RESULTS AND DISCUSSION The high degree of SSR polymorphism that was observed
Out of 86 primers tested, 51 produced other crop species [17, 18]. About 31% of the of SSR
non-polymorphic fragments, 1 gave non-scorable band markers were polymorphic in all cassava genotypes under
and 3 had no amplification. The remaining 31 primers study. SSR markers have been used to study genetic
amplified from 1 to 24 polymorphic fragments which diversity in a large number of plant species, including
ranged from 50 to 500 bp. Polymorphic and monomorphic wheat, sunflower and many other crops. In this study,
SSR loci were detected (Fig 1). In some cases, it could not they also showed clear distinctions in the cassava
be unambiguously determined whether a particular SSR genotypes.
locus was monomorphic or polymorphic. However, as In addition to measuring genetic diversity,
shown in Fig.1, lanes with no bands were observed, verification in mutual relatedness of these cassava
indicating either absence of alleles (null alleles) or alleles genotypes from different regions in Africa was
below the detection limit. Due to the limited resolution of assessed. The dendrogram constructed on NTSYS
the SFR gels to about 5 bp, the number of alleles using similarity index based on UPGMA showed
determined in this assay, represent a minimum estimate. genetic similarity among cassava genotypes, with the
The actual number of alleles per locus as well as the coefficient of genetic similarity ranging from 0.43 to
number of alleles per genotypes may be higher. 0.86. At 0.70 similarity coefficient, the 24 cassava
For some SSR loci, the bands observed on the SFR genotypes clustered into ten main groups (Table 2).
gels were larger than the expected size, based on the There was a strong genetic relationship between the
predicted location of the primers on the sequence. Nigeria landraces and strong similarities between
Since the primers for PCR were based on cDNA TME 1786 from Kenya and TME 530 from
sequences while the PCR reaction for amplification of the Malawi and between TME 225, TME 638 and TME 568
SSR was carried out on genomic DNA, these larger bands (Fig.2). This indicates the strength of SSR markers in
most likely indicate the presence of intron sequences. detecting relationships and diversity among germplasm.
in cassava in this study is comparable to the results of
Fig. 1: Allelic variation of selected SSR loci of cassava genotypes
a: Example