Carbon Isotope Discrimination is not Correlated with Transpiration Efficiency in Three Cool‐Season Grain Legumes (Pulses)

Abstract The carbon isotope discrimination (δ 13 C) of leaves has been shown to be correlated with the transpiration efficiency of leaves in a wide range of species. This has led to δ 13 C being used in breeding programs to select for improved transpiration efficiency. The correlation between δ 13 C and transpiration efficiency was determined under well‐watered conditions during the vegetative phase in six genotypes of lentil ( Lens culinaris Medikus), six genotypes of chickpea ( Cicer arietinum L.) and 10 cultivars of narrow‐leafed lupin ( Lupinus angustifolius L.). Biomass (dry matter) accumulation and water use (transpiration) varied among the genotypes in all three species and transpiration efficiency was 40% to 75% higher in the most efficient compared with the least efficient genotypes. However, δ 13 C and transpiration efficiency were not significantly correlated in any of the species. This suggests that the δ 13 C technique cannot be used in selection for transpiration efficiency in the three grain legumes (pulses) studied.