EFFECT OF LEAF STRUCTURE AND WATER STATUS ON CARBON-ISOTOPE DISCRIMINATION IN FIELD-GROWN DURUM-WHEAT

The relationships between leaf and kernel carbon isotope discriminatio ns (Delta) and several leaf structural parameters that are indicators of photosynthetic capacity were studied in durum wheat grown in the fi eld under three water regimens, A set of 144 genotypes were cultivated in two rain-fed trials, and 125 of these were grown under supplementa ry irrigation before heading. Total chlorophyll and nitrogen (N) conte nts, the dry mass per unit leaf area (LDM, the reciprocal of specific leaf area) and carbon isotope discrimination (Delta) were measured in penultimate leaves and Delta of mature kernels was also analysed, Both LDM and N per unit area showed significant (P less than or equal to 0 .001) negative correlation (r = -0.60 and r = -0.36, respectively) wit h leaf Delta in the wettest trial, Little or no correlation was found for any structural parameter and leaf Delta in the rain-fed trials, In contrast, in the two rain-fed trials LDM was the parameter with the s trongest positive correlation (P less than or equal to 0.001) with ker nel Delta (r = 0.47 and 0.30) and grain yield (r = 0.43 and 0.29), whe reas no correlation was found in the irrigation trial, These correlati ons, rather than representing a causal link between the amount of phot osynthetic tissue and Delta, were probably indirect associations cause d by a parallel effect or water status and phenology on leaf structure , grain Delta and yield, Correlations across trials (i.e. environments ) between leaf structure and either Delta and yield were very high, al though also spurious, Our results suggest that LDM should be used to c ull segregating population differences in leaf ii based on the interna l photosynthetic capacity only ire the absence of drought, Selecting f or kernel Delta and grain yield on the basis of LDM is worthwhile for rain-fed trials.