在选育玉米杂交种的过程中,通常选用一些骨干自交系与新选自交系进行测配,来鉴定生产上可用的优良新组合。然而,新选系往往带有某些常用系血统的二环系,致使获选的某些杂交种的生长优势不够强大,适应能力较小,抗逆性差,产量不够稳定。这就出现了一个值得重视的问题:随着杂交种面积的逐步扩大,它们的遗传基础将变得愈来愈窄。以目前采用的单交种而育,如果其中一个亲本自交系出了某些性状上或是使用上的问题,那末,这对玉米生产所造成的损失将是十分巨大的。适当地增加三交种和双交种的使用是一种可取的补充办法,因为它们的遗传基础比单交种要广泛一些,从而可以减缓生 In the selection of maize hybrids, some of the key inbred lines are usually selected for mating with the newly selected inbred lines to identify good new combinations available for production. However, the newly selected lines often contain some of the commonly used lineage of the blood system, resulting in the growth of some of the selected hybrids are not strong enough, less adaptability, poor resistance, yield is not stable enough. This presents a problem worth noting: With the gradual expansion of hybrids, their genetic basis will become narrower and narrower. With the current single cross breeding, if one of the parent inbreds has some traits or problems in its use, the losses to the corn production will be enormous. The appropriate addition of three and three crossbreds is a desirable complement as they have a broader genetic basis than single crossbreds,