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Study reveals bananas heavily inbred

Bunch of bananas

Bananas need sex if they are to survive into ripe old age(Source: RedHelga/iStockphoto)

Better bananas A study retracing the bananas' family tree has found their wild ancestors have rarely crossbred in the last seven thousand years, strengthening calls to diversify the popular crop.

The standard yellow banana currently found on most supermarket shelves are mass cultivated as infertile clones and are therefore genetically identical.

But this makes them particularly susceptible to disease, pests and ecological challenges, writes a team of European and Australian scientists in the journal Proceedings of the National Academy of Sciences.

Co-author Dr Mark Donohue, from the Australian National University in Canberra, says 85 per cent of cultivated bananas are for local consumption.

"This means that any disruption to the supply of bananas will have immediate consequences ... possibly leading to famines," he says.

Reduce vulnerability

In order to be able to generate diversity and improve future banana crops, the authors of the study believe it is necessary to understand which species were historically crossed and selected for breeding.

To reconstruct the banana's geographical spread and its road to domestication they analysed genetic, linguistic and archaeological data.

"The genetic descent is one thing, but knowing whether they [bananas] are being used by humans is another."

"The archaeologists could tell us when they were actually being used, the geneticists could tell us which direction and which kind of cross-breeding happened and, through the linguistics, we managed to get an idea of how culturally important bananas were for the regions they were in," explains Donohue.

Analysis of microscopic remains of banana leaves at the world heritage-listed Kuk swamp in New Guinea confirmed banana cultivation was taking place approximately 7000 years ago.

Genetic analysis showed that bananas in the islands around Southeast Asia and Western Melanesia hybridised into subspecies that could not have formed without human intervention.

Linguistic research identified more than 1100 terms from different languages that relate to banana varieties. They also found four key derivations of the term for banana, each suggestive of a different dispersal trajectory.

Survey of banana crops needed

While the new research may provide a basis on which to formulate a banana breeding strategy, Donohue believes we also need to encourage local diversity.

There are hundreds of varieties of bananas, from plantains to ladyfingers, and there are many more yet to be documented.

"Many parts of the world, like Indonesia, don't really know the sort of genetic diversity that's out there - there's never been a survey," says Donohue.

"Given the different kinds of climate we see, from New Guinea to South East Asia, there's probably a specialised variety, already being grown or present in the wild, that can hit that [disease resilient] niche quite well if we could only find it."

History never repeats?

In the 1950s, a fungal disease, known as Panama disease, led to huge losses of 'Gros Michel,' then the biggest export and most widely consumed banana variety.

Similarly, the Irish Potato famine in the 19th century was the result of over-reliance on a few varieties of potato.

Jonathan Eccles, CEO of the Australian Banana Growers' Council, says that while there are no banana breeding programs in Australia, they do evaluate different varieties through their research program.

"The whole supply chain has to be taken into account when evaluating different varieties," he says.

This includes whether there is consistent productivity and the length of transport time, as well as market attributes such as flavour characteristics.

"Offering a range of products, such as plantain, is a good way to encourage expansion of banana varieties," says Eccles.
