Growth of Phytophthora fragariae on Various Clarified Natural Media and Selected Antibiotics. S. W. George, Graduate Research Assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. R. D. Milholland, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Plant Dis. 70:1100-1104. Accepted for publication 21 July 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-1100.

Clarified frozen pea agar had outstanding clarity and supported excellent mycelial growth for Phytophthora fragariae races A-1, A-2, A-4, and A-6, growth that was significantly greater than that on cornmeal agar. Good to excellent mycelial growth of races A-2 and A-6 was recorded on hymexazol, nystatin, and PCNB concentrations through 100, 250, and 500 μg/ ml, respectively, and on penicillin and vancomycin through 1,000 μg/ ml. These races were very sensitive to benomyl at 100 μg/ ml and to streptomycin sulfate and rose bengal at the lowest concentrations tested. Nystatin and rifamycin severely affected zoospore germination at the lowest concentrations tested, but suppression was not as great for germ tube growth. Zoospore germination and growth was very good on hymexazol, vancomycin, and penicillin at concentrations up to 1,000 μg/ ml. Gallic acid at 500 μg/ ml and rifamycin at 10 μg/ ml provided excellent suppression of bacterial contaminants. Maximum recovery of P. fragariae was obtained when root segments were surface-disinfected in 70% ethanol, then plated on a selective medium containing benomyl, pimaricin, hymexazol, and rifamycin and incubated for 4–7 days at 20 C.