OCCURRENCE OF BARLEY YELLOW DWARF VIRUSES IN SOME COMMON GRASSES (GRAMINEAE) IN SOUTH-WEST ENGLAND

The incidence and distribution of aphid transmitted barley yellow dwar f (BYD) viruses (PAV-, RPV- and MAV-like isolates) are described in 14 species of common pasture and hedgerow grasses from five localities o f south-west England during 1987 and 1988. Isolates were identified by indirect 'sandwich' ELISA using the monoclonal antibodies MAC91: MAC9 2 and MAFF2. More infection was detected in 1987 than in 1988 but this was mainly due to a sharp decline at one site. Intensity of infection was greater in Poa annua and Lolium perenne populations than in most other species. BYD was not detected in Arrhenatherum elatius, Elymus r epens, Agrostis canina and A. stolonifera. All three isolates of BYD w ere widespread. MAV was associated more with localities further north and RPV more with those further south. PAV was common only at the sout hern-most site. This geographical distribution was reasonably consiste nt in both years. Given these trends, susceptible grass species fell b roadly into three groups with respect to isolate frequency, those pred ominently infected by RPV and MAV (seven spp.), those equally infected by all isolates (two spp.) and a single species, Poa annua, infected mainly by PAV. Some implications of these findings for the epidemiolog y and control of BYD viruses are briefly considered.