The genetic architecture of host response reveals the importance of arbuscular mycorrhizae to maize cultivation

Arbuscular mycorrhizal fungi (AMF) are ubiquitous in cultivated soils, forming symbiotic relationships with the roots of major crop species. Although studies in controlled conditions have demonstrated the potential of the symbiosis to enhance host plant nutrition and alleviate environmental stress, practical difficulties make it hard to estimate the actual benefit in cultivated fields, not least because of the lack of availability of suitable AMF-free controls. Furthermore, the response can vary depending on the plant variety in a manner which is not fully understood. Here, we implemented a novel strategy based on the selective incorporation of AMF-resistance into a genetic mapping population to evaluate maize response in the field. We found AMF to account for about one third of the grain production in a rain-fed medium input field, as well as to impact the relative performance of plant varieties. Characterization of the genetic architecture of host response allowed us to distinguish mycorrhizal benefit from dependence and indicated a trade-off between mycorrhizal and non-mycorrhizal performance, both at the level of individual QTL and genomewide. This approach is applicable to other crop species, permits further mechanistic analysis and is scalable to full yield trials.