GENETIC STRUCTURE OF AMERICAN CHESTNUT POPULATIOSS BASED ON NEUTRAL DNA YL4RIiERS

Microsatellite and R4PD markers suggest that American chestnut exists as a highly variable species. e\ en at the margins of its natural range. \+ ith a large proportion of its genetic \-ariabilir). occurring within populations (-95%). A statistically significant proportion also exists among populations. Although genetic differentiation among populations has taken place. no disjunct regional pattern of variation exists. A cline in allele frequencies and number of rare alleles occurs along the Appalachian axis. with the highest l e ~ e l s of gene diversir! and the greatest numbers of rare alleles being found in southwestern populations. Population pain+ ise estimates of genetic distance are significantly associated with the geographic distance bemeen populations. Geographicall\proximate populations are slightly more geneticall) similar than geographicall? distant populations. Genetic variability in American chestnut folio\+ s a pattern consistent u ith the h\.pothesis of a single metapopulation in nhich genetic drift plays a major ei olutionary role. Results of this stud) are based on neutral genetic loci and do not necessaril) reflect genetic differentiation for adaptike genes or gene complexes. Therefore. in order to assure that most of the ~ariation at these genes is also captured in consen-ation and breeding endeavors, sampling should focus on collecting a fair/) large number of individuals from each of se\ era1 geographic areas.