Factors Affecting Oospore Germination in Phytophthora cactorum, the Incitant of Apple Collar Rot

Light‐dependent Oospore Germination of Phytophthora cactorum in the Presence of Susceptible Host Plant

“…Among external factors, the presence of oxygen (Banihashemi, unpublished data) and favourable temperatures appear to be of great importance. Presence of nutrients and treatment of oospores with cell wall digesting enzyme (Banihashemi and Mitchell, 1976) and KMnO 4 (Shim and Ko, 1995) could not substitute light requirement for oospore germination. In the present study various treatments like low temperature incubation and exposure to light before oospore separation from hypha and presence of the host failed to induce oospore germination in the dark.…”

“…Light during gametogenesis increased germination of oospores of P. drechsleri (Klisiewicz, 1970) and P. citricola (Banihashemi, 1986) in the dark, but had no effect on P. cinnamomi , P. capsici and P. palmivora (Ribeiro et al., 1975). Mature oospores of P. cactorum germinated if they had received light for 36 h or more (Banihashemi and Mitchell, 1976) or less than 3 h of intermittent light (30 s exposure/30 min) during 172 h (unpublished data) whereas in P. citricola and P. iranica few minutes of exposure was sufficient (Banihashemi, 1986) and P. sojae had no light requirement (unpublished data).…”

“…Oospores of P. cactorum were produced in cleared V‐8 broth supplemented with 30 mg/l of β ‐sitosterol in cultures grown in the dark at room temperature for 2–4 months. Free oospores were obtained by deep freezing and sonication as reported earlier (Banihashemi and Mitchell, 1976). All preparation was carried out in the dark or under dim red light.…”

“…Oospores were photoactivated at 22°C by exposure to 40 W/m 2 using white fluorescent tubes unless otherwise specified. The number of activated and germinated oospores was determined using an inverted microscope at ×100 magnification (Banihashemi and Mitchell, 1976).…”

“…The fungus is a homothallic oomycete which produces oospores in culture and diseased plant tissues (Erwin and Ribeiro, 1996). These are considered to be the main survival propagules in soil (Sneh and McIntosh, 1974; Banihashemi and Mitchell, 1976). Although some isolates of P. cactorum produce chlamydospores in certain media (Darmono and Parke, 1990), there is no report of their production in plant tissue (Erwin and Ribeiro, 1996).…”