Syngonium podophyllum Schott, commonly known as arrowhead vine, goosefoot plant, or nephthytis, belongs to the family Araceae and occurs indigenously on humid forest floors of Central and South America (Croat, 1982). As a result of their attractive foliar variegation and tolerance to low-light environments, cultivars from S. podophyllum in their juvenile stage have been widely produced as ornamental foliage plants and used as living specimens for interiorscaping (Chen et al., 2005). There are ≈30 commercial cultivars available in the foliage plant industry with ‘White Butterfly’ being the most popular over the last 30 years (Chen et al., 2002). Traditionally, arrowhead vine is propagated through eye cuttings, one leaf with one or two stem nodes (Chen and Stamps, 2006). Eye cuttings, however, can carry and spread diseases such as Xanthomonas blight caused by Xanthomonas campestris pv. dieffenbachiae (Chase, 1989; Chase et al., 1988).
Since the late 1980s, arrowhead vine has been micropropagated using shoot tips (Kane, 2000; Miller and Murashige, 1976). Shoot tips are inoculated on Murashige and Skoog (MS) medium containing 14.8 μm N-isopentenylaminopurine (2iP) and 5.7 μm IAA for establishment (Stage I) and then cultured on MS medium containing 98.4 μm 2iP only for multiplication (Stage II) (Kane, 2000; Miller and Murashige, 1976). Stage II shoot clusters are divided into single microcuttings and rooted directly in soilless substrate (Kane, 2000). Chen and Henny (2008) estimated that 19 million plantlets of arrowhead vine are annually micropropagated worldwide, which has greatly reduced the incidence of diseases carried by eye cuttings. Recently, however, Myrothecium leaf spot (Myrothecium roridum Tode ex Fr.) has become the most common disease of arrowhead vine. This opportunistic airborne fungal pathogen particularly occurs during the ex vitro rooting of microcuttings after shoot culture because the cutting base is especially susceptible to this pathogen. Sometimes more than 80% of microcuttings are infected (Norman, personal communication). No commercial cultivars are resistant to this pathogen (Norman et al., 2003).
Replacing ex vitro rooting with ex vitro transplanting should offer a solution to controlling Myrothecium leaf spot in arrowhead vine. Microcuttings could be rooted in vitro and then transplanted ex vitro. Such a procedure, however, could be extremely labor-intensive and commercially difficult. Another solution could be the regeneration through either somatic embryos or protocorm-like bodies in which well-rooted plantlets could be produced for ex vitro transplanting. Regeneration through somatic embryos or protocorm-like bodies is also the desired system for genetic transformation. Somatic embryogenesis has been reported with S. podophyllum ‘Variegatum’ in which healthy plantlets were regenerated using petiole explants (Zhang et al., 2006). There is no reported protocorm-like body formation in the more commercially valuable S. podophyllum ‘White Butterfly’. Thus, the objective of this study was to develop an efficient method for regeneration of disease-free, well-rooted plantlets of S. podophyllum ‘White Butterfly’ for ex vitro transplanting.
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