Crop-adapted arbuscular mycorrhizal fungi in maize: from symbiotic function to field reliability

Arbuscular mycorrhizal fungi (AMF) can improve nutrient acquisition and stress responses in maize, yet inoculation benefits remain inconsistent across fields. Root colonization alone does not establish effective nutrient transfer or net crop benefit. This critical narrative review examines maize-associated AMF diversity, arbuscule-mediated exchange, host genotype effects, phosphorus availability, stress responses, rhizosphere and hyphosphere interactions, inoculant quality, and field evidence. We define crop-adapted AMF by demonstrated function in a specified maize–soil–management context, rather than fungal origin or colonization percentage alone. Drawing on mechanistic research and contrasting field outcomes, we propose a six-stage Maize–Soil–AMF Fit Framework linking native resource mapping, functional screening, compatibility tests, formulation quality, field integration, and ecological monitoring. The framework distinguishes practical agronomic evidence from advanced mechanistic measurements and permits three decisions: inoculate with a validated product, manage an effective native AMF network, or avoid intervention. It is a conceptual decision aid, not a validated predictive model. Reliable application requires replicated, genotype-aware field tests with appropriate native-AMF controls, prespecified crop outcomes, and transparent assessment of uncertainty and economic value.