GENOMIC REASSORTMENT OF BARLEY MILD MOSAIC-VIRUS - EVIDENCE FOR THE INVOLVEMENT OF RNA1 IN PATHOGENICITY

A reverse transcription-polymerase chain reaction (RT-PCR) was develop ed for specific detection of RNA1 and RNA2 of two barley mild mosaic v irus strains (BaMMV-Ka1 and BaMMV-Na1) and a barley yellow mosaic viru s strain (BaMMV-II-1). Mechanical inoculation of barley with a mixture of BaMMV-Ka1 and BaMMV-NA1, followed by RT-PCR to detect RNA componen ts in infected plants, revealed that the RNAs of the two strains were exchangeable in vivo to generate all nine possible combinations contai ning at least one RNA1 one RNA2. Infected plants with mixed or reasser ted RNAs were selected and used as inocula for further analysis of cul tivar reactions. The results demonstrate that the pathogenicity and sy mptomatology are determined solely by RNA1. In contrast, following ino culation with mixtures of BaMMV-II-1 and either BaMMV-Ka1 or BaMMV-Na1 , no heterologous combinations of their RNAs were observed.