The occurrence of Erwinia Salicis, the cause of Watermark disease, in the phyllosphere of Salix alba
1982
Zweep, P. | Kam, M.
Research on epiphytic populations of Erwinia salicis performed during 1979–1981 is reported. Periodic examination of 14 Salix alba trees in two subsequent years was executed. Trees in various parts of the country, including plants from other genera were examined, using direct immunofluorescence. The possible significance of these epiphytic populations for the dissemination of the Watermark disease is discussed. SUMMARY: During 1980–1981 every three weeks 14 Salix alba trees were examined on the presence of Erwinia salicis on the leaves. Likewise, 170 Salix alba trees from various localities were investigated on the occurrence of E. salicis in the phyllosphere, including samples from Crataegus, Alnus and other plant species. Detection of E. salicis bacteria was performed with the direct immunofluorescence technique (IF), after washing of the leaves and centrifuging of the liquid. The results are: — E. salicis is a common habitant of Salix alba leaves, especially when ‘wilting’ willows are present on a short distance — ‘wilting’ willows are the main source from which bacteria are spread by rain and wind to nearby standing trees and other vegetation, and — E. salicis bacteria isolated from leaves prove to be virulent. Though the exact role of the epiphytic E. salicis populations is not well understood, it is advised to eradicate willow trees as soon as wilting appears.
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