GWAS in a Sorghum NAM Population, a Diversity Panel and an Elite Breeding Population Identifies common Genomic Regions associated with Nodal Root Angle

Agriculture faces enormous challenges to feed a growing population in the face of likely negative impacts of climate change combined with dwindling soil and water resources for agricultural production. Sorghum, the fifth most important grain crop worldwide and a C₄ dryland crop with adaptation to drought conditions, will play an increasingly important role in feeding the world’s expanding population under such conditions. An important trait in sorghum which impacts on the potential ability of the crop to capture water is nodal root angle which influences vertical and horizontal root distribution in the soil profile. Considerable variation in root angle in sorghum seedlings has previously been reported and is predictive of the amount and timing of water uptake in adult plants grown in large root chambers. A high throughput nodal root angle screening methodology has been developed and applied to over 2500 individuals from 3 separate populations, including a Nested Association Mapping population, a Diversity Panel and a sorghum breeding population. In this study, we report on the identification of multiple genomic regions associated with nodal root angle across the three germplasm resources and identify candidate genes for nodal root angle in sorghum and use comparative genomics approaches to identify orthologues collocating with root angle QTL in maize and rice. Data from multi-environment trials indicates that narrow root angle is associated with the stay-green drought tolerance trait and with higher yield in most Australian sorghum growing environments and is thus relevant to drought adaptation. The identification of nodal root angle QTL and candidate genes presents new opportunities for improving drought adaptation mechanisms via molecular breeding to manipulate a trait for which selection has previously been very difficult.