Beloved by people the world over, bananas are delicious and nutritious. But are they in danger of extinction? Will eating too many kill you? And are banana peels really that slippery? Imma Perfetto takes a peek inside the fleshy yellow crescent. This article was originally published in the Cosmos Print Magazine, March 2023.
Whether you prefer them in a smoothie, smooshed on toast with a bit of peanut butter, split and smothered in ice-cream and your favourite sticky topping, or just peeled and eaten plain, bananas are a universally crowd-pleasing fruit. Except, strictly, they're not a fruit (we'll get to that in a moment).
Cultivated bananas are the fourth most important crop in developing countries - after rice, wheat, and corn - and about 100 megatonnes are produced globally each year. To get an idea of what that looks like, they reckon the Great Pyramid of Giza weighs a little less than 6Mt. That's a lot of banana splits, yes? For some reason bananas seem to attract more myth and rumour than most cultivated objects.
Have you heard that bananas are all clones of each other? How about that they're going to go extinct one day because of a wickedly infectious banana disease? Let's peel back the skin on these, and some other, big banana facts and rumours.
Bananas are actually the berries of various flowering plant species in the genus Musa, which are native to tropical South-East Asia. Berry, not fruit, did I hear you say? Indeed you did. And will probably wish you'd brushed it off. It's a botanical thing, and somewhat chaotic, if you're a person that prefers order.
Botanists will tell you that berries have three distinct fleshy layers: an outer skin (exocarp), fleshy middle (mesocarp) and inner part that contains the seeds (endocarp). Berries also can't have a hardened woody endocarp (so peaches and cherries don't qualify), and they must develop from only one ovary within a single flower. So here's the fun: when you think through these qualities, surely then oranges are a berry? Aha: because oranges have distinct segments, they're a berry subtype called a hesperidium.
Just to be clear: the bananas we're talking about in this article are the sweeter forms that are generally eaten uncooked. The starchy, banana-like fruits that are cooked when they're less ripe are called plantains.
There are more than 1,000 different varieties within the genus Musa, but we're concerned with the cultivated varieties - not the wild ones. These edible domesticated varieties come from a genetic mutation that resulted in the seedless fruit we know today.
Domesticated bananas are parthenocarpic, which means that the fruit grows without seed development or pollination and fertilisation. In other words, they're tasty but sterile, so to propagate them you have to clone them.
That's not as sci-fi as it sounds, because banana plants produce these things called "suckers", which are shoots that develop from the stem of the plant. These suckers can be cut off and planted, after which they grow into a genetically identical fruit-producing plants. This is a pretty routine plant propagation process, and you can do it at home with many of your own houseplants.
Unfortunately, this makes bananas incredibly vulnerable to disease outbreaks because there's no genetic diversity. So, if one plant in a variety is susceptible to a disease, they all are.
How do we know this? Through experience.
"Cultivated bananas are the fourth most important crop in developing countries - after rice, wheat and corn - and about 100 mega tonnes are produced globally each year. "
The popular dessert bananas you're familiar with are a subgroup of varieties named Cavendish. They dominate the market today, making up around 50% of global banana production and about 95% of exports.
But the Cavendish wasn't always the crowd favourite. Until the 1950s, Gros Michel, or 'Big Mike', was the number one variety grown in commercial banana plantations.
That was until a fungal disease called fusarium wilt, or Panama disease, nearly wiped them out completely. The disease is caused by the fungus complex Fusarium oxysporum and was first reported in Australia in 1874, before spreading to nearly all banana-growing regions.
Fusarium is a soil pathogen that infects the plants' root and vascular system and makes them unable to transport essential water and nutrients, and it forced the banana industry to cultivate Fusarium-resistant Cavendish varieties instead.
(Cool Fusarium fact: the fungus is able to dissolve gold, then precipitate it onto its surface, thus coating itself with gold. CSIRO scientists first observed this at Boddington, West Australia, and published the finding in Nature Communications in 2019. They posited that F. oxysporum might be of help in detecting hidden underground gold reserves.)
You're probably thinking "thank goodness for Cavendish".
Well, yes - at least up until the emergence of an extremely virulent strain of fusarium wilt known as Tropical Race 4 (TR4).
Cavendish, and other Australian-grown varieties, are vulnerable to TR4. It was first detected in South-East Asia in the 1990s but has since spread to Australia, East Asia, Africa, and recently South America.
Once Fusarium fungus is established in an area, it can't be removed through chemical or physical means. The only way to protect bananas is to prevent the fungus from spreading, or to develop resistant banana varieties.
Scientists are improving diagnostic tools to locate TR4, and are using breeding and genetic engineering to try to create resistant varieties. One approach has scientists introducing antifungal genes from other plant species; in another, a resistance gene from the TR4-resistant wild banana Musa acuminata ssp malaccensis, has been introduced into Cavendish varieties.
A recent study published in PLOS One found that scientists could induce disease resistance by inoculating Cavendish bananas with a non-virulent form of the Fusarium strain called Race 1.
Have you heard that eating too many bananas could kill you - or at least make you very sick? This isn't about over-eating; according to the rumour mill, bananas can give you a fatal overdose of potassium, or a deadly exposure to radiation.
Bananas are a good source of potassium and too much potassium can sometimes lead to a fatal condition called hyperkalemia, which can be caused by kidney failure, heavy alcohol use, low red-blood-cell count, or overdosing on potassium supplements.
A medium banana contains about 420 milligrams of potassium, so you'd have to eat 11 in one day just to meet the 4700mg recommended daily allowance of potassium for adults and children older than four years.
There's no established upper limit of potassium intake, but oral doses of more than 18 grams may lead to hyperkalemia. You'd need to eat 42 bananas in a short period to achieve this result.
But what about radiation? In fact, bananas are slightly radioactive, thanks to a particular isotope called potassium-40.
All atoms of the same element have the same number of protons, but they don't always have the same number of neutrons - these are what are known as isotopes. Radioactive isotopes aren't stable, and they break down, releasing energy as radiation.
Naturally occurring potassium has three isotopes, one of which, potassium-40, is radioactive. Potassium-40 makes up about 0.012% of the total amount of potassium found in nature.
The potassium-40 dose you get from eating one banana will expose you to roughly 1% of your average daily exposure to background radiation. To get over the line to a lethal dose of radiation you'd need to eat 35 million bananas in a day.
Comedic art
Italian conceptual artist Maurizio Cattelan's 2019 work Comedian (left) became a fruit sensation when it was entered into Art Basel Miami Beach. It is, as shown at left, a real banana, duct-taped to a wall. Two editions of the certified art piece sold for US$120,000.
After the exhibition, performance artist David Datuna ate the exhibit in an intervention he called Hungry Artist.
"Conceptually, I ate the concept of the banana," Datuna told Vogue. "It tasted like $120,000. It was delicious."
If you've ever played Mario Kart, you'd know that banana peels can stop you right in your tracks. But are banana peels actually that slippery?
In a 2012 study in the journal Tribology Online, Japanese researchers from Kitasato University measured the friction coefficient under Cavendish banana skins.
A lower coefficient of friction implies that a surface is more slippery. Their experiment simulated a slipping accident under a sliding shoe and found that banana peels have a friction coefficient of 0.07. For context, surfaces with a friction coefficient of less than 0.1 are considered well lubricated, like ice on ice.
Further inspection under a microscope revealed that banana skins are lined with lots of tiny sacs of a gooey substance called polysaccharide follicular gel.
When the peel is crushed under foot, these substances are released and combine to make a slippery solution that forms a lubricating film between the shoe and surface.
It has been a pleasure pealing on about bananas, and there's probably a bunch more things I could write, but I've got to split. As Groucho Marx is reputed to have said: "Time flies like an arrow; fruit flies like a banana."