Leaf stomatal traits, ∆13C grain carbon isotope discrimination, and grain yield of an elite double haploid bread wheat population under different moisture regimes.

Stomatal traits and carbon isotope discrimination (CID) are important determinants of photosynthetic efficiency and water relations in plants. To understand drought stress response and grain yield variations in 11 lines of a doubled haploid (DH) bread wheat population derived from Carberry/AC Cadillac, various physiological traits were studied under 8 growth environments (irrigated and rainfed; 4-year study). The lines, B0767&AG075 (registered as AAC Goodwin), B0767&AX125 and B0767&BF109 with higher grain yield demonstrated lower stomatal conductance as compared to the lines with low grain yield, especially under rainfed conditions. A significant variation was observed for adaxial and abaxial flag leaf stomatal density and size in these wheat lines. The line B0767&AD028 with higher stomatal density consistently yielded low in all environments. Interestingly, low yielding line B0767&AH156 have lowest stomatal density on both surfaces. In contrast, stomatal density was low on abaxial leaf surface of high yielding B0767&AG075 and B0767&AX125, with little difference on adaxial surface when compared to low yielding lines. Grain ∆13C positively correlated with grain yield in 2016 (R2=0.55; p<0.0001), 2017 (R2=0.86; p<0.0001), and 2018 (R2=0.88; p<0.0001). Similar trend was observed for normalized difference vegetation index at grain fill in these wheat lines. Results indicate that stomatal traits and CID analysis could be the potential targets in wheat breeding programs for low moisture areas, providing opportunity to minimize grain yield penalty in such conditions. Physiological understanding of stomatal numbers and function along with CID analysis should be a focus of future studies for yield stability genetic screening of wheat germplasm under dry environments.