VIEW ARTICLE

Etiology

Pathogenicity of Sclerotia- and Nonsclerotia-forming Isolates of Colletotrichum truncatum on Soybean Plants and Roots. Mahmood Khan, Graduate student, Department of Plant Pathology, University of Illinois at Urbana-Champaign (UIUC), 1102 S. Goodwin Avenue, Urbana, IL 61801-4709; J. B. Sinclair, Professor, Department of Plant Pathology, University of Illinois at Urbana-Champaign (UIUC), 1102 S. Goodwin Avenue, Urbana, IL 61801-4709. Phytopathology 82:314-319. Accepted for publication 24 September 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-314.

Three isolates (Ct-l, Ct-3, Ct-4) of Colletotrichum truncatum from soybean (Glycine max) soil or seeds produced microsclerotia in culture and in soybean tissues. The three sclerotia-forming and three nonsclerotia-forming isolates (Ct-2, Ct-AU, Ct-HL) were pathogenic to soybean roots in an aeroponics growth chamber. Sclerotia-forming isolates of C. truncatum and the pathogenicity of C. truncatum on soybean roots were not reported previously. Soybean cvs. A. K. (Kansas), Boone, Corsoy 79, and Williams 82, which differed in resistance to foliar anthracnose caused by C. truncatum, were all susceptible to root infection by all isolates; Williams 82 was most susceptible, followed, in descending order, by Corsoy 79, A. K. (Kansas), and Boone. Lesions on roots of plants growing in an aeroponics growth chamber were significantly longer with Corsoy 79 and Williams 82 inoculated with isolates Ct-1, Ct-AU, and Ct-HL than on roots inoculated with isolates Ct-2, Ct-3, or Ct-4. In field studies, yields were significantly suppressed below noninoculated plants for all cultivars except Boone when inoculated separately with isolates Ct-1, Ct-2, and Ct-3. Estimated yield loss due to anthracnose was 17% for A. K. (Kansas), 23% for Corsoy 79, and 30% for Williams 82.