Responses of Yielding Ability, Sink Size and Percentage of Filled Grains to the Cultivation Practices in a Chinese Large-Panicle-Type Rice Cultivar, Yangdao 4

A Chinese high-yielding large-panicle indica cultivar Yangdao 4 (YD) was examined for the response of yielding ability, sink size and percentage of filled grains (PFG), to the cultivation practice in comparison with a Japanese cultivar Hinohikari (HH) that had almost. the same growth duration in 2005 and 2006. Treatments included planting density and number of seedlings hill(-1), and supplement application of fertilizer to deep layer (SAFDL). Results revealed that the average sink size of YD was 17-28% target than that of HH due to the larger number of spikelets panicle(-1) and heavier grain weight. A significantly larger sink size was attained by the high density planting and SAFDL treatments in both cultivars, but not by changing the seedling number hill(-1). The sink size of YD responded more significantly to the cultivation practices than that. of HH. The average PFG in YD was about 10% higher than that in HH in both years. The PFG in both cultivars decreased with increasing sink size, but the decreasing rate in YD was 1/3 of that in HI-I and its yearly fluctuation was also less in YD than in HH. Consequently, the yield of YD increased with increasing sink size in contrast to HH. The average brown-rice yield of YD (640-653 g m(-2)) was, 41-51% higher than that of HH (418-454 g m(-2)). In comparison with HH, the stable PFG in YD at increased sink size could be attributed to the increase of carbohydrate accumulation in the panicle (Delta W+Delta T), larger amount of NSC in the LS+C and higher NSC/sink size.