By Angus Dalton
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At the start of this century, James Dale chose a formidable opponent.
The virulent fungal pathogen had arrived in Australia in 1997. Scientific name: Fusarium oxysporum f.sp. cubense. My suggestion: the Banana Boogeyman.
The fungus can lurk for years in soils, from cactus-studded deserts to icy tundra. When the fungus comes into contact with a banana plant’s roots, it deploys slender hyphae tentacles that snake into the plant through wounds opened by parasitic weevils and nematode worms.
Panama disease causing wilt in banana plants (left) and brown discolouration in the pseudostem (right).Credit: Department of Agriculture and Fisheries
The fungus strangles the plant’s vascular system and starves its host. By the time symptoms show – yellowing foliage, dead leaves collapsing into a brown skirt, younger leaves stunted to resemble spikes – it’s too late.
The plant dies and the fungus releases plumes of hardy spores. Just one microscopic speck is enough to infect the next plant.
This affliction, Panama disease, decimated the world’s former most popular banana, the Gros Michel. Now a strain of the disease called tropical race 4 threatens the existence of Cavendish bananas, which today make up half of global banana production and account for a $US20 billion ($29.6 billion) industry.
The culprit threatening to wipe out the Cavendish banana: a fungus called Fusarium oxysporum f. sp. cubense.Credit: Wikimedia
Dale, now a distinguished professor at the Queensland University of Technology, has been racing for 25 years to create a banana resistant to the disease. But his method is a controversial one.
The wild saviour
Back in the ’90s and 2000s, genetically modified crops had a bad rap. There were a number of small and disputed animal studies that claimed eating GM foods caused harm.
“Non-GMO” became a ubiquitous marketing slogan. Public suspicion drove a worldwide crackdown on GM crops, including a moratorium in NSW that began in 2003 and only lifted in 2021.
Professor James Dale studying Panama-resistance banana genes in the lab in 2001.Credit: Angela Wylie
But Dale was convinced genetic modification was the only way to save the banana.
As he hunted for a way to make the Cavendish resistant to Panama disease, an American plant pathologist, Ivan Buddenhagen, was in South-East Asia surveying crop fields razed by the fungus.
On one farm, a stand of banana plants grew lush and fruitful amid the destruction. They were wild plants. Buddenhagen gathered their seeds and sent them to Dale.
Seedless, sterile, and susceptible to death
By the hand of human selection, domestic bananas have become seedless and sterile, losing the evolutionary force that could have allowed them to adapt to Panama disease via natural selection.
“Luckily, there are still wild bananas that go through their normal evolutionary process,” Dale says.
In the wild bananas, Dale and his team identified the gene suspected to underpin resistance to Panama disease. A PhD student discovered the RGA2 gene was present in the kind of Cavendish they worked with, the Grand Nain, but it wasn’t “expressed”, or turned on. But it was turned on in the wild bananas. Bingo!
They set to work getting the RGA2 gene into Grand Nains. These were the days before the easy gene-editing tool CRISPR, so they hijacked bacteria to do their bidding.
Professor Dale with a GM banana plant ahead of a field trial in 2017.Credit: Anthony Weate
“Agrobacterium is a natural genetic engineer, that’s its lifestyle,” Dale says. “It infects huge numbers of plants and transfers a bit of its DNA into its host plant. That bit of DNA encodes sugars that only it can live on.”
By swapping out that sugar-producing DNA with the RGA2 gene, the scientists reprogrammed the agrobacterium to deliver the fungus-resistant gene to Grand Nains.
The most important test
Then Dale struck a problem – the team couldn’t do field trials because they weren’t allowed to bring Panama fungus into Queensland.
But then the plant pathologist Buddenhagen came back into frame: he’d met with a Northern Territory farmer who’d bought a patch of land riddled with the fungus in Humpty Doo near Darwin.
The QCAV-4 undergoes its most important test after 25 years of research.Credit: QUT
Buddenhagen introduced Dale to the farmer, who decided to help fund and host the trials. On his field, they tested seven kinds of GM banana plants and found one – QCAV-4 – was particularly resistant to Panama disease.
Their momentum was dashed again when they were forced to destroy those plants in 2015 due to biosecurity measures triggered to control an outbreak of a different disease, banana freckle. But in 2018 they returned to grow 50 QCAV-4 plants. Today, 47 of them are alive and thriving.
In February this year, the government approved the commercial release of the QCAV-4 banana after rigorous regulatory checks and, last week, QUT announced the fruit had passed its most important milestone: the taste test.
“They taste great,” Dale says. “They’re as good as any well-grown Cavendish.”
But will the broader public share this taste for GM fruit?
Allergens and vitamin A
Hundreds of pages of regulatory data submitted to Food Standards Australia New Zealand and the Office of the Gene Technology Regulator – and an enormous amount of work – got QCAV-4 over the line.
One of the regulatory tests involved screening the gene-edited crop for potential allergens and toxins, an important undertaking given that a 1996 study found when scientists transferred genes from brazil nuts into soybeans to improve the crops’ nutritional value, they also transferred allergens from the nuts that could cause anaphylaxis.
But Dale says onerous regulatory requirements hold back innovation in this space. “QCAV-4 is the first genetically modified crop that’s been developed at a university and released in Australia. That gives you an idea of how difficult it is.”
Professor Dale’s bananas biofortified with pro-vitamin A could save thousands of lives if grown in places where people die of nutrient deficiency, such as Uganda. The biofortification gives the GM bananas a “golden” colour (left).Credit: Jean-Yves Paul
He has also developed a “biofortified” banana that could help children suffering from vitamin A deficiency, which kills 750,000 children a year in places such as Uganda. The vitamin-rich plants are ready to go, but the biosecurity bill that would allow the deregulation of the potentially life-saving crop has been held up in the Ugandan parliament since the project started.
“It’s unbelievably frustrating,” Dale says.
Would you eat a GM banana?
Once they’re cleared for allergens and toxins, there’s no compelling evidence GM foods pose a risk to human health. A recent systematic review found studies that reported adverse effects were badly designed, prone to bias, and based on animal studies, “the lowest hierarchy of evidence”.
On home soil, it will be interesting to see how genetically modified foods are embraced as more hit the market. Dale says climate change will leave us no choice but to splice in heat-resistant genes to wheat, that won’t go to seed above certain temperatures.
He is also working on cisgenics, where scientists edit the DNA of crops but don’t introduce genetic material from other species. Cisgenic editing falls outside current definitions of “genetically modified” and skirts regulatory requirements because the process mimics that of natural evolution selecting for random mutations. (Some scientists argue this does constitute GM and that resulting products should be labelled as such.)
As for Dale’s GM bananas, although they have received regulatory approval, there are no plans to roll out QCAV-4 commercially until Panama disease spreads further and poses an existential threat to the industry.
“If it gets really serious, then that’s when we’ll talk with the Australian Banana Growers’ Council as to whether we pull the trigger and start to grow these commercially,” Dale says.
So, tell me, when that happens – will you bite?