Ribotypes of Polymyxa graminis in wheat samples infected with soil-borne wheat viruses in China

Polymyxa graminis is an obligate parasite and important vector of more than 14 soil-borne plant viruses that pose a significant threat to cereal crops in Europe, North America and Asia. Different ribotypes or formae speciales of P. graminis have been recognized and these may be associated with different cereal hosts or with transmission of different viruses. Two soil-borne viruses infecting winter wheat in China have been reported and well studied (Wheat yellow mosaic virus [WYMV, genus Bymovirus] and Chinese wheat mosaic virus [CWMV, genus Furovirus]) but there has been no reported characterization of P. graminis isolates associated with them. In this study, the rDNA ITS regions of P. graminis were examined from 63 wheat samples with apparent virus symptoms obtained from 16 sites within six Chinese provinces. Their associations with soil-borne viruses were investigated. Ribotype I (f. sp. temperata) and ribotype II (f. sp. tepida) of P. graminis were confirmed in winter wheat regions of China for the fir...