The effect of chemicals on the induction of systemic resistance in blackgram (Vigna mungo) against urdbean leaf crinkle virus (ULCV) was studied. Pre-inoculation spraying of blackgram plants with resistance-inducing chemicals, namely salicylic acid and benzothiadiazole at 100 ppm concentration was found to be effective in reducing ULCV infection and increasing the incubation period of the virus under controlled conditions. The treatment of blackgram plants with salicylic acid and benzothiadiazole significantly increased the phenylalanine ammonialyase (PAL), peroxidase (PO) and polyphenol oxidase (PPO) activities. New isoforms of peroxidase and polyphenol oxidase were also induced by these treatments. A two-fold increase in accumulation of total phenol was observed in plants treated with salicylic acid and benzothiadiazole.

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Blackgram (Vigna mungo (L.) Hepper) is one of the important pulse crops grown all over the world. Among the virus diseases of blackgram, leaf crinkle caused by Urdbean Leaf Crinkle Virus (Ungrouped/ ULCV) is an important disease which leads to considerable losses depending on the season and type of cultivar cultivated. Pre-inoculation spraying of blackgram plants with leaf extracts of Mirabilis jalapa or Bougainvillea spectabilis was found to reduce the leaf crinkle disease to about 90%. The suppression of the disease by the extract was not only due to direct inhibition of the virus. Pre-treatment of blackgram leaves with 10% leaf extracts of M. jalapa and B. spectabilis as foliar spray induced the accumulation of phenolics and enhanced the activities of peroxidase, phenylalanine ammonialyase and polyphenol oxidase. New isoforms of peroxidase and polyphenol oxidase were also induced by the treatments. The induced defense mechanism might have played a role in reducing the disease.

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