Journal of Plant Physiology and Breeding 2018, 8(1): 37-48 ISSN: 2008-5168 Assessment of remobilization variation of bread wheat cultivars under different irrigation and nitrogen fertilizer treatments Parisa Ghahramani 1 , Soleiman Mohammadi 2* and Hashem Hadi 1 Received: February 20 2017 Accepted: May 28 2017 1 Department of Agronomy, Faculty of Agriculture, Urmia University, Urmia, Iran 2 Seed and Plant Improvement Research Department, West Azarbaijan Agricultural and Natural Resources Research Center, AREEO, Urmia, Iran *Corresponding author; Email: soleyman_45@yahoo.com Abstract In order to investigate the effect of water treatment and nitrogen fertilizer application on remobilization and grain yield of bread wheat cultivars, an experiment was carried out as split-split plot design based on randomized complete blocks with three replications. Three levels of irrigation (full irrigation, withholding irrigation at heading, withholding irrigation at anthesis) were assigned to main plots, different times of nitrogen fertilizer application (application of 120 kg/ha nitrogen in four different times: 20 kg at sowing + 100 kg/ha at tillering, 20 kg at sowing + 100 kg/ha at bolting, 20 kg at sowing + 50 kg at tillering + 50 kg at bolting, 20 kg at sowing + 50 kg at tillering + 50 kg at heading) were randomized in sub-plots and five bread wheat cultivars (Zarrin, Pishgam, Urum, Zare, Mihan) were assigned to sub- sub-plots. Withholding irrigation at different developmental stages of wheat increased remobilization percentage of all cultivars. However, application of nitrogen at the heading stage reduced remobilization. The highest and lowest remobilization were recorded for Urum and Zarrin with 62.13% and 20.33%, respectively. Grain yield was significantly reduced with the reduction of water availability. Mean grain yield of all cultivars was 7.500 ton/ha under full irrigation, which reduced to 6.500 ton/ha when irrigation was withheld. Nitrogen fertilizer application improved the grain yield of wheat cultivars. The highest grain yield was obtained for Mihan by 9.39 ton/ha under full irrigation and nitrogen application at sowing + tillering + heading. The higher grain yield of tolerant cultivars under water deficit treatments was attributed to remobilization of unstructured carbohydrates from shoot to grain. It seems that selection of cultivars with higher translocation of dry matter and contribution of pre-anthesis assimilates in grain filling under water stress, can be a suitable strategy to produce high yielding cultivars under water deficit stress condition. Keywords: Fertilizer; Grain yield; Remobilization; Water treatment; Wheat Citation: Ghahramani P, Mohammadi S and Hadi H, 2018. Assessment of remobilization variation of bread wheat cultivars under different irrigation and nitrogen fertilizer treatments. Journal of Plant Physiology and Breeding 8(1): 37- 48. Introduction Water deficit is the most important limiting factor for crop production (Boyer 1982). A common effect of water deficit stress on crop plants is the reduction of dry biomass production. Plant productivity under water deficit stress is highly related to the processes of dry matter partitioning and temporal root distribution (Kage et al. 2004). The sensitivity of crop plants such as wheat (Triticum aestivum L.) to soil drought is particularly critical during the grain-filling period because the reproductive phase is extremely sensitive to plant water status (Saini and Westgate 1999). Carbon requirements for grain growth in wheat are mainly provided from current assimilation by photosynthesis and remobilization of reserves from the stems (Yang et al. 2000). One of the best approaches to achieve an acceptable wheat grain yield under drought conditions is to use the potential of carbohydrate remobilization to the growing grains. When the photosynthesis decreases after anthesis, assimilates produced prior the flowering, become