Lantana camara L. (Verbenaceae) is often grown as a container plant, groundcover, or accent plant. It is valued for its ability to produce bright flowers, attract numerous species of butterflies, and tolerate harsh environmental conditions with little maintenance (Arnold, 2002; Schoellhorn, 2004). Lantana has been a major component of the U.S. nursery industry for decades because it is easy to propagate and has short production cycles. (Arnold, 2002; Schoellhorn, 2004). A 2009 survey of the Florida nursery industry indicated that 19% of responding Florida growers produced lantana, generating an estimated annual sales value of over $40 million, which accounted for over 1% of Florida’s total nursery industry plant sales (Wirth et al., 2004).
Lantana camara originated in the Western Indies (Sanders, 2001) and was introduced by European explorers to almost all tropical regions by 1900 (Howard, 1969). Since then, it has escaped cultivation and become naturalized through most of the tropical and sub-tropical world (Sanders, 2006). In the United States, L. camara is found in 14 contiguous states from North Carolina to California as well as Hawaii, Puerto Rico, and the Virgin Islands (U.S. Department of Agriculture/National Resources Conservation Service, 2011). In Florida, escaped L. camara plants have hybridized with a Florida native lantana species, Lantana depressa Small. Sanders (1987a) recorded natural interspecific hybrids between L. camara and L. depressa, including its all three varieties, var. depressa, var. sanibelensis R.W. Sanders, and var. floridana (Moldenke) R.W. Sanders, at 60 locations in Florida. Presumably, such hybridization was facilitated by various insect pollinators, including butterflies and bees, which visit lantana flowers (Dehgan, 2006; Mathur and Ram, 1986; Schemske, 1976). Such interspecific hybridization has resulted in genetic contamination of the native species (Hammer, 2004) and has driven L. depressa to endangered status (Weaver and Anderson, 2010). The Florida Exotic Pest Plant Council (FLEPPC) began to list L. camara as a Category I invasive plant in 2001 (FLEPPC, 2001). Subsequently, the University of Florida’s Institute of Food and Agricultural Sciences (UF/IFAS) Assessment of Non-Native Plants in Florida’s Natural Areas recommended “No Use” of L. camara in south and central Florida and “Caution” in using L. camara in north Florida (IFAS Invasive Plant Working Group, 2014). The invasive species status of L. camara has become the most significant barrier for growers and landscapers who are interested in producing or planting L. camara.
The major determinant of the invasive potential of L. camara is its ability to produce viable pollen that can be transferred onto native lantana’s flowers by pollinators. Dehgan (2006) indicated the existence of a wide range of pollen stainability (from less than 5% in Patriot™ ‘Sunburst’ to more than 80% in ‘Professor Raoux’) in L. camara cultivars in reports to the USDA’s Current Research Information System database. However, pollen stainability data for many current lantana cultivars are not available. Other studies on the pollen viability of L. camara were mainly based on naturalized populations or wild swarms of lantana plants, where a wide range of pollen viability was observed (Raghavan and Arora, 1960).
The main method used in lantana pollen viability studies has been vital dye-based staining, including aniline stain (Sanders, 1987b; Spies, 1984c) and Alexander’s stain (Dehgan, 2006). Brewbaker (1967) showed that lantana pollen grains were binucleate. Attempts to germinate lantana pollen grains on artificial media were unsuccessful (Brewbaker and Kwack, 1963; Khaleel and Nalini, 1972), and the cause(s) of such in vitro germination failures remain to be identified. Thus, pollen stainability has been the primary parameter used in lantana pollen viability assessment.
This study was conducted to determine the ploidy levels and pollen stainability of 32 L. camara cultivars and breeding lines. The main objective was to gain a better understanding of the relationship between ploidy level and pollen stainability in L. camara and to assess the effectiveness of ploidy manipulation for producing sterile L. camara cultivars. A secondary objective was to identify male-sterile cultivars for commercial production and landscape use and examine pollen mother cells and microspores for meiotic abnormities that might lead to low pollen stainability.
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