A mushroom could annihilate banana forever

The banana – or at least the fruit as we know it – is facing an existential crisis. A deadly fungus that decimates banana plantations in Southeast Asia for 30 years has finally managed to do what scientists have long feared and then headed to Latin America – the heart of the market world banana exports.

On August 8, the Colombian Agricultural Institute announced that it had confirmed that the fungus – a strain of Fusarium oxysporum called Tropical Race 4 (TR4) – had been found in plantations in the north of the country. The country declared the state of national emergency by destroying crops and quarantining plantations in order to prevent the spread of the fungus.

But Latin America has already been in this situation. Until the 1950s, the most exported banana variety was Gros Michel, almost completely wiped out by a different strain of the Fusarium mushroom. The modern export banana – the Cavendish – took the place of Gros Michel because it was resistant to this variety of Fusarium. Today, 99% of the exported bananas are Cavendish, almost all grown in Latin America.

"We have an almost apocalyptic scenario in which we will probably lose Cavendish," says Sarah Gurr, Exeter University Chair in Food Security. Discovered in Taiwan in 1989, the TR4 is widespread throughout Southeast Asia. It has since been found in Lebanon, Israel, India and Australia. But until now, Latin America had completely avoided the pathogen.

"Once in a country, it's very difficult to get rid of it," says Dan Bebber, senior lecturer in biosciences at the University of Exeter. The TR4 lives in the ground and can be transmitted on dirty tires or boots, or spread from banana trees when they are replanted on different farms. Once present in the soil, it can remain dormant for years before infecting the banana trees through the roots, spreading into the conductive tissue of water and nutrients and depriving them of food.

Now that it's in Latin America – and it's probably more widespread than it's currently understood – it's controlling the spread of the fungus, says Bebber. Ensure that planting employees or visitors disinfect boots and tires before entering or leaving the site is helpful, as well as maintaining soil health, but no country failed to contain TR4 successfully. In 1997, TR4 was detected in the Northern Territory in Australia, but vigorous quarantine efforts could not stop the spread of the pathogen in northern Queensland in 2015.

"We were expecting a fairly fast spread [in Latin America]"Said Bebber. In the banana industry with extremely low margins, relatively little money is spent on finding new varieties of bananas that can withstand the disease. Over the last decade, the price of bananas in the United Kingdom has remained stable at £ 0.94 ($ 1.13) per kilogram. During the same period, the price of apples went from £ 1.51 ($ 1.82) to £ 2.08 ($ 2.51) per kilogram, an increase of almost 40%.

This relentless demand for extremely cheap fruit produced thousands of kilometers has led the industry to focus on a single banana crop, which allows for more standardized, and therefore less expensive, agriculture and transportation. But growing a single variety of banana has serious drawbacks. "Monocultures are a divine food ground for pathogens," Gurr says. When a pathogen arrives that infects a certain variety, such as Cavendish, there is no respite in sight.

While things are getting worse in Latin America, there is some hope on the horizon. Work is already underway to use the Crispr gene editing to create TR4-resistant Cavendish bananas. In 2018, plant biologist James Dale demonstrated that it was possible to modify the Cavendish genome using Crispr. In Norwich, a company called Tropic Biosciences is also experimenting with the use of Crispr for the production of resistant bananas.

It would also be possible to cross other varieties of bananas in the hope of creating offspring resistant enough to TR4 and tasty enough to be sold to consumers. However, all these efforts are still far from giving promising results. In July 2018, the Court of Justice of the European Communities questioned the future of gene-modified bananas after clarifying that Crispr-modified crops would not be exempt from regulations restricting the sale of genetically modified organisms .

Until a solution emerges, the only option facing Latin America is to overcome the TR4 crisis. But, as Bebber notes, TR4 is not the only challenge facing the banana sector. A devastating and costly fungal fungal disease called black Sigatoka is also widespread in Latin America, and climate change may dry out plantations, making it difficult for plants to grow.

For an industry that has barely survived with thin margins, one more challenge could be enough to tip it. Instead of looking for a replacement at Cavendish, the only long-term solution might be to admit that a single crop on such a scale is simply not sustainable. "Many people say that rethinking the entire production system is really what we need to do," says Bebber. "With this type of production system, you are in trouble."

This story originally appeared on WIRED UK.

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