RAPD-based genetic diversity study of fifty cassava (Manihot esculenta Crantz) genotypes

Fifty cassava clones were studied using RAPD technique. They included landraces from the Wenchi, Nkoranza, Dormaa Ahenkoro and Asonafo districts of the Brong Ahafo region of Ghana and three improved varieties. Genetic diversity of these genotypes was studied using four primers, OPK-01, OPR-02, OPR-09 and OPJ-14. A total of 41 different bands were detected. Levels of polymorphic fragments detected by the four primers ranged from 90% to 100%. By pooling bands from individual accessions together, mean number of fragments per accession per primer ranged from 5.50 +/- 1.04 for the Improved cultivars to 7.00 +/- 0.71 for populations of landraces from Dormaa. Mean frequencies of fragments not detected by the primers for the accessions were 0.524 +/- 0.12, 0.460 +/- 0.12, 0.561 +/- 0.12 and 0.523 +/- 0.12 for landraces from Wenchi, Nkoranza, Dormaa Ahenkro, Asonafo and the Improved varieties, respectively. The grand mean frequency of individuals showing fragments not present in populations was 0.522 +/- 0.10. Genetic diversity estimates ranged from 0.290 to 0.425 (mean 0.352 +/- 0.05) for primer OPK-01, 0.001 to 0.381 (mean 0.309 +/- 0.06) for primer OPR-02, 0.335 to 0.344 (mean 0.283 +/- 0.04) for primer OPR-09 and 0.152 to 0.352 (mean 0.261 +/- 0.07) for primer OPJ-14. Within the accessions mean gene diversity estimates were 0.316 +/- 0.03, 0.293 +/- 0.09, 0.331 +/- 0.02, 0.322 +/- 0.07 and 0.247 +/- 0.03 for accessions from Wenchi, Nkoranza, Dormaa Ahenkro, Asonafo districts and the Improved varieties, respectively. Interpopulational genetic divergence ranged from 0.069 to 0.203 (mean 0.119 +/- 0.04). Rate of nucleotide substitution among the landraces was 9.8 per cent per site per year, while that for the Improved varieties was 15 per cent.