Abstract:
Genetic diversity and phylogenetic relationships among 141 cowpea (Vigna unguiculata
L. Walp.) accessions collected throughout the nine geographical regions of Ghana were
evaluated using simple sequence repeat (SSR) molecular markers. Twenty-five primer combinations pre-selected by their ability to polymerase chain reaction amplify SSRs from a set of test
cowpea germplasm were evaluated. Of these, 20 primer combinations gave reproducible
polymorphisms among 97.2% of the cowpea accessions tested, with the remaining accessions
being found to be genetically identical. The informative primer combinations revealed a total
of 74 alleles at 20 loci with an average of 3.8 alleles detected per locus. Variation in heterozygosity among cowpea SSRs ranged from 0.01 to 0.84 with an average occurrence of 0.19.
The polymorphism information content varied from 0.07 to 0.66 with an average of 0.38.
The Ghanaian cowpea accessions clustered into five main branches, each of which was loosely
associated with the geographical regions from which samples were obtained. Accession
GH2288 was found to be the most divergent cowpea accession compared with all others
including the outgroup IT84S-2049, a breeding line from Nigeria. Our results provide a framework for future studies aimed at the conservation and management of cultivated cowpea
germplasm in Ghana, and a good starting point for the selection of parental lines for genetic
improvement programmes
