Induction of systemic resistance to Colletotrichum lindemuthianum in bean by a benzothiadiazole derivative and rhizobacteria

Plants have developed mechanisms to resist secondary infection upon inoculation with a necrotizing pathogen, chemical treatment as well as treatment with some non-pathogenic microorganisms such as rhizosphere bacteria. This phenomenon has been variously described as induced systemic resistance (ISR) or systemic acquired resistance. In the present study, the chemical benzo(1,2,3)thiadiazoie-7-carbothioic acid-S-methyl ester (BTH, acibenzolar-S-methyl), and the rhizobacteria Pseudomonas aeruginosa KMPCH and P. fluorescens WCS417 were tested for their ability to induce resistance to Colletotrichum lindemuthianum in susceptible and moderately resistant bean plants (Phaseolus vulgaris L.). BTH induced local and systemic resistance when bean leaves were immersed in 10(-3) to 10(-7) M BTH 3 days before the challenge inoculation. At a high concentration (10(-3) M), BTH induced resistance of the same order as resistance induced by the pathogen C. lindermuthianum, although at this high concentration BTH appeared to be phytotoxic. Soil and seed treatment with 1 mg kg(-1) BTH protected beans against anthracnose. BTH-mediated induced resistance was effective in susceptible and moderately resistant plants. P. aeruginosa KMPCH induced resistance in bean against C. lindemuthianum only in a moderately resistant interaction. KMPCH-567, a salicylic acid mutant of KMPCH, failed to induce resistance, indicating that salicylic acid is important for KMPCH to induce resistance in the bean-C. lindemuthianum system. P. fluorescens WCS417 could induce resistance to C, lindemuthianum in a susceptible and in moderately resistant interactions.