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Resistance

Disease Resistance, Virus Concentration, and Agronomic Performance of Soybean Infected with Cowpea Chlorotic Mottle Virus. O. R. Paguio, Departments of Plant Pathology and Agronomy, University of Georgia, Athens 30602; H. R. Boerma, and C. W. Kuhn. Departments of Plant Pathology and Agronomy, University of Georgia, Athens 30602. Phytopathology 77:703-707. Accepted for publication 14 October 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-703.

Virus concentration and agronomic performance of six soybean genotypes with different levels of susceptibility and resistance to the soybean strain of cowpea chlorotic mottle virus (CCMV-S) were studied under field conditions. In general, symptoms of mosaic and stunt were milder in a 1984 experiment than in two experiments in 1985. Virus concentration also was lower in 1984, particularly in the resistant genotypes. No seed yield loss was detected in 1984; however, Davis, a susceptible genotype, had a loss of 19% in one 1985 experiment and plant introduction (PI) 96983 had an average loss of 37% in the two 1985 experiments. Low seed quality was observed in five genotypes in one or more experiments. Plant height was the agronomic character that was affected most frequently by virus infection; reductions varied from 13 to 42%, with all genotypes affected in at least one experiment. Lodging, seed weight, and maturity date were affected to a limited extent by CCMV-S. Virus concentration was not always directly related to seed yield losses and plant height reductions. Only 315% as much virus was produced in PI 96983 as in Davis, yet seed yield losses and plant height reductions were consistently greater in PI 96983. PI 346304 and Bragg were similarly resistant to seed yield losses caused by CCMV-S under field conditions, and they have different types of resistance. Bragg reacted with necrotic lesions at the site of infection, and extremely low quantities of virus occurred in uninoculated leaves. Very mild or no symptoms were produced on PI 346304, which had a low concentration of CCMV-S.