Are bananas doomed?

Canadians eat approximately three billion bananas a year; it’s our favorite fruit. But a recent news story suggests the bananas we enjoy so much could be extinct within 10 years.

The villain is a fungus by the ominous name of Black Sigatoka that’s spreading out of control through the banana-growing countries of the world, threatening the handful of banana varieties that are the mainstay of the banana industry.

These bananas are vulnerable for the same reason they’re seedless: they’re the descendants of sterile mutants of wild bananas, which are so full of hard seeds they’re inedible. Thousands of years ago humans discovered the seedless variety, which propagates by putting out runners, and spread edible bananas around the world.

But because bananas propagate from runners, every edible banana of the same variety is essentially a clone of every other edible banana of that variety. It does not evolve, and so it cannot develop disease resistance. And that makes it that much easier for one particular disease or parasite, like the Black Sigatoka fungus, to spread like wildfire.

Bananas, everyone knows, grows on banana trees–but everyone is wrong. The banana tree isn’t a tree at all. It’s a herb–even though one wild variety can grow up to 15 metres high. As the leaves unfold, they overlap each other to form a “trunk”–properly called a “pseudostem.” The plant dies once the bananas are harvested, but first it puts out sideways stalks, or “ramifications,” which can be used to start new copies of the plant.

The plant flowers in its sixth or seventh month, then begins growing bananas, which can be harvested after nine to 12 months. Harvesting is a two-man job: one cuts the stalk and the other stands by to help maneuver the bunch (which can weigh 25 kilograms or more) onto a padded tray (to protect from bruising), which is then transported to the packing station.

Bananas ripen quickly and suddenly. When a banana starts to ripen, it produces a gaseous plant hormone called ethylene that kicks off a biochemical cascade of events: starches change to sugar, tissues soften, and the chlorophyll in the skin is destroyed, causing the skin to turn yellow. The ethylene emitted also hastens the ripening of other nearby bananas. Humans take advantage of this by ripening green bananas to demand in ripening halls; ethylene is released into the air to kick-start the process.

The sweet “dessert” bananas we like account for only about 15 percent of the 95 million tons of bananas grown annually. Most are plantains and other starchy cooking bananas that are used more like vegetables than fruit: they’re fried, grilled, boiled, stewed, dried when green and ground into flour for bread, turned into ketchup, brewed into beer. The stem and leaves also have uses as building materials and as a source of fibers for everything from clothes to fishing nets to banknotes

As a result, bananas are the world’s fourth most important food crop, after rice, wheat and maize. Nine out of every 10 bananas is consumed locally, providing vital nutrition for more than 400 million people–not only calories (some people rely on bananas for up to half their daily calories) but vitamins A, C and B6, and calcium, potassium and phosphorus, among other useful things. Which makes Black Sigatoka a serious threat indeed.

To be fair, “extinction” is too strong a word: bananas as a species aren’t going anywhere. There are more than 500 edible varieties, and more than 1000 varieties in all. Most of the edible ones, though, are only grown locally, in small plots. The banana industry depends primarily on plantains and the Cavendish dessert variety we eat, which took over as top banana (sorry) from the Gros Michel variety about 50 years ago–because the Gros Michel variety was almost wiped out by disease.

Because of that, a group of researchers are trying to sequence the genetic blueprint of the banana within the next few years. They’re focusing on inedible wild bananas which are resistant to Black Sigatoka, in the hope they might be able to use genes from those bananas to genetically engineer a new disease-resistant strain of edible banana.

They face challenges. Very few researchers are pursuing the work; the large banana producers aren’t backing the research because of the cost and because they’re afraid consumers won’t accept a genetically modified banana.

So enjoy your bananas now. In a few years, you may not be able to.

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