Occurrence and distribution of soybean viruses in Tennessee

Four commercial soybean fields were surveyed for virus occurrence in each of nineteen counties in the major production areas of Tennessee in 1987 and 1988. Six leaf samples, five symptomatic and one asymptomatic, were collected from each soybean field per county. Virus isolates were identified using the Protein A sandwich ELISA (PAS-ELISA) technique. Samples were tested with antisera specific to alfalfa mosaic virus (AMV), bean pod mottle virus, (BPMV), bean yellow mosaic virus (BYMV), cowpea chlorotic mottle virus (CCMV), cucumber mosaic virus (CMV), peanut mottle virus (PMV), peanut stunt virus (PSV), southern bean mosaic virus (SBMV), soybean mosaic virus (SMV), tobacco ringspot virus (TRSV), tomato spotted wilt virus (TSWV) and white clover mosaic virus (WCMV). In 1987, 49% of the leaf samples collected tested positive for virus. AMV, BPMV, BYMV, CCMV, CMV, PSV, SBMV, SMV, TRSV and TSWV were detected. BPMV was the most frequently detected, occurring in 75% of the leaf samples that tested positive for virus. Other viruses occurred in less than 5% of the total positive samples. In 1988, 32% of the leaf samples collected tested positive for virus. AMV, BPMV, BYMV, CCMV, CMV, PSV, SBMV and TRSV were detected. BYMV was the most frequently detected virus, occurring in 33% of the positive leaf samples followed by BPMV (30%) and TRSV (11%). This is the first report of BPMV, CCMV, SBMV and SMV in any crop in Tennessee and the first report of AMV, BYMV, CMV, PSV, TRSV and TSWV occurring in soybeans in this state.

Soybean cultivars in trials at the Agricultural Experiment Stations in Milan, Knoxville and Greenville, Tennessee were evaluated for virus occurrence and disease incidence. Thirty-one percent of the leaf samples collected tested positive for virus infection. AMV, BPMV, BYMV, CCMV, CMV, PSV, SBMV, SMV, TRSV and TSWV were detected from the leaf samples collected at Milan. BPMV, BYMV and SMV were detected at Knoxville. Alfalfa mosaic virus was the only virus found at Greenville. Virus incidence ranged from 0 to 9% with SMV being the most frequently detected virus occurring in 49% and 79% of the leaf samples that tested positive for virus at Milan and Knoxville, respectively.

In 1988, soybean cultivars 'Essex', 'Forrest', 'TN 5- 85' and 'York' were inoculated with BPMV, or SMV, or BPMV and SMV at Knoxville and Milan, Tennessee to evaluate the effect of the viruses on yield. All cultivars were equally susceptible to BPMV infection. BPMV incidence ranged from 2-20% in cultivars inoculated with BPMV alone or in cultivars inoculated with BPMV and SMV. No BPMV was detected in plants not inoculated with BPMV. Little or no SMV occurred in cultivar 'York' with any treatment; however SMV incidence ranged from 4-69% in 'Essex', 2-42% in 'Forrest' and 7-75% in 'TN 5-85'. Based on the analysis of variance, there were significant differences (P≤0.05) among blocks and cultivars but no significant differences among virus treatments or cultivar x treatment at Knoxville. However, significant differences (P≤0.01) were observed among all variables at Milan. According to Tukey's mean separation test (P≤0.05) there was a significant decrease in yield among cultivars inoculated with BPMV/SMV at Milan when compared to all other treatments. No significant differences were found among treatments at Knoxville. Significant differences were found among the cultivars at both locations. At Milan, yields of the cultivar Essex were significantly higher than Forrest, TN 5-85 and York. Yields of TN 5-85 were also significantly higher than Forrest and York. At Knoxville, cultivar TN 5-85 yielded significantly higher than Essex but not significantly higher than cultivars Forrest and York. According to Tukey's mean separation test (P≤0.05), there were differences in yield due to cultivar x treatment interactions at both locations; however no correlation between virus incidence and yield differences were apparent.