Study of the Effect of Calcium Chloride and Selenium on High Temperature Resistance Wheat (Triticum aestivum L.)

Introduction: The negative effects of heat stress on plants are seriously problems, which often cause damage to crops throughout the world. High temperature driven degradation of chlorophyll reduces photosynthetic capacity. Moreover, impaired transport of photosynthate (carbohydrate mobilization) from green organs (source) to anther tissues (sink) leads to high pollen mortality and thereby decreases grain yield. In environmental stress, plant tolerance should be increased. Therefore some chemical compounds are used to improve the metabolic activity of the plant, which calcium chloride is one of them. For this purpose, the present experiment was conducted to investigate the effect of calcium chloride and selenium foliar application on reducing the effects of heat stress on yield and yield components of two wheat cultivars.Materials and Methods: This experiment was carried out as a split factorial experiment based on a randomized complete block design with three replications at the experimental farm of Shahid Chamran University of Ahvaz during growing season 2017-2018. Three factors were investigated in this experiment. First factor including three planting dates (Nov 11, Dec 11, and Jan 10) was allocated in main plot. The second factor was three solution types  ( foliar application of tap water (control), foliar application of selenium (4 mg L-1), and foliar application of calcium chloride (10 mM) and third factor was two wheat cultivars (Chamran and Star) which were assigned in sub plots.Results and Discussion: According to the results of third planting date, the highest number of grains per spike (36) was obtained in the foliar application of calcium chloride and the least number of seeds per spike (25) was observed in control and selenium foliar application treatments. In calcium chloride foliar application in third planting date, the number of grains per spike decreased by 12% compared to the first planting date but in the control and selenium foliar application treatments, the number of grains per spike decreased by 36%. In the third planting date, the difference between treatments was more evident in grain yield. So, in this planting date, the decrease in grain yield compared to the first planting date was 49.3% and 49.9% in the control and selenium foliar application treatments, while in calcium chloride foliar application, yield reduction was 23.8%. In all three planting dates, when calcium chloride was used as foliar application, the grain filling duration was longer than treatments of control and selenium foliar application. Grain filling duration was prolonged when calcium chloride applied. This could be one of the most important factors that resulted in lower 1000 grain weight and grain yield than the other treatments. While in this condition, there is sufficient time to carry out photosynthesis and transfer the material to the filling grains. Finally, it can be concluded that the calcium chloride application can have a significant effect on reduction the effects of last season's heat stress on wheat by reducing the negative effects of heat stress during pollination, increasing the grain filling period and 1000 grain weight. The number of smaller seeds per spike indicates the effect of heat stress on the plant and reduced fertility of the seeds due to lack of proper inoculation and lack of sufficient photosynthetic material and the competition between the seeds for absorption of food. Increasing yield in calcium chloride treated plants can be due to better photosynthetic activity in these conditions. Because the use of calcium chloride increases the efficiency of the photosystem II and ultimately improves the function of photosynthesis.Conclusions: Calcium chloride may increase the 1000 grain weight by improving the transfer of photosynthetic products from leaves to seeds as physiological reservoirs, as well as increased grain filling duration. Therefore, it can be concluded that the calcium chloride application can have a significant effect on reducing the effects of last-season heat stress on wheat by reducing the negative effects of heat stress during pollination, increasing the grain filling duration and 1000 grain weight.