以18个杂交中稻组合材料，研究了超稀栽培与传统栽培间稻米整精米率的变异与组合间库源结构的关系。结果表明：中小穗型组合在超稀栽培条件下的整精米率会明显改善,而大穗型组合的整精米率反而降低。其原因在于中小穗型组合在传统栽培条件下的叶粒比和灌浆速率较高，改为超稀栽培后，叶粒比和灌浆速率明显降低，相对提高了籽粒容重，近而提高了整精米率。大穗型组合在传统栽培条件下的叶粒比和灌浆速率较低，改为超稀栽培后, 叶粒比和灌浆速率进一步明显降低，此时因库源比例失调，源明显不足以致籽粒充实度差， 从而相对降低了籽粒容重和整精米率。超稀栽培应选用传统栽培条件下着粒数不超过177粒的组合为宜。
Many studies on grain quality as affected by rice cultivation density have been conducted on one or two rice varieties, but there are few studies on varieties of hybrid midseason_rice. The hybrid midseason_rice grown in southern and eastern Sichuan Province has very low grain quality, especially the percentage of head milled rice, because of high temperatures and summer droughts. This paper explores the effects of low density cultivation on the percentage of head milled rice and source to sink ratios of varieties of hybrid midseason_rice, and it provides a theoretical and practical basis for improved cultivation. The experiment was conducted with eighteen mid_season rice hybrids grown at two densities, a low density cultivation and a traditional cultivation system, in a randomized block design with 4 replications using two hybrids (a big_panicle type hybrid `Gangyou 22‘ and a small_panicle type hybrid `II you 7‘) with 3 different treatments of grain or leaf cut. By using variance, correlation and regre ssion analysis, the results indicated that the percentage of head milled rice in creased in hybrids with small_medium panicles under low density cultivation but not for the hybrids with big_panicles. This was because of the significant decrease in the leaf to grain ratio and grain filling rate of hybrids for small_middle panicle under low density cultivation, as compared to the traditional cultivation system, resulting in an increase in the grain unit weight and percentage of head milled rice. The leaf to grain ratio and the grain filling rate of big panicle hybrids were low in traditional cultivation, and decreased significantly under low density cultivation, causing a decrease in the grain unit weight and percentage of head milled rice. These results were produced because of an imbalance in the leaf to grain ratios. Hybrids with less than 177 spikelets per panicle un der cultivation using traditional densities can adapt to the low density cultivation in the eastern and southern regions of Sichuan Province.