Fungus threatens world's bananas

Bananas are a staple and a major export in the developing world

March 2, 1999
Web posted at: 4:00 PM EST

A hungry fungal leaf spot disease is spreading through banana farms around the world, decimating banana foliage and destroying crops.

Until recently, only expensive chemical fungicides could destroy the fungus, however plant pathologists are now taking the lead to breed bananas that are genetically resistant to the disease, according to scientists at the American Phytopathological Society.

The fungus, black Sigatoka, was recently reported in Florida, but has been affecting crops in the developing world for years. Since bananas are a staple and a major export in developing countries, black Sigatoka is imposing a heavy toll on their food security and export economies.

"The black Sigatoka pathogen thrives under the warm, wet conditions that are found in the tropics," says Randy Ploetz, plant pathologist with the University of Florida and member of the American Phytopathological Society.

"In such environments, black Sigatoka severely damages banana leaves and reduces a plant's ability to capture the sun's energy. As a consequence, fruit production can be reduced by 50 percent or more. Black Sigatoka also causes premature ripening, which is a serious defect in exported fruit."

"In order to reduce the impact of this disease, it is essential that resistant bananas be developed," says Ploetz. "Chemical control is available but expensive and generally not available for poor farmers who depend on this crop. Moreover, the pathogen has a tendency to develop resistance or tolerance toward some types of fungicides."

Historically, genetic resistance in bananas to black Sigatoka and other diseases has been poor. The situation is changing, however, as a result of new hybrids that are being developed by banana breeding programs in Guadeloupe, Honduras, Nigeria, Uganda and other countries.

"Products of the breeding programs are bound to play increasingly important roles in subsistence agriculture," says Ploetz. "Whether new hybrids eventually replace cultivars that are used by the export trades, however, remains to be seen. In the end analysis, we believe that resistant bananas will be our best defense against diseases in subsistence and export situations alike."

For more information, contact Cindy Ash, American Phytopathological Society, (651)454-7250.

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