Introgression of an Exotic Germplasm for Improving an Adapted Maize Population1

Abstract

Maize (Zea mays L.) geneticists and breeders in the USA are concerned with the narrow base of Corn Belt germplasm. Numerous experiments using exotic germplasm from other countries have been conducted to broaden the germplasm base. Our study was undertaken to evaluate the potential use of an exotic germplasm source for the improvement of an adapted maize population and to determine the optimum proportion of exotic germplasm to be introgressed. Ninety S1 families from three populations representing three levels of introgression of exotic maize germplasm into an adapted population were developed and evaluated at two locations. The S1 families from the cross (50% adapted germplasm) yielded significantly less than those from adapted (100% adapted germplasm) and backcross (75% adapted germplasm). Both the adapted and the backcross populations were early maturing and yielded similarly. This suggests that major genes for lack of adaptation are acting in the cross population. A significant nonlinearelationship between S1 family means and proportion of adapted material in the base population was noted for all traits. The use of an exotic source has increased the genetic variation in the cross population. With an appropriate effective population size, the cross can be used as a base population in a selection program, if useful genes from the exotic source are at low frequencies.