QTLs Associated with Crown Root Angle, Stomatal Conductance, and Maturity in Sorghum

Three factors that directly affect the water inputs in cropping systems are root architecture, length of the growing season, and stomatal conductance to water vapor (g(k)). 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 rate (E) and thus throughout the vegetative phase conserves water that may be used during grain filling in water-limited environments. Additionally, growing early-maturing varieties in regions that rely on soil-stored water is a key water management strategy. To further our understanding of the genetic basis underlying root depth, growing season length, and g s we conducted a quantitative trait locus (QTL) study. A QTL for crown root angle (a proxy for root depth) new to sorghum was identified in chromosome 3. For g s, a QTL in chromosome seven was identified. In a follow-up field study it was determined that the QTL for g s was associated with reduced E but not with net carbon assimilation rate (A) or shoot biomass. No differences in guard-cell length or stomatal density were observed among the lines, leading to the conclusion that the observed differences in g s must be explained by partial stomatal closure. The well-studied maturity gene Ma1 was identified in the QTL for maturity. The transgressive segregation of the population was explained by the possible interaction of Ma1 with other loci. Finally, the most probable position of the genes underlying the QTLs and candidate genes were proposed.