Chapter Five

Double inoculation of soybean with Bean pod mottle virus (BPMV), a member of the Genus Comovirus, Family Comoviridae, isolates V-S98-1 and V-S98-15, together with Soybean mosaic virus (SMV) a member of the Genus Potyvirus, Family Potyviridae) isolates 2K-38, S98-51 and S98-52, was compared to single inoculation with each of the isolates, on Hutcheson, Hutcheson Roundup Ready® (RR BC3) and Hutcheson Roundup Ready® (RR BC5). The double inoculations caused severe foliar symptoms across all three cultivars with or without herbicide treatment, compared to the single inoculation of either BPMV or SMV isolates, respectively. The double inoculations also caused significant reduction in plant height, with Hutcheson and Hutcheson Roundup Ready® (RR BC5) being substantially affected by B1+S52 (BPMV V-S98-1+SMV S98-52) and B15+S52 (BPMV V-S98-15+SMV S98-52), respectively. Seed weight was also severely reduced by the same virus isolate combinations on the same cultivars. BPMV (B1)+SMV (S52) caused 100% reduction in seed weight on Hutcheson, as did B15+S52 on Hutcheson Roundup Ready® (RR BC5). Severe seed weight reduction was also caused by B1+S38 and B15+S38 across all cultivars. SMV 2K-38, S98-51 and S98-52 are SMV resistance breaking strains in Virginia soybean, while BPMV V-S98-1 and V-S98-15 are virulent isolates which have been isolated in Virginia. These combinations on Hutcheson and Hutcheson Roundup Ready® therefore pose a severe threat to soybean productivity, emphasizing the need for resistance to both viruses.