Searching ISR determinant/s from Bacillus subtilis IAGS174 against Fusarium wilt of tomato

Bacillus subtilis IAGS174 has been previously shown to induce systemic resistance in tomato plants against Fusarium wilt disease. In the present investigation, the resistance-inducing determinant was isolated from cell-free culture filtrates (CFCF) of this bacterium. For this purpose, CFCF was extracted by a series of organic solvents, and the fraction that showed induced systemic resistance (ISR) activity was further partitioned into sub-fractions by column chromatography by using a stepwise elution method. Gas chromatography/mass spectrometry analysis identified four compounds in the ISR-active sub-fraction viz. eugenol, 3-methoxy butyl acetate, pentachloroaniline and phthalic acid methyl ester (PAME). Subsequent bioassays proved that PAME is the potential ISR determinant that significantly ameliorated Fusarium wilt disease of tomato at concentrations of 0.01 and 0.1 mM. Furthermore, compared to the respective controls, tomato plants treated with PAME showed increased activities of defense-related enzymes such as phenylalanine ammonia-lyase, polyphenol oxidase, and peroxidase. Our research indicates that B. subtilis IAGS174 has great potential for use as a biological control agent, and PAME is the ISR determinant secreted by this bacterium into the rhizosphere. This determinant can effectively trigger defense responses in tomato plants.