Ewingella allii sp. nov. isolated from a diseased onion plant in the Columbia Basin of Washington State, USA

Isolation of strain 20WA0182^T from a diseased onion plant grown in the Columbia Basin of Washington State, USA, led to preliminary identification as a member of the genus Ewingella. The strain was characterised as a Gram-stain-negative, facultative anaerobe that is rod-shaped, motile with polar flagella, catalase positive, and oxidase negative. The strain 20WA0182^T isolated was pathogenic to yellow onion bulbs, weakly pathogenic on onion leaves of the cv. Ranchero, and caused a pathogenic response using the red onion bulb scale necrosis assay. Phylogenetic analyses using the 16S rRNA gene and four housekeeping genes, atpD, gyrB, infB, and rpoB, showed that strain 20WA0182^T formed a branch that clustered with E. americana strains, but on a separate node, indicating it is a novel species of this genus. Whole-genome sequencing of strain 20WA0182^T revealed a genome size of 4,604,541 nt, with 25 contigs and a G + C content of 53.8%, strain 20WA0182^T was 99.2% complete. The average nucleotide identity of strain 20WA0182^T compared with E. americana strains scores ranged from 92.85 to 93.96%, below the 95% threshold to classify strains as the same species. Similarly, dDDH scores were 56.0 to 56.2%, less than the 70% threshold required to delineate prokaryotes as the same species. Strain 20WA0182^T and Ewingella sp. CoE-038-23 shared the ANI score above 97.59% and 81.0% dDDH score to be classified as a novel species of Ewingella. As the type strain 20WA0182^T (= BD 3290^T = LMG 33618^T) was pathogenic to onion bulbs and leaves, the name Ewingella allii is proposed. GenBank accession number = JAWUDN000000000.