Rebuilding the Arbuscular Mycorrhizal Inoculant Pipeline: Integrating Quality-by-Design and Trait–Environment Matching

Arbuscular mycorrhizal (AM) fungi offer opportunities for low-input agriculture, but commercial inoculant performance remains variable. This narrative and conceptual review examines the evidence for this variability and proposes a framework for more reliable development. Three findings emerge. Independent assessments reveal recurrent composition and infectivity deficiencies among tested products, without establishing their market prevalence. Root colonisation does not guarantee host benefit, nor host benefit agronomic value. Provenance effects are context-dependent, so local origin can guide sourcing but confers no universal advantage. We distinguish six performance endpoints and five development bottlenecks, separating documented constraints from hypothesised cultivation-associated trait change. A hypothesis-generating trait–environment matching framework relates establishment and host benefit separately to environmental constraints and resident AM fungal community function. A complementary quality-by-design framework begins by diagnosing whether inoculation is needed and which function is required, then links selection, production, storage validation and batch release to targeted deployment. Practical priorities are to select isolates and consortia on demonstrated function, verify retention through production and storage, and test added value against management alternatives. These frameworks require experimental validation. Verified product quality is necessary but insufficient: the selected function must be expressed where its benefit justifies intervention.