Adaptation of tropical maize germplasm to temperate environments

Maize ( Zea mays L.) is one of few crops that can offer significant genetic gains with the utilization of genetic diversity. Genetically broad-based germplasm has the potential to contribute useful and unique alleles to U.S. Corn Belt breeding programs not present in current U.S. genome sequences (e.g. B73, NAM, etc.). Our objectives were to determine if unique tropical genetic materials have been effectively adapted to temperate environments and how their agronomic performance was relative to adapted populations. An important long-term objective of the Iowa and North Dakota maize breeding programs has been, in addition to the typical elite by elite line pedigree selection cultivar development process, to adapt exotic and unique germplasm, maximize their genetic improvement, and develop unique products for breeding and commercial uses. Stratified mass selection methodology for earliness has been utilized for the adaptation of tropical and temperate populations to Iowa and North Dakota environments. This method has allowed screening of up to 25,000 genotypes per population cycle at a rate of one cycle per year. In addition, the estimated cost per year our programs had for the adaptation of each population was less than $2,000 which could successfully be applied in any breeding program across the globe. This cost has been less than 1 % of the total cost for finding minor genes on the same trait. Our results showed the successful adaptation of exotic populations was independent from genetic background. We can speculate there are a few major genes responsible for most of flowering date expression. We encourage the use of technology to target traits according to their genetic complexity. Stratified mass selection at the phenotypic level has been successful. Each of the populations with either 25 of 100 % tropical germplasm are available for anyone who may desire to expand the germplasm base of their breeding programs with tropical germplasm adapted to temperate mid- and short-season U.S. Corn Belt environments.