Genome-wide association study of plant physiological parameters, yield, and nitrogen fixation-related traits in soybean under drought stress 
Creators: Kombala Liyanage, Dilrukshi KD
Publisher: name: University of Alberta Library
Year: 2022

<p>Soybean is one of the world’s leading legume crops. It fixes atmospheric nitrogen with the symbiotic relationship of rhizobia bacteria that inhabit root nodules. The global population is expected to exceed 9.7 billion by 2050, resulting in increased food demand, particularly for protein. In Canada, soybean is the third largest field crop in terms of farm cash receipts, and its production has recently grown significantly in the Canadian Prairies. The changing global climate is predicted to lead large areas of the world to experience extensive drought conditions over the next few decades. Drought will be a critical issue for western Canada as it has been experiencing frequent and severe droughts over the last few decades. Drought has negative impacts on soybean plant development, yield, and symbiotic nitrogen fixation. The main objective of this project is to identify the allelic variations associated with diverse short-season soybean varieties for plant physiological parameters, yield traits, and symbiotic nitrogen fixation under drought stress. A greenhouse pot experiment with 103 early-maturity Canadian soybean varieties was conducted to determine the above-mentioned traits. Seedlings were inoculated with Bradyrhizobium japonicum USDA 110, and the initial soil moisture content of the growing media was maintained at 80% field capacity (FC). Drought stress was applied after three weeks of plant growth, with half of the plants kept at 30% FC and the remaining at 80% FC until maturity. Plant physiological traits such as photosynthesis, transpiration, stomatal conductance, leaf chlorophyll, water-use efficiency, and intrinsic water use efficiency were collected during the flowering stage. At seed maturity, data on yield and nitrogen fixation-related traits, including number of pods, number of seeds, seed yield, 100-seed weight, seed nitrogen content, % nitrogen derived from the atmosphere (%Ndfa), total seed nitrogen fixed, and carbon isotope discrimination (CID), were collected. Drought stress reduced stomatal conductance and transpiration, resulting in greater water-use efficiency compared to well-watered plants at the flowering stage. In comparison to the well-watered treatment, drought-stressed soybean plants had lower seed yield, yield components (number of pods, number of seeds, 100-seed weight), seed nitrogen content, %Ndfa, and total fixed nitrogen. Specifically, drought reduced yield by 34.7%. %Ndfa by 13.4%, total seed nitrogen by 34.9%, and amount of seed nitrogen fixed by 42.1% compared to the well-watered treatment. Significant genotypic variability among soybean varieties was found for plant physiological parameters, yield parameters, nitrogen fixation traits, and water use efficiency. A Genome-Wide Association Study (GWAS) was conducted using 2.16M SNPs (2,164,465 SNPs) for above mentioned parameters for 30% FC, 80% FC and their relative performance (30% FC / 80% FC). In total, 13 quantitative trait locus (QTL) regions, including multiple candidate genes, were detected as significantly associated with different plant physiological traits, including photosynthesis, stomatal conductance, and water-use efficiency for 30% FC and relative performance. In terms of yield and nitrogen fixation-related characteristics, six QTL regions and candidate genes were identified as significantly correlated with %Ndfa and CID under drought stress and relative performance. These QTL regions may be useful in future breeding efforts to create drought-resistant soybean cultivars.</p>