Science and Natural History

P rior to the blight epidemic, American chestnut (Castanea dentata Borkh.) was one of the most important timber and nut-producing tree species in eastern North America (U.S. Census Bureau 1908). Its native range extended from southern Maine and Ontario in the north to Georgia, Alabama and Mississippi in the south (Sargent 1905). It now exists primarily as stump sprouts across its entire native range. After nearly a century of blight, numerous living stems of American chestnut still exist (Stephenson et al. 1991). Prolific stump sprouting and the fact that the blight fungus does not infect the root system have enabled American chestnut trees to persist. However, sexual reproduction is infrequent and its gene pool will likely face serious erosion when old root systems fail to produce sprouts and perish. In an attempt to restore the American chestnut to its former status as a dominant canopy component in eastern forests, The American Chestnut Foundation (TACF) has developed a vigorous backcross breeding program designed to introduce the resistance of Chinese chestnut (C. molLissima Blume) into American chestnut (Hebard 1994). TACF’s initial efforts have focused on American chestnut trees in southwest Virginia, but the goal is to restore the species throughout its entire native range. Hence, separate breeding programs have been started in a number of states. One question that is of primary interest to T,4CF and its State Chapters is how many breeding locations or separate programs will be needed across the entire range to capture most of the genetic variation still p,yesent in the species. Previously, little was known about how genetic variability is distributed in American chestnut. In an exploratory examination of genetic variabili’ ty, Huang et al. (1998) obtained results with allozyme and random amplified polymorphic DNA (RAPD) markers that suggest as many as four