The banana is dying. The race is on to reinvent it before it’s too late.

The world’s most popular fruit is facing extinction, and scientists are racing to use gene-editing to save it. To succeed, they’ll need to overcome an even bigger problem: opposition to GMO crops.

During the summer of 1989, Randy Ploetz was in his laboratory just south of Miami, when he received a package from Taiwan. Ploetz, who had earned his doctorate in plant pathology five years earlier, was collecting banana diseases and regularly received mysterious packages containing pathogens pulled out of the soil from far-flung plantations. But gazing down his microscope, Ploetz realised this Taiwanese pathogen was unlike any banana disease he’d encountered before, so he sent the sample for genetic testing. It was Tropical Race 4 (TR4) – a strain of the fungus Fusarium oxysporum cubense that lives in the soil, is impervious to pesticides, and kills banana plants by choking them of water and nutrients. It was a pathogen that would go on to consume the next three decades of his professional life.

TR4 only affects a particular type of banana called the Cavendish. There are more than 1,000 banana varieties in the world, but the Cavendish, named after a British nobleman who grew the exotic fruit in his greenhouses on the edge of the Peak District, makes up almost the entire export market. The Brazilian apple banana, for example, is small and tart with firm flesh, while the stubby Pisang Awak, a staple in Malaysia, is much sweeter than the Cavendish. But no banana has become as ubiquitous as the Cavendish, which accounts for 47 per cent of all global production of the fruit. According to the Food and Agriculture Organisation of the United Nations, this amounts to 50 million tonnes of Cavendish bananas every year – 99 per cent of all global banana exports.

The UK, which imports five billion bananas every year, has become used to this seemingly endless supply of cheap and nutritious fruits shipped from plantations thousands of kilometres away across the Atlantic. But the high-volume, low-margin banana industry has been balancing on a knife edge for decades. “It looks very stable because we’re getting bananas, but the environmental and social costs that allow that to happen have been high,” says Dan Bebber, a researcher at the University of Exeter who works on a UK government-funded project aimed at securing the future of the banana. If one part of this tightly-wound supply chain snaps, the whole export industry could come tumbling down.

Despite its ubiquity, the Cavendish is something of a genetic outlier among crops: because it has three copies of each chromosome, it is sterile and can only reproduce by creating clones of itself. This makes the Cavendish an ideal crop to grow at scale – farmers know how a plantation of Cavendish bananas will respond to pesticides, how fast its fruit will ripen, how many bananas each plant will yield. “You know what’s going to happen to a Cavendish banana when you pick it,” says Bebber. “When you put it in a refrigerated container, you know exactly what’s going to come out of the other end most of the time.” Cavendish plants are short, so they don’t blow over easily in a hurricane, are easy to spray with pesticides, and reliably produce lots of bananas.

By concentrating all their efforts on the Cavendish, banana exporters have built a system that allows a tropical fruit grown thousands of kilometres away to appear on supermarket shelves in the UK for less than £1 per kilo – undercutting fruits like apples which are grown in dozens of varieties much closer to home. “People want cheap bananas,” says Bebber. “The system is set up for a very uniform crop.” To put it bluntly – uniformity equals higher profits-per-plant for banana producers. “They are addicted to Cavendish,” says Ploetz, today a 66-year-old professor at the University of Florida’s Tropical Research and Education Centre. It is this genetic uniformity that lays the foundation for an $8 billion-a-year export industry.

A TR4infected banana plantation near Darwin Australia. To try and prevent its spread the region is subject to...
A TR4-infected banana plantation near Darwin, Australia. To try and prevent its spread, the region is subject to bio-quarantine rules.JEFF DANIELS

The Cavendish hasn’t always been popular. Before the 1950s, Europe and America’s banana of choice was the Gros Michel – a creamier, sweeter banana that dominated the export market. Unlike the Cavendish, which needed to be transported in boxes to protect its fragile skin, the robust and thick-skinned Gros Michel was ideally suited to long, bumpy journeys across the Atlantic. At the time, the thin-skinned and slightly bland Cavendish was seen as a second-rate banana.

However, Gros Michel had one weakness. It was susceptible to Tropical Race 1 (TR1), an earlier strain of the Fusarium fungus. TR1 was first detected in Latin America in 1890 and, in the 60 years that followed, it tore through banana plantations in Latin America, costing the industry $2.3 billion in today’s terms. Faced with no other choice, the major banana firms switched production to their backup banana: the Cavendish. In 1960, the world’s biggest banana exporter, United Fruit Company (now called Chiquita) began switching to the Cavendish, following the lead of its smaller rival, Standard Fruit Company (now called Dole) which switched in 1947. Despite all its shortcomings, the Cavendish had one huge advantage over the Gros Michel, which disappeared from US supermarket shelves forever in 1965: it was completely resistant to TR1.

But the Cavendish has no defence against TR4. When Ploetz first encountered the new pathogen, there had been just a handful of suspected infections reported. In 1992, Ploetz received packages containing TR4 from plantations in Indonesia and Malaysia. “At the time all we knew was that it was a new pathogen,” he says. “We didn’t know what to expect as far as its broader implications. The more samples we got from these export plantations, the more we began to realise that this was a bigger issue than we had ever anticipated,” he recalls. His prediction proved to be eerily accurate.

In 2013, TR4 was found for the first time in Mozambique. Ploetz thinks it had been carried on the boots and equipment of banana planters from southeast Asia. The pathogen has now travelled to Lebanon, Israel, India, Jordan, Oman, Pakistan and Australia. In 2018, it was found in Myanmar. “Then in southeast Asia,” Ploetz says. “It’s everywhere.”

When TR4 hits, the destruction is near-total. “It looks like somebody’s gone to the plantation with a herbicide,” Ploetz says. “There are big areas that no longer have any plants at all.” The fungus, which can live undetected in the soil for decades, enters banana plants through their roots and spreads to the water- and nutrient-conducting tissue within, eventually starving the plant of nourishment. Two to nine months after being infected, the plant – hollowed out from the inside – collapses in on itself. The soil it grew in, now riddled with the fungus, is useless for growing bananas.

So far, Latin America, which grows almost all of the world’s export bananas – including those for the US and Europe – has escaped TR4. But, Ploetz says, it’s only a matter of time. “Our concern in Central America is that if somebody has an outbreak on their property, they are going to keep their mouths shut, and then it’ll have spread widely by the time people realise it’s there,” he says.

Faced with a crisis that could see the Cavendish gone forever, a handful of researchers are racing to use gene-editing to create a better banana and bring the world’s first TR4- resistant Cavendish to the market. To get there, they will butt up against not only the limitations of technology, but resistance from lawmakers, environmentalists and consumers wary of GM crops. But as TR4 closes in on Latin America, gene-editing may be the last chance we have to save the one banana we have chosen above all others.

In a field outside a small town called Humpty Doo in Australia’s sparsely-populated Northern Territory, one solution to the TR4 epidemic has been growing for the last six years. “In the Northern Territory, [TR4] is in virtually all the banana growing areas,” says James Dale, a professor at Queensland University of Technology in Brisbane. “Most plantations are still shut down.” But in that one field, the world’s only TR4-resistant Cavendish bananas have been thriving, while all around them, plants have succumbed.

For eight years, the key to creating TR4-resistant bananas remained locked within Dale’s laboratory. In 2004, he isolated a single gene from a wild banana called Musa acuminata malaccensis. Unlike its distant offspring, Musa acuminata malaccensis is unlikely to ever find itself as a cereal-topper. Its small, thin fruits are filled with upwards of 60 hard seeds, each about half a centimetre in diameter. But the inedible plant has something else going for it. It is naturally resistant to TR4.

It wasn’t until he received a call from an Australian plantation owner that Dale got the chance to put his edited bananas to the test. Robert Borsato opened his banana plantation just outside Humpty Doo in 1996 – a year before TR4 was detected in Darwin, 40km away. By the late 2000s, Borsato’s farm was overrun with the disease. Desperate, he turned to Dale for help.

“I told him, ‘we’ve got this possible solution, but we have no idea whether these plants are resistant – would you work with us?’” recalls Dale, who is 68 and wears rimless glasses and a scruffy grey beard. “And we went up there and that really was bingo,” he says, grinning.

The three-year trial finished in 2015, but it would be two more years before Dale published his results in the journal Nature Communications. By the end of the trial, between 67 and 100 per cent of the plants without the resistance gene had been killed or infected with TR4. Of the five plant lines with the added RGA2 gene, four had much lower infection rates – below 30 per cent – and one line showed no signs of the disease at all. Another set of plants edited with a TR4-resistance gene from a roundworm showed similar survival rates.

After the success of the initial field trial, Dale is launching another study in Humpty Doo, encompassing an area more than ten times larger than the original site. He hopes to see the edited Cavendish on sale by 2021 – the first genetically-modified (GM) bananas ever sold in Australia. They would be the first GM bananas sold anywhere, but another trial Dale is running, a Bill and Melinda Gates Foundation-funded plan to engineer vitamin-A enriched Cavendish bananas in Uganda, will likely pip the Australian bananas to the post.

But Dale’s TR4-resistant bananas are still to pass a vital test. He hasn’t eaten a single one – not even on the sly, he insists, as the terms of his trial license prohibit anyone from tasting the fruit. “We actually have to squish them up and use them as mulch,” Dale says. Instead, all of his TR4-resistant bananas – the only ones of their kind anywhere in the world – are turned into fertiliser.

The problem is that Dale’s plants are classified as genetically-modified organisms (GMOs). His bananas contain genetic information from two organisms – the gene from Musa acuminata malaccensis is transplanted into the Cavendish genome by using bacteria as a “shuttle”. And under the Australian Office of the Gene Technology Regulator, experimenting with GMOs is only permitted under strict conditions designed to prevent any potential harm to humans and to minimise the chance that GM plants will breed with naturally-occurring plants and introduce genetic changes. A worry that, in the case of the sterile Cavendish, is unnecessary.

Dale recalls a field trial of GM bananas hit by a cyclone in North Queensland. “All of the bananas were on the ground – they were just blown down,” he says. The next morning he received a call from the Office of the Gene Technology Regulator asking whether there was GM banana material blown all over Australia. “I suspect so,” Dale told the regulator. But because Cavendish bananas are sterile, there was zero chance that any stray GM-banana DNA would end up in another plant. “Bananas are, probably of all the crops, the absolute safest to do both glasshouse and field trials on GM material. There’s no chance of escape.”

If his next trial is successful, Dale plans to apply for a tasting license and then bring the bananas to market. “During the next four to five years that it’s going to take to get these bananas through the regulation process, TR4 is going to become a really, really significant factor in the Australian industry,” Dale says. And since Australia bans the import of fresh bananas, the government may be forced to choose between accepting GM bananas or lifting its import restrictions. “My bet is they’ll have a GM Cavendish,” Dale says.

Outside of Uganda and Australia, the future for the GM banana looks bleak. In the EU, only 64 GM crops are approved for sale – all of them versions of cotton, maize, oilseed rape, soybean or sugarbeet – with the vast majority of them going into animal feed. Only one GM crop is cultivated in the EU – MON 810 – a form of maize genetically-engineered to be resistant to a moth that bores holes into the plant. Despite being relatively common in the US, GM fruit and vegetables have never been sold in the EU, and banana companies, too, have shunned GM fruit. “We’re a completely natural company,” an executive from Del Monte told me on the phone when I raised the question of gene-edited crops.

Dale knows that his TR4-resistant bananas are unlikely to ever leave Australia. “If the world accepted GM, then they’d be ready to go,” he says. Although scientists have been unable to find any long-term health impacts linked to any consumption of genetically modified food – a stance endorsed by the World Health Organisation and the American Medical Association – consumer and environmental groups have long opposed the technology.

Dozens of countries, including China, Russia, Japan, Australia, Brazil and the European Union, legally require GM food to be labelled. In the US, where many food companies place voluntary “No GMO” labels on their products, a law requiring the labelling of GM foods was signed by President Obama in July 2016, but food manufacturers have to date been slow to respond to the new regulations.

Dale suspects that – outside of a few unique cases – the world will never accept his GMO bananas. “We have lost the GM discussion,” he says. But, in 2016, as he was poring over the results from his field trial of TR4-resistant crops, Dale spotted an announcement that reignited his hopes for a superior Cavendish. In April, the United States Department of Agricultural (USDA) approved a mushroom that had been engineered to resist browning using a new gene-editing tool called CRISPR. In March 2018, the USDA clarified its position, saying that it would not regulate “a set of new techniques that are increasingly being used by plant breeders to produce new plant varieties that are indistinguishable from those developed through traditional breeding methods.”

Author: massamadmin

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