Immunodetection of Phomopsis Species in Asymptomatic Soybean Plants. R. K. Velicheti, Research Associate, Department of Plant Pathology, University of Illinois at Urbana-Champaign, 1102 South Goodwin Avenue, Urbana 61801-4709. C. Lamison, L. M. Brill, and J. B. Sinclair. Group Biologist, E. I. du Pont de Nemours & Company, Wilmington, DE; Former Graduate Research Assistant, and Professor, Department of Plant Pathology, University of Illinois at Urbana-Champaign, 1102 South Goodwin Avenue, Urbana 61801-4709. Plant Dis. 77:70-73. Accepted for publication 18 September 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0070.

An immunodiagnostic assay was developed for early detection of Phomopsis phaseoli, cause of pod and stem blight, and P. longicolla, cause of seed decay of soybeans (Glycine max), in asymptomatic soybean plant tissue using polyclonal antibodies developed against P. longicolla. Immunoblot analysis of the immunogen and cross-reactive fungal antigens showed a broad smear above 50 kDa. Analyses of P. longicolla and 17 other common soybean parasitic or saprophytic fungi resulted in strong reactions with all Phomopsis spp. and Colletotrichum truncatum. The reaction of these fungi to antibodies developed against P. longicolla was similar, whether developed against culture filtrates or mycelial extracts. An arbitrary "antigen unit" was devised to measure the amount of antigen in a sample instead of using absorption values. Stem samples from uninoculated (control) and inoculated greenhouse-grown soybean (cv. Hack) plants produced immunoreactions to P. phaseoli that agreed with bioassay results and confirmed epiphytic growth of the pathogen.