世上没有一成不变的事物。农作物的品种也是这样,没有永远不变的品种。一个优良品种选育成功,在生产上大面积推广以后,如果不注意防止混杂退化,很快会由优变劣,产量与品质明显下降,这在异交授粉作物和常异交授粉作物,如玉米、高粱、谷子、棉花等作物最为明显。玉米自交系原来生长整齐 There is no immutable thing in the world. The same is true of the crop varieties, there is no permanent species. A successful breeding of fine varieties, after extensive promotion in production, will quickly change from bad quality to good yield and quality if not paying attention to preventing hybrid degeneration. Maize, sorghum, millet, cotton and other crops most obvious. Inbred lines of corn grew well