Impact of plant breeding on the responsiveness of maize and wheat varieties to an arbuscular mycorrhizal fungal symbiont

Societal Impact Statement Field inoculation with arbuscular mycorrhizal fungi (AMF) offers a promising route to improve sustainable agriculture and food production, yet results are often variable. We investigated the mycorrhizal growth response of maize and wheat varieties recommended for farmers and found substantial variation under greenhouse conditions. The mycorrhizal growth response varied from +7% to −12% for maize and from +6% to −25% for wheat and varied by breeding company. Selecting suitable varieties is crucial to fully harness AMF benefits. Field trials under diverse climatic and biotic conditions are required to support AMF application to ultimately promote sustainable agriculture and food security. Summary Arbuscular mycorrhizal fungi (AMF) enhance plant nutrient uptake and can reduce reliance on external inputs. Yet, it is unresolved whether plant breeding influences the ability to benefit from AMF and whether certain modern varieties benefit more from AMF associations compared to older varieties. We tested 15 maize ( Zea mays ) and 15 wheat ( Triticum aestivum ) varieties recommended for farmers, as well as three older wheat cultivars under greenhouse conditions. The plants were inoculated with an AMF ( Rhizoglomus irregulare ), and effects on mycorrhizal root colonization and mycorrhizal growth response (MGR) were assessed. To explore whether genetic background influences AMF responsiveness, we assessed whether response patterns varied across breeding companies and differed when comparing modern and old plant varieties. For maize, most modern varieties showed positive or neutral MGR, ranging from +7% to −12%. In contrast, the majority of modern wheat varieties exhibited neutral or negative responses, with MGR ranging from +6% to −25%. Crucially, modern varieties did not respond uniformly; maize varieties from the same breeder tended to cluster together in terms of MGR, suggesting a strong influence of genetic background. Three old wheat varieties generally showed more positive responsiveness than modern ones, but variation remained within both groups. Our study demonstrates that modern crop varieties differ markedly in their responsiveness to AMF, and that genetic background is a key determinant. These findings suggest that breeding programs and variety testing should integrate beneficial microbial interactions as selection criteria. Such an approach would maximize crop benefits from soil microorganisms and advance sustainable agriculture.