Genetic Variation in Water‐Use Efficiency and Its Relation to Photosynthesis and Productivity in Lentil Germplasm

Abstract

Lentil (Lens culinaris L.) is predominantly grown in semi‐arid regions, and improving water‐use efficiency (WUE, dry matter/transpiration) has been of longstanding interest. Our objective was to evaluate germplasm for WUE and determine how WUE was related to photosynthesis and yield. In greenhouse experiments, variation in carbon isotope discrimination (Δ), a potential estimator of WUE, was observed among 32 diverse lentil accessions. Direct determinations of the leaf net CO2 assimilation to stomatal conductance ratio (A/gCO2) and WUE showed that PI 477921 cv. Redchief, with low Δ, had higher A/gCO2 and WUE than PI 543920 cv. Crimson with high Δ. Negative correlations (n = 20) were found between A/gCO2 and Δ (r = −0.65**), WUE and Δ (r = −0.61**). Values of Δ were also correlated with root to shoot ratios (r = 0.89**), indicating that high WUE and increased dry matter partitioning to shoots were related. Nine germplasm accessions were grown in the field at Pullman, WA, in 1991 and at Central Ferry, WA, in 1992. Grain weight was positively correlated with total shoot weight (including grain) at Pullman (r = 0.94**, n = 9) and with harvest index (HI) at Central Ferry (r = 0.79**, n = 9). At Central Ferry, Δ and HI were positively correlated (r = 0.67**, n = 9), indicating an association between increased dry matter partitioning to grain and lower WUE. The results show that genetic variation for WUE is present in lentil germplasm and can be estimated by Δ; however, Δ was not correlated with grain weight at either location. Because shoot weight and HI were more closely associated with yield than Δ, these traits would apparently be more effective for improving lentil productivity than selection for WUE.