Journal of Crop Production and Processing

In order to investigate the effects of temperature and radiation on rate and duration of grain filling and final grain weight in rice cultivars, a split plot experiment based on randomized complete block design with three replications was conducted at different transplanting times at the research field of University of Guilan, Rasht, Iran in 2013. Factors were: transplanting dates in main plots (5 May, 20 May and 5 June) and rice cultivars (Hashemi, Ali Kazemi, Sangejo, Khazar, Dorfak and Gouhar) in sub plots. The greatest grain weight (31.9 mg) was obtained in Gouhar at 20 May and the smallest grain weight (20.4 mg) was observed in Sangejo at 5 June transplanting dates. The longest effective filling period (32.9 days) was achieved in Gouhar at 5 May transplanting date and the shortest grain filling duration (13.9 days) was obtained in Hashemi. The greatest grain filling rate (1.62 mg day^-1) was obtained in the Hashemi and the smallest rate (0.92 mg day^-1) was observed in Gouhar. Significant correlations were observed between cumulative temperature and radiation with final grain weight (R = 0.689). There were significant and positive correlations between the cumulative temperature and irradiance with grain filling duration, in contrary to negative correlations with grain filling rate and grain filling period. The results of this experiment showed that the grain filling duration plays a greater role, than grain filling rate, in determination of the grain weight. It could be concluded that an early transplanting (5 May) brings about favorable temperature and radiation conditions for an appropriate grain filling period and a greater final grain weight.