Genetics: Making Elms Compatible

The long, elm-cast shadows that once drifted across campuses and evoked dreams of Main Street, U.S.A., are fading—the victims of Dutch elm disease. Caused by a fungus and carried by bark beetles, the incurable blight was first detected in the U.S. in 1930 and has since spread inexorably across the nation, leaving unsightly stumps in its path. Although most American elms seem doomed, there is now hope that a hardy new breed of elm will rise to take their place.

Aware that the less attractive Siberian elm is highly resistant to Dutch elm disease, scientists have long attempted to mate it with its American cousin in an effort to produce offspring both disease-resistant and beautiful. Their efforts have been fruitless so far, probably because Siberian elm cells have only half the number of heredity-bearing chromosomes found in the cells of their American cousins. To make the elms compatible, two retired Department of Agriculture scientists, Geneticist Haig Dermen, 71, and Plant Pathologist Curtis May, 70, decided to experiment with colchicine—an antigout drug that has a peculiar effect on the division of plant cells.

In normal cell division, the chromosomes split, forming two complete sets that migrate to opposite sides of the cell. The cell then divides down the middle forming two cells, each with a complete set of chromosomes. Treated with colchicine, however, the cell creates the additional chromosomes, but subsequently fails to divide, thus creating a cell with double the normal number of chromosomes.

Voluntarily continuing their research at the Agriculture Department's Beltsville, Md., Plant Industry Station—where they are affectionately called "wocs" for "without cost"—Dermen and May patiently placed colchicine on each new bud of Siberian elm seedlings, pruned off leaves and twigs that had normal chromosome counts, and rooted double-chromosome shoots until they had developed plants with only double-chromosome cells. A dozen of these tailored plants, each 15 in. high, were recently shipped to the department's Delaware, Ohio, research station, where they will be raised until they flower and then mated with American elms. That will take a minimum of five years, and years of testing must follow. "There is a very high probability of success," says May, "but you don't cheer until you see the baby."