Breeding to enhance crop productivity in scarce water conditions

To enhance crop yield per unit of scarce water requires both improved cultivars and better management. The challenge is to manage the crop or progress its genetic makeup to: capture more of the water supply for use in transpiration; exchange transpired water for CO₂ more effectively in producing biomass; and convert more of the biomass into grain harvest. The upper limit of water productivity of well-managed disease-free water-limited cereal crops is typically 20 kg ha⁻¹ mm⁻¹. When water is the predominant limitation, there is a little scope for improving overall water productivity by better matching the crop development to the pattern of water supply, thereby reducing evaporative and other losses and fostering a good balance of water-use before and after flowering, which is needed to give a high harvest index. Marker-assisted selection can help in controlling some root diseases that limit water uptake, and in maintaining fertility in water-stress. Apart from herbicide-resistance in crops, there are no genetic transformations in the immediate offing that are likely to improve water productivity greatly.