Genetic Variation and Population Structure of Castanea pumila var. ozarkensis

ADDITIONAL INDEX WORDS. Ozark chinkapin, conservation, genetic diversity, isozymes, randomly amplified polymorphic DNA, RAPD ABSTRACT. Genetic variation among nine populations of Ozark chinkapin ( Castanea pumila (L.) Mill. var. ozarkensis (Ashe) Tucker), threatened by their susceptibility to chestnut blight ( Cryphonectria parasitica (Murrill) Barr), was investigated. Population genetic parameters estimated from isozyme variation suggest the populations have a higher genetic diversity ( He = 0.227) than populations of the other Castanea Mill. species on the North American continent, the American chestnut ( C. dentata (Marsh.) Borkh. ) High levels of heterozygosity were detected within the populations, but nonsignificant differences in genetic diversity were observed among the different populations. Principal component analysis based on isozyme allele frequencies or randomly amplified polymorphic DNA phenotype frequencies showed clustering of the same populations. Populations with high levels of genetic diversity and unusual alleles should be the focal point of conservation biologists for capturing much of the genetic variation of the species. Dane, personal observation). The two varieties differ in reproduc- tive and vegetative characters, as well as in leaf micromorphology The genus Castanea contains several species, some of which like the American chestnut (C. dentata) and chinkapin (C. pumila) are susceptible to chestnut blight, caused by the fungus Cryphonectria parasitica. The fungus was introduced into North America at the beginning of this century on nursery stock of resistant Japanese chestnut (C. crenata Sieb.) species (Anagnostakis, 1992). Chestnut blight reduced the American chestnut from one of the most impor- tant timber and nut producing tree species in the deciduous forests of the eastern United States to an understory shrub. Considerable efforts have been made to transfer blight resistance from the Chinese chestnut (C. mollissima Bl.) into the American chestnut in an attempt to combine the blight resistance of the Chinese species with the desirable timber qualities of the American chestnut (Burnham, 1988; Hebard, 1996). Although the plight of the American chestnut is well known, the lesser known member of the genus, the chinkapin, has been ne- glected by taxonomists and field biologists and has even been considered as an example of one of the most mistreated and misrepresented native North American nut trees (Payne et al., 1994). The chinkapin is endemic to the eastern and southeastern United States from Pennsylvania to Florida, eastern Texas, south- western Missouri, and west-central Kentucky. It includes shrubs and trees that occupy dry, open, usually disturbed sites from near sea level to ≈1400 m in altitude. The species exists as two regional varieties (Johnson, 1988). Castanea pumila variety pumila, the Allegheny chinkapin, is widespread and a highly variable shrub or tree, while C. pumila var. ozarkensis, the Ozark chinkapin, is restricted to the Ozark plateau in Arkansas, where it persists mainly as trees or stump sprouts of various sizes (Johnson, 1988; Logan and