Induced Resistance Mechanism of Twisted Disease Suppression of Shallot by Bacillus spp.

Plant Growth Promoting Rhizobacteria has been known for its ability to induce plant resistance on shallot against twisted disease. Its ability as a bioprotectant agent is estimated to be comparable to the efficacy of Trichoderma which is currently widely used as a biological control agent.. This study aims to determine the content of jasmonic acid, salicylic acid, peroxidase, and disease suppression in shallot by application of Bacillus velezensis B-27, Bacillus cereus RC76, and application with combination of both rhizobacteria. The application was carried out  with tuber dipping for 30 minutes in each treatment with a bacterial density of 108 CFU mL-1. Application using Trichoderma was used as the comparison treatment, and the control plot was not given any treatment. Pathogen inoculation was carried out simultaneously as planting using Fusarium acutatum with a spore density of 106 CFU mL-1. The jasmonic and salicylic acids content was measured using the High-Performance Liquid Chromatography method, and the peroxidase content was determined using the spectrophotometric method. Disease suppression was measured at 10-day intervals. The results showed that treatment with Bacillus cereus RC76 increased jasmonic and salicylic acid levels, while application with Bacillus velezensis B-27 showed the highest level of peroxidase. Treatments with Bacillus spp. were able to suppress twisted disease by 72.2% to 100%. This study demonstrated that application Bacillus spp. suppressed twisted disease on shallot and increased the jasmonic and salicylic acid content as induced resistance mechanism against pathogens.