Characterization of Pseudomonas capsici and Pseudomonas cannabina pv. alisalensis causing bacterial leaf blight on Brassica leafy greens ( Brassica sp.) and spinach ( Spinacia oleracea L.) in the Southeastern United States

Recurrent outbreaks of bacterial leaf blight (BLB) in Brassica leafy greens and spinach have caused devastating yield losses for growers in the southeastern United States. Pseudomonas cannabina pv. alisalensis (Pcal) was previously identified as the causal agent of BLB, however, a new Pseudomonas species was recently reported to cause BLB on spinach in South Carolina. To investigate the diversity of BLB-causing pseudomonads, we characterized seven pathogenic Pseudomonas strains recovered from three commercial farms across South Carolina, five from Brassica leafy greens and two from spinach. Isolate characterization based on LOPAT scheme, rep-PCR and pathogenicity assays revealed distinct profiles from Pcal. Phylogenomic analysis and overall genome-related indices (OGRIs) including digital DNA-DNA hybridization and average nucleotide identity revealed that the five strains collected from turnip greens and two strains from spinach belonged to Pseudomonas capsici (Pcap). Apart from turnip greens (Brassica rapa) and spinach (Spinacia oleracea), Pcap strains were found to be pathogenic on mustard greens (Brassica juncea), swiss chard (B. vulgaris var. cicla), green beans (Phaseolus vulgaris), melon (Cucumis melo), tomato (Solanum lycopersicum), eggplant (Solanum melongena), pepper (Capsicum annum), and six different B. oleracea morphotypes, indicating a potentially wide-host range. To our knowledge, this is the first report of Pcap causing BLB in Brassica leafy greens and spinach, emphasizing the need for identification of resistance sources for this pathogen.