Abstract
Key messageCarbon isotope discrimination is a promising trait for indirect screening for improved water use efficiency of C4 crops.In the context of a changing climate, drought is one of the major factors limiting plant growth and yield. Hence, breeding efforts are directed toward improving water use efficiency (WUE) as a key factor in climate resilience and sustainability of crop production. As WUE is a complex trait and its evaluation is rather resource consuming, proxy traits, which are easier to screen and reliably reflect variation in WUE, are needed. In C3 crops, a trait established to be indicative for WUE is the carbon isotopic composition (δ13C) of plant material, which reflects the preferential assimilation of the lighter carbon isotope 12C over 13C during photosynthesis. In C4 crops, carbon fixation is more complex and δ13C thus depends on many more factors than in C3 crops. Recent physiological and genetic studies indicate a correlation between δ13C and WUE also in C4 crops, as well as a colocalization of quantitative trait loci for the two traits. Moreover, significant intraspecific variation as well as a medium to high heritability of δ13C has been shown in some of the main C4 crops, such as maize, sorghum and sugarcane, indicating its potential for indirect selection and breeding. Further research on physiological, genetic and environmental components influencing δ13C is needed to support its application in improving WUE and making C4 crops resilient to climate change.
Highlights
Improved water use efficiency to mitigate for the effect of changing climatic conditions Climate change comprises a variety of environmental changes, including increases in CO2 concentrations, temper‐ atures and unstable precipitation (Hatfield and Dold 2019)
Since this dependence is shared with water use efficiency (WUE), Δ13C is reflective of environmental conditions affecting CO2 assimilation, stomatal conductance and geno‐ typic differences in WUE
Using δ13C as an indirect trait to screen for WUE could facilitate the development of more water use efficient plants as one of the major challenges in breeding for climate resil‐ ience
Summary
Improved water use efficiency to mitigate for the effect of changing climatic conditions Climate change comprises a variety of environmental changes, including increases in CO2 concentrations, temper‐ atures and unstable precipitation (Hatfield and Dold 2019). These on-line measurements of Δ13C give a direct measure of the photo‐ synthetic discrimination, allow to follow short-term changes in response to changing environmental conditions and can be used to study different components of the C 4 pathway, including leakiness and mesophyll conductance (von Caem‐ merer et al 2014).
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