Why has breeding for water use efficiency not been successful? An analysis and alternate approach to exploit this trait for crop improvement.

摘要

Despite the importance of water use efficiency (WUE) in crop improvement, the available genetic variability in this trait has not been successfully exploited through breeding. Selection for high WUE often results in decrease in crop growth rates (CGR). Variations in WUE are brought about by stomatal diffusive characteristics (gs) and/or intrinsic photosynthetic capacity (gm). Most often plants have evolved to maximize WUE through a reduction in transpiration that is linked with the gs. Since dry matter production is strongly associated with total transpiration (T), any reduction in T results in reduced CGR. Since gs is associated both with T and internal CO2 partial pressure (Pi), WUE and T become strongly inter-dependent. However, if the variations in Pi and hence WUE are brought about by gm, the interdependency between T and WUE will be less and selection for WUE from such types will result in higher crop growth rates. A novel approach to estimate the time-averaged mesophyll efficiency is proposed, based on the carbon and oxygen isotope discrimination that occurs during photosynthesis and transpiration.