Arbuscular mycorrhizal fungi inhibit necrotrophic, but not biotrophic, aboveground plant pathogens: a meta-analysis and experimental study

center dot Microbial mutualists can profoundly modify host species ecology and evolution, by extension altering interactions with other microbial species, including pathogens. Arbuscular mycorrhizal fungi (AMF) may moderate infections by pathogens, but the direction and strength of these effects can be idiosyncratic.center dot To assess how the introduction of AMF impacts the incidence and severity of aboveground plant diseases (i.e. 'disease impact'), we conducted a meta-analysis of 130 comparisons derived from 69 published studies. To elucidate the potential mechanisms underlying the influence of AMF on pathogens, we conducted three glasshouse experiments involving six non-woody plant species, yielded crucial data on leaf nutrient composition, plant defense compounds, and transcriptomes.center dot Our meta-analysis revealed that the inoculation of AMF lead to a reduction in disease impact. More precisely, AMF inoculation was associated with a decrease in necrotrophic dis-eases, while no significant impact on biotrophic diseases. Chemical and transcriptome ana-lyses suggested that these effects may be driven by AMF regulation of jasmonic acid and salicylic acid signaling pathways in glasshouse experiments. However, changes in plant nutri-tional status and secondary chemicals may also regulate disease impact.center dot These results emphasize the importance of incorporating pathogen life history when predicting how microbial mutualisms affect disease impact.