Role of a phytotoxin produced by Fusarium oxysporum f. sp. raphani on pathogenesis of and resistance to the fungus

Abstract

In the course of a developing screening method for resistant radish to Fusarium oxysporum f. sp. raphani, we found that the fungus produces phytotoxic compound against Raphanus sativus. The culture filtrate of F. oxysporum f. sp. raphani KR1 represented the strongest phytotoxicity when the fungus was incubated in the malt extract broth with 150 rpm at 25°C for 14 days. Under bioassay-guided purification, we isolated a substance from liquid culture of F. oxysporum f. sp. raphani KR1, with phytotoxic effect against R. sativus. The compound was identified as fusaric acid by mass and nuclear magnetic resonance spectral analyses. Phytotoxicity of the compound against cruciferous vegetable crops, including radish, cabbage, and broccoli, was investigated. Fusaric acid represented phytotoxicity on radish seedlings by concentration dependant manner. And the phytotoxin demonstrated strong phytotoxicity on the resistant cultivars as well as susceptible cultivars of radish to F. oxysporum f. sp. raphani. In addition, fusaric acid isolated from the fungus also showed a potent phytotoxic efficacy against non-host Brassicaceae crops of the fungus such as cabbage and broccoli. The results demonstrate that fusaric acid produced by F. oxysporum f. sp. raphani is non-host-specific toxin and for screening of resistant radish to the fungal pathogen, spore suspension of the fungus without the phytotoxin has to be used. © 2013 Korean Society for Horticultural Science.