Journal of Food, Agriculture & Environment, Vol.8 (3&4), July-October 2010 857 www.world-food.net Journal of Food, Agriculture & Environment Vol.8 (3&4): 857-860. 2010 WFL Publisher Science and Technology Meri-Rastilantie 3 B, FI-00980 Helsinki, Finland e-mail: info@world-food.net Received 21 July 2010, accepted 30 October 2010. Effects of drought stress and nitrogen nutrition on seed yield and proline content in bread and durum wheat genotypes Farshad Sorkhi Lalelou *, Mohammad Reza Shakiba, Adel Dabbagh Mohammadi-Nassab and Seied Abolghasem Mohammadi 1 Department of Agronomy and Plant Breeding, Faculty of Agriculture, University of Tabriz, Tabriz, 51666, Iran. *e-mail: farsorkhy@yahoo.com Abstract This field study was conducted to evaluate the effect of drought stress after anthesis on proline content and seed yield of four wheat genotypes during 2009-2010 in Research Farm of Faculty of Agriculture, University of Tabriz, Iran, as a factorial split plot experiment based on randomized complete block design with three replications. Water stress levels were irrigation in 20, 40 and 60% field capacity depletions and used from flag leaf initiation. Nitrogen levels were 20, 40, 60 and 80 kg ha -1 . Studied genotypes were Alvand and Shahriar bread wheat and PGS 01-60-335 and IDW 01-61-130 durum wheat. The results showed that maximum amount of seed yield and proline content was obtained from 80 kg ha -1 nitrogen fertilizer application treatment. Result of combined analysis showed that the effect of year was significant on seed yield but it had no significant effect on proline content. Under severe water stress (60% field capacity depletion) conditions and 80 kg ha -1 nitrogen, seed yield of Alvand, Shahryar, Durum PGS 01-60-335 and Durum IDW 01-61-130 showed 72%, 75%, 54% and 44% decrease in the first year and 72%, 71%, 55% and 45% decline during the second year compared to normal conditions (20% field capacity depletion). Meanwhile, proline content of flag leaf in Alvand, Shahriar, Durum PGS 01-60-335 and Durum 01-61-130 were increased by 16.17, 15,76, 19.43 and 20.39 fold, respectively. Data showed that under 80 kg ha -1 nitrogen and lack of water stress (20% field capacity depletion), the maximum and minimum yield were recorded in Alvand and Durum IDW 01-61-130 during two years. In contrast, under severe water stress (60% field capacity depletion) conditions, maximum and minimum yield were recorded in Durum IDW 01-61- 130 and Shahriar. Under severe water stress conditions, the major decrease in seed yield and the minimum increase in proline content were documented in Alvand and Shahriar. However, the lowest decrease in seed yield, and the highlighted increase in proline content were measured in Durum PGS 01- 60-335 and IDW 01-61-130 genotypes. In total, water deficit stress had adverse effects on yield of wheat genotypes and nitrogen fertilization had negligible potential to compensate the deteriorative effects of drought condition. Key words: Nitrogen, proline, seed yield, water stress, wheat. Introduction Biotic and abiotic stresses are of main problems of agricultural systems 1 . Water stress is one of the most important abiotic stresses which adversely affects crop production in many regions of the world 2 . In most cereal crops grown in water deficiency conditions, drought stress affects approximately one-third of the yield potential of plants 3 . The main reason for a cross-over under conditions of variable water supply is an inherent difference among the tested cultivars in drought resistance, beyond difference in their yield potential 4 . This was also observed in international wheat variety trials where stress environments often were represented by mean yield of 4-5 t/ha as compared with a maximum yield of 8 t/ha in common wheat production areas 2, 3 . Osmotic adjustment is common physiological response of plants to most stress conditions where it is regulated by the accumulation of free amino acids, proline and sugars in the roots and shoots of stress-affected plants. Proline accumulation is a widespread plant response to environmental stresses such as low water availability. Proline has a unique role as an osmoticum under abiotic mainly water deficit conditions. In particular, because of its zwitterionic status and high hydrophilic characteristics, proline acts as a “compatible solute”, i.e. one that can accumulate to high concentrations in the cell cytoplasm without interfering with cellular structure and/or metabolism 5, 6 . There is presently no clear agreement about the function of drought-induced proline accumulation. Although, a role in osmo-regulation seems likely 6 . Other functions of proline accumulation have also been proposed, including stabilization of macromolecules, a sink of carbon and nitrogen for use after relief of water deficit conditions 6, 7 , radical detoxification and regulation of cellular redox status 8 . Nitrogen fertilization is one of the most important and effective implements in agriculture, stimulating a lot of vital processes in plants. The amount of applied nitrogen in plants must be carefully managed to ensure that N will be available throughout the growing season and the vegetative and reproductive development will not be restricted 9 . Nitrogen uptake and utilization by plants and wheat are determined by genotypic differences and are linked to a variety of morphological and physiological factors, including the length and activity of the root system, the intensity of nitrate uptake, activity of nitrate reductase, sink of grains, carbohydrate production and N losses due to soil characteristics and leaching 10 . Photosynthetic capacity of leaves in most crops is closely related to their nitrogen content, and chlorophyll quantity is a very stable parameter for soil nitrogen uptake estimation 4, 11 . Carbohydrate metabolism is also determined by the availability of nitrogen as the major limiting factor 10, 12 . At the present time, there is no general accepted physiological model for selecting the optimal fertilization regime in field crops. The objective of the