Restriction Analysis of the dspE Gene of Virulent Strains of Erwinia amylovora from Different Host Plants in the Po Valley

In the Po Valley (Northern Italy) the primary fire blight foci caused by Erwinia amylovora (Ea) were certified on pear plants in 1994. In the following years Ea was progressively spread in that valley. In 1997, a severe epidemic of fire blight occurred in the Emilia-Romagna region. The AFLP genomic profiles of Ea populations associated with this epidemic revealed that the isolates belong to the same clone [1]. From 1994 to 2001 systematic monitoring showed that the infection frequency was high and prevalent on pear plants (87.2%) whereas it was low in hawthorn shrubs (9.14%) and very low in apple trees (1.68%) [2]. Recently, an increasing infection frequency on apple trees was evidenced beside a widespread presence of the pathogen in hawthorn. The Phytosanitary Services assumed the occurrence of strains with different virulence. The pear clonal populations might have adapted to different host plants or new strains might have been introduced in the Po Valley. These hypotheses were tested studying the genomic profiles and the virulence either of the wild populations currently present in the area and of the experimental populations obtained through successive passages on different host plants. Here we report the results of the restriction fragment analysis of the virulence dspE gene in wild Ea populations from different host plants using the 1994 clone as reference strain.