Climate smart soybean: Drought resistance and enhanced N2 fixation for seed filling through improved mycorrhizal association

Objectives:

• Implement a targeted metabolomics approach to quantify the extent of soybean root colonization by arbuscular mycorrhiza fungi (AMF) under field conditions.
• Using the above approach, evaluate 250+ soybean accessions/cultivars for presence of functional diversity in AMF symbiosis. Test the selected, extreme genotypes (i.e., low, and high AMF) for their impact on drought tolerance and nitrogen (N₂) fixation.
• Perform a genome-wide association study (GWAS) to link plant genotypes with the AMF abundance, aiming to identify genomic regions associated with this trait.
• Develop molecular markers based on the GWAS mapping results to facilitate breeding soybean cultivars with improved AMF association and enhanced drought tolerance.
• Evaluate the AMF abundance and drought resilience of select Ontario elite cultivars.

Impacts:

• Once established, the targeted metabolomics approach for quantifying root AMF colonization can be adopted by soybean breeders and researchers to explore additional ways to enhance soybean-microbiome interaction.
• Genetic variants will be identified and molecular markers developed, which Ontario breeders can use to develop new cultivars with enhanced resource (water and nutrients) capture and improved productivity under drought conditions through a fortified microbiome.
• Knowledge of holobiome-based attributes for climate change adaptation (i.e., drought and persistence of N₂ fixation) will be generated, along with strategies for selection. This information can be used to optimize beneficial symbioses as important elements to agro-engineering aimed at enhancing resilience and productivity.
• An enhanced presence of AMF in soil will help mitigate pollution, including nitrate leaching from agricultural ecosystems.

Scientific Summary:

A evolving climate is changing the frequency and duration of drought, and soybean drought tolerance is poorly understood, which is a major hurdle for Ontario soybean breeders and producers. In particular, summer (July and August) drought negatively affects soybean pod formation and seed filling and thus causes significant yield loss. AMF, obligate root symbionts, are known to protect the plant from drought and other abiotic and biotic stress conditions. In spite of existing data on the important role of plant genetics in driving the responsiveness of crops to AMF, direct selection of soybean germplasm for superior AM symbiosis has not been performed. Breeding for root traits that drive the rhizosphere microbiome toward greater abundance of AMF and sustained N₂ fixation is a win-win strategy for lowering input requirements and enhancing plant tolerance to drought.

We propose here to use an innovative, targeted metabolomics-based phenotypic selection method, in combination with a large-scale field-based screening, to identify soybean genotypes that show enhanced AMF associations. This large-scale screen will take advantage of a collection of ca. 250 Canadian soybean accessions, including elite cultivars, that have already been genotyped during our AAFC-funded soybean project. The genomic regions associated with superior AMF symbiosis will then be identified by a genome-wide association study (GWAS). The genetic screen will also help identify the soybean genotypes with enhanced N₂ fixation, given the known synergism between AMF and rhizobia, the two keystone species of legume root microbiomes. The AMF-enhanced genotypes, carrying favourable alleles of genes associated with specific responses to AMF, will be selected. These soybeans will aid in the development of molecular markers that will be used to breed more resilient, drought tolerant soybeans, integrated into existing breeding programs in Ontario. In addition, elite lines among the selected genotypes will be introduced to farmers as available drought-tolerant varieties and will also serve as parental lines in future cultivar development attempts as sources of drought tolerance

External Funding Partners:

This research was funded in part by Agriculture and Agri-Food Canada (AAFC) through the Sustainable Canadian Agricultural Partnership AgriScience program.