Genotype and Distribution of Erwinia pyrifoliae Isolated from 2020 to 2024 in Korea

Black shoot blight in apple trees, caused by the gram-negative bacterium Erwinia pyrifoliae, was first reported in Korea in 1995 and has since been identified in the Netherlands and the United States, prompting recent research on differentiating this pathogen at the intraspecies level. To track its spread, 109 isolates collected in Korea from 2020 to 2024 were analyzed based on RsxC amino acid repeats. Three genotypes were identified: Rsx-1 (one repeat), Rsx-2 (two repeats), and Rsx-4 (four repeats), with Rsx-2 being the most prevalent. Phylogenetic analysis suggested Rsx-1 and Rsx-4 types differentiated from Rsx-2. Geographic distribution revealed Rsx-1 in Yeongju and Uljin in Gyeongbuk province, Rsx-2 in Gangwon, Gyeonggi, and Chungbuk provinces, and Rsx-4 in northern parts of Gyeonggi and Gangwon provinces as well as Gyeongbuk province. These results demonstrate valuable observations into the genetic diversity, evolutionary dynamics, and potential movement route prediction of E. pyrifoliae in apple trees.