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Sudden Death Syndrome of Soybean: Fusarium solani as Incitant and Relation of Heterodera glycines to Disease Severity. K. W. Roy, Professor of plant pathology, Mississippi State University, Mississippi State 39762; G. W. Lawrence, H. H. Hodges, K. S. McLean, and J. F. Killebrew. Assistant professor of plant pathology, professor of agronomy, graduate research assistant, and extension plant pathologist, Mississippi State University, Mississippi State 39762. Phytopathology 79:191-197. Accepted for publication 18 August 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-191.

Two morphologically distinct forms of Fusarium solani, designated FS-A and FS-B, were isolated from soybean plants with symptoms of sudden death syndrome, a disease of unproven etiology. Form FS-A was isolated seven to 17 times more frequently from symptomatic than from asymptomatic plants, whereas FS-B was equally frequent on symptomatic and asymptomatic plants. In pathogenicity tests. FS-A caused the symptoms characteristic of sudden death syndrome: FS-B caused root rot but no other symptoms characteristic of the disease. Dual inoculation of soybean with FS-A and the soybean cyst nematode (Heterodera glycines) caused more severe foliar symptoms than those caused by FS-A alone, but the nematode was not required for infection of soybean by FS-A. It was concluded that FS-A is the primary causal agent of sudden death syndrome. FS-A caused a reduction in plant height, root dry weight, shoot dry weight, number of seeds per plant, and seed yield, but only in continuously irrigated plants as compared with periodically irrigated plants.

Additional keywords: Fusarium spp., Glycine max, soybean cyst nematode.