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Poster: Biology & Disease Mgmt: Cultural Control


Thermal inactivation of Calonectria pseudonaviculata, the causal agent of boxwood blight
M. MILLER (1), M. Cubeta (2) (1) North Carolina State University, Department of Plant Pathology, U.S.A.; (2) North Carolina State University, U.S.A.

Thermotherapy is an effective method for eliminating viruses and microorganisms from seeds and bulbs, but little information is available on the use of this approach to inactivate pathogenic fungi in leaves of woody plants. In this study, we investigated the utility of hot water treatments for killing Calonectria pseudonaviculata (Cps), a fungal, foliar pathogen of boxwood (Buxus) during propagation. Experiments predicting the thermal death kinetics of Cps conidia, and experiments determining the ability of commonly grown, commercial boxwood cultivars to survive exposure to hot water were performed. Conidia of three field isolates of Cps were suspended in water and exposed to temperatures ranging from 45°C to 55°C for 0 to 20 min. Suspensions were then spread on potato dextrose agar, and percent spore germination was assessed after 24 h of incubation. Approximately 16 min were required to kill 90% of conidia exposed to 45°C, but only 4.5 min were required to kill 90% of spores when heated to 55°C. Cuttings from six partially resistant boxwood cultivars were submerged in water heated to 45°C, 50°C, and 55°C for 0 to 60 min. Treated cuttings were placed under mist and their rooting responses were rated 86 to 91 d later. The ability of boxwood cuttings to produce roots after hot water treatment at 45°C and 50°C varied by cultivar, whereas no cultivars survived treatment at 55°C. Further experiments will determine whether hot water can eliminate the pathogen in planta.