The shape of forests to come?

AuthorCharman, Haren
PositionGenetically modified plants in forest ecosystem

At the turn of the last century, nearly one out of every four trees in the eastern deciduous forests of the United States was an American chestnut. Averaging 30 meters tall and 2 meters wide, these majestic beauties ranged from Maine down through the Appalachian mountains and west to Michigan. The fast-growing and naturally rot-resistant chestnut was an important part of early American life, its timber widely used for log cabins, posts, and railroad ties and its abundant nut crop sustaining wildlife as well as livestock.

But within 40 years, a fungal blight had spread throughout the tree's range, felling virtually every chestnut it touched--some 3.5 billion in all. Brought in by a New York nurseryman on imported Asian chestnut seedlings that were then sent all over the country, the blight moved stealthily from tree to tree, entering through a break in the bark and producing an acid that lowered the tree's pH to toxic levels. Because it attacks new shoots before they can mature, the fungus has reduced the once dominant chestnut to little more than a short-lived shrub.

Ever since chestnut blight was first described at the Bronx Zoo in 1904, scientists have been struggling to defeat it. One of several efforts is going on in the labs of Chuck Maynard and Bill Powell, directors of New York State's American Chestnut Research and Restoration Project. The two scientists have been working since the late 1980s to genetically engineer a blight-resistant American chestnut. In the fall of 2004, they made a major breakthrough: shoots finally appeared on a handful of blight-resistant chestnut embryos in petri dishes in Maynard's lab. Each of the tiny embryos had a gene from wheat to give it an extra enzyme, oxalate oxidase, which neutralizes the oxalic acid produced by the blight.

Genetically engineering the chestnut (or any other plant) involves not only inserting foreign DNA into its cells but getting the altered, or "transformed," cells to regenerate into a whole plant. This is particularly difficult with chestnut, because unlike species such as poplar, it won't regenerate from leaf tissue. So Maynard and Powell had to work with immature embryo tissue, which is much more difficult. Unlike the natural transformation a tree seed undergoes in the forest, the method plant biotechnologists use--somatic embryogenesis--is a multi-step, highly sterile, precision operation. It demands vigilant monitoring, special chemical solutions, and filtering equipment to prevent contamination of the fledgling embryos and coax them into seedlings that can survive outside the lab.

[ILLUSTRATION OMITTED]

Barring unforeseen problems, Maynard and Powell hope to have potted plants by this summer, to begin field tests in either the fall or spring, and then to do three years of field trials. If all goes smoothly, they expect to begin deploying genetically modified (GM) American chestnut seedlings to forests in the United States in about four years. Because their goal is to reestablish this tree in its natural range, the two scientists want the Animal and Plant Health Inspection Service (APHIS), the branch of the U.S. agriculture department that regulates biotech plants, to allow their transgenic chestnut genes to spread as far and mix with as many chestnut stump sprouts as possible. In fact, they propose that transgenes from any GM tree in a forest restoration or disease eradication project be granted such regulatory freedom. (In addition to the chestnut, they've engineered transgenic elm seedlings to fight Dutch elm disease, field tested GM hybrid poplars, and identified other pathogens that affect butternut, white pine, beech, dogwood, and oak.)

But it's impossible to know in advance what kind of impacts transgenic trees will have on wild forests. Maynard and Powell see only a minuscule risk of ecological disruption (if any) with their GM chestnut, since it will contain just three or four foreign genes--the target trait plus a few others needed for the desired transformation. The scientists say greater unknowns exist with the conventionally bred and backcrossed American chestnut, which draws one-sixteenth of its genes from its naturally blight-resistant relative, the Chinese chestnut.

Others, however, aren't convinced that ecological safety depends merely on how many foreign genes a transgenic organism contains, particularly when GM organisms may include genes...

To continue reading

Request your trial

VLEX uses login cookies to provide you with a better browsing experience. If you click on 'Accept' or continue browsing this site we consider that you accept our cookie policy. ACCEPT