effects of transplanting time and canopy temperature on morphological traits and grain yield of rice cultivars

because of importance of morphological characteristics, canopy temperature and their relationship with grain yield in rice varieties, an experiment was conducted based on split plot in a randomized complete block design with three replications in two years (2013-2014) at the college of agriculture, university of guilan. the experiment consisted of three transplanting times (5, 20 may and 5 june) as main plot and six cultivars of rice (hashemi, sange jo, ali kazemi, dorfak, khazar and gouhar) as sub plots. the results showed that with delaying of transplanting time, number of fertilized tillers decreased up to 6.4 and 6.1 fertilized tillers at first and second year, respectively. with delaying in transplanting time, leaf area index decreased up to 1.6 and 1.51 in first and second year, respectively, and reduced tillering rate up to 0.08 tillers. comparison of the temperature difference between canopy and environmental showed that khazar cultivar had the highest temperature difference between canopies and environmental in amount of 2.69 and 3.11˚c in the first and second year, respectively, and exhibited lower temperature of canopy compared to environment. the results showed that grain yield of rice cultivars except khazar significantly reduced with delaying in transplanting time. so it should be noted that the khazar, with the number of fertilized tillers and lower canopy temperature than other cultivars at different times, could be maintained their functional stability in front of unfavorable conditions such as the high average temperature, lower intake cumulative temperature and radiation during the growing season, especially during the grain filling stage.