Breeding of American Chestnuts

Breeding of American Chestnuts

A majority of TACFs resources are put into the creation of blight-resistant stock where the donor of blight-resistant genes is of Asiatic origin. However, there is some evidence to suggest that American chestnuts have some low levels of blight-resistance.

TACF isn’t the only organization dedicated to American chestnut restoration. Another organization, the American Chestnut Cooperator’s Foundation (ACCF) is dedicated to restoring the American chestnut without using any hybridization step. Many members of TACF are also members of ACCF and in many cases, material of large, surviving American chestnut trees is traded between the organizations.

The program of crossing potentially non-hybridized, blight-resistant American chestnuts is often referred to as the LSA program. The term LSA refers to “Large, Surviving American”, perhaps an unfortunate term since just because a tree is large, and surviving, it may not necessarily be an LSA. What is difficult to determine is whether or not the tree has resistance.

If a tree has not become infected with the blight, one cannot know for certain that a tree is resistant. Just because an American chestnut tree is large (even upward of 36” dbh or more!), one cannot assume the tree is resistant. In almost all cases, that uninfected tree is more lucky than resistant. In order to make sure the tree is resistant, and therefore a true “LSA”, one must either confirm the tree is resisting the blight through observation of natural and/or artificial inoculation.

Once an American chestnut individual is confirmed as having resistance, it is either bred, using controlled pollination, with another LSA, and/or grafted into an LSA breeding orchard with other grafted LSAs. Breeding many LSAs together should pyramid, or increase the inherit resistance within the native American chestnut species.

For more information on resistance of American chestnuts, and the breeding LSAs, please see the following resources:

1. The website of the ACCF
2. Griffin et al. 1983. Survival of American chestnut trees: Evaluation of blight-resistance and hypovirulence of Endothia parasitica. Phytopathology. 73(7): 1084-1092.