Winter Iinjury of American chestnut seedlings grown in a common garden at the species' northern range limit

Hybridization of American chestnut (Castanea dentata) with Chinese chestnut (C. mollissima), followed by backcrossing to American chestnut, is conducted to increase the resistance of resulting stock to chestnut blight, caused by the fungal pathogen Cryphonectria parasitica (Murr.) Barr. Backcross breeding is being used to restore American chestnut throughout its range, including cold high elevation sites in southern and central regions, and along chestnut's northern range limits. Until now, a comparative analysis of the growth and cold hardiness of American chestnut seed sources grown in cold environments had not been conducted. We assessed first-year growth and winter shoot injury (terminal shoot mortality that reduces apical dominance and results in a shrubby form) of American chestnut seedlings from 13 genetic sources: four southern, four central, and five northern seed sources, each representing one or more half-sib families, grown in a common garden in Vermont. No differences in height or diameter growth or in winter shoot injury attributable to the region of seed source origin were detected. However, significant differences in growth and winter injury were detected among sources within each region. There appeared to be a tradeoff between growth and winter injury: sources that had the greatest growth were generally the most vulnerable to winter shoot injury.