Category: Breeding

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Was sunflower domesticated in Mexico or what?

I don’t know much about sunflower. That’s obvious enough from the cavalier fashion in which a recent Nibble of mine referred to a press release on a PNAS paper on sunflower domestication by David Lentz and others. ((David L. Lentz, Mary DeLand Pohl, José Luis Alvarado, Somayeh Tarighat and Robert Bye. Sunflower (Helianthus annuus L.) as a pre-Columbian domesticate in Mexico. Proceedings of the National Academy of Sciences 105: 6232-6237; published online as 10.1073/pnas.0711760105. The paper is behind a paywall but the supplementary material is available and gives a taste. Some nice pix.)) Briefly, that paper presented a range of archaeological, linguistic, ethnographic and ethnohistoric evidence for the domestication of sunflower in Mexico by 2600 BC. This would complement a separate, independent, well-attested domestication in the Mississippi Valley. That’s important not only academically but also for the insights it would give into genetic structure within the species, and hence possible breeding strategies.

But it looks like I unwittingly walked into a bit of a controversy. It seems things are a bit more complex than the press release made out. In a 2007 short communication in GRACE, the great Charles Heiser reverses himself with regards to some archaeobotanical material he had previously identified as a sunflower achene and as a result comes out against the Mexican domestication for the crop first advocated by Lentz in 2001. The available molecular evidence seems to support Heiser.

I don’t know much about sunflower. But after today, I know a little bit more. And I’ll be keeping an eye on this academic spat to learn more.

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Maize in Africa

An article in the latest Economist discusses the Malawi fertilizer subsidy programme. There’s been a fair amount in the media about this lately, and in particular about whether the bumper maize harvests of the past couple of years can be attributed to the extra fertilizer ((Incidentally, there’s an interesting NY Times video on what the rising cost of fertilizers means for farmers in the US.)) now finding its way onto farmers’ fields increasingly sown to modern varieties, or just to better rains. I think the jury is still out on that one, but check out this statement from the piece in The Economist:

…local seed varieties, little altered from those first brought by the Portuguese centuries ago…

I don’t know about you, but I think that rather underestimates the power of natural selection, drift and recombination. Not to mention 500 growing seasons’ worth of painstaking selection by twenty generations of African farmers.

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Cassava diversity 101

After hanging out with experts for three days here in Cali, this is what I think I know about cassava genetic diversity:

  • There’s a hotspot in Brazil, but Central America is pretty diverse too. Those two places are also where the wild species are most numerous. There is geneflow between wild and cultivated populations.
  • There’s little geographic structure within the New World diversity, except for Guatemalan material being way genetically distinct (and higher in protein to boot). Lots of geneflow, I guess.
  • The African material is less diverse than the American, but not much, and significantly distinct from it. Selection, and isolation.
  • Within Africa, the Nigerian material is somewhat distinct. In general, there is more geographic structure in Africa than in the Americas.
  • Asia received material historically from both Brazil (via Africa) and Mexico (via the Philippines), but there hasn’t been the differentiation there that is seen in Africa. There hasn’t been as much selection of natural hybrids in Asia as in Africa.
  • Weird mutants keep turning up, including “sugary cassava,” “ketchup cassava” (the pinkiness is due to lycopene), and amylose-free clones.