Can Science Save the Banana?

CC BY 2.0. Shubert Ciencia -- Cavendish bananas, the most common variety that comprises 99% of exports

The most popular fruit in the world is such a vast monoculture that it doesn't stand a chance in the face of fungal infestation.

The banana-chocolate muffins I made last night may soon be relegated to the annals of historical foods, much like eel and pigeon pies. The bright yellow bananas that are ubiquitous in every grocery store and fruit bowl are at the brink of a serious collapse, threatened by fungal diseases that could wipe out the entire global crop -- forever.

The bananas we know in North America and Europe are the Cavendish variety, developed to replace a sweeter breed called Gros Michel after it was wiped out completely in the 1960s and ‘70s, due to a fungal infestation that impeded the plants’ ability to draw in nutrients from the soil and permanently ‘poisoned’ the soil for subsequent crops.

Unfortunately bananas growers did not learn from that lesson, because now we stand poised on the brink of a similar collapse. Cavendish has taken over, accounting for 99 percent of bananas exported from tropical countries and 47 percent of bananas grown worldwide. Local markets sell other varieties, but these are virtually unknown in North America and Europe.

red bananas

Connie Ma -- Bananas come in many different shapes, sizes, and colors/CC BY 2.0

The Guardian explains what now threatens the Cavendish banana:

“The Cavendish unfortunately has its own weaknesses – most prominently susceptibility to a disease called Black Sigatoka. The fungus Pseudocercospora fijiensis attacks the plants’ leaves, causing cell death that affects photosynthesis and leads to a reduction in fruit production and quality. If Black Sigatoka is left uncontrolled, banana yields can decline by 35 to 50 percent.”

In addition, a strain of Fusarium oxysporum, which wiped out the Gros Michel bananas, also known as Panama disease, has been spreading through southeast Asia, Australia, and Africa. When it reaches Central America, which supplies 82 percent of the world’s bananas, the industry will be in very big trouble.

From the journal Nature:

“Half of the current production relies on somaclones derived from a single triploid genotype (Cavendish). Pests and diseases have gradually become adapted, representing an imminent danger for global banana production.”

What are growers and researchers doing?

Farmers employ temporary solutions, such as trying to prevent the pathogen from entering new regions by using clean planting materials and not transferring contaminated soil between farms. There is extensive use of pesticides, which is hard on the land and workers, while also making the disease harder to control over the long term, as the hardiest, most chemical-resistant pathogen strains are the ones that survive.

Seeking a more permanent solution, researchers have identified the genome sequences of the banana and the fungi that cause Fusarium and Black Sigatoka. As The Guardian explains,

“These studies helped illuminate some of the molecular mechanisms by which these fungal pathogens cause disease in the banana. That knowledge provides a basis for identifying disease-resistant genes in wild and cultivated bananas.”

Breeders are also getting better at identifying resistance genes in wild bananas and learning how to transfer those to Cavendish varieties, either through genetic engineering or regular plant-breeding techniques. These methods (from the online patent) relate to “increasing the resistance of a plant or part thereof that is susceptible to infection with a pathogen.”

Consumers can help by buying other strains of banana whenever possible. As Dan Koeppel, author of Banana: The Fate of the Fruit that Changed the World, says in an interview for Australia’s ABC Rural:

“There are alternative varieties of banana that are absolutely delicious. The Cavendish is a terrible tasting banana. So a banana market with a lot of variety and choice would not be a bad thing for consumers.”
bananas in Kuala Lumpur

McKay Savage -- Smaller, local bananas in Kuala Lumpur/CC BY 2.0

When living in northeastern Brazil, I loved eating the brownish-yellow, 4- to 5-inch bananas that are sold in every market, as well as plantains, which can be fried, boiled, mashed, or baked. My husband was so surprised that we couldn’t find bananas as we know them.

wax-dipped bananas

Karl Baron -- Organic bananas are sometimes dipped in wax to seal the end and prevent insects from entering to lay eggs, reducing need for pesticide/CC BY 2.0

It may be helpful to opt for organic bananas whenever possible, as it’s gentler on the land and on agricultural workers, and does not perpetuate the unhealthy cycle of making pathogenic strains stronger than ever.

Learn more at MNN: Can bananas fend off fatal fungus?