国内外生产实践证明,现代玉米种植业大幅度增产,首先靠的是成功地利用杂种优势,选育、推广优良杂交种;美国五十年代前玉米单产只有160多斤。五十年代后期起,由于推广玉米双交种,发展了单交种和三交 Production practice at home and abroad proves that the modern corn planting industry has greatly increased its production. First, the successful utilization of heterosis, breeding and popularization of fine hybrids are the first priority. Before the 1950s, the yield of maize in the United States was only 160 kilos. Since the late 1950s, as a result of popularizing corn double crosses, single crossbreeds and three crossbreeds have been developed