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 (Triticum aestivum 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 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 designated 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 carbon isotope discrimination, indicating higher WUE, the average difference in carbon isotope discriminiation between ABA classes was not significant in either the irrigated or drought-stressed regimes. However, slopes of regressions of grain yield on carbon isotope discrimination, 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.