Interconversion of chloroneb and 2,5-dichloro-4-methoxyphenol by soil microorganisms

Abstract

The stability of the chloroneb fungicide (1,4-dichloro-2,5-dimethoxybenzene) and its principal degradation product, 2,5-dichloro-4-methoxyphenol (DCMP), was tested in the presence of individual soil microorganisms. Both the fungicide and DCMP were unaltered in liquid shake cultures of the organisms when growth was minimal or static. However, in nutrient broth where active microbial growth was supported, several organisms converted chloroneb to DCMP and/or DCMP to chloroneb. Of 23 organisms grown in the presence of 5 μg chloroneb/ml, 13 demethylated the fungicide to produce DCMP. Liquid shake cultures of Fusarium spp. were most active in this respect, converting more than 50% of the chloroneb to DCMP in 5 days. When grown in the presence of 5 μg DCMP/ml, 8 organisms, especially Trichoderma viride and Mucor ramannianus, converted up to 20% of the DCMP to chloroneb. Cephalosporium gramineum, Rhizoctonia solani, Mucor ramannianus and Fusarium fungi could both methylate and demethylate DCMP to produce chloroneb and 2,5-dichlorohydroquinone, respectively. Microbial synthesis of chloroneb from DCMP, its principal degradation product, may account in part for the relative stability and long term effectiveness of the fungicide in soil.