Short communication Characterization of Erwinia amylovora strains from Croatia

Erwinia amylovora is the causative agent of fire blight, a destructive disease of rosaceous plants. The European population can be divided into several subtypes according to differences in restriction fragment length polymorphism of the XbaI genomic DNA digest analysed with pulsed-field gel electrophoresis. This technique was also used to determine the genetic relatedness of six Croatian isolates to the E. amylovora types found in the countries surrounding Croatia. The isolates belong to the Pt2 pattern type that is characteristic of the East Mediterranean basin. All tested isolates gave essentially the same total cell protein pattern in SDS-polyacrylamide gel electrophoresis. The number of short-sequence DNA repeats in plasmid pEA29 of six isolates was determined by PCR assays and ranged from four to seven. The isolates examined showed high pathogenicity in immature pear fruits. Differences were also revealed in microbiological assays such as amylovoran synthesis, levan formation, siderophore production and colour on coliform medium. Erwinia amylovora is the bacterium that causes fire blight, a destructive disease of apple and pear fruit trees as well as many other rosaceous plants. Severe losses, especially for apple and pear production, are due to partial destruction or death of infected plants. In Europe, the disease was first detected in 1955 in England and since then it has spread to most European countries (Bonn and van der Zwet, 2000). The symptoms of fire blight were first observed in Croatia in 1995, in the eastern part of the country near the city of Osijek (Cvjetković et al., 1996). Although many quarantine measures were undertaken, the disease spread to the adjacent counties in the West. The bacterium can be transmitted by many vectors such as insects, birds, wind and infected or contaminated plant material (van der Zwet and Beer, 1995). Commercial exchanges of plant material can play an important role in the dissemination of the bacterium. Characterization of the natural populations of E. amylovora can help to trace its spread and the ways the pathogen was dispersed. One of the methods used for differentiating bacterial strains is comparison of their total cell protein patterns obtained through polyacrylamide gel electrophoresis (Kersters and De Ley, 1975) and it was used earlier for the characterization of some E. amylovora strains (Vantomme et al., 1982). Recently, E. amylovora isolates have been characterized by assaying restriction fragment length polymorphism (RFLP) of their genomic DNA, using pulsed-field gel electrophoresis (PFGE) European Journal of Plant Pathology (2006) 114:435–440 Springer 2006 DOI 10.1007/s10658-006-0003-7