中文摘要：

以长江中下游地区5种生育类型中有代表性的56个粳稻品种为供试材料,研究了4种施氮水平下粳稻品种垩白性状的变化规律,并对其垩白变化的氮素敏感性及其品种类型特征进行了聚类分析和筛选评价。结果表明,在施N 0~300 kg/hm^2范围内,随着氮肥水平的增加,各品种类型的垩白度呈现不同程度的上升趋势,但垩白米率的变化则因品种的生育期类型不同而异。其中,中粳品种在高氮水平下的垩白米率有所增加,而晚粳品种则有所下降。根据粳稻垩白度对氮肥响应的敏感程度,供试品种可分为迟钝型、中间型和敏感型3种;并据此推荐了利于生产实践中改善外观品质的两类品种：一类是垩白度较低且在各氮肥水平下表现比较稳定的品种,另一类在高氮肥水平下垩白度较高,但其对氮肥响应较为敏感,通过适当减少施氮量也能获得较好外观品质。

英文摘要：

The appearance quality is one of the important aspects of rice quality.Nitrogen is the indispensable nutrient to rice production although over application of N could cause so many environment problems.The effect of nitrogen application rates on appearance quality is varied in different rice cultivars,especially in different genotypes.Therefore it is necessary to identify the responses of grain chalky traits to nitrogen application levels for different growth-period Japonica cultivars.In this research,a field experiment with four nitrogen levels（zero,low,medium and high） was carried out.About 56 Japonica rice cultivars which are representative in the region of Yangtze River were adopted to investigate the differences of the rice types under the four nitrogen levels.The chalkiness degree was clustered and selected in term of their different responses to the nitrogen application levels.The main results are as follows： 1） In the range of 0-300 kg/ha nitrogen fertilization,the effects of nitrogen application rates on rice chalkiness rate are genotype-dependent,with the increasing chalky-grain rate in high level for medium growth-period Japonica cultivars,while the dropping one for late growth-period Japonica cultivars.With the level of nitrogen increased,the chalkiness degree of Japonica rice cultivars is increased.2） All 56 rice cultivars can be classified into three types（insensitive,intermediate and sensitive） in term of their different responses of grain chalkiness degree to the nitrogen application levels.And two rice groups among them are also recommended.One group is the cultivars with low and stable chalkiness degree under all nitrogen levels;the other group is the cultivars which are sensitive to nitrogen application levels,and good appearance quality can be obtained through the proper reducing nitrogen application.