Isozyme marker characterization of an exotic maize population adapted to the Corn Belt climate

Exotic germplasm can be a useful source of new and valuable alleles for introgression into corn belt hybrids. Such use, however, requires selection for adaptation to local climate which can result in inadvertent loss of useful alleles because of their linkage to unfavorable alleles or by random genetic drift. A population (consisting of 268 full-sib families) derived from a cross of the populations Antigua and Tuxpeno was subjected to selection for adaptation at Lincoln, Nebraska. The present study was undertaken to determine the genetic diversity in the two parental populations Antigua and Tuxpeno, populations from intermediate stages of adaptation, and the final recombined population. Seedling tissue of Antigua, Tuxpeno, 50 S$\sb5$ lines, and the recombined population was sampled and analysed using isozyme electrophoretic markers at 23 loci. The material was found to be genetically diverse and included several alleles rarely observed in other corn belt material. Genetic diversity was largely conserved through the adaptation program, largely owing to leveling of allele frequencies. Heterozygote frequencies were greater than expected for many loci in the S$\sb5$ lines. Neither parent was conclusively favored by selection, although allelic distributions in the recombined population commonly diverged from expected midparent values. Variance components of agronomic traits were estimated in a lattice design field experiment. The 268 families of the recombined population and their parents (105 full-sib families) were grown at Lincoln, Nebraska and Mead, Nebraska. Parent-offspring regression and analysis of variance among full-sib families within each location showed consistent additive variance for most traits measured, however, over environments, genotype x environment interactions and possible epistatic effects masked genetic variance. Dominance variance estimates varied widely between locations. Analyses pooled over locations showed greater significance of genetic variance and additive genetic variance estimates similar to those observed within each location. Performance in terms of plot yield and plant height of the recombined population was good, especially given the lack adaptation of Antigua and Tuxpeno