Yes, We'll Have No Bananas - Thanks to Selective Breeding, our Favourite Fruit can Neither Reproduce nor Defend Itself from Disease

Published on
by
the Globe and Mail / Canada

Yes, We'll Have No Bananas - Thanks to Selective Breeding, our Favourite Fruit can Neither Reproduce nor Defend Itself from Disease

by
Robert Alison

The banana is about to disappear from store shelves around the globe. Experts say the world's favourite fruit will pass into oblivion within a decade. No more fresh bananas. No more banana bread. No more banana muffins or banana cream pie.

Why? Because the banana is the victim of centuries of genetic tampering. Scientists say they will be unable to prevent the extirpation of the banana as an edible commercial crop. And its demise may be one more powerful argument in the hands of those who are concerned about genetic modification of foods.

The banana's main problem is that it has become sterile and seedless as a result of 10,000 years of selective breeding. It has, over time, become a plant with unvarying genetic sameness. The genetic diversity needed to cope with environmental stresses, such as diseases and crop pests, has long ago been bred out of the banana. Consequently, the banana plantations of the world are completely vulnerable to devastating environmental pressures.

According to Emile Frison, newly appointed director-general of the Rome-based International Plant Genetic Resources Institute, science is helpless to prevent the demise of the banana. Already, he says, as much as 50 per cent of the world's banana harvest is lost to insects and disease.

When humankind first encountered this fruit thousands of years ago we were probably not impressed by the almost inedible giant wild bananas. Historic mutations, rare and accidental, produced seedless bananas through chromosome triplication. Ancient humans focused on these seedless, pollen-less mutants to generate progressively more edible crops. Eventually, edible banana flesh retained only a few vague traces of the viable seeds once carried in the ancestral wild stock.

Ancient plant breeders grew edible bananas by grafting sterile mutants onto wild stems. This process was repeated for thousands of years to produce the emasculated, sterile -- and defenceless -- plantation banana that currently feeds millions of people globally.

But the stage was set for the final act in the story of this beloved yellow fruit in the 1950s. By then, generations of selective breeding had long since inhibited natural banana reproduction, and genetic tinkering had all but obliterated most commercial varieties. Eventually, one morph remained, the Gros Michel variety. All domestic stock was its clone, an exact genetic copy of that one variety. Every tree was equally vulnerable to plant disease, crop pests and climate variables.

Then Panama disease, a soil fungus, attacked banana plantations and the genetically enfeebled Gros Michel banana was virtually wiped out. By 1960, the Gros Michel was no longer a viable crop. Tireless agricultural research eventually produced a successor, the Cavendish. For the past 40 years or so, the Cavendish has been virtually the only commercially grown stock available on store shelves in developed nations.

In the tropics, you can still find other, less desirable banana varieties, mainly grown as a starchy food staple rather than a sweet treat. But these tropical bananas aren't much like their commercial cousins in North American supermarkets. They taste bland. Their texture is often fibrous and mealy. North American consumers would probably find them quite unpalatable compared to the Cavendish, which is sweeter and smoother-textured.

But like its genetic predecessor, the Cavendish is also sterile, equally unprotected from diseases and crop pests. And now a powerful plant pathogen, the Black Sigatoka fungus, has appeared on the scene, attacking the Cavendish stock around the world. Banana yields have already dropped by 50-70 per cent, and banana-tree life spans have been reduced from about 30 years to just about two years. The genetic uniformity among Cavendish bananas has made them helpless to fight Black Sigatoka.

Nor can chemical spraying save the day. Commercial growers have long attempted to control the fungus using fungicides such as dibromochloropropane (now banned because it caused sterility and leukemia among banana industry workers). According to Dr. Frison, even powerful fungicides don't work against Black Sigatoka because the fungus is rapidly capable of developing resistance to them. Indeed, banana plantations in Costa Rica and the Amazon have already been largely destroyed.

The selective plant breeding that has brought us to this impasse is comparable to genetic engineering. Both change the genetic makeup of a plant, perhaps irreversibly. So the case of the banana gives ammunition to critics of genetic engineering and to their claim that much can go wrong when we tamper with plant genetics.

Such warnings aren't new. In 1995, biologists warned that changing the genetic makeup of a plant is like playing with fire. Even so, genetic alteration continues. At Oregon State University, scientists are at work on generating sterility in poplar trees; the Canadian Forest Service is looking into breeding insect resistance in white spruces; at the University of California, work is being done on changing root systems in walnut trees. And at the Independent University in Madrid, orange trees are being modified to promote early fruit-bearing and to grow oranges that are easier to peel.

The International Plant Genetic Resources Institute's Dr. Frison says biotechnology could still delay the loss of the banana, by providing the genetic blueprint of inedible wild varieties that can be genetically altered to create a genetically modified product. Does this hold out hope of an 11th-hour reprieve? Will consumers accept a GM substitute for the sweet fruit they enjoy so much?

The disappearance of the banana should be a wakeup call -- to what can result from reckless genetic manipulation, complacency and inattention. If this can happen to the world's most popular fruit with all humanity as its witness, imagine what could happen to more obscure, but no less useful plants whose fates are less publicized and open to public scrutiny.

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