Abstract The development of PCR-based, easily automated
molecular genetic markers, such as SSR markers,
are required for realistic cost-effective marker-assisted
selection schemes. This paper describes the development
and characterization of 172 new SSR markers for the
cassava genome. The placement of 36 of these markers
on the existing RFLP framework map of cassava is also
reported. Two similar enrichment methods were employed.
The first method yielded 35 SSR loci, for which
primers could be designed, out of 148 putative DNA
clones. A total of 137 primer pairs could be designed
from 544 putative clones sequenced for the second enrichment.
Most of the SSRs (95%) were di-nucleotide repeats,
and 21% were compound repeats. A major drawback
of these methods of SSR discovery is the redundancy
– 20% duplication; in addition, primers could not be
designed for many SSR loci that were too close to the
cloning site – 45% of the total. All 172 SSRs amplified
the corresponding loci in the parents of the mapping
progeny, with 66% of them revealing a unique allele in
at least one of the parents, and 26% having unique alleles
in both of the parents. Of the 36 SSRs that have
been mapped, at least 1 was placed on 16 out of the 18
linkage groups of the framework map, indicating a broad
coverage of the cassava genome. This preliminary mapping
of the 36 markers has led to the joining of a few
small groups and the creation of one new group. The
abundance of allelic bridges as shown by these markers
will lead to the development of a consensus map of the
male- and female-derived linkage groups. In addition,
the relatively higher number of these allelic bridges,
30% as against 10% for RFLPs in cassava, underscores
SSR as the marker of choice for cassava. The 100%
primer amplification obtained for this set of primers also
confirms the appropriateness of SSR markers for use in
cassava genome analysis and the transferability of the
technology as a low-cost approach to increasing the efficiency
of cassava breeding. Current efforts are geared towards
the generation of more SSR markers to attain a
goal of 200 SSR markers, or 1 SSR marker every 10 cM.