Genotypic variability in physiological characters and its relationship to drought tolerance in durum wheat

Yield and eight other related physiological characters [photosynthetic CO 2 exchange rate (CER), stomatal resistance (r s ), internal CO 2 concentration, water-use efficiency (WUE), chlorophyll a + b content (Chl), specific leaf weight (SLW), leaf area and shoot dry weight] were examined in 20 durum wheat (Triticum turgidum L. var. durum) genotypes grown under nonirrigated and irrigated field conditions in 1986 and 1987. Considerable genetic differences were evident for all characters under both nonirrigated and irrigated field conditions. Significant correlations between the genotype means of the 2 years and no significant genotype × irrigation interaction indicated that the genotypic rankings were generally consistent over different environments. Reduced water availability under nonirrigated conditions decreased yield, CER, shoot dry weight, leaf area, and internal CO 2 concentration and increased r s . Genotypes were separated into drought-tolerant or susceptible types based on yield potential and leaf water loss. The drought-tolerant genotypes had higher WUE, Chl, yield, leaf area and shoot dry weight and lower internal CO 2 concentration than the drought-susceptible genotypes. The group differences for the characters were significant only under nonirrigated field conditions.Key words: Physiological characters, drought tolerance, wheat (durum) Triticum turgidum L. var. durum