The effect of Salicylic Acid (SA) in inducing resistance in groundnut plants against Alternaria alternata was investigated. Foliar application of SA at the concentration of 1 mM significantly reduced the leaf blight disease intensity and increased the pod yield under glasshouse conditions. Changes in the activities of phenylalanine ammonium lyase, chitinase b-1,3 glucanase and in phenolic content on groundnut after application of SA and inoculation with A. alternate were studied. In SA-treated leaves (plants) an increase in phenolic content was observed five days after challenge inoculation with A. alternata in groundnut plants pretreated with SA. There was a marked increase in chitinase and pathogen inoculation in SA-treated leaves. In chitinase, b-1,3 glucanase activities were observed in response to plants with an increase in SA treated leaves. Foliar applications of SA-induced in peroxidase and polyphenol oxidase activities were observed upon challenge inoculation with pathogen.
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 b-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 pretreatment 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.
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