Induction of systemic resistance and defense-related enzymes after elicitation of resistance by rhizobacteria and silicon application against Ralstonia solanacearum in tomato (Solanum lycopersicum)

Bacterial wilt caused by Ralstonia solanacearum is a devastating plant disease affecting several economically important crops. To trigger plant-mediated systemic resistance against the pathogen, silicon and the rhizobacteria strain Bacillus pumilis were applied as elicitors. The impact of each elicitor in the induction of systemic resistance was evaluated by individual or dual application in pathogen inoculated tomato genotypes. Application of silicon and B. pumilis significantly reduced bacterial wilt incidence by 50.7 and 26.7%, respectively, in the King Kong 2 genotype (moderately resistant) and by 31.1 and 22.2%, respectively, in the L390 genotype (susceptible) but the dual application of the elicitors did not. The pathogen responsive lipoxygenase (LOX) activity was decreased in the silicon-treated tomato plants and no significant difference was detected in B. pumilis treated-pathogen inoculated plants compared to the control. In addition, a non-significant increases of peroxidase (PO) activity and phenylalanine ammonia lyase (PAL) activity were observed in either silicon/B. pumilis treated and pathogen inoculated plants. However, the PO, PAL and LOX activities declined during the dual application due to antagonistic effect of the two pathways triggered by the two elicitors. Therefore, separate application of each elicitor is recommended as the best strategy for induction of systemic resistance against bacterial wilt in tomato with silicon being a stronger inducer than B. pumilis.