Induced systemic resistence in watermelon by biocontrol agents against Alternaria alternata

Abstract

Seed treatment followed by foliar application of talc formulated biocontrol agents triggered systemic resistance in watermelon. As a response of ISR, the activities of defense related enzymes viz., phenylalanine ammonia lyase (PAL), peroxidase (PO), polyphenol oxidase (PPO) and β-1-3-glucanase were enhanced and the accumulation of phenols was also noticed in the watermelon upon challenge inoculation with Alternaria alternata, the causal agent for leaf blight in watermelon. The activities of enzymes reached a peak at six days after inoculation (DAI) with the pathogen. Though pre- treatment with all the six biocontrol agents enhanced the defense response in watermelon against the pathogen, a maximum increase in enzyme activity and phenol accumulation were accomplished in treatment with Bacillus subtilis (BsW1). Native PAGE analysis revealed the expression of an additional isoform of PO (POI) in plants pre-treated with Bsw1 and also the induction of an isoform of PPO (PPOI) in plants pre-treated with all the bioagents except BsT1 with response to challenge inoculation of pathogen.