Disease Note.

First Report of Sudden Death Syndrome of Soybean in Iowa. X. B. Yang, Department of Plant Pathology, Iowa State University, Ames 50011. S. S. A. Rizvi. 1994. Department of Plant Pathology, Iowa State University, Ames 50011. Plant Dis. 78:830. Accepted for publication 15 April 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0830D.

Symptoms of sudden death syndrome (SDS), caused by Fusarium solani (Mart.) Appel & Wollenweb., were observed on soybean plants at growth stages R2 to R3 in southeastern, central, and northern Iowa in the 1993 growing season, which was cool and wet. Diseased plants were in patches of two to three plants in these fields except in one that had a patch about 2 m2. Leaves on infected plants had scattered, interveinal chlorotic spots. On some leaves, the chlorotic spots became necrotic and coalesced, forming interveinal chlorotic streaks. Defoliation occurred in association with pod abortion on severely infected plants. Deterioration of taproots and lateral roots and light gray-brown discoloration of the root cortex were observed. Plants with severe chlorosis but less necrosis were also observed. Strains of bluish and bluish-green F. solani were isolated on PDA from plants with or without severe necrosis. These strains produced abundant macroconidia that match morphological descriptions by Roy et al (1) and Rupe et al (2). SDS symptoms were reproduced by inoculating plants (growth stage V2-V3, cultivar IA 2007) in a greenhouse; reddish lesions appeared on the base of stems I wk after inoculation, followed by chlorosis and necrosis of leaves 2 wk later. The pathogen was reisolated from inoculated plants. Koch's postulates were fulfilled with isolates from one location in southeastern and five locations in central Iowa.