IN VITRO STUDIES ON THE ANTIMICROBIAL ACTIVITY AND CHEMICAL CHARACTERIZATION OF SIX COVER CROPS AGAINST THE GRAPEVINE CROWN GALL PATHOGEN
Md.T. Islam, S.-Y. Ahn, V.K. Bajpai, Hae Keun Yun
Crude extracts from shoot and root tissues of Astragalus sinicus, Brassica napus, Dactylis glomerata, Lolium perenne, Lolium multiflorum and Vicia villosa were investigated for their antimicrobial activity against Rhizobium vitis, Bacillus subtilis, Aspergillus niger, Botrytis cinerea, Colletotrichum gloeosporioides, C. acutatum, and Elsinoe ampelina. Extracts were prepared from dried and powdered shoots and roots using common solvents (methanol, ethyl acetate, and water) with different degrees of polarity. The diameter of inhibition zones of the shoot (2,000 µg/disc) and root (2,500 µg/disc) extracts in water and ethyl acetate solvents against R. vitis and B. subtilis were found to be in the range of 9.8±1.3 to 18.0±2.0 mm and 9.0±0.7 to 16.4±0.5 mm, respectively. However, methanolic extract did not show any inhibitory activity. All the extracts showed a minute inhibition zone against A. niger which was not measurable, whereas the other tested fungi were not inhibited. The minimum inhibitory concentration (MIC) values of shoot and root extracts against the tested bacteria were in the range of 3.12 to 12.5 and 3.12 to 25 mg/ml, respectively. A preliminary phytochemical screening of all the tested extracts indicated the presence of alkaloids, flavanoids, saponins, cardiac glycosides, steroids and terpenoids. Total polyphenol contents of extracts positively correlated with their inhibitory activities, suggesting their potential antibacterial efficacy. Our findings suggest that crude extracts from the shoots and roots of these cover crops may be useful in preventing Rhizobium vitis-induced crown gall on grapes.