EPIDEMIOLOGY OF RPV-LIKE AND PAV-LIKE BARLEY YELLOW DWARF VIRUSES ON WINTER BARLEY IN CENTRAL SPAIN

The epidemiology of RPV- and PAV-like serotypes of barley yellow dwarf viruses (BYDVs) on winter barley in central Spain was studied by moni toring BYDV incidence, and the population dynamics of BYDV aphid vecto rs, in plots within a barley field. Virus incidence and virus vector p opulations were also monitored on alternative hosts, such as volunteer cereals and grass weeds in the autumn and winter, or grass weeds and irrigated maize in the summer. Two separate epidemiological systems, f or RPV- and for PAV-like serotypes of BYDV, appear to be superimposed. For the RPV-like BYDV, local sources of virus and virus vectors are i mportant and there is a high incidence of BYDV infection of barley dur ing winter. For the PAV-like BYDV system, long-distance sources for vi rus and vectors are most important and cause infection of barley in th e spring. Irrigated maize does not appear to be an important vector an d virus reservoir for the infection of winter barley, but can be infec ted by aphids migrating from barley in early summer.