Investigating the Relationship Between Large Chromosomal Rearrangements and Disease Aggressiveness in North American <scp> <i>Erwinia amylovora</i> </scp> Strains

ABSTRACT The phytopathogenic bacterium Erwinia amylovora is responsible for causing fire blight, a devastating disease affecting rosaceous plants, including apples and pears. E. amylovora strains exhibit differences in virulence depending on the genetic resistance status of the host and environmental factors. While genetic variations among E. amylovora strains are known to contribute to their genetic diversity, host range and biology, the impact of large chromosomal rearrangements on key bacterial phenotypes like disease aggressiveness is understudied. In order to investigate the relationship between large chromosomal inversions (LCIs) and fire blight aggressiveness of E. amylovora strains, we screened 16 E. amylovora isolates for their fire blight aggressiveness on immature Bartlett pears and continued with de novo genome sequencing of these strains originating from North America to characterise the association of detected LCIs with disease aggressiveness. The immature Bartlett pear assay showed significant differences in fire blight aggressiveness between the strains. Genome sequence comparison showed an average of 68 insertions, 11,166 single‐nucleotide polymorphisms (SNPs), and 10,773 insertions/deletions (indels) across the 16 isolates when compared to the reference strain Ea1189. Additionally, eight distinct LCIs were identified among sequenced isolates. All isolates carried the ubiquitous pEA29 plasmid, whereas EaRJO001 has an additional pEA27 plasmid. Although E. amylovora strains exhibited significant differences in fire blight aggressiveness, their association with LCIs remains unclear.