Relationship between Carbon Isotope Discrimination (Δ13C) and Water Use Efficiency of Durum Wheat in the Syrian Arab Republic. 1. Field Evaluation

Field experiments were conducted over three seasons (2004-2005, 2005-2006 and 2006-2007) using six durum wheat genotypes, similar in phenology, to minimize the genotype x environment (G*E) interaction, but varying in grain carbon isotope discrimination (CID, Δ13C or Δ). The four field sites at Tel Hadya, Breda, Muslmieh and Yahmoul were fully characterized according to environment and soil classification. Plant growth and development were monitored throughout the growing season. Δ was measured for every plot using grain or the 4th fully-expanded leaf. Also, ash and protein contents of grain were analyzed. Radiation use efficiency was measured at Tel Hadya only. Stomatal conductance and resistant as well as canopy temperature was also measured for the different sites and years. Soil water content throughout the growing season was measured at some sites to calculate water use. Variability between sites was mostly related to rainfall, with variability within a site being related to season. Δ was lower at the drier sites and higher at the wettest site, ranging from 12.88 to 16.62 per mille for grain, and 19.97 to 22.57 per mille for the 4th fully-expanded leaf. Positive correlations were found between grain Δ and yields of grain and biomass. The stronger correlations were at the drier sites, whilst at the wettest site (Yahmoul) there was no significant relationship. Δ was also related to ash and protein content. The genotypic variation in Δ (grain and leaf) was substantially independent of season or site. (author)