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Ecology and Epidemiology

Release and Dispersal of Conidia and Ascospores of Valsa leucostoma. P. F. Bertrand, Research Assistant, Department of Plant Pathology, University of California, Davis 95616, Present address of senior author: Mid-Columbia Experiment Station, Rt. 5, Box 240, Hood River, Oregon 97031; Harley English, Professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 66:987-991. Accepted for publication 13 February 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-987.

Release and dispersal of conidia and ascospores of Valsa leucostoma were studied. Conidia were trapped during rains occurring in all seasons, whereas, ascospores tended to be most common in the spring. Ascospores were water-borne (released during rain or other wetness) or air-borne (released following rain or other wetness). There was no evidence for any nonwater-borne release of conidia. Increasing time and/or temperature between rains and a high rate of rainfall were correlated with increasing numbers of conidia subsequently caught. Conidia were shown to be dispersed by wind-blown rain. The distance of dispersal was correlated with the mean wind velocity during the rain. Either conidia or ascospores were able to cause infection. Conidia, however, were 10 to over 4,000 times more common than water-borne ascospores. Pycnidia generally form during the first year after infection. The ascostromata do not form until 2 or 3 years later. Since prune orchards generally are pruned on a yearly basis to remove dead or excess wood, conidia probably serve as the major inoculum.