The genus Magnolia L. consists of over 250 species (Figlar and Nooteboom, 2004) and numerous hybrids and cultivars that can be cultivated in temperate and tropical climates worldwide. The diverse ornamental traits make the genus appealing for landscape use and breeding new cultivars. Magnolia [liliiflora ‘Nigra’ (4x) × stellata ‘Rosea’ (2x)] ‘Ann’ (NA 28344; PI 326570) is a member of the “Little Girl” series of magnolias that have become very popular (United States National Arboretum, 2003). Magnolia ‘Ann’ is characterized by a desirable combination of traits including prolific and remontant flowering and a shrub-like form. Parris et al. (2010) confirmed M. ‘Ann’ to be a triploid (2n = 3x = 57) and the cultivar is sterile. In vitro propagation procedures may be an efficient means for rapid, large-scale production.
Previous micropropagation studies on Magnolia sp. focused on conservation efforts and included M. acuminata var. cordata (Michx.) Sarg. (Merkle and Wiecko, 1990; Merkle and Wilde, 1995), M. dealbata Zucc. (Mata-Rosas et al., 2006), M. denudate Desr. (Bi et al., 2002), M. fraseri Walt. (Merkle and Wiecko; 1990, Merkle and Wilde, 1995), M. macrophylla Michx. (Merkle and Watson-Pauley, 1993; Merkle and Wilde, 1995), M. obovata Thunb. (Kim et al., 2007), M. officinalis Rehd. and Wilson. (Tong et al., 2002), M. pyramidata Bartram. (Merkle and Watson-Pauley, 1994; Merkle and Wilde, 1995), M. sieboldii Koch. (Lu et al., 2008), M. sinicum Law. (JunLi and Mingdong, 2007), and M. virginiana Linn. (Merkle and Wiecko, 1990; Merkle and Wilde, 1995). However, less research has been conducted on micropropagation of ornamental Magnolia taxa with the exception of M. ×soulangeana Soul.-Bod. (Kamenicka and Lanakova, 2000; Maene and Debergh, 1985; Marinescu, 2008), M. grandiflora L. (Sakr et al., 1999; Tan et al., 2003), M. delavayi Franchet. (Luo and Sung, 1996). M. stellata Sieb. Zucc., and the hybrids ‘Elizabeth’ and ‘Yellow Bird’ (Biedermann, 1987). These studies indicated basal salt composition and plant growth regulators were important factors influencing in vitro propagation of magnolia.
Culture media comprised of Murashige and Skoog (1962) basal salts and vitamins have been widely used for in vitro propagation of magnolia (Biedermann, 1987; Marinescu, 2008). Merkle and Watson-Pauley (1993, 1994) used Blaydes modified basal medium (Blaydes, 1966) for somatic embryogenesis of Magnolia sp. Several alternative media compositions such as Driver and Kuniyuki (1984) walnut basal salt mixture and WPM (Lloyd and McCown, 1981) have been tested with a wide range of woody plant species with only limited investigations with Magnolia (Kamenicka and Lanakova, 2000).
Although several cytokinins have been used to induce shoot proliferation, BAP has been used most often for magnolia. For Magnolia ×soulangeana, 1.2 μM BAP was shown to produce greater shoot proliferation than 2iP, kinetin, or thidiazuron (Marinescu, 2008). However, BAP has been shown to induce hyperhydricity, reduce shoot quality, and inhibit rooting in some taxa (Amoo et al., 2011; Bairu et al., 2007). Meta-topolin, a naturally occurring cytokinin similar in structure to BAP, has not been associated with hyperhydricity (Bairu et al., 2007; Werbrouck et al., 1996) and has been effective for micropropagation of many species (Amoo et al., 2011; Meyer et al., 2009).
Micropropagation of magnolia has been reported to be difficult because of the presence of phenolic substances (JunLi and Mingdong, 2007; Sakr et al., 1999). AC and PVP are used commonly in media to bind phenolics. Ascorbic acid was effective in micropropagation of Magnolia ×soulangeana (Radomir and Radu, 2008) and may reduce oxidative processes that lead to phenolic accumulation. Although AC and PVP have not been evaluated for Magnolia, these have been effective phenolic binding agents (PBAs) used in micropropagation of many plant species (Roy, 1991; Thomas, 2008). The objective of the current study was to evaluate a range of basal media compositions, cytokinins, and PBAs to improve in vitro growth conditions for M. ‘Ann’ as a means for micropropagation and future ploidy manipulation. Ex vitro establishment protocols were also examined to ensure viable protocols exist to propagate plants or for commercial production.
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