H. Miranzadeh - Department of Crop Production and Plant Breeding, College of Agriculture, Shiraz University, Islamic Republic of Iran.
Y. Emam - Department of Crop Production and Plant Breeding, College of Agriculture, Shiraz University, Islamic Republic of Iran.
P. Pilesjö - GIS Center, Department of Physical Geography and Ecosystem Analysis, Lund University, Sweden.
H. Seyyedi - GIS Center, Department of Physical Geography and Ecosystem Analysis, Lund University, Sweden.

It is suggested that cultivars of wheat (Triticum aestivum L.) with regulated growth and development would be able to produce higher yields under water-limited conditions, which is crucial in future food production. Water use efficiency (WUE) is worthy of exploration in this regard. In this study, the effects of nitrogen fertilizer levels (۰, ۴۰ and ۸۰ kg Nha-۱) and a plant growth retardant (Chlormequat Chloride = CCC) on WUE of four dryland wheat cultivars (Agosta, Nicknejad, Azar-۲ and Fin-۱۵) were examined in a field experiment during ۲۰۰۶-۰۷ and ۲۰۰۷-۰۸ growing seasons at College of Agriculture, Shiraz University, Iran. The results showed that there existed significant differences between cultivars for grain yield, biomass and WUE. In the first season, the highest grain yield and biomass production (۱۹۲.۴ and ۴۳۱.۲ gm-۲, respectively) were obtained from Nicknejad cultivar, CCC application and using ۸۰ kg Nha-۱, and in the second season, from Azar-۲ cultivar (۱۲۱.۵ and ۳۳۳.۵ gm-۲, respectively). CCC and nitrogen had significant effects on photosynthesis rate and WUE in both seasons. Interaction of CCC and ۸۰ kg Nha-۱ on WUE were significant in both seasons (۱.۲۴ and ۲.۷۲ gm-۲mm-۱, respectively). It is suggested that interactive application of CCC and nitrogen fertilizer could have beneficial effects on wheat grain yield under similar agro-climatic conditions.

Grain yield, WUE, Drought Stress, Chlormaquat chloride, Photosynthesis Rate (An), Stomatal Conductance (gs)