Variation in sensitivity to tomatine and rishitin among isolates of Fusarium oxysporum f.sp. lycopersici, and strains not pathogenic on tomato

Abstract

Studies of several fungal plant pathogens have found an association between greater virulence and increased tolerance of the host's defense compounds among different isolates of that pathogen species. This study examined 17 Fusarium oxysparum isolates to determine if tolerance of either of two fungitoxic compounds produced by tomato, rishitin and tomatine, would correlate with virulence or pathogenicity on tomato. Among the 12 pathogenic isolates (forma specialis lycopersici), quantitative levels of virulence were significantly correlated with rishitin tolerance and, in more limited circumstances, with tomatine tolerance. A group of four highly virulent isolates displayed a relatively high tolerance of both tomatine and rishitin compared to the other isolates. When these pathogenic isolates were compared to five F. oxysporum isolates nonpathogenic on tomato, the nonpathogens generally displayed the highest sensitivity to tomatine, but not to rishitin. Although these results do not prove a role for rishitin or tomatine tolerance in virulence or pathogenicity, they do indicate that sufficient natural variation in these traits exists for them to contribute to an isolate's disease potential on tomato.