Bringing Back the Chestnut: Breeding and a Wheat Gene at the Refuge

Nut Trees for the Refuge

1The Laurel Fork National Wildlife Refuge protects mountain forest in the eastern United States. Each fall, staff and volunteers survey the animals that feed on nuts. They set trail cameras under oak and hickory trees and count visits by deer, wild turkeys, black bears and squirrels. Eighth grader Hazel Odhiambo joined the survey this year with her science club. Refuge forester Lucas Bjornstad told the club that the forest once had another nut tree that fed these animals: the American chestnut.

2In parts of these forests, about one tree in four was once an American chestnut. Early in the 1900s, a fungus from Asia that causes chestnut blight reached North America. The fungus enters cracks in the bark and makes an acid that kills the living tissue under the bark. The dead patch, called a canker, spreads around the stem until the part of the tree above it dies. Within about 50 years the blight had killed most large American chestnuts. Roots often survive and send up sprouts, but the sprouts usually get blight before they grow big enough to make many nuts.

3The refuge is testing two ways to bring back chestnuts that resist the blight. The first is breeding. A few large American chestnuts lived through the blight for decades with only small cankers. Breeders crossed these survivor trees, tested the young trees and chose the ones with the smallest cankers as parents of the next generation. A control line was bred from American chestnuts whose parents were picked at random, and young trees in both lines got the same test. To test a tree, workers make a small cut in the bark of a young tree, add the blight fungus and measure the canker one year later. Chestnut trees often take about six years to make their first nuts.

4The second way is genetic engineering. Scientists at a university copied a gene from wheat and added it to American chestnut cells, then grew whole trees from those cells. The wheat gene carries the instructions for an enzyme that breaks down the acid the blight fungus makes. Each engineered tree has one copy of the added gene. Later, pollen from an engineered tree was used on a regular American chestnut, and the young trees from those nuts were checked for the gene.

5All of the trees were grown in one refuge test plot with the same soil and care, and Hazel's club helped measure the cankers. Chinese chestnuts, which grew alongside the fungus in Asia and usually get only small cankers, were planted for comparison.