Conservation Biology Of Rhododendron Meddianum

Rhododendron meddianum belongs to the evergreen plants of the genus Rhododendron,Subgen.Hymenanthes,Sect.Ponticum,Subsect.Thomsonia,distribute in northwestern Yunnan,China and northeastern Myanmar.R.meddianum has beautiful plant shape,large bell-shaped corolla with clusters of branches,and bright red color,which is of good ornamental values.Currently,only seedling cultivation have been studied on this species.The population was widely surveyed,and its genetic diversity and structure were studied by SNP analysis.The endangered mechanism of R.meddianum were revealed in terms of seed germination traits,breeding system and investigation of wild resources,and put forward the corresponding protection and management measures.The divergence time of R.meddianum and its relative,R.cyanocarpum,was revealed by SNP analysis.The results were summarized as follows:1.Habitat and wild resources of R.meddianumThrough specimen data,literature review and field investigations,only three wild populations with narrow distribution were found in China,which grow in the azalea-bamboo forest and Rhododendron shrub above 3 000 m.All the investigated populations were affected by human disturbance.The total number of wild mature individuals was less than 5 000,and the total distribution area was about 1 929 km².In addition,there are many old plants,few middle age plants,few seedlings under the forest,and the population regeneration ability is weak,which has been endangered.2.Floral syndrome and breeding system of R.meddianumThe results showed that R.meddianum flowered from late April to May.Each inflorescence flowering lasted 12 to 14 days and individual flower lasted 8 to 10 days.Floral syndrome could attract pollinators.During the flowering phase,the pistil matured before stamens.At the same time,there were space interval between stigma and anthers.Combining with the outcrossing index and artificial pollination studies,the breeding system of R.meddianum is partly self-compatible,outcrossing,and pollinators are required.3.Seed physiology of R.meddianumThe seeds of R.meddianum were photosensitive seeds,and the suitable temperature for seed germination is 25℃,but the seed germination rate was very low with only 4.01±0.31%.Low concentration of GA₃ had no effect on the seed germination of R.meddianum,and the highest seed germination rate was found when the concentration of GA₃ reached 1 000 mg/L,which could reach 21.33±6.54%.The seeds of R.meddianum were able to resist mild drought stress,and the germination rate was significantly increased.With the increase of PEG-6 000concentration,the germination rate of R.meddianum was increased.The seed germination of R.meddianum was 49.33±1.17%when the concentration of PEG-6 000 was 10%.However,the germination was inhibited when concentration of PEG-6 000 was 13%.Thus,certain GA₃ and stress treatment can improve the seed germination rate of R.meddianum,which is conducive to seed reproduction.4.Genetic diversity of R.meddianumThe 3 377 neutral SNPs screened by dd RAD were used to analyze the genetic diversity and structure of R.meddianum.The results showed high genetic diversity（H_E=0.0 713±0.0021,π=0.0 741±0.0 022）in R.meddianum.Among the total genetic variation,19.88%was found between populations and 80.12%was found within populations.STRUCTURE,PCA and NJ tree analysis showed that the three populations of R.meddianum were divided into three different genetic clades,corresponding to three geographical populations.The higher genetic diversity and genetic differentiation of R.meddianum could be explained by life history characteristics,pollen restriction,and distance isolation.The population demographic analysis based on Stairway Plot revealed that the population of R.meddianum had experienced contraction events in history.5.Evolutionary history of Rhododendron meddianum and its relative,R.cyanocarpumIn addition,the 1 495 SNPs screened by dd RAD were used to STRUCTURE,PCA and NJ tree analysis of Rhododendron meddianum and R.cyanocarpum.The results showed that there were significant genetic structure between two species,and the seven wild populations could be divided into two genetic groups,i.e.Rhododendron meddianum and R.cyanocarpum.Fastsimcoal2 model analysis revealed that the divergence time between the two species occurred about 3.05 million years ago（Ma）,which may be related to the intense uplift of Hengduan Mountains in 3.4 Ma and the drier climate by the Asian winter monsoon in the late Pliocene.6.Endangered mechanism and conservation strategiesIn conclusion,the seed germination rate of R.meddianum is extremely low and its natural regeneration ability is weak.In addition,a series of human disturbances brought about by road construction,wind farm construction and grazing was badly damaged the wild population and habitats of R.meddianum.Therefore,protection of this endangered species is urgently needed.It is suggested to establish a protected community to protect its natural habitats.At the same time,because the three populations have their own genetic structure,each population should be set up the corresponding protection management unit.Finally,the appropriate concentrations of GA₃ and PEG-6 000were used to promote the germination of its seeds,and the corresponding artificial breeding techniques were developed to create conditions for the ex situ protection of R.meddianum,the population’s return to natural domestication and the garden utilization.