SELECTING SUGARCANE VARIETIES WITH HIGHER TRANSPIRATION EFFICIENCY

ACHIEVING HIGH water use efficiency is important in both rainfed and irrigated crops. Developing sugarcane varieties with high transpiration efficiency (TE) is one approach to help achieve this goal. However, sugarcane breeding programs currently do not explicitly target improved water use efficiency. A question arises as to whether faster progress toward yield or profitability in water-limited environments could be made by targeting this trait. This paper considers this question. A brief review of past work relating to transpiration use efficiency indicates complications in selecting directly for TE, particularly an expected negative genetic correlation between TE and rate of water use, which could reduce or reverse otherwise expected genetic gains for yield. Recent results from a pot experiment with sugarcane indicate a high level of genetic variation among 20 sugarcane genotypes for TE. Contrasting relationships between TE and yield and water use were observed in plants grown under water stress versus well watered plants. Possible mechanisms for this variation are considered, as are steps towards practical application in sugarcane breeding programs. It is suggested that selection for higher TE should target two different components: firstly stomatal conductance response to external factors, and secondly level of assimilation/photosynthesis at any given level of stomatal conductance.