Allozyme variation in black locust (Robinia Pseudoacacia)

Seedlings from 23 seed sources representing the natural range of black locust (Robinia pseudoacacia L.) were electrophoretically analyzed at 40 structural loci representing 18 enzyme systems. Genetic diversity was high for an insect-pollinated, early-successional species. On average, 71% of the loci were polymorphic (99% criterion). Average and effective numbers of alleles per locus were 2.61 and 1.58, respectively. Mean expected heterozygosity was 0.291, ranging among the seed sources from 0.250 to 0.322. Most of the genetic diversity (88%) resided within seed sources. Few geographic patterns were evident. The most differentiated sources were located in disjunct sites in Georgia and the Ozark Mountains of Arkansas and Missouri, and in Pennsylvania. The widespread planting of native and European black locust seed sources may have contributed to the lack of geographic patterns. Based on this and other studies, it was concluded that initial selections in black locust breeding programs should concentrate on intrapopulational variation.