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Genetic variability of leaf net photosynthesis rate (An) and its relation to productivity in durum wheat (Triticum turgidum L. var. durum) is not well defined. Two field experiments were conducted at the experimental area of the Faculty of Agriculture, in the University of Çukurova, Turkey, to evaluate the differences between old and modern cultivars in An and productivity. Experiments with sowing dates in November 1996 and February 1997 were performed under rainfed and irrigated conditions, respectively. Measurements included leaf gas exchange and agronomic traits. Old cultivars (OC) were later flowering and taller than modern cultivars (MC) and their harvest indexes were lower. Before the onset of leaf senescence, most of the OC exhibited higher An values than most of the MC, but the extent of variability was not great. High An was correlated with high stomatal conductance (gs), but no overall correlation between An and the ratio of internal [CO2] to [CO2] in the air was observed. In spite of higher An, OC showed no superiority in grain yield. The results indicate that mesophyll conductance rather than gs has an effect on variation in An, and that preanthesis dry matter distribution and total flag leaf photosynthesis and its duration appear to be more relevant than An for grain yield, especially under drought.

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Turkey is one of the most important durum wheat (T. turgidum L. var. durum Desf.) producers in West Asia and North Africa (WANA). There appears to have been a lack of progress in wheat yields in WANA over recent decades. Most of the modern cultivars grown in WANA are related to crosses produced by the International Maize and Wheat Improvement Center (CIMMYT). During 1999 and 2000, a chronological set of 11 cultivars related to CIMMYT crosses was evaluated using two irrigation regimes near Şanlıurfa, Turkey.Average yields ranged from 386 g/m2 (local cultivar, Karakılçık-33) to 614 g/m2 (Ege-88). When wheat cultivars were grown with irrigation until physiological maturity, cessation of irrigation near anthesis reduced average grain yields of all cultivars by 6·2–25·7%. Since the introduction of the first generation of CIMMYT cultivars in 1975, CIMMYT grain yields have increased by about 0·60% per year compared with that of Karakılçık-33. This rate increased up to 1·08% per year until 1988. No further progress in yield was measured for varieties released in the 1990s. The average rate was 0·76% per year. After the introduction of the CIMMYT cultivars, yield changes fitted better in a quadratic function. Compared with Karakılçık-33, the yield increases of CIMMYT cultivars have resulted from an increase in harvest index associated with reduced height and the development of more and heavier grains. Grain quality traits decreased with the introduction of the first CIMMYT cultivar but recovered slightly thereafter with no clear trend. The results are discussed with consideration of breeding priorities and specific WANA conditions.

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