Microbial degradation of mefenoxam in rhizosphere of Zinnia angustifolia

The fate of the fungicide mefenoxam was studied in a containerized rhizosph ere system. The rhizosphere system used Zinnia angustifolia (Tropic Snow) i n a bark/sand potting mix and was compared to bulk potting mix (no plants). Rhizosphere microbial populations were allowed to establish for 3 weeks pr ior to fungicide addition (20 mug per g mix). Mefenoxam and degradation pro duct concentrations were determined by High HPLC or capillary electrophores is after extraction. Seventy eight percent of the fungicide originally appl ied to the rhizosphere was degraded after 21 days compared to 44% in bull; system (no plant). The primary degradation product was the free acid N-(2,6 -dimethylphenyl)-N-(methoxyacetyl)-DL-alanine, which accounted for 71% of t he applied parent chemical after 30 days. N-(2,6-dimethylphenyl)-acetamide was also detected, but in lesser amounts. Bacterial populations in the rhiz osphere increased during the 30-day period, which correlated with an increa se in degradation of the parent compound. Pure cultures of Pseudomonas fluo rescens and Chrysobacterium indologenes isolated from the rhizosphere syste m could degrade the applied fungicide (10 mug/ml) almost completely to the free acid within 54 h. (C) 2001 Elsevier Science Ltd. All rights reserved.