A staple of grocery store bins and household fruit bowls around the world, you might be forgiven for assuming the humble, ubiquitous banana would be around forever. But evolving fungal diseases are threatening the global banana industry, and a total "bananageddon" could wipe out the fruit within a decade. Researchers at University of California, Davis (UC Davis) have sequenced the genomes of the fungi to find a way to fight back.

The most common type of banana the western world eats is the Cavendish, which is produced through vegetative reproduction – instead of growing from seeds, cuttings of the plant's shoots are replanted and cultivated, making all Cavendish bananas essentially "clones" of one specific plant. Without genetic variety, as diseases gain a foothold over the fruit, they're equipped to potentially take out the entire worldwide crop.

"The Cavendish banana plants all originated from one plant and so as clones, they all have the same genotype – and that is a recipe for disaster," says Ioannis Stergiopoulos, plant pathologist at UC Davis.

Currently, close to 120 countries produce about 100 million tons of bananas each year, but 40 percent of the yield is spoiled by Sigatoka, a fungal disease complex comprised of three strains: yellow Sigatoka, black Sigatoka and eumusae leaf spot. To combat the ever-present threat, farmers need to apply fungicide to their crops 50 times a year, which isn't only costly, but can pose a threat to the environment and human health.

"Thirty to 35 percent of banana production cost is in fungicide applications," says Stergiopoulos. "Because many farmers can't afford the fungicide, they grow bananas of lesser quality, which bring them less income."

The Cavendish variety rose to market prominence in the second half of the 20th century after the previously ubiquitous species, the Gros Michel, was all but wiped out by a similar fungus, Panama disease. To try to prevent a similar bananapocalypse, Stergiopoulos and the UC Davis team set about sequencing the genome of the fungi to determine how it attacks its hosts and, hopefully, how it can be overcome.

With the genome of yellow Sigatoka already sequenced, the team did the same for the other two diseases, then compared the results of all three. It was found that the fungi not only shuts down the host plant's immune system, but adapts its own metabolism to match that of its host, allowing it to produce enzymes that break down the cell walls and release the sugars and carbohydrates for it to feed on. Armed with that knowledge, the team hopes that further research will lead to a solution.

"This parallel change in metabolism of the pathogen and the host plant has been overlooked until now and may represent a 'molecular fingerprint' of the adaption process," says Stergiopoulos. "It is really a wake-up call to the research community to look at similar mechanisms between pathogens and their plant hosts."

The research was published in the journal PLOS Genetics.

Source: UC Davis

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