Bananas might have gained a new weapon against a devastating disease: The green pepper.
By genetically modifying bananas with two green pepper genes, scientists have managed to give bananas resistance to Banana Xanthomonas Wilt (BXW), a bacteria that is sweeping through plantations in East and Central Africa. BXW causes about half a billion dollars in damage each year.
There is currently no good way to stop BXW. There are no varieties of banana that are resistant to it. And there are many other diseases like it spreading worldwide.
"Once this disease is in the field, that's an absolute loss because farmers cannot save anything," said Leena Tripathi, a plant biotechnologist at the International Institute of Tropical Agriculture in Kampala, Uganda. "The economic consequences are quite high."
Bananas are one of the most important sustenance crops in the world. In Uganda, Tripathi said, a single person often eats more than three pounds of banana a day. In the United States, people eat more bananas than any other fresh fruit, according to the United States Department of Agriculture, averaging about 26 pounds per person each year.
Despite their ubiquity in grocery stores and in cereal bowls, a number of diseases threaten bananas, and farmers often have no way to fight back. One reason is that bananas have lost their ability to produce fertile seeds, so they can't reproduce sexually.
As a result, there are a limited number of banana varieties. And an entire plantation generally consists of genetically identical plants. So, if a disease hits one, it usually hits them all.
Because bananas are sterile, there's no way to improve them through breeding, added Scot Nelson, a plant pathologist at the University of Hawaii at Manoa.
BXW first hit bananas in Ethiopia more than 40 years ago. It has since spread to Uganda, Tanzania, Kenya, the Congo and nearby areas. Symptoms of the disease include wilting and yellowing of leaves, oozing yellow excretions, premature ripening and rotting of fruit.
In 2005, Tripathi and colleagues started investigating the potential of two genes from green peppers that have been infused into other plants and have provided resistance to bacterial diseases. In lab conditions, they found that normal bananas developed severe symptoms of BXW in just 12 days.
Six out of eight lines of their transgenic bananas, on the other hand, developed no symptoms at all. They reported some of their findings in the journal Molecular Plant Pathology.
The green pepper genes seem to work by killing plant cells that come into contact with the BXW bacteria. Cell death prevents the disease from spreading. Tripathi and colleagues are now planning to test the plants outside.
"Even in field conditions, they should give 100 percent resistance," Tripathi said. "That's what we're hoping."
If successful, it would be a huge advance, Nelson said. Even though BXW is currently only in Africa, it could easily spread elsewhere, and there are other banana diseases like it.
As long as transgenic bananas don't cause allergies or other human health problems, the technique should be safe, he added. Because bananas don't reproduce sexually, the genes can't escape into other crops.
"It's a very significant thing that's been done here and I am really happy to see that they've done this research," Nelson said. "This is one of the worst diseases of bananas in an area of the world where they need this crop desperately."