Abstract:

Chalkiness of the grain is one of the most important quality indexes of rice，affecting badly the milling，apparent，cooking and taste qualities of rice. In order to study and document the reasons and influencing factors，much researches，such as physical and chemical properties，cellular features of chalkiness formation as well as the factors influencing chalkiness formation including source-sink relation and grain-filling characteristics，have been done recently，the difference between dynamic changes of chalkiness formation in vigorous and weak grains during filling stage and the differences in the chalk degree of the grains in various parts in a same panicle were also preliminarily studied. Thus，the endosperm starch structure characteristics such as starch grain shape, size, developing degree and arrange pattern in chalky milled grains，the relations between chalkiness formation and dynamic variations of grain filling such as dry matter accumulation in grain，filling velocity and dehydrating velocity during filling stage were preliminarily investigated. In addition，correlative researches also indicate that it is remarkable differences in the chalk degree of the grains in various parts in a same panicle and the chalk degree of the vigorous grains are usually smaller than that of the weak grains.
The objective of this study was investigate the distribution of chalkiness degree (CD) and chalky grain percentage (CGP) for different grains on a panicle in two rice cultivars Yangdao 6 (indica rice) and Wuyujing 3 (japonica rice) in the yield, three levels of nitrogen, 0, 120 kg/ha, and 240 kg/ha, were applied at pre-planting and topdressing. All primary branches on a panicle were evenly divided into three parts of the upper, middle and basal. The grains were numbered as 1 to 6 on a primary branch and 1 to 3 or 4 on a secondary branch from the top to base. Generally, CD and CGP for the grains on a secondary branch were greater than those on a primary branch at the same part of a panicle. The grain 6 showed the greatest CD and the grain 1 the least on a primary branch. On a secondary branch, the grain 1 had the greatest CD and the grain 3 or 4 the least. CGP on the branches at the upper parts of a panicle exhibited the greatest, at the middle part the middle, and at the basal part the least. CGP was the greatest for the grain 2 and the least for the grain 1 or 6 on a primary branch, and the grain 1 on a secondary branch. Application of fertilizer-nitrogen reduced CD and CGP when amount of nitrogen was between 0 and 240 kg/ha.

Key words: Rice, Grain position, Chalkiness degree, Chalky grain percentage, Nitrogen