One of the highest-profile plant projects undertaken by geneticists in the college does not involve genetic modification—at least not by Penn State scientists. It is the effort to introduce a blight-resistant strain of American chestnut tree back into eastern forests. This a chestnut seedling growing at the Penn State Arboretum.

“In genetic engineering, the genes responsible for a desirable trait are isolated and then inserted into a DNA vector that carries the gene into the modified organism. Genes can be introduced into a plant by either a gene ‘gun’ or agrobacterium. Then the cells that have been transformed are selected and regrown into an entire plant using tissue culture.”

A major difference between modern genetic modification and traditional genetics, according to Carlson, is that with GM techniques, scientists insert just one gene at a time into an organism to see how it functions. “The traditional, tried-and-true method of breeding involves taking all the genes from two organisms and mixing them together, and then breeding away all but a few desirable new genes,” he says. “That’s a long process. GM is precision genetics—more exact. One gene at a time is tested to see if it produces the desired trait.

“Finding genes that underlie important traits has become a field of research itself, known as genomics,” Carlson adds. “Genomics is simply trying to look at all the genes in an organism at the same time, usually in the lab, to try to find the genes responsible for certain traits that we are interested in. Much of our work revolves around genomics research and finding ways to apply information from genomics in forestry.”

Although many people equate modern genetics with genetic engineering, one of the highest-profile plant projects undertaken by geneticists in the college does not involve genetic modification—at least not by Penn State scientists. It is the effort to introduce a blight-resistant strain of American chestnut trees back into eastern forests. In this case, the genetic modifications have been done through decades of traditional crossbreeding, mostly by scientists and volunteers working for the American Chestnut Foundation.

A fungus from Asia accidentally introduced into American forests a century ago created a blight that wiped out American chestnut trees across the Northeast. The huge trees—with their valuable lumber and bountiful nuts for both humans and wildlife—were once the dominant species in Pennsylvania forests.

More than 60 years ago, U.S. Department of Agriculture scientists hybridized American chestnut with Chinese chestnut trees—which resist the blight they have long been exposed to—and then made a single backcross of that hybrid to American chestnut. Because trees from that early breeding work still survive, foundation scientists have continued the backcrossing work with additional American parents during the past 20 years to develop a tree that is essentially an American chestnut with blight resistance.

Carlson and forest biologist Kim Steiner are monitoring the genetic makeup of the hybrid trees to select strains that have the most American chestnut traits. “The goal is to end up with an American chestnut tree that has no traits from the Chinese chestnut except blight resistance,” says Carlson.

He and a graduate student spent two years developing a simple, inexpensive test using a decades-old molecular technique, called a dot-blot, to examine the genomes of blight-resistant chestnut trees produced by the American Chestnut Foundation breeding program. “We want to repopulate the forest with trees that are as much like the old American chestnut trees as possible,” Carlson adds. “So it was important to create an index of how much American chestnut genetic material is in each of the new blight- resistant trees. There are at least 30,000 genes that make up a chestnut tree. The simple and quick dot-blot technique lets us make a very broad assessment of the genetic makeup of each tree at the DNA level, and it has proven to be highly accurate. The dot-blot technique is so widely used and taken for granted, it is almost embarrassing that no one previously tried using it for this task.”