Inhibitory Activity of Forty Kinds of Chinese Herbal Medicines against Phytophthora nicotiana

In this study, antifungal activities of ethanol extracts of 40 species of Chinese herbal medicines against P. nicotiana in vitro were determined. The results showed that antifungal plant resources in Laoshan Mountain were rich. The inhibitive rates of eleven species (27.5%) reached 100% at the concentration of 10 g/L. 28 species had good inhibitive effects over 80% against P. nicotiana. Determination of the antifungal activities of four fractions with relatively high content in the extracts of clove showed that 10-fold dilution of eugenol possesses the highest inhibitive rate (100%) against P. nicotiana, while the inhibitive rate of eugenyl acetate was 60.19%. This study suggests that a big variety of plant species in Laoshan Mountain have antifungal activities, and the active ingredient eugenol of clove extracts has good potential as a biocontrol agent to control tobacco black shank disease.