Intra-host competition and interactions between Soybean mosaic virus (SMV) strains in mixed-infected soybean.

Over the past two decades, the dominant Soybean mosaic virus (SMV) strain in South Korea has changed from G5 to G7H. To examine the dominance of G7H, intra-host competition between G7H and G5 was evaluated in soybean plants infected with a mixture of SMV strains. The distribution patterns of the two SMV strains in soybean plants inoculated with G7H, G5 and G7H/G5 were investigated at designated time points by RT-PCR/RFLP analysis, which enables the specific differentiation of low concentrations of SMV strains and the detection of mixed infection at any given time. When leaves of 'Kwangankong' and 'Tawonkong' were infected with both strains, the upper leaves had only the G7H strain in simultaneous infections. In sequential inoculations, the leaves exhibited mosaic symptoms caused by G7H, and the G5 strain was not detected in plants pre-inoculated with the G7H strain before inoculation with the G5 strain. In the reverse treatment, both G5 and G7H were present at every vegetative stage. In addition, interactions between the virulence and dominance of G7H, G5, and G1, a less virulent strain, were investigated. Three landrace soybeans were co-inoculated with G7H/G5, G7H/G1, G5/G1, and G7H/G5/G1 sets. There was no significant difference between virulence and dominance. These results demonstrate the dominance of G7H in mixed infections and could explain the prevalence of G7H in South Korea.