Reproductive Biology And Conservation Genetics Of Rhododendron Sinofalconeri

Rhododendron sinofalconeri belongs to the evergreen shrubs of the genus Rhododendron,subg.Hymenanthes,sect.Ponticum and subsect.Falconera,distributed in southeastern Yunnan and northern Vietnam.Rh.sinofalconeri has a high ornamental value as a precious breeding parent because of its yellow corolla which is rare in Rhododendron plants.Through multi-site field investigation,combining with the records of Chinese flora and specimens,only two wild populations were found in Daheishan and Laojunshan.It is listed as a vulnerable species in the Red list of Rhododendron,while according to the IUCN(version 3.1)standard associate with field survey results,we upgraded it to the endangered level [CR B1b(iv,v)c(iii,iv)].1.Biological characteristics and wild resources of Rh.sinofalconeri.Through specimen data,literature review and field investigation,only two remnant populations were found,about 500 individuals in Daheishan population in Kaiyuan and about 1000 individuals in Laojunshan population in Wenshan.Most of the individuals of Daheishan population are elderly individuals,and there is a small number of seedlings of the two populations.2.Reproductive biology of Rh.sinofalconeriThe petals of Rh.sinofalconeri are light yellow,and the average number of flowers per inflorescence is 21.63 ±2.89.The single flower and single inflorescence could last 7.6 ±1.19 days and 9.15 ±0.38 days respectively.Under natural conditions,the seed setting rate is 52.3%,and the average number of fruits per inflorescence is 11.5.The Corolla color of Rh.sinofalconeri is congruent with the color preference of bees.According to the results of hybridization index,pollen-ovule ratio and artificial pollination,Rh.sinofalconeri are facultative self-pollination and cross-pollination with the participation of effective pollinator,Apis cerana indica.Pollination biology studies show that Apis cerana indica is an effective pollinator of Rh.sinofalconeri,and its high frequency of visitation to the inflorescence could counteract the effect of less pollen transferred to stigma during a single flower visit by Apis cerana indica.3.Genetic diversity assessment of Rh.sinofalconeri with Genotyping by Sequencing We employeed GBS(genotyping-by-sequencing)to characterize the genetic variation and diversity of this species of Laojunshan population and Daheishan population.A total of 103,133 high quality SNP locis were screened and adopted to analyze genetic character of populations.Results revealed that relicts maintained a low level of genetic dversity(Ne=1.3086,Ho=0.1878,He=0.1856,PIC=0.1504,Pi=0.2059)and moderate high differentiation(Fst=0.1765).A weak Gene flow was detected between populations(Nm=1.1674).Principal Component Analysis Clustering and Structer Anlalysis showed that 36 individuals were clustered into two distinctive groups.4.Endangered mechanism and protection strategiesAccording to the results of this study,the sexual reproduction of Rh.sinofalconeri has not been hindered yet.A series of anthropogenic disturbance originating from road construction and agricultural production activities,such as fragment distribution,population isolation and insect pests caused by environmental changes,are the main factores that threaten the survival of the remnant populations.Both populations could bearfruits naturally,but the number of undergrowth seedlings and young plants was small,which was mainly due to the high canopy density and insufficient light in the undergrowth of the azaleas,as well as the difficulty in the normal growth of the seeds and seedlings distributed on the slopes due to the artificial excavation of the surface humus soil.Therefore,it is urgent to protect the two Rh.sinofalconeri populations in situ.First of all,joint efforts from both scientists and local residents should be important in the protection of wild plants,in order to reduce human disturbance.Individuals distributed on the top of the mountain Dahei are seriously damaged by pests.At the same time,seed germination,asexual reproduction and seed resource collection should be carried out to promote ex-situ conservation.In addition,the pollination of Rh.sinofalconeri relies on Apis cerana indica,local residents should avoid breeding alien honeybee species to reduce the possible negative influence to the pollination progess.In order to strengthen the genetic communication between the two populations,mutual introduction between six subpopulations is crutial.All populations should be covered during introduction and domestication to increase their gene flow and genetic diversity.