Role of β-amino butyric acid (BABA) in the induction of resistance against cucumber downy mildew and activities of defense-related enzymes

Cucumber downy mildew caused by Pseudoperonospora cubensis is one of the most important diseases of cucumberin Iran. In this investigation the role of β-Aminobutyric acid (BABA) in reducing this disease was studied via spraying of leaves and soil drench. The plants were treated with BABA and after 24 hours leaves were detached and inoculated with the pathogen and kept in a plastic box with favorable conditions for the disease agent. The disease was evaluated six days after inoculation with pathogen by scoring the leaves between 0-9 and the disease index calculated. Result showed that spraying the leaves by BABA had no effect on the disease reduction but soil application of this compound statistically reduced the disease (p≤0.05). The second phase of the experiment was done for evaluating the effect of BABA on the activity of enzymes such as β-1,4-Glucanase, phenylalanine ammonia-lyase, peroxidase and polyphenol oxidase. Enzymes activity was assayed at 0, 24, 48, 72 and 96 hours after inoculation with the pathogen. Results showed an increas jn enzyme activity at 48-hours post-inoculation with the pathogen and then β-1,4-Glucanase, PAL, and POX enzymes activities decreased slowly, while PPO enzymes activity decreased rapidly.