Castanea dentata

From Steve Nix,
A New Breed!
Advances in genetics have shown us where those early researchers went wrong in working with the chestnut. The American Chestnut Foundation (TACF) is confident that "we now know we can have this precious tree back." However, it still is a very complex process and will take years of work.Advances in genetics have shown us where those early researchers went wrong in working with the chestnut.

The American Chestnut Foundation (TACF) is confident that "we now know we can have this precious tree back." However, it still is a very complex process and will take years of work.
In 1989, The American Chestnut Foundation established the Wagner Research Farm in Meadowview, Virginia. The purpose of the farm was to continue a breeding program developed by the late Dr. Charles Burnham and Philip Rutter.
Under the supervision of a full-time researcher, chestnut trees have been planted at the farm, crossed, and grown over the last eight years. In 1995, the farm was filled to capacity with over 5,800 chestnut trees at various stages of genetic manipulation.
TACF's breeding program is designed to do two things:
Introduce into the American chestnut the genetic material responsible for blight resistance
Preserve the genetic heritage of the American species.
Preserving the genetic heritage of the American species is the hard part.
Old science told us that resistance is controlled by numerous genes running a very complex system. Scientists simply flooded chestnut progeny with Chinese chestnut genes by crossing their Chinese-American hybrids with other promising Chinese-American hybrids. The result was consistently a blight-resistant but very Chinese chestnut-like chestnut tree.
New techniques are now being used. By an elaborate and time consuming system of backcrossing and intercrossing, TACF's breeding program is attempting to develop a chestnut that will exhibit virtually every American characteristic. The desired tree is one that is fully resistant and when crossed, the resistant parents will breed true for resistance.
The method of breeding entails crossing the Chinese and American trees to obtain a hybrid which is one-half American and one-half Chinese. The hybrid is backcrossed to another American chestnut to obtain a tree which is three-fourths American and one-fourth Chinese, on average. Each further cycle of backcrossing reduces the Chinese fraction by a factor of one-half.
The idea is to dilute out all of the Chinese characteristics except for blight resistance down to where trees are fifteen-sixteenths American, one-sixteenth Chinese. At that point of dilution, most trees will be indistinguishable by experts from pure American chestnut trees.
TACF indicates that "the process of producing seeds and testing seeds for blight resistance now requires about six years for each backcross generation and five years for intercross generations. Since our first group of third backcross seeds were planted in 1995, we can expect progeny from the first intercross in 2000. We'll have progeny from the second intercross - and our first line of blight resistant American chestnuts - ready for planting in ten to fifteen years!"
The American chestnut may just be back in a few years...