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Title: Susceptibility of boxwood accessions from the National Boxwood Collection to Boxwood Blight and potential for differences between Calonectria pseudonaviculata and C. henricotiae

Author
item LAMONDIA, JAMES - Connecticut Agricultural Experiment Station
item Shishkoff, Nina

Submitted to: Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2017
Publication Date: 6/1/2017
Citation: Lamondia, J.A., Shishkoff, N. 2017. Susceptibility of boxwood accessions from the National Boxwood Collection to Boxwood Blight and potential for differences between Calonectria pseudonaviculata and C. henricotiae. Horticultural Science. 52(6):873–879.

Interpretive Summary: Boxwood blight caused by the fungal pathogen Calonectria pseudonaviculata is a recent introduction to North America, first recognized in the fall of 2011 in Connecticut and North Carolina and now reported from 21 states and three Canadian provinces. The disease was previously reported in the United Kingdom, many countries in Europe, and New Zealand. A second species of boxwood blight pathogen, C. henricotiae, is present in Europe and poses an additional risk to the US boxwood industry. Boxwood is a major ornamental in the USA with over $118 million in wholesale nursery production in 2014 according to the USDA-NASS Census of Horticultural Specialties. Forty Buxus accessions from the National Boxwood Collection of the U.S. National Arboretum were evaluated for susceptibility to boxwood blight caused by C. pseudonaviculata and nine boxwood cultivars were evaluated against both species of pathogen in order to determine if differences in susceptibility existed in the boxwood gene pool, allowing breeding programs to develop resistant stock. A wide range of susceptibility to C. pseudonaviculata was seen in the boxwood accessions, suggesting that breeding for resistance would be possible, and the pattern of resistance to the second pathogen species was similar to the first, suggesting that breeding for resistance to one would also breed resistance to the other.

Technical Abstract: Forty Buxus accessions from the National Boxwood Collection of the U.S. National Arboretum were evaluated for susceptibility to boxwood blight caused by Calonectria pseudonaviculata and nine boxwood cultivars were evaluated against both species of Calonectria causing boxwood blight, C. pseudonaviculata and C. henricotiae. Of the 40 accessions, B. harlandii (1 accession), B. sinica (3), B. microphylla (7) and B. bodinieri (1) had fewer lesions per plant than B. microphylla × sempervirens (6), which had fewer lesions than B. sempervirens (20 accessions). B. wallichiana (1 accession) was the most susceptible species (>160 lesions). Variation within species was also observed. B. sinica var. aemulans (accession 60705*H), B. sempervirens (36365*J) and B. harlandii (18834*H) were the least susceptible with < 10 lesions per plant. B. sempervirens ‘Scupi’ (9548*H), B. microphylla ‘Compacta’ (4899*CH), B. sempervirens 'Arborescens' (57953*H), B. sinica var. insularis 'Pincushion' (51898*H) and B. microphylla var. japonica 'Jim Stauffer' (72213*H) each had < 20 lesions. These data differ from previous detached leaf and unrooted cutting assays. Plant size may affect inoculation and disease, normalizing increased variability for individual accession rankings, but did not result in significant differences in species susceptibility ranking. Nine boxwood cultivars evaluated against both species exhibited a range of susceptibility against four pooled isolates each of C. pseudonaviculata and C. henricotiae. Although small differences in disease severity were observed between species, there was no interaction of cultivar and pathogen species, suggesting that a cultivar rated resistant to one species was resistant to the other. These results may aid in the development of boxwood resistance to boxwood blight.