In 2007, leaf spots were observed on arugula (Eruca vesicaria subsp. sativa cv. My Way) grown under sprinkler irrigation for fresh market in conventional and organic production fields located above 1,200 m (4,000 feet) in Nevada (NV). Approximately 30% of each planting was affected. Initially, symptoms consisted of small (0.80) to P. syringae. Amplification of DNA between repetitive bacterial sequences (rep-PCR) using the BOXA1R primer resulted in identical banding patterns for the NV arugula strains and P. syringae pv. alisalensis from arugula in California (1). Koch's postulates were completed by confirming pathogenicity of the isolated strains on the arugula cvs. Italian and Astro. Strains were grown on nutrient agar for 48 h at 27°C, adjusted to 108 CFU/ml in sterile 0.01 M phosphate buffer (pH 7.0), and spray inoculated until runoff onto 2- to 3-week-old plants. Control plants were similarly sprayed with sterile phosphate buffer. Plants were held for 2 days in a mist chamber and 7 days on a greenhouse bench (24 to 26°C). Angular lesions similar to symptoms observed on the original plants developed on leaves of all inoculated arugula plants. In addition, some plants developed blackening of the smaller veins accompanied by chlorosis of the surrounding interveinal tissue in 10- to 20-mm diameter areas of the leaves. Small black lesions (as much as 10 mm long) were also observed on the petioles. Bacterial strains reisolated from the symptomatic tissue were identical to P. syringae pv. alisalensis by rep-PCR. Control plants remained symptomless. Similar inoculation and incubation methods confirmed that the host range of the NV arugula isolates was identical to that of known strains of P. syringae pv. alisalensis. The arugula and P. syringae pv. alisalensis isolates caused leaf spots on broccoli raab (Brassica rapa subsp. rapa cv. Sorento) and oats (Avena sativa cv. Montezuma). Pathogenicity tests were repeated. This confirms that the leaf spot observed on conventionally and organically grown arugula in NV was caused by P. syringae pv. alisalensis. To our knowledge, this is the first report of this disease on arugula in NV. References: (1) C. T. Bull et al. Plant Dis. 88:1384, 2004. (2) R. A. Lelliott. J. Appl. Bacteriol. 29:470, 1966.