Effect of Planting Date on some Growth and Physiological Characteristics and Heat Tolerance in Three Rice Cultivars in Khouzestan

This study was carried out evaluate the effect of planting dates on the trend of leaf surface growth indicator, growth, and net photosynthesis rates and also the yield of rice cultivars through a split plots experiment based on a randomized complete block design with three replications in the north region of Khuzestan. Main factor was the date of planting at three levels (26 May, 10 Jun, 26 Jun) and the subordinate factor included three cultivars of Red Amber (long and short grains), and Champa. Results of variance analysis indicated that there was a significant difference between different dates of planting and all properties, but no significant difference observed in the interaction of both factors. In addition, the maximum LAI, CGR, and net photosynthesis rate was related to the first date and the highest yield of grain was related to the third date of planting. Evaluating the trend of leaf area indices and crop growthrate on 26 May, which had the maximum thermal stress at the reproductive stage, they reached the maximum growth in a shorter period of time. However, after that, the leaf area indices and the growth rate rapidly reduced, which can be referred to a mechanism of escaping the heat, while the rate of net photosynthesis reached its maximum changes on 26 May. Among the cultivars, short-grain Amber had the minimum changes in above characteristics and Champa had the maximum yield with an average of 3795.4 kg/ha.