The concept of “planting natives” has become broadly accepted by our society and is often required by federal, state, or local laws or policy. Native plantings have become a common practice in many national/state parks and are increasingly common in highway roadside treatments (Rogers and Montalvo, 2004). Native flowers (forbs) are one group of native plants that have been frequently used. Many states have adopted native wildflower planting programs for highway beautification and revegetation. For example, the Texas Department of Transportation (TxDOT) recently purchased and sowed 18,000 to 27,000 kg of wildflower seeds per year and actively managed 323,742 ha of highway rights-of-way in Texas for wildflowers (Markwardt, 2005). Use of native wildflowers along roadsides has not only increased aesthetic values and attracted tourists, but also reduced maintenance costs, enhanced wildlife habitats and biodiversity, augmented soil erosion control, and suppressed noxious weeds (Bryant and Harper-Lore, 1997). Members of Asteraceae are among the native wildflowers commonly planted. More than one-fifth of the wildflowers in Texas belong to this family (TxDOT, 2011).
An important consideration in native planting is the need to maintain the genetic diversity and integrity of the selected plant taxa during seed production and planting (Rogers, 2004; Rogers and Montalvo, 2004). This is critical for the successful establishment and performance as well as for the sustainability of the native plant taxa, particularly for those taxa that are narrowly distributed (Havens, 1998; Rogers and Montalvo, 2004).
When different but cross-compatible taxa are brought into close proximity for seed production or planting, interspecific pollen-mediated gene flow (PMGF) can occur (Ellstrand et al., 1999). This type of gene flow can lead to genetic contamination of the native wildflower seeds being produced. When the hybrids show reduced seed viability and/or plant fitness, the effects of such gene flow can result in poor establishment, performance, and/or sustainability of the transplanted materials. This type of gene flow may also disrupt native taxa’s local adaptation and genetic structure that have developed during natural selection and evolution (Laikre et al., 2010). Certain rare native taxa have been driven by this type of gene flow to the point of extinction (Largiadèr, 2007). The potential negative impacts of interspecific PMGF on the genetic diversity and integrity of native taxa in large-scale production and transplanting is a major concern to native plant seed producers, growers, and users. Monitoring and preventing undesirable PMGF has become a very active research area in recent years.
The genus Coreopsis, a member of the family Asteraceae, is Florida’s state wildflower. One species, Coreopsis leavenworthii, is widely distributed in Florida but has been reported only in two counties outside of Florida, thus it is nearly endemic to Florida [U.S. Department of Agriculture (USDA), 2011; Wunderlin and Hansen, 2004]. Its habitats include roadside ditches, wet pine flatwoods, and other moist disturbed sites, which are common along highways in Florida (Kabat et al., 2007). Plants of this species can form a dense flower cover over the foliage. These characteristics make C. leavenworthii desirable for use in highway beautification projects. Seeds of this species have been in high demand. Commercially produced seeds are expensive (up to $258/kg in 2006) and seeds costs for planting are high ($2900 to $4300/ha). The quality of C. leavenworthii seed, including their genetic diversity and integrity, is critical for wildflower growers who produce seeds and end users of this native wildflower.
Coreopsis tinctoria naturally occurs in all states of the United States except Alaska, Nevada, and Utah and has been recommended for highway beautification in several states. Seeds of C. tinctoria are commercially produced in a number of states, mainly Texas. Naturalized C. tinctoria populations have been observed in several counties in Florida where C. leavenworthii also exists. Both species belong to the Calliopsis section and are known to be outcrossing species that are insect-pollinated (Clewell, 1985; Wunderlin, 1998). Parker (1973) showed that C. leavenworthii and C. tinctoria were cross-compatible after hand pollination. Their F1 hybrids showed reduced pollen stainability when grown in a greenhouse. Meiotic chromosome configuration analyses suggested that the two taxa might have several structural differences, including reciprocal translocations, between their genomes (Smith, 1976). These studies raised concerns that naturalized or newly planted C. tinctoria may hybridize with C. leavenworthii and the resulting interspecific PMGF may compromise seed quality, plant fitness, and genetic integrity of C. leavenworthii. However, information is lacking for the rates of PMGF between C. tinctoria and C. leavenworthii under field conditions and the effectiveness of physical separation for minimizing undesirable PMGF.
The objectives of this study were to determine 1) the cross-compatibility between C. leavenworthii and C. tinctoria; 2) the inheritance of potential morphological markers for detecting PMGF from C. tinctoria to C. leavenworthii; and 3) the rates of PMGF from C. tinctoria and C. leavenworthii under field conditions and the effects of separation distances on reducing PMGF from C. tinctoria to C. leavenworthii.
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