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The genus Coreopsis L. is Florida’s state wildflower; there is a strong interest in commercial production and large-scale planting of Coreopsis seed in Florida, especially the seed of Coreopsis leavenworthi Torr. & A. Gray (COLE) and Coreopsis tinctoria Nutt. (COTI). Both species belong to the same section [Calliopsis (Reichenb.) Nutt.] within Coreopsis and were known to be cross-compatible and produce interspecific hybrids when hand-pollinated or grown in close proximity. Little was known about the effects of such hybridization on progeny growth, development, and reproduction, which are very important to seed production and planting. F1 and F2 interspecific populations between COLE and COTI were created in the greenhouse and then evaluated in replicated field studies in two growing seasons. Results showed that interspecific hybridization between COLE (as the maternal parent) and COTI (as the paternal parent) significantly increased the plant height (by 11.4% to 18.7%), plant dry weight (by 38.6% to 63.9%), and time to flower (by 3.7 to 9.8 days) of the F1 and F2 progeny of COLE · COTI crosses. By contrast, interspecific hybridization between COTI (as the maternal parent) and COLE (as the paternal parent) did not cause significant changes in these characteristics of the F1 and F2 progeny of COTI · COLE crosses. The differences between the two species in responding to interspecific hybridization suggest that COTI played a more dominant role in controlling plant height, dry weight, and time to flower in its hybrids with COLE. Results pooled from all F1 or F2 progeny of reciprocal interspecific crosses showed that interspecific hybridization did not seem to affect the plant height and seedling emergence of F1 and F2 progeny but affected the dry weight, time to flower, pollen stainability, and seed production (per seed head) of these progeny. Heterosis was observed in the time to flower of F1 progeny in 2009. Heterosis was also evident in F1 progeny’s dry weight but followed with slight hybrid breakdown in F2 progeny. Pollen stainability and seed production both showed significant breakdown in F1 and F2 progeny: 53.3% to 81.1% reduction in pollen stainability and 12.6% to 38.2% reduction in seed production, respectively. Chromosome mispairing resulting from reported reciprocal translocations between the chromosomes of COLE and COTI might be the primary cause of low pollen stainability and seed production in F1 and F2 progeny. Maternal effects were detected in plant height and dry weight of F1 and F2 progeny. These results showed that interspecific hybridization between COLE and COTI would result in deleterious effects to both species; thus, it is very important to prevent crosspollination and hybridization between them in commercial seed production and native plantings. 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 Received for publication 19 Sept. 2014. Accepted for publication 10 Oct. 2014. This is part of a PhD dissertation of Sarah Smith. Dr. David Clark (co-chair of the graduate committee) and Drs. Jeffery G. Norcini, Frederick G. Gmitter, Jr., and Kenneth H. Quesenberry (committee members) provided very valuable reviews, comments, and suggestions, for which we are very grateful. We thank Joyce Jones and Gail Bowman for their technical assistance and the Florida Wildflower Foundation, Inc. for financial support of this study. Former Graduate Student. Current address: HM-Clause, 9241 Mace Boulevard, Davis, CA 95618. Corresponding author. E-mail: zdeng@ufl.edu. J. AMER. SOC. HORT. SCI. 140(1):27–37. 2015. 27 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. Materials and Methods Seed source and initial parental plants The COLE and COTI seed used in this study were collected by N. Bissett from a natural COLE population at the Reedy Creek Mitigation Bank in Polk County, FL, and purchased from the Wildseed Farms in Fredericksburg, TX, respectively. Seed were germinated as previously described by Smith and Deng (2012). The initial COLE parental plants consisted of 40 individuals from the previously mentioned seed source, and the initial COTI parental plants were made up of 35 individuals from that seed source. Parental plants were grown in 3.2-L plastic containers (one individual per container) in a greenhouse at the University of Florida Gulf Coast Research and Education Center, Wimauma, FL (GCREC). Containers were filled with a commercial potting mix [Vergrow Container Mix A (VCMA); Verlite Co., Tampa, FL] and top-dressed with 8.6 g of 15N–3.9P–10K controlled-release fertilizer (Osmocote 5-6 month; Scott’s, Marysville, OH) per container. Temperatures in the greenhouse were between 23.9 and 29.4 C. Plants were grown under natural light and photoperiods. Hand pollination and population development Hand pollination was performed on these parental plants from June to Aug. 2007 to make interspecific crosses and produce interspecific F1 seed (Fig. 1). In the meantime, hand pollination was done to make intraspecific outcrosses within each species to produce seed for the reference populations. Subsequently, F1 hybrids were grown and hand-pollinated in Nov. 2008 to produce interspecific F2 populations (Fig. 1). INTERSPECIFIC CROSSES AND HYBRID POPULATIONS. Reciprocal interspecific crosses between COLE and COTI were made to produce F1 hybrid seed. For simplicity, seed and progeny from the COLE · COTI crosses were referred to as COLE F1, and seed and progeny from the COTI · COLE crosses were referred to as COTI F1. Pollen collection, flower bagging, flower pollination, seed harvesting, and seed processing were performed as previously described by Smith (1976) and Smith and Deng (2012). To avoid potential se

journal of the american society for horticultural science

Interspecific Hybridization between Coreopsis leavenworthii and Coreopsis tinctoria Differently Affected Growth, Development, and Reproduction of Their Progeny