BACTERIAL-BLIGHT OF BROCCOLI RAAB - A NEW DISEASE CAUSED BY A PATHOVAR OF PSEUDOMONAS-SYRINGAE

Bacterial blight is a new disease of broccoli raab or rappini (Brassic a rapa subsp. rapa) that has developed on commercially grown crops in the Salinas Valley (Monterey County) in California. Symptoms consist o f small, angular, water-soaked flecks on lower foliage that are visibl e from both adaxial and abaxial sides of the leaves. These flecks expa nd and become surrounded by bright yellow borders. With time, multiple leaf spots coalesce and result in large, irregular necrotic areas, ex tensive leaf yellowing, and eventual leaf death. If symptoms develop o n the uppermost leaves attached to the inflorescence, the shoot loses market quality and will not be harvested. Pseudomonas syringae was con sistently isolated from symptomatic plants, and selected strains cause d similar symptoms when inoculated onto broccoli raab test plants. Bro ccoli raab strains caused leaf spot symptoms on nine other Cruciferous plants, as well as on three grass species (California brome, oat, and common timothy). Conversely, broccoli raab was not infected by P. syr ingae pathovars coronafaciens, maculicola, and tomato. Broccoli raab s trains were positive for coronatine toxin production. Fatty acid analy ses indicated that the P. syringae from broccoli raab was most closely related to P. syringae pvs. coronafaciens and maculicola, but its dis tinct host range suggests that it may be considered a separate pathova r.