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Welcome to the American Chestnut Foundation's research farm
The purpose of the farms is to breed American chestnut trees for resistance to the blight disease, so that they might be grown again in the mountains to provide a valuable resource for both humans and wildlife.
Our primary approach is to introduce the blight resistance into the American chestnut from the Chinese chestnut. We only want the blight resistance, so we use the backcross method to dilute out other undesirable characteristics of the Chinese parent. The backcross method entails breedingthe two trees to obtain a tree which is half American and half Chinese.
This first hybrid, called an F1 is backcrossed to a different American chestnut to create offspring that are 3/4 American. We introduce a new American at every stage of the breeding program to increase genetic diversity and give the tree a better chance to fight back against the adaptable fungus.
We follow this cycle twice more to produce a tree that is 15/16 American. Plant breeders have found that these third backcrosses are indistinguishable from the recurrent parent, in this case American chestnut. A final step is to intercross third backcrosses with each other to produce trees with a chance of inheriting blight resistance from both parents. They will produce the nuts we use for reforestation.
Among our more advanced crosses, the Price Research Farm has about 3818 15/16 American chestnut trees, derived from about 2700 7/8 American trees at Wagner farms. The parents of the 15/16 trees were selected for moderate levels of resistance, comparable or better than that found in the first hybrid between Chinese and American.
Dr. Fred Hebard stands beside a beautiful, blight resistant 3/4 chestnut hybrid. The smoothness of its trunk is an excellent sign that it will not succumb to the blight (gall wasps may be another matter).
We also selected for American chestnut traits, such as those that are economically important--tall, straight trunks--and those that may indicate a more American genotype--non-hairy twigs and leaves.
We screen the trees for blight resistance by inoculating them with the blight fungus and measuring canker size, picking the trees with the smallest cankers. Trees that die because of our inoculation do not have the resistance gene, and so are removed naturally from the breeding program.
The prospects for success in our backcross breeding program are bright if only a few genes control blight resistance. However, if numberous genes are needed to confer resistance, the chances dim. Either some genes would be lost during breeding, leaving the trees with inadequate resistance, or so many associated Chinese chestnut traits would be retained that the trees would not resemble American chestnut.
Results over the last 10 years indicate that our prospects are bright. It seems that only a few (2 or 3) genes control blight resistance and we should be able to backcross it into the American chestnut. We were able to recover blight-resistant progeny when we intercrossed each generation: F1, 3/4 American, and 7/8 American.
Additional support comes from genetic studies. Using molecular and morphological markers, we have made genetic maps of the chestnut genome, and blight resistance mapped to only a few gene locations.
We have begun intercrossing 15/16 American trees derived from the Clapper tree at the Price farm. We currently have 12,376 trees produced from these nuts. We began selecteing blight-resistant progeny from them in 2004, and some of those blight resistant progeny began bearing nuts in 2005.
Unfortunately, we can only truly prove our success after trees from those nuts have grown for 50 years in the forest. Only our children will be able to see wheter we succeeded in producing trees that grow like the American chestnuts of old.
The Glenn C. Price research farm stretches into the distance of southern Virginia Appalachians.
