Mechanisms of Action Exerted by Biocontrol Agents Against Alternaria alternata That Causes Leaf Blight of Watermelon

摘要

Among the foliar diseases of cucurbits, leaf blight incited by Alternaria alternata and Alternaria cucumerina are wide spread and frequently reported from India on watermelon and other cucurbits. Leaf blight causes damage by defoliating the vines, andreducing fruit size, yield and quality. A.alternata causes fruit rot under conducive climatic condition. The isolates of Pseudomonas fluorescens ( PfC6 and PfCIAH-196), Bacillus subtilis (BSW1 and BST1), Trichoderma isolate - CIAH 175 and T.harzianum were effective in reducing the disease incidence of A.alternata in watermelon. Hence, these isolates were studied for the mechanisms of action in disease suppression. The results showed that the non-volatile antibiotics produced by the bacterial isolates inhibited the growth of the pathogen. The antibiotics produced by B.subtilis caused swelling of germ tube while P.fluorescens modified hyphae of the pathogen into a chain of knotted cells. Volatiles from Trichoderma isolate CIAH 175 caused a maximum reduction in growth of A. alternata. Among the bacterial antagonists, production of siderophores and HCN was maximum in PfCIAH-196, salicyclic acid production was more in PfC6. The isolate of B.subtilis - BSW1 produced more quantity of indole acidic acid andbeta-1-3 glucanase.