Japanese barberry (Berberis thunbergii DC.) is a deciduous spiny woody shrub of the barberry family (Berberidaceae). This species is native to Japan and was introduced to the United States in the late nineteenth century (Dirr, 1998). It is currently naturalized in ≈30 states across the eastern and central United States (Silander and Klepeis, 1999). Many cultivars of B. thunbergii have been developed for use as ornamental plants and currently there are over 60 cultivars in the market and more continue to be introduced (Dirr, 2009). Berberis thunbergii cultivars are hardy, easy to grow, and resistant to deer browsing (Dirr, 1998, 2009; Lubell et al., 2008). The cultivars are characterized by variations in growth habits ranging from dwarf to tall, and their foliage can be red, purple, green, yellow, or variegated (Dirr, 2009). All these characteristics make B. thunbergii cultivars attractive as garden and urban landscaping plants.
Plants of the genus Berberis are known to be alternate hosts of the fungus Puccinnia graminis Pers., which causes black stem rust (BSR) disease in wheat (CFIA, 2012; USDA, 2002). Therefore, the movement of B. thunbergii plants across some state and international borders is restricted. For instance, only 11 B. thunbergii cultivars classified as highly resistant to BSR are allowed entry into Canada (CFIA, 2012). Identification and verification of approved cultivars is mainly by visual inspection of their morphological characteristics. However, it is often difficult to distinguish cultivars, especially those with similar morphological traits. Furthermore, plants are sold when young and the morphological traits used for their identification are not very distinct at this stage. Additionally, morphological characteristics can be influenced by variation in environmental and growing conditions making it difficult to accurately identify and differentiate B. thunbergii cultivars. Modern technology using molecular markers offers a reliable and efficient way to identify and differentiate plant cultivars. Molecular markers are not influenced by variable environmental conditions where plants are grown and can be applied at almost any stage of plant development, thus presenting a great potential for use in a barberry authentication program. Also, because molecular marker profiles can be unique to each cultivar, they can be used to provide protection of plant breeders’ intellectual property rights when applying for plant patents for new cultivars.
AFLP is one of the techniques that could be used to develop molecular markers to identify and differentiate B. thunbergii cultivars. AFLP is a DNA fingerprinting assay that combines restriction enzyme digestion and polymerase chain reaction (PCR) amplification of DNA fragments (Vos et al., 1995). The technique is highly reproducible, does not require prior knowledge of the target genome, and uses genome-wide distribution of restriction enzyme sites to yield abundant informative molecular markers (Mueller and Wolfenbarger, 1999; Vos et al., 1995). AFLP markers have been successfully used to evaluate genetic relationships in several ornamental plants, including Dieffenbachia (Chen et al., 2004), Prunus (Hu et al., 2005), Cornus (Smith et al., 2007), and Ficus (Fang et al., 2007). Also, previous studies have used AFLP markers to identify and differentiate B. thunbergii cultivars and interspecific hybrids (Cote and Leduc, 2007; Lubell et al., 2008).
In this study, our objectives were to use AFLP markers to: 1) authenticate the trueness-to-name of B. thunbergii plants from different nurseries and control for mislabeled plants in the market; 2) evaluate the occurrence of genetic variants within cultivars; and 3) develop a molecular key that could be used by regulatory personnel to ascertain cultivar identity to facilitate international trade of B. thunbergii cultivars where wheat rust is a concern. The presence of genetic variants or subclones in some B. thunbergii cultivars in the market has been long suspected by the nursery industry, but their occurrence has not been evaluated genetically.
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