Discussion
The percentage of polymorphism between two parents
of each population screened with 542 SSR markers
was 21 %on average among the nine populations. The
moderately low level of polymorphism may be due to
low molecular diversity among the parental genotypes
as earlier suggested by Mace et al. (2006). The fact
that the two populations in which each of the four SSR
markers (SSRY68, NS323, [ESTs]SSRY7 and
[ESTs]SSRY47) was found to be polymorphic shared
one parent in common suggests that the common
parent might be the source of the QTL to which such
marker is associated.
In this study, nine molecular markers linked to EB
in cassava were identified by BSA. The inability to
find any of the 542 molecular markers linked with
QTLs associated with EB in the remaining three
populations may be due to the fact that cassava genetic
map is still unsaturated (Okogbenin 2004). A marker
may fail to be detected as polymorphic between the
two bulks in spite of linkage to a QTL if the frequency
of the rare allele in a bulk is sufficiently high that it can
alter the banding pattern to one indistinguishable from