Variability in Growth of Phytophthora cinnamomi in Relation to Temperature

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Abstract
Growth of 187 isolates of P. cinnamomi (20 A1, 167 A2 mating type) from 24 countries and 59 hosts was compared at 25.degree. 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 range 41-85 mm. Nutrition affected the growth-temperature response; some isolates grew rapidly on one medium and slowly on another medium at 25.degree. C. On minimal medium at 25.degree. C with and without .beta.-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 2 mating types. At 30.degree. and 33.degree. C on minimal medium, 3 A1 isolates grew more rapidly than 16 other isolates that included 12 A2 and 4 A1 types. The cardinal temperatures for P. cinnamomi are minimum, 5-16 C; optimum, 20-32.5.degree. C; and maximum, 30-36.degree. C.

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