Biochemical defense induction in Indian mustard (Brassica juncea L.) and rapeseed (B. napus L.) by salicylic acid and benzothiadiazole

Alternaria blight, caused by Alternaria brassicae (Berk.) Sacc., is one of the serious diseases of Brassica species. A field experiment was conducted to evaluate the effects of two elicitors, salicylic acid (SA) and benzothiadiazole (BTH), on defense response induction in Brassica juncea and B. napus against Alternaria blight. Four different treatments of SA and BTH were given to 10 week old plants upto 4 consecutive weeks. Chitinase and β-1,3-glucanase enzyme activities; and ascorbic acid and pigment contents were assessed 72 hr after treatment and disease incidence recorded a week after spray. Hydrolytic enzymes activities attained maximum level after 2^nd spray in treatment combinations BTH (3 ppm) + SA (33 ppm) and BTH (7 ppm) + SA (17 ppm). An increase in ascorbic acid and pigment contents was observed in all the treatments after 1^st, 2^nd and 3^rd spray followed by a decrease after 4^th spray. Maximum increase was seen in treatment combinations of elicitors. These treatments also reduced Alternaria blight severity in both the species. The elicitors, applied in combinations, showed synergistic effect on the induction of hydrolytic enzyme activities as well as ascorbic acid and pigment contents in comparison to the individual applications. The study showed that the elicitor combinations can be used effectively to combat Alternaria blight in Brassica species.