Variations In The Quality Of Grains At Different Positions Within A Rice Panicle And Their Influence Factors

With typical indica and japonica rice cultivars as materials, the variation and distribution of the quality of grains at different positions within a rice panicle were investigated; the reasons for the difference and their mechanisms were analyzed in respects of grain filling, enzymes and hormones; and the effects of ecological and cultural conditions (temperature, light, soil moisture and nitrogen) on rice quality were studied. The main results were as follows:1. The distribution of the quality of the grains at different positions within a rice panicle(1) The spikelets that flowered earlier produced greater grain weight than those flowered later. However, the change in grain weight was not very identical with the following sequence. (2) The indexes of milling quality of the grains on a primary branch were greater than those on a secondary branch at the same part of a panicle, and those of the upper and mid parts were greater than those of the basal part, and the brown rice rate (BRR) and head rice rate (HRR) for different grains on a primary branch were not associated with flowering sequence of a grain. The degree of milling quality of grains at different parts within a rice panicle was consistent with the degree of development and filling of endosperms. (3) The average length of the grains on a primary branch, in general, was greater than that on a secondary branch, and that of the earlier-flowered spikelets was greater than that of later-flowered spikelets on the same branch; and the ratio of length to thickness (L / T) of the grains at the basal was greater than that at the upper or mid part. (4) Grains on the branches at the upper part of a panicle exhibited the least chalky grain percentage (CGP), followed by those at the mid part, and those at the basal part showed the greatest, those at the upper part exhibited the least chalkiness degree (CD). The 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 first grain showed the least CD on a primary branch. On a secondary branch, the first grain had the least CD and the third or the fourth grain the greatest. (5) Grains on the branches at the basal part of a panicle had smaller gel consistence (GC) and greater amylose content (AC) and crude protein content(CPC)than those...