Plant biotechnology: the future for sustainable banana
and plantain production in Africa
Nicolette Schinzl
 The fourth most important food crop in the world after rice, maize and wheat,
is the humble banana and its relative, the plantain. Millions of people in
Africa (one hundred million in Africa alone), South America and Asia rely on it
as part of a staple diet, although it has many other uses.
Its leaves are used to cook and transport food, to make baskets and
handcrafts, and it is even used to produce liquor. In Africa, a mere one per
cent of the annual 20 million tons of banana produced by the Eastern and
Southern African regions is exported, while the Western and Central African
regions export only four per cent of their 11 million tons annually. This shows
the tremendous dependence on it as a food source of high nutritional
content.
But crops are not keeping pace with population growth, and banana and
plantain production in Africa is hampered by many constraints, having direct
implications on issues of food security. This is compounded by a lack of
resources and money to control diseases and pests by means of expensive chemical
pesticides which are all too often ecologically unsound options anyway. In order
to find safe and affordable alternatives to controlling banana diseases and
pests, research surrounding plant biotechnology, in combination with plant
molecular genetics, is essential to finding viable solutions for the cultivation
of superior plants and ultimately, optimal and healthy harvests.
Banana disease research
The Banana Diseases Research Project (BDRP) forms part of the Forestry and
Agricultural Biotechnology Institute (FABI) at the University of Pretoria in
South Africa. FABI is a multi-disciplinary, post-graduate academic institution
aimed at producing plant scientists sensitive to the agricultural needs of the
African continent. The project is headed by Dr. Altus Viljoen and includes a
team of research scientists and post-graduate students who are enrolled with the
Departments of Microbiology, Plant Pathology and Botany. The programme
researches banana disease and pest control, banana microbial phylogenetics,
banana functional genomics and banana tissue culture, all of which have ongoing
student research projects. Roughly divided into two areas, the programme
consists of integrated pest and disease management (IPDM), and banana
biotechnology, which naturally overlap and incorporate aspects of one another.
Since bananas are seedless, they do not rely on the germination of seeds to
propagate themselves. As a result, their genetic diversity is very limited.
Breeding in order to develop new cultivars that are not only disease-resistant
but also able to withstand environmental extremes in Africa is difficult.
Cultivars must be vegetatively propagated using plant tissue culture and this is
a time-consuming and costly process requiring large tracts of experimental
fields. Also, fruit characteristics in new cultivars are seldom acceptable to
the very conservative taste of the consumer.
Banana biotechnology
Banana tissue culture is a first-generation plant biotechnology tool used to
curtail the spread of pests and diseases, especially fungal and bacterial wilt
diseases, by making disease-free planting material available for the propagation
of new crops. Simple tissue culture techniques such as shoot-tip and embryo
culture are well-developed in Africa and have greatly improved banana breeding,
whereby the shoot meristem is extracted from the male flower and aseptically
multiplied into hundreds of shoots for eventual planting in fields.
 Fungal diseases are a major source of concern in Africa, which have, over the
centuries, been introduced to the continent via infected plant material or other
yet unknown routes. Among the fungal diseases most prominently found in Africa
is the Sigatoka complex comprising two types: black and yellow Sigatoka. In
Africa, the more virulent black Sigatoka has rapidly become the most serious
constraint to banana and plantain production. It has in some countries reached
epidemic proportions. This disease makes the banana fruit prone to premature and
uneven ripening, causing reduced yields. It also affects the leaves, which
shortens the banana's lifespan and makes it difficult to market because a
minimum of five functional leaves is needed to transport the fruit successfully.
 Black Sigatoka can reduce crop yields by 75%, severely endangering the food
supply of resource-poor subsistence communities in Africa. Another serious
fungal disease in Africa is Fusarium wilt or Panama disease, which attacks the
roots of the banana plant, affecting the vascular system required for mineral
and water transport. It has evolved into three races that attack certain banana
species only. Race 4, a sub-tropical variant of race 3, is a strain affecting
bananas in South Africa specifically and can only be controlled by using banana
cultivars that are disease-resistant. In addition to this, once a crop of
infected bananas has been harvested, the field from which it is taken cannot be
used again for some time because the fungal pathogen remains active in the soil
for years.
Combating the banana weevil
One of the studies being conducted within the BDRP at the moment is
investigating ways of combating the banana weevil, a pest that causes rapid
plantation decline in Eastern Africa and a phenomenon called "yield decline
syndrome" in Western Africa.
 The weevil's eggs are deposited inside the banana tissue and once hatched,
they tunnel through the corm for feeding and growth. This reduces water and
mineral transport, weakening the plant, impeding bunch weight (yield) and
causing plants to topple during windstorms. Although cultural weevil control
methods have helped, they unfortunately require high labour and material input.
Consequently, the breeding of weevil-resistant plants as a way of long-term
intervention has gained momentum, especially for small-scale farming enterprises
in Africa.
The study is led by Andrew Kiggundu (PhD) of Uganda, and uses plant
biotechnology in an attempt to identify candidate genes for genetically
modifying and enhancing traits in weevil-susceptible banana plants (the ones
preferable to consumers). The strategy aims at transferring well-characterised
traits from other plant species that are widely used for food production, into
banana plants. More specifically, the project focuses on transferring the gene
responsible for producing proteinase inhibitors in plants. These inhibitors are
small proteins found in many plant seeds such as beans, a food regularly eaten
by humans.
Their function in plants is to act as a natural defense against insect
infestation by preventing efficient food digestion in the gut of insects and
also in nematodes. The elegance of this natural defense mechanism has yielded
several studies that have demonstrated the effectiveness of using proteinase
inhibitor gene transfer technology. For example, using a proteinase inhibitor
from a papaya plant, weevil larvae reared on banana stems containing a
proteinase inhibitor solution showed a reduction of up to 76% of early larval
growth.
Markers for disease resistance
 Other projects at the BDRP focus on molecular biology-based genetic
techniques, such as DNA and protein marker-assisted selection for pathogen and
pest identification, and to isolate banana traits such as fungal and weevil
resistance. Although this technology is not as highly developed for bananas as
for other major crops, the application of developed markers to improve the
banana genetically has the potential to notably enhance the efficiency and speed
of the process. One of the challenges lies in developing genetic markers that
will allow for the rapid diagnosis of asymptomatic planting material, soil and
irrigation systems for pathogens, and to use molecular and genetic markers to
understand pest and pathogen population structures as an aid to effective pest
management programmes.
These are but a few of the research methodologies being explored by the BDRP
at present. They and other initiatives throughout the continent of Africa are
dependent not only on the financial support of domestic and foreign governments
and organisations, but also on the furtherance of training opportunities for
young African scientists in plant biotechnology, to be made accessible both
abroad and under African conditions.
If African countries are to move away from mainly subsistence production of
banana crops to a broadened share in local and international markets, it is
vital that adequate and effective mechanisms for disease and pest control are
driven aggressively. Successful commercialisation and consumer acceptance of a
genetically modified product is tantamount to its export potential: consumers'
fears regarding bio-safety need to allayed by competent, accurate and
transparent research. No doubt the BDRP's programmes and FABI as a whole will
continue to play an invaluable role as a collaborator in such important research
with other industry partners worldwide, for the future development of IDPM and
genetic improvement of banana crops.
More Information
Infrastructure and research capacity of FABI
· Situated at the University of Pretoria, FABI houses research laboratories,
seminar rooms and greenhouses, and is equipped with sophisticated instruments
such as a Licor-DNA analyser, a DNA sequencer and a DNA micro-arrayer. A large
nursery and greenhouse facility forms part of the University's experimental
farm.
· FABI caters for students from all parts of the world, and its teaching body
is made up of scientists who hold full-time positions as lecturers or
professors, all rated by the National Research Foundation of South Africa.
· FABI conducts diagnostic and plant pathology services, and samples of plants
suspected of being diseased may be sent to them for analysis from farmers and
producers.
· FABI conducts regular field visits to banana growing regions in South Africa.
Disease surveys are done, and various activities on disease identification and
management are undertaken in an effort to interact with producers and other
interested parties.
· Prospective post-graduate students from South Africa and other African
banana-growing countries are encouraged to contact Dr. Altus Viljoen at FABI for
information pertaining to future projects, grants and internships (Email: altus.viljoen@fabi.up.ac.za).
· For more information relating to all aspects of FABI's research activities,
visit their comprehensive website at www.fabi.up.ac.za
Andrew Kiggundu is supervised by Prof. K. Kunert (UP, FABI); Dr. A.
Viljoen (UP, FABI); Michael Pillay (International Institute of Tropical
Agriculture [IITA], Uganda); Cliff Gold (IITA, Uganda).
Glossary
plantain - a green fruit resembling a banana, eaten cooked as a staple food
biotechnology - the use of biological organisms or living microorganisms in
industrial production
phylogenetics - the study of the evolutionary history of a species, genus or
group, as contrasted with the study of the development of an individual
genomics - the study of the relationships between gene structure and
biological function in organisms
cultivar - a variety of a cultivated plant that is developed by breeding and
has a designated name
meristem - embryonic plant tissue that is actively dividing, such as is found
at the tip of stems and roots
aseptic - free of disease-causing microorganisms
virulent - extremely poisonous, infectious, or damaging to organisms
epidemic - an outbreak of a disease that spreads more quickly and more
extensively than would normally be expected
subsistence (farming) - farming that generates only enough produce to feed
the farmer's family, with little or nothing left over to sell
vascular system - the fluid-carrying vessels of a plant
pathogen - something that causes disease, such as a bacterium or virus
corm - short swollen underground stem base in some plants, that stores food
over winter and produces new foliage in spring
proteinase - an enzyme that catalyses (sets off) the hydrolysis (chemical
reaction of a compound reacting with water, causing it to break down) of a
protein into its component amino acids
inhibitor - a substance that stops or slows a chemical reaction
nematode - a worm, often microscopic, with a cylindrical unsegmented body
protected by a tough outer skin
diagnosis - the identification of an illness or disorder in a person, animal
or plant
asymptomatic - not showing or producing signs of a disease
pathology - the scientific study of the nature, origin, progress and cause of
a disease
Bibliography: Encarta World English Dictionary, Bloomsbury/Microsoft Encarta, Bloomsbury
Publishing Plc, 1999 ed.
Public Understanding of Biotechnology website www.pub.ac.za
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