concerning the relationship between Apennines and alpine population, PCA analysis showed a clear genetic similarity among Maritime Alps populations and individuals of AP1 population. Considering the geographical and ecological peripheral condition of these populations and the high impact of the climatic changes on their habitat, we suggest the combination of in situ and ex situ conservation strategies to preserve the genetic diversity of this species in the Northern Apennines.
M. Cantos, J. Linán, J. García, M. García-Linán, M. Domínguez, and A. Troncoso, “The Use of in Vitro Culture to Improve the Propagation of Rhododendron Ponticum Subsp. Baeticum (Boiss. & Reuter),” Open Life Sciences, vol. 2, no. 2, pp. 297–306, Jun. 2007.
doi: 10.2478/s11535-007-0018-x.
Rhododendron ponticum subsp. baeticum is endemic in the southern region of the Iberian Peninsula. The relict populations of this species are vulnerable, due mainly to difficult conditions for the establishment of seedlings, resulting in a virtual lack of sexual recruitment. In order to preserve the surviving populations, in vitro culture methods have been applied for both the sexual and the agamic propagation of the species. The in vitro germination of seeds was high when conducted with Anderson’s medium without plant growth regulators. The self-rooted seedlings obtained were easily transplanted to outside conditions. The presence of growth regulators in the medium interfered with the development of the seedlings, causing heavy callus formation. The in vitro growth of explants took place readily in Anderson’s medium plus 0.072 mg L−1 of BA and 0.036 mg L−1 of NAA although the explants did not form roots. Rooting was achieved by the basal dipping of the explants in hydroalcoholic solutions of 500 mg L−1 IAA during the outside transplanting process. Therefore, the combination of in vitro grown explants together with ex vitro rooting, results in a good method for the agamic propagation of Rhododendron ponticum subsp. baeticum.
K. S. Choi, K. S. Song, D. E. Koo, H. N. Lee, H. I. Sung, and J. J. Kim, “Characteristics of Seed and Germination of Rhododendron mucronulatum by Collection Dates and Germination Temperatures,” Journal of Korean Society of Forest Science, vol. 107, no. 3, pp. 237–244, 2018.
doi: 10.14578/jkfs.2018.107.3.237.
본 연구는 우리나라 자생수종인 진달래(Rhododendron mucronulatum Turcz.)의 열매 및 종자의 특성을 조사하여 종자를 통한 대량번식 기술의 기초자료를 확보하고자 실시하였다. 진달래 열매는 강화군 고려산(435 m)에서 2013년 8월 26일, 9월 5일, 9월 12일, 10월 4일에 각각 채취하였다. 채취된 종자의 발아 온도 실험은 5, 10, 15, 20, 25, }30\^{∘}C{에서 실시하였다. 열매의 함수율은 2013년 9월 5일 채취 열매에서 54.5%로 가장 높았으며, 채취일자에 관계없이 열매의 종자개수는 91.3~116.3개였다. 종자의 길이는 10월 4일 채취 종자에서 }1947.4{μ}m{, 폭은 9월 12일에서 }727.3{μ}m{로 가장 컸다. 발아율은 종자의 채취시기에 관계없이 }25\^{∘}C{에서 높았으며, 9월 12일 채취한 종자에서 27.3%로 가장 높았다. 한편, 채취시기와 관계없이 5, 10 및 }30\^{∘}C{에서는 전혀 발아가 되지 않았다. }T_{50}{과 평균발아일수는 온도가 높아질수록 짧아지는 경향을 보였으며, 발아균일도는 채취시기가 늦을수록 낮아지는 경향을 보였다. 발아속도는 }25\^{∘}C{에서 가장 빠른 것으로 조사되었다. 본 실험의 결과를 종합해 볼 때 진달래 종자의 적정 채취시기는 9월 12일~10월 4일 경이며, 적정 발아 온도는 }25\^{∘}C{인 것으로 판단된다. This study was carried out in order to secure basic data of seedling mass propagation technique of Rhododendron mucronulatum which is the native tree species of Korea by surveying the characteristics of its fruit and seed. The fruits were collected at Mt. Goryeo in Ganghwa-gun on different dates in 2013; August 26th, September 5th, September 12th, October 4th. The seed germination test was carried out at 5, 10, 15, 20, 25 and }30\^{∘}C{. Moisture content of the fruit was highest (54.5%) in the fruit collected on September 5th. Number of the seeds in a fruit was 91.3 to 116.3, regardless of the collection date. Seed length was highest (}1947.4{μ}m{) in the seeds collected on October 4th and seed width was highest (}727.3{μ}m{) in the seeds collected on September 12th. Germination rate of the seeds was highest at }25\^{∘}C{ regardless of the seed collection date, which showed the highest value(27.3%) in the seeds collected September 12th. Meanwhile, the seeds were not germinated not at all at 5, 10 and }30\^{∘}C{. }T_{50}{ and mean germination time of the seeds got shorter at the higher temperature. Germination uniformity got lower when the collection date got later. Germination speed of the seeds was fastest at }25\^{∘}C{. According to the results of this study, it seems that the appropriate time to collect fruit and seed is between September 12th and October 4th, and the appropriate temperature for the seed germination is }25\^{∘}C{.
L. Dai et al., “Multiple Biological Activities of Rhododendron Przewalskii Maxim. Extracts and UPLC-ESI-Q-TOF/MS Characterization of Their Phytochemical Composition,” Frontiers in Pharmacology, vol. 12, 2021.https://www.frontiersin.org/article/10.3389/fphar.2021.599778.
Backgroud:Rhododendron przewalskii Maxim. is an evergreen shrub that is used as a traditional medicine in China. However, the modern pharmacology and the chemical components of this plant has not been studied. In this paper, we aimed to investigate the antifungal, anti-inflammatory and antioxidant activities and underlying mechanism of its aqueous and ethanol extracts, and analyze their chemical composition and active compounds of R. przewalskii.Methods: The antifungal activity was determined in vitro, and anti-inflammatory and antioxidant activities and underlying mechanism of its aqueous and ethanol extracts were evaluated in vitro and in RAW 264.7 cells. The chemical composition were analyzed using UPLC-ESI-Q-TOF/MS, and the contents of six compounds were determined via HPLC.Results: Both extracts of R. przewalskii showed promising anti-inflammatory activity in vitro; decreased the production of four inflammatory cytokines, namely, nitric oxide, IL-1β, IL-6 and TNF-ɑ, in RAW 264.7 cells induced by lipopolysaccharide; and exhibited weak cytotoxicity. The extracts significantly scavenged DPPH radicals, superoxide radicals and hydroxyl radicals to exert antioxidant effects in vitro. The two extracts also exhibited cellular antioxidant activity by increasing superoxide dismutase and CAT activities and decreasing malondialdehyde content in RAW 264.7 cells induced by LPS. However, the antifungal activity of the two extracts was weak. Nine flavonoids were identified by UPLC-ESI-Q-TOF/MS. Of these, six compounds were analyzed quantitatively, including avicularin, quercetin, azaleatin, astragalin and kaempferol, and five compounds (myricetin 3-O-galactoside, paeoniflorin, astragalin, azaleatin and kaempferol) were found in this species for the first time. These compounds demonstrated antioxidant activities that were similar to those of the R. przewalskii extracts and were thought to be the active compounds in the extracts.Conclusion:R. przewalskii extracts presented promising anti-inflammatory and antioxidant activities. The extracts contained amounts of valuable flavonoids (8.98 mg/g fresh material) that were likely the active compounds in the extract contributing to the potential antioxidant activity. These results highlight the potential of R. przewalskii as a source of natural antioxidant and anti-inflammatory agents for the pharmaceutical industry.
E. Daly, “Achieving Effective Rhododendron Control by Investigating Novel Methods of Forest Vegetation Management,” PhD thesis, Waterford Institute of Technology, 2014.https://repository.wit.ie/2949/.
In Ireland one of the most serious invasive alien species which poses a threat to local biodiversity, particularly to our native woodlands, is Rhododendron ponticum L.. Rhododendron was first introduced to Ireland during the 19th century as an ornamental garden plant and has since become an established invasive species throughout Ireland. Rhododendron has also, in recent decades, become a significant management issue in plantation forests throughout Ireland. This study sets out to improve our understanding of the auto-ecology and invasion dynamics of rhododendron in Irish forests and to investigate control options to inform future rhododendron management plans. The study was divided into three broad areas. The first study sought to investigate the efficacy of a recently discovered Irish isolate of the fungal pathogen Chondrostereum purpureum as an inhibitor of rhododendron and Betula pendula (birch) sprouting in Ireland. The treated stumps were monitored for fungal colonisation and adventitious sprouting for the ensuing 18 months. The results demonstrated that a combination of mechanical cutting and the subsequent application of C. purpureum is not an effective method of vegetation management for either rhododendron or birch. As a successful primary invader, rhododendron is often found in areas when recent land management activities have taken place. Disturbed substrate coverage and the absence of predators provide rhododendron with optimum regeneration conditions. Many land management practices (particularly in a forestry situation) expose soil. To assess how the disturbance of vegetation relates to successful rhododendron establishment the degree to which the depth of substrate affects the germination of rhododendron seeds was tested. This second study demonstrated that even small decreases in forest litter depth, sufficient to expose bare substrate, facilitates rhododendron seedling establishment. The third study set out to investigate whether the prevention of grazing of native scrub species in woodland sites could be used to prevent the spread of rhododendron. The findings to date suggest that fencing does increase the survival of native scrub species birch and Ilex aquifolium (holly). Also of note, in some of the plots, the holly and holly/ birch mix have successfully suppressed the re-growth of rhododendron. In conclusion, rhododendron has become a huge problem in plantation forest habitats and in order to control it effectively and economically an integrated pest management strategy will have to be employed utilising a mixture of novel bio-controls, innovative management strategies exploiting weaknesses such as seed longevity, viability and litter depth, and ensuring that other plant species can compete free of grazing pressures.
In Ireland one of the most serious invasive alien species which poses threats to local biodiversity is Rhododendron ponticum L. Once established on a susceptible site, R. ponticum can kill other plant species in the ground vegetation layer and prevent the regeneration of trees and shrubs, thereby also indirectly affecting the local fauna. Forest floor litter negatively impacts on the germination success of many plant species, and both the amount and distribution of forest litter can influence the establishment of invasive alien species. Many land management practices, particularly in forestry, disturb ground cover leading to soil exposure, which may increase the risk of R. ponticum invasion. In this study, the effect of forest floor litter on the germination of R. ponticum seeds in five different litter types was assessed. The treatments included bare soil; 1 cm, 3 cm and 5 cm depths of broadleaved litter; and 2 cm conifer litter depth. The results showed a clear relationship between litter type and seed germination success with seeds having poorer success rates in deeper forest litter. This study demonstrated that even small decreases in forest litter depth, sufficient to expose bare soil, facilitates R. ponticum seedling establishment. These findings will inform guidelines and standard operating procedures for future forest management plans, particularly in areas that are sensitive to R. ponticum invasion.
N. Davidson, “Micropropagation of Heritage Rhododendron Collections at the Royal Botanic Garden Edinburgh,” Sibbaldia: the International Journal of Botanic Garden Horticulture, no. 17, pp. 189–200, Feb. 2019.
doi: 10.24823/Sibbaldia.2019.274.
The most recent efforts at micropropagation of Rhododendron species started at the Royal Botanic Garden Edinburgh in 2013. This paper outlines the methods and practices adopted, and highlights some of the problems and pitfalls encountered throughout the process. At the close of 2017 the first plants propagated using in vitro techniques were planted at Benmore Botanic Garden in Argyll, Scotland.
B. Davison, “Reports - Australian Rhododendron Groups,” The Rhododendron, vol. 52, pp. 7–12.
doi: 10.3316/informit.020237962801281.
K. Dehnen-Schmutz and M. Williamson, “Rhododendron Ponticum in Britain and Ireland: Social, Economic and Ecological Factors in Its Successful Invasion,” Environment and History, vol. 12, no. 3, pp. 325–350, Aug. 2006.
doi: 10.3197/096734006778226355.
Rhododendron ponticum is the most expensive alien plant conservation problem in Britain and Ireland. It was introduced in the eighteenth century, probably in 1763 from Spain, and was then described as a not fully hardy plant. It was expensive to buy. It was made hardier by artificial and natural selection and by hybridisation with Appalachian and other Rhododendron species. It is easy to propagate and became cheap and popular in the mid and late nineteenth century as an ornamental, for game cover and as a root stock for other ornamental rhododendrons. The lowest price was in about 1880 by which time it had escaped widely. The escapes were ignored by botanical recorders for over 50 years. It was scarcely recognised as a problem until between the two world wars. Major control projects date from the second half of the twentieth century.
K. Dokane, L. Mertena, D. Megre, and U. Kondratovics, “Changes in Photosynthetic Parameters During Graft Union and Adventitious Root Formation in Cutting Grafts of Rhododendron Subg. Hymenanthes,” Acta Horticulturae, no. 990, pp. 457–464, May 2013.
doi: 10.17660/ActaHortic.2013.990.59.
K. Dokane, M. Lazdane, and U. Kondratovics, “Endophytic Fungi - Development and Colonization of Roots of Elepidote Rhododendron Cuttings,” 2012, pp. 15–17.https://elibrary.ru/item.asp?id=29658491.
Roots of 2 years old rooted cutting of elepidote rhododendron cultivar «Lavanda» and leaf-bud cuttings during adventitious root formation were studied for root endophytic fungi. Roots of rooted cutting were colonized by mycor rhizal fungi forming coils typical to ericoid mycorrhiza. Both stems and roots of leaf-bud cuttings were studied. Arbuscules and coils forming fungi were present in stem cortex of leaf-bud cuttings. At the end of the experiment hyphal coils were detected also in roots of cuttings. These results indicate that mycorrhizal fungi are present in rooting substrate and probably colonization of adventitious roots takes place already in primordial state. Further studies are necessary
F. Du and W. Lv, “Rapid Reproduction Technology System of Rhododendron Dauricum — Selection of Medium and Explant,” in 2011 Second International Conference on Mechanic Automation and Control Engineering, 2011, pp. 2410–2413.
doi: 10.1109/MACE.2011.5987468.
A rapid reproduction method of Rhododendron dauricum was studied in this paper.The result shows as follows: the basic medium is WPM; the optimal sterilization of explants is with 1.5-2cm long stem or apex; the best surface sterilants is 70% alcohol 30s and 0.1%HgCl2 10 min; the best season for picking the experiment material is between the middle of March and May.
D. Dufour et al., “Antioxidant, Anti-Inflammatory and Anticancer Activities of Methanolic Extracts from Ledum Groenlandicum Retzius,” Journal of Ethnopharmacology, vol. 111, no. 1, pp. 22–28, Apr. 2007.
doi: 10.1016/j.jep.2006.10.021.
Labrador tea (Ledum groenlandicum Retzius) is an ericaceae widely distributed in North America. The leaves and twigs were used in Native American traditional medicine to treat several inflammatory pathologies such as asthma, rheumatisms and burns. Reactive oxygen species as well as reactive nitrogen species such as nitric oxide (NO) contribute significantly to these pathologies. In this study, the antioxidant, anti-inflammatory and anticancer activities of crude methanol extracts of leaves and twigs from Ledum groenlandicum were investigated. Both extracts showed a strong antioxidant activity using the ORAC method and a cell based-assay. Moreover, the twig and leaf extracts showed significant anti-inflammatory activity, inhibiting NO release, respectively, by 28 and 17% at 25 microg/ml in LPS-stimulated RAW 264.7 macrophages. In comparison, N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, reduced NO release by 24% at 25 microg/ml. The twig extract was also found to be active against DLD-1 colon carcinoma and A-549 lung carcinoma cells, with IC(50) values of 43+/-1 and 65+/-8 microg/ml, respectively. The bioguided study of the twig extract resulted in the isolation and identification of ursolic acid, a known triterpene. Ursolic acid was active against DLD-1 (IC(50): 9.3+/-0.3 microM) and A-549 (IC(50): 8.9+/-0.2 microM), suggesting it is, in part, responsible of the anticancer activity of the twig extract.
F. Dunemann, R. Kahnau, and I. Stange, “Analysis of Complex Leaf and Flower Characters in Rhododendron Using a Molecular Linkage Map,” Theoretical and Applied Genetics, vol. 98, no. 6, pp. 1146–1155, May 1999.
doi: 10.1007/s001220051179.
A molecular linkage map of Rhododendron has been constructed by using a segregating population from an interspecific cross. Parent-specific maps based on 239 RAPD, 38 RFLP, and two microsatellite markers were aligned using markers heterozygous in both parents. The map of the male parent ‘Cunningham’s White’ comprised 182 DNA markers in 13 linkage groups corresponding to the basic chromosome number. In the female parent ‘Rh 16’ 168 markers were located on 18 linkage groups. An assignment of putative homologous linkage groups was possible for 11 groups of each parent. QTL analyses based on the non-parametric Kruskal-Wallis rank-sum test were performed for the characters “leaf chlorosis” and “flower colour” scored as quantitative traits. For leaf chlorosis, two genomic regions bearing QTLs with significant effects on the trait were identified on two linkage groups of the chlorosis-tolerant parent. RAPD marker analysis of additional lime-stressed genotypes tested under altered environmental conditions verified the relationship between marker allele frequencies and the expression of chlorosis. Highly significant QTL effects for flower colour were found on two chromosomes indicating major genes located in these genome areas. The prospects for utilization of a linkage map in Rhododendron are discussed.
T. Eeckhaut, J. Van Huylenbroeck, S. De Schepper, and M. C. Van Labeke, “Breeding for Polyploidy in Belgian Azalea (Rhododendron Simsii Hybrids),” Acta Horticulturae, no. 714, pp. 113–118, Sep. 2006.
doi: 10.17660/ActaHortic.2006.714.13.
T. Eeckhaut, K. Janssens, E. De Keyser, and J. De Riek, “Micropropagation of Rhododendron,” in Protocols for In Vitro Propagation of Ornamental Plants, S. M. Jain and S. J. Ochatt, Eds. Totowa, NJ: Humana Press, 2010, pp. 141–152.
doi: 10.1007/978-1-60327-114-1_14.
Methods for in vitro initiation and multiplication and general culture practices of Rhododendron are presented. Also acclimatization procedures are described. Protocols for callus, shoot, and root induction are described. Several protocols for breeding applications are highlighted in more detail.
T. Eeckhaut, G. Samyn, and E. Van Bockstaele, “In Vitro Polyploidy Induction in Rhododendron Simsii Hybrids,” Acta Horticulturae, no. 572, pp. 43–49, Feb. 2002.
doi: 10.17660/ActaHortic.2002.572.4.
K. J. Elliott and J. M. Vose, “Age and Distribution of an Evergreen Clonal Shrub in the Coweeta Basin: Rhododendron Maximum L.,” The Journal of the Torrey Botanical Society, vol. 139, no. 2, pp. 149–166, 2012.https://www.jstor.org/stable/41678790.
Rhododendron maximum L. is an evergreen, clonal shrub that forms a dominant sub-canopy layer and is a key species in southern Appalachian forests. We investigated the age and distribution of R. maximum across the Coweeta Basin, a 1626 ha watershed in western North Carolina. We selected 16 perennial, second-order streams and used a Global Positioning System to establish site boundaries and map the coverage of R. maximum across the hillslopes from stream to ridge. In each site, three transects from stream edge to the ridge were used to measure diameters of overstory trees (> 2.5 cm dbh), tree saplings (< 2.5 cm dbh) and shrubs including R. maximum stems. Along each transect, we cut cross-sections of R. maximum ramets and extracted increment cores from nearest neighbor trees to determine ages. The 16 sites ranged in size from 0.3 to 1.9 ha depending on the distance from stream to ridge. Rhododendron maximum cover ranged from 25 to 100% and ages ranged from 6 to 120 years. Rhododendron maximum establishment year showed a skewed unimodal distribution with the peak establishment occurring between 1928 and 1940. Although the R. maximum age and distance-from-stream relationship was statistically significant, the relationship was not meaningful as distance-from-stream only explained 2.6% of the variation in R. maximum age (r 2 = 0.026, P = 0.0003, n = 487). Distance from stream only explained 4.2% of the variation in overstory tree age (r²= = 0.042, P = 0.0015, n=237). It appears that R. maximum has not expanded upslope over the last 100 years; rather the ranges in sizes and ages suggest that ramets are recruiting under established R. maximum canopies particularly in the wetter, near stream locations.
A. Erfmeier and H. Bruelheide, “Comparison of Native and Invasive Rhododendron Ponticum Populations: Growth, Reproduction and Morphology under Field Conditions,” Flora - Morphology, Distribution, Functional Ecology of Plants, vol. 199, no. 2, pp. 120–133, Jan. 2004.
doi: 10.1078/0367-2530-00141.
The objective of this paper is to identify the factors that promote the invasiveness of Rhododendron ponticum L. by the means of comparative field observations. Rhododendron ponticum (Ericaceae) is an evergreen shrub with a natural distribution in the Mediterranean and Black Sea area and was introduced to the British Isles in 1763. Thenceforward, the species has been considered as a major threat to natural ecosystems there. We compared native and invasive populations of Rhododendron ponticum with respect to trait patterns that are associated with invasiveness. Six populations each in the natural part of its range, in Georgia (Caucasus) and Spain as well as six invasive ones in Ireland were examined with regard to biometrical, morphological and ecological characteristics. Invasive Irish populations differed from non-invasive ones mainly in growth patterns and showed much higher rates of annual shoot growth in the field and higher rates of seedling recruitment. In contrast, native Spanish populations were discriminated by their shape and age; whereas native Georgian rhododendron, above all, showed distinctive leaf characteristics. In general, the relationship between Irish and Spanish populations was closer than to the Georgian ones. Our results suggest that both genotype and environment account for the trait pattern found in Irish populations. Differences in genetically fixed traits had a greater effect in morphological differences to Georgian provenances. In contrast, the invasive Irish rhododendron were favoured by a more benign environment than the Spanish populations.
A. Erfmeier and H. Bruelheide, “Invasibility or Invasiveness? Effects of Habitat, Genotype, and Their Interaction on Invasive Rhododendron Ponticum Populations,” Biological Invasions, vol. 12, no. 3, pp. 657–676, Mar. 2010.
doi: 10.1007/s10530-009-9472-x.
The extent and nature of biological invasions are mainly influenced by either the genotype of the invading species, the suitability of the new habitat or by genotype-habitat interactions expressed in adaptations to the new environment. The relevance of these factors was assessed for the invasive evergreen shrub Rhododendron ponticum. Habitat characteristics of soil, climate and community properties were analysed in six native populations in both Georgia (Caucasus) and Spain and in six invasive ones in Ireland. Growth variables of rhododendron individuals and seedling occurrences in the field served as response variables. We performed a reciprocal transplant experiment with rhododendron cuttings and determined survival of transplants in all countries. Due to low survival rates in Georgia and Spain, vegetative increase was only analysed for Ireland. The Irish sites benefited from significantly higher nutrient supply than the Spanish and Georgian sites. We found both strong positive correlations of nutrient supply and negative correlations of seasonal temperature amplitude with growth variables of shoots and seedling density. Origin, target site and interaction effects were significant in the survival of transplanted rhododendron individuals. The Irish site was more favorable for all genotypes, but the invasive genotypes did not perform better than the native ones. The total increase in shoot length of transplants in Ireland was highest in the Irish genotypes, which might suggest adaptation of the Irish populations to their new area. In conclusion, we found evidence for invasiveness of Irish Rhododendron ponticum populations, but only in the invaded habitat. Nonetheless, habitats in the new range also seem to be well suited to native Spanish populations, supporting the idea that invasibility of these new sites also contributes to rhododendron invasion success.
A. Erfmeier and H. Bruelheide, “Invasive and Native Rhododendron Ponticum Populations: Is There Evidence for Genotypic Differences in Germination and Growth?,” Ecography, vol. 28, no. 4, pp. 417–428, 2005.
doi: 10.1111/j.0906-7590.2005.03967.x.
Previous studies have shown that the invasive spread of Rhododendron ponticum in the British Isles is influenced by the more favourable environmental conditions in the new territory than in the species’ home range. In this study, we asked whether the species’ invasion success might also involve a genotypic background for higher growth and germination rates in invasive populations. We tested the hypotheses that invasive populations have higher absolute germination rates, germinate faster and exhibit higher growth rates. We present data from greenhouse and climate chamber experiments with seed material and Rhododendron cuttings from six populations each of native Georgian, native Spanish and invasive Irish populations subjected to different temperature environments. There were no differences in the maximum germination rate and optimum germination temperature between native and invasive origins. We found significant differences in germination velocity with the Irish seeds responding most rapidly to all germination treatments. Accordingly, in the growth experiment the invasive Irish origins had the highest relative growth rates in all environments tested. Our results provide evidence for a genetic shift in invasive populations towards an increased investment in growth and towards a faster germination rate. Both traits would contribute to explaining this species’ range expansion. The underlying evolutionary mechanisms for this shift are discussed, including the possibility of hybridisation or of an ecological release from hitherto experienced constraints in the native area.
N. Escaravage, S. Questiau, A. Pornon, B. Doche, and P. Taberlet, “Clonal Diversity in a Rhododendron Ferrugineum L. (Ericaceae) Population Inferred from AFLP Markers,” Molecular Ecology, vol. 7, no. 8, pp. 975–982, 1998.
doi: 10.1046/j.1365-294x.1998.00415.x.
In the European Alps, Rhododendron ferrugineum can constitute dense populations with almost 100% of cover. The developmental pattern by layering and the resulting complexity of population structure make it difficult to identify distinct clones even by excavation. Therefore genotypic structure of a R. ferrugineum population, in the French Alps, was inferred from AFLP markers. In a first step, we analysed 400 samples using AFLP profiles generated by one selective primer pair. Seventeen bands out of 25 were polymorphic (68%). We identified a total of 32 multilocus genotypes. In a second step, the 32 genotypes were verified by applying two additional primer pairs to the two most distant samples from each genotype. The mean similarity (proportion of band sharing) between pairs of clones was 0.85 (range from 0.52 to 0.94). The spatial distribution of clones showed that vegetative spreading mainly occurred down a slope. Based on an annual shoot mean growth of 2.6 cm/year and the size of the widest clone, we estimated the age of the oldest individual to be at least 300 years. A single genotype can occupy a large surface and sometimes form a dense patch, suggesting that this species adopts a phalanx growth form with limited intermingling of some genets.
N. Escaravage and J. Wagner, “Pollination Effectiveness and Pollen Dispersal in a Rhododendron Ferrugineum (Ericaceae) Population,” Plant Biology, vol. 6, no. 5, pp. 606–615, Sep. 2004.
doi: 10.1055/s-2004-821143.
Thieme E-Books & E-Journals
N. Escaravage, E. Flubacker, A. Pornon, B. Doche, and I. Till-Bottraud, “Stamen Dimorphism in Rhododendron Ferrugineum (Ericaceae): Development and Function,” American Journal of Botany, vol. 88, no. 1, pp. 68–75, 2001.
doi: 10.2307/2657128.
The function of stamen dimorphism in the breeding system of the alpine shrub Rhododendron ferrugineum was studied in two populations in the French Alps. This species has pentameric flowers with two whorls of stamens: an inner whorl of five long stamens and an outer whorl of short stamens. We studied the development of stamens from buds to mature flowers (measurement of the filament, anther, and style lengths at five successive phenological stages) and compared the size and position of reproductive organs at maturity in control and partially emasculated flowers (removal of long-level stamens) to determine whether the presence of long-level stamens constitutes a constraint for the development of the short-level ones. Stamen dimorphism can be observed early in stamen development, from the bud stage of the year prior to flowering. At this early stage, meiosis had already occurred. Emasculation of the long-level stamens induced the short-level ones to grow longer than in normal conditions. We also performed seven pollination treatments on ten randomly chosen individuals in each population, and the number of seeds following each treatment was recorded. Results from these treatments showed that R. ferrugineum produced spontaneous selfed seeds in the absence of pollinators. However, no seed was produced when short-level stamens were emasculated and pollinators excluded, suggesting that long-level stamens are not responsible for selfing in the absence of pollinators and that reproductive assurance is promoted by short-level stamens.
T. L. Ettinger and J. E. Preece, “Aseptic Micropropagation of Rhododendron P.J.M. Hybrids,” Journal of Horticultural Science, vol. 60, no. 2, pp. 269–274, Jan. 1985.
doi: 10.1080/14620316.1985.11515628.
Shoot tips established in vitro better than single nodes. Five-cm shoot tips gave better Stage I results than 2-cm shoot tips. The best microshoot proliferation rates were obtained with isopentenyladenine (2iP) at 5 and 10 mg l−1; tetrahydropyranyl-benzyladenine was ineffective. Microshoots rooted well, regardless of the level of 2iP in the Stage II medium. Stem-cutting-macropropagated plants generally were more variable in height, had less basal branching and were more erect than plants from microculture.
W. H. Gensel and F. A. Blazich, “Propagation of Rhododendron Chapmanii by Stem Cuttings,” Journal of Environmental Horticulture, vol. 3, no. 2, pp. 65–68, Jun. 1985.
doi: 10.24266/0738-2898-3.2.65.
Two experiments were conducted to determine the feasibility of propagating Chapman’s rhododendron (Rhododendron chapmanii A. Gray) by rooting stem cuttings. In the first experiment, semi-hardwood terminal cuttings taken from native plants, rooted in moderate percentages (43 to 63%) with the percentage of commercially acceptable cuttings (cuttings having a distinct root ball) being less (22 to 53%). The second experiment used hardwood terminal and subterminal cuttings taken from containerized stock plants that originated from cuttings rooted in the first experiment. Percent rooting for total and commercially acceptable cuttings ranged from 81 to 94% and 39 to 64%, respectively. For both experiments, indolebutyric acid (IBA) treatments resulted in an increase in the percentage of commercially acceptable cuttings.
M. P. N. Gent, “Long-Term Effects of Triazol Growth Regulators on Stem Elongation of Rhododendron and Kalmia,” HortScience, vol. 32, no. 3, pp. 436E–436, Jun. 1997.
doi: 10.21273/HORTSCI.32.3.436E.
The persistence of effects of paclobutrazol or uniconazol on stem elongation was determined for several years after large-leaf Rhododendron and Kalmia latifolia were treated with a single-spray application of these triazol growth-regulator chemicals. Potted plants were treated in the second year from propagation, and transplanted into the field in the following spring. The elongation of stems was measured in the year of application and in the following 2 to 4 years. Treatments with a wide range of doses were applied in 1991, 1992, or 1995. For all except the most-dilute applications, stem elongation was retarded in the year following application. At the highest doses, stem growth was inhibited 2 years following application. The results could be explained by a model of growth regulator action that assumed stem elongation was inversely related to amount of growth regulator applied. The dose response coefficient for paclobutrazol was less than that for uniconazol. The dose that inhibited stem elongation one-half as much as a saturating dose was about 0.5 and 0.05 mg/plant, for paclobutrazol and uniconazol, respectively. The dose response coefficient decreased exponentially with time after application, with an exponential time constant of about 2/year. The model predicted a dose of growth regulator that inhibited 0.9 of stem elongation immediately after application would continue to inhibit 0.5 of stem elongation in the following year.
M. P. N. Gent, “Persistence of Triazole Growth Retardants on Stem Elongation of Rhododendron and Kalmia,” Journal of Plant Growth Regulation, vol. 16, no. 4, pp. 197–203, Dec. 1997.
doi: 10.1007/PL00006996.
Triazole growth retardant chemicals may inhibit stem elongation of woody ornamental species for several years after application. Potted plants of large-leaf Rhododendron catawbiense and Kalmia latifolia were treated with a single spray application of paclobutrazol or uniconazole in the 2nd year from propagation. They were transplanted into the field the next spring. The elongation of stems was measured in the year of application and in the next 2–4 years. Treatments with a wide range of doses were applied in 1991, 1992, or 1995. For all except the most dilute applications, stem elongation was retarded in the year after application. At the highest doses, stem growth was inhibited for 2 years after application. The results were fit to a model of growth regulator action which assumed that stem elongation was inversely related to the amount of growth regulator applied. For paclobutrazol, the dose per plant that inhibited stem elongation half as much as a saturating dose was tenfold that for uniconazole, about 0.5 and 0.05 mg, respectively. For both chemicals, the dose-response coefficient decreased exponentially with time after application, with an exponential time constant of about 2 year−1. A dose of growth regulator which reduced stem elongation by half immediately after application would only inhibit 12% of stem elongation the next year. However, a tenfold greater dose would result in less than half the stem elongation of untreated plants in the next year.
C. T. Glenn, F. A. Blazich, and S. L. Warren, “Secondary Seed Dormancy of Rhododendron Catawbiense and Rhododendron Maximum,” Journal of Environmental Horticulture, vol. 17, no. 1, pp. 1–4, Mar. 1999.
doi: 10.24266/0738-2898-17.1.1.
Seeds of Rhododendron catawbiense Michx. (Catawba rhododendron) and Rhododendron maximum L. (rosebay rhododendron) were germinated at 25C (77F) or an 8/16 hr thermoperiod of 25/15C (77/59F) with constant light after imbibed seeds were maintained in total darkness for 0, 9, 18, 27, 36, 45, 54 or 63 days at the same temperatures. Maintenance of imbibed seeds of R. catawbiense in darkness at 25C (77F) for up to 63 days caused no induction of secondary dormancy while induction occurred for seeds in darkness at 25/15C (77/59F). When imbibed seeds of R. catawbiense were subjected immediately to light following imbibition, 30-day germination at 25C (77F) was 98% compared to 95% for imbibed seeds maintained in darkness for 63 days and then exposed to light. If germinated at 25/15C (77/59F), immediate light exposure resulted in 99% germination which decreased significantly to 76% after 63 days of dark treatment. Seeds of R. maximum maintained in darkness developed secondary dormancy at both temperatures. Thirty day germination of seeds subjected immediately to light following imbibition at 25C (77F) was 82% which decreased to 29% after dark treatment for 9 days. Further reductions in germination continued as the length of dark treatment increased with < 10% germination after maintenance in darkness for 27 days. At 25/15C (77/59F) induction of secondary dormancy was not as dramatic as that at 25C (77F). Without dark treatment, 30-day germination at 25/15C (77/59F) was 99% which decreased significantly to 88% after dark treatment for 18 days. Reductions in germination continued up to 63 days with 67% germination. Partial removal of secondary dormancy in seeds of R. maximum was achieved by subjecting seeds to moist-chilling.
L. R. Griffin, “Modelling the Spread of an Invasive Woody Taxon: Rhododendron Ponticum L.,” Master's thesis, Durham University, 1994.http://etheses.dur.ac.uk/5591/.
Simulation of the present-day distribution and abundance of rialRhododendron ponticum L. at the Glen Etive study site in the Western Highlands of Scotland was achieved using a simple deterministic model (MIGRATE). The model utilises the demographic and dispersal parameters characteristic to a species and a knowledge of the environmental history of the area through which it spreads to simulate patterns of spread. Biotic parameter values were derived from simple field measures and from data in the literature. "Habitat maps" were constructed on the basis of observations made in the field as to the likely relationships of Rhododendron to biotic and abiotic features of the habitat. Habitat features and their attributes were digitised and recorded in an ARC/INFO Geographical Information System (GIS). The simulation of changes in habitat through time was attempted using different habitat maps composed of cells containing unique values for relative carrying capacities, which were representative of the state of the habitat at a certain time. These habitat maps could only influence the dynamics of spread at the intervals between generations. Implementation of habitat changes was dependent on the cohort structure of the model which limited the resolution and exact order of changes that could be taken into account. Model simulations were tested for accuracy against the present-day distribution and abundance of the invading population as mapped in the field, and as seen in aerial photographs from 1946."Null" simulations showed that environmental factors were important determinants of the migration rate. Having achieved accurate simulation of a past and present distribution at a fine spatial scale from two initial foci of introduction in 1910, predictions were made as to the likely pattern of future spread. Predictions for the future were then made considering the effects of control regimes. The importance of the implications of the pattern of spread to migration research and to conservationists, considering the ecological impacts of Rhododendron observed at the study site are discussed in relation to previous findings. More specifically the importance of the long-distance dispersal function to the invasion process is highlighted, and it is suggested that evolution should favour strategies resulting in long-distance dispersal. The reason for large seed crops is discussed in this light. This project represents an integration of field techniques, biotic data available from the literature, a deterministic model, a GIS and aerial photography.
P. Halliday, “55. Rhododendron Fortunei Subsp. Discolor: Ericaceae,” The Kew Magazine, vol. 3, no. 2, pp. 51–55, 1986.https://www.jstor.org/stable/45066443.
O. B. Hansen and J. R. Potter, “Rooting of Apple, Rhododendron, and Mountain Laurel Cuttings from Stock Plants Etiolated under Two Temperatures,” HortScience, vol. 32, no. 2, pp. 304–306, Apr. 1997.
doi: 10.21273/HORTSCI.32.2.304.
Dormant stock plants of apple (Malus domestica Borkh.) rootstocks M.26 and Ottawa 3; Rhododendron ‘Britannia’, ‘Purple Splendour’, and ‘Unknown Warrior’; and mountain laurel (Kalmia latifolia L.) ‘Ostbo Red’ and seedlings were forced to grow at 18 or 28 °C in continuous darkness or 14-h photoperiods. Etiolated shoots were then acclimated to light with or without aluminum foil wrapped around their bases to keep the bases etiolated. Shoots forced in diurnal light were neither etiolated nor wrapped and served as controls for the etiolation treatments. Compared to controls, wrapping etiolated stems improved rooting of M.26 (60% vs. 82%) and ‘Ottawa 3’ (81% vs. 97%) apple and of ‘Britannia’ (76% vs. 90%) and ‘Unknown Warrior’ (80% vs. 91%) rhododendron. Etiolation improved rooting percentage of ‘Unknown Warrior’ regardless of wrapping. Regardless of etiolation, forcing ‘Ottawa 3’ at 18 °C improved rooting percentage (92% vs. 74%) and roots per cutting (12 vs. 7) compared to forcing at 28 °C. Etiolated mountain laurel cuttings generally rooted best at 18 °C; control cuttings rooted best at 28 °C.
It is concluded that the genus Ledum is congeneric dodendron can be considered to be present in Ledum, with Rhododendron, and the two generic names, which were published simultaneously, were chosen. THE INCLUSION OF LEDUM IN ,. . , , , . ,, , RHODODENDRON of the \^VCry *pparently monophyletic) genus Rhododendron: the long mul Kron and Judd (1990) performed a cladistic analysis ticellular trichomes, the multicellular glands, the to test the presumed monophyletic nature of the gerevolute position of the leaves in the bud, the only nus Rhododendron L. s. lato and to investigate the narrowly sympetalous corolla (not truly choripeta cladistic relationships of the subgenera of Rhododenlous in Leduml), and a capsule opening from the base. dron with a few related genera, such as Ledum L. Conversely, the zygomorphic corolla typical of Rho They concluded that the genus Ledum is congeneric dodendron can be considered to be present in Ledum, with Rhododendron. Of these two generic names, too, as the corolla is zygomorphic at the bud stage which were published simultaneously, they chose in the latter genus (though admittedly actinomorphic Rhododendron for the united genus. Within Rhodowhen opened). dendron, Ledum is treated as a subsection fairly Four further features point toward a very close close to subsect. Edgeworthia (Hutch.) Sleumer: relationship between Rhododendron and Ledum. Rhododendron L. subg. Rhododendron sect. RhodoFirstly, Bocher et al. (1968) report an apparent na dendron subsect. Ledum (L.) Kron & Judd. tive hybrid between Rhododendron lapponicum (L.) To merge the well-established classical Linnean Wahlenb. and Ledum decumbens (Aiton) Lodd. ex genus Ledum with the very large genus RhododenSteud. from Greenland. Secondly, a characteristic dron, especially when not according it a higher rank "winter position" of the leaves occurs in both gen than that of subsection, appears truly radical, parera. Thirdly, in both the stamens are mostly zygo ticularly from a European point of view. However, morphically arranged. And fourthly, I myself have Kron and Judd (1990) present many characters, noted in two Finnish specimens of L. palustre L. mostly derived from the literature, which support this capsules that open from their apices; in one of the merger. In fact, the classical characteristics of Lespecimens such a capsule occurred among normal dum are found separately in scattered subsections ones.
F. Hébert and N. Thiffault, “The Biology of Canadian Weeds. 146. Rhododendron Groenlandicum (Oeder) Kron and Judd,” Canadian Journal of Plant Science, vol. 91, no. 4, pp. 725–738, Jul. 2011.
doi: 10.4141/cjps2010-012.
F. Hébert, N. Thiffault, J.-C. Ruel, and A. D. Munson, “Comparative Physiological Responses of Rhododendron Groenlandicum and Regenerating Picea Mariana Following Partial Canopy Removal in Northeastern Quebec, Canada,” Canadian Journal of Forest Research, vol. 40, no. 9, pp. 1791–1802, Sep. 2010.
doi: 10.1139/X10-124.
C. J. Hebert, F. A. Blazich, and A. V. LeBude, “Seed Germination of Five Populations of Rhododendron Vaseyi: Influence of Light and Temperature,” Journal of Environmental Horticulture, vol. 28, no. 3, pp. 166–172, Sep. 2010.
doi: 10.24266/0738-2898-28.3.166.
Seeds from five populations of Rhododendron vaseyi A. Gray (pinkshell azalea), representing the entire distribution of the species, were germinated at 25C (77F) or an 8/16-hr thermoperiod of 30/20C (86/68F) with daily photoperiods at each temperature of 0 (total darkness), 8, 12, or 24-hr (continuous light). Germination was recorded every 3 days for 30 days. Responses to light and temperature of all populations were similar. Light was required for germination regardless of temperature. As photoperiod increased, germination increased for all populations with the alternating temperature partially compensating for the light requirement. The highest cumulative germination for all populations ranged from 51 to 67% and was achieved at 30/20C with a 24-hr photoperiod. These germination percentages, although at a moderate level, were due in part to rigorous cleaning and grading of seeds collected across a broad range of plants and growing conditions prior to initiation of the study, suggesting seed viability of R. vaseyi is inherently low.
T. Holt, B. K. Maynard, and W. A. Johnson, “The Effect of Substrate pH on the Rooting of Rhododendron with Subirrigation,” HortScience, vol. 32, no. 3, pp. 447A–447, Jun. 1997.
doi: 10.21273/HORTSCI.32.3.447A.
Subirrigation is a viable alternative to mist for the cutting propagation of many woody and herbaceous plants. However, poor success has been reported with rhododendron cuttings. This study evaluated the rooting of two Rhododendron cultivars in a subirrigation system maintained at two different levels of substrate pH. Stem cuttings of Rhododendron ‘PJM’ and R. ‘Catawbiense album’ were wounded, treated with Dip ‘n Grow (1:10 dilution), and rooted in subirrigated perlite subirrigated with tap water (pH 7.5), or tap water adjusted to pH 4.5 with weak sulfuric acid (1N H2SO4). Percent rooting and root ball displacement were recorded after 7 weeks. The pH of the subirrigation system dramatically affected root initiation and development. At pH 4.5 ‘PJM’ cuttings rooted 100% with an average displacement of 7.6 ml; cuttings of ‘Catawbiense Album’ rooted 88% with an average displacement of 12.1 ml. At pH 7.5, ‘PJM’ cuttings rooted 52.5%, with an average displacement of 0.8 ml, while ‘Catawbiense album’ rooted 73% with an average displacement of 2.5 ml. A root ball displacement of ≥3 ml was judged to be commercially acceptable for rooted cuttings of ‘PJM’ rhododendron, ≥4.5 ml for ‘Catawbiense album’. At pH 7.5 only 15% of the ‘Catawbiense album’ cuttings and none of the ‘PJM’ cuttings produced commercially acceptable rooted cuttings. At pH 4.5, 83% of the ‘Catawbiense album’ cuttings and 93% of the ‘PJM’ cuttings were commercially acceptable. Subirrigation is a suitable method of irrigating rhododendron cuttings during rooting if a low substrate pH is maintained.
T. A. Holt, B. K. Maynard, and W. A. Johnson, “Low pH Enhances Rooting of Stem Cuttings of Rhododendron in Subirrigation,” Journal of Environmental Horticulture, vol. 16, no. 1, pp. 4–7, Mar. 1998.
doi: 10.24266/0738-2898-16.1.4.
Semi-hardwood terminal stem cuttings of Rhododendron L. ‘P.J.M.’, R. ‘Catawbiense Album’ and R. ‘Purple Gem’ were treated with a solution of 0.1% indolebutyric acid and 0.5% napthaleneacetic acid and inserted into perlite for rooting under subirrigation, without overhead mist, at solution pH of 4.5 or 7.5. All cultivars rooted in higher percentages and produced larger root balls at pH 4.5 than at pH 7.5. A second study with softwood stem cuttings of R. ‘P.J.M.’ and both softwood and semi-hardwood stem cuttings of R. ‘Purple Gem’ confirmed these findings and included an additional subirrigation treatment, a sphagnum peat slurry, pH 4.1, which produced nearly identical results to the pH 4.5 treatment.
P. M. I, O. M. Yu, V. V. I, and T. S. O, Ecological and Biological Bases of Rhododendron Introduction. Potere della ragione Editore, Rome, Italy., 2021.http://lib.udau.edu.ua/handle/123456789/7606.
Rhododendrons, as highly decorative representatives of the world flora, are characterized by a variety of shapes, size and color of flowers and leaves, crown type and plant size. Under conditions of introduction, they can be deciduous, evergreen and semi-evergreen. All this contributed to the widespread popularization of these plants in Europe, Asia and North America. Wide ecological plasticity of rhododendrons promotes their use in park building, landscaping of cities, settlements and industrial enterprises. Рододендрони, як високо декоративні представники світової флори, характеризуються різноманітністю форм, розміром та забарвленням квіток та листків, видом крони та розміром рослин. В умовах інтродукції вони можуть бути листопадними, вічнозеленими та напіввічнозеленими. Все це сприяло широкій популяризації цих рослин в країнах Європи, Азії та Північної Америки. Широка екологічна пластичність рододендронів сприяє використанню їх у паркобудівництві, озелененні міст, селищ та промислових підприємств.
G. Iapichino, T. H. H. Chen, and L. H. Fuchigami, “Adventitious Shoot Production from a Vireya Hybrid of Rhododendron,” HortScience, vol. 26, no. 5, pp. 594–596, May 1991.
doi: 10.21273/HORTSCI.26.5.594.
An efficient adventitious shoot production protocol has been developed for Rhododendron laetum × aurigeranum. Shoot tips taken from greenhouse-grown plants were cultured on Anderson’s medium supplemented with 74 μM 2iP. Axillary shoots were excised and cultured on medium containing 23 μM IAA and 74 μM 2iP. After 6 months, brown callus developed at the cut surfaces of the shoot-tip explants. This callus produced many adventitious shoots (up to 70 per explant). Clusters of adventitious shoots were divided, subculture, and continued to proliferate shoots. An estimated 1600-fold increase in the number of shoots could be readily achieved in 6 months. In vitro rooting of adventitious shoots was accomplished in 4 weeks. Seventy-three percent of shoots rooted on 1/4 strength Anderson’s medium supplemented with 28 μm IAA. Plantlet survival was 100%3 weeks after transfer to soil. Chemical names used: 1-H-indole-3-acetic acid (MA); N-(3 -methy1-2-butenyl) -1H-purine-6 amine (2iP).
M. Ishikawa, M. Ishikawa, T. Toyomasu, T. Aoki, and W. S. Price, “Ice Nucleation Activity in Various Tissues of Rhododendron Flower Buds: Their Relevance to Extraorgan Freezing,” Frontiers in Plant Science, vol. 6, 2015.https://www.frontiersin.org/article/10.3389/fpls.2015.00149.
Wintering flower buds of cold hardy Rhododendron japonicum cooled slowly to subfreezing temperatures are known to undergo extraorgan freezing, whose mechanisms remain obscure. We revisited this material to demonstrate why bud scales freeze first in spite of their lower water content, why florets remain deeply supercooled and how seasonal adaptive responses occur in regard to extraorgan freezing in flower buds. We determined ice nucleation activity (INA) of various flower bud tissues using a test tube-based assay. Irrespective of collection sites, outer and inner bud scales that function as ice sinks in extraorgan freezing had high INA levels whilst florets that remain supercooled and act as a water source lacked INA. The INA level of bud scales was not high in late August when flower bud formation was ending, but increased to reach the highest level in late October just before the first autumnal freeze. The results support the following hypothesis: the high INA in bud scales functions as the subfreezing sensor, ensuring the primary freezing in bud scales at warmer subzero temperatures, which likely allows the migration of floret water to the bud scales and accumulation of icicles within the bud scales. The low INA in the florets helps them remain unfrozen by deep supercooling. The INA in the bud scales was resistant to grinding and autoclaving at 121∘C for 15 min, implying the intrinsic nature of the INA rather than of microbial origin, whilst the INA in stem bark was autoclaving-labile. Anti-nucleation activity (ANA) was implicated in the leachate of autoclaved bud scales, which suppresses the INA at millimolar levels of concentration and likely differs from the colligative effects of the solutes. The tissue INA levels likely contribute to the establishment of freezing behaviors by ensuring the order of freezing in the tissues: from the primary freeze to the last tissue remaining unfrozen.
H. U. Jihong, C. Guixin, Y. Huiting, K. Jianban, and G. a. N. Daikui, “Technology for Rapid Propagation in Vitro of Ancient Four-Season Rhododendron Tree in Longyuan of Pingnan,” Chinese Journal of Tropical Crops, vol. 41, no. 4, p. 755, Apr. 2020.
doi: 10.3969/j.issn.1000-2561.2020.04.017.
Rapid propagation in vitro was explored using the apical buds of an an...
I. Jing, S. K. Chaturvedi, and N. Puro, “Pollination Biology of Rhododendron Macabeanum Watt Ex Balfour f. of Ericaceae in Nagaland, India,” p. 6.
The pollination biology, breeding system including pollen-ovule ratio, fruit and seed-set and viability of seeds in some marked plants of Rhododendron macabeanum Watt ex Balfour f. were made at Khonoma Dzukou, Kohima District of Nagaland (North-East India) at an altitude ranging between 2500 – 2700 m amsl. The flowers which are present in trusses of 20 – 28 flowers are yellow with a purple blotch on the throat are foraged and get pollinated by the birds of the genus Yuhina. The other foragers like beetles and flies are insignificant pollinators of this taxon. The only attractant for the foragers is nectar which is secreted in the five nectaries present at the base of the corolla tube. The pollens are present in tetrads which are held together by viscin threads. The flowers of R. macabeanum are self-compatible and the plants show high percentage of fruit-set in open pollinated flowers. The climatic conditions like rain and sloppy habitat have been identified the vital factors for poor seedling establishment in the natural locality and hence, are also responsible for the depletion of population of this important taxon which is endemic to Nagaland and Manipur states of North-east India.
J. R. Jones, A. V. LeBude, and T. G. Ranney, “Vegetative Propagation of Oconee Azalea (Rhododendron Flammeum) by Stem Cuttings and Mound Layering,” Journal of Environmental Horticulture, vol. 28, no. 2, pp. 69–73, Jun. 2010.
doi: 10.24266/0738-2898-28.2.69.
Deciduous azaleas (Rhododendron L.) offer a range of desirable ornamental characteristics and can be valuable nursery crops. Availability in the nursery trade, however, can be limited by the lack of effective propagation protocols. Therefore, the objectives of this research were to develop and optimize vegetative propagation protocols for Oconee azalea, Rhododendron flammeum (Michx.) Sarg., utilizing stem cuttings or in-field mound layering. An optimal method for producing rooted stem cuttings with large root systems (> 20 cm2) was to collect softwood stem cuttings from hedged stock plants followed by treatment with 10,000 ppm of the potassium salt (K-salt) of indolebutyric acid (K-IBA). Mound layering was also effective. Fifty percent of the stems on each mound resulted in rooted layers and approximately six layers were produced per mound regardless of mounding season (March or June), with or without wounding, or application of 5000 ppm K-IBA to stems prior to mounding in June. Both softwood cuttings and mound layering can be utilized to produce high quality plants.
E. F. Karlin and L. C. Bliss, “Germination Ecology of Ledum Groenlandicum and Ledum Palustre Ssp. Decumbens,” Arctic and Alpine Research, vol. 15, no. 3, pp. 397–404, 1983.
doi: 10.2307/1550834.
Optimal substrate conditions for germination and establishment of Ledum groenlandicum include pH around 5.5, mean daily temperatures ≥ 17°C, no shading, and constant moisture. Seed longevity of L. groenlandicum was not pronounced, and most seed lost viability within a year. Although closely related, L. groenlandicum and L. palustre ssp. decumbens had significantly different rates of germination, with 94.3% of the total germination occurring within 12 d for 1-mon-old seed of L. palustre ssp. decumbens, while the corresponding value for groenlandicum was 36.4%. Both species require light in order to germinate, although germination of L. groenlandicum was reduced in far-red rich light regimes while that of L. palustre ssp. decumbens was not.
E. F. Karlin, “Major Environmental Influences on the Pattern of Ledum Groenlandicum in Mire Systems,” ERA. 1978.
doi: 10.7939/R3DB7W197.
Doctoral thesis. Study of determine the cause of the pattern of Ledum groenlandicum in mires (peatlands). Field research centered...
D. M. Kenyon, G. R. Dixon, and S. Helfer, “The Repression and Stimulation of Growth of Erysiphe Sp. on Rhododendron by Fungicidal Compounds,” Plant Pathology, vol. 46, no. 3, pp. 425–431, 1997.
doi: 10.1046/j.1365-3059.1997.d01-25.x.
Erysiphe sp. is a causal agent of powdery mildew on Rhododendron. A novel in vivo method permitting the screening of fungicides on woody plants is described. Eight fungicides were evaluated for activity against Erysiphe sp. using Rhododendron ponticum microplantlets grown in vitro. Pathogen development changed with both the type of fungicidal compound and the concentrations applied. The most active materials were fenpropidin and penconazole, which showed high activity at the lowest concentrations. Six of the compounds performed more effectively than a mixture of bupirimate + triforine (Nimrod T), the standard recommendation for control of this pathogen on Rhododendron. All fungicides affected the sporulation of Erysiphe sp., with propiconazole, pyrazophos and triadimenol causing a significant increase in sporulation at the lowest concentrations. At higher concentrations, sporulation was significantly reduced by all treatments. No phytotoxic effects were detected with any fungicide at any concentration. The growth of plantlets in most treatments showed no significant difference from the untreated controls. The results of the study are discussed in relation to strategies for control and the epidemiology of Erysiphe sp. infecting Rhododendron.
L. P. Khlebova, O. N. Mironenko, and E. S. Brovko, “In Vitro Micropropagation of Wild Rare Plant Rhododendron Ledebourii Pojark,” IOP Conference Series: Earth and Environmental Science, vol. 723, no. 2, p. 022033, Mar. 2021.
doi: 10.1088/1755-1315/723/2/022033.
Rhododendron ledebourii Pojark. is a highly decorative rare species of the flora of Siberia (Russia) and can be used as a source of biologically active substances, as well as in landscaping. We have optimized the in vitro propagation protocol for this species. Sterilization of annual shoots of field plants with 5% lysoformin-3000 provided 70% aseptic viable explants. The addition of 2 mg L−1 glycine to Anderson’s medium in combination with 8 mg L−1 2-isopentyladenine and 3 mg L−1 indolyl-3-acetic acid stimulated a high multiplication rate and active growth of axillary and adventitious shoots. The adaptation of regenerants in a hydroponic installation containing ¼ of the basic composition of macro- and microsalts according to Murashige and Skoog’s medium promoted the development of powerful roots for subsequent successful acclimatization to ex vitro conditions. This approach ensured the survival rate of 90% microplants.
N. Y. Kim, K. H. Bae, Y. S. Kim, H. B. Lee, and W. G. Park, “Habitat Environment and Cutting, Seed Propagation of Rare Plant Rhododendron micranthum Turcz,” Journal of Forest and Environmental Science, vol. 29, no. 2, pp. 165–172, 2013.
doi: 10.7747/JFS.2013.29.2.165.
The habitats characteristics of Rhododendron micranthum Turcz. were investigated to compile basic data for conservation and restoration. Natural habitats were located at altitudes of 100-500 m with inclinations of }10-35\^{∘}{. Rhododendron micranthum population was classified into Pinus densiflora dominant population. In the study sites, soil organic matter, total nitrogen, available phosphate, exchangeable potassium, exchangeable sodium, exchangeable calcium, exchangeable magnesium, cation exchange capacity and soil pH were 4.10-8.64%, 0.18-0.46%, 8.69-26.70 }mgkg\^{-1}{, 0.10-0.23 }cmol\^+kg\^{-1}{, 0.06-0.10 }cmol\^+kg\^{-1}{, 0.85-4.10 }cmol\^+kg\^{-1}{, 0.24-0.64 }cmol\^+kg\^{-1}{, 12.76-20.90 }cmol\^+kg\^{-1}{, 4.34-5.15. Rooting rate is too low, cutting propagation, breeding methods are not good. Also, this study was investigated seed germination of R. micranthum depends on soaking treatment. R. micranthum was soaked with tap water for four days, the average values of germination day were represented of 70%/1 week.
S. L. Krebs, “Rhododendron,” in Ornamental Crops, J. Van Huylenbroeck, Ed. Cham: Springer International Publishing, 2018, pp. 673–718.
doi: 10.1007/978-3-319-90698-0_26.
Genus Rhododendron, which includes plants commonly referred to as rhododendrons and azaleas, contains over 800 immensely diverse and ornamental species. For the past 200 years, this natural variability has provided the raw material for Western plant breeders who have recombined ornamental and adaptive traits in novel hybrids, which number over 25,000 at the present time. Overwhelmingly, the focus has been on aesthetic attributes because hybridizing is mostly done by enthusiasts and collectors who are doing it for enjoyment’s sake rather than for public consumption or commercial reward. This chapter draws attention to a need for better adapted plants that will perform well in challenging conditions and to functional diversity in the wild that can provide these adaptations for breeding purposes. Increased tolerance of abiotic stresses such as temperature and moisture extremes, alkaline soils, or high salt concentrations, in addition to improved resistance to pathogens and pests, will benefit public horticulture by making landscape rhododendrons and azaleas easier to grow and suitable for broader markets.
N. Kuzmanović et al., “A Novel Group of Rhizobium Tumorigenes-Like Agrobacteria Associated with Crown Gall Disease of Rhododendron and Blueberry,” Phytopathology®, vol. 109, no. 11, pp. 1840–1848, Nov. 2019.
doi: 10.1094/PHYTO-05-19-0167-R.
Crown gall is an economically important and widespread plant disease caused by tumorigenic bacteria that are commonly affiliated within the genera Agrobacterium, Allorhizobium, and Rhizobium. Although crown gall disease was reported to occur on rhododendron, literature data regarding this disease are limited. In this study, an atypical group of tumorigenic agrobacteria belonging to the genus Rhizobium was identified as a causative agent of crown gall on rhododendron. Genome analysis suggested that tumorigenic bacteria isolated from rhododendron tumors are most closely related to Rhizobium tumorigenes, a new tumorigenic bacterium discovered recently on blackberry in Serbia. However, R. tumorigenes and novel rhododendron strains belong to separate species and form a homogenous clade within the genus Rhizobium, which we named the “tumorigenes” clade. Moreover, tumorigenic bacteria isolated from rhododendron seem to carry a distinct tumor-inducing (Ti) plasmid, compared with those carried by R. tumorigenes strains and Ti plasmids described thus far. To facilitate rapid identification of bacteria belonging to the “tumorigenes” clade, regardless of whether they are pathogenic or not, a conventional PCR method targeting putative chromosomal gene-encoding flagellin protein FlaA was developed in this study. Finally, our results suggested that this novel group of tumorigenic agrobacteria occurs on blueberry but it cannot be excluded that it is distributed more widely.
R. E. Lee, “Cultivar Development and Marketing in Two Woody Ornamentals, Rhododendron Hyperythrum and Rhaphiolepsis Umbellate,” Acta Horticulturae, no. 977, pp. 361–362, Feb. 2013.
doi: 10.17660/ActaHortic.2013.977.44.
G. E. Lee, Y. N. Song, and H. O. Hong, “Studies on the wild Rhododendron fauriei for rufescens in Korea [R.]: with special reference to the seed germination,” Journal of the Korean Society Horticultural Science (Korea R.), 1982.https://eurekamag.com/research/001/257/001257979.php.
The present experiment was done to know the germination ability for the effective propagation of Rhododendron fauriei for. rufescens. The optimum temperature for seed germination of R. fauriei for reference might be 20 degrees Centigrade. The rate of seed germination varied with the storage of seed and decreased when the seeds were washed in water for a long period of time. Among the thiourea treatments, one percent level gave the highest rate of seed germination was apparent in the early stage of germination but not in the late stage. In the plots of IAA (Indole Acetic Acid) and GA (Gibberellic Acid) treatment kept in darkness, few of the seed germination were seen in the treatment with IAA, while there was fifty percent of seed germination with the treatment of GA
B.-R. Lee, K.-E. Lee, and K.-C. Yoo, “A Study on the Wild Rhododendron Micranthum for Landscape Use,” Journal of the Korean Institute of Landscape Architecture, vol. 18, no. 3, pp. 137–141, 1990.https://www.koreascience.or.kr/article/JAKO199015875824699.page.
This study was carried out to investigate the propagation methods of the Rhododendron micranthum as a landscape plant The results obtained are as follows : 1. The optimum temperature for seed germination was }20\^{∘}C{, and the seed germination needs light. 2. GA and thiourea did not affect the seed germination under light, but GA gad substitutive effect. 3. 87% and over of germination rates were obtained in room temperature and }5\^{∘}C{ dry storages. 4. The rooting rate was high on sandy loam, vermiculite, and vermiculite 50%+sand 50%, at softwood and hardwood cutting(hardwood ; 45~48%, softwood ; 45~48%). 5. The significant effects on rooting were found with the treatment of NAA 500~2000ppm.
C. C. Lim, S. L. Krebs, and R. Arora, “A 25-kDa Dehydrin Associated with Genotype- and Age-Dependent Leaf Freezing-Tolerance in Rhododendron: A Genetic Marker for Cold Hardiness?,” Theoretical and Applied Genetics, vol. 99, no. 5, pp. 912–920, Sep. 1999.
doi: 10.1007/s001220051312.
Dehydrins are plant proteins that may play a critical role in stabilizing cell functions during freezing and other dehydrative stresses. This study examines whether dehydrin expression in leaves is associated with varying levels of freezing-tolerance among F2 segregants, species, and cultivars of evergreen Rhododendron. Experiments were also conducted to determine whether physiological and chronological aging affects freezing-tolerance and dehydrin accumulation in Rhododendron leaf tissues. Our results indicate that in cold-acclimated F2 populations, levels of a 25-kDa dehydrin were closely associated with differences in leaf freezing-tolerance (LFT) among segregants. Studies of wild and cultivated plants indicated that LFT increased with both chronological age and developmental phase-change (juvenile to mature plants) and that this trend was accompanied by increased accumulation of the 25-kDa dehydrin. It is suggested that presence or absence of the 25-kDa dehydrin could serve as a genetic marker to distinguish between super cold-hardy and less cold-hardy rhododendron genotypes. Similarly, the relative level of this protein within a genotype can serve as a physiological indicator of freezing-tolerance status under a range of phenological (acclimation) or developmental (age) conditions.
Winter survival in woody plants is controlled by environmental and genetic factors that affect the plant’s ability to cold acclimate. Because woody perennials are long-lived and often have a prolonged juvenile (pre-flowering) phase, it is conceivable that both chronological and physiological age factors influence adaptive traits such as stress tolerance. This study investigated annual cold hardiness (CH) changes in several hybrid Rhododendron populations based on Tmax, an estimate of the maximum rate of freezing injury (ion leakage) in cold-acclimated leaves from juvenile progeny. Data from F2 and backcross populations derived from R. catawbiense and R. fortunei parents indicated significant annual increases in Tmax ranging from 3.7 to 6.4°C as the seedlings aged from 3 to 5 years old. A similar yearly increase (6.7°C) was observed in comparisons of 1- and 2-year-old F1 progenies from a R. catawbiense × R. dichroanthum cross. In contrast, CH of the mature parent plants (>10 years old) did not change significantly over the same evaluation period. In leaf samples from a natural population of R. maximum, CH evaluations over 2 years resulted in an average Tmax value for juvenile 2- to 3-year-old plants that was 9.2°C lower than the average for mature (~30 years old) plants. A reduction in CH was also observed in three hybrid rhododendron cultivars clonally propagated by rooted cuttings (ramets)—Tmax of 4-year-old ramets was significantly lower than the Tmax estimates for the 30- to 40-year-old source plants (ortets). In both the wild R. maximum population and the hybrid cultivar group, higher accumulation of a cold-acclimation responsive 25 kDa leaf dehydrin was associated with older plants and higher CH. The feasibility of identifying hardy phenotypes at juvenile period and research implications of age-dependent changes in CH are discussed.
L.-C. Lin and C.-S. Wang, “Influence of Light Intensity and Photoperiod on the Seed Germination of Four Rhododendron Species in Taiwan,” Pakistan journal of biological sciences, vol. 20, no. 5, pp. 253–259, Jan. 2017.
doi: 10.3923/pjbs.2017.253.259.
Background and objectiveThere are 15 native Rhododendron species in Taiwan, among which 11 species are endemic and compose 73% of these native species. Although researchers predominantly use cuttings to propagate Rhododendron shrubs, there are no studies on the seed germination of Rhododendron species. The objective of this study was to evaluate the seed germination of four Rhododendron species in Taiwan under different light intensities and photoperiods.Materials and methodsTwo experiments on the seed germination percentage of R. breviperulatum, R. kanehirai, R. ovatum and R. simsii were conducted in this study. The first experiment was to identify the seed germination percentage of these four Rhododendron species using different light intensities (0, 700, 1400 and 3200 lux). The second experiment was to clarify the seed germination percentage of these four Rhododendron species using different photoperiods (0, 1, 4 and 16 h). All statistical analyses were performed using Statistical Package for the Social Science (SPSS12.0) for Windows software program. The data were analyzed using Tukey’s multiple range test at the pResultsAfter 30 days, no seed germination occurred in darkness. The highest average seed germination percentages were all observed at 700 lux: R. breviperulatum (83.3%), R. kanehirai (68.9%), R. ovatum (85.6%) and R. simsii (92.2%). The highest average germination percentages of seeds were observed in R. breviperulatum at 16 h (83.3%), R. kanehirai at 1 h (60.0%), R. ovatum at 16 h (84.4%) and R. simsii at 16 h (85.6%). According to the results, these four Rhododendron species required light for germination. There were significant differences (pConclusionThe seed germination percentage of R. breviperulatum, R. ovatum and R. simsii increased with increasing photoperiod.
Y. Ma et al., “Conservation of the Giant Tree Rhododendron on Gaoligong Mountain, Yunnan, China,” Oryx, vol. 46, no. 3, pp. 325–325, Jul. 2012.
doi: 10.1017/S0030605312000750.
A. Malciūtė, J. R. Naujalis, and A. Svirskis, “Resistance to Low and Negative Temperatures of Rhododendrons (Rhododendron) in the Botanical Garden of Šiauliai University in 2002-2007,” Notulae Botanicae Horti Agrobotanici Cluj-Napoca, vol. 36, no. 1, pp. 59–62, 2008.https://epublications.vu.lt/object/elaba:3401704/.
Rhododendrons are not native to Lithuania, but are often cultivated in botanical gardens, various public and private green plantations. Resistance to low temperatures are among the most important criteria in evaluating the condition of the rhododendron collection in the Botanical Garden of ŠU. The research initiated in the ŠU Botanical Garden will help in the selection and propagation of ornamental and tolerant to low temperatures representatives of species and cultivars, suitable for cultivation in northern Lithuania.
A. A. Malek, “Sexual Propagation and Culture of Flame Azalea (Rhododendron Calendulaceum (Michx.) Torr); and Mountain Laurel (Kalmia Latifolia L.),” p. 1, 1992.https://elibrary.ru/item.asp?id=5839672.
Degree: Ph.D.DegreeYear: 1991Institute: North Carolina State UniversitySeeds of flame azalea and mountain laurel were germinated at 25C and 25/15C with daily photoperiods of 0, ~ ~{1\over 2}, ~ ~{1\over 2} twice daily, 1, 2, 4, 8, 12, or 24 h. Both species exhibited an obligate light requirement and increasing photoperiods increased germination at 25C. The alternating temperature of 25/15C enhanced germination when light was limiting.Seedlings of flame azalea and mountain laurel were grown under long days at 9-h day temperatures of 18, 22, 26 and 30C in factorial combination with 15-h night temperatures of 14, 18, 22 and 26C. For each species, optimum temperature varied with the growth parameter. Maximum total plant dry weight of flame azalea occurred at a 26C day temperature in combination with 18 to 26C night temperature. For mountain laurel, total plant dry weight was optimized at a day/night temperature of 26/22C. Dry matter production of each species was low when the night temperature was 14C... Degree: Ph.D.DegreeYear: 1991Institute: North Carolina State UniversitySeeds of flame azalea and mountain laurel were germinated at 25C and 25/15C with daily photoperiods of 0, ~ ~{1\over 2}, ~ ~{1\over 2} twice daily, 1, 2, 4, 8, 12, or 24 h. Both species exhibited an obligate light requirement and increasing photoperiods increased germination at 25C. The alternating temperature of 25/15C enhanced germination when light was limiting.Seedlings of flame azalea and mountain laurel were grown under long days at 9-h day temperatures of 18, 22, 26 and 30C in factorial combination with 15-h night temperatures of 14, 18, 22 and 26C. For each species, optimum temperature varied with the growth parameter. Maximum total plant dry weight of flame azalea occurred at a 26C day temperature in combination with 18 to 26C night temperature. For mountain laurel, total plant dry weight was optimized at a day/night temperature of 26/22C. Dry matter production of each species was low when the night temperature was 14C. Net leaf photosynthetic rate of mountain laurel was highest at a day temperature of 26C, and increased with day temperature for flame azalea.Seedlings of flame azalea were subjected to selected manual pinching treatments at the 10-, 12-, 14-, or 16-leaf stage. Generally, the number of lateral shoots increased with the leaf stage at which manual pinching was imposed. The greatest number of lateral shoots was produced by removing the terminal two nodes at the 16-leaf stage. In a second experiment, both nonpinched and manually-pinched plants were sprayed with different concentrations of dikegulac. The number of lateral shoots increased linearly up to 4000 ppm. Dry weights of leaves, stems, and roots decreased as the concentration increased. However, the number of lateral shoots and dry weights of leaves, stems and roots of pinched and nonpinched plants were not significantly different when treated with dikegulac. function show_abstract() { \(’#abstract1’).hide(); \(’#abstract2’).show(); $(’#abstract_expand’).hide(); } ▼Показать полностью
M. Malicki, W. Pusz, M. Ronikier, and T. Suchan, “Population Characteristics, Habitat, and Conservation Status of Rhododendron Ferrugineum L. (Ericaceae), a Glacial Relict New to Poland,” Acta Soc Bot Pol, p. 9, 2019.
The first reliable information on the occurrence of Rhododendron ferrugineum in the Karkonosze Mts (excluding spots of directly acknowledged anthropogenic origin) was provided by A. Boratyński in 1983, but the status and origin of the plants were unknown. A recent phylogeographical study proved the natural character and relict status of the aforementioned population, which makes it the northernmost and most isolated site within the whole distribution of the species. In this study, we characterized the basic aspects of the ecology and conservation status of the population and, more specifically, focused on assessing the size of the population, general health of individuals, generative propagation ability, habitat conditions, and potential threats for the species. The population persists in the Sowia Dolina (east part of the Karkonosze Mts), in a microtopographically controlled, treeless microrefugium. Shrubs of R. ferrugineum are part of an acidophilous dwarf-heath plant community, similar to those occurring in the Alps and the Pyrenees, although less species-diverse. The plant community in the Karkonosze Mts has been preliminarily classified into the Genisto pilosae-Vaccinion alliance. The R. ferrugineum population consists of 68 individuals: 57 fully grown and juvenile and 11 seedlings. In 2017, 10 individuals flowered, seven of which developed fruits, while in 2018, 15 individuals produced flowers and eight developed mature fruits. Seeds collected in 2017 germinated in high numbers. Plants in the Karkonosze population hosted some fungal parasites typically found in Rhododendron species, but no intense disease symptoms strongly influencing plant fitness were observed. A combination of significant isolation, genetic distinctness, and high genetic diversity implies a high conservation priority for the R. ferrugineum population in Karkonosze. Despite the theoretical threats, including stochastic risks, the R. ferrugineum population seems to have been stable for a long time and, importantly, it is composed of individuals of different ages, from large flowering plants to seedlings.
A. A. Mao et al., “In Vitro Micropropagation of Three Rare, Endangered, and Endemic Rhododendron Species of Northeast India,” In Vitro Cellular & Developmental Biology - Plant, vol. 47, no. 6, pp. 674–681, Dec. 2011.
doi: 10.1007/s11627-011-9377-0.
In vitro propagation of three rare, endangered and endemic rhododendron species—Rhododendron dalhousiae var. rhabdotum, R. elliottii, and R. johnstoneanum—was attained. Nodal explants were used for multiple shoot induction studies. Three cytokinins (isopentenyladenine, benzyladenine, and kinetin) were evaluated in all three species. Isopentenyladenine performed better in all three species, especially at the concentration of 39.36 µM. Testing of combinations of growth regulators revealed that explants grown on Anderson medium supplemented with 39.36 µM isopentenyladenine and 4.90 µM indole butyric acid gave optimum results with 100% multiple shoot induction, 18 shoots per explant, and shoot length of 2.07 cm with R. johnstoneanum. Indole butyric acid was found to be the best auxin for root formation. Around 60% of the in vitro-raised plants of R. elliottii, R. johnstoneanum, and R. dalhousiae var. rhabdotum were able to establish ex vitro.
A. A. Mao, D. Vijayan, S. Pradhan, and R. K. Nilasana Singha, “In Vitro Propagation of Rhododendron Macabeanum Watt Ex Balf.f., an Endangered and Endemic Rhododendron Species from Manipur and Nagaland, India,” Indian Journal of Plant Physiology, vol. 22, no. 3, pp. 339–345, Sep. 2017.
doi: 10.1007/s40502-017-0309-9.
An efficient and reproducible protocol for in vitro propagation of R. macabeanum, an endemic and endangered species from North East India was carried out successfully. Both ex vivo and in vitro seed germination was studied. Effect of activated charcoal (0.2%) in the Anderson medium (AM) was studied for seed germination but higher germination was obtained on basal medium alone. Different explants viz., apical shoots, nodal and root segments from in vitro raised seedlings were used for multiple shoot induction. Out of the three cytokinins studied in AM for multiple shoot induction, 2-isopentenyladenine (2iP) was the most responsive with optimum concentration at 19.68 µM following which experiments were also carried out with 2iP in different basal media viz., AM, modified Anderson medium and woody plant medium (WPM). The number of multiple shoots produced was higher and healthier in WPM with 8.15 ± 0.20a shoots per explant and an average shoot length of 2.13 ± 0.02a cm. 100% in vitro rooting was attained in WPM with 0.2% activated charcoal and successfully transferred from lab to land with about 90% survival rate.
A. A. Mao, D. Vijayan, R. K. Nilasana Singha, and S. Pradhan, “In Vitro Propagation of Rhododendron Wattii Cowan—a Critically Endangered and Endemic Plant from India,” In Vitro Cellular & Developmental Biology - Plant, vol. 54, no. 1, pp. 45–53, Feb. 2018.
doi: 10.1007/s11627-017-9869-7.
Rhododendron wattii Cowan is a rare and endangered plant found in northeast India. In an effort to boost specimen numbers, experiments of in vitro seed germination, shoot induction on different media supplemented with the cytokinin isopentenyladenine (2iP), and root induction with auxins α-naphthaleneacetic acid (NAA), indole-3-butyric acid (IBA) and indole-3-acetic acid (IAA) in woody plant medium (WPM) were carried out. A maximum mean shoot number of 7.72 per explant were obtained from nodal explants cultured on WPM and 39.36 μM 2iP with a maximum mean shoot length of 2.30 cm per explant. Among the auxins investigated for root induction, IBA at 2.45 μM was found to produce the most and the longest roots, when compared to other treatments. However, WPM supplemented with 0.2% (w/v) activated charcoal also showed 100% root formation with shoots having broader leaves compared to auxin treatments. About 60% of in vitro rooted plantlets transferred from lab to greenhouse conditions survived. Sixty acclimatized plants were reintroduced in the vicinity of their natural habitat at Naga Heritage Village, Kisama, Nagaland, in May 2016 for ex situ conservation. Survival of the reintroduced plants was confirmed during the field visit conducted in November 2016.
\relax C. A. P. R. A. R. Marin, M. Cantor, and C. Sicora, “Research on Optimization to Generative Multiplication of Rhododendron Luteum Sweet Species,” p. 4, 2013.
Natural range of the Rhododendron luteum Sweet species includes Caucasus, Asia Minor, and smaller regions in Europe found in countries such as Poland, Ukraine, Slovenia, Austria and Greece. In many of these countries the species is on the international red list of endangered species, because of small area surfaces. The paper presents the results obtained on seeds propagation. Regarding seeds propagation the determinations and observation consists in establishing the percentage of seeds germination and the best variant of nutrient mixture for seedling.
R. B. Mazzini-Guedes, M. R. Nogueira, M. V. Ferraz, A. K. D. Bezerra, S. T. S. Pereira, and K. F. L. Pivetta, “Rooting of Azalea Cuttings (Rhododendron x Simsii Planch.) Under Indolebutyric Acid and Boron Concentrations,” International Journal of New Technology and Research, vol. 3, no. 11, p. 263183, Nov. 2017.https://www.neliti.com/publications/263183/.
Read on Neliti
M. M. McCartney et al., “Effects of Phytophthora Ramorum on Volatile Organic Compound Emissions of Rhododendron Using Gas Chromatography–Mass Spectrometry,” Analytical and Bioanalytical Chemistry, vol. 410, no. 5, pp. 1475–1487, Feb. 2018.
doi: 10.1007/s00216-017-0789-5.
Phytophthora ramorum is an invasive and devastating plant pathogen that causes sudden oak death in coastal forests in the western United States and ramorum blight in nursery ornamentals and native plants in various landscapes. As a broad host-range quarantine pest that can be asymptomatic in some hosts, P. ramorum presents significant challenges for regulatory efforts to detect and contain it, particularly in commercial nurseries. As part of a program to develop new detection methods for cryptic infections in nursery stock, we compared volatile emissions of P. ramorum-inoculated and noninoculated Rhododendron plants using three gas chromatography–mass spectrometry methods. The first used a branch enclosure combined with headspace sorptive extraction to measure plant volatiles in situ. Seventy-eight compounds were found in the general Rhododendron profile. The volatile profile of inoculated but asymptomatic plants (121 days post-inoculation) was distinguishable from the profile of the noninoculated controls. Three compounds were less abundant in inoculated Rhododendron plants relative to noninoculated and mock-inoculated control plants. A second method employed stir bar sorptive extraction to measure volatiles in vitro from leaf extractions in methanol; 114 volatiles were found in the overall profile with 30 compounds less abundant and one compound more abundant in inoculated Rhododendron plants relative to mock-inoculated plants. At 128 days post-inoculation, plants were asymptomatic and similar in appearance to the noninoculated controls, but their chemical profiles were different. In a third technique, volatiles from water runoff from the soil of potted healthy and inoculated Rhododendron plants were compared. Runoff from the inoculated plants contained four unique volatile compounds that never appeared in the runoff from mock-inoculated plants. These three volatile detection techniques could lead to innovative approaches that augment detection and diagnosis of P. ramorum and oomycete pathogens in nurseries and other settings.
J. O. S. É. A. MEJÍAS, \relax J. U. A. N. ARROYO, and \relax F. E. R. N. A. N. D. O. OJEDA, “Reproductive Ecology of Rhododendron Ponticum (Ericaceae) in Relict Mediterranean Populations,” Botanical Journal of the Linnean Society, vol. 140, no. 3, pp. 297–311, Nov. 2002.
doi: 10.1046/j.1095-8339.2002.00103.x.
In the southern Iberian Peninsula, Rhododendron ponticum occurs in restricted and vulnerable populations as a Tertiary relict. Population structure and the main phases of the reproductive process were examined in order to shed light on recruitment patterns and limitations. Rhododendron ponticum flowers are self-compatible and attract a diverse array of insects, which are responsible for a considerable number of seeds set in the populations. Nevertheless, only adults form populations, whilst seedlings are scarce and saplings virtually absent (only two juveniles out of 2489 adults sampled). Non-specialized vegetative multiplication by layering was observed. Recruitment failure seems to depend on the scarcity of safe microsites, which are free from drought, for seedling establishment. The observations contrast with R. ponticum’s reputation as an aggressive invader in temperate Atlantic areas. It is proposed that the species shows a variable balance between sexual reproduction and vegetative multiplication depending on environmental conditions. At present, only the latter seems to be prevailing in relict populations in the Iberian Peninsula. This flexible reproductive strategy is also discussed as a mechanism allowing persistence during geological climatic oscillations.
L. D. Moore, R. C. Lambe, and W. H. Wills, “Influence of Ozone on the Severity of Phytophthora Root Rot of Azalea and Rhododendron Cultivars,” Journal of Environmental Horticulture, vol. 2, no. 1, pp. 12–16, Mar. 1984.
doi: 10.24266/0738-2898-2.1.12.
The susceptibility of 21 azalea and rhododendron cultivars to colonization by Phytophthora cinnamomi and to injury caused by ozone was determined. Resistance to P. cinnamomi was lacking in most cultivars with only 3 rhododendron cultivars ‘Caroline,’ ‘Chionoides’ and ‘English Roseum’ and 3 azalea cultivars ‘Hinodegiri,’ ‘Sweetheard Supreme’ and ‘Tradition’ having resistance. All of the rhododendron cultivars, except ‘Nova Zembla,’ were highly resistant to ozone injury. Of the azalea cultivars, only ‘Delaware Valley White,’ ‘Roadrunner’ and ‘White Water’ exhibited injury following fumigation with 0.20 ppm ozone for 6 hours on 3 consecutive days. The fumigation of P. cinnamomi-inoculated plants with ozone significantly increased the severity of Phytophthora root rot only in ‘Hinodegiri’ plants, but a trend towards greater disease severity was evident in many cultivars.
S. Moore-Parkhurst and L. Englander, “A Method for the Synthesis of a Mycorrhizal Association Between Pezizella Ericae and Rhododendron Maximum Seedlings Growing in a Defined Medium,” Mycologia, vol. 73, no. 5, pp. 994–997, Sep. 1981.
doi: 10.1080/00275514.1981.12021429.
V. S. Negi, R. K. Maikhuri, L. S. Rawat, and A. Chandra, “Bioprospecting of Rhododendron Arboreum for Livelihood Enhancement in Central Himalaya, India,” p. 10, 2013.
Non-timber forest products (NTFP) are extensively extracted from Indian forests, and their role in rural and forest economies is immense. A number of wild plants used by rural and tribal population contributing significantly to livelihood and food security have escaped recognition and scientific inquiry in many developing countries. The wild edibles are gaining increased attention as potential food supplement or cheaper alternative of commercial fruits across the world. The Himalayan region is comprised of a large variety of wild-growing plants that are used for food and other subsistence needs by the local communities. Rhododendron arboreum is a wild plant species possesses high ecological importance and the flower of the species having unique medicinal and nutritional value. The flowers of the tree are edible and are used in the preparation of a refreshing drink in mountain region of Central Himalaya. The paper highlighted medicinal, nutritive and potential of R. arboreum for bioprospecting by making value added products to improve the livelihood of hill farmers in Himalaya region.
S.-C. Ng and R. T. Corlett, “The Ecology of Six Rhododendron Species (Ericaceae) with Contrasting Local Abundance and Distribution Patterns in Hong Kong, China,” Plant Ecology, vol. 164, no. 2, pp. 225–233, Feb. 2003.
doi: 10.1023/A:1021292227583.
Six native Rhododendron species grow in thedegraded, fire-prone landscape of Hong Kong: R. simsii andR. farrerae are common and widespread, R.moulmainense is relatively restricted, and R.championiae, R. hongkongense, and R.simiarum are rare. For all species except the rare R.simiarum, there was direct or indirect evidence of regrowth afterfire, but only the two smallest and commonest species grow in sites which arefrequently burned. Both flowered within 18 months of a fire. Most populationsofall species, except R. simiarum, had a deficiency ofindividuals in the smaller basal circumference classes. Seedlings were foundonly in three out of four plots of R. simiarum, and one ofR. farrerae. A few seedlings of the other rare specieswereseen in open, litter-free microsites outside the study plots, but no seedlingsof the most common species, R. simsii, were seen anywhere.In logistic regression models, one or more measures of plant size weresignificant positive predictors of flowering at least once in the three yearstudy period for all species, while percentage cover by surrounding vegetationhad a significant negative impact on all except R. simsiiand R. farrerae, for which no populations arestrongly-shaded. Although the absence of current recruitment is not necessarilya cause for concern in long-lived species that can resprout after fire, werecommend that active vegetation management should be tried to enhance thesurvival and reproduction of R. moulmainense, R.championiae and R. hongkongense, and that newpopulations of these species and R. simiarum should becreated.
“Bulletin UASVM Horticulture, 68(1)/2011,” p. 6.
Rhododendrons and azaleas are more exacting in their cultural requirements than many commonly grown plants and so will not readily grow in every garden. Wherever successfully grown, rhododendrons are without equal as landscape plants. The research initiated in the Botanical Garden Jibou in 2002-2010, will help in the selection and propagation of ornamental and tolerant to low temperatures representatives of species, suitable for cultivation in Northwestern Romania. This paper presents the behavior in our climatic conditions of 27 Rhododendron species received from botanical gardens and arboretums, native from different areas.
Explore millions of resources from scholarly journals, books, newspapers, videos and more, on the ProQuest Platform.
“The Propagation of Rhododendron Section Vireya from Seed,” p. 20.
The pollination process is briefly described and compatible pollinations within sect. Vireya are examined, including the anomalous behaviour of R.kawakamii var. flaviflorum. The morphology, storage and germination of pollen are illustrated, and seed harvesting techniques described. Details are given of seed morphology, its longevity, storage and the requirements for germination. The germination process is illustrated by following the progress of R.konori from seed to small seedling. The characteristics of seedlings within sect. Vireya are illustrated and the environmental conditions favouring rapid growth are tabulated. The development from seed to flowering plant is described for R.lochiae.
“Species of Rhododendron Acclimatization in the Botanical Garden of Jibou and Their Promotion in Landscape,” p. 4.
“Underutilized Fruit Crop,” p. 24.
“In Vitro Propagation of Rhododendron Griffithianum Wt.: An Endangered Rhododendron Species of Sikkim Himalaya,” Journal of Applied Biology & Biotechnology, 2016.
doi: 10.7324/JABB.2016.40211.
A reproducible protocol for in vitro propagation of R. griffithianum has been established. Multiple shoot proliferation from shoot-tip explants was occurred in the presence of 2-isopentenyl adenine (2-iP) alone or in combination with indole 3-butyric acid (IBA) in Anderson’s medium. The best treatment for shoot regeneration was Anderson’s medium supplemented with 5 µM 2-iP and 1.0 µM IBA, which promoted shoot proliferation in more than 75% culture with an average of 11.00 shoots per explants after twelve weeks. These shoots were successfully rooted on Anderson’s liquid medium supplemented with 1.5 µM IBA. The rooted plantlets were hardened in greenhouse with 84% survival rate.
S. Nongbri, K. Upadhaya, and harendra N. Pandey, “Seed Germination, Seedling Survival and Growth of Rhododendron Arboreum – a High Altitude Tree Species of Meghalaya, Northeast India,” International Journal of Ecology and Environmental Sciences, vol. 40, no. 4, pp. 255–260, Dec. 2014.http://nieindia.org/Journal/index.php/ijees/article/view/559.
The present study was carried out to understand the regeneration behaviour of Rhododendron arboreum in terms of seed germination and seedling survival and growth in different microsites i.e., open, periphery and interior of Swer and Sohrarim forests under natural condition and also along light gradients (high, intermediate and low) under net house conditions. The germination percentage at room temperature in the laboratory was 54 %. The seeds of the species showed 15 % viability after two years of storage. The survival of the seedlings were high in the open microsites of both the forests (72 - 76%) as compared to periphery (31- 40%) and forest interior (11 - 33%). The seedling mortality was high during rainy season. The RGRH and RGRW of the species were high during spring and rainy season as compared to dry season. Similarly, the survival and growth of the seedlings was better under high light condition. Results of the study indicate that besides temperature, soil moisture and nutrients, light was the key factor for seedling survival and growth in different microsites of the two forests.
A. Okamoto, M. Yamashita, and Y. Kajitani, “Breeding and Production of Kurume Azaleas (Rhododendron Obtusum Planch.),” p. 4.
Kurume azalea” is a brand name for evergreen azalea cultivars bred in Kurume, Fukuoka, which is located in northern Kyushu, and belong to Rhododendron obtusum Planch. with small to medium sized flowers. It is generally accepted that their foundation stocks are hybrids between R. kiusianum Makino and R. kaempferi Planch., and R. sataense Nakai. However, it was recently clarified that some cultivars show characteristics of R. macrosepalum Maxim. and R. ripense Makino. Kurume azaleas were created about 170 years ago, in the end of Edo era and appreciated indoors as potted plants (bonsai). Originally, they had been grown as a hobby among plant lovers. In the 1900’s, breeding improvement, production and marketing were greatly advanced by eager floricultural growers. The production of Kurume azaleas has outstandingly increased since the 1950’s because of a great demand as a green plant for parks and other public spaces. Kurume azaleas were introduced to Europe and the United States in the 1870’s. In Europe, they were loved as a pot culture, and were thus called Belgian florist azaleas. On the other hand, Kurume azaleas were to be loved in the United States because improvement of florist azaleas in Europe were for reduced height and cold hardiness. They are also used as parents to breed evergreen azaleas with increased cold hardiness and flower quality for gardens.
M. L. Osório, J. Osório, and A. Romano, “Chlorophyll Fluorescence in Micropropagated Rhododendron Ponticum Subsp. Baeticum Plants in Response to Different Irradiances,” Biologia Plantarum, vol. 54, no. 3, pp. 415–422, Sep. 2010.
doi: 10.1007/s10535-010-0076-1.
The aim of this study was to investigate acclimation of micropropagated plants of Rhododendron ponticum subsp. baeticum to different irradiances and recovery after exposure to high irradiance. Plants grown under high (HL) or intermediate (IL) irradiances displayed higher values of maximum electron transport rate (ETRmax) and light saturation coefficient (Ek) than plants grown under low irradiance (LL). The capacity of tolerance to photoinhibition (as assessed by the response of photochemical quenching, qp) varied as follows: HL > IL > LL. Thermal energy dissipation (qN) was also affected by growth irradiance, with higher saturating values being observed in HL plants. Light-response curves suggested a gradual replacement of qp by qN with increasing irradiance. Following exposure to irradiance higher than 1500 μmol m−2 s−1, a prolonged reduction of the maximal photochemical efficiency of PS 2 (Fv/Fm) was observed in LL plants, indicating the occurrence of chronic photoinhibition. In contrary, the decrease in Fv/Fm was quickly reverted in HL plants, pointing to a reversible photoinhibition.
J. Padrutt, H. Pellett, and P. Ascher, “Postpollination Reproductive Biology of Rhododendron Prinophyllum (Small) Millais,” Journal of the American Society for Horticultural Science, vol. 117, no. 4, pp. 656–662, Jul. 1992.
doi: 10.21273/JASHS.117.4.656.
Complete diallel matings were performed during two consecutive seasons in a full sibling population of Rhododendron prinophyllum, the pinkshell azalea. Examination of pollen tubes from collected and fixed styles revealed no differences in growth, rate of pollen tubes between selfs and outcrosses. Penetration of pollen tubes through the ovular micropyle region occurred 4 to 7 days after pollination, regardless of pollen source. Embryogenesis was studied in pistils collected from forced greenhouse plants of the same population. All ovules appeared to develop for a short period before senescing. Percent capsule set data from both years’ diallel pollinations indicated that some active form of self-recognition and rejection was operating and that environmental stresses and resource allocation were also influential. Additional information gathered included ovule counts, seed count to capsule size correlations, and germination trials. These pointed to a reduction in reproductive success at each developmental stage. Self-incompatibility (SI), defined as inability to set seed following self-pollination, is clearly not applicable here. There are inherent difficulties in separating an active, late-acting self-recognition/rejection system from inbreeding depression, which is a passive accumulation of homozygous recessive lethal and sublethal genes.
B. F. Palser, J. L. Rouse, and E. G. Williams, “Coordinated Timetables for Megagametophyte Development and Pollen Tube Growth in Rhododendron Nuttallii from Anthesis to Early Postfertilization,” American Journal of Botany, vol. 76, no. 8, pp. 1167–1202, 1989.
doi: 10.1002/j.1537-2197.1989.tb15100.x.
Rhododendron nuttallii T. W. Booth (Ericaceae) was used to derive concurrent timetables for megagametophyte, pollen tube and early postfertilization development from anthesis through 3 wk after pollination, based on timed collections of self-pollinated pistils. Stages of development were determined for over 33,500 cleared ovules, including, for selected collection dates, stages on different portions of the placenta. Pollen tube information was obtained by fluorescence microscopy of pistil squashes stained with aniline blue. Because of the very large number of ovules observed, it was possible to recognize a much more closely graded series of stages in megagametophyte development than is usually the case. While a range of stages occurred on all days, development progressed steadily from a majority of functional spores and 2-nucleate gametophytes on the day of anthesis to mostly a late zygote-primary endosperm stage at 18 days, and some 2-celled endosperm stages at 21 days, after pollination. At all times the most advanced stages, including first pollen tube entries, occurred on the outer surface of the lower half of the placenta, and the youngest on the inner surface of the uppermost portion. Fertilizable ovules were not found in any frequency until 8 days after pollination (then in only about 34% of the ovules); a few fertilized ones were seen after 10 days but constituted less than 5% until 12 days after pollination, thereafter increasing to about 60%. Fertilization occurred in any one of three morphologically recognizable stages distinguished by position and state of fusion of polar nuclei. Pollen germinated on the stigma 1–2 hr after pollination, and pollen tubes grew at a rate of about 1–1.25 cm/day, reaching the top of the ovary in 8–9 days with the first ovule entries seen after 10 days. There was a close correlation between megagametophyte development and pollen tube growth, with large numbers of functionally mature ovules not being found until pollen tubes had reached the ovary. While nuclei within ovules could not be distinguished in the squashes, three gametophyte stages that could be recognized—unelongated, elongated either without or with a pollen tube—were tallied for almost 29,000 ovules. The progression in these general stages corresponded well with that documented in more detail from cleared ovules. Unpollinated pistils showed a similar progression of gametophyte stages until the time fertilization would start to occur, after which there was continued accumulation of functionally mature ovules. A variety of abnormally developed and/or collapsing(ed) ovules or gametophytes were seen; collectively, they averaged over 8.6% of all ovules.
J. L. Parke and C. Lewis, “Root and Stem Infection of Rhododendron from Potting Medium Infested with Phytophthora Ramorum,” Plant Disease, vol. 91, no. 10, pp. 1265–1270, Oct. 2007.
doi: 10.1094/PDIS-91-10-1265.
Phytophthora ramorum has been detected in soil and potting media, but the potential for root infections is not fully understood. To determine whether the root system could become infected and transmit disease, rhododendron ‘Nova Zembla’ plants grown from rooted cuttings and native Pacific rhododendron (Rhododendron macrophyllum) plants grown from seed were transplanted into a potting medium artificially infested with P. ramorum. Inoculum consisted of V8-brothvermiculite cultures of P. ramorum, chopped infected leaves, or zoospores. Plants were watered from the bottom to prevent splash dispersal of inoculum onto stems and foliage. Both infested amendments and applications of zoospores resulted in plant mortality within 3 to 7 weeks. P. ramorum was isolated from hair roots, large roots, and stems above and below the potting medium surface. Noninoculated control plants remained healthy and did not yield P. ramorum. Epifluorescence microscopy of tissue culture plantlets inoculated in vitro revealed attraction of zoospores to wounds and root primordia, and colonization of the cortex and vascular tissues of roots and stems, including the xylem. Transmission of P. ramorum from infested potting media to stems via infected, symptomless root tissue demonstrates the need to monitor potting media for presence of the pathogen to prevent spread of P. ramorum on nursery stock.
F. Pasche, A. Pornon, and T. Lamaze, “Do Mature Leaves Provide a Net Source of Nitrogen Supporting Shoot Growth in Rhododendron Ferrugineum?,” New Phytologist, vol. 154, no. 1, pp. 99–105, 2002.
doi: 10.1046/j.1469-8137.2002.00370.x.
• Nitrogen transfers in mature (c. 40-yr-old) Rhododendron ferrugineum plants from mature leaves to growing shoots (Sh0) were estimated in the field at the branch scale. • Before bud break, the N pool of either 1-yr-old (L1) or 2-yr-old (L2) leaves of selected branches was labelled with 15NH4Cl. The N dynamics were then investigated on three occasions during shoot growth. Mineral N uptake by roots was estimated by supplying seedlings with 15NH4+ or 15NO3− (glasshouse) and mature plants with 15NH4+ (field). • Approximately 60% of the 15N supplied was recovered in the labelled branches (40% in L1 leaves and 19% in Sh0) 78 d after L1 labelling. A similar pattern was observed for L2 labelling. Only traces of 15N were detected in 1- and 2-yr-old-stems. Although changes in the isotopic contents showed the occurrence of N transfer from mature leaves to the shoot, total L1 and L2 leaf N content was not modified. Simultaneously, exogenous 15N uptake by the roots was very low. • We conclude that, despite the internal N cycling, mature leaves do not constitute a net source of nitrogen supporting shoot growth. The latter depends mainly upon endogenous nitrogen stored in woody stems and roots.
D. Paterson, “Repatriation of Rhododendron Plants to China,” Sibbaldia: the International Journal of Botanic Garden Horticulture, no. 1, pp. 29–34, Jan. 1970.
doi: 10.24823/Sibbaldia.2003.92.
A Darwin Initiative grant awarded to the Royal Botanic Garden Edinburgh in 1994 gave the opportunity to train some Chinese horticulturists and repatriate a number of rhododendrons back to China from the Garden in Edinburgh. The Chinese partners in the programme were Hua Xi Alpine Botanic Garden and Guizhou Botanic Garden. The initial stages of the project involved training and the selection of suitable species. Following some trials and discussion about possible genetic contamination of native populations from imported material, work on propagating the plants started. Once rooted the plants were packed and transported to China. Following site preparation the young plants were planted in nursery beds. Two hundred and thirty plants, representing almost 100 species, were planted. Of these more than 80% established successfully. Seed was also collected in China from small populations of endemic species of rhododendron to include in the project. The final stage of the project involved help with garden design at Hua Xi.
M. L. Pathak, D. Lamichhane, L. B. Neupane, and K. B. Nepali, “Rhododendron Arboreum: Propagation through Seeds, Cultivation, Diseases and Control Methods,” no. 1, p. 5, 2021.
This paper aims to discuss about the seed germination process, problems during cultivation, diseases and control methods of Rhododendron arboreum. Germination test was carried out at National Botanical Garden, Godavari from the seeds collected from there. The problems during seedling transplantation and disease appeared were observed in Hupsekot Rural Municipality, Nawalparasi District at elevation of about 1500 m asl. The seed germination period was found more than one year with about eighty percent germination percentage with 90–95% survival rate. It was also found that the R. arboreum was acid loving plant. Powdery mildew was the common disease appeared in the field. Some recommendations are proposed for prevention and cure of Rhododendron related diseases.
D. Pavingerová, J. Bríza, K. Kodýtek, and H. Niedermeierová, “Transformation of Rhododendron Spp. Using Agrobacterium Tumefaciens with a GUS-Intron Chimeric Gene,” Plant Science, vol. 122, no. 2, pp. 165–171, Feb. 1997.
doi: 10.1016/S0168-9452(96)04544-X.
The five Rhododendron cultivars, ‘America’, ‘Catawbiense grandiflorum roseum’, ‘Madame Carvalho’, ‘Mars’ and ‘Nova Zembla’ were used for transformation by Agrobacterium tumefaciens carrying T-DNA with the gusA gene encoding β-glucuronidase (GUS) gene and the neomycin phosphotransferase II gene as a selectable marker gene. The GUS reporter gene was successfully transferred into all five cultivars as indicated by fluorimetric staining, polymerase chain reaction (PCR) and Southern blot analysis. Some primary transformants appeared to be chimeric as both GUS expression and GUS nucleotide sequences were lost during vegetative propagation.
M. Piercey, M. Thormann, and R. Currah, “Saprobic Characteristics of Three Fungal Taxa from Ericalean Roots and Their Association with the Roots of Rhododendron Groenlandicum and Picea Mariana in Culture,” Mycorrhiza, vol. 12, no. 4, pp. 175–180, Aug. 2002.
doi: 10.1007/s00572-002-0166-9.
Simultaneous associations among ectotrophic and ericoid mycorrhizal hosts and their mycorrhizal fungi are expected in boreal bogs where ericaceous shrubs and conifers coexist rooted in an organic matrix dominated by Sphagnum mosses. We were thus prompted to examine, in vitro, the abilities of three ericoid mycorrhizal fungi [Hymenoscyphus ericae, Oidiodendron maius, and Variable White Taxon (VWT)] to associate with Picea mariana (Pinaceae), with both P. mariana and Rhododendron groenlandicum (Ericaceae) simultaneously, and to decompose Sphagnum fuscum. Hymenoscyphus ericae and VWT developed an intracellular association with roots of P. mariana and with roots of R. groenlandicum. Two strains of O. maius did not form typical infection units in R. groenlandicum, nor did they colonize the root cells of P. mariana. Mass losses incurred by sterilized S. fuscum plants inoculated with these three taxa indicated that O. maius could be more efficient as a free-living saprophyte on this material than either H. ericae or VWT and may in part explain why atypical associations with the roots of ericaceous hosts were formed.
A. Pornon and B. Doche, “Age Structure and Dynamics of Rhododendron Ferrugineum L. Populations in the Northwestern French Alps,” Journal of Vegetation Science, vol. 7, no. 2, pp. 265–272, 1996.
doi: 10.2307/3236327.
Abstract. The ericaceous shrub Rhododendron ferrugineum occupies large areas at the subalpine level (1600–2200 m) of the northwestern French Alps. It frequently reaches 90–100 % cover, accumulates 60–70t/ha (dry weight) above-ground biomass and is able to dominate many subalpine landscapes by outcompeting other species. We formulated the hypothesis that the species shows a rapid and invasive seedling establishment and a fast population development. We investigated the age structure and development of two populations. Although classic colonization stages can be identified, and variation did occur depending on the site, R. ferrugineum populations showed a surprisingly slow development compared with other ericaceous species. Curves obtained from polynomial regression equations of cover on age allowed us to predict the future development of populations. Thus, depending on the site, it would take 150 to 250 yr to achieve total cover. We discuss the factors involved that could explain this slow development and discuss which biotic and abiotic factors may be responsible for the large extension of this species in the subalpine belt.
A. Pornon, N. Escaravage, I. Till-Bottraud, and B. Doche, “Variation of Reproductive Traits in Rhododendron Ferrugineum L. (Ericaceae) Populations along a Successional Gradient,” Plant Ecology, vol. 130, no. 1, pp. 1–11, May 1997.
doi: 10.1023/A:1009724216796.
Sexual and vegetative reproduction in the alpine species Rhododendron ferrugineum was studied along a successional sequence (meadow → open heathland → closed heathland) at two sites and in a wet heathland. This study aims to determine (1) the characteristics of sexual reproduction in R. ferrugineum populations (2) when and how these populations develop layering (adventitious rooting) and (3) whether reproductive traits and reproductive strategies develop relative to the degree of population closure and maturity. The variables used to describe sexual reproduction were inflorescence density (per m(2) of Rhododendron cover), number of flowers per inflorescence and per m(2) of Rhododendron cover, and seeds production (per fruit and m(2) of Rhododendron cover). Flowering and fruiting phenologies were also recorded. For describing clonal development, we investigated layering variables such as length and annual growth rate of prostrate stems, rooting occurence and ramet density. The results show that the direction toward which the clones extend is mainly determinated by the topography, and that layering steadily increases with increasing population closure and maturity. Reproductive potential of R. ferrugineum is enormous (0.4–2.4 million seeds m(-2)) but reproductive effort remains low with respect to total biomass of seeds (3–21 g m(-2)). Reproductive effort of R. ferrugineum populations could be reduced as a conterpart of layering development only when the shrub draws more matter and energy in layering stems than to aerial stems. The variations in reproductive traits observed on our sites could be due to primarily to phenotypic response to variable microhabitat features, rather than to genetically deterministic processes.
W. S. Price, H. Ide, Y. Arata, and M. Ishikawa, “Visualisation of Freezing Behaviours in Flower Bud Tissues of Cold-Hardy Rhododendron Japonicum by Nuclear Magnetic Resonance Micro-Imaging,” Functional Plant Biology, vol. 24, no. 5, pp. 599–605, 1997.
doi: 10.1071/pp97049.
1H nuclear magnetic resonance (NMR) micro-imaging was used to study the freezing behaviour of wintering flower buds of Rhododendron japonicum (A. Gray) Suringer. Amulti-slice multi- echo pulse sequence was used to acquire images at different subfreezing temperatures. The images obtained predominantly reflected the density of mobile (i.e. non-ice) protons mainly from unfrozen water. By comparing these images taken at various subfreezing temperatures, we could determine which tissues produced high temperature exotherms and low temperature exotherms in differential thermal analyses. In flower buds of the cold-hardy R. japonicum, typical extra-organ freezing was successfully imaged. The scales readily froze at –7°C but some florets remained supercooled even at –21°C. The size of the supercooled florets was reduced with decreasing temperature which indicated a gradual decrease in floret water content. With decreasing temperature, there was a gradual decrease in the signal intensity of the flower bud axis including the peduncle and immature pith tissues, which implies either dehydration or partial freezing of these tissues. Deep supercooling in the entire mature pith tissues was also clearly visible in these images. Due to its non-invasive nature, NMR micro-imaging is a useful tool for studying freezing behaviours in various plant tissues, especially for imaging organised or harmonised freezing in complex organs as well as for clarifying the diversity and mechanisms involved in freezing behaviours.
J. Qiu et al., “Flowering Biology of Rhododendron Pulchrum,” Horticulturae, vol. 7, no. 11, p. 508, Nov. 2021.
doi: 10.3390/horticulturae7110508.
To study the flowering biology of Rhododendron pulchrum, we used scanning electron microscopy (SEM) and paraffin sectioning to observe the microstructures of its floral organs, a methyl thiazolyl tetrazolium (MTT) colorimetric assay to detect pollen viability in different periods, continuous observations to study flowering phenology, and artificial pollination and a benzidine-hydrogen peroxide method to determine stigma receptivity. R. pulchrum exhibited a centralized flowering phenology. The protogynous stigmas of R. pulchrum were able to receive pollen before flowering. The pollen grains of R. pulchrum fused into tetrads, the average ratio of the polar axis length to the equatorial axis length (P/E) was 1.05, and the pollen viability was highest in the initial flowering period, reaching 88.98%. The pollen/ovule (P/O) ratio was 266–328, and the outcrossing index (OCI) was 4; the vitality of R. pulchrum pollen remained high in the initial flowering and blooming periods. Compared with the lifespan of a single flower, pollen vitality remained high for most of the experimental period, thereby improving male fitness. The P/O ratio suggests that R. pulchrum may have a facultative outcrossing breeding system. The OCI estimation suggests that R. pulchrum is partially self-compatible, most likely requiring pollinators to complete pollination.
E. S. RAND, "The Rhododendron and American Plants."A Treatise on the Culture, Propagation, and Species of the Rhododendron, Etc. Hurd and Houghton, 1876.
M. Riedel, S. Werres, M. Elliott, K. McKeever, and S. Shamoun, “Histopathological Investigations of the Infection Process and Propagule Development of Phytophthora Ramorumon Rhododendron Leaves,” Forest Phytophthoras 2(1). doi: 10.5399/osu/fp.2.1.3036, vol. 2, no. 1, 2012.
doi: 10.5399/osu/fp.2.1.3036.
Studies on the relationship between rhododendron and Phytophthora ramorum include the influence of wounds on leaf infection and on the development of leaf necrosis (De Dobbelaere et al. 2010; Denman et al. 2005), the influence of the inoculum type (Widmer 2009), and tissue colonization by P. ramorum (Brown and Brasier 2007; Parke and Lewis 2007; Pogoda and Werres 2004). There are only a few studies on the development of the pathogen on the leaf surface (Moralejo and Descals 2011; Moralejo et al. 2006) and there is no information on the infection process on leaves. Therefore the aim of the present study was to learn more about the infection process on rhododendron leaves after zoospore application, as well as the capacity for sporulation and the development of chlamydospores and gametangia.
’Rhododendron citrinum’ (Section Eurvireya, Subsection Malesia) is found in Sumatra, Java and Bali growing in montane forest between 1,000 and 2,900 m (Argent). ’R. citrinum’ was introduced into cultivation in the 1980s from western Java. Vireyas are not well represented in Java, with only seven species, relatively few when compared with neighbouring islands of Sumatra (22 species), Borneo (54) and Sulawesi (29).
D. B. Rowe, S. L. Warren, and F. A. Blazich, “Seedling Growth of Catawba Rhododendron. I. Temperature Optima, Leaf Area, and Dry Weight Distribution,” HortScience, vol. 29, no. 11, pp. 1298–1302, Nov. 1994.
doi: 10.21273/HORTSCI.29.11.1298.
Catawba rhododendron (Rhododendron catawbiense Michx.) seedlings of two provenances, Johnston County, N.C. (35°45′N, 78°12′W, elevation = 67 m), and Yancey County, N.C. (35°45′N, 82°16′W, elevation = 1954 m), were grown in controlled-environment chambers for 18 weeks with days at 18, 22, 26, or 30C in factorial combination with nights at 14, 18, 22, or 26C. Shoot and root dry weights and total leaf areas of seedlings of the Yancey County provenance (high elevation) exceeded (P ≤ 0.05) those of the Johnston County (low elevation) provenance at all temperature combinations. Leaf area was maximal at 22/22C, 18/26C, and 22/26C and minimal at 30/14C (day/night). Shoot dry weight responded similarly. Root dry weight decreased linearly with increasing day temperature, but showed a quadratic response to night temperature. Leaf weight ratio (leaf dry weight: total plant dry weight) increased, while root weight ratio (root dry weight: total plant dry weight) decreased with increasing day temperature. Leaf weight ratio was consistently higher than either stem or root weight ratios. Day/night cycles of 22 to 26/22C appear optimal for seedling growth.
H. Salley, “The Delp Hybrids: Part I, A Passion for Rhododendron Hybridizing,” Journal American Rhododendron Society, vol. 49, no. 1, 1995.
G. K. Schmilewski and R. Härig, “Raised Bog Peat as the Basic Material for the Production of Rhododendron and Azaleas - Formation, Excavation, Processing, Substitutes,” Acta Horticulturae, no. 364, pp. 101–110, May 1994.
doi: 10.17660/ActaHortic.1994.364.12.
S.-K. Shen, F.-Q. Wu, G.-S. Yang, Y.-H. Wang, and W.-B. Sun, “Seed Germination and Seedling Emergence in the Extremely Endangered Species Rhododendron Protistum Var. Giganteum—the World’s Largest Rhododendron,” Flora - Morphology, Distribution, Functional Ecology of Plants, vol. 216, pp. 65–70, Sep. 2015.
doi: 10.1016/j.flora.2015.08.006.
Big tree rhododendron, Rhododendron protistum var. giganteum (Ericaceae) is an endangered and important germplasm source with high ornamental value in China. To design appropriate germination and seedling establishment protocols for a species conservation and restoration program, we studied the effects of temperature, photoperiod, storage, and gibberellic acid (GA3) treatment on seed germination in a laboratory experiment. The effects of soil substrate and sowing depth on seedling emergence were studied in a greenhouse experiment. We hypothesized that photoperiod is a limiting factor for seed germination of big tree rhododendron, and soil type and sowing depth would affect seedling emergence. Results showed that seeds of big tree rhododendron were non-dormant, and temperature significantly affected germination percentages (GP) and mean germination time (MGT). The optimal temperatures for seed germination were relatively low (15°C and 20°C). High temperature negatively affected seed germination. The seeds had less than 5% of GP when incubated in complete darkness, suggesting that darkness significantly inhibits seed germination. Storage period and temperature had significant effect on GP and MGT of big tree rhododendron seeds, and the effect of their interaction on MGT was also significant. GA3 treatment increased GP and germination speed. Soil substrates did not significantly affect seedling emergence, but native soil is beneficial to seedling growth. When the seeds were sown on the soil surface, seedling emergence was higher than 80%, but it decreased with increasing sowing depth, and no seedling emerged at 3cm soil depth. We present some suggestions for the ex situ conservation and restoration program, including seed germination and seedling artificial propagation of big tree rhododendron based on the research results.
H. B. Sifton, “Lysigenous Air Spaces in the Leaf of Labrador Tea, Ledum Groenlandicum Oeder.,” New Phytologist, vol. 39, no. 1, pp. 75–79, 1940.
doi: 10.1111/j.1469-8137.1940.tb07122.x.
K. K. Singh, B. Gurung, L. K. Rai, and L. H. Nepal, “The Influence of Temperature, Light and Pre-Treatment on the Seed Germination of Critically Endangered Sikkim Himalayan Rhododendron (R. Niveum Hook f.),” p. 7.
R. niveum Hook f. is a beautiful and endangered rhododendron that has limited distribution in the Sikkim Himalaya. In an effort to improve and promote the propagation of this over-exploited plant, the effect of temperature and light on the germination of seeds was investigated with various presoaking treatments of plant growth substances (GA3, Kinetin and BAP) and nitrogenous compound (KNO3). The combined effect of GA3 with Kinetin or BAP (25 µM) was also examined. Seeds were given a presoaking treatment with GA3, BAP or a combination of both to influence germination. A temperature of 21oC was found optimum and showed 34.33% germination, with 21 days for onset and 50 days for final germination under 16 hr light condition. The seeds of R. niveum need light to trigger the germination and no germination was observed in darkness. Though the seed viability was 86% as determined by tetrazolium staining, maximum germination of 63.67 % was obtained only when the seed was soaked in GA3 + BAP (25 µM each) solution for 24 h and incubated for germination at 21oC, constant temperatures in 16 hr photoperiod. The other treatments were far less effective in promoting the germination of this endangered species. The present study indicates that constant 21oC, temperature incubation and 16 hr photoperiod have a positive relationship with seed germination of R. niveum even under no pre-treatments. Seeds stored at low temperature (4 oC) could maintain viability for less than six month. Here, it is the first time we have described the seed germination requirements of R. niveum, which are under threat due to anthropogenic pressure [Journal of American Science 2010;6(8):172-177]. (ISSN: 1545-1003).
K. K. Singh and B. Gurung, “Regeneration of Plants from Alginate-Encapsulated Shoots of Rhododendron Dalhousiae Hook. F.,” Journal of Applied and Natural Science, vol. 3, no. 1, pp. 29–33, Jun. 2011.
doi: 10.31018/jans.v3i1.149.
A method has been developed for plant regeneration from alginate-encapsulated nodal segments of Rhododendron dalhousiae. Shoot tips collected from in vitro proliferated shoots were used for synthetic seed production. For encapsulation, nodal segments were mixed with MS medium supplemented with 3% sodium alginate and incubated with calcium chloride (60 mM). The maximum frequency (69%) of conversion of encapsulated shoot tips into plantlets was achieved on MS medium containing 25 ?M 2-isopentenyladenine (2iP) along with additive such as, 100 mg L-l polyvinyl pyrrolidone (PVP), 100 mg L -l ascorbic acid, 10 mg L-l citric acid. The presence of 2iP (25 ?M) with IAA (0.6 ?M) improved re-generation. Amongst the two gelling agents used higher shoot proliferation as well as better growth were observed in cultures grown on Agar in comparison to Phytagel medium. Encapsulated nodal segments stored at 4°C for 25 days also showed successful conversion, followed by development into complete plantlets when returned to regeneration medium. Liquid medium was superior over solid medium for root formation and growth. IBA (1.0 ?M) was more effective than other auxins for root induction. Plantlets with developed shoot and roots were hardened off to survive ex vitro conditions and successfully established in greenhouse. Possibility of direct sowing of synthetic seeds in the soil was also examined.
K. K. Singh and B. Gurung, “In Vitro Propagation of R. Maddeni Hook. F. an Endangered Rhododendron Species of Sikkim Himalaya,” Notulae Botanicae Horti Agrobotanici Cluj-Napoca, vol. 37, no. 1, pp. 79–83, Jun. 2009.
doi: 10.15835/nbha3713100.
A protocol is described for rapid and large scale propagation of an endangered, important Sikkim Himalayan rhododendron (R. maddeni Hook. f.) by in vitro culture of cotyledonary nodes from 15 days old seedlings. Several cytokinin types were evaluated for their effect on shoot multiplication from cotyledonary nodes. Maximum numbers of shoot (12.00 ±0.58) were observed on the AM containing 7 mg/l 2iP, 0.1 mg/l IAA after eight weeks of culture. Incorporation of 0.1 mg/l IAA in the medium during the first subculture after establishment and initiation of shoot buds significantly improved the shoot elongation. Regenerated shoots were separated and rooted on same strength AM medium supplemented with 0.2 mg/l of IBA alone for three weeks. Well-developed complete plantlets were transferred on to specially made plastic cup containing soilrite. The rooted plantlets were hardened and successfully established in greenhouse, the plants were transferred to field site at Pangthang arboretum of the Institute and the ‘Rare & Threatened Plant Conservation Park’ of Zoological Park, Gangtok, Sikkim.
K. K. Singh and L. K. Rai, “In Vitro Propagation of Rhododendron Niveum Hook f,” vol. 2, p. 8, 2013.
An efficient protocol for plant regeneration through multiple shoots induction from shoot tips of Rhododendron niveum was established. The highest percentage (68±1.15) of multiple shoot induction and number of shoots (8.66±0.57) per explants were found on AM supplemented with 5.0 mg/l 2-isopentyladenine (2iP). Then the 2ip (5.0 mg/l) combined with 0.1 mg/l IAA (Indole acetic acid) was found to be more suitable for getting more number of shootlets (9.00±0.33). The induced shoots were excised and inoculated on to liquid AM containing different concentrations of NAA or IBA on Filter Paper Bridge for rooting. The highest percentage (70) of root induction and the highest number of roots per shoot (6.67 ± 0.33) was found on liquid AM having 0.2 mg/l IBA. Well rooted plantlets were transferred to small polythene bags containing peat moss and soil (1:3) and maintained with a high humidity for acclimation. This is the first report for in vitro regeneration of R. niveum where large number of plant have been successfully produced and maintained in polyhouse/misthouse. 70% of the plants survived and all were morphologically normal.
T. A. R. Society, “JARS - Journal American Rhododendron Society,” Virginia Tech Scholarly Communication University Libraries. Digital Library and Archives of the Virginia Tech University Libraries, 1947.https://scholar.lib.vt.edu/ejournals/JARS/.
Scholarly Communication is a dynamic landscape, and we are continually evolving. Many scholarly communications activities have spun-off into their own departments, such as VT Publishing and Digital Imaging and Preservation Services, and Digital Library Development. Our focus is on supporting the creation and dissemination of scholarship.
W. Spethmann, “Long Term Growth Comparison of Different Propagation Techniques in Rhododendron (Grafting; Cutting; in Vitro),” Acta Horticulturae, no. 364, pp. 45–52, May 1994.
doi: 10.17660/ActaHortic.1994.364.5.
M. C. Starrett, F. A. Blazich, and S. L. Warren, “Initial Growth of Rosebay Rhododendron Seedlings as Influenced by Day and Night Temperatures,” HortScience, vol. 28, no. 7, pp. 705–707, Jul. 1993.
doi: 10.21273/HORTSCI.28.7.705.
Rosebay rhododendron (Rhododendron maximum L.) seedlings were grown in controlled-environment chambers for 14 weeks under long (9-hour) days at 18, 22, 26, or 30C in factorial combination with 15-hour nights at 14, 18, 22, or 26C. Total dry-matter production was lowest for 18C days and highest for 26C days. A similar response occurred for top, leaf, root, and stem dry weights. Nights at 22C maximized total plant, top, leaf, and stem dry weights. The optimum day/night cycle for dry-matter production was 26/22C. Leaf area was optimum with 18C nights. Leaf weight ratio (leaf dry weight: total plant dry weight) increased with an increase in night temperature to a maximum at 22C. Root weight ratio (root dry weight: total plant dry weight) decreased with an increase in night temperature to a minimum at 22C. Stem weight ratio (stem dry weight: total plant dry weight) and shoot: root ratio (top dry weight: root dry weight) were not influenced significantly by day or night temperature. A day/night cycle of 26/22C seems to be optimal for producing-salable plants.
K. Takahashi and T. Itino, “Measurement of Inbreeding Depression in Rhododendron Kaempferi: Seed Production, Germination, Juvenile Survival, and Growth,” Botany, pp. 1–7, Nov. 2021.
doi: 10.1139/cjb-2021-0038.
I. Tamaki, W. Yoichi, Y. Matsuki, Y. Suyama, and M. Mizuno, “Inconsistency between Morphological Traits and Ancestry of Individuals in the Hybrid Zone between Two Rhododendron Japonoheptamerum Varieties Revealed by a Genotyping-by-Sequencing Approach,” Tree Genetics & Genomes, vol. 13, no. 1, p. 4, Dec. 2016.
doi: 10.1007/s11295-016-1084-x.
The morphological traits and genetic backgrounds of hybrid individuals in a hybrid zone reflect the history of that zone. In the hybrid zone between Rhododendron japonoheptamerum var. hondoense (RJH) and R. japonoheptamerum var. kyomaruense (RJK), flower morphological traits that can be used to distinguish the two varieties were measured and leaves were sampled for DNA extraction. Reference populations consisting of pure RJH and RJK were also used. Genotype data for individuals were obtained by the multiplexed ISSR genotyping by sequencing (MIG-seq) method. RJH and RJK in the reference populations were morphologically and genetically clearly differentiated. In the hybrid zone studied, although there were morphologically pure RJH and RJK, and hybrids between them, most individuals, including those that were morphologically pure, had ancestries from both RJH and RJK. There were no significant correlations between morphological traits and the proportion of ancestry within an individual. These results suggest that this hybrid zone originated from the hybridization between the RJH and RJK in the past. The result of model comparison among population demographic models also supported this hypothesis, and the time when the hybrid zone was established was estimated to be 410,000 years ago. It is considered that accumulation of recombinations subsequent to the formation of the hybrid zone contributed to the inconsistency between the morphological traits and the fraction of each ancestral genome within an individual.
M. Tang, X. Liu, M. Xiao, and F. Liu, “Study on Seedling Propagation Techniques and Laws of Different Provenances of Rhododendron,” p. 7.
The adaptability and growth characteristics of different red carp provenances in different regions were selected to select suiTable good provenances. In this paper, the leaf traits, ground diameter and plant height growth of different provenances of red peony were observed. Test and related analysis. It indicates that there are extremely significant differences between different provenances, regardless of ground diameter, plant height, or length and width of compound leaves, length and width of leaflets, and number of leaflets. This paper also discusses the breeding and breeding techniques of red carp, as well as the growth pattern.
L. G. Taylor, “The Influence of in Vitro KCl Treatments on the Water Relations and Acclimatization of Tissue-Cultured Flame Azalea (Rhododendron Calendulaceum),” Thesis, Virginia Tech, 1990.https://vtechworks.lib.vt.edu/handle/10919/42231.
Propagation by tissue culture is effective for many woody ornamental plants, but propagules often become desiccated and die during the acclimatization period. This loss is due in part to stomata that fail to close in response to the reduced humidity outside of the culture environment. KCl was used in in vitro treatments to determine if an additional K supply would improve microshoot stomatal function and water status during acclimatization. The effects of the KCl treatments upon subsequent microshoot rooting and percent fresh weight gain were also evaluated. In preliminary experiments, microshoots of the flame azalea (Rhododendron calendulaceum) were subcultured onto modified Woody Plant Medium amended with a wide range of KCl concentrations for various time periods. It was determined that microshoots did not grow well when cultured at in vitro KCl levels above 50 mM, so treatments were adjusted to 0, 30, and 60 mM KC1, with 9 days of in vitro exposure. After treatment, percent tissue K was determined by atomic absorption spectrophotometry and microshoot water potentials were measured by thermocouple psychrometry. The capacity for the microshoots to resist desiccation after in vitro KCl treatment was determined by percent rooting and fresh weight gain after exposure to dehydration stress, and by gravimetric weight loss of microshoots placed in isopiestic tubes. In addition, microshoots from in vitro KCl treatments were evaluated for percent stomatal closure and water potential during a 38-day acclimatization period. In vitro KCl treatments induced elevated tissue K levels in microshoots and reduced microshoot water potentials, but it could not be shown that these effects specifically enabled the microshoots to resist desiccation. Rooting and percent fresh weight gain were not affected by in vitro treatments, nor was gravimetric weight loss. Microshoot maturation, as a function of days out of culture, had the greatest effect upon increased stomatal function, which, coupled with the onset of rooting, improved microshoot water status.
Rhododendron is a large genus, which includes rhododendrons and azaleas, of more than 1,000 species of shrubs and small trees in the family Ericaceae. Prized for their glossy foliage and showy clusters of blooms, Rhododendron spp. may be evergreen or deciduous and grow in a wide range of conditions. Hybridization has resulted in thousands of cultivars with various foliage and flower characteristics, as well as improved hardiness. There are rhododendrons and azaleas for just about every landscape situation. Rhododendrons have many potential disease and insect problems, including root rot, powdery mildew, rust, petal blight, lace bugs, Japanese beetle and vine weevil.
O. N. Tiwari and U. K. Chauhan, “Rhododendron Conservation in Sikkim Himalaya,” Current Science, vol. 90, no. 4, pp. 532–541, 2006.https://www.jstor.org/stable/24088945.
A review on the rhododendron conservation effort in the Sikkim and other parts of Indian Himalaya is presented here, with particular emphasis on ecology, baseline assessment, uses, growth studies, ex situ and in situ conservation initiatives. Identification of major gaps and constraints of forestry policy and plans and current practices of rhododendron conservation and management have been made. The impact of land use and management on the conservation of diversity is analysed and discussed. Species richness and diversity are significantly lower in heavily utilized forest. This study emphasizes that the forest rhododendrons in the habitats are severely threatened. Deforestation is the consequence of the tourist pressure for fuelwood along with other reasons in Himalaya. The degradation of rhododendrons in Himalaya is also due to lack of appropriate policy to guide the legal, institutional and operational development for the conservation. There is a need to implement the conservation obligations by transforming them into regulations in order to make them legally binding.
O. N. Tiwari and U. K. Chauhan, “Seed Germination Studies in Rhododendron Maddenii Hook.f. and Rhododendron Niveum Hook.f.,” vol. 12, no. 1, p. 7, 2007.
The genus Rhododendron constitutes a very important dominant combination in temperate, subalpine and alpine region of the Sikkim Himalaya. The present investigation was undertaken to examine the effect of various physical and chemical agents and plant growth regulators for enhancing uniform seed germination. Among the various plant growth regulators and chemicals tried, only a few could significantly influence seed germination over control. Seeds of Rhododendron maddenii, R. niveum in MS medium treated with GA3 (250 µM) recorded maximum germination. The BAP did not enhance the seed germination in R. maddenii; BAP (250 µM) was infact inhibitory. On the other hand, in R. niveum, BAP enhanced seed germination. The combined treatments of gibberellins and BAP resulted in reduced germination in R. maddenii and enhanced germination in R. niveum. Among nitrogenous compounds, KNO3 decreased germination in R. maddenii, and increased in R. niveum. However KOH solution was found to be beneficial in both concentrations. Seed germination percentage and seed vigour were decreased with the increase of storage time.
S. Tomsone and D. Gertnere, “In Vitro Shoot Regeneration from Flower and Leaf Explants in Rhododendron,” Biologia Plantarum, vol. 46, no. 3, pp. 463–465, Apr. 2003.
doi: 10.1023/A:1024363210872.
Rhododendron shoot regeneration was accomplished using either flower explants (each consisting of ovary with pedicel) of Rhododendron cvs. Nova Zembla and Irina or leaves isolated from in vitro grown Rhododendron catawbiense Michx. Multiple shoot tip clumps were obtained on Anderson’s medium containing 0.5 to 1.5 mg dm−3 thidiazuron (TDZ) in combination with 12 to 15 mg dm−3 N6-[2-isopentenyl]adenine (2iP) and 1 to 3 mg dm−3 indole-3-butyric acid (IBA). After 16 weeks on the regeneration media, explants with shoot tip clumps were transferred for shoot elongation to Anderson’s medium with 3 mg dm−3 2iP. Two months later, the shoots have reached 5 to 40 mm in length and were fit for subcultivation.
M. Ünsal and B. Altun, “Effects of Applications of Different Coloured Led Lights on Emerging and Seedling Growth of Rhododendron Luteum Sweet Seeds,” Uluslararası Tarım ve Yaban Hayatı Bilimleri Dergisi, vol. 6, no. 1, pp. 28–34, Apr. 2020.
doi: 10.24180/ijaws.654168.
This study was conducted to determine the effects of LED lights in different colours (Daylight LED, Blue LED, Red LED and Blue LED + Red LED (50%+50%)) on emerging rates of R. luteum seeds and seedling growth). The LED lights were applied to the seeds grown on the acidic peat in foam cups superficially in the form of 16:8 hours (light:dark). The results showed that the emerging rates in seeds subjected to Daylight, Red LED, Red + Blue LED and Blue LED light were determined as 61%, 45.66%, 43%, and 35%, respectively. The effect of different light colors on plant height was significant (p<0.01). Red + Blue LED, Red LED, Blue LED and Daylight LED subjected plants’ heights were determined as 10.342 cm, 10.262 cm, 75.06 cm, 7.139 cm, respectively. Diameters of seedlings were determined in Daylight, Blue LED, Red LED, Red + Blue LED subjected seedlings as 0.147 mm, 0.104 mm, 0.085 mm, 0.077 mm, respectively (p<0.01). The number of leaves were determined as 3.547, 2.000, 1.550, 1.302 in daylight, blue LED, red + blue LED and red LED subjected plants, respectively (p<0.01). To conclude, the best emerging rate and seedling growth were obtained from daylight treatment. Although the higher seedlings were obtained from Red+Blue LED and Red LED treatments, these seedlings were found as weak with thinner stem and less leaves.
A. Väinölä, “Polyploidization and Early Screening of Rhododendron Hybrids,” Euphytica, vol. 112, no. 3, pp. 239–244, Apr. 2000.
doi: 10.1023/A:1003994800440.
Polyploid induction represents a useful tool for breeders of floral crops as larger flowers, longer flowering period and deeper colors can be achieved through chromosome doubling. This study aimed at testing the efficiency of colchicine and oryzalin in inducing polyploidy in three Rhododendroncultivars grown in vitro. The chemicals were used in two concentrations with 24 h and 48 h treatment durations. The survival of the plants was better in colchicine than in oryzalin solutions. The higher concentration of both chemical skilled more plantlets. The treatment duration in oryzalin did not affect the survival, but 48 h in colchicine was more destructive than 24 h. The low survival rate may not be a disadvantage, if the treatment induces desired ploidy. The ploidy levels were screened with flow cytometry. Oryzalin was more efficient than cochicine in inducing polyploidy, the treatment duration and the concentration did not have significant effects as main factors. The biggest proportion of solid tetraploids (18.2% of the survived plants) was obtained from the 24 h treatment in 0.005% oryzalin. Immediately after the treatment the polyploids grew very slowly, whereas most of the unaffected diploids were vigorous from the very beginning. More mixoploids than solid tetraploids were obtained in all treatments. Most of the mixoploids retained their chimerism, one third shifted todiploidy and one single plant to tetraploidy.
Vipasha, Sanyam, and N. S. Kaler, “Pre-Sowing Seed Treatment Effect on Germination Behaviour of Rhododendron,” Journal of Hill Agriculture, vol. 9, no. 2, p. 244, 2018.
doi: 10.5958/2230-7338.2018.00044.7.
M. I. Voloshchuk and M. I. Shumik, “Features of the Reproductive Biology of Rhododendron Myrtifolium Schott and Kotschy in the Ukrainian Carpathians and the Prospects of Introduction,” Plant Introduction, vol. 53, pp. 37–45, Mar. 2012.
doi: 10.5281/zenodo.2543885.
The results of many years of research on the reproductive biology of populations of Rhododendron myrtifolium Schott and Kotschy in their natural habitat are generalized. The features of vegetative reproduction, seed production, seed germination are determinated. The ways and prospects for its introduction in connection with narrow ecological adaptation of the species are outlined.
L. C. Walker, A. V. LeBude, F. A. Blazich, and J. E. Conner, “Seed Germination of Pinkshell Azalea (Rhododendron Vaseyi) as Influenced by Light and Temperature,” p. 6.
X. Wang, W. Zhao, L. Li, J. You, B. Ni, and X. Chen, “Clonal Plasticity and Diversity Facilitates the Adaptation of Rhododendron Aureum Georgi to Alpine Environment,” PLOS ONE, vol. 13, no. 5, p. e0197089, May 2018.
doi: 10.1371/journal.pone.0197089.
Four small oval populations and five large intensive populations of Rhododendron aureum growing at the alpine in Changbai Mountain (China) were studied in two types of habitat (in the tundra and in Betula ermanii forest). Identification and delimitation of genets were inferred from excavation in small populations and from amplified fragment length polymorphism (AFLP) markers by the standardized sampling design in large populations. Clonal architecture and clonal diversity were then estimated. For the four small populations, they were monoclonal, the spacer length (18.6 ± 5.6 in tundra, 29.7 ± 9.7 in Betula ermanii forest, P < 0.05) was shorter and branching intensity (136.7 ± 32.9 in tundra, 43.4 ± 12.3 in Betula ermanii forest, P < 0.05) was higher in the tundra than that in Betula ermanii forest. For the five large populations, they were composed of multiple genets with high level of clonal diversity (Simpson’s index D = 0.84, clonal richness R = 0.25, Fager’s evenness E = 0.85); the spatial distribution of genets showed that the clonal growth strategy of R. aureum exhibits both guerilla and phalanx. Our results indicate that the clonal plasticity of R. aureum could enhance exploitation of resource heterogeneity and in turn greatly contribute to maintenance or improvement of fitness and the high clonal diversity of R. aureum increase the evolutionary rates to adapt the harsh alpine environment in Changbai Mountain.
S. Wang, Y. Zheng, L. Leus, M.-C. Van Labeke, and J. Van Huylenbroeck, “Screening and Evaluation of Rhododendron Progenies for Alkaline pH Tolerance,” Acta Horticulturae, no. 1331, pp. 95–100, Dec. 2021.
doi: 10.17660/ActaHortic.2021.1331.13.
Y. Watanabe and M. Higa, “Seed Germination Characteristics of an Endangered Evergreen Broadleaf Tree, Rhododendron Uwaense,” Journal of Forest Research, vol. INVALID_SCITE_VALUE, no. INVALID_SCITE_VALUE, pp. 1–5, Mar. 2022.
doi: 10.1080/13416979.2022.2052566.
The importance of plantation forests in the conservation of endangered species has increased over time. Rhododendron uwaense is a small, endangered, evergreen broadleaf tree first described in 1984. This species only occurs in plantations and secondary forests on a small watershed in Shikoku, western Japan. Between the first observation of the species and 2017 no forest management practices had been conducted within the species’ range; however, the landowner began thinning operations in 2017. If this species has light requirements for germination as like some Rhododendron species, forest management practices that improve light availability may facilitate the establishment of the species. To reveal the germination characteristics and the appropriate storage conditions and length for R. uwaense seeds, we assessed differences in the germination of seeds stored under different conditions (indoor, outdoor, moist chilled and dry chilled) and for varying durations (45, 90, 136, 180, 225 days) by the gradually increasing and decreasing temperature method. Germination was higher in the increasing temperature regime. This trend is common among plant species with physiological dormancy that is broken by chilling, allowing seeds to germinate in the spring. Seeds that were collected during the dispersal period germinated immediately after collection, but germination required the presence of light. Seeds stored indoors for more than 180 days failed to germinate. Seeds stored dry chilled for 225 days still maintained a germination rate of more than 60%. Improvement of forest floor light conditions and seed storage under dry chilled conditions are recommended for seed germination and propagation.
X. Wei, J. Chen, C. Zhang, and Z. Wang, “In Vitro Shoot Culture of Rhododendron Fortunei: An Important Plant for Bioactive Phytochemicals,” Industrial Crops and Products, vol. 126, pp. 459–465, Dec. 2018.
doi: 10.1016/j.indcrop.2018.10.037.
Plants in the genus Rhododendron L. produce more than 200 compounds and have been considered an important source for bioactive phytochemicals. Production of these plants, however, requires healthy and genetically uniform propagules. This study evaluated effects of culture media and growth regulators on axillary shoot induction of R. fortunei Lindl. as well as auxin for in vitro and ex vitro rooting of microcuttings. Protocols for in vitro shoot culture of this species were developed. Two-node explants were cultured on either Economou and Read (ER) medium or woody plant medium (WPM) supplemented with 4.0 mg L−1 6-(4-hydroxy-3-methylbut-2-enylamino) purine or zeatin (ZT) and 1.0 mg L−1 naphthaleneacetic acid (NAA). More than 10 axillary shoots were produced per explant regardless of medium. The axillary shoots were used to produce additional two-node explants or as microcuttings for rooting. Two-node explants derived from the axillary shoots cultured on the same media produced even higher numbers of shoots, ranging from 17 to 20 on both ER medium and WPM from the second to the third or fourth cycle of culture, shoot numbers started decreasing in the fourth or fifth cycle. Microcuttings were easily rooted in vitro with rooting percentages of 100% on ER and 84.0% on WPM supplemented with 1.0 mg L−1 indole-3-butyric acid (IBA). The rooting percentages were almost 100% in a peat-based substrate irrespective IBA treatment. Micropropagated plants were morphologically stable and grew vigorously with a 95% survival rate in a greenhouse. The established methods could be used for rapid propagation of disease-free and genetically uniform liners which can be used to produce feedstocks for extracting bioactive phytochemicals.
B. XiaoLi, M. WenBao, J. HuiJuan, and X. JianHui, “Seed Germination and Early Seedling Growth of Rhododendron Species in Biochar-Amended Peat Substrates,” Communications in Soil Science and Plant Analysis, vol. 51, no. 17, pp. 2310–2321, Sep. 2020.
doi: 10.1080/00103624.2020.1822380.
Peat is a natural resource that regenerates very slowly, and the research for seeking low-cost and environmentally friendly alternative products is encouraged. This study evaluated the feasibility of corncob biochar (CB) and rice-husk biochar (RB) as peat substitutes in growth media for rhododendron species cultivation. We used aqueous extract (1/10 w/v) from biochar to assess its potential toxicity on seed germination of four rhododendron species by petri dish bioassay. For R. calophytum Franch., R. delavayi Franch. and R. molle G. Don, RB and CB had positive or neutral effect on seed germination, respectively. In contrast, both biochar additions inhibited R. decorum Franch. seed germination. A greenhouse pot experiment was conducted to assess the effects of CB and RB at varying rates (0%, 10%, 20%, and 40% by volume) on early seedling growth of R. decorum and R. molle. In the RB-containing substrates, the shoot biomass and chlorophyll content of R. molle were increased at the rates of 10–40%, and R. decorum performed well with a maximum does of 20%. However, the growth of the two rhododendron species seedlings was significantly inhibited in peat: CB (60:40 by volume) mixed substrates, which is attributed to the high alkaline and salinity, unsatisfactory hydrophysical properties, together with decreased N and P availability. The results indicated RB could be safely used as a peat substitute at the rates of 20–40% by volume for the cultivation of rhododendron species, due to ideal physico-chemical properties and balanced nutrient supply of the peat:RB mixed substrates.
T. Y. Ü. C. E. L. Yazici and B. Altun, “Effects of Seed Sowing Methods on Emergence and Seedling Growth of Some Rhododendron Species,” Anadolu Tarım Bilimleri Dergisi, vol. 36, no. 3, pp. 408–417, Oct. 2021.
doi: 10.7161/omuanajas.911128.
This study was conducted to determine the effects of different seed sowing methods on emergence rate, densities of seedling emergence and seedling growth of five Rhododendron species (Rhododednron ponticum L., R. luteum Sweet, R. caucasicum Pallas, R. simirnowii Trautv and R. ungernii Trautv). Four different sowing methods were tested, namely manual sowing in row (control), mixing with plant agar, mixing with Murashige and Skoog Basal medium (MS) and mixing with stream sand. The highest seed emergence rates were obtained by manual sowing in row (control) with R. ponticum species (76%) followed by R. luteum (66.6%), R. smirnowii (55.33%), R. ungernii (24%) and R. caucasicum (15.33%), respectively. Similarly, the values closest to ideal seed distribution for homogenous seedling density were obtained by hand-sowing in row method. The highest seedling height was obtained in MS medium with R. ponticum (2.11 cm), followed by R. luteum (3.08 cm), R. smirnowii (4.07 cm), and R. ungernii (1.39 cm), while the effect of seeding method on seedling growth of R. caucasicum species was not significant. To conclude, the best homogeneous distribution of seedling emergence densities of Rhododendron species was obtained by controlled manual seeding method. However, the seed sowing with MS mixing increased significantly seedling growth in all Rhododendron species.
N. Yoshizawa, A. Watanabe, Y. Wakita, and S. Yokota, “Plant Regeneration from the Mass of Shoot Primordia in Rhododendron Pentaphyllum Maxim. Var. Nikoense Komatsu,” Plant Biotechnology, vol. 15, no. 2, pp. 71–75, 1998.
doi: 10.5511/plantbiotechnology.15.71.
A mass of shoot primordia were induced effectively from the shoot apex of Rhododendron pentaphyllum Maxim. var. Komatsu on WP media containing 30μM 2iP+IAA (10, 30, 100μM). Of the shoot primordia obtained, those cultured on WP medium supplemented with 10μM IAA and 30μM 2iP showed the most active proliferation, being 2-4 times in size, after one month of subculture. When shoot primordia obtained were transferred onto the differentiation media, multiple shoots were formed on WP media containing zeatin (1, 10μM) or 0.1μM CPPU after one month of culture, irrespective of the presence of IAA. The multiple shoots induced on the medium containing 10μM IAA and 10μM zeatin showed active elongation growth. Rooting from the multiple shoots subcultured on the same fresh medium occurred two months after the shoot differentiation.
C. Zhang, L. Yin, and S. Dai, “Diversity of Root-Associated Fungal Endophytes in Rhododendron Fortunei in Subtropical Forests of China,” Mycorrhiza, vol. 19, no. 6, pp. 417–423, Aug. 2009.
doi: 10.1007/s00572-009-0246-1.
To investigate the diversity of root endophytes in Rhododendron fortunei, fungal strains were isolated from the hair roots of plants from four habitats in subtropical forests of China. In total, 220 slow-growing fungal isolates were isolated from the hair roots of R. fortunei. The isolates were initially grouped into 17 types based on the results of internal transcribed spacer-restriction fragment length polymorphism (ITS-RFLP) analysis. ITS sequences were obtained for representative isolates from each RFLP type and compared phylogenetically with known sequences of ericoid mycorrhizal endophytes and selected ascomycetes or basidiomycetes. Based on phylogenetic analysis of the ITS sequences in GenBank, 15 RFLP types were confirmed as ascomycetes, and two as basidiomycetes; nine of these were shown to be ericoid mycorrhizal endophytes in experimental cultures. The only common endophytes of R. fortunei were identified as Oidiodendron maius at four sites, although the isolation frequency (3–65%) differed sharply according to habitat. Phialocephala fortinii strains were isolated most abundantly from two habitats which related to the more acidic soil and pine mixed forests. A number of less common mycorrhizal RFLP types were isolated from R. fortunei at three, two, or one of the sites. Most of these appeared to have strong affinities for some unidentified root endophytes from Ericaceae hosts in Australian forests. We concluded that the endophyte population isolated from R. fortunei is composed mainly of ascomycete, as well as a few basidiomycete strains. In addition, one basidiomycete strain was confirmed as a putative ericoid mycorrhizal fungus.
L. Zhang, S. Wang, W. Guo, Y. Zhang, W. Shan, and K. Wang, “Effect of Indole-3-Butyric Acid and Rooting Substrates on Rooting Response of Hard- Wood Cuttings of Rhododendron Fortunei Lindl.,” p. 2.
G. Zhanying, C. Xun, and W. Huamei, “(351) Production of Rhododendron Delavayi Franch.,” HortScience, vol. 40, no. 4, pp. 1061C–1061, Jul. 2005.
doi: 10.21273/HORTSCI.40.4.1061C.
Rhododendrondelavayi Franch. is an evergreen tree up to 5 m tall. Since few tree rhododendron are available in the market, the demand for this plant is high. Unfortunately, the supply is limited due to production difficulty. Under natural conditions (control), seed germination rates were 3% to 5%. When a special propagation bed was set up with mixed media of humus, loess, and sand, the germination rate reached 75% if the temperature was set from 20–25 °C, humidity was 80% to 90%, and irrigation water pH was 6–-6.5. In growing Rhododendrondelavayi, medium pH, water-holding capacity, aeration, and organic matter were considered. The medium, mixed with cinder, loess, humus, and perlite, yielded a 95% survival rate and the tallest plants. To produce aesthetically pleasing plants with flowers, apical dominance was removed and the growth of lateral buds was promoted by pinching the terminal buds of the seedlings in their second year. Also, 3N–1P–1K fertilizer should be used to increase seedling growth. With proper pruning, the seedlings were flowering and ready for market in 3–4 years (instead of 8 years under natural conditions). The acceptable germination rate, better growing conditions, and feasible cultural practices should enable growers to produce quality plants, which ultimately enhance the popularity of Rhododendrondelavayi.
B. Zhao, “Effect of Temperature and GA₃ on Seed Germination and Seedling Establishment of Rhododendron Purdomii Rehd. et Wils,” 2014.https://pubag.nal.usda.gov/catalog/7062010.
Rhododendron purdomii Rehd. et Wils is an endemic and important ornamental plant species in China. The effect of temperature (20°C, 30°C and 20°C (16 h)/30°C (8h) and GA₃ (0, 200, 400, 600, 800 and 1000 mg/l) on R. purdomii seed germination and early seedling establishment were studied. The results showed that there was little difference among the effects of three temperatures on germination time and germination speed, it significantly affected germination percentage, germination vigour and early seedling growth. High temperature had negative effects on seed germination, and the germination vigour at 20°C were significantly higher than those at two other temperature treatments, germination percentage and germination vigour were the lowest at 30°C; and the survival rate and leaf length of the seedlings at 20°C/30°C were far better than those at two other temperature treatments. Treatment with 600 mgl⁻¹ GA₃ for 24 h and 20°C/30°C temperature has a much higher survival rate and growth performance. Therefore, the findings from this study would greatly help the R. purdomii germplasm propagation, conservation and utilization.
Y. Zhou et al., “Seed Morphology and Germinating Characteristics of Cultivars and Wild Species of Rhododendron in Hubei,” Acta Horticulturae, no. 1035, pp. 149–155, May 2014.
doi: 10.17660/ActaHortic.2014.1035.17.