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ARS Home » Northeast Area » Frederick, Maryland » Foreign Disease-Weed Science Research » Research » Publications at this Location » Publication #346439

Research Project: Biology, Epidemiology, and Detection of Emerging Plant Pathogenic Oomycetes

Location: Foreign Disease-Weed Science Research

Title: Thermal sensitivity of Calonectria henricotiae and Calonectria pseudonaviculata conidia and microsclerotia

item MILLER, MEGAN - North Carolina State University
item Shishkoff, Nina
item CUBETA, MARC - North Carolina State University

Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2018
Publication Date: 4/20/2018
Citation: Miller, M.E., Shishkoff, N., Cubeta, M.A. 2018. Thermal sensitivity of Calonectria henricotiae and Calonectria pseudonaviculata conidia and microsclerotia. Mycologia. 110:546-558.

Interpretive Summary: Boxwood blight caused by Calonectria pseudonaviculata is a disease recently introduced to North America, first recognized in the fall of 2011 in Connecticut and North Carolina and now reported from 22 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. Methods for treating plant material and greenhouse surfaces for eradication of the pathogen is urgently needed. This paper investigates the possibility of using heat treatments for eradication of spores and resting structures of both species of pathogen. It was found that hot water treatment at 50, 52.5 and 55 C would rapidly (within 15 minutes or less) eliminate germination of the fungal propagules. This is probably sufficient to make hot water practical as a method of tool and substrate sterilization, but may be too long to allow heat treatment of boxwood cuttings.

Technical Abstract: Knowledge of conidial and microsclerotial thermal sensitivity is useful for developing plant disease management approaches that deploy heat to inactivate infectious vegetative propagules of fungal pathogens. For boxwood blight disease, heat treatment of cuttings or plant debris on or in soil that harbor conidia and microsclerotia would provide a useful management tool for suppressing the pathogenic activity of Calonectria pseudonaviculata (Cps; present in the US) and C. henricotiae (Che; a quarantine pathogen not present in the US). In this study, we investigated the thermal sensitivity of conidia and microsclerotia of the boxwood blight pathogens Che and Cps treated in water at 45 C, 47.5 C, 50 C, 52.5 C, and 55 C. For conidia, as time of exposure increased at each temperature, the proportion of germinated conidia decreased. The predicted time required to inactivate 90% of Cps conidia (LD90) decreased as water temperature increased from 45 C to 55 C and ranged from 26 to 3 min, respectively. Conidia inactivation was dependent on isolate, species of Calonectria and length of exposure at each temperature tested. Microsclerotia of Che and Cps displayed reduced germination with increasing exposure and higher temperatures of hot water. Microsclerotia of Che were significantly more resistant to heat treatment than Cps at 47.5 C and 50 C, while microsclerotia of both species were rapidly killed at 55 C.