Disease Reactions, Resistance, and Viral Antigen Content in Six Legume Species Infected with Eight Isolates of Peanut Mottle Virus

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Abstract
Disease reactions to eight isolates of peanut mottle virus (PMV) were determined in peanut (Arachis hypogaea), pea (Pisum sativum), bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), lima bean (Phaseolus lunatus) and soybean (Glycine max). No resistance to any of the isolates was found in 70 peanut and seven pea genotypes. Four bean genotypes and four cowpea genotypes were extremely resistant to all eight PMV isolates; the virus was localized in inoculated leaves of bean, and no virus could be detected in uninoculated leaves of resistant cowpea. In soybean, reactions were variable; specific genotypes were susceptible to some PMV isolates and extremely resistant (no symptoms and virus not detectable in uninoculated leaves) to others. A differential host range utilizing four plant species (bean, Chenopodium amaranticolor, peanut, and soybean) provided a means to distinguish the eight PMV isolates. Viral antigen content of all PMV isolates was higher in pea, peanut and bean than in lima bean, soybean, and cowpea. More viral antigen was detected in all six plant species infected with the necrosis isolate than with any of the other PMV isolates. We conclude that four isolates are distinct enough to be considered strains of PMV: mild (type), chlorotic stunt, necrosis, and necrosis/chlorosis. Disease reactions of the other four isolates are similar to each other and to the mild strain on all hosts except soybean and C. amaranticolor.