Reactions of Mid-Southern U.S. Soybean Cultivars to Bean Pod Mottle Virus and Tobacco Ringspot Virus

Bean pod mottle virus (BPMV) and Tobacco ringspot virus (TRSV) are two important viral pathogens causing reduction of seed yield and quality in soybean (Glycine max (L.) Merr.). Various BPMV and TRSV isolates have been observed, but no host resistance has been reported. The objective of this study was to screen a set of modern soybean cultivars for resistance or tolerance to BPMV and TRSV. A total of 303 cultivars currently grown in the mid- southern United States were screened in the greenhouse for their reactions to BPMV and TRSV. Each cultivar was inoculated with a mild and a virulent isolate of each virus. None of the cultivars tested was resistant to BPMV, but a range of tolerance to this virus was observed among the cultivars. An enzyme-linked immunosorbent assay (ELISA) confi rmed the presence of BPMV in the high and low tolerance cultivars. Tolerance to BPMV is associated with less of a reduction in plant height and biomass on infected plants. Cultivars were classifi ed into four groups, high, moderate, low, and very low tolerance, on the basis of their having exhibited ≤20, 21 to 40, 41 to 60, or >60% of a reduction in plant height and ≤25, 26 to 50, 51 to 75, and >75% plant biomass reduction, respectively. None of the cultivars was resistant to TRSV, and all showed bud blight symptoms by 10 d after inoculation. However, 55 cultivars recovered 5 wk after inoculation, with more than 80% of the plants growing out of the bud blight symptoms and forming new leaves. The recovered plants, although systemically infected, clearly showed tolerance to TRSV at a later stage. These results may be helpful to soybean producers for selecting tolerant cultivars to grow in areas where BPMV and/or TRSV may cause problems in production.