Battling for Bananas
Ladies and gentlemen, guard your breakfasts: the banana is under attack. A plague pursues the United States' favorite fruit--in fact, two plagues.
To explain the concern and the fight to solve it, one must first delve into banana history. Although commonplace today, bananas only became a staple in North America's diet late in the last century. They could do so because of a genetic freak--a spontaneous mutation in a kind of banana native to Southeast Asia.
The new banana was big, sweet, and seedless. (Those little black flecks near the center of a banana are vestigial seeds, mere echoes of the real thing. A full banana seed is big, hard, and neighborly; scores of them stud a seeded banana.) It was a natural triploid, meaning it had three sets of chromosomes instead of the normal two.
The new mutation also had a characteristic that made long-distance transport possible: all the bananas on a stalk ripen at once, about three weeks after they've grown to harvestable size. A ripening banana, like some other fruits, gives off ethylene gas, which triggers ripening in nearby fruit. In older banana varieties, a fruit or two ripens quickly after cutting.
That triggers a cascade of ripening, with the probability of rotten fruit arriving at a distant destination.
The French transported cuttings of the new plant to the Caribbean, where it thrived. They named it Gros Michel.
The Gros Michel was a true commercial banana, and the variety that won the hearts of people living outside the tropics. It was the banana found in the first supermarkets in Alaska, and the one most of us grew up with--unless we haven't reached middle age by the kindest calculation. For the Gros Michel had a serious weakness: it was susceptible to two kinds of fungus diseases.
One, called yellow sigatoka, could be controlled by spraying. The other was soil-borne Panama disease, a kind of fusarium wilt, and could not be cured or prevented. The growers' only option was to keep moving banana plantations to fresh land. By the 1960s, even the United Fruit Company couldn't find new land suitable for banana cultivation.
Instead, they found a new banana. This one, christened Cavendish, was discovered in a Saigon botanical garden. It too was a big, sweet, seedless triploid that ripened weeks after harvest, but it resisted Panama disease. Swiftly and with no fanfare, Cavendish bananas replaced Gros Michel. The Cavendish is now the banana of commerce.
Fungus can mutate too. Matching the tough new banana came a tougher new disease, black sigatoka. Far more virulent than yellow sigatoka, it kills leaves and triggers premature ripening in immature fruit. It quickly develops immunity to fungicides; so far, growers have gone through three different formulations. Worse, a new and nastier strain of Panama disease is now decimating Cavendish stands in Taiwan, South Africa, and Australia. It's only a matter of time before the Central American groves fall under attack.
This isn't an extraordinary event in agriculture. Plant breeders have had to develop new varieties of most crops to heighten disease resistance. But when they work with wheat, corn, or tomatoes, crossbreeding is relatively easy: those plants have seeds.
The old Gros Michel may come to the rescue. Scientists at the Honduras Foundation for Agricultural Research, the world's chief center for studies of banana diseases and banana breeding techniques, have found that certain varieties of Gros Michel can be forced to produce a few seeds if their flowers are hand-pollinated with pollen from diploid, seeded bananas. From 10,000 bananas, they can expect one seedling.
The offspring of those crosses between commercial and disease-resistant wild plants are tetraploids--that is, they have four sets of chromosomes (and many big, hard seeds). The Honduran team is busy making backcrosses, trying to get a new banana that resists disease, tastes good, ripens properly, and doesn't have seeds.
It's slow work, because each banana generation takes three years. Right now they believe they're two or three crosses away from success. By the year 2000 we'll be able to tell if they've won this round. If they do, we'll probably be no more aware that we're eating a new kind of banana than we were when the Cavendish replaced the Gros Michel. If the fungus diseases win, we'll be confronting bowls of naked cornflakes--at least between strawberry seasons.
