Study On Genetic Diversity Of Rubber Tree Powdery Mildew Population In Hainan Province

Rubber tree(Hevea brasiliensis)is the primary source of natural rubber,which is a critical raw material to industries.Hainan is one of the main rubber tree plantation areas in China.Powdery mildew,caused by Erysiphe quercicola,is the most serious leaf disease on rubber trees in China.Population genetic analysis of pathogen can provide useful information for disease epidemic zoning,dispersal route and regional control of the disease.In this paper,sixteen SSR molecular markers was used to study the temporal genetic structure of E.quercicola populations in three cities(counties)including Leong,Qiongzhong and Danzhou in Hainan,where overwintering inoculums were found in 2021 and samples were collected at different disease occurrence periods(overwintering,early epidemic and late epidemic).In addition,population structures of the pathogen in five regions(Leong,Danzhou,Qiongzhong,Haikou and Qionghai)in Hainan were analyzed to study the spatial differences.The following results were obtained:1.The results of permutational multivariate analysis of variance(Permanova)indicated that there was significant difference among the population structure of E.quercicola in different epidemic stages as the late epidemic populations had higher genetic diversity than the other two stages.Discriminant analysis of principal components(DAPC)and Structure analysis showed that the E.quercicola samples grouped into four clusters.And one of the clusters only included samples from the late epidemic stage while the other three clusters included samples from all three sample stages.Further analysis also confirmed that there were significant(P =0.001)genetic differences among these four clusters.These findings suggest that the epidemic of rubber tree powdery mildew is not only established by local inoculum sources,but also may be by inoculum drifting from other plantations or through host jumps from other hosts.2.The results of molecular variance analysis and genetic differentiation coefficient showed that there was no significant difference in population structure of E.quercicola in five regions in Hainan.Principal component analysis(DAPC)and Structure analysis showed that the tested samples grouped into three clusters and each cluster had samples from all five regions.Further analysis also confirmed that there was significant genetic difference among the three clusters(P =0.001).These inferred the spread of the pathogen in different regions in Hainan.3.The analysis of molecular variance showed that there were significant differences among the overwinter populations and the populations from the adjacent tapping rubber plantations in Ledong,Danzhou and Qiongzhong.However,there was no significant difference between the late-epidemic populations and the populations from the adjacent tapping rubber plantations in ledong,Danzhou and Qiongzhong.There was significant difference between the early-epidemic populations and the populations in the adjacent rubber plantations in Danzhou.The multilocus genotypes(MLGs)were repeated at different sample stages and the adjacent tapping rubber plantations.All these suggested that rubber nursery and volunteer seedlings could provide inoculums for the occurrence of the disease in the adjacent tapping rubber plantation in spring.