杂交稻“三系”中的保持系和恢复系是自交群体,长期自交促使基因型纯合和遗传的稳定;不育系繁殖时和保持系组成回交群体,连续回交可以维持由核质共同控制的雄性不育系的长期稳定;在制种过程中,不育系和恢复系组成异交群体,增强了对突变、漂变或选择影响的缓冲能力。这些都是杂交稻高度稳定的内在基础。杂交稻普遍混杂退化的问題是机械混杂和生物学混杂所造成的。杂交稻良种繁育的中心环节是做好防杂保纯工作。以改良混合选择和不育系育性鉴定为主要手段的“三系七圃法”原种生产技术,强调维持“三系”综合性状的典型性为选择的主要目标,对数量性状采用众数选择法或平均数选择法.四年来,经过四百万亩大面积生产实践检验,“三系七圃法”周期短、投资少、种子多、质量好,广泛受到各地的欢迎. The maintainer and restorer lines of “three lines” of hybrid rice were selfing populations, and the long-term selfing could promote the homozygous and genetic stability of genotypes. When the sterile lines were propagated and the maintainer lines were composed of backcross populations, The long-term stability of male sterility lines under common control of nuclear and cytoplasm; in the process of seed production, male sterile lines and restorer lines formed outcrossing groups, which enhanced the buffering capacity of mutation effect, drift or selection. These are all the internal bases for a highly stable hybrid rice. The problem of widespread hybrid degeneration of hybrid rice is caused by the confounding of machinery and biology. Hybrid rice seed breeding center is to do a good job of anti-hybrid pure work. In order to improve the hybrid selection and fertility identification of sterile lines as the main means of production technology of the “three lines and seven nurseries” species, it is emphasized that the typical characters of the “three lines” comprehensive characters should be selected as the main target. For the quantitative characters, Selection method or average selection method.In the past four years, after four million mu of large-scale production and practice tests, the “three-series and seven-garden method” has a short cycle, less investment, more seeds and good quality and is widely welcomed by all over the world.