Grain yield, carbon isotope discrimination and mineral content in mature kernels of barley under irrigated and rainfed conditions

The relationship between yield, carbon isotope discrimination and ash content in mature kernels was examined for a set of 13 barley (Hordeum vulgare) cultivars. Plants were grown under rainfed and well-irrigated conditions in a Mediterranean area. Water deficit caused a decrease in both grain yield and carbon isotope discrimination (Δ). The yield was positively related to Δ and negatively related to ash content, across genotypes within each treatment. However, whereas the correlation between yield and Δ was higher for the set of genotypes under well-irrigated (r=0.70, P<0.01) than under rainfed (r=0.42) conditions, the opposite occurred when yield and ash content were related, ie r=-0.38 under well-irrigated and r=-0.73, (P<0.01) under rainfed conditions. Carbon isotope discrimination and ash content together account for almost 60% of the variation in yield, in both conditions. There was no significant relationship (r=-0.15) between carbon isotope discrimination and ash content in well-irrigated plants, whereas in rainfed plants, this relationship, although significant (r=-0.54, P< 0.05), was weakly negative. The concentration of several mineral elements was measured in the same kernels. The mineral that correlated best with ash content, yield and A, was K. For yield and Δ, although the relationship with K followed the same pattern as the relationhip with ash content, the correlation coefficients were lower. Thus, mineral accumulation in mature kernels seems to be independent of transpiration efficiency. In fact, filling of grains takes place through the phloem pathway. The ash content in kernels is proposed as a complementary criterion, in addition to kernel Δ, to assess genotype differences in barley grain yield under rainfed conditions.Rendement en grain, discrimination isotopique du carbone et teneur en minéraux dans les grains mûrs d'orge en conditions irriguée et non irriguée. La relation entre la production, la discrimination isotopique et le contenu en cendres dans les grains mûrs a été examinée dans 13 cultivars d'orge (Hordeum vulgare L). Les plantes ont été cultivées dans 2 conditions : l'une en déficit hydrique et l'autre en régime d'irrigation, en zone méditerranéenne. Le déficit hydrique a causé une diminution de la production et de la discrimination isotopique du carbone (Δ). La production a été positivement corrélée avec Δ et négativement avec le contenu en cendres, entre les génotypes de chaque traitement. Cependant, tandis que la corrélation entre la production et Δ a été plus haute dans l'ensemble des génotypes sous conditions d'irrigation (r=0,70 ; P <0,01) que chez les non irrigués (r=0,42), le contraire se produit quand la production et le contenu en cendres sont mis en rapport ( r=-0,38 sous conditions d'irrigation et r=-0,73, (P < 0,01) sous conditions de sécheresse). La discrimination isotopique du carbone et le contenu en cendres expliquent ensemble environ 60% de la variation dans la production dans les 2 conditions. Il n'y a pas eu de relation significative (r=-0,15) entre la discrimination isotopique du carbone et le contenu en cendres dans les plantes irriguées, tandis que dans les non irriguées, cette relation, bien qu'elle ait été significative (r=-0,54; P