Pollen-mediated Gene Flow from Coreopsis tinctoria to Coreopsis leavenworthii: Inheritance of Morphological Markers and Determination of Gene Flow Rates as Affected by Separation Distances

The genus Coreospsis is Florida's state wildflower. One species, Coreopsis leavenworthii, is nearly endemic to Florida and is highly desirable for use in highway beautification. Maintaining genetic integrity is critical for C. leavenworthii producers, growers, and users. Coreopsis tinctoria is closely related to and shares similar habitats with C. leavenworthii in Florida. Previous studies indicated that the two species could hybridize and the F-1 hybrids showed chromosomal aberrations and reduced pollen stainability. There has been strong concern that pollen-mediated gene flow from C. tinctoria could contaminate the gene pool and compromise the genetic integrity of C. leavenworthii. In the current study, hand pollination showed that C. leavenworthii and C. tinctoria were highly compatible. F-1 hybrids were fertile and readily produced F-2 and BCI individuals. Inheritance studies indicated that the maroon spot on the ray flower is controlled by a single dominant allele and is homozygous in C. tinctoria. This spot serves as a reliable, easy-to-score morphological marker to detect pollen-mediated gene flow from C. tinctoria to C. leavenworthii. Following a discontinuous design, gene flow studies were conducted under field conditions in central Florida over 2 years. The highest rate of pollen-mediated gene flow from C. tinctoria to C. leavenworthii was 4.2% and occurred when the two species were grown 1.5 m apart. Gene flow from C. tinctoria to C. leavenworthii under field conditions followed a leptokurtic curve. Based on the obtained regression equation, separating the two species by 60 m or more could lower the pollen-mediated gene flow from C. tinctoria to minimal levels and protect the genetic integrity of C. leavenworthii.