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Ecology and Epidemiology

Biology of Chlamydospores, Sporangia, and Zoospores of Phytophthora cinnamomi in Soil. S. C. Hwang, Graduate Research Assistant, Department of Plant Pathology, University of Hawaii, Beaumont Agricultural Research Center, Hilo, HI 96720, Present address of the senior author: Taiwan Banana Research Institute, Chiuju, Pingtung, Taiwan; W. H. Ko, Professor, Department of Plant Pathology, University of Hawaii, Beaumont Agricultural Research Center, Hilo, HI 96720. Phytopathology 68:726-731. Accepted for publication 14 October 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-726.

Among three spore types of Phytophthora cinnamomi tested, chlamydospores were the most persistent in soil, sporangia were intermediate, and zoospores were least persistent. Zoospores were capable of extending the survival time by colonization of dead plant tissues or parasitization of live plant roots. Survival of P. cinnamomi in either artificially or naturally infested soils was better under moist than submerged conditions. Colonies of P. cinnamomi recovered from natural soil originated mainly from free chlamydospores and chlamydospores imbedded in organic matter. Sporangia of P. cinnamomi also were detected in natural soil. At high inoculum levels, encysted zoospores were less infective to ohia seedlings than chlamydospores and motile zoospores. There was no difference in infection potential between chlamydospores and motile zoospores at any level of inoculum. Among the three spore types tested, chlamydospores were the most effective in colonizing dead tissues in soil, whereas colonization potential of motile and encysted zoospores was about the same.

Additional keywords: nonspecialized parasities, root-infecting fungi.