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Dispersal of Phytophthora palmivora Sporangia by Wind-Blown Rain. J. E. Hunter, Associate Plant Pathologist, University of Hawaii, Beaumont Agricultural Research Center, Hilo 96720, Present address of senior author: Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456; R. K. Kunimoto, Research Associate, University of Hawaii, Beaumont Agricultural Research Center, Hilo 96720. Phytopathology 64:202-206. Accepted for publication 13 August 1973. DOI: 10.1094/Phyto-64-202.

Sporangia of Phytophthora palmivora produced on papaya could not be recovered on Hirst spore trap slides, even though infected fruits surrounding the trap or in wind tunnels were subjected to a wide range of meteorological conditions suitable for release of dry sporangia of Phytophthora infestans from potato leaves. However, wind-blown rain collected from severely diseased orchards contained sporangia. Rain-splash experiments showed that sporangia are readily released in splash-droplets formed when rain drops impact on disease lesions. Detached sporangia held at relative humidities lower than 100% dehydrated in 2-4 min and failed to germinate when placed in water. There was an inverse relationship between temp and survival of detached sporangia. Sporangia attached to papaya fruits can survive drying conditions, therefore these spores serve as a source of inoculum which can be dispersed by wind-blown rain. Intermittent showers capable of detaching sporangia are common during the night in Hawaii and survival of the sporangia would be expected because the humidity is usually 100% for 8-9 h each night of the year. Thus, wind-blown rain is an ideal spore release and dispersal mechanism for survival of this species.

Additional keywords: Phytophthora colocasiae, Colocasia esculenta, epidemiology.