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Disease Detection and Losses

Soybean Seed Quality Losses Associated with Bean Leaf Beetles and Alternaria tenuissima. B. J. Shortt, Graduate research assistant, Department of Plant Pathology, 1102 S. Goodwin Avenue, University of Illinois at Urbana-Champaign (UIUC), Urbana 61801; J. B. Sinclair(2), C. G. Helm(3), M. R. Jeffords(4), and M. Kogan(5). (2)Professor, Department of Plant Pathology, 1102 S. Goodwin Avenue, University of Illinois at Urbana-Champaign (UIUC), Urbana 61801; (3)(4)Assistant supportive scientist and field entomologist, Section of Economic Entomology, Institute of Natural Resources, Illinois Natural History Survey, UIUC, 607 E. Peabody Drive, Champaign 61820; (5)Professor of agricultural entomology, UIUC, 607 E. Peabody Drive, Champaign 61820. Phytopathology 72:615-618. Accepted for publication 25 August 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-615.

Abnormally high populations of the bean leaf beetle (Cerotoma trifurcata) in 1980 caused extensive injury to soybean (Glycine max) pods in some areas of Illinois. Pods and seeds of six soybean cultivars grown near Urbana were examined for injury and assayed for fungal infection and loss of seed germinability. Pod injury was most severe on late-maturing cultivars and least on Elf, the most pubescent cultivar tested. The incidence of seedborne A. tenuissima was correlated with pod injury (r = 0.53) and loss of seed germinability (r = 0.63). However, the correlations between pod injury and seed germinability losses varied among cultivars. Alternaria alternata was inconsistently observed on seeds infected with A. tenuissima, and was less pathogenic. Seed treatment with a mixture of captan plus benomyl increased the germination of seeds from injured pods. In a greenhouse study A. tenuissima consistently decayed seeds within artificially injured pods, but did not infect seeds within uninjured pods. A. alternata, A. tenuissima, and eight other species of fungi known to infect soybeans were isolated from adult bean leaf beetles.