Abstract: 【Objective】 The objective of this study is to clarify the distributionand genetic diversity of Barley yellow striate mosaic virus (BYSMV) in major wheat production areas in northern China, and to provide a theoretical basis for the early warning, prevention and control of epidemic diseases. 【Method】During 2008-2016, about 864 suspected virus-infected samples were collected from 66 districts in Hebei, Shandong, Jiangsu, Anhui, Henan, Shaanxi and Shanxi provinces, all the three viruses including BYSMV, Rice black-streaked dwarf virus (RBSDV) and Northern cereal mosaic virus (NCMV) were identified using one-step multiplex RT-PCR. L and N gene fragments of BYSMV were obtained by RT-PCR amplification and cloned, and then determined by nucleotide sequence analysis. The sequences were analyzed by softwares of MEGA, DnaSP, and PAML to elucidate the phylogenesis and genetic diversity of BYSMV isolates. 【Result】 A total of 336 samples collected from 48 districts in 7 provinces were detected with BYSMV and the detection rate was 38.89%. The virus was mainly distributed in Shaanxi, Hebei, Shanxi and Shandong. In addition, it was also distributed in Henan and northern Anhui. Xuzhou and Pizhou in Jiangsu Province were only localized. Phylogenetic analysis showed that the population could be divided into two subgroups (I and II) based on fragments of L and N genes. The isolates in subgroup I were derived from all 7 provinces, but isolates in subgroup II were only from Shaanxi and Shanxi provinces. It was indicated that Iran isolate was related to the subgroup II isolates based on the phylogenesis of L gene sequence. The clustering of the isolates was related to their geographical origins, and not to the host plants or sampling dates. Genetic analysis by using 7 softwares of the RDP package showed that there was no evidence supported for the recombination. Selection stress analyses showed that the ω (dN/dS) values varied from 0.02 to 0.19 which were far less than 1 within or between subgroups. It was indicated that the population was undergoing purifying selection. Haplotype diversity (Hd) values (0.90909 and 0.99524) of L and N gene fragments were greater than 0.5 and nucleotide diversity (π) values (0.01324 and 0.01224) were higher than 0.005, indicating that there was a high level of genetic diversity in the population of BYSMV in China. genetic differentiation based on L and N gene fragments showed that the fixation indices F_ST (0.32201 and 0.37326) of eastern and western subpopulations were greater than 0.25. The difference of statistical test was significant, which indicated that the BYSMV population in eastern and western regions was seriously differentiated. The Nm values (0.53 and 0.42) were less than 1, which indicated that the limited gene flow was the main reason of genetic differentiation.【Conclusion】 BYSMV is widely distributed in wheat producing areas of northern China, and occurred in Hebei, Shandong, Jiangsu, Anhui, Henan, Shaanxi and Shanxi provinces on different levels. The population of BYSMV had a high level of genetic diversity in China, and there is a severe genetic differentiation between the eastern and western subpopulations.

Key words: Barley yellow striate mosaic virus (BYSMV), phylogenesis, genetic diversity, selection pressure, genetic differentiation