Wheat: Out with the new, in with the old
By Robert C. Cowen
In science, the old sometimes works as well as the new. Throw politics into the mix and the old starts to look a whole lot better.
That's what appears to be happening with wheat breeders and their battle against a huge nemesis: the Hessian fly.
It turns out that scientists have found the genes needed to make wheat more resistant to the plant-eating insect. The big question is how they get those genes into the wheat: through traditional plant breeding or genetic engineering?
The experience in wheat is an example of the renaissance of plant breeding and could lead to better food without the politics.
At the scientific level, both techniques work. Genetic engineers can snip an insecticide gene from the DNA of a bacterium and paste it into the DNA of corn.
Voilà, corn that makes its own insecticide.
But when that corn hit the global market, many consumers rejected it. Moving genes by such unnatural means disturbs many people.
Traditional plant breeders, meanwhile, have shuffled genes for millenniums. Sharing genes among plant varieties that interbreed - even if humans facilitate it - hasn't challenged anyone's worldview.
However, traditional breeding has seemed cumbersome compared with the speed with which genetic engineering can change a crop plant's DNA. Breeders have to do more than find a donor plant with the traits they want. Genes for those traits have to reside in the donor's DNA at locations that facilitate the transfer through crossbreeding. That's not easy to assess when looking at a plant from the outside.
Now, technology that lets genetic engineers study a plant's genome also helps plant breeders find what they are looking for. Then, through crossbreeding, they can give crop plants carefully selected genes for such traits as resistance to insects or drought.
The wheat research Christie Williams and colleagues are conducting at Purdue University in West Lafayette, Ind., illustrates this. They are targeting resistance to the Hessian fly.
Currently, this pest is controlled by constantly developing resistant strains of wheat, rather than through chemicals. Some 30 fly-resistance genes are known. However, when a line of wheat has only one such gene, the fly can evolve fairly rapidly to overcome the resistance.
Professor Williams explains that the best protection is afforded when several different genes are combined in one plant. These must be located at different points along the plant's genome for the synergy to work. And to transfer correctly, they must be located in the right spot of the donor plant.
The Purdue team recently reported finding one such gene in soft red winter wheat. It is positioned in such a way that it can be usefully bred into a wheat strain that already has a different gene for fly resistance.
Now the team is after a donor plant with a third such gene. Williams predicts that, with three properly located resistance genes in one wheat plant, the durability of the fly resistance of that line of wheat will be extended by many years.
Interestingly, it's the scientific advance in genetic analysis that has made this old-fashioned method viable. The result should be more robust wheat produced in a way that raises nobody's hackles.
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