P-009 - Genotyping of Erwinia amylovora strains by large chromosomal inversions to understand structural diversity shifts over time or location

Erwinia amylovora, the causal agent of fire blight disease, impacted apple and pome fruit production for over 200 years, causing significant economic losses. The objective of this study was to determine E. amylovora strain diversity by genotyping and investigate their distribution across Washington (WA) and other U.S. regions to understand potential patterns of pathogen spread over time and/or location. Previous studies using large chromosomal inversions (LCIs) in E. amylovora as molecular markers have identified 10 LCI types. In this study, PCR-based molecular markers were used to genotype 191 isolates collected from 2022–2024 in WA state. Our results showed that these 191 isolates all belong to four common LCI types, i.e. Ea1189 (n=107), CFBP1430 (n=54), Ea273 (n=14), and Ea401 (n=16). Additional 60 isolates isolated from earlier years from WA, New York, Tennessee, Idaho, Montana were also characterized as Ea1189 (n=39), Ea273 (n=9), CFBP1430 (n=4), Ea401 (n=1), and MAGFLLF-2 (n=7) LCI types. Most WA state orchards contain one or two LCI types in 2022 (Ea1189 and CFBP1430) and up to three LCI types in 2023 (Ea1189, CFBP1430, and Ea273). In 2024, we found that all four common LCI types, including Ea401, were present in a single pear orchard in Wapato, WA. Our results highlight the importance of monitoring the spread of different types of pathogens in orchard, which might provide insights into pathogen evolution and disease epidemiology.