Chlamydospores of Phytophthora cactorum: their production, structure, and infectivity

Abstract

Chlamydospores of Phytophthora cactorum are described and compared with oogonia and sporangia. Chlamydospores (average diameter 39.7 μm) were generally larger than either oogonia or sporangia, were usually produced terminally on long supporting hyphae and had single, two-layered walls. They were readily formed in vitro in V8 juice broth supplemented with 2 g L−1 CaCO3 after incubation for 20 days at 4 °C. No chlamydospores were produced at 8, 12, 16, 20, or 32 °C, but chlamydospores sometimes developed at 24 and 28 °C. Chlamydospores also formed on mycelial mats buried in pasteurized potting mix after incubation for 20 days at 4 °C. Germination of chlamydospores after freezing at −23 °C for 24 h was 60–80%. Chlamydospores prepared in this way were infectious to American ginseng (Panax quinquefolium) seedlings. All 11 isolates of P. cactorum examined produced chlamydospores. Key words: Phytophthora cactorum, chlamydospores, temperature, ginseng, Panax quinquefolium.

Phytophthora in Finnish nurseries

“…The difference in incubation time might result also in different stages of maturation in P. ramorum chlamydospores. P. cactorum chlamydospores have been shown to germinate well following a 24 hours treatment of -23 °C (Darmono & Parke 1990). Here, P. cactorum remained viable in apple tissue as well as on MEA for two weeks at -5 °C (III, IV).…”

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

“…The major survival structure in this pathogen is oospores (Sneh and McIntosh, 1974; Banihashemi and Mitchell, 1975). The formation of chlamydospores in this species has been only shown in cultures under certain nutritional and environmental conditions (Darmono and Parke, 1990), but not in soil or infected plant tissues (Erwin and Ribeiro, 1996). Thus, its significance to survival of the pathogen is not known.…”

“…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).…”

Phytophthora species isolated from alpine and sub-alpine regions of Australia, including the description of two new species; Phytophthora cacuminis sp. nov and Phytophthora oreophila sp. nov

“…Similarly, incidence and severity of P. cactorum increased with increased wetness duration (1-12 hours) over a temperature range of 10-30 °C on pears, and 7 -10 °C on apples under controlled environmental conditions (Grove and Boal, 1991). Phytophthora cactorum has been reported to readily form chlamydospores in V8A juice broth and mycelial mats buried in pasturized soil at 4 °C after 20 days of incubation (Darmono and Parke, 1990). Chlamydospores had high (60-80%) germination rates even after incubating at -23 °C for 24 hours (Darmono and Parke, 1990).…”

“…Phytophthora cactorum has been reported to readily form chlamydospores in V8A juice broth and mycelial mats buried in pasturized soil at 4 °C after 20 days of incubation (Darmono and Parke, 1990). Chlamydospores had high (60-80%) germination rates even after incubating at -23 °C for 24 hours (Darmono and Parke, 1990). It is considered to have been introduced to lowlands in Australia and then spread to mountain ecosystems by human activities (Burgess et al, 2017b).…”