Disease suppression and growth promotion in cucumbers induced by integrating PGPR agent Bacillus subtilis strain B4 and chemical elicitor ASM

This study describes the combined use of the plant growth-promoting rhizobacteria (PGPR) agent, Bacillus subtilis strain B4 (B4) and acibenzolar-S-methyl [benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester; ASM], a commercial systemic acquired resistance (SAR) elicitor to increase the efficacy of the control of anthracnose disease in cucumber plants caused by Colletotrichum orbiculare (Berk. & Mont.) Arx. We evaluated populations of B4 bacterial cells and found them to be more numerous when cultured in a growth medium amended with ASM than when cultured alone. A spectrophotometer analysis revealed an increase in a broad range of compounds found in the culture filtrate from B4 + ASM compared with filtrate from B4 alone. An increased l-tryptophan utilization in the production of indole acetic acid (IAA) was observed when B4 was combined with ASM relative to when B4 was used alone. The application of B4 combined with ASM resulted in an additive effect, eliciting growth promotion and systemic resistance against anthracnose infection in cucumber plants. There was an increased growth as measured by plant height, leaf length, and leaf width for the combined application when compared to the individual applications of B4 or ASM or untreated control. Anthracnose disease in cucumbers was significantly suppressed by application of the combined B4 and ASM when compared with the individual applications. Thus, the integrated use of the chemical elicitor, ASM and the PGPR agent B4 might serve as an alternative management strategy against anthracnose disease in cucumbers.