In order to study the effects of seed number per hill on the yield and physiological source-sink relations of three rice cultivars in Khouzestan climate conditions (South West of Iran), this research was conducted in form of a split plot experiment with Randomized Complete Block Design (RCBD) with three replications in the experimental field of Islamic Azad University - Khouzestan Science and Research Branch in the 2008 cropping season. Three rice cultivars including Danial, Red Anbouri and Champa were used as the main plots, and seed numbers per hill of 2, 4, 6 and 8 as the secondary factors were placed in the subplots. To calculate the source limitation, the upper and the lower halves of rice panicles were cut. The contributions of flag leaf and the sub flag leaf were assessed through cutting them at the pollination stage. Results showed that the highest yield was obtained from 6 seeds per hill. With an average yield of 4011 kg ha-1, Danial outweighed the other two cultivars. The highest 1000-grain weights in the upper and the lower halves of the panicle by cutting the flag leaf and the sub flag leaf were obtained from the Danial breeded cultivar. All the cultivars revealed a significant difference in terms of grain weight between the control and the removal of the flag leaf and the sub flag leaf treatments. Due to the removal of the flag leaf and the sub flag leaf, all the cultivars had a decrease in grain weight compared to the control. Therefore, it seems that all the studied cultivars lacked sink limitation. Grain weight potential in both spikelet cutting treatments (upper and lower halves of the panicle) showed a significant difference. With the decrease in the number of the economical sink, grain weight in all cultivars increased compared to the control, which indicates that there was a source limitation.
Key words: Rice, seed number, hill, cultivar, source-sink relations.
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