Abstract:

There have been a lot of reports on the relationship between source-sink state and yield, milling quality and appearance quality in rice, but few reports on the relationship between source-sink state and the RVA profile of rice starch, as well as the relationship between rice quality and grain filling process in rice in the high altitude region. With a purpose of revealing the substantial base of quality formation in rice, the effects of source-sink state on rice quality and the relationship between grain-filling process and rice quality were studied in this paper. The experiments were conducted in a high altitude region by sunshine shading, leaf-cutting and spikelet-removing treatments. The results were as follows: The milled rice rate was reduced but the head milled rice rate increased by sunshing shading, especially for superior grains(Table 2). Under the sunshine shading condition, the chalkiness degree was varied with cultivars and grain positions. The chalkiness degree was increased by leaf-cutting and reduced by spikelet-removing (Table 3). The amylose content，the value of peak viscosity and breakdown viscosity of RVA profile of rice starch were reduced, but the length of rice gel was elongated by sunshine shading in the two experimental cultivars(Table 4). The source-sink state showed a big effect on the grain filling process (Table 5). The area and the degree of chalkiness were negatively correlated with the final grain weight and positively correlated with the days to maximum grain filling rate. The peak and breakdown viscosity of rice starch were positively correlated with the final grain weight and negatively correlated with the days to maximum grain filling rate(Fig.1). The grain-filling rate, the amount of dry-matter filled and its ratio to total weight during the early filling stage(in 15 days after full heading) had the most effect on rice quality, less effect during the late filling stage(30 days latter after full heading) and the least effect during the middle filling stage(15－30 days after full heading). During the early filling stage, the grain-filling rate, amount of dry matter filled and its ratio to total weight increased, the area and degree of chalkiness decreased and the peak and breakdown viscosity of rice starch increased. While during the late filling stage, the grain-filling rate, amount of dry matter filled and its ratio to total weight were increased, the area and degree of chalkiness increased and the peak and breakdown viscosity of rice starch decreased (table 6). The rice quality is influenced not only by the total amount of grain-filling matter, but also by the grain-filling process. The effect of sunshine shading on rice quality in the high altitude region is not fully similar to that in low altitude regions.

Key words: Rice, Source-sink state, Rice quality, High altitude region