Molecular methods for the detection of polymyxa graminis F.sp. temperata and P.graminis F.sp. Tepida in association with bymo-and furoviruses

Vaïanopoulos, Céline [UCL] Bragard, Claude [UCL] Maraite, Henri [UCL] Legrève, Anne [UCL]

Polymyxa graminis is the vector of bymo-and furovirus responsible for several cereal diseases in temperate areas. Two formae speciales P. graminis f.sp. temperato and P. graminis f.sp. tepida distinguished on the basis of their ribosomal DNA sequences , have been identified in these areas. Nested and multiplex PCR, RFLP analysis of PCR-amplified rDNA and quantitative real-time PCR, using specific primers or restriction enzymes targeting the specific sequences of the internal transcribed spacers one or two(ITS1 or ITS2) of these formae characterize the P. graminis populations colonizing barley, rye and wheat roots in a biossay on two Belgian soils and one French soil infested by one or more of the bymoviruses, Barley yellow mosaic virus (BaYMV), Barley mild mosaic virus or Wheat spindle streak mosaic virus (WSSMV) and/or the furovirus, Soil-borne cereal mosaic virus and related virus species. Both P. graminis f. sp. temperata and P. grminis f. sp. tepida were isolated from the three soils tested but the former was found mainly on barley and the latter on wheat. On rye, a different ribotype was obtained,with a sequence closer to P. graminis f. sp. temperata than P. graminis f. sp. tepida. Co-infection of bymoviruses (BaYMV and WSSMV) and/or furoviruses with P. graminis f.sp. temperata and/or P. graminis f.sp. tepida was observed on both barley and wheat. These findings demonstrated a greater diversity in the vector populations than previously reported in Belgium and France. The results also suggest a certain but not exclusive specialization in plant/P. graminis formae speciales/virus interactions. The relevance of these observations to the epidemiology of the P. graminis - transmitted viruses is discussed.