Study of genetic diversity among improved maize (Zea mays) varieties in Ghana using morphological traits and simple sequence repeat markers

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August, 2015
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Information on genetic diversity among Ghana maize cultivars is not known. Genetic diversity is important for germplasm enhancement, heterotic breeding and for prevention of losses that may arise due to large-scale cultivation of genetically uniform cultivars. This research was carried out to determine the extent of genetic diversity among 17 maize cultivars comprising populations, Open-pollinated Varieties and hybrids developed between 1987 and 2012 in Ghana using morphological, agronomic and molecular evaluations. Morphological and agronomic measurements were analysed by means of analyses of variance, correlations, heritability estimates, UPGMA cluster analysis, and principal components. Molecular evaluations were determined using Simple Sequence Repeats profiling. Wide variability was detected among OPVs while populations and Hybrids demonstrated little variation. There were no significant differences among the three classes of genotypes for earliness, anthesis-silking interval, plant and ear height, stay green, as well as ear and kernel characteristics. However, significant (P≤ 0.05) differences were observed for tassel length, ear leaf characteristics and also for number of kernels per row, hundred kernel weight and grain yield. Cultivar ‘Akposoe’ was most early with the smallest values for ear leaf characteristics, plant height, ear length and stalk diameter while cultivar ‘Obatanpa’ had the largest ear dimensions and grain yield. The least number of days to anthesis and silking was 49 and 51 days, respectively. Highest grain yield was 3.36 Mgha-1. Earliness was negatively correlated to grain yield while weak to moderate and highly significant correlations were found between tassel length, ear leaf length and ear leaf width. Heritability estimates were low among hybrids and populations but high in OPVs. Earliness demonstrated high heritability estimates, plant characteristics showed moderate estimates in OPVs, grain yield exhibited null heritability estimates across the genotypes. UPGMA morphological cluster analysis grouped the accessions into three main groups. ‘Okomasa’ and ‘Abontem’ were the most dissimilar accessions whiles accessions ‘M0826-7F’ and ‘M0826-12F’ were identical. The first three components, with eigenvalues higher than 1.0, accounted for 74.91 % of total the variance. The first component alone explained 49 % of the total variation and was positively associated with AD, SD, TL, ELL, ELW, PLHT, EHT, NL, EP, StD, EL, KL, NKR, NRE, CD, EWT and YLD. Marker genotyping of the 17 maize accessions using 12 SSR markers revealed a total of 31 alleles, detected at 11 polymorphic loci and one monomorphic locus. The number of alleles identified by each marker ranged from 2 to 4 with a mean of 2.82. A total of seven rare alleles were revealed in five accessions. Polymorphism information content ranged from 0.21 to 0.64 with an average of 0.43. Dice genetic similarity coefficient among the accessions based on the molecular data ranged from 0.36 to 0.94 with an average of 0.61. 46.67 % of the estimated coefficients had values greater than 0.61, reflecting a high degree of genetic similarity among the cultivars whiles 31.11 % of the coefficients were equal to or less than 0.50, suggestive of considerable diversity. Dendrogram constructed based on SSR data revealed three main clusters of maize accessions with distinctive genetic profiles. The cluster patterns in most instances, revealed evidence of associations related to their pedigree records. The information generated in this study might be useful to breeders in Ghana for maize improvement through selective and cross breeding programs. It is thus recommended that accessions which revealed rare alleles such as ‘Obatanpa’, ‘Enibi’, ‘Etubi’, ‘Honampa’ and ‘Kwadaso Local’ be incorporated into breeding programs.
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements for the award of the Degree of Master of Philosophy in Agronomy (Plant Breeding), 2015