Carbon Isotope Discrimination, Gas Exchange, and Yield of Spring Wheat Selected for Abscisic Acid Content

Because of its role in controlling stomatal closure, abscisic acid (ABA) may be a useful selection criterion for improving drought resistance of wheat (L.). Spring wheat lines previously selected for low and high dehydration-induced ABA accumulation in laboratory tests were studied in the field to determine if ABA accumulation potential is related to leaf water-use efficiency (WUE), carbon isotope discrimination (Δ), and grain yield. Plants were grown in irrigated or drought-stressed regimes under a rain shelter in 1987 and 1988. In the field, there was a trend for class differences in bulk-leaf ABA content to be the reverse of those obtained in the laboratory drought test. The class originally disignated low-ABA (had in general a slightly higher ABA content in the field) and tended to have lower stomatal conductance (g), higher WUE, and a much greater biomass than the original high-ABA class. The original labels were retained, for consistency in reporting. The ABA classes differed significantly in yield components and harvest index. In one experiment with only two low- and two high-ABA selections, grain yields did not differ overall, but in another experiment with 20 low- and 20 high-ABA selections, grain yield of the low-ABA class was significantly higher. Biomass decreased more under drought in the low-ABA class than the high. Although drought resulted in lower ∆, indicating higher WUE, the average difference in ∆ between ABA classes was not significant in either the irrigated or drough-stressed regimes. However, slopes of regressions of grain yield on ∆, which were positive, differed significantly (nearly two-fold) between high- and low-ABA classes, with low-ABA selections having a steeper regression slope under drought conditions. The possible role of ABA in determining the results in discussed.