A steady supply of an
important staple crop that is being threatened by disease may be assured,
thanks, in part, to plant biotechnology.
Researchers from around
the world are working to develop biotech bananas that are resistant to two of
the fruit's worst enemies — black Sigatoka and Panama fungal diseases. On some
banana plantations, black Sigatoka has reduced yields by 80 percent.1
Researchers are working
to map the entire genetic code of a wild banana from East Asia in the hopes it
will reveal the genes that provide resistance to these devastating diseases. 2
Once identified, researchers
hope to copy the genes from the wild banana and insert them into edible
varieties so they, too, can resist the diseases that have laid waste to a crop
that is the fourth most important staple food in the developing
world
— and a healthy snack for many in the developed world.3
This strategy has
worked well for other crops. Researchers, for example, have successfully inserted
a gene from a wild plant related to the potato into an edible potato — which is
not yet commercially available — to make it completely resistant to the disease
that triggered the Irish potato
famine of the 1840s.
And a different plant
biotech technique was used to successfully combat a virus that had decimated
the papaya industry
in Hawaii. Biotech papayas are now being commercially grown in the United
States and the technique for growing them is now being transferred to several
developing countries where papaya is a staple.
Background
Researchers say plant
biotechnology could be particularly beneficial to bananas because they are very
vulnerable to disease and difficult to crossbreed using conventional methods due
to their complex genetic structure. 4
In addition, at least
half of the more than 300 varieties of bananas bred for cultivation are sterile
— they've lost the ability to make seeds — and therefore can't be crossbred with
a wild relative to boost resistance to disease.
5
Banana farmers
typically restock their plantations by replanting below-ground offshoots of
existing banana plants. Using this technique means once a disease or pest has
taken hold in one plant, it can ravage an entire orchard of genetically similar
plants.
This problem is faced
by the United States' third most-consumed fruit, the sweet Cavendish banana, as
well as many of the starchier varieties that developing countries rely on for
sustenance.
As a result, some
varieties of bananas have vanished. In the 1960s, an earlier strain of Panama
disease wiped out the Gros Michel species, once the primary sweet banana grown
for export to the United States.6
Black Sigatoka, a
leaf-spot disease, stunts the plants and shrinks harvests. 7
Panama disease lives permanently in the soil, and when it infests the plants, it
kills them outright. Other pests and diseases include yellow Sigatoka, bunchy top,
root nematodes and banana weevil.8
In West Africa,
disease and pests have cut banana production in half over the last 30 years. In
Kenya, the combined onslaught of weevils, nematodes, Panama disease and black
Sigatoka have cut average banana yields on traditional farms to 14 tons per
hectare, less than one-third of the crop's potential under humid tropical conditions,
according to biotech researcher Florence Wambugu,
founder of A Harvest Biotech Foundation International. 9
Since the lion's
share of the annual global banana output of 86 million tons are harvested and
consumed locally by poor subsistence farmers in the developing world where food insecurity is
frequently a top concern, any agricultural technique that can boost production
is viewed as a benefit.10
Tissue-cultured bananas
Using plant tissue
culture — where a cell is extracted from a plant and grown in a sterile medium
such as a petri dish — to grow bananas is one such technique that has worked.
In the early 1990s,
researchers from the International Service for the Acquisition of Agri-biotech
Applications (ISAAA) began using tissue culture to grow disease-free plantlets.
The process works because even a diseased banana plant contains a few cells that
are free of disease. A technician removes those disease-free plant cells under
sterile conditions, places them in a growth medium, and allows new plantlets to
sprout up a few inches.
These plantlets are
then allowed to generate roots and grow until they are strong enough to
transfer to a farmer's field.11
This technique allows a field of banana plants to be less susceptible to
disease, because, not only does each plantlet start out disease-free, but a
field of plants grown from several different parent plants is less susceptible
to disease than an entire field grown from offshoots of one parent.
Since 1996, ISAAA has
collaborated with the Kenya Agricultural Research Institute, the Ministry of
Agriculture and women's groups to distribute thousands of these tissue-cultured
plantlets to farmers
in Kenya, which have increased fruit production by as much as 50 percent. 12
Disease-resistant bananas
Researchers are now working
to develop bananas that don't just elude these diseases — as is the case with
tissue-cultured varieties — but that actually
resist disease.
Using plant
biotechnology, researchers from the International Network for the Improvement
of Banana and Plantain (INIBAP) in Montpellier, France, and Katholieke
Universiteit Leuven in Belgium have been growing test crops of genetically
enhanced bananas to resist black Sigatoka and Panama diseases.13
Emile Frison, director
of INIBAP, is also the driving force behind a global consortium of publicly
funded institutes working to sequence the genome of a wild banana from East
Asia to help identify genes that could be used to create disease-resistant
edible varieties.14
Other researchers
around the world are also working to develop disease-resistant bananas. For
example, the Queensland University of Technology in Brisbane, Australia, has
teamed up with Farmacule BioIndustries, also of Brisbane, and Demegen, Inc., of Pittsburgh, Pa., to develop
biotech banana varieties resistant to black Sigatoka.15
Recognition is growing that biotechnology may be
the only way to save the banana from the ever-changing pests and diseases that
prey on it. The United Nations Food and
Agriculture Organization (FAO) supports this view.
"Since more than 50 percent of the banana germplasm
are sterile, biotechnology and mutation breeding are important tools that can
improve banana varieties," states an FAO press release.16
For more information:
The Most
Important Disease of a Most Important Fruit — The Plant Health Instructor
Yes, We Will Have
Bananas: Rejuvenating Banana Orchards in Eastern Africa — International
Service for the Acquisition of Agri-biotech Applications
Scarce-Banana Care: But Don't
Kiss That Banana Good-Bye Yet — Science News
Fungal
Resistance — CropBiotech Net
Banana Genome To
Be Unraveled — New Scientist
