Date of Award

2008

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Natural Resources

Abstract

The American chestnut (Castanea dentata (Marsh.) Borkh.) is a tree species of unique ecologic and economic value that was virtually eliminated by a fungal blight approximately 100 years ago. In order to restore this valuable species multiple restoration approaches have been evaluated. However, only one technique – producing highly resistant trees via the hybridization of American and Chinese chestnuts with backcrosses to American chestnut – shows promise for near-term restoration. The American Chestnut Foundation (TACF) is leading this hybridization/backcrossing effort, and the University of Vermont and the USDA Forest Service have begun research to enhance the TACF breeding program to better support species restoration in the cold north. There are three issues of particular importance to species restoration in the north: 1) providing germplasm from locally-adapted American chestnut through controlled pollinations; 2) identifying new sources of germplasm for future pollinations; and 3) evaluating if inadequate cold hardiness could hinder restoration. In order to provide backcrossed chestnut with germplasm from Vermont-adapted trees, controlled pollinations of wild American chestnut growing in northern Vermont were conducted in 2006 and 2007. In 2006, two trees were pollinated, with a yield of 165 seeds. In 2007, three trees were pollinated, with a yield of 171 seeds. Seeds from controlled pollinations are planted in a chestnut-breeding orchard in Shelburne, VT where resulting trees will eventually be tested for blight resistance. An inventory of existing chestnut in Vermont was begun to expand the current registry of locally adapted sources of germplasm. A wide range of forest professionals and outdoor enthusiasts were asked to report existing chestnuts throughout the state. American chestnut exists in Vermont as healthy and blighted mature trees, as well as blighted sprouts. At each new site visited, basic tree measurements and other data important to the breeding program were gathered and site GPS coordinates recorded. All information was incorporated into a spatial database. Thus far, over 20 sites have been identified, including at least 15 trees with pollination potential. Preliminary evaluations of potential limitations in tissue cold tolerance that could restrict chestnut restoration within the northern limits of the species’ historical range were conducted during November 2006, and February and April 2007. We tested the cold tolerance of the shoots of American chestnut and backcross chestnut saplings growing in two plantings in Vermont to assess their cold tolerance relative to ambient temperature lows. Shoots of two potential local competitors, northern red oak (Quercus rubra L.) and sugar maple (Acer saccharum L.), were also tested for comparison. During the winter, American and backcross chestnut were approximately 5°C less cold tolerant than red oak and sugar maple (P < 0.0002), with a tendency for American chestnut to be more cold tolerant than the backcross chestnut (P = 0.0745). Terminal shoots of American and backcross chestnut also exhibited significantly more freezing damage in the field than nearby red oak and sugar maple shoots (P <0.0001), which showed no visible injury. Although these findings suggest that limited cold tolerance could complicate species restoration within northern forests, cold tolerance levels could potentially be improved through genetic selection or cultural means.

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