Genetic diversity and heterotic orientation of South Africa maize inbred lines towards tropical and temperate testers

An efficient hybrid breeding program defines and utilizes a few heterotic groups. Objectives of this study were to determine genetic diversity and alignment of South Africa maize inbred lines collection towards tropical and temperate testers. Forty-four maize inbred lines were genotyped with 56,110 single nucleotide polymorphism (SNP) markers. A total of 40 lines were crossed to two tropical and two temperate inbred line testers. Due to seed shortages, testcross hybrids containing 14 and 18 lines were used in 2014/2015 and 2015/2016 seasons, respectively. Genotypes and specific combining ability (SCA) effects of hybrids were significantly different (P < 0.05) for grain yield. There was a weak correlation between molecular genetic distances and both grain yield mean performance and SCA effects of hybrids, indicating that productivity of maize inbred lines could not be reliably determined based on molecular genetic distances. The SCA data classified these maize inbred lines into three heterotic groups with respect to both tropical and temperate testers. The study also indicated high level of diversity among the maize inbred lines, which was shown by both the dendogram and molecular genetic distances. The SNP marker data classified the inbred lines into 11 clusters that could be simplified into three major groups of normal maize endosperm and two groups of quality protein maize endosperm types. However, the SNP data indicated that maize lines were more aligned towards the tropical than temperate inbred testers. This information would be useful for simplifying heterotic classification of the lines with profound implications for breeding progress.