Pollen-Mediated Gene Flow From Coreopsis Tinctoria to Coreopsis Leavenworthii: Detection, Effects of Planting Distance, and Insect Pollinators Involved

            Coreopsis tinctoria and Coreopsis leavenworthii are closely-related and can produce interspecific hybrids in controlled pollinations.  This has caused concerns that insect pollinators may transfer pollen from C. tinctoria to C. leavenworthii in the field, resulting in gene flow from the former to the latter.  Similar concerns exist in other native wildflowers when used for seed production and mass plantings.  Such pollen-mediated gene flow can cause genetic and ecological consequences, such as gene pool contamination and outbreeding depression.  The objectives of this study were 1) to confirm the inheritance pattern of the maroon spot of C. tinctoria and its reliability in detecting gene flow, 2) to assess the effects of planting distance on pollen-mediated gene flow from C. tinctoria to C. leavenworthii, and 3) to identify insect pollinators that may be involved in the gene flow.  Segregation of the maroon spot in F₁, F₂, and backcross populations was examined, and all results confirmed our previous findings: the maroon spot is dominant over non-spotting and is controlled by one gene, and the maroon spot can be used reliably as a morphological marker to detect gene flow from C. tinctoria to C. leavenworthii.  C. leavenworthii plants were planted 5, 10, 25, 50, 100, 150, 200, 250 and 300 ft from C. tinctoria plants in three blocks in each of two seasons.  Interspecific hybrid plants were identified in plots 5 to 200 ft and 5 to 50 ft from C. tinctoria in the first and second seasons, respectively.  In both seasons, the percentage of interspecific plants decreased as the planting distance increased.  All insects visiting Coreopsis flowers were Hymenoptera belonging to six families and genera.  Three species of insects were found on both Coreopsis species.  These results suggest that C. tinctoria and C. leavenworthii plantings should be separated by at least 250 ft away from each other to avoid natural pollen-mediated gene flow.