| Ninety S(,1) families from three populations representing three levels (0%, 25% and 50%) of introgression of exotic maize germplasm into an adapted population were developed and evaluated at two locations. A theoretical approach to the problem of finding an intensity of selection and effective population size which maximizes the final chance of fixation of favorable alleles in different foundation stocks was examined.;A significant quadratic relationship between S(,1) family means and proportion of adapted material in the foundation stock for grain yield indicates that a second backcross to the adapted population would not produce a significant increase in grain yield. Greater genetic variance and predicted gain from selection in the population cross compared to the adapted and backcross populations indicate possible benefits from the use of exotic germplasm in long-term selection programs.;The choice of using one or two generations of backcrossing to the adapted population does not seem to be useful when, for a given locus, p(,A) (frequency of favorable allele in adapted population) is low and p(,E) (frequency of favorable allele in exotic population) takes values larger than .5. While the N (effective population size) in cross population, that makes the final probability of fixation of favorable allele greater than .9, needs to be doubled when going from high to low p(,A) and p(,E), the required N that makes the probability of fixation in BC(,1) (first backcross to adapted population) and BC(,2) (second backcross to adapted population) greater than .9, should be tripled and quadrupled, respectively.;The S(,1) families from the cross yielded significantly less than those from adapted and backcross populations. Adapted and backcross populations yielded similarly. This suggests that major genes for lack of adaptation are acting in the cross population. |
