Lokko et al. 2005; Rabbi et al. 2014). Landraces have
been considered as a valuable source for useful genes
in breeding programmes, including resistance to
CMD, because they contain co-adapted gene complexes
with tolerance and adaptation to disease and
specific ecological conditions (Zeven 1998; Akano
et al. 2002; Okogbenin et al. 2007, 2012).
The conventional breeder has the challenge of
screening for large numbers of progenies and difficulty
in screening at the seedling stage where most genotypes
look vigorous and healthy until a later stage.
There are several cycles of selection (preliminary,
advanced and uniform yield trials) before the multilocation
yield trials, a process that takes not less than
8 years. The number of years required for the evaluation
of promising genotypes, approximately
10 years, is prohibitive and is a bottleneck to increased
productivity. Hence an effective means to speed up
identification of genotypes with high performance is
clearly required for effective breeding. Biotechnology
offers this opportunity with tools such as Marker
Assisted Selection (MAS).
In the past decade many research institutes and
breeding companies have started applying MAS to
increase the effectiveness of selection in breeding to
shorten the time required developing varieties (Ribaut
and Hoisington 1998; Goff and Salmeron 2004). In
cassava, the application of MAS has been developed
more recently compared to other major crops, with the
construction of genetic linkage maps (Akano et al.
2002).
Current resistance against CMD in Africa is of two
types, where the first is quantitative resistance derived
from Manihot glaziovii and the second is qualitative
resistance from a single gene (CMD2) which is a major
dominant gene (Rabbi et al. 2014). It was first
identified in landraces from Nigeria and other West
African countries (Akano et al. 2002). Genetic mapping
of the qualitative resistance found a locus on
linkage group 16 which explained 74 % of the
phenotypic variance in CMD, which was most likely
the CMD2 locus reported by Akano et al. (2002), but
with a higher mapping resolution of this locus (Rabbi
et al. 2014).
The objectives of this study were to use a marker
assisted breeding approach to evaluate progeny of
crosses of CIAT genotypes with CMD resistance with
locally adapted genotypes in Ghana with varying
degrees of resistance to CMD, and to search for