Biology Reference
In-Depth Information
Table 15.2.
Root yield and dry matter content of cassava genotypes bred for CMD resistance via MAS and nominated for
release in Tanzania
Clones
Pedigree
Root yield (t/ha)
Dry matter (%)
CI85-4
AR37-38 x Kifumulo
63.8
31.5
C119-3
CR52A-19 x Namikonga
50
30.8
C7-46
Kalolo x AR9-44
57.5
33.9
C61-1
Amani x CR20A-6
53
32.4
C17-27
Namikonga x AR9-18
77.5
29.4
B201-97
Mkiwa
73
34.1
B2013-44
AR9-18
75
35.5
C170-11
AR30-4 x Kifumulo
86.9
31.5
C211-49
Namikonga x AR30-3
53.8
32.4
C179-4
AR17-25 x Kifumulo
54
34.2
C150
AR38-30 x Muzege
76.9
52.1
Kiroba
Local check
14
36.4
to improve the introduced germplasm for CBSD
resistance. The marker-assisted breeding scheme
used is summarized as follows:
of the clones at many locations with high
CMD and CBSD pressure.
9. In collaboration with the seed regulatory
body in Tanzania, national performance tri-
als, and distinctiveness, uniformity and sta-
bility tests were conducted.
10. Release of cultivars.
1. CIAT cassava elite lines that are high yield-
ing and resistant to CMD (screened using
markers for
CMD2
) were introduced from
CIAT into Tanzania.
2. Tanzania's farmer-preferred germplasms
that are generally low yielding but toler-
ant/resistant to CBSD were selected.
3. Field evaluation of germplasm from CIAT
and Tanzania to select parents for hybridiza-
tion program.
4. Introgression of genes from CIAT
germplasm to Tanzania's elite germplasm.
5. Screening of F
1
progenies from Tanzania for
CMD2
resistance at CIAT, using markers for
CMD.
6. Field evaluation of CMD-resistant clones
and phenotypic selection of clones with dual
resistance to CMD and CBSD.
7. Intensive farmer-participatory research con-
ducted to identify farmer preferences and
criteria used in selecting suitable cassava
clones. Also phenotypic selection for high
yield
(d) Transfer of Novel Traits to Africa
Cassava has been transformed from a food crop
into a cash and industrial crop, and breeding to
improve its quality and commercial traits has
assumed high importance in cassava growing
countries. Improvement for quality traits in cas-
sava is mainly targeted at enhancing the low
cyanogenic potential in the roots; increasing pro-
tein content in the roots, the waxy starch con-
tent, beta carotene content, and dry matter con-
tent; reducing post-harvest physiological deteri-
oration; and reinforcing other consumer prefer-
ences related to cooking quality. Unfortunately,
the genetic variation for these traits is highly lim-
ited in
M. esculenta.
Wild
Manihot
species pro-
vide a wealth of useful genes for the cultivated
species,
M. esculenta
.
M. esculenta
sub spp.
flabellifolia
,
M. peru-
viana
and
M. tristis
have been identified as
sources of high levels of nitrogenous compounds
(with
and
dual
resistance
to
CMD
and
CBSD.
8. Field resistance to CMD and CBSD con-
firmed (phenotypically) by intensive testing
possible
implications
for
high
protein
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