A deadly fungus almost killed off one of the world’s most popular varieties of banana in the middle of the last century. Now, a new strain is again devastating plantations across the globe.

It’s already hit Australia, Africa and Asia. And the Fusarium fungus has recently arrived in Colombia, one of the world's biggest growers of bananas, prompting the government to declare a national emergency.

Popularly known as Panama Disease, the fungus wiped out vast amounts of the world’s stock of Gros Michel banana plants during the 20th century. Farmers then switched to growing the Cavendish banana because it was resistant to Fusarium - a variety that now accounts for 97% of world banana exports.

So producers were horrified to discover that the new strain of Panama Disease, Tropical Race 4 (TR4), could overcome the Cavendish banana’s resistance. Even worse, TR4 poses a threat to other local varieties of banana – a staple food for hundreds of millions of people worldwide.

A global favourite

Colombia exports 1.8 million tonnes of bananas every year, mostly to Europe. Across the world, 100 million tonnes are eaten annually, with most consumed in the countries where they are grown. While less than 20% of bananas produced are exported, the world banana trade is worth almost $12 billion a year.

The UN Food and Agriculture Organization (FAO) says there is currently no fully effective treatment to control or cure Fusarium. Its spores remain in the soil for decades and are impossible to eradicate.

TR4 kills banana plants by blocking tissue in their stems, starving the plant of water and causing its leaves to wilt and die.

Quarantining infected farms can help, but the biggest challenge with the fungus is how easily it spreads. The fungus travels through infected plant material and soil particles attached to vehicles and farm equipment, as well as through irrigation, drainage water and floods.

Worse still, there's currently no fungus-resistant variety that could replace the Cavendish - a major issue given its new vulnerability to TR4 and it's near total dominance of the global export market.

Image: UN Food & Agriculture Organisation (FAO)

GM bananas, anyone?

Scientists believe gene editing may be the only way to create fungus-resistant bananas. But Europe - the world’s largest banana importer, buying 6 million tonnes last year - may resist a push towards genetically modified crops due to strict existing laws.

The outbreak has highlighted a fundamental flaw in the global food system. Relying on a single export variety grown in monoculture plantations, with no other plants, has created a situation where the world may find itself with no bananas to eat.

Moreover, global trade allows pathogens such as Fusarium to easily travel between continents, prompting fears about biosecurity.

The World Economic Forum’s 2019 Global Risks Report warns the world is unprepared for major biological threats, and calls for countries to cooperate more closely in an increasingly globalized world.