Thermal sensitivity of Calonectria henricotiae and Calonectria pseudonaviculata conidia and microsclerotia

ABSTRACT

Knowledge of the thermal sensitivity of conidia and microsclerotia 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 that harbor conidia and microsclerotia would provide a useful management tool for suppressing the pathogenic activity of Calonectria pseudonaviculata (present in the United States) and C. henricotiae (a quarantine pathogen not present in the United States). In this study, we investigated the thermal sensitivity of conidia and microsclerotia of the boxwood blight pathogens C. henricotiae and C. pseudonaviculata treated in water at 45, 47.5, 50, 52.5, 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 C. pseudonaviculata conidia (LD₉₀) decreased as water temperature increased from 45 to 55 C and ranged from 35.4 to 5.6 min, respectively. Inactivation of conidia was dependent on isolate, species of Calonectria, and length of exposure at each temperature tested. Microsclerotia of C. henricotiae and C. pseudonaviculata displayed reduced germination with increasing exposure and higher temperatures of hot water. Microsclerotia of C. henricotiae were significantly more resistant to heat treatment than C. pseudonaviculata at 47.5 and 50 C, whereas microsclerotia of both species were rapidly killed at 55 C.

KEYWORDS:

• Heat treatment
• survival structures
• thermal death
• thermotolerance

ACKNOWLEDGMENTS

We would like to thank Miranda Ganci and Kelly Ivors for their technical expertise in providing protocols for conducting research with the pathogen and disease and Bennett Saunders for providing boxwood plants for our experiments. We thank Elaine Cerchin, Bianca Hoch, Dr. Farivar Eskandari, and Kristine Johnson for technical assistance.

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Funding

Funding for this research was partially supported by the United States Department of Agriculture-Animal Plant Health Inspection Service-Center for Plant Health Science and Technology (USDA-APHIS-CPHST) through the FY2013, FY2014, FY2015, and FY2016 Farm Bills received in collaboration with Cristi Palmer, IR-4 Project, and Gregory Parra, United States Department of Agriculture-Animal Plant Health Inspection Service Plant Protection and Quarantine (USDA-APHIS-PPQ) Science and Technology. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA. The USDA is an equal opportunity employers and provider.