Bacterial Blight on Arugula, a New Disease Caused by Pseudomonas syringae pv. Alisalensis in California

Plant Disease
C T BullS T Koike

Abstract

Beginning in 1995, a leaf spot disease has occasionally developed on the leafy crucifer arugula (Eruca vesicaria subsp. sativa) that is grown in coastal California as a fresh market commodity used mostly in bagged salad mixes. Initially, symptoms consist of small (<2 mm in diameter), angular, water-soaked spots that are visible from both sides of the leaf. The spots later enlarge, remain angular in shape, and turn brown to tan. A purple margin sometimes occurs around the spots. An important diagnostic feature is that this disease closely resembles downy mildew infections that have not produced sporangia (3). A blue-green fluorescent pseudomonad was consistently isolated from both types of lesions on King's medium B. Strains were levan positive, oxidase negative, and arginine dihydrolase negative. Strains did not rot potato slices but induced a hypersensitive reaction on tobacco (Nicotiana tabacum L. cv. Turk). These data indicated that the bacteria belonged to Lelliot's LOPAT group 1 (4). This was confirmed with data from fatty acid methyl ester analysis (MIS-TSBA version 4.10; MIDI, Inc., Newark, DE), which indicated that the strains were highly similar (similarity > = 0.758) to Pseudomonas syringae. Amplification of repetitiv...Continue Reading

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