Biology Reference
In-Depth Information
M. Walkerae
(Wae 001)
SM909-25
X
Three cycles of evaluation of
delayed PPD confirmed transfer of
the trait from the wild parent
F
1
CW429-1
SM909-25
MTAI8
X
Evaluation, genotyping and QTL
mapping of delayed PPD to
develop markers for MAS
CMD Resistant
Parental Lines
...C4, AR30-3,
C33, C144 -1...
BC
1
3 families
X
Shipment of BC
2
families to NARs
partners and selection of best lines
for crosses to elite line for variety
development
CIAT and NARs
Elite Lines
BC
2
24 families
X
Evaluation of BC
3
families to NARs and CIAT and selection
of best lines that combine delayed PPD, resistance to CMD,
and other end-user preferred traits
BC
3
40 families
Fig. 15.7.
Modified advanced backcross scheme used for introgressing delayed post-harvest deterioration from
M. walkerae
into
M. esculenta
species in combination with MAS for CMD resistance. For a color version of this figure, please refer to the
color plate.
content) (Asiedu et al. 1992; CIAT 2004; Akinbo
et al. 2011). The only source of post-harvest
physiological deterioration (PPD) has been iden-
tified in an interspecific hybrid between cas-
sava and
M. walkerae
(Bertram 1993). Backcross
derivatives have been developed from
M. walk-
erae
for delayed PPD and for protein content
(Blair et al. 2007). The only source of resistance
to the cassava hornworm was identified in fourth
backcross generation progenies of
M. glaziovii
(Jennings 1976; Chaviarriaga et al. 2004). These
genetic resources hold immense opportunities
for the cassava crop, but their full utilization is
dependent on their being improved for adaptation
in targeted ecologies and countries. Pre-breeding
activities to transfer genes from wild relatives
into cassava is being done and progenies show-
ing the traits of interest are utilized to transfer
those traits to partners.
Gene mining of wild relatives of cassava in
order to introgress useful genes from the wild
gene pool into LA cassava was done at CIAT
using an advanced backcross scheme (Blair et al.
2007). A modified advanced backcross scheme
(Figure 15.7) was used to introgress high pro-
tein and delayed PPD into cassava. The acces-
sions of wild relatives of cassava with high
protein or with delayed PPD were crossed to
elite cassava parental lines and traits were then
evaluated. The first backcross generations (BC
1
)
developed as shown in the scheme (Figure 15.7)
were found to show the target traits. These acces-
sions were then backcrossed again to cassava
with CMD resistance, which were then selected
with
CMD2
markers before shipment to Africa.
About 140 genotypes of protein-rich accessions
developed for CMD resistance via MAS, desig-
nated as CRCR lines, were shipped to Ghana,
Nigeria, Tanzania, and Uganda. Similarly, about
500 genotypes of delayed PPD and MAS-bred
for CMD resistance were shipped to the same
African countries under the cassava-breeding
Community of Practice (CoP) project supported
by the CGIAR GCP.
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