Wheat is the most widely-cultivated cereal crop on Earth and is a staple food source for several billion people worldwide. While the ‘Green Revolution’ in the mid-20^th Century saw yields increase substantially through the introduction of dwarfing varieties and enhanced synthetic fertiliser availability and application, this growth has recently slowed. Feeding the world’s population at the end of this century, projected to be 10 billion, will require further yield increases. Moreover, agricultural output must be enhanced by sustainable intensification – increasing output while minimising deleterious environmental and ecological impact. A better understanding of the roles of soil microbes in crop growth may prove vital in this sustainable intensification. In part, this is due to the fact that all cereal crop species grow in symbiosis with arbuscular mycorrhizal fungi (AMF), which can have considerable impact on plant growth.

The AMF comprise around 250 species of soil fungi which are abundant in agricultural soils, despite disruptive cultivations and chemical inputs. These fungi grow within plant roots and extend into the soil, acting as a root extension for the plant. AMF may enhance plant nutrient uptake and growth, drought tolerance, pest and pathogen resistance, and improve soil structure, but they sometimes act as parasites rather than mutualists, causing growth suppression in host plants. Closely related plants, e.g. different cultivars of wheat, can show dramatically different response to AMF colonisation; biomass may be significantly increased or decreased depending on cultivar identity. Ensuring crop plants respond positively to colonisation is therefore a research priority; understanding what determines whether AMF are beneficial or parasitic on their crop hosts is the focus of this project.

Using a mapping population of 99 wheat lines derived from crossing cultivars Avalon and Cadenza, we have found substantial variation in response to AMF colonisation. Shoot biomass was increased by up to 85 % and decreased by as much as 30 % in various lines, indicating a considerable effect of plant genotype on AMF responsiveness. Our collaborators at ADAS are undertaking the next step of the project, using quantitative trait locus (QTL) analysis to identify regions of the wheat genome which are associated with these growth responses. Once identified, these regions can then be used as targets by plant breeders, with the aim of selecting any genes correlated with positive response to AMF colonisation, while excluding those linked to negative responses. Further work at Sheffield will identify which fungal species from our mixed AMF inoculum have colonised our wheat roots, allowing us to compare the relative importance of fungal identity and plant genetic variation in determining wheat responses to mycorrhizal colonisation.