Correlation and co-localization of QTLs for stomatal density, canopy temperature, and productivity with and without drought stress in Setaria

Mechanistic modeling indicates that stomatal conductance could be reduced
to improve water use efficiency (WUE) in C4 crops. Genetic variation in
stomatal density and canopy temperature was evaluated in the model C4
genus, Setaria. Recombinant inbred lines (RILs) derived from a Setaria
italica × Setaria viridis cross were grown with ample or limiting water
supply under field conditions in Illinois. An optical profilometer was
used to rapidly assess stomatal patterning, and canopy temperature was
measured using infrared imaging. Stomatal density and canopy temperature
were positively correlated but both were negatively correlated with total
above-ground biomass. These trait relationships suggest a likely
interaction between stomatal density and the other drivers of water use
such as stomatal size and aperture. Multiple quantitative trait loci
(QTLs) were identified for stomatal density and canopy temperature,
including co-located QTLs on chromosomes 5 and 9. The direction of the
additive effect of these QTLs on chromosome 5 and 9 was in accordance with
the positive phenotypic relationship between these two traits. This, along
with prior experiments, suggests a common genetic architecture between
stomatal patterning and WUE in controlled environments with canopy
transpiration and productivity in the field, while highlighting the
potential of Setaria as a model to understand the physiology and genetics
of WUE in C4 species.