Effects of pyraclostrobin and fipronil on spore germination of three species of arbuscular mycorrhizal fungi in subtropical soil.

Arbuscular mycorrhizal fungi (AMFs) are soil organisms that contribute to essential ecosystem services, such as carbon cycling and improving plant nutrition. The growing interest in using them as risk indicators in ecological risk assessments of pesticides has motivated researchers to improve existing ecotoxicological methods. In Brazil, data regarding the effects of pesticides on AMF in natural soils is scarce. We aimed, through this work, to evaluate the effect of a fungicide based on the active ingredient (a.i.) pyraclostrobin (0; 2.5; 5; 10; 25; 50; 100 mg kg-  1) and a commercial insecticide based on fipronil (0; 25; 50; 100; 250; 500; 750 mg kg-  1) on the spore germination of Rhizophagus clarus, Gigaspora albida, and Gigaspora margarita, in tests conducted in a Red Oxisol. The results demonstrated that pyraclostrobin negatively affected all species tested, with G. albida being the most sensitive (IC50: 61.23 mg kg-  1). The insecticide fipronil reduced spore germination of R. clarus and G. margarita, with no observed effects on G. albida. Considering the predicted environmental concentrations (PEC) estimated of 0.27 mg kg-  1 for pyraclostrobin and 0.033 mg kg-  1 for fipronil, the lowest toxicity-exposure ratio (TER) calculated was 226.8 for pyraclostrobin in G. albida. The magnitude of the TERs suggests that the risk of the substances for the tested species spore germination may be minimal under field conditions in Brazilian Oxisols. Different response trends observed between species also reinforces potential specie-specific pesticide-AMF relationships. Overall, the use of a natural soil in ecotoxicological tests increases ecological relevance of the data and could be used as a further step for Tier I tests with culture media or artificial soil.