Functional moiety for the antifungal activity of phytocassane E, a diterpene phytoalexin from rice

Large amounts of phytoalexins were produced in suspension-cultured rice cells by treatment with a mycelial extract of the potato pathogenic fungus Phytophthora infestans. Among them, a new cassane-type diterpene, designated phytocassane E, was isolated and identified as 1β-hydroxy-12,15-cassadien- 3,11-dione. The ED₅₀ values of phytocassane E in the prevention of spore germination and germ tube growth of the rice pathogenic fungus Magnaporthe grisea were 6 and 2 μg ml^-1, respectively. This result, together with earlier results, suggests that the hydroxyl group at the C-1 position is the main functional moiety for the high antifungal activity of phytocassane E.