Abstract: Measurement of excavated rice kernels of Hemudu, China revealed that seed size(L/W ratio) varied from 1.8 to 3.8 with a mean of 2.75 which fell well into the "normal distribution". A comparison was made firstly to the rice seeds born on F₂ plants population of short-grain (glutinous, sd 1) and long-grain (nonglutinous, sd6) hybrid of California semi-dwarf cultivars. They all fell into the same category of variation with only mode difference. Then a comparison was further made with data reported by Wasano(1994), 5000 to 7000 years old kernels excavated from six sites including Hemudu at the delta of Yangtze River. It showed similar continuous variation although slightly different among sites. Judging the results from the above, the so-called subspecies, japonica and indica, or keng-hsien polymorphism has not showed up at the time of prehistoric China. The broad genetic variability of seedshape found in Hemudu suggested that outcrossing pollination took place in which characteristic of wild rice is remained. Race development was possibly automatic after rice of proto-type became a self-fertilization of an annual crop on the time of dissemination. It is assumed that segregation of seed-shape, short to long, was derived from originated heterogeneous population. They gradually became homogeneous and were accelerated under the pressure of natural environment and associated with human efforts resulted in "disruptive selection" of seed shape when these rice dispersed into north and south peripheries. This can be comparable to those crosses of japonica-indica grown them into cool and warm locations. Discussion was extended to the pattern difference of esterase isogenic genotype found in wild rice in China whether or not related to keng-hsien phenotype differentiation.

Key words: differentiation, excavated rice kernels, genetic variability, hybridization, mutation, polymorphism

摘要： 对河姆渡出土谷粒的长宽进行了测定，其长宽比在1.8～3.8间连续变异，符合常态分布。邻近太湖地区各地出土五千至七千年米粒亦有报告具有相似的连续变异。比较现代圆糯(粳)和长籼(非糯)品种杂交有正常育性的F2世代各株粒型，发现相隔五千年以上古今两群体的变异方式吻合，从已经分化的现代品种杂交可复得古代稻种的变异而推论，上古稻是一遗传的异质体集团。再研究太湖各地史前的稻米年代差异，所现出粒型的变化，所谓的日本型印度型亚种并未在史前中国稻中显现。而古稻粒型的变异大，启示野生稻的异花授粉特性仍在。原始型栽培稻向各地传播时演变成为自交作物，从异质遗传接合族群中分离同质化，在不同自然环境压力下及人为选择，粒型常态分布的中央部份不如两端的短粒及长粒发展而逐渐分开形成粳籼多型性。从遗传学、分子生物学、突变、进化、农艺实证、生殖隔离物种分类学等观点对种内品种分化，及粳籼型杂交育种的效率，新遗传型的提高抗病力加以综合分析。

关键词: 出土稻米, 遗传变异性, 种内分化, 粳籼多型性, 稻作传播, 杂交育种, 突变