QTLs and Candidate Genes for Root Architecture and Reduced Stomatal Conductance in Sorghum.

As the competing demand for water resources is expected to intensify, we need to improve the water use efficiency of our cropping systems. Two factors that directly affect the water inputs of cropping systems are root architecture and stomatal conductance to water vapor (g_s). Deeper rooted cultivars will perform better under water limited conditions because they can access water stored deeper in the soil profile. Reduced g_s limits transpiration and thus conserves water through the vegetative phase that may be used during grain filling in water-limited environments. Breeding for deeper rooted crops with reduced g_s offers great potential to improve the water use efficiency of our cropping systems. Sorghum (Sorghum bicolor), a drought adapted, widely grown crop is a good model organism to study the genetic bases of the observed variation in these traits. Since the public release of the sorghum genome sequence, the amount of bio informatics resources available for sorghum researchers has greatly increased. In this study, we constructed a high-density genetic map for the identification of candidate genes associated with crown root angle and reduced stomatal conductance. The resolution and accuracy of our mapping approach was validated by the identification of the Ma1 gene within a 229 kb region, as delimited by the LOD support interval of the quantitative trait locus (QTL) for days to maturity. We identified strong candidate genes for root angle and reduced stomatal conductance supported by the narrow QTL regions, homology with genes studied in rice and Arabidopsis, and co-location with previously identified QTLs.