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Marker
assisted selection (MAS) deployment of the novel CMD resistance gene (CMD2) in African cassava gene pools
O. Ariyo,
A.G.O.
Dixon, N. Morante, H. Ceballos & M. Fregene
The
Rockefeller foundation funded project on the molecular mapping of genes
conferring resistance to the molecular markers tightly associated to a
new source of resistance cu in cassavas designated CMD2 have been identified. The
effectiveness of CMD2 against
a wide spectrum of virus strains in sub Saharan Africa, including the
aggressive Ugandan variant (UgV), makes its deployment very appealing in
protecting cassava production against the ravages of CMD in Africa.
Deploying CMD2 widely in African cassava gene pools requires breeding for
other biotic stresses, particularly CBB and CGM, as the CMD2 donor
parents have been found to be very susceptible to both.
A marker-assisted selection (MAS) project was initiated to
combine CMD2 with good genes for CBB and CGM resistance. MAS drastically reduces, by as much as 95% (for four genes),
the number of progenies carrying all required genes at the seedling
stage thereby increasing the efficiency and cost-effectiveness of
breeding. Several good
sources of CBB resistance and an excellent source of CGM resistance were
crossed to the donor genotypes TME3 and TME9, two sources of the CMD2
gene, or their resistant progenies. The progenies were evaluated by MAS
and phenotypically for CMD, CBB, and CGM.
The cost of using markers vs. conventional, phenotypic selection
against no markers was calculated to determine the cost effectiveness of
MAS. The logistics
and practicality of setting up and running a MAS laboratory is also
discussed.
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