Suppressive effects of seed-applied fungicides on arbuscular mycorrhizal fungi (AMF) differ with fungicide mode of action and AMF species

•Seed-applied fungicides were assessed for their effects on mycorrhizal development.•Systemic fungicides restricted mycorrhizal colonization and host growth.•Contact fungicides had minimal effects on mycorrhizal colonization and host growth.•Pyrosequencing analysis revealed AMF community composition changes by fungicides.•Fungicidal effect on AMF development depends on specific fungicide-AMF interactions. Seed-applied fungicides are commonly used to prevent or suppress fungal disease organisms in pulse crop production. However, non-target beneficial fungi, such as arbuscular mycorrhizal fungi (AMF), also may be affected. Seed-applied fungicides Agrox® FL (active ingredient: captan), Allegiance™ FL (metalaxyl), Apron Maxx® RTA® (fludioxonil and metalaxyl), Thiram 75WP (thiram), Vitaflo® 280 (carbathiin and thiram), Crown® (carbathiin and thiabendazole), and Trilex® AL (trifloxystrobin and metalaxyl) were assessed in a greenhouse study for their effects on colonization and development of AMF in pea and chickpea, and the consequent impact on plant growth. In the absence of disease pressure, systemic fungicides Allegiance™ FL, Apron Maxx® RTA®, Vitaflo® 280, Crown® and Trilex® AL restricted mycorrhizal colonization, host growth and P uptake to different levels. In contrast, contact fungicides Agrox® FL and Thiram 75WP had minimal effects on mycorrhizal colonization, host growth and P uptake. Although consequent sporulation and glomalin-related protein production were not significantly affected by fungicides at an early host growth stage, the compositional structure of the AMF community in host roots was significantly altered in response to Agrox® FL, Allegiance™ FL, Apron Maxx® RTA®, and Trilex® AL as revealed by pyrosequencing-based analysis of fungal 18S rRNA. These results indicate that the suppressive effects of seed-applied fungicides on AMF development depend on specific fungicide-AMF interactions.