CARBON ISOTOPE DISCRIMINATION AND GRAIN-YIELD IN BARLEY

Grain yield and grain carbon isotope discrimination (DELTA) were measured in yield trials with barley over two seasons at three sites varying in expected seasonal rainfall in northern Syria, and in irrigated and droughted conditions at Cambridge, UK. Discrimination was least (water-use efficiency was greatest) at the lowest-rainfall sites, trial mean J ranging from 14.41 X 10(-3) at Breda, Syria, to 19.29 x 10(-3) in the irrigated trial at Cambridge. Variation in trial mean J was closely associated with trial mean grain-yield, which ranged from 135 to 374 g m-2. Phenotypic correlations between DELTA and grain-yield in individual trials were negative (r = -0.53) in the least droughted trials and strongly positive (r = 0.84) in the most droughted trials. In nine out of the ten trials, DELTA was negatively correlated with days to ear emergence. Correlations between J measured in the two seasons and DELTA-measured in different trials within a season were generally positive and significant. It was concluded that. for barley lines grown in water-limited Mediterranean environments, a large discrimination against carbon-13 may be a useful indication of good yield.