Ribotype Identification Of Polvmyxa Graminis And Genetic Variation Of Wheat Yellow Mosaic Virus RNA2 In Winter Wheat Region Of China

Polymyxa graminis is a vector of more than 14 soil-borne plant viruses and poses a significant threat to crop hosts in Europe,North America and Asia.In China winter wheat region,two wheat viruses are transmitted by P.graminis:Wheat yellow mosaic virus(WYMV)and Chinese wheat mosaic virus(CWMV).Phylogenetic analysis indicated that there are six ribotypes of P.graminis in the world based on the ITS region.However,ribotypes of P.graminis in China winter wheat region are still not reported.In this study,molecular detection method for ribotypes of P.graminis in China was well established in lab,and 63 ITS sequences of P.graminis from 16 regions of 6 provinces were further analyzed.Our results indicated that there are two ribotypes of P.graminis presented in China:ribotype Ⅰ(Ic,specific ribotype for China till now)and Ⅱ(Ⅱa).Furthermore,characteristic of ribotypes and the viruses it transmit was also found through molecular detection in the lab as following:1.The majority ribotype of P.graminis in China winter wheat region is Ⅰc,and both Ic andⅡa were widely distributed in infected area;2.Ribotype Ⅰc and Ⅱa can infect a same wheat host simultaneously,while no single infection was found for ribotype Ⅱ;3.Ribotype Ic can carry WYMV or/and CWMV singly or simultaneously.Polymorphism analysis of WYMV RNA2 for 32 different isolates derived from different regions showed that both PI and P2 exhibits with low level of genetic diversity;Recombination detection revealed that there are 4 recombination events for P2 within the 32 isolates while no recombination was detected for PI.In addition,much more amino acid mutations were found in P2 compare to P1.The recombination tendency and high mutation rate of WYMV P2 might help to facilitate the expansion and transmission for the virus.Furthermore,no clear geography dependency was observed for the 32 WYMV isolates based on the phylogenetic analysis indicating gene exchange might occurred between different infected regions.