Is this thing still on? Excellent. A big meeting is scheduled for next week in St Petersburg, Russia, to consider new discoveries about some of the holdings at the Pavlovsk Experiment Station and, perhaps, the station’s future, so it seemed like a good idea to make sure that this site was up and running and ready to broadcast whatever intelligence it might receive. As ever, it’s easy to make contact. Rather than just clearing my throat, though, here’s some substance.
African rice, Oryza glaberrima, differs in many respects from Asian rice, O. sativa. Yields are lower, partly because the seeds shatter more easily from the plant, although African rice is better able to withstand stress. The grains are often coloured red rather than white. And it may well be more nutritious, partly because it is harder to polish than Asian rice, and polishing removes essential micronutrients. Certainly average protein levels are higher.  And Africans say it fills them up properly, which might indicate a lower glycemic index (not that the official glycemic index contains anything as useful as either O. glaberrima or African Rice among its entries).
African rice has of course been crossed with Asian rice to create the wildly successful NERICA (NEw RICe for Africa) varieties, and some might think that it’s game over for pure African rice, but there’s still a lot to be learned.
The history of its domestication has been confused.  Jack Harlan originally suggested that it was domesticated by selection from O. barthii, the wild ancestor, at many places across its wide range. Archaeological evidence suggested a more circumscribed area, around the Middle Niger delta in what is now Mali, although given the relatively late date of the remains found there — around 500 years BCE — the possibility remains that it had been introduced from elsewhere.
A new DNA study by Chinese scientists confirms that African rice was domesticated in the Middle Niger delta and that the original selection may have taken place just once.  The scientists sequenced DNA from 20 samples of O. glaberrima and 20 samples of O. barthii, looking at the detailed sequence of 14 unlinked genes. While there was some variation in the diversity of the individual genes, overall the wild relative samples were about four times more diverse than the cultivated samples. That said, the actual diversity of both species is very low indeed, lower than all previously sampled crops and their wild relatives.
An obvious explanation for the low genetic diversity of O. glaberrima would be a genetic bottleneck during its domestication from a small initial population of O. barthii. … [T]he extremely low nucleotide diversity in African rice can be explained by severe bottleneck during domestication, with high value of the bottleneck intensity … which is consistent with its single origin in west Africa.
O. barthii and O. glaberrima are both largely self-pollinating, which would also account for the low genetic diversity. As for the place of domestication, there were 7 O. barthii samples that were clustered closely with all the O. glaberrima samples. All 7 were from previously postulated centres of domestication, three from the Middle Niger delta and two each from brackish mangrove areas of Guinea and the upland areas between Sierra Leone and Ivory Coast. There was no evidence for the kind of multiple domestication proposed by Harlan. More extensive sampling, the authors say, might reveal the precise place where O. glaberrima originated.
Quite apart from the satisfaction of knowing a little more about the origin and domestication of an important crop, this research is also important because in revealing the lack of genetic diversity within African rice and its wild progenitor, it provides insights into how best to conserve the diversity of both species and also suggests that the wild relative might still be able to donate important characteristics to African rice and, perhaps, to NERICA varieties too.
- Kennedy, G., & Burlingame, B. (2003). Analysis of food composition data on rice from a plant genetic resources perspective Food Chemistry, 80 (4), 589-596 DOI: 10.1016/S0308-8146(02)00507-1 [↩]
- Linares OF (2002). African rice (Oryza glaberrima): history and future potential. Proceedings of the National Academy of Sciences of the United States of America, 99 (25), 16360-5 PMID: 12461173 [↩]
- Li ZM, Zheng XM, & Ge S (2011). Genetic diversity and domestication history of African rice (Oryza glaberrima) as inferred from multiple gene sequences. TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik PMID: 21400109 [↩]