SUMMARY
Fire blight of rosaceous plants is an easy spreading and difficult to 
control disease, mainly affecting pear and apple fruit trees, as well 
as ornamental plants. Erwinia amylovora, an enterobacterial pathogen, 
is the causal agent of this disease and it is considered a quarantine 
organism in the European Union. This bacterium has been identified in 
most Northern and Eastern European countries, and in the last two 
decades it has also spreaded around the Mediterranean countries. 
In Spain, several foci have been detected since 1995 in different hosts
 and regions, followed by intensive eradication programs in most of the affected areas.
In this study, a phenotypical and genotypical characterization of a 
wide collection of Spanish E. amylovora isolates from different 
geographical origins, host and years of isolation has been carried out.
 The data obtained from the physiological, biochemical and molecular 
analysis performed have been evaluated, showing a scarce phenotypic and
 genotypic diversity of the Spanish strains. Nevertheless, the results 
of molecular characterization by means of pulsed-field gel 
electrophoresis and other techniques, support two hypothesis about the 
origin and dispersal of fire blight in our country: 1) the introduction
 of infected plant material from other European countries as a possible
 cause of several of the Spanish outbreaks and 2) the existence of, at
 least, three distinct sources of inoculum. On the other hand, the 
first report of a strain of E. amylovora naturally lacking pEA29 
plasmid represents a novelty with important consequences for molecular 
diagnosis of this disease, as well as for making hypothesis about the 
role of this plasmid in the virulence of the fire blight pathogen.