Why Are Bananas Seedless? A Fruit Bred Into a Dead End

Wild bananas, Musa acuminata and Musa balbisiana, grow across the forests from India to New Guinea, and their seeds are spread by the bats and birds that eat the fruit. Somewhere in the region, probably more than 7,000 years ago, a plant produced fruit whose flesh developed without the seeds being fertilised, a trick called parthenocarpy, and people who found it kept it. Hybrids between the two wild species and, crucially, plants that had ended up with three sets of chromosomes rather than two, were sterile: with an odd number of chromosome sets the cells cannot pair them up to make viable pollen or eggs, so the fruit swells without seeds. Triploidy is what makes a banana edible and what makes it a dead end at the same time, and the same trick produces seedless watermelons and the seedless grapes that the trade prefers.

The banana plant is the world's largest herb. What looks like a trunk is a tight roll of leaf bases, the true stem is a corm underground, and after a plant has flowered and fruited once it dies, to be replaced by suckers growing from the base of the corm. Those suckers are how bananas have always been propagated: cut one off, plant it, and it grows into a genetically identical copy. The plants in a commercial plantation are now more often started in a laboratory from a few cells in a test tube, which multiplies them faster and free of disease, but the result is the same. A plantation, a country, a whole continent's banana crop can be one individual, repeated.

Until the 1950s the banana of world trade was the Gros Michel, a bigger, sweeter and more robust variety than anything sold now, and the reason it disappeared was a soil fungus, Fusarium, that causes Panama disease. It reached the plantations of Central America in the 1890s, spread through the soil and the water and on the boots of workers, and killed the plants from the roots up; no fungicide reaches it and the spores survive in the ground for decades. Because every plant was the same, none was resistant, and the companies dealt with it by abandoning infected land and clearing new forest until they ran out. The replacement was the Cavendish, a Chinese variety grown in a Derbyshire greenhouse in the 1830s, less flavoursome, bruising easily, but resistant to the strain of the fungus then loose. The artificial banana flavour of sweets, based on the Gros Michel, is the taste of a fruit almost nobody alive has eaten.

In the 1990s a new strain, Tropical Race 4, appeared in Taiwan and Malaysia, and it kills the Cavendish. It has since reached the Philippines, Australia, the Middle East, Africa and, in 2019, Colombia, the first case in Latin America, where most of the export crop grows. The response so far:

• •Quarantine: fencing, foot baths and the destruction of infected fields, which slows the fungus without stopping it
• •Breeding: crossing the sterile Cavendish is nearly impossible, so breeders work with rare fertile relatives and with the wild species, and the few resistant hybrids so far taste different
• •Gene editing: a Cavendish given a resistance gene from a wild banana proved immune in Australian field trials in 2017, and a modified variety was approved for growing there in 2024, though whether consumers and importers will accept it is open
• •Diversity: growing several varieties, as smallholders in Africa and Asia always have, so that no single disease takes everything

The banana is the extreme case of a pattern that runs through modern farming. A single high-yielding clone or variety, planted across a continent, is efficient and uniform and defenceless, and the Irish potato of 1845, the wheat rusts of the twentieth century and the citrus greening now emptying Florida's groves are versions of the same story. The banana's answer will probably be a resistant Cavendish, edited or bred, planted in exactly the same way, and the fungus will in time find a way round that too, because a crop that cannot breed cannot evolve and the fungus can. Meanwhile it remains the most eaten fruit in the world, the cheapest item in most supermarkets, and a staple that half a billion people in the tropics depend on in the form of the starchy cooking bananas that the export trade never touches.

Bananas are seedless because the cultivated plant is a sterile hybrid with three sets of chromosomes, whose fruit swells without fertilisation, and it has been propagated for thousands of years by cutting suckers from the base, so that every commercial banana is a genetic copy of one plant. The Gros Michel clone was destroyed by a soil fungus in the 1950s and replaced by the Cavendish, which a new strain of the same fungus is now killing across Asia, Africa and Latin America, and a fruit that cannot breed cannot outrun it.