More blogging about research, without a Research Blogging logo, because this is way outside my area of expertise – but it looks interesting. I spotted it going through the accepted papers list at Annals of Botany and seriously considered putting this forward for a press release. I decided not to – I don’t fully understand it – and blog it instead. So I’ve been waiting for this to come out and slightly miffed that I missed it due to a cold. It’s not in the printed journal yet, but you can see it now, and look at what I get wrong because it’s an open access paper.
The reason I’m going to make a fool of myself and blog it anyway is that this is research that is important to the origins of agriculture, one of the BIG archaeological problems. And it’s about bananas, and everyone’s familiar with bananas.
Bananas are actually strange. Aside from the fact that banana plants ‘walk’ (not really, see this excellent blog post), they’re also all clones. I also have to admit that if I saw a banana in the tropics I probably wouldn’t recognise it. The big yellow curvy fruit I think of as a banana is just one of many varieties. As a starchy plantain Musa (some of which are bananas) are a staple diet in Asia. They have been for thousands of years and they’re sterile so there’s a bit of a mystery. How can they still be here?
The bananas we have today are the products of thousands of years of careful selection for specific traits by farmers. The ancient people doing this had no concept of ‘genes’, but if we were to do the same sort of thing today we’d be genetically engineering the plant. The reason ancient people did this is because edibility and seeds are probably not compatible in bananas. Get a mutation without seeds and you have an edible berry. You don’t have seeds though so you have to start propagating it more inventively.
Lack of banana sex means that the genetic diversity of these plants is very limited. If you have a pest that can kill one plant, you’ve got a pest that can wipe your entire crop and you neighbours’ crops. So it would be amazingly helpful to be able to trace back the genetic history of bananas to see where they came from and how they were domesticated into their current form. That’s what the authors of ‘Did backcrossing contribute to the origin of hybrid edible bananas?‘ propose to do.
What they’ve found is that it looks like edible bananas are hybrids. That might not be such a surprise. What they’ve also found though is evidence of careful thought in hybridisation to favour some traits over others, using a technique called backcrossing. I had to have this explained to me.
You have two banana plants A and B. If you cross them you can get a hybrid banana AB.
Banana Genetics
Backcrossing is when you take this hybrid and cross it back with an earlier generation. So if you take your AB banana and backcross it with an A banana you get banana with much more A genes in it than B genes. You can take this new hybrid and backcross it again with A or B to produce the next generation and so on. The authors have a mathematical model for this and I won’t pretend I understand it. It’s a shame, because that’s most of the paper.
With my archaeological hat on, it’s a useful paper. If you’re interested in how the transition to agriculture occurred in south Asia then clearly understanding banana domestication is important. The ancient bananas themselves have long rotted away, to being able to pull apart the genes of a banana to see how it was domesticated is a massive help. If this paper is right, and the authors propose a few experiments to test the idea, then the banana is the result of some very clever and selective breeding.
The reason I’m particularly excited is that Annals of Botany also had a paper on domestication of Pitaya di Mayo recently by ethnobotanists. This was a study of domestication as it happens. The kind of local selections for specific traits that Mexican farmers are using for pitaya look like they’d produce the kind of complex genetic history being found in bananas.
I live in a temperate zone, so the limit of my banana experience till now has been that it’s a delicious, yellow and sometimes humourous fruit. Papers like this show that the banana going soft in your fruit bowl is an eight thousand year old connection to some very clever farmers.