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van der Zwet, T., and S.V. Beer. 1999. Fire Blight-Its Nature, Prevention, and Control: A Practical Guide to Integrated Disease Management. U.S. Department of Agriculture, Agriculture Information Bulletin No. 631, 97 pp. Fire blight is a serious bacterial disease of apples, pears, quinces, and several plants in the rose family (Rosaceae), including hawthorn, cotoneaster, firethom (pyracantha), mountain ash, blackberry, and raspberry. Outbreaks of this disease are usually most severe in areas with a warm, humid climate, especially when these conditions occur during the bloom period of the tree or plant involved. This publication is aimed especially at growers of apples and pears, as many varieties and rootstocks of these fruit are very susceptible to the disease. This bulletin serves as a practical guide for the recognition of conditions conducive to disease development, identification of symptoms, prevention of disease development, and control of fire blight, including disease prediction. Key references are included for additional information on different aspects of fire blight. Keywords: Erwinia amylovora, fire blight, control, development, prediction, symptoms, integrated orchard management, pome fruits, nursery practices Mention of trade names in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture or Cornell University over others not mentioned. Copies of this publication may be purchased from the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402. The United States Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or family status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA's TARGET Center at 202-720-2600 (voice and TDD). To file a complaint of discrimination, write USDA,

This chapter discusses the distribution and the economic impact of fire blight (Erwinia amylovora), particularly in North America, Europe, eastern Mediterranean, and the Pacific Rim.

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Recent examination of the relationships of the dry necrosis-inducing (necrogenic) erwinias using 16S rDNA sequences demonstrated that these bacteria comprise a polyphyletic group and, therefore, have been subdivided into three distinct genera, Erwinia, Brenneria and Pectobacterium, with the classical ' amylovora ' group species now being distributed nearly evenly among the first two. To further assess the molecular evolutionary relationships between current necrogenic Erwinia and Brenneria species, as well as between these genera and the exclusively soft-rotting genus Pectobacterium, the glyceraldehyde-3-phosphate dehydrogenase (gapDH) genes from 57 Erwinia and Brenneria isolates along with Pectobacterium type strains were PCRamplified, sequenced and subjected to phylogenetic analysis. Pairwise alignments of cloned gapDH genes revealed remarkably high interspecies genetic diversity among necrogenic isolates. Four evolutionary clades of necrogenic species were described that assorted more closely to known softrotting species than to each other. Interclade comparisons of gapDH nucleotide sequences revealed as much genetic divergence between these four necrogenic clades as existed between necrogenic and soft-rotting clades. An examination of the phylogenetic utility of the gapDH gene in light of current 16S rDNA clustering of these species revealed varying levels of taxonomic congruence between these genes for the structure of Erwinia, Brenneria and Pectobacterium. These analyses suggest that, while gapDH possesses sufficient genetic variation to fully differentiate Erwinia and Brenneria species, the gene may not accurately reflect interspecies taxonomic relatedness among all three phytopathogenic genera.