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MARK HEISTAD: The year was 1970, one of the worst ever for corn belt farmers like Phil Specht. He was working a 900-acre farm in East Central Iowa at the time and well remembers the news a neighbor delivered one hot Sunday afternoon that August.

PHIL SPECHT: I knew something was up, but I figured something was up. And he says, hop in the truck. So there was something going on. So I hop in the truck, and he said, the corn is dying.

MARK HEISTAD: Phil Specht's corn was dying of a blight, a new strain of Southern corn leaf blight.

PHIL SPECHT: We just started driving around. We just went over the whole Township and just got out, stopped the truck, and walked into whoever field had happened to be, and the blight was everywhere. It had spread to every field in the area.

In fact, by the end of that summer, the new blight had spread to fields from Florida to Nebraska. 20% of the nation's crop was destroyed, 50% in parts of the South. The total lost, about a billion bushels of corn. That blight spent all but forgotten by most Americans and a lot of farmers, but it's still very much in the minds of scientists and plant breeders because it provided a graphic example of just how vulnerable American agriculture may be to disease epidemics.

GARRISON WILKES: In theory, what we're doing or the direction that we're headed is a very dangerous. one.

MARK HEISTAD: And the direction we're headed, says Massachusetts biologist Garrison Wilkes, is more and more towards monoculture-- farming thousands and thousands of acres all planted with the same crop. The huge Midwestern corn belt is a good example, or the vast Western seas of wheat that now spread from Texas to Canada. It has proven, says Wilkes, to be a very productive way to grow food.

GARRISON WILKES: We've seen three and four-fold increases worldwide since the 1950s. But at the same time, we've seen it with less and less gene diversity.

MARK HEISTAD: Gene diversity is the crux of this problem. Modern breeding programs have made these basic food crops genetically quite uniform. There are lots of brand names and variety numbers, but the corn seed in one company's catalog contains much of the same genetic material as the seeds offered by every other firm. Stephen Smith is a plant scientist with Pioneer Hi Bred, the world's largest corn breeding firm. He's been studying this issue of diversity.

STEPHEN SMITH: Genetic diversity is really important for two main reasons. One is the immediate problem with a lack of genetic diversity, and that's a high incidence of disease.

MARK HEISTAD: A high incidence of disease, says Smith, because as a crop like corn becomes more and more uniform genetically, it becomes more uniformly susceptible to disease. In 1970, the problem was a group of genes called T cytoplasm. Several decades earlier, breeders had found that these genes help to control pollination. That's important to ensure the purity of breeding stocks and hybrid seeds. Don Duvick is chief corn breeder at Pioneer Hi Bred.

DON DUVICK: The thing that we didn't know was that in addition to causing male sterility, this type of breeding carried a susceptibility to Southern corn leaf blight.

MARK HEISTAD: Duvick has been a leader in the effort to make sure the disaster of 1970 is not repeated. They no longer use the T cytoplasm, for example, and they've made an effort partially successful to increase the genetic diversity of corn and other basic food crops. For his part, Phil Specht is not reassured by those developments. In large part, because of the 1970 corn blight, he's given up monoculture farming, the fencerow to fencerow corn he used to grow. He's a dairy farmer now, and his fields used for grazing dairy cattle contain a diversity of plant life that's rarely found on American farms.

PHIL SPECHT: On this side of the fence over here, I tried sprouting alfalfa. I mixed that with improved pioneer number and also just threw in some Kansas vernal. I've got three different kinds of alfalfa. And then there's Timothy and brome grass and orchard grass, mixture for grass mixture.

MARK HEISTAD: Specht figures that seeding all these different kinds of plants into one field reduces the possibility that any one disease will claim his cattle feed. Few other farmers though can afford this approach. They're find out she knocked into the intensive monocultures that dominate American agriculture, be they corn, soybeans, wheat or vegetables. And the economic realities make it vital that they use only the very highest yielding varieties. As breeders freely admit, that means they all rely on basically the same seeds.

Now, that actually may not be as dangerous as it seems, says, Stephen Smith. So long as breeders have genetically diverse enough breeding stocks that will increase the chances, says Smith, that breeders will be able to react to any new disease or weather pattern with specialized new varieties.

STEPHEN SMITH: There are basically two ways in which you can create new varieties. You can reshuffle genes that are already existing in the breeding lines or you can introduce new genes from exotic or wild sources.

MARK HEISTAD: Now, by and large, breeders have been able to produce today's high yielding varieties simply by reshuffling our existing genetic deck, what scientists call our gene pool. There are fears though that pool may be too small. That it may not contain whatever specific genes breeders will find they need in the future for new breakthroughs in yield and disease resistance.

The history of US Food crops explains a lot about that concern. Each of our basic food crops actually originated somewhere else in the world, mostly in the third world near the equator. They've been transplanted here, many of them centuries ago, some in just the past few hundred years. And in most cases, just a few varieties were imported. For example, says biologist Garrison Wilkes, the corn Midwestern farmers are now planting is descended from just two ancient Central American varieties.

GARRISON WILKES: To put those numbers in perspective, we have to realize that the Indigenous people of the Americas planted about 250 to 280 different races from Canada to Chile.

MARK HEISTAD: Wilkes and others in his field are now calling for a massive effort to infuse new genetic material into the breeding stocks of American crops by breeding in genes from those wild varieties. He says that in the few crops where that's been seriously pursued, the results have been rewarding.

GARRISON WILKES: If you take a crop such as tomatoes, they've used the wild relatives of the tomato to overcome disease problems, to increase the solids so that the value added to the American tomato crop is somewhere in excess of $20 million a year from the superior genotypes.

MARK HEISTAD: But doing that kind of work is a lot easier said than done. It takes years of breeding, all the more reason to start now, say many breeders. And while the new biotechnologies, gene splicing and the like, may shorten the time it takes to breed in specific genes, there is growing concern about the future of those important wild varieties. They're dying out at a record pace, raising fears that the genetic foundation of future American food crops may be in danger. This is Mark Heistad reporting.