KELLY MCEVERS, HOST:
The banana, at least the kind we usually see at the grocery store, is in trouble. An incurable fungal disease has been slowly spreading through banana-growing regions of the world, and scientists are on the hunt for a new version that is immune to the fungus. If they succeed, it could mean new banana flavors. NPR's Dan Charles reports.
DAN CHARLES, BYLINE: In the U.S., the bananas you find in the store are pretty much all alike. But in the market in Mayaguez, Puerto Rico, where shop owners get their bananas from farms on the island, you have choices.
BRIAN IRISH: (Speaking Spanish).
CHARLES: Brian Irish, a scientist who works for the U.S. Department of Agriculture's Tropical Research Station here, shows me lots of different bananas. There are tiny ones, red-skinned ones, plump ones.
IRISH: There's a very popular banana here called Manzano, or apple banana.
CHARLES: He buys a few of them, and we go out to his car for a tasting.
IRISH: Manzanos have a little bit of acid, a little puckering of your mouth, especially if they're not very ripe.
CHARLES: This is a fabulous banana, though.
IRISH: Tasty. It's one of my favorite, too. I really like it.
CHARLES: But all of these bananas are vulnerable. There's a deadly fungus that attacks banana plants. In the past century, one version of this fungus wiped out commercial plantings of a variety called Gros Michel that used to dominate the global banana trade. And now history may be repeating itself.
A new version of the fungus, called Tropical Race Four, is killing off the current king of the bananas, a variety called Cavendish. That's the kind you see in every supermarket. Tropical Race Four has marched across China and Southeast Asia, laying waste to banana plantations. It's killing bananas in Australia, and cases have been reported in Southern Africa. So far, the fungus has not spread to Latin America, but it can travel on the smallest particle of soil. So when Brian Irish visited a banana plantation in Australia recently, he decided to leave his boots right there.
IRISH: And not bring them back with me.
CHARLES: If you had really been attached to those boots, what would you have had to do?
IRISH: (Laughter) Cry. No, I mean, it's such a small sacrifice to make for such an important cause.
CHARLES: Some people probably don't take those precautions, though. Gert Kema, an expert on tropical plant diseases at Wageningen University in the Netherlands, says the banana industry probably should prepare for the worst.
GERT KEMA: I think it's very realistic that this fungus will simply continue to spread.
CHARLES: So scientists, including Kema, are starting to search for a banana that could replace Cavendish, one that's immune to Tropical Race Four. And the search starts with banana collections like the one at the USDA's Tropical Research Station in Puerto Rico. Brian Irish walks me through this small forest of banana diversity. Bunches of red fruit dangle from some of the tall stalks, big green fruit from others. And some plants have barely any fruit at all.
IRISH: Many of them are wild. The have fruit very small with seeds in them.
CHARLES: Irish grabs one tiny yellow banana and splits it open. It's full of black seeds hard as rocks.
IRISH: And how many in this small fruit - hundreds. So it's impossible to eat the pulp around these seed.
CHARLES: It may be useless to eat, but if it could withstand Tropical Race Four, it would be priceless. The only way to know is by exposing it to the disease - not here in Puerto Rico, of course. That would be crazy. Gert Kema is doing these experiments in greenhouses at Wageningen University, one of Europe's biggest centers of agricultural research. He's tested about 200 different kinds of bananas so far. Just a few can survive the disease.
KEMA: Less than 10 percent of the material we have tested is resistant to Tropical Race Four.
CHARLES: And those plants that are often are varieties like that wild one with all the seeds, or they're plantains, not sweet bananas.
KEMA: Right now, we have nothing to replace Cavendish.
CHARLES: So the nightmare scenario is the disease slowly destroys large-scale banana production everywhere. But there's an optimistic scenario, too. Kema says plant breeders can take those few disease-resistant bananas and mate them with others that taste good, looking for offspring that contain the best traits of both. It can be done, Kema says, and in the best of all worlds, this breeding effort would come up with multiple varieties, not just one.
KEMA: Bringing more diversity into banana cropping is, I think, part of solving this problem.
CHARLES: And if big plantations grow these varieties for export, consumers here might actually see the variety of banana colors and tastes that you could find now in the markets of places like Puerto Rico. Dan Charles, NPR News.