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

Abstract

Summary 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. 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. 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 diseases, while no significant impact on biotrophic diseases. Chemical and transcriptome analyses 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 nutritional status and secondary chemicals may also regulate disease impact. These results emphasize the importance of incorporating pathogen life history when predicting how microbial mutualisms affect disease impact.

The Interaction between Arbuscular Mycorrhizal Fungi (AMF) and Grass Endophyte (Epichloë) on Host Plants: A Review

“…Grass endophytes confer prominent advantages to host plants, such as alkaloid production, induction of expression of anti-herbivore feeding genes, and alteration of volatile substance composition, which discourages feeding by herbivores [ 78 ]. The enhancement of plant resistance by AMF is undeniable [ 25 , 79 ]. However, studies on the interactions between grass endophytes and AMF and the resulting repulsion of herbivores and other biological stresses by the host plant remain scanty.…”

“…AMF increases the root absorption surface area, thereby enhancing the uptake of nutrients such as nitrogen and phosphorus, promoting photosynthesis, and regulating photosynthetic product distribution, ultimately improving plant growth [ 12 , 13 , 14 , 15 ]. Furthermore, AMF promotes the host plant’s resistance to adverse environmental stressors, including drought, heavy metals, microplastics, and biotic stresses such as pathogens and herbivory insects [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. In reciprocation, plants supply AMF with the necessary carbon sources for their growth and survival [ 26 , 27 ].…”

Contrasting effects of sheep and cattle grazing on foliar fungal diseases by changing plant community characteristics

“…We found negative effects of biodiversity on disease severity for biotrophic, rather than necrotrophic pathogens, which agrees with a previous meta‐analysis (Liu et al., 2020). Obligate biotrophic pathogens are generally relatively specialised (Duplessis et al., 2011; Liu et al., 2024), meaning that higher plant species richness may inhibit their transmission by reducing encounter probabilities between pathogens and their hosts (i.e. susceptible host regulation; Keesing et al., 2006) or by increasing the interception of spores by non‐hosts (i.e.…”