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

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. 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 tolerant boxwood cultivars. Hundreds of boxwood accessions from the National Boxwood Collection at the U.S. National Arboretum were screened for tolerance using a lab-based detached leaf assay. Comparisons of these results with those of multiple other disease resistance assays indicated that results of these studies were often inconsistent regarding which cultivars were most tolerant. We compiled and evaluated data from six studies to produce a list of cultivars sorted by their tolerance to boxwood blight. Despite the diversity in materials and methods of the studies, our method of combining and analyzing many trials in this analysis was successful in finding a consistent ordering of the boxwood cultivars.