| Subproject Description
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Pesticides are not currently used on cassava
in Africa. The problem of whiteflies as pests and vectors on cassava
is an issue of food security.
Cassava is the third largest source of carbohydrates for human food
in the world, with an estimated annual yield of 136 million tons,
and Africa is the largest center of production; 57 million tones of
cassava were grown on 7.5 million hectares in Africa in 1985 (Fauquet
& Fargette, 1990). If one uses the definition that a staple food
is one that accounts for more than 200 calories per day in the diet
of an individual, then cassava is the second most important staple
food, after maize, in sub-Saharan Africa. Nearly 200 million people,
or 40% of the Sub-Saharan Africa population relies on cassava. And,
in some countries people derive approximately 1000 calories a day,
or 50% of daily food intake) from cassava (IITA, 1988).
Although Africa is the greatest producer of cassava, yields are low:
7.4 tones per hectare in 1989 (FAO), compared with a potential of
between 30 and 50 tones per hectare. There have been major research
successes in combating exotic pests which have devastated cassava
in Africa following their introduction from South America. Most prominent
amongst these has been the biological control of the cassava mealybug.
The effective continent-wide management of this pest resulted in incalculable
benefits to cassava farmers in Africa. The indigenous African cassava
mosaic disease (ACMD), however, is arguably responsible for even
greater reductions in the continent's cassava yield than were attributed
to cassava mealybug.
Responses to an international questionnaire sent to all cassava-producing
African countries (Fauquet & Fargette 1987) showed that ACMD is
present wherever cassava is grown (Figure 4). A survey of 20 farms
in Ghana revealed an average 96% of plants infected. Similarly, ACMD
incidence exceeded 80% in some districts of Kenya, and nearly 100%
in Ivory Coast. Subsequently, the ESCaPP Project has identified ACMD
as a key problem in Ghana, Benin, Nigeria and Cameroon, with overall
incidence of infection of 72, 55, 82 and 66%, respectively.
Presence and relative importance of African cassava mosaic disease
(ACMD) as estimated by agronomic services of different African countries
that produce cassava (Fauquet & Fargette, 1990).
Yield losses with individual cultivars have been reported from different
countries to range from 20 to 95% (Table 5; Fauquet & Fargette,
1990). Yield losses depend upon the mode and time of infection. In
Kenya, ACMD causes a loss of about 70% in tuber yield of plants derived
from infected cuttings (Bock, 1982). On the basis of available data,
the total reduction of cassava yield in Africa in plants derived from
diseased cuttings is at least 50%, or 50 million metric tones, per
year and may be equivalent to $2 billion ($US) (Fauquet & Fargette,
1990).
In 1988, reports were received of serious damage to cassava in northern
Uganda. Plants were severely affected by ACMD and resulted in such
low yields that local food shortages and starvation occurred. By 1989,
a severe epidemic was reported in the West Nile Region of northwestern
Uganda. A comprehensive survey of cassava in the area revealed that
the disease was spreading rapidly and causing crop failure. By April
1992, most fields were 80-90% infected and cassava production had
virtually ceased due to the poor yields of the diseased crops. In
some zones the area planted to cassava decreased by 95% because farmers
were aware of the futility of planting infected cuttings of the available
varieties. This epidemic has now covered 3/4 of Uganda and is moving
southwards at a rate of 10 to 20 km per year. It is estimated that
over 150,000 ha of cassava growing land is abandoned, equivalent to
over 2.2 million metric tones (US $440 million). This has caused food
shortages and famine in a number of districts particularly in the
eastern and northern regions where the crop has been a major staple.
The current epidemic in Uganda is a threat to cassava production in
all neighboring counties (Otim-Nape, 1996).
It is necessary to better-characterize the distribution and impact
of ACMD in the cassava-growing belt of Africa. In addition, special
efforts, such as phytosanitation, introduction of whitefly-resistant
cassava clones and disease monitoring, should be continued to both
understand and slow down the Uganda ACMD epidemic.
Current knowledge suggests that two cassava mosaic geminiviruses occur
in Africa with partially-overlapping distributions (Hong et al., 1993;
Swanson & Harrison, 1994). East African cassava mosaic virus
(EACMV) has been identified from coastal East Africa, Madagascar,
Malawi and Zimbabwe, and African cassava mosaic virus (ACMV) from
West, Central Africa and Kenya. Both viruses are transmitted by Bemisia
tabaci. Recent evidence, however, suggests that this classification
may be an oversimplification. New research suggests that the ACMd
epidemic in Uganda may be caused by a geminivirus distinct from both
EACMV and ACMV. And, the rate of expansion of the epidemic in Uganda
(approx. 20km per year) has also suggested the possible involvement
of a novel biotype of B. tabaci.
In summary, in spite of the devastating pest outbreaks and epidemics
being caused by WFs and WTVs, our knowledge in the tropics is quite
incipient. Without first generating a clearer picture of the nature
and extent of the whitefly problem, it will be impossible to develop
rational IPM programs.
Project Purpose :: To gather, generate and analyze, through
scientific and grower networks, baseline data relevant to the diagnosis
and characterization of whitefly and WTV problems in the tropics,
in order to propose a sound research agenda for improved understanding
of pest and disease dynamics, IPM development and IPM implementation.
Project Outputs ::
- International network for whiteflies and WTVs in the tropics
established
- Socio-economic and environmental impact assessed
- Epidemiological characterization initiated
- Agronomic characterization initiated
- Preliminary studies for Phase 2 conducted
Project Impact :: The immediate beneficiaries of Phase 1
of the Project will be a) IARC scientists, b) NARS scientists, c)
small holder farmers, and d) donor agencies. Additional, indirect,
beneficiaries will be the general community of whitefly and WTV
scientists and government policy makers.
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Partner institutions
and collaborating professionals :: |
Uganda
International Institute of Tropical Agriculture IITA - Kampala
Mr. Peter Sseruwagi
Mr. Geoffrey Okao-Okuja
National Agricultural Research Organization - NARO
Dr. William Otim-Nape
Mr. William Sserubombwe
Natural Resources Institute NRI - Uganda
Valentin Aritua
Centro Internacional de la Papa - CIP
Dr. Nicole Smit
Benin
International Institute of Tropical Agriculture IITA - Benin
Dr. Braima James
Mr. Brice Gbaguidi
National Agricultural Research Institute of Benin - INRAB
Mr. Norbert G. Maroya
Direction de l'Agriculture/Service Protection des Végétaux
- DRAGRI/SPV
Symphorien Saizonou
Ghana
Plant Protection and Regulatory Services Division - PPRSD
Mr. Anthony Cudjoe
Mr. Joseph Gyamenah
Nigeria
National Root Crop Research Institute - NRCRI
Thank-God N.C. Echendu
J.B. Ojo
Cameroon
University of Buea
Mr. Nelson Ntonifor
Agricultural Research Institute - IRA
J. Ambe Tumanteh
Kenya
Kenya Agricultural Research Institute - KARI
Dr. Joseph Kamau
Tanzania
Lake Zone Agricultural Research and Development Institute -
LZARDI
Mr. Joseph Ndunguru
Mr. Sato Jeremiah
Dr. Regina Kapinga
Malawi
Chitedze Research Station
M. P. K. J. Theu
Madagascar
Centre National de la Recherche Apliquee au Development - FOFIFA
Sahondramalala Ranomenjanahary
Ms. Jocelyn Ramelison
Zambia
Mt. Makulu Research Station
Mr. George Kaitisha
United Kingdom
John Innes Centre - JIC
Dr. Peter Markham
Robert Briddon
Gina Banks
Natural Resources Institute - NRI
Dr. Richard Gibson
Dr. Michael Thresh
Germany
Biologische Bundesanstalt für Land und Forstwirtschaft
- BBA
Dr. H. Josef Vetten
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