Fungal threat may wipeout bananas within 10 years

Scientists are concerned that three fungal diseases have the ability to decimate the world’s banana plant population and cripple the multi-billion dollar industry.

Courtesy of: UC Davis
Courtesy of: UC Davis

Plant pathologist Ioannis Stergiopoulos says discovery of how three fungal diseases attack banana plants should be a “wake-up call” to the research community.

Updated Aug 18, 2016

The fate of the banana is at risk. Researchers are working diligently to ward off an impending “bananapocalypse” from decimating millions of hectares and billions of dollars worth of the fruit. Three fungal diseases are at the centerpoint of a worldwide epidemic, one that could end the life of bananas in 5-10 years.

“A recipe for disaster”

Thanks to modern gene-mapping techniques, scientists are dissecting a new fungal threat at the molecular level. Three closely related fungal diseases are being studied, and in a research paper published online this week, scientist may have found out how these fungi spread, infect, and ultimately destroy bananas. Known as the Sigatoka complex, this triad of fungi are currently responsible for a total annual loss of about 40 percent of the world’s banana yield.

University of California at Davis' plant pathologist Ioannis Stergiopoulos led a team examining these fungi more closely. He reported that “[The fungal disease causes] 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.” What that means is that the fungi can shut down the plant’s immune system and produce chemicals which break down the banana’s sugars and carbs, giving food and fuel to the fungus.

The Modern Banana

Cavendish is what most people think of when they hear ‘banana’, although they may not know it. Taken from a single tree generations ago, nearly every store bought banana on earth is a genetically identical clone; brought forth through a method of farming known as ‘splicing’.

The price of bananas is displayed on a digital price tag

Today, bananas aren’t grown from seeds. Instead a shoot clipping is taken from a living tree, and replanted elsewhere, thus creating a clone of the original plant, all of which can be traced back to a single ancestral donor. This mode of plant propagation has created a single self-replicating form of life, and an easy target for diseases.

“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,” Stergiopoulos said.

“Two of the three most serious banana fungal diseases have become more virulent.”

Genetic diversity has been nature's way of ensuring that any given species isn’t mortally vulnerable to an attack by a single disease. With diversity comes safety against viruses, bacteria, and in this case fungi. In order to destroy an entire species of fruit, a disease must be able to target all variants, and at the same time.

Unfortunately in this instance, the attacking organism doesn't have to adapt to endless varieties in order to end an entire species. It just has to infect one plant. One genome. One target. And it’s doing just that.

Deja Vu

Before the Cavendish, there was another species of banana called the Gros Michel, aka “Big Mike”, which was the only banana sold in America for nearly 200 years. A larger, heartier, and by many accounts, tastier variety, it too was a clone and as such, faced an identical threat. In the early part of the 1950s, the entire Gros Michel population was wiped out.

Internal browning of stems and corms is the key diagnostic symptom of Panama disease

The banana tree lost a ruthless battle against a fast spreading root fungus called fusarium oxysporum, which caused the notorious Panama Disease. One fungus, easily able to adapt to the only strain of banana plant around, caused a temporary global collapse of the banana trade. Quick to find a more robust replacement, the now universally known Cavendish was a logical substitute. Thought to be immune to the root disease, it was hailed as a savior fruit by farmers everywhere. That was, until more recently.

History repeats itself

As it turned out, the Cavendish banana was only safe against one specific strain of the Panama Disease, that which decimated the Gros Michel. Now decades later, the banana tree is fighting off a relative to the same root fungus that wiped out Big Mike, along with an even more destructive disease, the aforementioned Sigatoka complex.

"For [each] five [infected] plants, I think they have been removing 10 hectares surrounding these five plants."

Another study authored by Dr. Gert Kema at the Netherlands University of Wageningen last year confirmed that it was indeed a mutated form of the original Panama Disease, dubbed Panama Tropical Race 4 (TR4) that was responsible for infecting and killing thousands of new crops. Global trade routes had spread infected fungal spores around the planet before anyone noticed what was going on.

A crop duster plane sprays fungicide on a Mindanao banana plantation

With infestations spotted throughout Asia, Malaysia, Taiwan, the Philippines and Africa, all efforts are behind stopping the Panama Disease’s Cavendish killing counterpart TR4 from entering Central and Latin America, which supplies of over 80 percent of the the world’s bananas. Last week’s findings from the team at UC Davis will give researchers much needed information on how these fungi attack their hosts, and create possible strategies for curing for the ailing plant.

A global market at risk, again

As a commonly described ‘staple food’, bananas are everywhere, and where there’s demand, supply must flow. The global banana market is an estimated $11 billion dollar industry, with Latin American and Caribbean countries easily accounting for nearly 60 percent of the pie.

World banana exports by country

Producers and exporters are worried. If the fungus isn’t stopped, or a new and genetically superior banana strain isn’t concocted, it would be ruinous for small family farmers and export countries alike.

In the cases where contamination is confirmed, Dr. Kema explains the ramifications of the established quarantine methods, "For five plants, I think they  have been removing 10 hectares surrounding these five plants," Dr. Kema continued. 

"If you work in a country with millions of smallholders, or hundreds of thousands of smallholders, that usually have only a few hectares or less, you essentially tell a farmer, give up banana growing. That's a very severe method."

Already, great cost is being spent on trying to fight the fungi.

“Thirty to 35 percent of banana production cost is in fungicide applications,” UC Davis’ Stergiopoulos explained. “Because many farmers can’t afford the fungicide, they grow bananas of lesser quality, which bring them less income.”

Costa Rica, the world’s third largest producer, employs 8 percent of it’s population in the banana trade. Ecuador, the largest producer and exporter of bananas, already loses 40 percent of its yearly crop to the Sigatoka complex fungi. A TR4 outbreak would seriously dampen its already fragile economy and very likely spike the already high 25 percent poverty rate.

With the need for a plant that tastes good, travels well, ripens correctly, and is immune to disease, botanists and scientists are working together quickly to find a solution.

Author: Omar Elwafai

TRTWorld and agencies