Reduction of yield components by barley yellow dwarf infection in susceptible winter wheat and winter barley in Virginia

Five field studies, during 3 yr (1990-1993) and at two locations, were cond ucted in eastern Virginia to determine the effect of naturally occurring ba rley yellow dwarf virus (BYDV) infection on yield components of susceptible 'Barsoy' winter barley (Hordeum vulgare L.) and susceptible 'Wakefield' wi nter wheat (Triticum aestivum L.) At each study site, yield components were compared for grain harvested from 25 disease loci and 25 adjacent asymptom atic areas. Rhopalosiphum padi L. and Sitobion avenae Fabr. aphid populatio ns were monitored weekly by visual inspection of plant leaves and stems. Ap hid numbers were low in all studies, with only one site exceeding the econo mic threshold of 15 aphids/row ft at any time during the season. The BYDV, PAV strain, was present in all five studies; the MAV strain was present at only one location in 1990-1991. Fall infection was predominant and occurred in all studies, with plants showing typical disease symptoms. Symptoms con sistent with spring infection were observed in only one study. With few exc eptions, fall infection significantly reduced tiller height, head number, s eed number, number of seed per head, 1000 seed weight, and yield. Yield com ponents were not equally affected, Seed number, number of seed per head and yield were reduced the most, by 28%, 22%, and 34%, respectively, compared with only about a 5 to 13% reduction in the other components. Spring infect ion significantly reduced number of seed per head and 1000 seed weight, but not the other yield components.