Genetic characterization of seedling root and shoot growth in soybean
Authors:   , Ngo Kevin Khoa 
Published: November 2024

[EMBARGOED UNTIL 08/01/2025] The effects of climate change have contributed to more frequent extreme weather such as drought, heat, and flooding. As a result, these abiotic stresses hinder the regular growth of crops and significantly reduce crop yield production. To address the growing need to ensure global food security, crop improvements are needed to improve their resiliency to these abiotic stresses. Roots play a critical role in water and nutrient uptake. Larger roots were reported to alleviate some abiotic stress damage by increasing exploration for water and nutrients in soybeans to support canopy development during and/or after stresses. In soybean, previous research has mainly focused on root traits aiming to understand how to develop a larger and deeper root that can facilitate water and nutrient uptake. However, changing the root size usually will affect shoot biomass accumulation, with either increased shoot biomass due to overall improved carbon fixation or reduced shoot biomass due to the limitation of the overall carbon fixation. Either effect would lead to change in canopy development and consequently affect yield under nonstress or stress conditions. Therefore, it is imperative to understand the genetic diversity and mechanisms of carbon partition between root and shoot to develop ideal soybean plants with a relatively larger root system for abiotic resilience with minimal yield penalty under nonstress conditions. This project aims to understand genetic diversity and architecture in carbon accumulation and partition between root and shoot at the seedling stage in a diverse set of soybean germplasm lines. This research revealed genetic diversity in carbon accumulation and partition between root and shoot and promising genotypes for R/S ratio were identified. Root biomass and shoot biomass strongly correlate with each other (r = 0.85) and root biomass also has a significant correlation (r = 0.52) with Root/Shoot (R/S) ratio. There was no significant correlation between shoot biomass and R/S ratio, suggesting that selection for R/S ratio would not change shoot carbon allocation significantly. Genome-wide-association-study (GWAS) was conducted for all the three traits. Nine QTL clusters (chromosomal regions) were identified to be associated with root biomass (7), shoot biomass (4) and Root/Shoot (R/S) ratio (3). Among the nine QTL clusters, four QTLs were identified to be associated with both root and shoot biomass and one QTL was identified to be associated with root biomass and R/S ratio. There was no common QTL regulating both shoot biomass and R/S ratio which confirmed that selection for R/S ratio QTLs should not negatively affect shoot growth. These results support the breeding strategy of using R/S ratio as selection criteria to develop relatively larger roots for abiotic stress resilience. Further testing under field conditions is necessary to validate the genotypes with promising R/S ratio and genetic contribution of these identified QTLs. The promising germplasm lines, QTLs for R/S ratio, and corresponding haplotypes can be utilized to direct future crossing and marker-assisted selection to develop climate smart soybean with relatively stronger roots to protect yield under various abiotic stress conditions.