Sudden Death Syndrome of Soybean:Fusarium solanias Incitant and Relation ofHeterodera glycinesto Disease Severity

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Abstract
Two morphologically distinct forms of Fusarium solani, designated FS-A and FS-B, were isolated from soybean [Glycine max] 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.