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Ecology and Epidemiology

Scanning Electron Microscopy of Apple Blossoms Colonized by Erwinia amylovora and E. herbicola. M. J. Hattingh, Visiting professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Present address: Department of Plant Pathology, University of Stellenbosch, Stellenbosch 7600, South Africa; S. V. Beer(2), and E. W. Lawson(3). (2)Associate professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853; (3)Research and teaching support specialist, Department of Plant Biology, Cornell University, Ithaca, NY 14853. Phytopathology 76:900-904. Accepted for publication 5 March 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-900.

Based on scanning electron microscopy of apple blossoms sprayed with suspensions of E. herbicola (strains 159 and 252) and E. amylovora (strain 273), we found these strains multiplied mostly on the stigmatic surface. E. herbicola 252, which effectively inhibits the development of fire blight, and E. amylovora 273 occupied similar niches on stigmas. Bacterial colonies with distinct cells occurred in regions between papillae and in underlying tissue. E. herbicola 159, a less effective antagonist of E. amylovora, was more intimately associated with the deteriorating stigmatic cuticle. Bacterial cells usually developed to produce indistinct amorphous aggregates. We suggest that the effective antagonist restricts the pathogen on apple flowers by competing for the same site on the stigmatic surface.