Synergistic effect of acetyl salicylic acid and DL-Beta-aminobutyric acid on biocontrol efficacy of Bacillus strains against tomato bacterial wilt

This study was conducted to assess the biocontrol efficacy of Bacillus subtilis (strain 4812) and Bacillus methylotrophicus (strain H8) individually or in combination with two plant defense inducers including Acetyl salicylic acid (ASA) and DL-Beta-aminobutyric acid (BABA) against tomato wilt caused by Ralstonia solanacearum. The pathogen was significantly inhibited by all treatments in the greenhouse and in vitro tests. The treatments H8+ASA and 4812+H8 were found to be the most effective treatments in in vitro tests. Applied on tomato seeds and as soil drenching, the disease was most inhibited by H8 whereas 4812+H8+ASA was the least effective treatment. High activity of phenylalanine ammonia-lyase was observed in the plants treated with 4812+H8, H8+ASA and 4812+H8+ASA. The highest expression of peroxidase and polyphenoloxidase enzymes was found in the plants treated with H8, 4812+H8 and H8+ASA. The result of real time PCR showed that concentration of the pathogen in stem tissues was significantly reduced in all treated plants and H8+ASA was the most effective treatment. This study revealed that combined application of Bacillus strains can be considered as a more effective biocontrol agent against tomato bacterial wilt. Furthermore, the synergistic effect of plant defense inducers was variable to different Bacillus strains.