Metabolism of fungicidal cyanooximes, cymoxanil and analogues in various strains of Botrytis cinerea.

BACKGROUND

The metabolism of cymoxanil [1-(2-cyano-2-methoxyiminoacetyl)-3-ethylurea] and fungicidal cyanooxime analogues was monitored on three phenotypes of Botrytis cinerea Pers. ex Fr. differing in their sensitivity towards cymoxanil. For this purpose, labelled [2-(14)C]cymoxanil was added either to the culture medium of these strains or to its cell-free extract.

RESULTS

In the culture medium of the most sensitive strain, four main metabolites were detected. Three were isolated and identified. Cymoxanil was quickly metabolised by at least three concurrent enzymatic pathways: (i) cyclisation leading, after hydrolysis, to ethylparabanic acid, (ii) reduction giving demethoxylated cymoxanil, (iii) hydrolysis followed by reduction and then acetylation leading to N-acetylcyanoglycine. In the cell-free extract of the same strain, only the first and the second of these enzymatic reactions occurred. By comparing the metabolic profile of the most sensitive strain with that of the less sensitive ones, it was shown that the decrease in sensitivity to cymoxanil correlates with a reduced acetylcyanoglycine formation. Among all metabolites, only N-acetylcyanoglycine is active against the most sensitive strain. Moreover, in a culture of this strain, two other fungicidal cyanooximes were also metabolised into this metabolite.

CONCLUSION

The formation of N-acetylcyanoglycine may play an important role in the fungitoxicity of cymoxanil and cyanooxime derivatives.