Ranking Resistance of Buxus Cultivars to Boxwood Blight – an Integrated Analysis1

Abstract Boxwood (Buxus L. spp., Buxaceae) are popular woody landscape shrubs grown for their diverse forms and broad-leaved evergreen foliage, with an estimated $126 million economic impact in the U.S. alone. Boxwood plants grown in temperate zones worldwide are now threatened by a destructive blight disease caused by the ascomycete fungi, Calonectria pseudonaviculata and C. henricotiae. While the disease can be mitigated somewhat through cultural practices and fungicides, the most sustainable long-term solution is the development of disease-resistant boxwood cultivars. Hundreds of boxwood accessions from the National Boxwood Collection at the U.S. National Arboretum were screened for resistance using a lab-based, detached-leaf assay. Initial comparisons of our results with those of multiple other disease resistance assays found inconsistent ranking of cultivar resistance among studies. We used a meta-analysis approach on compiled data from six studies and were able to produce a consistent ordering of cultivars sorted by their susceptibility to boxwood blight, despite the diversity in materials and methods of the studies. Index words: Boxwood, Calonectria pseudonaviculata, Cylindrocladium buxicola, meta-analysis, plant breeding, resistance screening. Species used in this study: Buxus bodinieri H. Lev.; B. harlandii Hance; B. microphylla Seibold & Zucc.; B. sempervirens L.; B. sinica var. insularis (Nakai) M. Cheng; B. wallichiana Baill.; Calonectria pseudonaviculata (Crous, J.Z. Groenew. & C.F. Hill) L. Lombard M.J. Wingf. & Crous 2010.