The Banana Wars against Fungus

By Mario Osava Reprint | | Print |

RIO DE JANEIRO, Feb 24 2003 (IPS) - 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. 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.