Ecotoxicological effect of imidacloprid on spore germination of phylogenetically distinct arbuscular mycorrhizal fungi species

Arbuscular mycorrhizal fungi (AMF) establish a mutualistic symbiosis with most terrestrial plants. Mycorrhizal colonization begins with fungal spore germination in soil, a critical stage for symbiosis establishment, and is therefore highly susceptible. Among the compounds that may negatively affect AMF, imidacloprid has been identified as a potential stressor. In this context, the present study aimed to investigate the effects of the insecticide imidacloprid, as the active ingredient, on the pre-symbiotic phase of Acaulospora morrowiae, Gigaspora margarita, and Rhizophagus clarus. The substrate used for the in vitro assays was tropical artificial soil (TAS). The concentrations tested were 0, 2, 4, 8, 16, 32, 64, 128, 256, and 512 mg imidacloprid kg–1 of TAS for A. morrowiae and G. margarita; and 0, 1, 2, 4, 8, 16, 32, 64, 128, and 256 mg imidacloprid kg–1 of TAS for R. clarus. Imidacloprid reduced spore germination in all AMF species across all tested concentrations. However, A. morrowiae was the most sensitive species, with an IC50 of 23 mg kg–1. Although all AMF species evaluated in this study showed inhibition of spore germination upon exposure to imidacloprid, their responses differed among species, likely due to distinct morphological characteristics.