Lantana is an important ornamental because of its low-maintenance characteristics and prolific flowering. Lantana is also known to attract multiple species of butterflies, honeybees, sunbirds, and hummingbirds with its brightly colored flowers (Winder, 1980). The plant is commonly cultivated in containers, hanging baskets, and landscapes (Schoellhorn, 2004). Lantana is easy to propagate through stem cuttings and has a short production cycle, attributing to its popularity. A survey conducted by Wirth et al. (2004) reported that 19% of the Florida nurseries responding to the survey produced lantana. Wholesale value of lantana in Florida was estimated at $40 million a year (Wirth et al., 2004).
The genus Lantana contains 129 accepted species (The Plant List, 2013). L. camara is the most commonly cultivated species, with hundreds of cultivars around the world (Sanders, 2012). L. montevidensis is also a popular species, but with a smaller scale in production. Both species originated from Central and/or South America and have been introduced to more than 60 countries and islands around the globe (Day et al., 2003). These species are known to escape cultivation and invade natural and agricultural lands through their bountiful seed production and pollination (Florida Exotic Pest Plant Council, 2019; Henderson, 1969). For example, L. camara in Florida has invaded natural and agricultural land, and hybridized with a native species (L. depressa) to the point where the native lantana has become an endangered species (Florida Department of Agriculture and Consumer Services, 2018). Similarly, L. camara has spread widely in Australia, India, South Africa, and other countries, and has caused substantial economic and ecological damage (Day et al., 2003). In Australia alone, L. camara has invaded 5,000,000 ha of land throughout coastal areas of Australia (Queensland Department of Agriculture and Fisheries, 2016). L. montevidensis has become an aggressive weed in Australia by taking over native grasslands during periods of drought (Weeds Australia, 2011). Although it has not yet been listed as a weed of national significance like L. camara, it does have potential and its use is restricted (Steppe et al., 2019). Considering the invasive potential of these lantana species, the environmental horticulture industry has been urged to produce and use more native and/or sterile lantana species (Hammer, 2004). Lantana species native to the continental United States include L. canescens, L. depressa, L. involucrata, etc. (Sanders, 2001). The genus Lantana is often split into four distinct sections: Calliorheas, Sarcolippia, Rytocamera, and Camara (Briquet, 1895; Day et al., 2003). Lantana camara and L. depressa are both categorized in the Camara section, whereas L. canescens, L. involucrata, and L. montevidensis fall under the Calliorheas section.
Cytological studies of lantana throughout the years have focused most attention on L. camara. Patermann (1938) was the first to report a chromosome number for the Lantana genus, identifying L. trifolia as 2n = 48. Since then, a range of ploidy levels have been identified in L. camara, from 2n = 22 to 55 with a base number of x = 11 (Fedorov, 1969; Goldblatt, 1981; Natarajan and Ahuja, 1957; Ojha and Dayal, 1992; Raghavan and Arora, 1960; Sanders, 1987; Sen and Sahni, 1955; Singh, 1951; Sinha and Sharma, 1982, 1984; Spies, 1984; Spies and Stirton, 1982a, 1982b; Tandon and Chandi, 1955). Both triploid (2n = 36) and tetraploid (2n = 48) cytotypes of L. montevidensis have been reported in Australia (Henderson, 1969). Chromosome numbers have been reported for lantana species native to the United States—L. involucrata (2n = 24, 36), L. depressa (2n = 22), and L. canescens (2n = 24) (Natarajan and Ahuja, 1957; Raghavan and Arora, 1960; Sanders, 1987)—but no information is available on their karyotypes.
Flow cytometry has been used to determine polyploidy in lantana (Czarnecki and Deng, 2009; Czarnecki et al., 2014). To interpret ploidy accurately from relative or absolute nuclear DNA contents, it is essential to understand the variation of nuclear DNA content among plant species and establish proper references (Doležel et al., 2007). Nuclear DNA content is often expressed in picograms per 2C value or picograms per somatic cell (Greilhuber et al., 2005). 2C nuclear DNA content for L. camara (2n = 22) was reported previously as 2.75 pg (Ohri et al., 2004). Steppe et al. (2019) reported 2C nuclear DNA content for triploid and tetraploid forms of L. montevidensis measuring 2.80 to 2.85 pg/2C and 3.98 pg/2C, respectively. Nuclear DNA content for other species and cultivars of lantana remains to be reported. Ojha and Dayal (1992) were the first to record chromosome measurements and classify lantana chromosomes based on size. The study classified chromosomes of L. camara, L. montevidensis, and L. fucata in India and used ideograms to visualize differences. Giemsa banding and fluorescence in situ hybridization have been used to analyze a tetraploid cultivar of L. camara (Brandão et al., 2007). However, a karyogram was not constructed and chromosome measurements were not recorded in the study, likely because of the low clarity of the chromosome spreads.
Much is known about the chromosome numbers of many lantana species, but the ability to visualize clear, well-stained metaphases has limited cytological analysis in lantana. The purpose of this study was to identify cytological features of three lantana species native to the United States and two introduced, cultivated species. The main objective was to obtain clear, darkly stained metaphase chromosome spreads of five species of lantana. Additional objectives were to produce karyotypes for each of the lantana selections and determine nuclear DNA content and its relationship with chromosome number. It is anticipated that information gathered from this study will help in the preservation of native lantana species and assist in the production of new cultivars through plant breeding.
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