Effect of the methoxyiminoacetamide fungicide, SSF129, on respiratory activity in Botrytis cinerea

(E)-2-Methoxyimino-N-methyl-2-[2-(2,5-dimethylphenoxymethyl)phenyl]acetamid e (SSF129) has been developed as a broad-spectrum systemic fungicide for co ntrol of cereal and fruit diseases. This compound inhibited NADH-oxidation by submitochondrial particles from mycelial cells of Botrytis cinerea, with an EC50 value of 14.5 nM, due to blockage of electron transport through th e cytochrome bc(1) complex in the mitochondrial respiratory chain. However, SSF129 did not suppress, but rather increased, oxygen consumption by mycel ial cells of the fungus. This was because mycelial cells contain an alterna tive oxidase protein and the cells have the ability to rapidly switch elect ron flux from the main cytochrome pathway to the alternative pathway on blo ckage of the former by SSF129. The alternative pathway of the mycelia seems not to be operative when the cytochrome pathway is functional. Naturally o ccurring flavonoids inhibited the alternative oxidase of the mycelial cells in a dose-dependent manner, with EC50 values of 68.4 mu M for flavone and 63.7 mu M for flavanone. These observations suggested that plant components play an important role in control of gray mould by SSF129. (C) 1999 Societ y of Chemical Industry.