Reaction of soybean to single and double inoculation with different Soybean mosaic virus strains

Two soybean genotypes [Glycine max (L.) Merr.] were inoculated either singly with eight Soybean mosaic virus (SMV) strains, or doubly with combinations of two strains, to examine the interactions between strains and determine if complementation, interference, or synergism is evident. Inoculated plants were monitored for symptom development and assayed for strain identity. Virus replication and movement were also monitored by enzyme-linked immunosorbent assay and by a leaf imprint immunoassay. Plants with resistance genes inoculated with two avirulent SMV strains remained healthy and virus was not detected by immunoassays, indicating no apparent complementation between avirulent strains to break resistance. Virulent necrosis-inducing or mosaic-inducing strains, in the presence of an avirulent strain, induced necrosis or mosaic symptoms, respectively, and only the virulent strains were recoverable from the mix-inoculated plants. A necrotic strain inoculated together with a mosaic strain resulted in mosaic symptoms and only the mosaic strain was recovered. Inoculation with two mosaic strains gave rise to mosaic symptoms and only the more virulent mosaic strain was recovered. Thus, following mixed inoculation, the interaction appears to be that of interference. Mosaic strains predominate over necrotic strains, and both predominate over avirulent strains. There is no evident complementation among avirulent strains or phenotypic synergism between two mosaic strains. (C) 2004 Elsevier Ltd. All rights reserved.