Bacterial blight on arugula caused by Pseudomonas syringae pv. alisalensis in Greece

Arugula (Eruca sativa) of the Cruciferae is an annual leafy plant that is eaten as fresh vegetable in salads. In spring 2007, leaf samples from several parts of Greece showed disease symptoms that were not recorded for any of the known diseases of arugula Initial isolations indicated a bacterial pathogen as the causal agent. Symptoms appeared exclusively on the leaf surface. Specifically, small, water-soaked lesions 2-5 mm with or without a pale chlorotic ring, restricted between the secondary leaf veins, appeared on the adaxial and abaxial sides of the leaf. As disease developed, lesions retained angular edges, turned grey-brown and became necrotic and often with a papery appearance. They coalesced resulting in complete necrosis of the leaf. All isolations made from the infected leaves, showed the fluorescent Pseudomonas bacteria. In the LOPAT assays, isolations exhibited the phenotype [+ --- +] of the la group that includes Pseudomonas syringae pathovars. Based on the morphological, biochemical and physiological phenotype and on the pathogenicity of the isolates from infected arugula plants, we conclude that the causal agent is probably Pseudomonas syringae pv. alisalensis. Our results may be confirmed by the molecular identification of the pathogen. This is the first report of the bacterium in Europe.