AbstractAn isolate of BYDV (BYDV‐OC), from barley in Northwest Italy with typical symptoms of yellowing and dwarfing, was transmitted byRhopalosiphum padi, Sitobion fragariae. S. avenae, Metopolophium festucae, R. maidisandM. dirhodum, but not byMyzus persicaeorSchizaphis graminum. It reacted in DAS‐ELISA with monoclonal and polyclonal antisera to PAV, but not with antibodies to MAV, RPV and RMV. A polyclonal antiserum prepared to BYDV‐OC did not react with MAV‐like, RPV‐like, or RMV‐like isolates of BYDV in ELISA or in Western blots. The concentration of BYDVOC inAvena byzantinaplants decreased from weeks 1 to 10 after inoculation, but the total virus content per plant increased up to weeks 7 to 8, following the increase of p