Effect of Calcium Chloride Application Time on Reducing the Effects of Heat Exhaustion on Yield and Yield Components of Wheat in Ahvaz

Introduction The negative effects of heat stress on plants are serious problems, which often cause damage to crops throughout the world. In addition, the issue of global warming increases the importance of the heat stress. Currently, to increase the resistance of plants to environmental stresses, some chemical compounds are used that improve the metabolic activity of the plant. Calcium chloride is one of them and finding the appropriate time to use it is important. For this purpose, the present experiment was conducted to investigate the effect of calcium chloride application on reducing the effects of heat stress on yield and yield components of wheat in Ahvaz.Materials and Methods This experiment was carried out on wheat (Chamran cultivar) plant in a factorial experiment based on a complete randomized block design with three replications at the experimental farm of Shahid Chamran University of Ahvaz during a growing season 2016-2017. The solution type was used as the initial factor: 1- foliar application with distilled water, 2- foliar application with calcium chloride (10 mM).The application time was used as the second factor: 1- 15 days before flowering (A), 2- flowering (B), 3- 15 days after flowering (C), 4- 15 days before flowering and flowering (A*B), 5- flowering and 15 days after flowering (B*C), 6- 15 days before flowering and 15 days after flowering (A*C) and 7- 15 days before flowering, flowering, 15 days after flowering (A*B*C). Results and Discussion Regarding the mean comparison of traits, a calcium chloride foliar application on traits such as plant height, number of spikelet’s per spike, grain yield per plant and harvest index were not significant (P≤0.05). The 1000 grain weight increased under different time traits of calcium chloride foliar application. The highest 1000 grain weight belonged to the calcium chloride foliar application during two weeks before flowering. Foliar application of calcium chloride at the flowering time as well as flowering and two weeks later increased the shoot dry weight. Grain weight per plant was increased in all treatments with calcium chloride except for foliar application at flowering and two weeks before and after flowering. The highest amount of grain weight per plant was obtained in the calcium chloride foliar application during two weeks before flowering and flowering, but no significant difference was observed with other treatments with calcium chloride. Conclusions Looking at the research, the positive effects of the use of calcium chloride in some plants have been shown under stress conditions, but there is no consensus on the best time or best type of it. Induction of heat stress at the onset and during the flowering period by decreasing pollen and ovarian grain yields prevent fertility and thus decrease grain yield. On the other hand, when the plants were in the post-flowering stage and in the grain filling stage exposure to high temperatures, heat stress accelerates this stage and reduces the grain filling period, thus reduces yield. Under heat stress conditions, the use of calcium chloride improved some properties such as number of spikes per plant, seed weight per plant and 1000-grain weight, and the destructive effects of heat stress on the plant. According to the results of this study, application of 10 mM calcium chloride concentration two weeks before flowering is recommended to reduce the damaging effects of heat stress in wheat.