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Report 2 (of 5): Stopping
the Rot - Mozambique
Introduction
Having gained independence in 1975,
Mozambique suffered two decades of civil war that
devastated the country and destroyed its farming industry
- the foundation of the economy. The destruction of
agricultural land severely affected many livelihoods
and led to dependence on a humble tuber: cassava.
Traditionally a subsistence food crop and a staple
food across Africa, cassava provides an important
source of energy for millions of people in tropical
countries. The crop provides a livelihood for up to
500 million farmers, processors and traders worldwide.
It has long been used as a famine reserve and food
security crop and Africa now produces more cassava
than the rest of the world combined.
Mozambique is the fifth largest producer
of cassava in Africa. The crop has helped to feed
and provide income to millions of poor farmers, but
a new danger is threatening to stop the road to recovery.
Large areas of cassava on the northern coast of the
country are being attacked by a little known disease,
cassava brown streak. Scientists at the Natural Resources
Institute (NRI) and the University of Bristol in the
UK have been working to identify the virus and its
disease-spreading carrier and to produce virus-free
material for distribution to farmers. The work is
part of the UK Department for International Development's
Crop Protection Programme, managed by Natural Resources
International, which aims to develop environmentally-friendly
technologies to reduce crop losses from pests and
diseases in developing countries.
Cassava
Cassava (Manihot esculenta)
is a hardy, drought-resistant tuber with an edible
root which grows in tropical and subtropical areas
of the world. Also known as yuca, manioc and mandioca,
it has become a staple food because of its tolerance
to drought, poor soil conditions and generally difficult
crop environments.
Cassava forms the basis of many products,
including food. In Africa and Latin America cassava
is mostly used for human consumption, while in Asia
and parts of Latin America it is also used commercially
for the production of animal feed and starch-based
products.
Cassava provides an important source
of energy for poor people in Africa, and forms a larger
part of total calorie intake than maize and sorghum.
Cassava root products are wide and varied and include
cooked fresh roots, flour, gari (roasted cassava),
pastes, starches, granules, drinks and medicines.
In most of the cassava-growing countries of Africa
the leaves are also consumed as a green vegetable,
which provides protein and vitamins A and B.
Growing
The production of cassava is dependent
on a supply of good quality stem cuttings, but it
is perhaps the only crop whose production is not specific
to a particular ecological region. In Africa, cassava
is mostly grown on small farms, usually intercropped
with vegetables, plantation crops (such as coconut,
oil palm or coffee), yam, sweet potato, melon, maize,
rice, peanut (groundnut), or other vegetables. Cassava
has the ability to grow on marginal lands where cereals
and other crops do not grow well; it can tolerate
drought and can grow in low-nutrient soils. Cassava
roots can be stored in the ground for as long as 24
months and some varieties for up to 36 months, enabling
harvests to be delayed until market, processing, or
other conditions are at their most favourable.
Food Security
In Mozambique, food security is a
big problem, and one third of the total population
is considered chronically food insecure. Subsistence
agriculture is the main form of livelihood, providing
more than 80 per cent of basic food needs.
Cassava is the basic staple in the
tropical and sub-tropical belt, as well as having
other uses. It is an important source of food security
because it can be grown on less productive land, and
it is a cheap source of income and food. As there
is no specific point at which it is mature, harvest
can be delayed until conditions are at their most
favourable. This flexibility gives cassava an important
added bonus.
Threats
Although cassava is a hardy crop that
grows well in Mozambique's dry climate, there are
several potential threats to its food value - toxicity,
pests and diseases.
Unripe cassava can contain high levels
of cyanogenic glucosides or cyanide in its edible
roots and leaves. These toxins affect the central
nervous system in humans, causing the medical condition
known as Konzo. The amounts of these toxic compounds
vary according to the species and growing conditions.
Sweet varieties usually have such small amounts that
they are considered harmless, while bitter varieties
have sufficiently high levels to require processing
to remove most of the toxins.
Also known as cassava poisoning, Konzo
is associated with eating poorly processed cassava.
Farmers who cultivate cassava have developed many
methods of detoxifying cassava. Boiling and drying
is used to make cassava with low cyanide levels safe
for consumption, but more rigorous procedures such
as grating, fermenting, and sun-drying are necessary
to effectively remove cyanide from those with a higher
toxicity.
Outbreaks of Konzo tend to occur where
populations have little food and have not been able
to wait until their cassava crop has fully ripened
before consumption. In Mozambique agricultural crises
caused by drought and civil war have forced the population
to eat insufficiently processed bitter cassava, often
after only one day of sun-drying.
The reproduction rate of cassava stem
cuttings is very low compared to grain crops, which
are grown from true seeds. The stem cuttings are bulky,
and highly perishable as they dry up within a few
days. They are also vulnerable to the pests and diseases,
which lead to the risk of yield losses for farmers.
Pests and diseases can account for
up to 50 per cent of yield losses. Common pests include
green mite and cassava mealybug, while cassava brown
streak disease and cassava mosaic disease are among
the most devastating crop viruses known to occur in
Africa.
Cassava Brown Streak Disease
Leaves from a plant affected by CBSD expressing
a range of symptoms.
© Cassava Protection Programme (CPP)
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Cassava brown streak disease (CBSD),
so called because of the brown lesions that appear on
the green stems of affected plants, causes damage to
the edible roots of cassava. The disease is transmitted
by whiteflies or by reproduction, where an infected
plant cutting is bred with a non-infected plant. Unlike
the more common cassava mosaic disease (CMD), which
has been extensively studied, CBSD is much less well
understood and more difficult to identify. It can be
undetectable until the crop has been harvested and the
brown lesions are then visible on the roots.
The symptoms of CBSD are very variable
and leaf symptoms may disappear when the plant regrows
after the dry season. Root rot begins to appear in
sensitive varieties from 4 months after planting a
diseased cutting. It then becomes severe 6 to 8 months
after planting, but in the least sensitive varieties
its appearance may be delayed until after the greatest
yield has been achieved, 12 to 15 months after planting.
CBSD in Mozambique
Natural Resources International's
Crop Protection Programme (CPP) has identified CBSD
as the most important cassava disease in coastal East
Africa, occurring from Malindi in Kenya through Tanzania
to the Zambezi River in Mozambique.
One method used to avoid severe CBSD
is to harvest early, but this still produces low crop
yields. In working to produce a better alternative
- a virus-free material for farmers - the CPP has
found locally cultivated varieties in Tanzania and
Mozambique that are resistant to or tolerant of CBSD.
These are being tested and only those that show potential
resistance to the disease are multiplied for distribution
to selected farmers. In Mozambique, local NGOs and
agencies carry out distribution of improved cassava
varieties. Farmers are then able to decide which varieties
they prefer to grow from cuttings in order to multiply
and pass on material to neighbours and nearby villages.
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A plant recently affected by CBSD
© Cassava Protection Programme (CPP)
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Using knowledge gained in Tanzania,
the CPP and NRI are working with World Vision and Save
the Children in Mozambique to help farmers turn abandoned
land into productive farms. A programme has been developed
to produce virus-free and CBSD-resistant varieties of
cassava for small-scale farmers in Zambezia and Nampula
Districts. These are two of the worst affected areas
- in Nampula CBSD has significantly reduced cassava
yields, causing food shortages in coastal districts
where this crop is the main staple food.
Controlling the Future
The key to managing CBSD is raising
awareness among farmers. Encouraging farmers to make
sure planting material stays free of the virus, not
only in areas where the disease is widespread, but
also in areas where the disease could become established,
is extremely important. Organisations involved in
distribution of cassava planting material must also
ensure that cuttings are free of any disease.
As a result of the project in Mozambique,
CBSD has been made a priority by the International
Institute of Tropical Agriculture (IITA) in their
programme to improve crop varieties in East Africa.
IITA's biological control programme has been working
to solve pest problems in cassava for many years using
natural and environmentally friendly methods. They
are developing improved cassava varieties that are
disease and pest resistant, low in cyanide content,
drought resistant, early maturing and high yielding.
For further information, please contact:
Natural Resources International
Frances Kimmins
CPP Programme Manager
Park House
Bradbourne Lane
Aylesford
Kent ME20 6SN
United Kingdom
Tel. +44 1732 878686/7
Fax +44 1732 220498/9
Email: info@nrint.co.uk
Website: http://www.nrinternational.co.uk/
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Websites
http://www.cpp.uk.com/
All the information on the CBSD project can be found
on the Crop Protection Programme website. The CPP
is managed by NR International and funded by the UK
Department for International Development.
www.iita.org/crop/cassava.htm
The International Institute of Tropical Agriculture's
improved cassava varieties programme
http://www.globalcassavastrategy.net/
http://www.cassava.org/
Further Reading
Books from ITDG Publishing
Village-Level Cassava Processing:
Distance learning package (10 Field guides and 1 tutor's
manual)
Z. Bainbridge and K. CNT US Wellings
£20.00, NRI, 1997, ISBN: 0859544567
CPP Publications
Management of Cassava Virus Diseases
in Southern Tanzania: Final Technical Report
R.J. Hillocks
Visit reports to Mozambique, 25 March
and 27 July 2001
These can be downloaded from the CPP
website in Word or PDF formats.
Cassava mosaic and cassava brown
streak virus diseases in Africa. Roots, 7
(1) Special issue.
R.J. Hillocks and J.M. Thresh
Cassava mosaic and cassava brown
streak virus disease in Zanzibar. Roots, 5
1998
J.M. Thresh and M.W. Mbwana
The Roots leaflets can be obtained
from:
Dr N. Mahungu, Regional Scientist SARRNET, IITA/SARRNET
Chitedzi Research Station
PO Box 30258, Lilongwe, Malawi
This document is an output from
a project funded by the UK Department for International
Development (DFID) and the European Commission (EC)
for the benefit of developing countries. The views
expressed are not necessarily those of DFID or the
EC.
Acknowledgements
ITDG wishes to thank Benedikte
Wolter and Penelope Silverside at Natural Resources
International for their assistance.
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