Molecular identification and characterization of viral pathotypes and isolates of Polymyxa graminis responsible for the small grain cereal mosaics in Wallonia. Development of molecular tools for detection by RT-PCR of viruses and vectors based on known sequences. Development of a multiplex RT-PCR for the quantification of Polymyxa. Typing of populations present in Wallonia. Study of the specialisation of P. graminis and of the viral pathotypes.