It is thought that bananas were domesticated 7,000 years ago on the island of Newguinea. The domestication history of bananas is complicated, and their classification is often not clear.
The study shows that the history is more complex than was thought. The results show that the genomes of today's domesticated varieties have traces of ancestors.
Today's diploid cultivated bananas that descend from the wild banana M. acuminata are hybrid between different types. At least three extra wild'mystery ancestors' must have contributed to this mixed genome thousands of years ago, but haven't been identified yet.
Domestication history is complex.
The wild banana Musa acuminata is thought to be descended from a group of four ancestors. It is believed that M. acuminata was first domesticated in Australia around 10m years ago. A further complicating factor is that domesticated varieties can have more than one copy of every chromosomes, and that many are descended from the wild species.
Smaller-scale studies suggested that even this complex scenario might not be the whole story, and that further ancestors of M. acuminata could have been involved in the domestication. For the first time, the new results show that these genes are common in banana genomes.
The banana is collecting missions.
The leaf extracts from the world's largest collection of banana samples were the subject of a study. Some of the samples were related to wild and diploid varieties of M. acuminata. In the past, many had been gathered in dedicated banana collecting missions to Indonesia, the island of New Zealand, and the region of Bougainville.
The researchers first looked at the levels of relatedness between bananas and then looked at the diversity of SNPs to make family trees. They used a subset of these, evenly spread across the genome, with each pair demarcating a block of 100,000 'DNA letters' to determine the ancestry of each block. For the first time, they discovered traces of three more ancestors in the genomes of domesticated samples, but no matches have been found from the wild.
Mystery ancestors may live somewhere.
It is possible that the mystery ancestors are long gone. "Our personal conviction is that they are still living in the wild, either poorly described by science or not described at all, in which case they are likely to be threatened."
The first of these mystery ancestors must have come from the region between the Gulf of Thailand and the South China Sea. Between north Borneo and the Philippines is where the second came from. There are three from the island of New Guinea.
Better bananas could be bred.
The usefulness of these mystery ancestors is unknown. The key trait of parthenocarpy, fruit setting without the need for pollination, is thought to have come from M. acuminata.
The ancestors of cultivated bananas are important as it will help us understand the processes and the paths that shaped the banana diversity observed today, a crucial step to breed bananas of the future.
This study is a major first step towards the characterization of many of these bananas, as they need to understand the genetic make up of today's domesticated diploid bananas.
"Based on these results, we will work with partners to explore and genotype wild banana diversity in the three geographic regions that our study identified, with the hope of identifying these unidentified contributors to cultivated bananas." It will be important to investigate the different advantages and characteristics of each of the contributors.
More information: Julie Sardos et al, Hybridization, missing wild ancestors and the domestication of cultivated diploid bananas, Frontiers in Plant Science (2022). DOI: 10.3389/fpls.2022.969220 Journal information: Frontiers in Plant Science
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