Population Genetics and Scarification Requirements of Gymnocladus dioicus

The Kentucky coffee tree (Gymnocladus dioicus) is an endangered tree species native to the American Midwest and Southwestern Ontario. Significant habitat loss and fragmentation due to agricultural, industrial and urban development has caused gradual decline across its native range. The aims of this study were to investigate: (1) patterns of genetic diversity and, (2) genetic differentiation (3) relative levels of sexual vs. clonal reproduction, and (4) potential for reduced genetic diversity at range edge for wild G. dioicus populations. An analysis of variation at nine microsatellite loci from populations in the core of the species distribution in the U.S.A. and 4 regions of Southwestern Ontario indicated that G. dioicus has remarkably high genetic similarity across its range (average pairwise FST= 0.05). Germination trials revealed that the seed coats require highly invasive treatments (e.g. 17.93 mol/L H2SO4) to facilitate imbibition, with negligible germination observed in treatments meant to emulate prevailing conditions in natural populations. Low levels of sexual reproduction, high genetic similarity, and habitat degradation are issues that exist across the entire native range of G. dioicus.