Carbon isotope discrimination and mineral composition of three organs in durum wheat genotypes grown under Mediterranean conditions

Carbon isotope discrimination (Delta) has been proposed as a good criterion for transpiration efficiency and grain yield improvement. Its measurement, however, remains very expensive. Ash content (m(a)) has been proposed as an alternative criterion for Delta in bread wheat and barley. The aims of this study were (i) to analyse the relationships between Delta and mineral composition in different durum wheat plant parts and (ii) to compare the variation of these traits between landraces and improved varieties from different geographic origins. For this purpose, Delta, m(a), and composition in four minerals (K, Mg, P and Si) were assessed in flag leaves and awns at anthesis, and in mature grains often durum wheat genotypes grown under rainfed Mediterranean conditions. The three plant parts differed significantly for the measured traits. Significant correlations were noted between Delta and m(a) in the flag leaf and in the grain. Silicon content in flag leaves and potassium content in awns were also positively related to Delta of the considered plant part. The coefficient of correlation between Delta and m(a) was generally higher than that observed between individual mineral content and Delta, suggesting that m(a) is the better alternative criterion for Delta. In addition, grain yield was related to grain Delta and both m(a) and potassium content in awns. Harvest index was correlated with Delta and m(a) of grain and flag leaf. These results emphasised that m(a) values in flag leaf and grain represent the efficiency of carbon partition i ng to the grain. Improved varieties showed higher Delta and m(a) values than landraces. Differences between Middle-East and West Mediterranean genotypes for the measured traits were also presented and discussed. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.