If TR4 hits, banana farmers will only be able to watch helplessly as their plantations die. There is no antidote for the fungus.
A research team has now developed a genetically modified line of Cavendish bananas, which are now predominantly grown in plantations for export. It is resistant to TR4 – and was recently approved for human consumption in Australia. Is QCAV-4 the salvation of the globally threatened banana industry? “I believe that this will be the solution,” says plant pathologist Remco Stam from the Christian Albrechts University in Kiel.
Bananas are popular
It is called Panama disease when the fungus Fusarium oxysporum TR4 causes the death of Cavendish banana plants – by far the most important commercial variety in the world. In Germany, Cavendish bananas have a market share of around 99 percent, says Andreas Brügger, managing director of the German Fruit Trade Association (DFHV).
And they are well liked by fruit buyers: “Usually second only to apples.” According to an analysis by the Agricultural Market Information Society (AMI), in 2022 households would have even bought slightly more bananas than apples per capita.
According to experts, a main reason is probably the price: Bananas are often unbeatably cheap in supermarkets, despite the long transport in refrigerated ships. This is due to the comparatively low production costs in the main supplier countries in South and Central America, but also because supermarkets often use bananas as a kind of yellow advertising banner: they are one of the things that are bought frequently and where there is not a great variety of products – ideal for easily comparable lure offers. A kilo of bananas is often significantly cheaper than a kilo of German apples, says Brügger. “And you know what you’re getting; there are comparatively few differences in quality and taste.” The annual net import to Germany is currently around one million tons.
The dangerous mushroom
Although TR4 (Tropical Race 4) has been spreading from Southeast Asia into Cavendish-growing regions since around 1990, there has been no noticeable increase in prices so far. This is mainly because the producers in Latin America, which are crucial for Germany, are keen to give the fungus as few chances as possible – Ecuador, Colombia, Costa Rica and Guatemala are among the largest banana exporters in the world.
TR4 was detected for the first time in northeastern Colombia in 2019. But even five years later, according to the banana farmers’ association (Augura), the situation in the country is still largely under control. “Out of 53,000 hectares on which we grow bananas for export, only 300 hectares are affected by the disease,” said association President Emerson Aguirre Medina recently. However, there have also been outbreaks in Venezuela and Peru.
Ultimately, Stam is convinced that the fungus will neither be completely suppressed nor permanently contained. Once TR4 is in a plantation, it can no longer be used: “The fungus survives in the soil for several decades.” Digging up entire plantations is not a practical solution and the use of immense amounts of fungicides in the soil is not a desirable one.
Is the popular banana variety over?
The industry’s downfall is that it relies so much on a single variety. While you can still find at least a few different varieties of apples and tomatoes in supermarkets, when it comes to dessert bananas it is almost exclusively Cavendish. “Such a monopoly of a single variety is unique,” explains Stam. “And this is also a clone, so there is no genetic adaptation in the course of sexual reproduction.”
Cavendish perennials are grown exclusively from cuttings, all are genetically exactly identical, and the fruits contain no seeds. “The Cavendish is an absolutely unnatural plant,” says Stam.
It wouldn’t be the first global end for a banana variety: Fusarium oxysporum, then still TR1, was already the downfall of the previously dominant commercial variety Gros Michel – tastier and easier to harvest and transport thanks to its thicker peel. By around 1960, a large part of the holdings had been destroyed. Gros Michel was then replaced by Cavendish, who came from Vietnam.
Unlike back then, this time there seems to be no replacement suitable for mass cultivation in sight. There are now more than 1,500 banana varieties registered. But only very few have the necessary resistance and other properties and even fruits that are suitable for consumption, as Stam explains. There is currently no variety that can compete with Cavendish in terms of yield, transportability and taste.
The plan for rescue
That’s why research teams are working primarily on making Cavendish resistant to TR4 – through traditional breeding or genetic engineering approaches such as that of the team led by James Dale from the Queensland University of Technology (QUT). The scientists have inserted a gene – the resistance gene RGA2 from a wild banana – into plants of the Cavendish variety. According to information, the first genetically modified banana was created.
The cultivation of bananas called QCAV-4 has been tested in field trials for several years. It has now been released in Australia as suitable for human consumption. However, QCAV-4 bananas are not yet available in supermarkets – and it should stay that way for the time being.
QCAV-4 was created using older genetic engineering methods – such foods often have to carry special labeling, which can be off-putting to consumers. However, plants and their fruits produced with the Crispr genetic scissors do not need such labeling in many countries, as Stam says.
Dale’s goal is now to create a Crispr banana: The RGA2 gene is in principle also present in Cavendish, but is not active, as Stam explains. It is hoped that a Crispr process could be used to reactivate RGA2 and thus make the variety resistant to TR4.
EU states continue to struggle to relax genetic engineering rules
Companies see this as an interesting approach: the QUT project receives millions of dollars in funding. It is currently unclear whether a Crispr banana could be sold in the EU without a genetic engineering label: a proposal from the EU Commission to relax the strict genetic engineering rules is currently stuck.
The project was presented in Brussels a good eight months ago, but so far the EU states have not been able to agree on a position. In addition, a compromise must then be found with the European Parliament. It is unlikely that this will happen before the elections in the summer.
Even if all kinds of breeding and various defense measures are being worked on: Stam is convinced that the Crispr banana will ultimately be the only way out of the TR4 crisis. This is completely unproblematic because only a gene is reactivated that is already present in the variety and in wild bananas.
According to Stam, fungi in particular could generally cause more problems in the future: wherever there are more warm and humid phases as a result of climate change. “Mushrooms like it warm and moist, and they often have an easier time when plants are weakened by heat.”
