A. G. Condon1,, R. A. Richards1, G. J. Rebetzke1 and G. D. Farquhar2
1CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia
2Research School of Biological Sciences, Australian National University, Canberra, ACT 2601, Australia
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There is a pressing need to improve the water-use efficiencyof rain-fed and irrigated crop production. Breeding crop varietieswith higher water-use efficiency is seen as providing part ofthe solution. Three key processes can be exploited in breedingfor high water-use efficiency: (i) moving more of the availablewater through the crop rather than it being wasted as evaporationfrom the soil surface or drainage beyond the root zone or beingleft behind in the root zone at harvest; (ii) acquiring morecarbon (biomass) in exchange for the water transpired by thecrop, i.e. improving crop transpiration efficiency; (iii) partitioningmore of the achieved biomass into the harvested product. Therelative importance of any one of these processes will varydepending on how water availability varies during the crop cycle.However, these three processes are not independent. Targetingspecific traits to improve one process may have detrimentaleffects on the other two, but there may also be positive interactions.Progress in breeding for improved water-use efficiency of rain-fedwheat is reviewed to illustrate the nature of some of theseinteractions and to highlight opportunities that may be exploitedin other crops as well as potential pitfalls. For C3 species,measuring carbon isotope discrimination provides a powerfulmeans of improving water-use efficiency of leaf gas exchange,but experience has shown that improvements in leaf-level water-useefficiency may not always translate into higher crop water-useefficiency or yield. In fact, the reverse has frequently beenobserved. Reasons for this are explored in some detail. Cropsimulation modelling can be used to assess the likely impacton water-use efficiency and yield of changing the expressionof traits of interest. Results of such simulations indicatethat greater progress may be achieved by pyramiding traits sothat potential negative effects of individual traits are neutralized.DNA-based selection techniques may assist in such a strategy.
Key words: Carbon isotope discrimination, drought resistance, transpiration efficiency, wheat
Source: Journal of Experimental Botany 2004 55(407):2447-2460