白菜是最主要的叶菜之一。在生产上都用种子繁殖,有大株留种和小株留种。大株留种,就是把秋冬期间采收的叶球,贮藏过冬,到翌年春暖后,移栽到留种田开花结籽,但生长期长,繁殖系数低,成本高;而小株留种,是在初冬(江南一带)或早春(华北一带)播种,到4～6月间开花、结籽,其特点是成本低,管理方便,但未进行叶球选择,不能保持品种纯正。为了育种的目的,可用无性繁殖,以保持品系的遗传特性。近年来采用“叶——芽”扦插繁殖,可以大大增加繁殖系数,提高自交不亲和系或雄性不育系的繁殖率,并可在大田群体中,经过选择优良种株和抗病单株,能保持品种的纯度, Cabbage is one of the most important leafy vegetables. Breeding in the production of seeds, a large plant to stay species and small plants to stay species. Large plant to stay species, that is, during the harvest of autumn and winter leaves of the ball, the storage of winter, to the following year after the spring, transplanting to stay farming flowering and seed, but the long growing season, low breeding coefficient, high cost; It is planted in early winter (in the south of Yangtze River) or in early spring (in the north of China), and blooms and flowers between April and June. It is characterized by low cost and convenient management. However, it can not maintain the pure variety without leaf ball selection. For breeding purposes, asexual reproduction can be used to maintain the genetic character of the line. In recent years, the “leaf - shoot” cutting propagation, can greatly increase the breeding coefficient, increase self-incompatibility or male sterile line breeding rate, and in the field population, through the selection of elite strains and disease-resistant single Strain, to maintain the purity of varieties,