Yield and water use efficiency of low and high abscisic acid wheat lines under water stress

Scope of study. Based on its role in stomatal closure under water stress, the plant hormone, abscisic acid (ABA), might improve photosynthetic water use efficiency (WUE) and drought resistance. Stable carbon isotope discrimination ({dollar}triangle{dollar}) is an indirect method of selecting for WUE in C{dollar}sb3{dollar} plants. Spring wheat lines selected divergently for ABA accumulation potential were grown in well-watered and drought-stressed regimes under a rain shelter. Leaf water relations, bulk-leaf ABA content and WUE were measured on 2 low and 2 high ABA selections in 1987 and 1988. Biomass, grain yield and {dollar}triangle{dollar} were determined at maturity. Biomass, grain yield and {dollar}triangle{dollar} were determined in 20 low and 20 high ABA selections in 1988. Laboratory experiments were conducted to compare steady-state photosynthesis and water relations in leaves of three low and three high ABA selections under water stress.; Findings and conclusions. Among four ABA selections, WUE tended to be higher in the low-ABA class than the high-ABA class, in association with lower stomatal conductance. Averaged over 1987 and 1988, biomass was higher in the low-ABA class. Among 40 ABA selections, grain yield and biomass were higher in the low-ABA class, while harvest index was higher in the high-ABA class. Although ABA classes did not differ in {dollar}triangle{dollar} under watered or stressed regimes variation among ABA selections for {dollar}triangle{dollar} was significant. Positive correlations between grain yield and {dollar}triangle{dollar} were measured. Regression equations predicted low-ABA selections have a twofold higher grain yield per unit increase in {dollar}triangle{dollar} than high-ABA selections under drought. In the laboratory, mesophyll capacity for photosynthesis was significantly higher in the low-ABA class. Stomatal conductance decreased slightly more in the high-ABA class, but the magnitude of the reduction in CO{dollar}sb2{dollar} assimilation was similar for both ABA classes under water stress. WUE was higher in the low-ABA class under well-watered conditions, but ABA classes did not differ in WUE under water stress. In conclusion, gas exchange measurements showed higher WUE in low-ABA selections than high-ABA selections, but measurements of {dollar}triangle{dollar} did not reflect this difference. Low-ABA selections were more productive than high-ABA selections under well-watered or water-stressed conditions.