Sugarcane for water-limited environments: Theoretical assessment of suitable traits

In Australia water stress is estimated to cost the sugar industry an average of $260 million (AUD) per annum in lost production. With the predicted increased frequency of drought events the industry is now considering breeding for drought adaptation after water stress inflicted yield losses of more than $400 million in the years 2002-2004, in one region alone. Defining drought adaptation broadly, including both short and long periods of water stress, we took the first step in improving sugarcane for such conditions by assessing the potential benefits of a number of traits in a simulation study. The APSIM-Sugarcane model was used to simulate the biomass yield response to traits that may confer adaptation to drought in a range of climates, some extremely dry at times, and in a shallow and a deep soil. Among the traits studied, increased rooting depth resulted in 0-21% increase in mean dry biomass yield depending on the climate and soil type. This trait was more beneficial in the shallow than the deep soil which had a smaller fraction of additional stored water to offer the more vigorous root system. The simulations showed that breeding for reduced stomatal or root conductance (conductance) would increase biomass yield by about 5% only in the driest climates and better soils. Other traits which conserved water such as leaf and stalk senescence were generally unsuccessful in conferring adaptation to the water-limited production environments considered. Simulations indicated that increased transpiration efficiency (TE) at the leaf level would nearly always help to improve sugarcane biomass yields in water-limited environments if the increased TE arose from up-regulation of intrinsic water use efficiency. However if increased TE was increased through reduced conductance, which effectively reduces VPD during transpiration, yields could be reduced in high rainfall climates and shallow soils and they could increase in moderate rainfall climates and deeper soils. Thus increased rooting depth, increased intrinsic water use efficiency and to a lesser extent, reduced conductance leading to increased TE, are suggested as the best traits to consider for selection of sugarcane clones in water-limited environments in the tropics and sub-tropics. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.