How PNG gave us bananas 7,000 years ago
20 October 2022
Researchers have gone bananas over this fruit’s complex ancestry. Most agree that Papua New Guinea is where domesticated bananas as we know them first appeared
| Science | Edited extracts
WASHINGTON - 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 has revealed the existence of three previously unknown—and possibly still living—ancestors.
And today’s banana experts want to track down these mysterious forebears to see whether their genes might help keep modern banana crops healthy.
About 7,000 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 trunk-like 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.
Scientists do know the banana’s predominant wild ancestor is a species named Musa acuminata, which occurs from India to Australia.
Today, there are many banana varieties—more than 1,000 at last count.
And most researchers agree that Papua New Guinea is where domesticated bananas as we know them today first appeared.
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.
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 a year, is threatened by problems 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.
Introducing genes from distant ancestors could help make modern-day bananas more resistant to disease.
Nabila Yahiaoui, a banana genomics scientist at the French Agricultural Research Centre, and colleagues 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, in 2020 they proposed 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 focussed on banana varieties with two sets of chromosomes, as they are likely more closely related to the first domesticated bananas.
They sampled the DNA of 68 wild relatives and 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.
The comparison provided more evidence that bananas were originally cultivated in PNG 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 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.
Scientists have yet to identify the three species; their data suggest one came from PNG, one from the Gulf of Thailand, and the third from somewhere between north Borneo and the Philippines.
Denham was surprised to find that the modern banana varieties in PNG are more genetically diverse than their wild ancestor.
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.
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 also may yield a stock resistant to disease that can be crossbred with commercial bananas.
Posted by: William Dunlop | 20 October 2022 at 04:22 PM