Carbon Isotope Discrimination May Predict Grain Yield In Durum Wheat Under Mediterranean Conditions

Carbon isotope discrimination (Δ) has been proposed as a criterion for the indirect selection to improve transpiration efficiency and grain yield in bread wheat and barley. Less interest has been devoted to durum wheat (Triticum durum Desf.) despite its economic importance in the Mediterranean basin. The Δ genetic variation and its relationship with productivity in durum wheat is investigated in this study. For this purpose, field experiments were conducted under Mediterranean conditions (South of France) on 144 durum wheat accessions, during three consecutive years with contrasting climatic conditions. Grain yield (GY), above-ground biomass (AGB), harvest index (HI) and carbon isotope discrimination of flag leaf (ΔL) and kernel (ΔG) were measured. Differences among years were noted for ΔL and ΔG, which were probably related to the variation in water availability between years. A large genotypic variation was also noticed for ΔL and ΔG. The two traits were found positively correlated with GY within and across years, which confirms the interest of Δ for selection for grain yield improvement under Mediterranean conditions. ΔG and ΔL correlated better with HI than with GY, suggesting that Δ could reflect the efficiency of carbon partitioning to the grain. The lack of correlation between ΔL and both HI and GY in the favourable water conditions (1996) was probably due to the difference in water availability between the period until flag leaves sampling (favourable conditions) and the strong water stress which accompanied the grain filling. DG correlated better with both HI and GY than ΔL. Moreover, higher broad-sense heritability (h²) was obtained for ΔG than for ΔL. As a result, ΔG appeared to be a better predictive criterion for efficiency of the carbon partitioning to the kernel (harvest index) and hence for grain yield than ΔL.