Tracing the Pattern of Maize Introduction and Spread in Africa using Chloroplast DNA Markers
A genetic assessment of maize landraces from 14 African countries was conducted in order to determine relationships among the landraces so as to infer the pattern of spread after introduction. Seeds were planted and DNA was extracted from ten randomly selected seedlings per accession. Eight published chloroplast SSR primers were used in PCR and purified products were directly sequenced. Allele size data from the chloroplast microsatellites were organized in MS Excel spreadsheets and sorted into haplotypes. Mantel‟s test and Principal Component Analysis were used in determination of haplotype diversity and biogeography of alleles. Results indicated that there was considerable variation in the geographic range of alleles. However, Mantel tests performed to examine the correlation between genetic and geographical distances likewise showed no association between genetic and geographic distances (r = -0.0138, p = 0.5600, 1000 permutations). Furthermore, principal component analysis provided little evidence for population differentiation based on geographical region; projection of the populations over the first two planes revealed two outlier accessions whilst the rest appear to be sub-accessions associated with South Africa. Hence, results from this study support a hypothesis of successive introductions of landraces in Africa with South Africa as one of the likely entry points.
Key Words: Maize Landraces, SSR Markers, Haplotype, Genetic Diversity, Africa.