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Thermal Inactivation of Phytophthora cinnamomi for Control of Fraser Fir Root Rot. D. M. Benson, Assistant Professor, Department of Plant Pathology, North Carolina State University, Raleigh, NC 27607; Phytopathology 68:1373-1376. Accepted for publication 18 April 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1373.

Thermal inactivation of two isolates of Phytophthora cinnamomi (from a root of Fraser fir and the other from a rhododendron root) was determined by exposing agar disks that contained mycelium of the isolates to hot water at various temperatures for different periods. The ED50 values (time required for 50% inactivation) were interpolated at 39 C as 26.3 and 51.7 min, and at 43 C as 2.7 and 3.3 min for the two isolates, respectively. Temperature coefficients (Q10) were 304 and 970 for the Fraser fir and rhododendron isolates, respectively. Dormant seedlings of healthy Fraser fir tolerated hot water at 45 C for 120 min with only slight injury, but infected seedlings were severely injured by that treatment. Therapy of inoculated seedlings was successful at 45 C for 15 min if given within 14 days of inoculation. Therapeutic treatment of naturally-infected seedlings at 45 C for 15 to 120 min was unsuccessful.

Additional keywords: thermotherapy, hot-water therapy.