Effect of Drought Stress on Water Use Efficiency and Root Dry Weight of Wheat (Triticum aesativum L.) and Rye (Secale cereale L.) in Competition Conditions

Introduction Deficiency of water during the plant growth is one of the main factors which reduce the crops production around the world. Drought stress is one of the most important tensions that may occur around the low rainfall, high temperature and wind blowing environments. Plant response to this stress depends on the stage of plant growth and drought intensity. Weeds are unwanted and harmful plants with disturbance in agricultural practices which make increase the cost of crop production and reduce the crop yields. Rye (Secale cereal L.) is one of the most important weeds at wheat fields in Iran (Baghestani and Atri, 2003). Low expectations, allelopathic effects and similarity of life cycle and morphology, caused increasing of rye density in winter wheat fields. Water use efficiency (WUE) as an important physiological characteristic indicates the ability of plants to water stress. WUE may be affected by climatic and soil or plant factors. In plant communities, competition is one of most important physiological topics (Evans et al, 2003). At Inter-specific competition, weeds interfere to absorbing of light, water and nutrients through the adjacency with crop and so affect the growth and yield of crops. Weeds often compete with crops for soil water and reduce the accessibility of water. Competition between weeds and crops decrease the soil moisture and cause water stress which might decrease the weeds and crops growth. When the supply of water is limited, water drainage overlap areas in soil profile could be occurred relatively fast at early of in the crop life cycle. Materials and Methods In order to study the effects of drought stress on water use efficiency and root dry weight of wheat (Triticum aesativum L.) and rye (Secale cereale L.) in competition conditions, a pot experiment was conducted in the greenhouse of Agriculture Faculty , University of Birjand in 2012. The experiment was arranged as factorial based on completely randomized design with three replications. The treatments were included four wheat density (0, 8, 16 and 24 plants per pot), four rye density (0, 2, 4 and 6 plants per pot) and two levels of drought stress (irrigation after depletion of 20 and 60 % of field capacity moisture). Results and Discussion The results showed that all interaction effects were significant (P < 0.01) on water use efficiency of wheat, but only the interaction effect between inter-species competition and drought stress was significant (P < 0.01) on water use efficiency of rye. Interaction effect between drought stress, wheat and rye density was significant (P < 0.01) on root dry weight of wheat. The results revealed that water use efficiency decreased 17 % in wheat and increased 34 % in rye by increasing of drought stress. The water use efficiency of wheat and rye increased 10.4 and 28.2 % under intra-species competition and decreased 57.4 and 81 % under inter-species competition, respectively. Drought stress did not affect root dry weight of wheat, but with increasing of rye and wheat density, root dry weight decreased 64.3 and 48.9 %, respectively. Also root dry weight of rye decreased 37.1, 47.4 and 33.6 % under drought stress conditions, inter and intra-species competition, respectively. Intra-specific competition decreased biological yield and water use efficiency through decreasing growth characters, yield and components yield of wheat. Increasing stress intensity reduced leaf photosynthesis and increased sugar requirements for cell osmotic adjustment, so availability of assimilates reduced and root growth stopped. In the other words, root dry mater of plants reduced in drought stress conditions. Conclusions The results of this study indicated that drought stress reduced root dry mater of rye and water use efficiency of wheat and rye. Increasing inter-specific competition between wheat and rye reduced water use efficiency and root dry matter in two plants, but increasing intra-specific competition increased the studied traits. Generally, because of the overlap area of root development in wheat and rye, and more extensive root system of rye than the wheat, rye has higher competitive strength for water uptake.