Abstract
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.
Highlights
Advances in maize breeding have an important role in continually developing and deploying new maize164 Page 2 of 16 cultivars, exhibiting improved grain yield and desirable agronomic characters
The single nucleotide polymorphism (SNP) markers divided the South Africa germplasm into 11 clusters (Table 1)
The South Africa maize inbred lines were on the same side with the tropical testers, CML444 and CML312 (Fig. 1), indicating that they were more inclined towards the tropical CIMMYT testers than the USA temperate testers
Summary
Advances in maize breeding have an important role in continually developing and deploying new maize164 Page 2 of 16 cultivars, exhibiting improved grain yield and desirable agronomic characters. When inbred lines from different known and unknown origins are used, a large number of hybrid combinations are made which are later evaluated in multi-location environments (Bidhendi et al 2012). This is labour-intensive, lengthy and costly (Aguiar et al 2008). When heterotic groups are formed, undesirable combinations are avoided by crossing inbred lines from the existing and divergent groups (Aguiar et al 2008) This allows the exploitation of maximum heterosis (Melchinger and Gumber 1998) among selected lines in hybrid combination, reduces the chance of missing superior hybrids and subsequently improves breeding efficiency. The information on simplified heterotic orientation is crucial for setting up an efficient maize breeding program
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