Boxwood (Buxus L. spp.) are slow-growing evergreen shrubs and small trees. They are commonly grown as hedges and for topiary and are commercially important components of managed landscapes. Over 13 million boxwood plants are sold in the United States each year with an annual market value of over $100 million (USDA-NASS, 2010). Boxwood blight, caused by the fungus Calonectria pseudonaviculata (Crous et al.) L. Lombard et al. (syn. Cylindrocladium pseudonaviculatum, C. buxicola), is a destructive leaf-drop and stem-lesion disease and is of significant concern throughout Europe, especially the United Kingdom, since the early 1990s (Henricot and Culham, 2002). The disease was recently discovered in North America, first confirmed in Nov. 2011 in Connecticut and North Carolina (Ivors et al., 2012). It has now been confirmed in 14 states (Alabama, Connecticut, Delaware, Georgia, Massachusetts, Maryland, North Carolina, New Jersey, New York, Ohio, Oregon, Pennsylvania, Rhode Island, Virginia) and three Canadian provinces (British Columbia, Ontario, Quebec) (Elmhirst and Auxier, 2013; Hagan and Conner, 2013; Malapi-Wight et al., 2013; Williams-Woodward, 2014).
Fungicidal management of the pathogen has been effective (Henricot et al., 2008; LaMondia, 2014); however, developing blight-resistant cultivars is the preferred long-term management strategy for boxwood blight. The genus Buxus contains ≈90 species with more than 350 cultivars representing diverse forms, sizes, and foliage characteristics (Batdorf, 2004). The American boxwood (B. sempervirens) and the English boxwood (B. sempervirens ‘Suffruticosa’) are two of the most widely grown types in the United States (Batdorf, 2005). Identifying which of this diverse material is most tolerant to boxwood blight is necessary for beginning a breeding program to develop blight-resistant cultivars and the screening of potentially thousands of seedlings from controlled hybridizations. Effective screening of whole plants has been reported (Ganci et al., 2013), but it requires space for multiple replications of large containerized plants or in-ground assays with obvious disease containment issues to manage. The objective of this study was to develop simple and rapid assays using detached stems and two inoculation methods to screen plants for resistance to boxwood blight.
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