Chapter Two

Field surveys to collect isolates of Bean pod mottle virus (BPMV), a member of the genus Comovirus, were done in 1997, 1998 and 2001 in research centers and growers’ commercial fields in Virginia. The isolates were collected by taking leaves from symptomatic plants and confirming the presence of virus using leaf blot immunoassay, followed by propagation of selected positive samples in the greenhouse. A total of five BPMV isolates were collected during this period. All of the isolates came from Warsaw and Mount Holly area, in Richmond and Westmoreland counties of Virginia, respectively. Double gel diffusion confirmed that all isolates of BPMV were serologically similar when tested against several antisera to BPMV. To ascertain biological characteristics and effects on soybeans, isolates were inoculated onto different soybean cultivars in the field. Two experiments were conducted in hill plots in 1999 and one in 2000 to determine effects of BPMV isolates on plant height, days to maturity, seed coat mottling and seed weight. Three isolates of Soybean mosaic virus (SMV, Genus Potyvirus, Family Potyviridae) were included in one of the 1999 hill plot experiments, for comparison. The isolates produced different foliar symptom severity when inoculated onto different soybean cultivars. BPMV V-S98-1 and V-S98-15 caused more severe symptoms on cultivars than V-W1, V-W2 and V-S01-10. For SMV isolates, G1 was more severe than S98-51 and S98-52, causing higher yield reductions in five out of nine cultivars, with V98-4076 (Rsv1-n) realizing only 0.8 g per 0.91 m row. Both SMV isolates, S98-51 and G1 showed substantial seed yield reduction in at least five cultivars compared to three for S98-52, and were lower than the control. There were different levels of isolate cultivar interactions that produced varying responses on plant height, days to maturity, seed coat mottling and seed weight. BPMV V-S98-1 and V-W2 as well as SMV G1 caused the most significant variations compared to other isolates. BPMV isolates V-S98-1 and V-S98-15, significantly reduced seed yield compared to the noninoculated control by 23.9 and 15.2%, respectively. Neither V-W1 nor V-W2 caused