Azoxystrobin and soil interactions: degradation and impact on soil bacterial and fungal communities.

AIMS: To provide an independent assessment of azoxystrobin effects on nontarget soil bacteria and fungi and generate some baseline information on azoxystrobin's persistence in soil.

METHODS AND RESULTS: Plate based assay showed that azoxystrobin exhibited differential toxicity upon cultured fungi at different application rates. While (14)C labelled isotopes experiments showed that less than 1% of azoxystrobin was mineralized, degradation studies revealed over 60% azoxystrobin breakdown over 21 days. PCR DGGE analysis of 16S and 18S rRNA genes from different soil microcosms showed that azoxystrobin had some effects on fungal community after 21 days (up to 84 days) of incubation in either light or dark soil microcosms. Light incubations increased fungal diversity while dark incubations reduced fungal diversity. Bacterial diversity was unaffected.

CONCLUSIONS: Significant biotic breakdown of parent azoxystrobin occurred within 21 days even in the absence of light. Azoxystrobin under certain conditions can reduce fungal soil diversity.

SIGNIFICANCE AND IMPACT OF THE STUDY: One of the few independent assessments of azoxystrobin (a widely used strobilurins fungicide) effects on soil fungi when used at the recommended rate. Azoxystrobin and metabolites may persist after 21 days and affect soil fungi.