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New crops from old genes
But why don’t we simply press ahead with the existing, modern varieties? Why bother to maintain old-fashioned types and wild plants? Many are low yielding, and are often unable to respond to higher doses of fertilizer, becoming lush or lanky when given extra nitrogen. Sometimes, contrary to the stereotype, traditional types may be highly susceptible to particular diseases. Through much of the past few centuries many economists, scientists, farmers and industrialists have argued in just this kind of way: why bother with what seems obsolete? Yet for many reasons--political, economic, social, scientific--such thinking is very dangerous.

Part of the reason has already been given: we need a constant stream of new varieties at the best of times, and in the century to come, that stream must be broader and swifter. And as global conditions take forms that are completely novel, breeders will have to be more radical than in normal times, producing crops that are able to grow in strange new regimes of temperature and day length, with specific resistance to disease where none may have been needed before.

Genes are the breeder’s raw materials: their stock in trade. Genes do not by themselves ‘determine’ the form or behaviour of an organism. Always the genes are in dialogue with the overall environment. But they are half of that dialogue: in general, if you alter the genes you alter the organism. There can be no such thing as a perfect crop--all crops, like all airplanes or motor cars, are compromises between different requirements--but some come closer than others to the targets that are set for them. To achieve the best that is possible, breeders and farmers (to some extent abetted these days by ‘genetic engineers’) must create crops that contain genes appropriate to specific tasks and, even more importantly, must provide good combinations of genes that work well together.

Traditionally, good combinations of appropriate genes are produced by selecting and crossing. In ‘mass selection,’ the breeder (or the farmer) simply picks out the individuals in a population of plants that come closest to his or her particular criteria (the top 50 percent, or 30 percent or whatever), and discards the rest. Or the breeder selects individuals that have some of the required features, individuals that have other good points, and mates (or ‘crosses’) the two, hoping to produce offspring that combine the best qualities of both. Often, breeders also cross individuals from related but different types, again hoping to combine the best qualities of both parents. Some modern crops contain genes derived from hundreds or even thousands of parent ‘lines’, produced through many hundreds of crosses made over many generations. Even by such ‘classical’ breeding it is sometimes possible to combine genes from different species: modern bread wheats have at least three species of ancestral grass in their ancestry. With genetic engineering it is possible to transfer genes between any two or more organisms, in principle at will: bacterium into cabbage, cabbage into cow, if that was required. As the techniques develop, the limits of possibility will be set only by aesthetics, ethics, and economics.

Sometimes new crop varieties can be produced just by crossing two or more existing commercial varieties. But often--increasingly often as conditions change--the genes that the breeder requires to do the job are simply not to be found in the plants that are close to hand. To make significant advances, the breeder or the genetic engineer is liable to have to spread the net very wide indeed. The plants that contain the required genes may themselves look unprepossessing. Traditional varieties on far-flung farms may sometimes appear vastly inferior to modern types--smaller grain, misshapen tubers--and yet may contain vital qualities: for pest-resistance, drought-resistance, protein content, flavour, or a hundred other qualities. Sometimes the required genes do not exist even in traditional cultivated varieties, but are to be found in the crop’s wild relatives, if these can be found and identified. If the necessary genes are found in species related to the crop in hand, they often can be introduced by standard breeding techniques. But sometimes genes from other species can be acquired only by genetic engineering. Whatever the source, and whatever the route adopted, the breeder--and hence the world at large-- needs the widest possible ‘pool’ of genes from which to draw.
Of course, to some extent it is possible to add to the genes available in any one breeding programme without recourse to exotic varieties and wild species. Often new genes arise by spontaneous mutation of existing ones; then it’s a matter of spotting that this has happened, and cosseting whatever spontaneous novelties seem valuable. Many a ‘garden variety’ has arisen in just this way. Since the 1920s it has been possible to create new mutations artificially, for example by x-rays and chemicals. Today, it is feasible in principle to synthesize new genes to order: genes are constructed from DNA and the chemical manipulation of DNA is now well advanced.

But the genes that we can add artificially, although sometimes very significant economically, are the gilt on the gingerbread. The overwhelming mass of genetic variation of world crops is contained within the plants themselves and the result of millions of years of evolution in nature and refined in cultivation over many thousands of years. On ancient farms and in the wild, there are many millions of genetic variants. In this resource lies the future of our crops and hence our own fate. This is why the plants that contain those genes (or their seeds or tubers) must be conserved. They are the world’s most valuable capital.

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