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The Banana Wars against Fungus |
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By Mario Osava*
Researchers are trying to protect
the banana from its numerous enemies, and one of the tools they
could use is to develop genetically modified varieties that are
more resistant to pests. In Brazil, the greatest threat is black
sigatoka fungus.
RIO DE JANEIRO - Growing bananas is a war against
fungus infestations. In this battle, farmers apply an array of agro-chemicals,
scientists work to develop resistant banana varieties, and the authorities
try to stop the spread of all such pests.
Brazil, the world's fourth producer of bananas
after India, Uganda and Ecuador, has been living for years with
two of the fruit's main enemies: Panama disease and yellow sigatoka,
which it is fighting through the use of fungicides and increasing
the resistance of the banana trees themselves.
But the worst threat is black sigatoka, which
entered the country through the northern Amazon border some five
years ago. Now there is great fear that the fungus will attack the
regions of greatest banana production, in Brazil's central-south.
It is there that varieties of the Cavendish
banana are grown, the most exported banana in the world -- and also
the most vulnerable to black sigatoka.
"Black sigatoka is more aggressive, and
even pushes out yellow sigatoka" as it rapidly spreads, Sebastiao
de Oliveira e Silva, an agronomist at a northeast Brazil laboratory
of the governmental Brazilian Enterprise for Agricultural Research
(EMBRAPA), told Tierramérica.
Banana growers here already have tree varieties
that are resistant to black sigatoka, a pest that has led to great
losses in Central America and the Andean countries, pushing up production
costs.
These banana varieties belong to the group
known as Plata, which is the most grown type in the country, alongside
the Pacovan Ken (resistant to the two sigatoka fungi and to Panama
disease), developed by EMBRAPA, Silva said.
There are more than 500 banana varieties in
Brazil, which exports just 13 percent of its annual harvest of 100
million tons.
But the Nanica banana, of the Cavendish group,
is still beset by plagues.
The Agronomy Institute of Campinas, located
near Sao Paulo, developed the IAC 2001 variety, which was resistant
to black sigatoka, but that all-important trait was lost after two
growing seasons in the Amazon region.
Obtaining improved banana varieties takes time
because the life cycle of the tree lasts longer than a year, slowing
the process of evaluations, cross-pollinations and verification.
EMBRAPA is also looking for solutions at its
National Center for Genetic Resources and Biotechnology (CENARGEN),
in Brasilia.
The traditional method of conventional genetic
crosses is very limited in the case of the banana, because many
varieties -- and the most cultivated types in particular -- bear
sterile fruit, explains Manoel Teixeira Souza, a CENARGEN researcher.
EMBRAPA is part of a consortium from 14 countries
working to decipher the banana genome, and to develop genetically
modified varieties.
"Our priority is to identify the genes
resistant to the fungus infestations and transfer them to the Nanica
and Plata varieties," Souza said.
And the strategy is to compare the banana genome
to that of rice, the most studied grain, and to concentrate research
on genes that are expressed in the plant's leaves, where the black
sigatoka attacks, he explained.
Efforts are also under way to identify genes
from other species that might boost the resistance of the banana
tree through genetic transference, said Souza.
The hope is that scientists will find "candidate
genes" in the project's initial phase, through 2004, and then
carry out experiments to determine whether gene transference --
genetic modification -- is effective, he said.
Souza says he regrets the controversy over
genetically modified organisms in Brazil, which is mostly centered
on a variety of soy, Roundup Ready, developed by the transnational
seed and agro-chemical giant Monsanto for use with its own herbicide,
Roundup.
"The debate is blocking further research,"
he complains.
EMBRAPA researcher Silva says he is not opposed
to genetic modification as a "faster" potential solution
to the banana fungus problem, or for resolving some of the "difficult
details" of conventional crop improvement.
"But new technologies pose new risks,"
he said, adding that it is a matter of implementing safeguards.
Regina Vilarinho, coordinator of the EMPRAPA
plant health network, told Tierramérica that while researchers
look for solutions, it is important that the media disseminate information
about the crop pests so that farmers and the population in general
do not transport contaminated material.
The Cavendish banana varieties, chief among
exports, also face the danger of the so-called race 4 of Panama
disease, caused by the fusarium fungus, which attacks the tree at
its root. There are no pesticides available to fight it.
This banana disease is found in Australia,
southern Africa and some Asian countries. The International Network
for the Improvement of Banana and Plantain believes its arrival
in Latin America is just a matter of time.
The banana is the fourth leading food crop
worldwide, after rice, maize and wheat.
* Mario Osava is an IPS correspondent.
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