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Etiology and Epidemiology

Variability in Growth of Phytophthora cinnamomi in Relation to Temperature. G. A. Zentmyer, Professor, Department of Plant Pathology, University of California, Riverside 92502; J. V. Leary(2), L. J. Klure(3), and G. L. Grantham(4). (2)(3)(4)Assistant Professor, and Staff Research Associates, Department of Plant Pathology, University of California, Riverside 92502. Phytopathology 66:982-986. Accepted for publication 4 February 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-982.

Growth of 187 isolates of Phytophthora cinnamomi (20 A¹, 167 A² mating type) from 24 countries and 59 hosts was compared at 25 C on potato-dextrose agar. The frequency distribution obtained for these isolates closely approximated a normal curve, with 90 isolates below the mean and 97 above. Colony diameters after 4 days of growth ranged from 41 to 85 mm. Nutrition affected the growth-temperature response; some isolates grew rapidly on one medium and slowly on another medium at 25 C. On minimal medium at 25 C with and without β -sitosterol the mean growth rate for A¹ mating type isolates of P. cinnamomi was significantly slower than for A² isolates; on clear V-8 agar there was no significant difference between the two mating types. At 30 and 33 C on minimal medium, three A¹ isolates grew more rapidly than 16 other isolates that included 12 A² and 4 A¹ types. Our studies, plus other reports, indicate that the cardinal temperatures for P. cinnamomi range from: minimum, 5-16 C; optimum, 20-32.5 C; and maximum, 30-36 C.