We’ll have no bananas?

BananasReports of the imminent demise of the world’s most popular fruit have surfaced repeatedly over the course of the last decade. Bananas, particularly those grown in large monocultures for the hungry markets of the EU and the US, are vulnerable to a number of diseases, and fears are mounting that the tide is turning against our prevention and mitigation strategies. How much stock should we put in these reports – are the days of the banana truly numbered? Jon Fuhrmann investigates.

A fungal disease called Fusarium wilt, also known as Panama disease, is causing the most concern among banana producers. In the last 20 years, a new and particularly dangerous strain called Tropical Race 4 (TR4) has infected the Cavendish banana, the only widely available banana type in western supermarkets. Reports of the disease are now coming in from the Middle East and East Africa, a long way from the disease’s Southeast Asian origins.

Panama disease itself is not an unknown entity. In the first half of the 20th century, a different strain (Race 1) effectively wiped out the Gros Michel-type banana, which dominated the world markets at the time. Those who have tasted Gros Michel wax lyrical of its superior taste and texture, sweeter and more delicate than the Cavendish-type bananas we buy in supermarkets today.

Indeed, the Cavendish bananas are merely a second-best solution, adopted after Panama disease rendered Gros Michel commercially infeasible. The big banana exporting companies clung to Gros Michel because consumers preferred the taste and their hardiness meant lower transport costs compared to those needed for the Cavendish fruit. While possibly apocryphal, the song ‘Yes! We Have No Bananas’ may relate to the difficulties that American consumers faced after Panama disease destroyed the Gros Michel crops that supplied the US.

As a result, Cavendish bananas, which are resistant to the fungus, became the bulk of worldwide trade and have remained so for the past sixty years. During this time, a variety of bacterial and fungal diseases have plagued banana plantations and prompted ever more extreme levels of fungicide spraying, which affects both plants and plantation workers – but Cavendish continues to dominate.

Tilting at windmills

In the early 1990s, a new strain of Fusarium wilt was discovered in Southeast Asia and christened tropical race 4 (TR4) due to its prevalence in tropical regions. Cavendish bananas are highly susceptible to TR4, which is resistant to fungicides and spreads rapidly through a plantation after initial infection. The fruit are unable to evolve resistance to the fungus because all Cavendish bananas are genetically identical and grown from a homogenous seed stock.

Confined to Southeast Asia and the Pacific region for the best part of a decade after its discovery, TR4 did little harm to the West African and Latin American plantations supplying western markets. In the last decade, however, reports of the disease have appeared from Oman, Jordan and Mozambique. The disease is clearly on the move – but how did it spread over such large distances so suddenly? Unsurprisingly, human action is the probably to blame. Workers, machinery and plant material all move between banana-producing regions, and contaminated soil on tools or boots can introduce TR4 to new regions.

The end of Cavendish?

It is unlikely that TR4 will cause Cavendish-type bananas to become extinct – although it may cause significant problems to the huge monocultures in which the plants are grown, as was seen with Gros Michel. Fusarium wilt spreads rapidly through adjacent plants but is not easily spread over large distances like some other air- or waterborne pathogens such as Phytophthora ramorum, which causes sudden oak death. This means that smallholders are much more likely to be able to grow Cavendish bananas even if the larger export market is in decline. Again, this is true of the Gros Michel variant, which can still be found in marketplaces in Southeast Asia.

Of course, there is a chance that Cavendish bananas will become commercially infeasible if TR4 continues to spread through Africa or reaches the Americas. To prevent this, stringent controls are needed to halt the spread of the fungus. Examples of this exist in Australia, where the state of Queensland has implemented strict biosecurity measures and has so far managed to keep Fusarium wilt at bay despite its prevalence in the adjacent Northern Territory. It may prove more difficult to enforce such measures across the multiple borders present in Latin America.

Are there alternatives?

While Cavendish is by far the most common banana used in export, there are a large number of other banana varieties cultivated around the world. These bananas feed millions of people around Asia and Africa, and scientists are testing them to find which ones are resistant to TR4. This means that while Cavendish is, of course, an important food crop in many parts of the world, its disappearance from mass production is unlikely to cause a food security crisis in low- or middle-income countries, as alternatives are available.

As for western countries importing bananas, the situation is less straightforward. While the precedent of Gros Michel’s fate in the 20th century gives us some idea of a potential outcome, the difference is that when Gros Michel became infeasible, the Cavendish variety was already known as a potential replacement. Currently, there is no such replacement for Cavendish.

Mitigating the Musa menace

While many researchers think it likely that TR4 will eventually spread to the Americas, delaying this event allows more time for effective countermeasures to be put in place and for research to continue on resistant banana varieties.

For Western consumers and exporting companies, the task at hand is twofold. Scientists are working to develop resistant varieties that display as many of Cavendish’s positive attributes as possible. While a few such Cavendish-based varieties have been made, they either require prohibitively expensive modifications to the transportation process or are unlikely to be accepted by consumers because their shape or taste are too different.

Additionally, consumer tastes will have to change if a new kind of banana is to find widespread acceptance and commercial success. It may be that the banana of the future will be a different average size or shape, or that it ripens differently so that greener or browner bananas become more common on supermarket shelves.

Fortunately, it seems unlikely that bananas will be lost forever. As the downfall of Gros Michel shows, even a crash in the world’s most grown banana will not lead to a complete demise of the fruit. Research, information dissemination and appropriate management can combine to produce a brighter future for bananas.

Jon Fuhrmann

The Society has recently produced a briefing document on banana disease, which further outlines the problems facing banana growers. You can find it here.

Image credit: Ian Ransley on Flickr
This entry was posted in Environmental Microbiology, Food Microbiology and tagged , . Bookmark the permalink.

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