Planting natives has become increasingly common in national/state parks, highway right-of-ways, and home landscapes (Rogers and Montalvo, 2004). One group of native plants frequently used in such plantings in the United States is native wildflowers. Many states have implemented wildflower planting programs for highway beautification and revegetation (Kabat et al., 2007; Texas Department of Transportation, 2011). Planting native wildflowers has resulted in multiple benefits, including increased aesthetic values, enhanced wildlife habitats, and reduced maintenance costs (Bryant and Harper-Lore, 1997). Members of the family Asteraceae are among the native wildflowers commonly planted in the United States.
When cross-compatible native plant species are brought into close proximity for seed production or planting, interspecific hybridization can occur (Ellstrand, 1992). Interspecific hybridization could lead to genetic contamination of native wildflower seed being produced. If interspecific hybrids have reduced seed viability and/or plant fitness, interspecific hybridization can result in poor establishment, performance, and/or sustainability of the transplanted materials. Interspecific hybridization may also disrupt native taxa’s local adaptation and genetic structure that have developed during natural selection and evolution (Laikre et al., 2010). Interspecific hybridization might have contributed to the demise of some rare plant species (Largiadèr, 2007; Levin et al., 1996). The potential adverse effects of unintended interspecific hybridization on native plants have become a major concern to native plant producers, growers, and users.
The genus Coreopsis (Asteraceae) is Florida’s state wildflower (Florida Legislature, 2014). One of its species, Coreopsis leavenworthii, is distributed widely in Florida (U.S. Department of Agriculture, 2012; Wunderlin and Hansen, 2004). COLE habitats include roadside ditches, wet pine flatwoods, and other moist disturbed sites (Kabat et al., 2007). COLE plants can produce a dense flower cover over the foliage and are highly desirable for use in highway beautification projects. Seed (achenes) of this species have been and continue to be in high demand in Florida. Commercially produced COLE seed were sold for as much as $258 per kilogram (in 2006), and the seed costs for planting COLE along highways reached as high as $4300 per hectare. COLE seed germination and progeny growth, development, and sustainability are very important to COLE seed producers and end users.
A closely related species of COLE, Coreopsis tinctoria, is distributed in all states of the United States except Alaska, Nevada, and Utah, and it has been highly recommended for highway beautification in several states. COTI seed are commercially produced in a number of states, mainly Texas. Naturalized COTI populations are codistributed with COLE populations in several counties in Florida (Wunderlin, 1998). There has been a significantly increased interest in planting more COTI along Florida highways. COLE and COTI both belong to the Calliopsis section within Coreopsis and are known to be outcrossing species (Smith, 1976; Wunderlin, 1998). When grown in close proximity in Florida under field conditions, COLE was cross-pollinated by COTI to some extent, resulting in the production of unwanted interespecific hybrids (Smith and Deng, 2012). Parker (1973) showed that COLE and COTI were cross-compatible after hand pollination in the greenhouse, and their F1 hybrids showed reduced pollen stainability. Smith (1976) indicated the existence of several structural differences, including reciprocal translocations, between the chromosomes of COLE and COTI. Thus, some levels of male and/or female sterility would be expected in the interspecific hybrids of COLE and COTI. However, no studies have been carried to quantify the actual effects of COLE and COTI interspecific hybridization on their progeny’s plant growth, development, and reproduction. This study aimed to fill this knowledge gap by creating COLE and COTI interspecific hybrids in the greenhouse and evaluating their hybrids in replicated field studies. This study also intended to assess the plant growth, development, and reproduction of F2 interspecific hybrids to gain a better understanding of the persistence of the effects of interspecific hybridization on COLE and COTI hybrids.
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