Low genetic diversity at allozyme loci in Juglans cinerea

Butternut (Juglans cinerea L.) is a minor component of the temperate decidu ous forest region of northeastern North America, but it is severely affecte d by the butternut canker (Sirococcus clavigignenti-juglandacearum Nair, Ko stichka, and Kuntz) in the southern part of its natural range. Genetic dive rsity and population structure in as-yet unaffected or only slightly affect ed natural populations were evaluated at 12 isozyme loci. The genetic diver sity estimates were low with values much below those estimated in other spe cies of the same genus or in boreal tree species, with 25 and 13.9% polymor phic loci at the species and population levels, respectively; 1.3 and 2.3 a lleles per locus and per polymorphic locus, respectively, at the species le vel; and an average observed heterozygosity of 0.028. Population differenti ation was low, with the exception of one unique population. The implication s for advanced conservation are discussed.