Over at the Vaviblog is a detailed discussion (though not nearly as detailed as the paper) of a new paper outlining a new theory for the origin of the cultivated banana. ((De Langhe, E., Hribova, E., Carpentier, S., Dolezel, J., & Swennen, R. (2010). Did backcrossing contribute to the origin of hybrid edible bananas? Annals of Botany DOI: 10.1093/aob/mcq187))
Edible bananas have very few seeds. Wild bananas are packed with seeds; there’s almost nothing there to eat. So how did edible bananas come to be cultivated? The standard story is that some smart proto-farmer saw a spontaneous mutation and then propagated it vegetatively. Once the plant was growing, additional mutants would also be seen and conserved. In fact this “single-step domestication” is considered the standard story for many vegetatively-propagated plants, such as potato, cassava, sweet potato, taro and yam. And while it may be true for those other crops, evidence is accumulating that it may not be the whole story for bananas.
Leaving the details aside, De Langhe and his colleagues propose that instead of a single step, at least two were involved, with a proto-cultivated banana back-crossing with one of its wild relatives and then being seen by the proto-farmer as an improvement to be added to her proto-portfolio of agricultural biodiversity. Something very like that is going on today among cassava farmers, for example; they allow volunteer seedlings, the product of sexual reproduction between already favoured clones and wild relatives, to flourish in their fields and then select among them. ((Pujol, B., Mühlen, G., Garwood, N., Horoszowski, Y., Douzery, E., & McKey, D. (2005). Evolution under domestication: contrasting functional morphology of seedlings in domesticated cassava and its closest wild relatives New Phytologist, 166 (1), 305-318 DOI: 10.1111/j.1469-8137.2004.01295.x)) Banana farmers could easily have done the same.
To quote again from The Vaviblog:
The big question, of course, is “what does any of this matter?”. And the surprise is that it really does. Banana breeding is difficult at the best of times; no seeds, no pollen, you can imagine. But if the backcross hypothesis is true, then the current approach to banana breeding, which De Langhe et al. describe as “substituting an A genome allele by an alternative derived from a AA diploid source of resistance or tolerance to biotic and abiotic stress”, might be misguided. If the chromosomes are not “pure” A or B, and if backcrosses were involved in the origin of banana varieties, maybe breeders should look again at some of the diploid offspring from their crosses and see whether they could be further backcrossed to come up with types that are more use to farmers.
Now, what I really need is for one of the handful of people who really understand this stuff to tell me where I’ve misunderstood it.
Trying presenting this at grist.org in the food section. You might get your answer.
Thanks.
I wax and wane in my enthusiasm for Grist. The contributions are mostly great, although on occasion I have been surprised at quite how insular some of the people there can be. right now, I’m not even sure how to submit the post, because the link to “Find out more about sending a query” on the Writer’s Guidelines page is broken. If you’re involved in Grist, maybe you could let them know. Meanwhile, maybe I’ll just submit this blog and see whether they are interested.