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Research Project: Systematics and Diagnostics of Emerging and Quarantine-Significant Plant Pathogenic Fungi

Location: Mycology and Nematology Genetic Diversity and Biology Laboratory

Title: First report of boxwood blight caused by Calonectria pseudonaviculata in Delaware, Maryland, New Jersey and New York

Author
item Malapi-wight, Martha - Rutgers University
item Hebert, Julie - Rutgers University
item Buckley, Richard - Rutgers University
item Daughtery, Margery - Cornell University - New York
item Gregory, Nancy - University Of Delaware
item Rane, Karen - University Of Maryland
item Tirpak, Sabrina - Rutgers University
item Crouch, Joanne

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2013
Publication Date: 5/1/2014
Citation: Malapi-Wight, M., Hebert, J.B., Buckley, R., Daughtery, M.L., Gregory, N., Rane, K., Tirpak, S., Crouch, J. 2014. First report of boxwood blight caused by Calonectria pseudonaviculata in Delaware, Maryland, New Jersey and New York. Plant Disease. 98(5):698.

Interpretive Summary: Boxwood blight disease is caused by a fungal parasite that cause significant damage to boxwood in the United States. Boxwood is a popular ornamental evergreen shrub, prized for their brilliant foliage, deer-resistance and ease of care in the landscape. After severe outbreaks of boxwood blight disease destroyed boxwood during 2011-2012 in North Carolina and Connecticut, boxwood growers and gardeners are concerned that the disease will spread throughout additional regions of the United States. This research describes multiple outbreaks of boxwood blight disease throughout the eastern seaboard during 2013, the first time this disease was observed from New Jersey, New York, Delaware and Maryland. Knowledge of the distribution of this disease will be useful to plant regulatory officials working to control the spread of boxwood blight in the United States.

Technical Abstract: Boxwood (Buxus spp.) are commercially important evergreen ornamental plants with an annual market value of over $103 million in the United States. The recent U.S. incursion of boxwood blight disease caused by the fungus Calonectria pseudonaviculata (syn. Cylindrocladium pseudonaviculatum, Cy. buxicola) threatens the health and productivity of boxwood in both landscape plantings and nursery production. The first confirmed reports of the disease were made from Connecticut and North Carolina in November 2011 (1,2), followed by diagnoses in ten additional states during 2012-2013 (www.boxwoodblight.org). By August 2013, symptoms consistent with boxwood blight had been observed from B. sempervirens in Delaware, Maryland, New Jersey and southeastern New York. Affected plants showed rapid onset of dramatic symptoms: dark brown to black spots or diffuse dark areas on leaves, followed by defoliation. Narrow, elongate black cankers also formed on current season shoots. Infected stems and leaves were placed in petri dishes with moistened filter paper at 22oC for 3 d under continuous light. Conidiophores were excised, then placed on full strength potato dextrose agar amended with streptomycin and neomycin. Resultant colonies showed dark brown pigmentation at the colony center surrounded by white mycelia. Conidia (n=30) were hyaline, cylindrical, rounded at both ends, with a single septum (45 to 76 µm × 4 to 6 µm; = 63 × 5 µm). Conidiophores (n=20) comprised a stipe, a hyaline septate stipe extension (length 119 to 192 µm; =150 µm) and a terminal ellipsoidal vesicle (diameter 4 to 10 µm; =7 µm). Based on morphological characteristics, the causal agent was identified as C. pseudonaviculata (2,3). Voucher specimens were deposited in the U.S. National Fungus Collections (BPI 892698-701). To verify morphological diagnosis, genomic DNA was extracted from fungal biomass and a portion of the ß-tubulin gene (TUB2) was PCR amplified and sequenced bidirectionally using primers Bta/Bt2b (4). BLASTn searches of NCBI GenBank databases using the TUB2 sequences demonstrated 96-100% sequence identity with other C. pseudonaviculata isolates. Sequences were deposited in GenBank (Accession Nos. XXXXXXXX-XXX). To confirm pathogenicity, 5-month-old B. sempervirens and B. microphylla seedlings were spray-inoculated with a spore suspension of 1x104 conidia/ml. One isolate from each state was independently tested with four replicates each. Non-inoculated water-sprayed plants served as the control. Plants were maintained in a growth chamber at 22ºC under constant light. Blight symptoms developed 4-5 d post inoculation. C. pseudonaviculata was re-isolated from inoculated plants; no symptoms or signs were observed from control plants. To our knowledge, this is the first report of C. pseudonaviculata in the states of Delaware, Maryland, New Jersey and New York. This report demonstrates that C. pseudonaviculata is now widespread across the U.S. eastern seaboard and represents a substantial threat to boxwood plants in North American landscapes and nurseries.