Effect of drought on leaf gas exchange, carbon isotope discrimination, transpiration efficiency and productivity in field grown durum wheat genotypes

Under drought prone conditions, wheat productivity is strongly related to photosynthetic activity and transpiration efficiency. In the present study, photosynthesis related traits were assessed at anthesis under rainfed and irrigated conditions on five durum wheat (Triticum durum Desf.) cultivars grown under Mediterranean conditions. Carbon isotope discrimination was also evaluated in flag leaf at anthesis (ΔLa) and grain at maturity (ΔGm). Under rainfed conditions, highly significant correlations were found between both ΔLa and ΔGm, and leaf CO2 exchange rate (CER), stomatal conductance (gs) and internal to ambient CO2 concentration ratio (Ci/Ca). ΔGm was correlated negatively with transpiration efficiency (measured as CER/gs) under rainfed conditions, and positively under irrigated conditions. Under both conditions, ΔGm was positively associated with grain yield. No significant correlation was observed between mesophyll conductance and CER. In contrast, the latter trait was positively related to gs under irrigated conditions suggesting that CER was driven by stomatal limitations. No correlation was found between ΔLa and grain yield. It is concluded that breeding for high ΔGm would lead, under Mediterranean drought conditions, to higher stomatal conductance, lower transpiration efficiency and higher grain yield.