Using Carbon Isotope Discrimination to Assess Genotypic Differences in Drought Resistance of Parental Lines of Common Bean
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Accurate assessment of crop water uptake (WU) and water use efficiency (WUE) is not easy under field conditions. Carbon isotope discrimination (Delta C-13) has been used as a surrogate of WUE to examine crop yield responses to drought and its relationship with WU and WUE. A 2-yr study was conducted (i) to characterize genotypic variation in Delta C-13, grain yield, and other physiological parameters in common bean (Phaseolus vulgaris L.) parental lines, and (ii) to examine the relationships between grain Delta C-13, shoot Delta C-13, and grain yield under well-watered and terminal drought stress conditions. All measured plant traits were strongly influenced by water availability, and genotypic differences in grain yield, shoot Delta C-13, and grain Delta C-13 were found in both watered and terminal drought stress environments. The parental lines were classified into two drought adaptation groups, drought resistant and drought sensitive, based on a yield drought index. High yields under drought conditions were related to (i) greater water uptake, as indicated by high Delta C-13 in genotypes previously shown to have deeper roots (e.g., SEA 5 and BAT 477), and (ii) increased WUE, denoted by lower Delta C-13 and greater pod harvest index (PHI) (e.g., SER 16). Coupling of Delta C-13 measurements with measured yield and yield components analyses, such as PHI, provided an avenue to distinguish different physiological traits among drought resistant genotypes underlying adaptation to water deficit stress.
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