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Factors Affecting Oospore Germination in Phytophthora cactorum, the Incitant of Apple Collar Rot. Z. Banihashemi, Associate Professor, Department of Plant Protection, College of Agriculture, Pahlavi University, Shiraz, Iran; J. E. Mitchell, Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 66:443-448. Accepted for publication 10 September 1975. DOI: 10.1094/Phyto-66-443.

Oospores of Phytophthora cactorum produced in cultures grown in the dark required light for germination. A few oospores produced under continuous light germinated in the dark, but light was required for good germination. Germination increased with increasing light intensity up to 4,330 lux. Germination was greatest in light passing an indigo filter (440 nm) and lowest in that passing an orange filter (575 nm). The optimum temperature for oospore germination was 20 C and oospores failed to germinate on water agar at 28 C, the optimum temperature for mycelial growth. Both aging and treatment with 1% Glusulase (glucuronidase and sulfatase) increased oospore germination. Germination was decreased by adding CaCl2 at concentrations above 25 µg/ml. Germination was not affected by agar concentration, by 100 µg/ml Tergitol NPX, or by 200 µg/ml vancomycin. Germination was decreased when pimaricin concentration exceeded 7.5 µg/ml and was only 17% of the control with 100 µg/ml pimaricin. Likewise, germination was decreased 50% by 0.5% D-glucose and 1% sucrose, and 40% by 200 µg/ml polymyxin B.

Additional keywords: Malus sylvestris, soil-borne pathogen, light, soil extract.