Development Of SSR Markers For Powdery Mildew In Rubber Trees And Study Of Their Population Genetic Structur

Rubber tree powdery mildew,caused by Erysiphe quercicola,is a serious threat to rubber plantations worldwide.There were only a few studies for population structure of this pathogen due to the lack of polymorphic molecular markers.The whole-genome sequence provides the possibility for developing SSR markers.In this study,sixteen polymorphic microsatellite loci were developed based on the whole-genome sequences of the pathogen.Powdery mildew samples were genotyped using 16 polymorphic microsatellite markers to understand the population genetic structure of E.quercicola from the main rubber tree growing regions including Yunnan（YN）,Hainan（HN）,western Guangdong（YX）and eastern Guangdong（YG）in China.The number of alleles per microsatellite marker ranged from 4 to 14 and the gene diversity varied from 0.240 to 0.787.In total,309 multilocus genotypes（MLGs）were observed for the 387 tested samples indicated that most of samples had a unique MLG.YN had higher genotypic diversity（Simpson’s indices）,genotypic evenness,Nei’s gene diversity,allelic richness and private allelic richness than the other regions.Both STRUCTURE analyses and DAPC analyses showed that samples from HN were clustered with samples from WG and EG while most samples from YN were clustered alone.Pairwise divergence showed that the YN population differed significantly from the other populations while the genetic differentiation was small among the other three populations.The gene flow among HN,WG and EG is frequent.Analysis of molecular variance indicated that the variability among regions accounted for 22.4%of the total variability.Genetic differentiation was significantly positively correlated(R_xy=0.772,P=0.001)with geographic distance.Linkage equilibrium analysis suggested possible occurrence of sexual recombination.The analysis of the historical dynamics of the population shows that YN population and other regions have a common ancestor and have differentiated in the process of evolution.The results suggested that although significant genetic differentiation of E.quercicola occurred between YN and the other regions,pathogen populations from the other three regions lacked genetic differentiation.