| Fine-scale spatial genetic structure(FSGS)is mainly used to describe the features of spatial distribution of genetic variation within population.It is depends on the spatial extent of gene diffusion and the characteristics of species'biology characteristics,for instance,mating systems.Study on the FSGS of plants is useful for understanding its ecological adaptability,exploring the role of various evolutionary factors,and also providing a theoretical basis for formulating corresponding conservation strategies.Rhododendron species are the essential component of the plateau mountain forest ecosystems in southwest of China.In recent years,however,with the increasing of human social and economic activities,wild Rhododendron germplasm resources have been damaged severely,and some species have been in rare or endangered status.Therefore,it is imperative to conduct research on conservation biology of endemic or endangered Rhododendron plants on the basis of space genetics.In the present study,4Rhododendrons species in the southwestern plateau mountains of China[Rhododendron rex subsp.rex(endemic/endangered);R.pubicostatum(plant species with extremely small populations);R.protistum var.giganteum(endangered);R.spinuliferum(endemic)]were selected to study their FSGS using microsatellite markers(Simple Sequence Repeats,SSR)SSR molecular markers.The presults will provide the scientific guide for the protection strategies of these Rhododendron species'germplasm.The genetic diversity and FSGS of 4 Rhododendron species and corresponding its age stages were analyzed by SSR,Moran's I and Fijj kinship coefficients.The main findings are as follows:1.The population of Rhododendron rex susp.rex manifested significant SGS within13 m.The speices has a medium level of spatial genetic strength(Sp=0.0420).The?g value of gene diffusion of the Rhododendron rex susp.rex population was 15.38-34.46 m.Among the different age stages of Rhododendron rex susp.rex,seedlings have higher genetic diversity(NA=10.857,NE=5.293,Ho=0.485,HE=0.730)than that in saplings(NA=8.429,NE=4.727,Ho=0.383,HE=0.662)and adult trees(NA=6.857,NE=4.661,Ho=0.446,HE=0.703).The analysis of the spatial genetic structure of different age stages indicated that there are significant spatial genetic structures in seedlings,saplings,and adult trees within a short distance(15 m).The spatial genetic structural strength of seedlings(Sp=0.0699)is higher than that of the saplings and adult trees(Sp=0.0346).The values of?g for each age stages were 16.22-35.81 m,25.72-58.45 m and 30.90-69.49 m,respectively.2.The population of R.protistum var.giganteum had no significant spatial genetic structure,suggesting that the sampled individuals are randomly distribution.Among different age stages of R.protistum var.giganteum,the genetic diversity of saplings(HE=0.703,Ho=0.414)and adult trees(HE=0.703,Ho=0.404)is higher than seedlings(HE=0.574;Ho=0.382).The adult trees have a relatively higher inbreeding coefficient(FIS=0.391)among the age stages.Studies on the spatial genetic structure of R.protistum var.giganteum at different age stages showed that there is no significant spatial genetic structure at different age stages.The adult trees have a medium level of spatial genetic strength(Sp=0.0346).The value of?g ranged between 41.42 m and 92.85 m in adult trees.3.The population of R.pubicostatum had a significant spatial genetic structure within 9 m,and a moderate level of spatial genetic strength(Sp=0.0217).The?g value of the population was 30.72-68.67 m.The genetic diversity of adult trees(Ho=0.598;HE=0.709)is higher than that of seedlings(Ho=0.542;HE=0.699)and saplings(Ho=0.515;HE=0.697).The saplings have the highest inbreeding coefficient(FIS=0.273)of the population.The analysis of the spatial genetic structure of different age stages showed that there was no significant spatial genetic structure in the seedlings and saplings of R.pubicostatum population.However,the adult trees had a significant spatial genetic structure within 9 m.The seedlings'spatial genetic structure strength(Sp=0.0057)was lower than that of the saplings(Sp=0.0163)and the adult trees(Sp=0.0388).The?g values of each age stage are 62.32-140.33 m,35.82-80.64 m,and 23.22-51.90 m,respectively.4.R.spinuliferum population has significant spatial genetic structure within 8 m.The spatial genetic strength is low(Sp=0.0110).The value of its population?g ranged between 30.72 m and 68.67 m.The saplings of R.spinuliferum population(Ho=0.532;HE=0.641)and adult trees(Ho=0.537;HE=0.621)have higher genetic diversity than the seedlings(Ho=0.533;HE=0.591).The saplings exshibited highest inbreeding coefficient(FIS=0.198)in population.There was no significant spatial genetic structure of R.spinuliferum at different age stages.The spatial genetic strength varied among different age stages.The spatial genetic strength of seedlings(Sp=0.0490)is higher and the adult trees(Sp=0.0025).However,the Sp value of the sapling population cannot be revealed.The values of?g of the seedlings and adult trees were 28.60-65.38 m and 80.62-180.23m,respectively.Based on the above research results,four Rhododendrons species have higher relatively levels of genetic diversity in the genus of Rhododendron.The fine-scale spatial genetic structure analysis indicated that R.rex subsp.rex,R.pubicostatum,and R.spinuliferum had significant spatial genetic structures within 13 m,9 m,and 8 m,respectively.However,R.protistum var.giganteum had no significant spatial genetic structure.Among these four Rhododendron species,R.rex subsp.rex had the strongest spatial genetic strength.Therefore,the presence of FSGS in the present study implies that seeds for ex situ conservation of R.rex subsp.rex and R.pubicostatum,should be collected from trees at least 15 m and 9m apart to reduce genetic similarity between neighboring individuals.Furtheremore,the expand of surviving space for R.protistum var.giganteum will helpful to the population size of this plant species with extremely small populations. |
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