New bacterial disease of broccoli raab in California (US)
Broccoli raab (Brassica rapa subsp. rapa) is a leafy vegetable which is cultivated for its tender leaves and immature inflorescence (e.g. a picture can be viewed on Internet, http://www.neseed.com/veggie/broccoli.htm). During the last 3 years, a new bacterial blight disease has been observed in commercial crops in the Salinas Valley, California (US). Diseased plants show small, angular, water soaked flecks on lower leaves which expand and become surrounded by bright yellow borders. These flecks coalesce and result in large, irregular necrotic areas, leaf yellowing and eventually leaf death. If symptoms develop on the upper leaves attached to the inflorescence, shoots lose their market quality and are not harvested. Pseudomonas syringae was consistently isolated from symptomatic plants and the isolated strains caused similar symptoms when inoculated onto broccoli raab plants. These strains also caused leaf spots symptoms when artificially inoculated to other Cruciferaceae (rocket (Eruca sativa), bok choy (Brassica campestris subsp. sinensis cv. Joi Choi), broccoli (B. oleracea subsp botrytis cv. Greenbelt), cabbage (B. oleracea subsp. capitata cv. Grenedere), cauliflower (B. oleracea subsp. botrytis cv. White Rock), Chinese cabbage (B. campestris subsp. pekinensis cv. Cha-Cha), Japanese mustard (B. campestris subsp. nipposinica cv. Mizuna), red mustard (B. juncea subsp. rugosa cv. Red Giant), tah tsai (B. campestris subsp. narinosa cv. Tokita).
According to morphological, biochemical and physiological studies the authors felt that this disease could be due to a new pathovar of Pseudomonas syringae. In addition, field observations tend to suggest that it could be seed-borne but this has not been demonstrated
Sources
Koike, S.T.; Henderson, D.M.; Azad, H.R.; Cooksey, D.A.; Little, E.L. (1998) Bacterial blight of broccoli raab: a new disease caused by a pathovar of Pseudomonas syringae.
Plant Disease, 82(7), 727-731.