Banana Domestication More Complex Than Previously Thought

People like to know where their food comes from, but even experts are throwing up their hands when it comes to the origins of the modern banana.

An extensive genetic analysis of more than 100 varieties of wild and cultivated bananas unpeels the fruit’s tangled history of domestication and reveals the existence of three previously unknown—and possibly still living—ancestors.

Banana experts want to track down those mysterious forebears to see whether their genes might help keep modern banana crops healthy.

“Banana domestication is much more complicated than I had realized previously,” says Loren Rieseberg, an evolutionary biologist at the University of British Columbia, Vancouver, who was not involved in the study.

About 7000 years ago, bananas were not the seedless, fleshy fruits we know today. The flesh was pitted with black seeds and nearly inedible. Instead, people ate the banana tree’s flowers or its underground tubers. They also stripped fibres from the trunklike stem to make rope and clothes. Banana trees back then were “very far from the bananas we see in people’s fields today,” says Julie Sardos, a genetic resources scientist at the Alliance of Bioversity International, which stockpiles banana varieties.

Scientists do know the banana’s predominant wild ancestor is a species named Musa acuminata, which occurs from India to Australia. Most researchers agree that Papua New Guinea is where domesticated bananas as we know them first appeared. Today, there are many banana varieties—more than 1000 at the last count.

Over the course of their domestication, the modern bananas available in supermarkets lost their seeds and became fleshier and sweeter. But it’s been hard to pin down exactly how and when that domestication occurred.

Complicating matters, some bananas have the usual two sets of chromosomes, whereas others have three sets or more, suggesting at least some modern bananas are hybrids that resulted from the interbreeding of two or more varieties, or even different species.

There’s good reason to try to tap into the modern banana’s deep historical gene pool: The $8 billion banana industry, which produces 100 billion bananas annually, is threatened by diseases such as Panama disease and banana bacterial wilt.

Banana breeders are scrambling to find ways to combat such pathogens, particularly the ones that attack the Cavendish banana, which accounts for more than half of all the bananas exported to the United States and Europe.

Some are collecting wild relatives and obscure varieties that are more resistant to disease. But introducing genes from distant ancestors could also help steel modern-day bananas. Genetic analyses can help piece together the history of domestication and pin down living members of those ancestral fruits.

Nabila Yahiaoui, a banana genomics scientist at the French Agricultural Research Centre for International Development in Montpellier, and colleagues previously compared DNA from 24 collected samples of wild and domestic bananas.

In a few of them, they found something puzzling: DNA that didn’t match that from any of the other samples. Based on that finding, they proposed in 2020 that, in addition to M. acuminata and other known wild relatives, two unknown species contributed DNA to the modern banana.

In the new study, Sardos and her colleagues expanded on that work, focusing on banana varieties with two sets of chromosomes, as they are likely more closely related to the first domesticated bananas. (The Cavendish has three sets.) They sampled the DNA of 68 samples of wild relatives and of 154 types of cultivated bananas, including 25 varieties Sardos’s team collected in Papua New Guinea. That’s an impressive number of cultivars, some of which can be hard to obtain, says Tim Denham, an archaeologist at Australian National University who was not involved with the work.

The comparison provided more evidence that bananas were originally cultivated on New Guinea and suggested an M. acuminata subspecies named “banksia” was the first to be domesticated.

The same subspecies subsequently contributed to more widespread cultivated varieties, Sardos and colleagues report this month in Frontiers in Plant Science. “This [conclusion] is significant,” Denham says. “It confirms previous archaeological, botanical, linguistic, and genetic studies.”

The samples also pointed to the existence of a third unknown source of banana genetic material, the team reported. Scientists have yet to identify the three species; their data suggest one came from New Guinea, one from the Gulf of Thailand, and the third from somewhere between northern Borneo and the Philippines.

Denham was surprised to find that the modern banana varieties on New Guinea are more genetically diverse than their wild ancestor. “This runs counter to most genetic arguments that speculate that initial domestication results in a bottleneck,” he says. He suspects that even as banana growers worked to improve bananas, there was rampant interbreeding with wild relatives, leading to bunches of varieties with different genetic ancestries.

“This work further confirms the importance of hybridization in the evolution of [certain] crops,” says Rieseberg, whose work with sunflowers has demonstrated that interbreeding can be important for evolution.

The field remains ripe with possibility: Sardos and other banana aficionados are hoping to visit small farms and other sites in the ancestral bananas’ homelands to see whether they can find more modern descendants. They, too, may yield a stock resistant to disease that can be crossbred with commercial bananas. “There is a lot of unsampled banana diversity out there,” Rieseberg says.