People love to know where their food comes from, but when it comes to the origins of modern bananas, even experts wave their hands
.
An extensive genetic analysis of more than 100 species of wild and cultivated bananas uncovered the tangled history of bananas during domestication, revealing the existence
of three previously unknown ancestors who may still be alive.
Banana experts want to track down these mysterious ancestors to see if their genes helped keep modern banana crops healthy
.
Loren Rieseberg, an evolutionary biologist at the University of British Columbia in Vancouver, said: "The domestication of bananas is much
more complex than I previously realized.
He was not involved in the study
.
About 7,000 years ago, bananas were not the seedless fleshy fruit
we know today.
The flesh has black seeds and is almost inedible
.
Instead, people eat the flowers of a banana tree or its underground tubers
.
They also stripped fibers from the trunk-like trunk to make rope and clothing
.
The banana trees at that time were "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 that the main wild ancestor of bananas is a species called Musa acuminata, which grows from India to Australia
.
Most researchers agree that Papua New Guinea is where we know the first domesticated bananas
appeared.
Today, according to statistics, there are many varieties of bananas, more than 1000 species
.
During domestication, modern bananas available in supermarkets lost their seeds and became fleshy and sweeter
.
But it is difficult to determine exactly how and when domestication occurred
.
To complicate matters further, some bananas usually have two sets of chromosomes, while others have three or more, suggesting that at least some modern bananas are hybrids of two or more varieties, or even different varieties
.
There is every reason to tap into the deep historical gene pool of modern bananas: the $8 billion banana industry, which produces 100 billion bananas a year threatened by diseases such as Panama disease and banana wilt
.
Banana growers are scrambling to find ways to deal with the pathogen, especially those that attack Cavendish bananas, which account for more than
half of exports to the United States and Europe.
Some are collecting wild relatives and unknown varieties that are more resistant to disease, however, the introduction of distant ancestral genes has also contributed to the steelification
of modern bananas.
Genetic analysis helps piece together the history of domestication and identify living members
of these ancestral fruits.
Nabila Yahiaoui, a banana genomics scientist at the French Centre for International Development of Agriculture in Montpellier, and colleagues previously compared DNA
from 24 wild and domestic banana samples.
In some of these samples, they found something puzzling: a mismatch
in DNA from other samples.
Based on this finding, they proposed in 2020 that two unknown species, in addition to M.
acuminata and other known wild relatives, contributed DNA
to modern bananas.
In the new study, Sardos and her colleagues expanded the work to focus on banana varieties with two sets of chromosomes because they may be more closely
related to the first domesticated bananas.
They collected DNA samples from 68 wild relatives and 154 cultivated bananas, including 25 banana varieties
collected by Sardos' team in Papua New Guinea.
Tim Denham, an archaeologist at the Australian National University, said it was an impressive number of species, some of which could be hard to come by
.
This comparison provides more evidence that bananas were originally cultivated in New Guinea and suggests that the subspecies named "banksia" by M.
acuminata was the first to be domesticated
.
The same subspecies later led to a wider range of cultivars
.
"That conclusion makes a lot of sense," Denham said
.
It confirms previous archaeological, botanical, linguistic and genetic studies
.
The samples also indicated the presence of a third banana genetic material
of unknown origin.
Scientists have yet to identify these three species; Their data shows that one is from New Guinea, one from the Gulf of Thailand, and a third is from somewhere between northern Borneo and the Philippines
.
Denham was surprised to find that modern banana varieties in New Guinea had more genetic diversity
than their wild ancestors.
This runs counter to most genetic arguments that speculate on initial domestication, leading to bottlenecks, he said
.
He suspects that even as banana growers are working to improve their bananas, hybridization with wild relatives is rampant, resulting in a bunch of varieties
with different genetic ancestors.
"This work further confirms the importance of hybridization in [certain] crop evolution," said Rieseberg, whose research on sunflowers has demonstrated the importance of
hybridization for evolution.
The land still has the potential to ripen: Sardos and other banana lovers want to visit small farms and other locations in the ancestral homeland of bananas to see if they can find more modern offspring
.
They can also produce a disease-resistant variety that can be crossed
with commercial bananas.
"There's a lot of unsampled banana diversity
there," Rieseberg said.
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