To Beet or Not (Just) to Beet: Ecology, Virulence and Genomic Insights Into the Leaf Spot Disease Causative Pseudomonas syringae pv. aptata

TAXONOMY: Kingdom Bacteria; Phylum Proteobacteria; Class Gammaproteobacteria; Family Pseudomonadaceae; Genus Pseudomonas; Species Pseudomonas syringae species complex, Genomospecies 1, Phylogroup 02b. BIOLOGY: Gram-negative, aerobic, motile, rod-shaped with polar flagella, oxidase negative, arginine dihydrolase negative, levan production positive, potato rot negative, tobacco hypersensitivity positive. VIRULENCE FACTORS: T3SEs, toxins (syringomycin, syringopeptin, syringolin, mangotoxin, tabtoxin). DISEASE SYMPTOMS: Pseudomonas syringae causes disease symptoms on beet leaves characterised as circular or irregular, dark-edged, white to light brown necrotic spots that merge and spread over the entire leaf surface. Young leaves become completely necrotic within 7 days after the first symptom appears. HOST RANGE: Reported disease incidence mainly occurs on beets and cucurbits in temperate regions. Greenhouse trials showed an extremely wide host range for the strains isolated from diseased beets, causing disease on plants from nine different families and 16 different plant species. DISEASE CONTROL: Preventive measures focus primarily on sanitary and cultural practices. Integrated control programmes benefit from the regular application of copper formulations. The susceptibility of sugar beet cultivars to leaf spot disease varies, but no cultivar is completely resistant to the pathogen. Biological control may involve beneficial bacteria that suppress pathogens via metabolites and resource competition or by inducing systemic resistance in beet plants. USEFUL WEBSITES: https://www.pseudosonseed.org/chenopods-diseases/; https://www.cabi.org/isc/datasheet/44993; https://www.ncbi.nlm.nih.gov/assembly/?term=pseudomonas%20syringae%20pv.%20aptata; https://www.uniprot.org/proteomes?query=pseudomonas%20syringae%20pv.%20aptata; https://pnwhandbooks.org/plantdisease/host-disease/beet-red-beta-vulgaris-bacterial-leaf-spot.