Can We Manage Indigenous Arbuscular Mycorrhizal Fungi to Benefit Field Crops in Sustainable Production Systems?.

Arbuscular mycorrhizal fungi (AMF) have been shown to provide macro and micronutrients to their host plants, protect them from biotic and abiotic stresses, improve the quality of soil for their root systems and influence biodiversity of plants in the same ecosystem. Maximum benefit is associated with rapid colonisation of the host, which is most readily achieved if extraradical mycelium (ERM) is the dominant propagule. Minimizing soil disturbance can help maintain ERM intact. However, our knowledge of functional diversity within ERM is limited, so ensuring that the most effective strains of AMF will be those colonizing a new crop is essential. Experiments investigating Mn toxicity and Fusarium oxysporum f.sp. radicis-lycopersici as stressors suggest ways to determine the assemblage of strains that will colonize the new host plants and provide the necessary protection. Under manganese (Mn) toxicity, the presence of an intact ERM enhanced arbuscular colonization 21 days after planting by 1.82 and 3.3 times in wheat and sub-clover, respectively, relative to other type of AMF propagule. Shoot growth of both crops more than doubled and was significantly correlated with a reduction in the Mn concentration of shoots of wheat and in the roots of sub-clover. If the plant establishing the intact ERM was a member of the Fabeacea shoot growth was almost double that of a plant colonized by ERM formed by a host from the Poaceae, although there were no differences in AMF colonization or in plant manganese concentrations.  In the field, a barley cover crop was used to develop an intact ERM and tomato plugs were planted into soil, which contained Fusarium oxysporum that had reduced yields by 20 tha^-1 in the previous season.  Compared with the crop that did not have the agronomy directed towards optimizing AMF protection, yields were 30% greater and plant mortality was 17% less.