Bacterial Blight, a New Disease of Broccoli Caused by Pseudomonas syringae in California

In 1998 and 1999, a new disease was detected in commercial broccoli (Brassica oleracea var. botrytis) grown in the Salinas Valley, Monterey County, CA. Initial symptoms consisted of large, water-soaked, dark green, angular leaf sections that were bordered by major leaf veins. Diseased areas were as large as 10 × 3 cm. As the disease developed, affected areas turned tan and papery, and leaf margins sometimes became tattered. The numerous small (6 CFU/ml, and misted onto broccoli (cvs. Patriot and Titleist) and broccoli raab (B. rapa subsp. rapa cv. Spring). Control plants were misted with sterile nutrient broth. After 4 to 5 days in a greenhouse (24 to 26°C), large angular leaf lesions developed on all inoculated broccoli and broccoli raab plants. Strains were reisolated from symptomatic tissue and identified as P. syringae. Control plants remained symptomless. The results of two sets of pathogenicity tests were the same. Unlike most P. syringae strains, those isolated from broccoli were sensitive to a bacteriophage recovered from a P. syringae pathovar that infects broccoli raab. These results suggest that the broccoli pathogen may be related to the bacterial blight pathogen of broccoli raab (1). This is the first report of this pathogen causing a disease on commercially grown broccoli. Reference: (1) S. T. Koike et al. Plant Dis. 82:727, 1998.