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One super-susceptible clone, a versatile fungus and failing fungicides – black Sigatoka and banana

Why do we accept just one banana variety in Western supermarkets? It’s unsustainable and threatens livelihoods and food security.

Gert KemaBy Gert HJ Kema, Professor of Tropical Phytopathology, Wageningen University and Research Center, Wageningen, the Netherlands.

Competing Interests: Gert HJ Kema is an author of articles discussed in this blog.

Image Credit: Gert HJ Kema


Cavendish bananas saved the entire banana industry a century ago as the then most-planted variety “Gros Michel” was being wiped out by the soil-borne fungal pathogen Fusarium oxysporum causing Fusarium wilt or Panama disease, characterized by severe and progressive wilting and eventually plant death. This was a blow to the developing export trade, but primarily of course to the growers and all associated workers, leading to huge societal unrest and economic collapse. The major banana companies that had dominated the entire chain and unscrupulously protected their business were in dire straits, despite massive land claims and forced political instability, turning many Central American countries into the so-called “banana republics”.


Cavendish bananas at a supermarket. Image Credit: GHJ Kema

Cavendish, which like “Gros Michel” is a natural clone from South East Asia that was a mere peculiarity in some high society botanical gardens, appeared to be resistant to the Fusarium fungus. It gradually replaced “Gros Michel” and eventually it was back to business as usual. Over time, the entire logistic chain was professionalized and tailored to these Cavendish clones. Currently, these bananas dominate the global export trade and are also very important for major domestic markets in China and India. Anywhere in the world, supermarkets offer Cavendish, sourced from hundred-thousands of hectares planted to a single clone. The majority of consumers have no choice and hence have never experienced the far better tasting alternatives or the diversity offered at local markets. A great majority of consumers have neither the faintest idea nor interest in where and how food is produced – ignorance is omnipresent. Hence, ridiculous prices of less than one Euro per kilogram of bananas are considered normal and retailers promise to never change it, willingly binding consumers to – again – Cavendish. A vicious cycle of a lack of education and low-price lures strangle local growers, despite increasing production costs.


The end-result is a suite of Cavendish clones that are grown around the world and essentially represent one global banana clone. From the agronomical perspective this is a far from ideal situation, putting thousands of farmers at risk as such a “clonal highway” is an ideal vehicle for the dissemination of pathogens that kill Cavendish. The ongoing Panama disease epidemic is a good and eye-catching example.


Symptoms on banana leaf. Image Credit: GHJ Kema

However, not many people know that Cavendish bananas are also super-susceptible to Pseudocercospora fijiensis, the black Sigatoka fungus. As this is an airborne fungus, fungicides are the way to go – there is no resistant and commercially-viable banana in the pipeline of breeding programs. The number of applications to control black Sigatoka is outrageous, 50-70 times per year is currently common practice from Central America to the Philippines, resulting in an enormous selection pressure that results in increasingly resistant fungal populations, needing even more fungicide applications to manage the disease. Clean foliage is the driver for these control methods as black Sigatoka induces defoliation that switches on the early ripening process in the fruits, hence a large number of rejects for export and consequently enormous costs for the growers. The major class of fungicides that is being used are the so-called azole fungicides. New chemistry, such as the described QOI’s or strobilurins, were a great new option for a diversified palette of fungicides helping to protect the efficacy of azoles. However, a single point mutation in the cytochrome b gene rendered strobilurins completely ineffective and hence we are back to azoles. Clearly, the increasing cycles of fungicide applications have to stop. We cannot load the environment with fungicides. Despite being targeted at black Sigatoka, the vital biological diversity in many tropical countries, off-target problems of fungicides, as well as occupational health issues and water pollution, should all be taken seriously.


Aerial spraying of fungicides on a banana plantation. Image Credit: GHJ Kema.

What can turn the tide? Host resistance. Any other crop in the world has dedicated breeding efforts to continuously outsmart fungal pathogens. Not so in banana. Hence, the industry, commercial breeding companies, technology providers and funding agencies have to get together to develop a professional, commercial and highly technological banana breeding program targeted at the various markets. Only in this way can continued access to the top fruit of the world be guaranteed. More importantly, this is the only way forward to secure food for millions of people as banana – cooking bananas and plantains – is a staple food in many countries.


In our latest published paper in PLOS Genetics, we address the need for different solutions as the genome research clearly indicated massive issues on fungicide sensitivity, but also revealed huge opportunities for resistance as effectors from related pathogens and the black Sigatoka fungus are recognized in wild banana germplasm. Therefore, let’s explore and exploit these possibilities by unlocking the available biodiversity and move away from a single clone in the supermarket. This requires a concerted effort from all stakeholders, not least the retailers and consumers, to secure food and fruit for future generations.


Along with the Research Article by Gert HJ Kema and colleagues, PLOS Genetics also published another Research Article on the Sigatoka Disease Complex on banana and a Perspective Article, which frames the content and implications of both studies.


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