Yes, We Have No Bananas

by Melissa A. Schilling, December 20, 2017

Of the roughly 1500 types of bananas in the world, you probably only know and love one of them -- the Cavendish – and they are all genetically identical clones descended from a single plant painstakingly transplanted to an estate of the Duke and Duchess of Devonshire in 1830. The Cavendish banana’s story is movie worthy. The head gardener of the estate at the time, Joseph Paxton, was always on the lookout for new and exotic plantings and he immediately recognized that a sample that had arrived from Mauritius was special. He carefully nurtured the little plant in a hothouse, and five years later it bloomed and bore over one hundred large, delectably sweet bananas. It was a beautiful novelty that was great for impressing guests.

A few years later the Duke sent two crates of banana pups (yes, the offspring that grow from banana rhizomes are called “banana pups”) to Samoa with a missionary. All but one of the plants, and the missionary, died. But that one remaining banana pup gave rise to the Samoan banana industry. Banana pups were also sent with missionaries to other islands, to unknown fates. At this time the top banana of the world was the Gros Michel (“Big Mike”). Gros Michel’s sweet flavor, thick skin and dense clusters of fruit made it the banana of choice for exporting. Until the 1950s it completely dominated commercial banana production, and if you ate a banana in the Western World, it was probably a Gros Michel grown on a plantation somewhere in Central America.

However, in the 1950s, a fungus known as Panama Disease swept through Central America and wiped out the Gros Michel bananas. It was an economic disaster – eliminating roughly $2.3 billion in revenues for economies reliant upon banana exports, and doing even more damage to local banana consumption. As Panama Disease spread, banana growers frantically sought a replacement. Most bananas, however, weren’t up to the job. They either had thin skin that bruised too easily, mushy flavorless flesh, or giant seeds that made eating the banana a less rewarding experience. Fortunately, Paxton’s Cavendish came to the rescue. It had a thick skin that was easy to peel, a lovely golden color, and a light sweet flavor. Most importantly, it was immune to Panama disease. Soon the Cavendish was the world’s new top banana. Banana gourmands complained that the Cavendish was bland, but for most of us a blandly sweet banana worked just fine.

Fungi are wily and persistent creatures, and Panama Disease has now found a way to target the Cavendish. There is no known way to eradicate this fungus once it is established. This means that roughly 50 billion tons of bananas – almost 50% of world banana production could be on the verge of collapse. This would have a huge economic impact on countries that rely heavily on Cavendish exports (e.g., Ecuador, Costa Rica, the Philippines, Columbia, Guatemala). Is also has implications for food security: bananas are the fourth most important dietary staple (after rice, wheat and corn) in the world. The United Nation’s Food and Agricultural Organization estimates that bananas may account for roughly 25% of total caloric intake in many rural parts of Africa. They are also by far the most popular fruit in many parts of the Western World (in the US, for example, more bananas are eaten than apples and oranges combined).

While some scientists are scouring the globe for a lesser known banana to try to raise to stardom as we did in the 1950s when the Gros Michel crop collapsed, others are taking a new approach this time: biologists are using gene modification to create transgenic bananas that might be able to survive the fungus. Early results have shown signs of success, but how long the new bananas will be able to fend off Panama disease, and how long it will take to replace existing banana crops with a transgenic variety remains to be seen.

The banana crisis is just one example of a more general problem known as “monoculture”. When one version of a crop appears tastier, more productive, or in any other way more profitable than all others, farmers around the world convert to this version. There are some big short run advantages to this strategy, however the loss of variety dramatically increases the vulnerability of food production to the armies of bacteria, viruses, fungi and insects that are continually evolving to exploit a food source. If a pathogen mutates to successfully target a large food crop, the effects can be swift and dire. An apt example is provided by Ireland’s great famine of the mid-1800s when heavy reliance on the Lumper potato led to rapid spread of a potato blight, and an estimated one million deaths. By contrast, when smaller plots of land are dedicated to a crop and more varieties of crops are grown, it is easier to contain the spread of a pathogen, and gives us (and Nature) more time to create hybrids that resist it. Put more generally, biodiversity helps to create ecosystem resilience. (There are analogous effects of idea diversity in the learning processes of social systems.)

Genetic modification throws a pretty big wild card into the biodiversity debate. On the one hand, the ability to use genetic modification means we can manufacture diversity even after natural genetic diversity has been lost. That’s a pretty massive capability – like an agricultural superpower. On the other hand, it is difficult to know (or quantify) the risks that are involved in directly altering a species that has evolved over millions of years in close, complex interdependence with thousands of other species. Some people will argue that genetic modification is no different from the selective breeding we have long used to create bigger tomatoes and more interesting dogs, but that’s a fallacy. Evolution works incrementally, over a very long time scale, and with constrained choices (and even then, the vast majority of mutations are failures). Artificial selection (e.g., selective breeding) is faster than evolution because the combinations are planned and induced, but the combinations are still highly constrained by the existing genetic code. Genetic modification, on the other hand, can entail large-scale change over a short time scale, and can include changes that would never have been possible through nature. If evolution is like solving a Rubik’s cube, genetic modification is like peeling all the stickers off, painting on whatever you like, and gluing a few Lego bricks on for good measure. Genetic modification may turn out to be the superhero in our story, but like all good superhero stories, there may be a risk of it inadvertently inflicting massive destruction in its reckless adolescence. 

Is there anything else we can do? Increasing awareness is a start. The vast majority of people probably have no idea that heavy reliance on a few of the most productive crops puts us at risk of crop collapse. Understanding the importance of food diversity may help to change consumer buying habits. Informed consumers can seek out more diverse foods, and can also demand that government policies create incentives for growing more diverse crops. There are also innovation opportunities: Just as computer-aided manufacturing made it possible to economically produce many smaller batches of products on a single production line – which in turn enabled firms to better meet the demands of different market segments – there may be technological solutions that make farming diverse crops as efficient as farming a single crop. Can any of these solutions, or others, outrace Panama Disease? Let’s hear your thoughts.