Morphological and molecular based diversity studies of some cassava (<i>Manihot esculenta crantz</i>) germplasm in Ghana

Abstract

Cassava (Manihot esculenta Crantz) is an important food crop in many tropical countries in Africa, South America and Asia. However, yields are below the productivity of the crop. This requires breeding and selection for improved varieties. The current study therefore investigated genetic diversity among some Ghanaian preferred accessions which could be used for breeding purposes. Genetic diversity of 43 cassava accessions was determined using 14 morphological descriptors and 20 SSR primer pairs. Principal component analysis (PCA) indicated that the first three principal components accounted for 72.7% of the total variation with PCA1, PCA2 and PCA contributing 46.6, 14.7 and 11.4%, respectively. The size of amplified alleles ranged from 75 to 350 bp, most of which were closed to the published values. The polymorphic information content (PIC) values ranged from 0.07 for SSRY181 to 0.75 for SSRY175, with an average of 0.52. Gene diversity was high and the average observed heterozygosity was 0.77. Both morphological descriptors and SSR markers were able to group the accessions into distinct clusters independent of locality of collection. However, where the morphological descriptors indicated some accessions were the same, SSRs markers were able to distinguish them into distinct genotypes with some located in different clusters. The wider genetic diversity observed using SSR markers would be valuable for efficient management of germplasm and for effective utilization of materials in breeding programmes to produce hybrids of desirable characteristics. Therefore, the application of morphological descriptors in management of germplasm should be backed by the use of molecular markers.

Key words: Cassava germplasm, simple sequence repeat (SSR), morphological descriptors, genetic diversity