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Ecology and Epidemiology

Influence of Environment and Variation in Host Susceptibility on a Disease of Bracken Fern Caused by Ascochyta pteridis. R. R. Webb, Department of Plant Pathology, University of California, Berkeley 94720, Current address: College of the Virgin Islands, P.O. Box 920, Kingshill, St. Croix, Virgin Islands 00850; S. E. Lindow, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 77:1144-1147. Accepted for publication 30 January 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-1144.

Virulence of isolates of Ascochyta pteridis from diseased bracken fern in various geographical areas differed significantly in greenhouse inoculations. Isolates also differed significantly in desiccation survival and spore production in vitro. Infection of bracken fern occurred at temperatures as low as 10 C, but a leaf wetness duration of at least 18 hr was required for infection at this temperature. Infection frequency increased with increasing incubation temperatures up to 20 C. Decreasing durations of leaf wetness required for infection were observed as temperature during leaf wetness periods increased from 10 to 20 C. The susceptibility of bracken fern to infection by A. pteridis decreased greatly with increasing frond maturity after 2 wk. Infection of mature bracken fern fronds by A. pteridis was less than about 12% of that of immature fronds. Frond tissue showed two distinct classes of susceptibility to infection. Immature frond tissues and some parts of fronds of intermediate maturity had an ED50 for A. pteridis infection of about 103 spores per milliliter. Mature fronds and portions of fronds of intermediate maturity had an ED50 of 2 104 spores per milliliter.