Breeding for Yield Potential has Increased Deep Soil Water Extraction Capacity in Irrigated Wheat

The global wheat (Triticum aestivum L.) growing area under irrigation has risen to approximately 20%. However, future availability and quality of irrigation water is likely to decline due to competition from the needs of the expanding population combined with the effects of climatic change. Recent genetic improvements of the yield of irrigated spring wheat lines reported by CIMMYT have been associated with significantly higher biomass, suggesting that either crops are becoming more water use efficient or are extracting more water from their environment. Water uptake characteristics of eight CIMMYT spring bread wheat cultivars-released during the period between 1950 and 2009-were measured in three contrasting irrigation regimes in northwestern Mexico during 2009/2010 and 2010/2011 and compared with crop growth. Increases in yield and biomass of genotypes were associated with additional water uptake in all environments whilst the water use efficiency for yield and biomass production was unchanged across cultivars but increased as a main effect of reduced water supply. Modern cultivars showed increased ability to extract moisture from deeper soil profiles (60-120 cm) especially during grain filling, associated with higher stomatal conductance in the fully irrigated environment and lower canopy temperatures in all environments. Expression of C isotope discrimination was progressively lower with increasing water stress. Results indicated increased water uptake by roots especially from deeper soil profiles allowing greater water harvest.