Where diversity flourishes — 1

The foods we eat did not just spring out of the ground and assemble themselves into pizza, stir-fried vegetables, spinach salads, peanut butter and jelly sandwiches, and warm loaves of freshly-baked bread. Each individual part of the foods we eat today originated somewhere, and in wild form.

The potato, for example, originated in the Andean region of South America, as did the tomato, squash, and red pepper. Oranges are believed to have originated in China, and so did soybean, sugar cane, and oats. Very few of our most valued plants started out in North America, by the way. They include blueberries, cranberries, and sunflowers. Why do food plants have “home towns” and regions? One big reason is that they evolved in places where the environment welcomed them. Potatoes, for example, thrive in places where the nights are cool. The hills and valleys of the Andes Mountain chain are ideal hosts for potatoes and other vegetables that are categorized as roots and tubers.

Scientists have a term for these places: “Centers of origin.” Plants also have what is called “centers of diversity.” These are the places where each plant’s diversity — that is, its wild relatives and varieties cultivated by farmers — are greatest. Such places often, but not always, overlap the centers of origin. Don't feel bad if you get the two confused; many experts do, too.

In the centers of diversity, genes move between food crops and their wild relatives. Very often, the transfer is a result of a breeze that picks pollen up from one plant and deposits it on another. Or sometimes it's a bee or bird. This “gene flow,” as it is known to scientists, produces lots of variation on each species.

The several kinds of peas that Gregor Mendel used in his heredity experiments are an example of this: Different colors, shapes, and stem lengths of the same basic plant are caused by gene flow and are examples of diversity. Since these centers of diversity are the places where specific crops have thrived through the years, they hold special interest for agricultural scientists.

Why? Suppose a disease was threatening farmers’ plantings of maize, or peppers. Where would you look for a relative of your maize or peppers that, when bred with your existing varieties, might provide resistance to the disease? You’d go to a place where the maize or peppers were most diverse (their centers of diversity, which might be the same as their centers of origin) and look for plants that were resistant to the disease. You would breed (“cross”) the newly-found variety with the existing variety and hope that the offspring would (1) possess the same characteristics, such as taste and color, that made your existing variety popular with farmers and consumers, and (2) possess the disease resistance from the new-found variety.

Plant breeders do this all the time. They would be the first to tell you that it’s nowhere near as simple as the description above. Breeding desirable qualities into food crops is a long and tedious business, full of dead ends and failures. But the payoff can be great.

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