| Rice kernel chalkiness, which is the opaque portions in grain endosperm, is an important grain quality character usually regarded as a negative index for the appearance quality of rice. Chalkiness existing in grain predisposes the grain to crack and results in higher breakage in milling, then the head milled yield decreases. Those rice kernels could be easily broken or loosen when cooked, thus the cooking and eating quality of them get very poor. With the development of crop production and improvement of people's living standard, the emphasis of rice production has been changed from on high yield to on both of high yield and good quality. Presently, the poor quality rice in southern China mainly comes from early indica rice with more chalkiness. Therefore, reducing the chalkiness of early indica rice kernel and raising commercial value of it has become an urgent task in rice kernel quality improvement projects, especially those for early indica rice.Using several early indica rice varieties (Oryza sativa L. sp. indica) with markedly different chalkiness as the materials, is intended to develop an objective method to measure the rice kernel chalkiness and respectively investigate the varietal differences of chalkiness formation, effects of environmental factors on chalkiness formation, 'source-sink' character of rice plant during filling stage andCendogenous plant hormonal levels on rice kernel chalkiness formation. The obtained results are as follows:1.The chalkiness measuring system, which is composed of a scanner, a computer and a special software Chalkiness 1.0, has been established. Compared with some traditional eye-judging methods, the method can describe objectively and quantitatively the true state of rice kernel chalkiness. Experiments showed that the chalkiness measuring system was objective, quick and accurate. Its development is an important breakthrough in measuring rice chalkiness. This method had given a reliable assurance to the following study on chalkiness formation mechanism. In addition, it will help other rice researchers with an objective, quantitative chalkiness measuring method in the future.2.Chalkiness formation of rice kernel is controlled by both the genetic and the environmental factors. Their effects on chalkiness formation were exerted by means of dynamic variation of grain filling. There were more chalkiness for varieties in different sowing dates which had great fluctuation of filling velocity and dehydrating velocity of grain during filling stage. For those varieties, the periods of filling were short, and vice versa.3.The correlation between 'source-sink' character of rice plant and rice kernel chalkiness was significant. The net assimilation ratio of flag leaf, 'source-sink' ratio and sink activity (radioactivity ratio of grain) of less chalkiness varieties in different sowing dates were obviously higher than that of more chalkiness varieties in different sowing dates. Therefore, higher photosynthetic efficiency and proper 'source-sink' ratio and stronger sink activity are the key factors of good quality grain with less or no chalkiness. After analyzing the distribution percentage of '4i in rice organs, it could be supposed that assimilates exporting from mesophyll cell or loading on phloem were partlydblocked, but their transporting in phloem and unloading from phloem had not been blocked.4.The levels of endogenous plant hormones and their balances in rice plant had played an important role in regulating 'source-sink' relation in early filling stage. The contents of IAA and ZT in flag leaf or grains of early indica rice plant with less chalkiness were higher than that of varieties with more chalkiness. The ABA content rapidly increased in flag leaf after heading and its content was significant negative correlated with rice kernel chalkiness during early filling stage. The increasing of ABA content in flag leaf during filling stage could alleviate the harm of high temperature to rice plant and avoid great fl...
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