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The Cassava Breeding Community of Practice in Africa
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Molecular Marker Analysis and Validation of Resistance to Cassava Mosaic Disease
in Elite Cassava Genotypes in Nigeria
E. Okogbenin,* C. N. Egesi, B. Olasanmi, O. Ogundapo, S. Kahya, P. Hurtado, J. Marin, O. Akinbo,
C. Mba, H. Gomez, C. de Vicente, S. Baiyeri, M. Uguru, F. Ewa, and M. Fregene
Cassava (Manihot esculenta Crantz), a highly heterozygous crop, is devastated by cassava mosaic disease (CMD).
The discovery of the CMD2 dominant gene is helpful in the genetic analysis of CMD resistance. Molecular markers
for CMD2 gene were used to introgress CMD resistance into Latin American cassava genotypes and validated in the
field for 4 yr for stability of resistance conferred by CMD2.
Field screening identifyed 64 Latin American genotypes with stable resistance to CMD.
Resistance to CMD of two Nigerian cassava cultivars (TMS 97/2205 and TMS 98/0505) was analyzed with markers
and in the field. Molecular data indicated that CMD resistance in the two Nigerian cultivars was mediated by the
CMD2 gene. Results showed TMS 97/2205 to be highly resistant to CMD in three ecological zones in Nigeria.
Further genetic analysis of this genotype as a source of high level of resistance to CMD using a segregating F1
population derived from a TMS 97/2205 × NR 8083 cross was initiated using 530 simple sequence repeat (SSR)
markers to identify quantitative trait loci (QTL) for CMD resistance.
A marker (NS198) associated with a QTL for CMD resistance, explaining 11% of the phenotypic variance observed,
was identified.
The combined effect of this QTL and CMD2 may account for the high level of resistance of TMS 97/2205.
The resistance profile of the evaluated CMD2 genotypes in growth cycle was not uniform and was affected by
genetic background. The discovery of a new QTL (CMD3) for CMD resistance in TMS97/2205 offers new
opportunities for pyramiding CMD genes for enhanced durability of CMD
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Written by Administrator
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Tuesday, 14 May 2013 19:51 |
Phenotypic approaches to drought in cassava: review
Emmanuel Okogbenin1*, Tim L. Setter 2, Morag Ferguson3, Rose Mutegi3, Hernan Ceballos4,
Bunmi Olasanmi1 and Martin Fregene5
1 Cassava Program/Biotechnology Program, National Root Crop Research Institute, Umudike ,Abia,Nigeria
2 Department of Crop and Soil Science,Cornell University,Ithaca,NY,USA
3 International Institute of Tropical Agriculture,Nairobi,Kenya
4 International Center for Tropical Agriculture,Cali,Colombia
5 Donald Danforth Plant Science Center,St.Louis,MO,USA
*e-mail:
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Cassava is an important crop in Africa, Asia, Latin America, and the Caribbean. Cassava can be produced adequately in drought conditions making it the ideal food security crop in marginal environments Although cassava can tolerate drought stress, it can be genetically improved to enhance productivity in such environments. Drought adaptation studies in over three decades in cassava have identified relevant mechanisms which have been explored in conventional breeding. Drought is a quantitative trait and its multigenic nature makes it very challenging to effectively manipulate and combine genes in breeding for rapid genetic gain and selection process. Cassava has a long growth cycle of 12–18 months which invariably contributes to a long breeding scheme for the crop. Modern breeding using advances in genomics and improved genotyping, is facilitating the dissection and genetic analysis of complex traits including drought tolerance, thus helping to better elucidate and understand the genetic basis of such traits.A beneficial goal of new innovative breeding strategies is to shorten the breeding cycle using minimized, efficient or fast phenotyping protocols. While high throughput genotyping have been achieved, this is rarely the case for phenotyping for drought adaptation. Some of the storage root phenotyping in cassava are often done very late in the evaluation cycle making selection process very slow. This paper highlights some modified traits suitable for early-growth phase phenotyping that may be used to reduce drought phenotyping cycle in cassava. Such modified traits can significantly complement the high throughput genotyping procedures to fast track breeding of improved drought tolerant varieties. The need for metabolite profiling, improved phenomics to take advantage of next generation sequencing technologies and high throughput phenotyping are basic steps for future direction to improve genetic gain and maximize speed for drought tolerance breeding.
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Written by Administrator
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Monday, 13 May 2013 19:47 |
Performance of nine cassava (Manihot esculanta Crantz) clones across
three environments
Peprah Bright Boakye1*, Ofori Kwadwo2, Asante Isaac K.3 and Elizabeth Yaa Parkes1,4
1Crops Research Institute, Fumesua, Kumasi, P. O. Box 3785, Ghana.
2Department of Crops Science, University of Ghana, Legon.
3Department of Botany, University of Ghana, Legon.
4International Institute of Tropical Agriculture, Ibadan, Oyo State, Nigeria.
Accepted 18 March, 2013
The study was carried out to quantify the genotype × environment interaction
(G × E) and to estimate the phenotypic stability by genotype genotype × environment
(GGE) biplot of nine cassava clones comprising 5 hybrids, 3 parent checks and 1
improved variety. The study was planted across three different environments; Fumesua, Pokuase
and Ejura representing forest, coastal savanna and forest transition zones, respectively.
Genotype main effect was significant (P < 0.001) for fresh root yield and dry matter content,
G × E interaction effect was significant (P < 0.001) for fresh root yield only and
environment main effect was significant (P < 0.01) for only fresh root yield. The most stable
clone for fresh root yield with above average performance was La02/026 (hybrid).
The high genotype and low environment effects, and the relatively low interaction on dry matter
content imply that evaluation and selection can be effectively done in fewer environments to
select clones with high performance for the trait whiles fresh root yield requires multiple
environments to identify clones with broad and specific adaptation.
Key words: Genotype genotype × environment (GGE) biplot, stability, fresh foot yield, dry matter content,
*Corresponding author. E-mail:
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Cassava can become Africa's new crash crop |
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Written by Administrator
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Friday, 19 April 2013 16:53 |
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Cassava can become Africa's new crash crop
Cassava is crucial to the food security of millions of people in sub-Saharan Africa,
but historically it hasn't had quite the same level of attention or research that maize,
rice and wheat have. That is now starting to change, with new varieties of the plant
addressing some of its nutritional and physiological shortcomings and helping to
transform cassava into an African cash crop with a more versatile role to play in development |
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