Effect of different physiological traits on grain yield in barley grown under irrigated and terminal water deficit conditions.

Drought is the main factor limiting the productivity of crops in Mediterranean areas. The introduction of physiological traits into crops that improve their tolerance to drought is necessary if yields under these conditions are to be efficiently improved. The effect of drought on different gas exchange variables, i.e. net photosynthesis (A), stomatal conductance (g s ) and leaf chlorophyll concentration (Chl), and the relationship of these variables with yield were studied in 12 barley genotypes grown under irrigated and terminal drought conditions. The variable most sensitive to water deficit was g s (mean reduction 43% with respect to control conditions), followed by A (mean reduction 34%). The mean reduction of yield by terminal drought was 27%. A significant correlation was seen between these physiological traits and yield. The effect of water deficit on A, g s and Chl was smaller in the breeding lines than in the traditional varieties assayed, in agreement with the results found for yield. These results suggest a potential indirect selection of physiological characteristics in these breeding lines that allow greater tolerance to drought. The response of the different genotypes examined was not homogeneous across all the variables analysed. This variability is important in programmes aiming to obtain drought-tolerant genotypes via the optimization of traits such as those above.