Heterotic Grouping of ARC Maize (Zea mays L.) Inbred Lines Based on Yield-Specific Combining Ability Data and SNP Markers

Maize is an important staple food in South Africa. Successful development of improved maize hybrids requires a well-arranged germplasm which provides maximum heterosis. Heterotic groups and patterns facilitate hybrid breeding, and a small number of heterotic groups results in higher breeding progress. The objective of the study was to classify 42 maize inbred lines into heterotic groups based on yield-specific combining ability (SCA) and Single Nucleotide Polymorphism (SNP) markers.

Forty-two maize inbred lines from seven known heterotic groups were evaluated in testcrosses with four testers representing heterotic group A (B73 and CML312) and B (MO17 and CML444). Testcrosses were evaluated in South Africa, in two environments for two growing seasons (2014/15 and 2015/16). The Inbreds were further genotyped with SNP markers to estimate genetic distances.

Based on yield SCA data, the inbred lines were classified into heterotic group A and B; only two inbred lines were not clearly distinguished for classification. A UPGMA dendogram based on SNP marker data formed three groups of inbred lines. Classification of most inbred lines by SNP markers corresponded with their known pedigrees. However, the correlation between yield SCA and marker-based estimated genetic distances was low suggesting that predicting heterosis from molecular data alone might not be sufficient. These classifications would be potentially useful in the ARC maize breeding program to obtain higher-yielding maize hybrids under common abiotic stresses in South Africa, mainly drought and low nitrogen soil stress. The results obtained will also provide the opportunity for better management and utilization of maize germplasm.