Herbicidal potential of ophiobolins produced by Drechslera gigantea

Drechslera gigantea, a potential mycoherbicide of grass weeds, was isolated in Florida from naturally infected large crabgrass (Digitaria sanguinalis); it produces phytotoxic metabolites in liq. culture. The main metabolite was identified by spectroscopic methods and optical properties as ophiobolin A, a well-known phytotoxic product of several phytopathogenic fungi of important crops and already extensively studied for its interesting biol. activities. The other 3 minor metabolites proved to be related to ophiobolin A and were identified using the same techniques as 6-epi-ophiobolin A and 3-anhydro-6-epi-ophiobolin A and ophiobolin I. Assayed on punctured detached leaves of several grass and dicotyledon weeds, ophiobolin A proved to be on av. more phytotoxic as compared to the other related compds. Some structural features appear to be important for the phytotoxicity, such as the hydroxy group at C-3, the stereochem. at C-6, and the aldehyde group at C-7. Grass weeds usually proved to be more sensitive to the phytotoxins than dicotyledons, on which ophiobolin A caused the appearance of large necrosis even at the lowest concn. assayed. This is the first report about the prodn. of ophiobolins from D. gigantea and of the proposed use as potential natural herbicides against grass weeds.