Genetic diversity and heterotic grouping of tropical and temperate maize populations adapted to the northern U.S. Corn Belt

Abstract

Understanding the genetic relationships among broad-based populations is a good starting point for breeding programs. These utilize introduction and adaptation of tropical and temperate populations to broaden the genetic resources for genetic improvement. A diallel of 16 maize populations adapted to the northern U.S. Corn Belt was used to estimate population genetic parameters. These were used to assess genetic diversity and assign the populations to heterotic groups. Using the general combining ability (g i ) estimates, 19 agronomic and grain quality traits showed large contribution on the variability of the first two principal components. All traits were used to characterize the genetic similarities among the populations. The cluster analysis formed three groups and a singleton based on genetic distances (GD) of g i estimates. The specific heterosis (s ij ) estimates for grain yield were used to assign the 16 populations to heterotic groups, since there was a positive correlation between GD and s ij . Four heterotic groups were established. These showed a good agreement with that formed using GD. The heterotic grouping agreed with genetic background information and heterotic group’s specific and general combining ability estimates. The EARLYGEM 21 populations with exotic background were assigned to a unique heterotic group. They showed high heterosis when crossed with a tropical population and populations belonging from other heterotic groups. The heterotic groupings among the 16 populations validated former heterotic groups, and new heterotic patterns were created. These results will increase breeding efficiency in developing new cultivars for the northern U.S. Corn Belt.