Effect of inter and intra-specific competition on morphological and growth characteristics of wheat (Triticum aestivum L.) and rye (Secale cereale L.) under drought stress conditions

In terms of production and area under cultivation, wheat is the most important crop in Iran. Weeds problem is possibly the mostserious agricultural problems in the wheat growing regions of the world (Kafi et al., 2005). Rye as an annual plant with long stems is frequently seen as weed in wheat fields around our country (Krimi, 2004). Low environmental demands and allelopathic ability of rye accompanied with similar morphology and life cycle to wheat has increased its stability and occupied area in winter wheat fields (Pester et al., 2000). Competition is one of key issues in ecophysiological debates of plant communities. In competition as a type of Interference, weeds compete for light, water and nutrient resources with neighbor crops and thereby affect growth, development and yield of them (Evans et al., 2003). Considering the severe restriction of water resources in most regions of our country, drought stress is the most important stress, affecting crops (Kafi et al., 2009). Both resource availability and environmental conditions affect the result of a competition. Weed competition for water decreases soil water content which could finally causes water stress and reduces weed growth and crop yield. There are few studies about mechanisms of competition for water. Most of these studies have been implemented under controlled conditions. Nevertheless, these studies have led to an insight intothese possible mechanisms of competition for water (Zand et al., 2004).
In order to study the effect of inter and intra-species competition on morphological and growth characteristics of wheat (Triticum aesativum L.)and rye (Secale cereale L.)under drought stress conditions, a pot experiment was conducted in the greenhouse of college of Agriculture at University of Birjand in 2012. The experiment had factorial arrangement based on completely randomized design with three replications. The factors were wheat density (0, 8, 16, 24 plants/pot), rye density (0, 2, 4, 6 plants/pot) and drought stress (irrigation at 20 and 60% moisture depletion of field capacity). Number of leaves and their SPAD index in wheat and rye were measured at the time of spikes emergence of wheat, while plant height, peduncle and cluster length and stem diameter of wheat were measured at 95 days after planting (the end of the growing period).
Results showed when density of wheat and rye increased, height (maximum of 23.51% and 13.39% in wheat and 24.45% and 6.56% in rye respectively), leaf numbers (35.80% and 30.73% in wheat and 71.37% and 31.71% in rye respectively) and SPAD (12% and 11.38% in wheat and 13.75% and 0.38% in rye respectively) were significantly decreased. Drought stress also significantly decreased the height and leaf number of wheat (17.58% and 8.48% respectively) and rye (7.64% and 26.75% respectively) and significantly increased the SPAD index of wheat and rye (20% and 7.78%, respectively). Increasing of drought stress however had not effect on cluster length, significantly decreased the peduncle length (26.03%) and stem diameter (3.49%). When the rye and wheat density increased, length of wheat cluster (maximum of 13.70% and 24.21% respectively), length of wheat peduncle (maximum of 17.39% and 22.72% respectively) and wheat stem diameter (maximum of 11.11% and 18% respectively).
Result totally showed that in drought stress conditions, intra specific competition had just significantly affected on SPAD index, but inter specific completion had significantly affected on both SPAD index and leaf number of wheat and height and leaf number of rye. Simultaneous presence of drought stress and plant competition resulted in severe reduction of these traits with a further reduction in wheat compared to rye. Accordingly, in the wheat fields where rye is considered as an important weed, the damage of this weed is even higher when drought stress occurs and therefore, controlling this weed in water limited conditions is of major importance.