Hybrid rice is produced by crossing different rice seeds with each other. Rice is a self-pollinated crop, which is not conducive to the preparation of hybrid seeds. In order to cross two different rice varieties, the stamens of one variety should be emasculated or killed artificially, and then the stamen pollen of the other variety should be given to the emasculated variety, so that there will be no false hybrid rice which is self-pollinated by the emasculated variety. However, if technicians use artificial methods to emasculate and pollinate tens of thousands of rice flowers, the workload is huge, and it is actually impossible to solve a large number of seeds used in production. So a kind of rice was bred as the female parent, which has a special personality, with thin stamens and withered anthers. You can't fertilize and sow with your own pollen.

In order not to cut off the offspring of the mother, we should find two objects for it. The characteristics of these two objects are different: the first object looks very much like the female parent, but has sound pollen and developed stigma. When its pollen was given to its female parents, it gave birth to a daughter. She looks exactly like her mother, and she is also a female parent. The stamens are thin and degenerate, the anthers are withered and deformed, and there is no fertility. The other object is completely different from the female parent in appearance, generally taller than the female parent, and also has sound pollen and developed stigma. After its pollen was given to the female parent, it gave birth to a son, stronger than both parents. This is the hybrid rice that technicians need, a female parent and its two objects. According to their different characteristics, people have given three names respectively: the female parent is called sterile line, and two objects, one is called maintainer line and the other is called restorer line, which is called "three lines" for short. With the "three-line" system, technicians will know how to prepare hybrid rice in production: a breeding farm and a seed production farm should be planted in production, and a sterile line and a maintainer line should be planted in the breeding farm. When both flowers bloom, the pollen of the maintainer line will be transferred to the sterile line by the wind, and the sterile line will get normal pollen results, and the offspring will still be sterile, thus achieving the purpose of breeding the sterile line. Technicians can keep a part of the propagated sterile line seeds for further propagation in the next year, and the other part can be used for seed production together with the restorer line. When both the sterile line and the restorer line in the seed-making field bloom, the pollen of the restorer line is transferred to the sterile line, and the offspring produced by the sterile line is the hybrid rice seeds planted in the field. Because the male and female stamens of the maintainer and restorer lines are normal and self-pollinated, the seeds they produce are still the descendants of the maintainer and restorer lines.