Induced resistance in Brassica juncea L. against Alternaria blight by foliar application of arachidonic acid

The effect of arachidonic acid on the induction of resistance against Alternaria blight in leaves of Brassica juncea L. (var. RLM 619) was studied. Eight week old Brassica juncea L. plants grown in pots (when first signs of disease appeared naturally) were sprayed thrice with an interval of one week with 10 ppm and 50 ppm concentrations of arachidonic acid. Defense related enzymes viz. peroxidase, phenylalanine ammonia lyase, superoxide dismutase and phenolics were analysed after treatment with arachidonic acid. Studies showed that foliar spray with arachidonic acid at 10 ppm concentration significantly elicited peroxidase and superoxide dismutase activity, whereas 50 ppm was effective in increasing the phenylalanine ammonia lyase activity. Phenolics viz. total phenols, o-dihydroxyphenol and f1avanols showed similar trend to that of defense related enzymes as they are involved in their synthesis. Studies revealed that foliar spray of arachidonic acid induces defense related enzymes and phenolics in Brassica juncea L. that trigger the protection against fungal infection.