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Five field studies, during 3 yr (1990-1993) and at two locations, were conducted in eastern Virginia to determine the effect of naturally occurring barley yellow dwarfvirus (BYDV) infection on yield components of susceptible 'Barsoy' winter barley (Hordeum vulgare L.) and susceptible 'Wakefield' winter wheat (Triticum aestivum L.) At each study site, yield components were compared for grain harvested from 25 disease loci and 25 adjacent asymptomatic areas. Rhopalosiphum padi L. and Sitobion avenae Fabr. aphid populations were monitored weekly by visual inspection of plant leaves and stems. Aphid numbers were low in all studies, with only one site exceeding the economic threshold of 15 aphids/row ft at any time during the season. The BYDV, PA 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 consistent with spring infection were observed in only one study. With few exceptions, fall infection significantly reduced tiller height, head number, seed number, number of seed per head, 1000 seed weight, and yield. Yield components 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 infection significantly reduced number of seed per head and 1000 seed weight, but not the other yield components. |
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