PA-TACF
Pennsylvania Chapter
The American Chestnut Foundation
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Background: Early Research Beginning in the 1920s and for decades thereafter, the Department of Agriculture and the Connecticut Agriculture Experiment Station (CAES) attempted to breed blight-resistant chestnuts by crossing Chinese and Japanese chestnuts with the American species. Their efforts were fully blight-resistant while having characteristics closely resembling the American chestnut in nut or timber quality. TACF’s Early Efforts In the late 1970s, TACF’s founder Dr. Charles Burnham proposed a methodology of breeding to incorporate blight resistance into the American chestnut tree. By using a well-established plant and breeding technique known as “backcrossing,” Dr. Burnham hypothesized that one could marry the best characteristics of both the American and Asiatic species. |
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Biology of the Tree: Controlled Pollination
The first step to making TACF’s breeding stock is to find American chestnuts with which to cross Chinese and advanced backcrossed pollen. Whenever a proper tree is found, great efforts are made to incorporate that tree into TACF’s national breeding program through the process of controlled pollination. Pollen from the male flower (catkin) of one tree is crossed with the female flower (bur) of another tree.
Chestnut burs
Biology of the Tree: Genetics and Incorporating Native Diversity
Based on the research of early researchers at CAES, it was determined that blight resistance was controlled by two or three genes acting in an incompletely dominant fashion. This means that when a fully-resistant Chinese tree (RRRRRR) is crossed with a fully susceptible American chestnut (rrrrrr), the resulting F1 progeny would be moderately resistant to the blight (RrRrRr). With the exception of the intercross (BC3,F2 and BC3, F3) generations, the most resistance possible is moderate resistance. In order to select which trees have the best resistance of those planted, TACF grows the trees for about 5-8 years and then challenges (inoculates) them with the blight fungus.
In order to avoid breeding in the long term, TACF seeks to perform the backcrossing process with as many surviving native American chestnuts as possible. To date, over 500 American chestnut trees have been incorporated into the various generations breeding program, and more are added every year.
The following documents provide visual summaries of the backcrossing process:
TACF Backcross Breeding Program (pdf)
The Path to Most Resistance (pdf)
Biology of the Tree: Planting and Growing
TACF has been able to make great advances in the standardization of planting and growing of all matter of chestnut stock. After pollination in the spring, the resulting nuts are ready to harvest in the fall. Chestnuts require a period of dormancy for approximately 1-3 months. Seeds are refrigerated until planting time. The seeds are typically planted in the ground and protected from rodents and deer using several methods, depending on the site and resources available. The trees are grown for 5-8 years until they are inoculated and selected for resistance and American character.
Biology of the Tree: Inoculation and ResistanceOnce the trees reach a proper size for the technique (usually 1/5” diameter at breast height), the trees are inoculated with the blight fungus. Two different strains of the fungus, one relatively weak, one very strong, are inserted into small wounds created in the tree. The trees are then rated for resistance after 5 months and again after 11 months. Those trees with little to no resistance are removed from the planting. Only those that have the highest degree of resistance will be bred into subsequent generations. This continues for a minimum of 6 generations. With excellent care, TACF is able to complete a generation in 6 years or less.
Inoculum
Inserting inoculum
Testing Ourselves
By consulting with a diverse network of colleagues, TACF increases its scientific focus and methodologies as part of its overall mission and enhances its ability to partner with high profile organizations throughout the country. In 1999, and again in 2006, TACF contracted with nationally and internationally known scientists for an independent audit of its science program. In each of these years, TACF’s national breeding program received high marks indicating an excellence in scientific procedures.
Interested in Blight-Resistant Chestnut Seed?
Please read the following document for more information:
Blight Resistance Status (doc)
814-863-7192 phone | mail@patacf.org