CASsava Sustainable Advancement & Nurturing by discovery of Disease Resistance Alleles
Project consortium and funding
Prof. H. Vanderschuren
University of Liège (Belgium)
Prof. M.E.C. Rey
University of the Witwatersrand (South Africa)
Dr J-L Gallois
INRA – Avignon (France)
Prof. Evans Nyaboga
University of Nairobi
Prof. Kahiu Ngugi
University of Nairobi
Thematic and geographic area of the project:
- Sustainable food security
- Plant sciences
- Pest and disease control
Cassava is the most important staple root crop in the world, providing food energy intake for nearly a billion people and supplying raw material for diverse industrial purposes worldwide. In several regions of Africa, cassava is also considered as a food security crop because of its relatively good performance in adverse environments and flexible harvest period. However, cassava production is largely constrained by viral diseases, the most damaging biotic stress in cassava fields in Africa. In particular cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) causes yield losses estimated at 24% and 90%, respectively. Cassava brown streak disease (CBSD) often leads to necrosis of storage roots making them unfit for consumption and unsuitable for industrial processing.
In order to limit the impact of cassava viral diseases, a multipronged approach will be taken:
A) SOURCING SUSTAINABLE AND ROBUST VIRUS RESISTANCE
We will investigate natural resistance against cassava viral diseases as follows:
- identification of resistance gene(s) underlying the reported CMD2- and CMD3-based resistance/tolerance against CMD in cassava,
- identification and characterization of recessive resistance alleles against CBSD and,
- analysis of cassava allelic forms from elongation factor genes known to confer recessive resistance against viruses causing CBSD
B) BUILDING STRATEGIES FOR CONTINUOUS SUPPLY OF DISEASE-FREE PLANTING MATERIAL TO FARMERS
Distribution of virus resistant cassava (identified and developed in A) to local farmers should be part of a sustainable cassava seed system. The consortium in collaboration with the National Agricultural Research Systems (NARS) and Community Based Organizations (CBOs) will develop novel and locally adapted solutions to produce virus-free planting material.
Project’s main objective(s):
The CASSANDRA proposal intends 1) to identify and characterize natural virus genetic resistances in the cassava germplasm for rapid introgression in farmer-preferred varieties and 2) to develop methods for on-field sanitation of planting material.
Theory of Change and Impact Pathway
Summary ToC with assumptions
Cassava is an important food security and industrial crop in Sub-Saharan Africa. Viral diseases are the most important biological constraint to cassava production in Africa. Cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) causes yield losses estimated at 24% and 90%, respectively. Cassava brown streak disease (CBSD) often leads to necrosis of storage roots making them unfit for consumption and unsuitable for industrial processing. The problem of cassava viral diseases is exacerbated by the propagation method used by farmers. The vegetative multiplication of stem (stem cuttings) is the most common practice for propagation and promotes the dissemination and maintenance of viral diseases in the field. Current methods to mitigate cassava viral diseases includes the breeding and distribution of virus resistant cassava varieties as well as the large scale in vitro multiplication of disease-free cassava planting material. The in vitro multiplication is not cost-effective and therefore not affordable to small scale farmers. Two promising options to reduce the impact of viral diseases in cassava production include: 1) identification and characterization of natural resistance (against CMD and CBSD) for rapid combined introgression into farmer-preferred varieties (middle to long term impact) and 2) development of easy and cost-effective methods to reduce viral loads in cassava planting material that can be readily used by farmers and seed multipliers.
Expected outcomes and impact:
The implementation of innovative research programs aiming at identifying or creating natural recessive resistance against CBSD in the cassava germplasm is an essential step to provide durable resistance to farmers. The complete characterization of genes involved in natural resistance against CMD is also key to advance breeding lines combining resistances against both viruses. In parallel, the development, in close collaboration with NARS and CBOs, of simple and cost-effective methods to reduce viral loads in cassava seeds (stem cuttings) will serve as an immediate action plan to mitigate the impact of viral diseases in Africa. Our consortium includes key stakeholders (national research centers (KALRO and ARC) as well as CBOs) to ensure impact for resource poor small-scale farmers. Since smallholders account for 100 percent of cassava producers in Kenya, increasing cassava production through sustainable management of virus diseases will increase income of the resource poor farmers. The greater productivity of the superior, disease resistant varieties will also result in less land utilization, hence reduced land degradation. In addition, due to the use of virus resistant, superior cultivars, there will be reduced application of seed dressing and foliar insecticides, hence a safer environment.