Infection of Soybean with Soybean mosaic virus Increases Susceptibility to Phomopsis spp. Seed Infection

Abstract

Infection of soybean [Glycine max (L.) Merr.] plants with Soybean mosaic virus (SMV) has been reported to enhance Phomopsis spp. seed infection, which reduces seed quality. The objective of this study was to determine the influence of SMV on Phomopsis spp. seed infection and seed germination and vigor. During 1995 to 1997, plants of two SMV‐susceptible cultivars (Clark and Williams) and their SMV‐resistant isolines (L78‐434 and L78‐379, resistant to SMV strains G1‐G6) were mechanically inoculated with SMV (G2 strain) at growth stages V4, V8 or R2, and Phomopsis spp. inocula were applied to all plants. Seeds harvested from SMV‐resistant isolines were consistently SMV free, whereas seeds from SMV‐inoculated susceptible cultivars accumulated SMV in seedcoats. Although environmental conditions were favorable, the incidence of Phomopsis spp. seed infection was consistently less than 12% in SMV‐resistant plants, and up to 14‐times greater in SMV‐inoculated susceptible plants, with primary infection occurring after seeds reached physiological maturity (at or after yellow pod stage). Seeds from SMV‐resistant isolines had high average standard germination (88%) and higher vigor (67% accelerated aging; 7 mS m−1 g−1 conductivity), whereas seeds from SMV‐inoculated susceptible cultivars had low standard germination (48%), low vigor (30% accelerated aging; 13 mS m−1 g−1 conductivity). Thus, infection by SMV at or before growth stage R2 increased the susceptibility of soybean seed to Phomopsis spp. infection, and resulted in poor seed quality and low vigor.

Bean pod mottle virus: A Threat to U.S. Soybean Production

“…Phomopsis seed infection tends to be higher in BPMV-infected soybean plants (1,85). SMV infection also increases Phomopsis seed infection (40). Seed infection by Phomopsis occurs during the R7 and R8 growth stages, when pod and seed moisture decline.…”

Effects of Virus Infection on Susceptibility of Soybean Plants to Phomopsis longicolla

“…Similar results were reported by Stuckey et al (32), who reported that SMV had no effect on seed infection by Phomopsis spp. In previous studies, only highly virulent SMV isolates caused an increase in seed infection by Phomopsis spp., and the effect differed among cultivars (8,15,16). only in plants co-infected with SMV and BPMV.…”

“…Koning et al (16) observed a significant increase in seed infection by Phomopsis spp. due to inoculations with a SMV-G2 strain, which was likely to cause an extension of the seed development interval in SMV-susceptible cultivars.…”

“…Abney and Ploper (1) consistently observed an effect of BPMV increasing seed infection by Phomopsis spp. Koning et al (16) also noted that virus-induced predisposition occurred in some years when there was no effect of virus infection on plant maturity. However, in our study, seed infection by P. longlcolla of Spansoy 201 was increased even in the absence of any effect on plant maturation.…”

“…(1,8,16,32); however, the mechanism for this predisposition is unclear. (1,8,16,32); however, the mechanism for this predisposition is unclear.…”