Phytotoxicity of Culture Filtrate fromFusarium solani,the Causal Agent of Sudden Death Syndrome of Soybean

Abstract

An isolate of Fusarium solani that caused sudden death syndrome (SDS) of soybean was grown in a semidefined liquid medium. The phytotoxicity of cell-free fungal culture filtrates was determined on soybean calli grown on tissue culture medium amended with fungal culture filtrate. The mean calli brown rating increased as culture filtrate increased in the medium. There were significant (P < 0.05) positive correlations between SDS severity from field microplot data and calli browning due to culture filtrates. Seedlings of five soybean cultivars inoculated with the fungus under greenhouse conditions had significantly (P < 0.05) different foliar severity ratings and relative plant fresh weights. Sensitivity of calli of the same five cultivars to culture filtrate also had significantly (P < 0.05) different brown ratings and relative fresh weights. There were significant (P < 0.05) correlations between variables measured on inoculated soybean seedlings and calli sensitivity. Pathogenicity and phytotoxicity of F. solani isolates from different hosts were tested on soybean plants and calli, respectively. Isolates from hosts other than soybean did not cause SDS symptoms, and their culture filtrates had significantly lower toxicity to soybean calli than did that of soybean SDS-causing isolates.