You may not know it. But your bananas have been under attack for more than a decade by a small fungus, Fusarium oxysporum. Half of the global production of bananas is in a variety called Cavendish which has become susceptible to a new strain of the fungus. A previous strain of Fusarium wiped out the Gros Michel variety of bananas which used to dominate world markets until the 1950s.
The Cavendish seemed immune to the previous strain and could therefore be planted on the same land—Fusarium lives in the soil—that the Gros Michel occupied. The Cavendish is what is mostly exported to countries that do not grow bananas and therefore what most people see in modern supermarkets and greengrocers. It is named after William Cavendish, the sixth Duke of Devonshire, who received a shipment from a friend who had gotten them from Mauritius. Cavendish’s gardener proceeded to cultivate them in the duke’s greenhouses.
If you are a banana eater, you may have noticed that the Cavendish you peel and eat every morning has no seeds. It turns out that the Cavendish is propagated by cloning—which means that Cavendish banana trees around the world are genetically identical. And so, every one of them will likely eventually succumb to the new strain of Fusarium as it spreads worldwide.
The response to this “banana apocalypse” is revealing. The first line of defense is to figure out how to counteract the fungus. There is currently no known treatment for it. Banana growers seek to prevent contaminated soil from making its way into uninfected groves. But wind and weather do not obey the commands of banana growers. Beyond this, small amounts of contaminated soil can travel undetected in shipping containers—which probably accounts for the fungus’s worldwide spread.
The second line of defense is to create a new variety that will satisfy customers accustomed to the Cavendish but that would be immune to the new strain of Fusarium. It turns out that the success of the Cavendish has resulted in very little work understanding the genome of banana trees. No one needed a new variety to replace the Cavendish—until now. So, it will take some time to figure out if plant breeding could lead to a successor to the Cavendish. The short-cut of genetically engineering the Cavendish also awaits a better understanding of banana genetics across varieties—and might be greeted with hostility by a public increasingly wary of genetically modified food.
There does, however, seem to be one obvious solution. But the imperative of uniformity in worldwide consumer markets prevents the authors of the linked articles above from seeing it. The authors mention that there are already around 1,000 varieties of bananas grown around the world. This diversity is what normally protects a species from being wiped out by one disease. But could consumers across the world get used to, say, four or five other varieties? Demand for more than one variety would require the maintenance of diversity across the banana industry and protect it from a future wipeout by a single organism.
I bring this up because we face a similar (though not identical) problem with many widely grown food crops. They have little genetic diversity which means that an unexpected, virulent and easily transmitted disease could vastly diminish output dramatically of one or more of these crops and lead to food shortages. I refer, of course, to corn, wheat, and soybeans. There are, of course, more than one variety of these crops. But there are by no means 1,000 varieties of each currently being cultivated as is the case with bananas. And farmers tend to focus on the few that are commercially available and often genetically engineered to resist certain herbicides.
The banana industry will probably figure out how to replace the Cavendish banana that we are all used to seeing in the produce section. But the problem of the Cavendish banana brings to the fore a critical problem in our current food system: Lack of genetic diversity. That problem cannot be solved by doing more of what we’ve been doing in agriculture for over two centuries, namely, focusing on fewer and fewer crops and making them more and more uniform so that they will better fit in with modern mass production and marketing.
