Defensive-related enzyme response in plants treated with a mixture of Bacillus strains (IN937a and IN937b) against different pathogens

In previous research, a mixture of Bacillus amyloliquefaciens strain IN937a and Bacillus pumilus strain IN937b consistently provided systemic protection against multiple diseases in various crops. The objective of this study was to investigate defense-related enzyme responses in plants induced by a mixture of IN937a and IN937b against different pathosystems. Four plant/pathosystems, tomato with Sclerotium rolfsii and Ralstonia solanacearum and pepper with Sclerotium rolfsii and Colletotrichum gloeosporioides, were used to test the efficacy of the mixture in greenhouse assays. Treatments consisted of non-challenged healthy control, nonbacterized pathogen control, and bacterized with a mixture of IN937a and IN937b and challenged later with pathogens. Total superoxide dismutase (SOD) and peroxidase (PO) activities were investigated. Before pathogen inoculation, higher levels of SOD and PO activities were observed in plants treated with a mixture of IN937a and IN937b compared with non-challenged healthy and nonbacterized pathogen controls. After challenge with all pathogens, plants treated with the bacterial mixture had SOD and PO activity levels 25-30% greater than the nonbacterized pathogen control. Additionally, significant disease protection in each plant pathosystem was observed with the bacterial mixture. Low levels of natural SOD and PO activities in the non-challenged healthy control occurred during the assay. In conclusion, a mixture of IN937a and IN937b induced similar responses of SOD and PO activities against different pathogens, and these physiological changes were associated with disease protection with all the tested pathogens. (c) 2007 Elsevier Inc. All rights reserved.