Phytotoxicity to Crop Plants and Herbicidal Effects on Weeds of Viridiol Produced byGliocladium virens

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Abstract
When the biological control agent, G. virens, was grown on an autoclaved rice medium, it produced a phytotoxin that caused necrosis of cotton seedling radicles. The phytotoxin was identified as viridiol, a compound previously reported from G. virens. Viridiol, a close relative of the antifungal compound viridin, had little antibiotic activity against a variety of fungi and bacteria, but it was herbicidal to germinating pigweed seed [Amaranthus retroflexus] when used in vitro. Because of its instability, viridiol was not an effective herbicide when it was introduced into field soil. However, when a dried and ground preparation of G. virens cultured on rice was worked into pigweed-infested soil above planted cotton seed, viridiol apparently was produced in sufficient quantity and duration to prevent pigweed emergence without apparent harm to emerging cotton seedlings. The longevity of G. virens in the dried rice preparation and the ease with which it is stored and applied, suggest its possible use as a biological control agent to suppress pigweed in cotton plantings.

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