Ratio of kernel ∆13C/δ18O improves the selection potential of bread wheat for increased grain yield under different water regimes: A physiological perspective for direct application in wheat breeding.

A doubled haploid (DH) bread wheat population “B0767&” (Carberry/ AC Cadillac) comprising a set of 208 lines was grown for six years under irrigated and dryland environments to explore the potential of using the ratio of ∆13C/δ18O of mature kernels for selecting wheat germplasm with higher grain yield. Through principal component analysis (PCA) over 50% of variation in grain yield was explained by growing environments, with a major contribution by irrigated environments. PCA biplot analysis was used to select ten DH lines with contrasting grain yield for physiological characterization. Analysis of mature kernels for ∆13C and δ18O for 2016‒2018 showed that grain yield was positively correlated with ∆13C under irrigated (R2=0.67) and dryland (R2=0.31) conditions, whereas it was negatively correlated with δ18O under irrigated (R2=0.74) and dryland (R2=0.68) conditions. Use of kernel ∆13C/δ18O ratio to predict grain yield, increased the coefficient of determination value in both irrigated (R2=0.91) and dryland (R2=0.61) environments. The line B0767&AG075 with high ∆13C/δ18O ratio and high grain yield also demonstrated cooler canopy and lower spike temperature, compared to the line B0767&AD028 with low grain yield, under both environments. Flag leaf stomatal conductance (gs) was lower in high yielding lines under dryland conditions showing a linear negative correlation with grain yield, but this relationship was polynomial under irrigated conditions. Our results indicate that the kernel ∆13C/δ18O ratio can reliably select wheat germplasm with high yield potential in both irrigated and dryland environments.