Common cherrylaurel is a species of evergreen stone fruit native from eastern Europe to southwest Asia. In some parts of the Mediterranean, this species is grown for food and medicinal purposes (Kolayli et al., 2003). In the United States and Europe, cultivars of this species are common ornamental landscape plants. Popular compact cultivars include; Mount Vernon, Otto Luyken, Schipkaensis, and Zabeliana. Many cultivars are susceptible to bacterial and fungal pathogens that cause shot-hole disease [e.g., Pseudomonas syringae pv. syringae, Xanthomonas arboricola pv. pruni, Wilsonomyces carpophilus, Microgloeum pruni, and Cercospora sp. (De Boer, 1980; Marchi et al., 2014; Pscheidt and Ocamb, 2014; Williams-Woodward, 1998)]. Shot-hole disease presents with numerous small circular holes in the leaves of plants, these holes are caused by loss of necrotic leaf tissue in areas killed by pathogens. This can greatly reduce ornamental appeal, and in severe cases, cankers that girdle stems may kill infected plants. Due to abundant fruit production, this species has become naturalized across areas of the North American west coast (U.S. Department of Agriculture, 2006), and in other regions is considered invasive (Hättenschwiler and Körner, 2003).
In attempts to address shot-hole symptoms and the weedy tendencies in this species, we created chromosome doubled forms of the cultivar Schipkaensis. Although many studies have compared morphological variability in ploidy series (Huang et al., 2015; Kermani et al., 2003; Li et al., 1996; Ulrich and Ewald, 2014), we have found none that addressed adventitious rooting of stem cuttings. Successful vegetative propagation is an important consideration in determining plant potential for large-scale production (Hartmann et al., 2011). We wanted to assess if alteration in ploidy level had an effect on vegetative propagation of this plant.
Previous research seeking to optimize vegetative propagation of common cherrylaurel successfully rooted hardwood cuttings at high percentages (Ribeiro et al., 2010; Sülüşoğlu and Çavuşoğlu, 2009; Yazici, 2009). Ribeiro et al. (2010) reported exogenous application of IBA improved rooting percentage compared with a control without IBA, but IBA ranging from 1000 to 7500 ppm (0.1% to 0.75%) produced no statistically significant difference among treatments. Other sources report taking semihardwood cuttings in summer is also effective (Adams, 1983; Dirr, 2009; Sülüşoğlu and Çavuşoğlu, 2010). The cultivar Schipkaensis, in particular, has been reported to root as quickly as 3 weeks (Adams, 1983). Our objective was to determine if rooting percentage and other root traits vary between natural [2n = 22x = 176 (Meurman, 1929)] and chromosome doubled (2n = 44x = 352) ploidy levels of ‘Schipkaensis’ common cherrylaurel.
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