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Title: First report of bacterial streak of fennel (Foeniculum vulgare) in California caused by Pseudomonas syringae pv. apii

item Jardini, Teresa
item KOIKE, STEVE - University Of California - Cooperative Extension Service
item Bull, Carolee

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2011
Publication Date: 11/10/2011
Citation: Jardini, T.M., Koike, S.T., Bull, C.T. 2011. First report of bacterial streak of fennel (Foeniculum vulgare) in California caused by Pseudomonas syringae pv. apii. Plant Disease. 96:285.

Interpretive Summary: Bacterial diseases of plants limit the supply of high quality food and fiber to consumers. Disease control and prevention is dependant upon understanding what organisms are causing the diseases. Recently a bacterial streak disease on fennel was observed in the Salinas Valley of California, which is one of the most important vegetable growing regions in the US. This manuscript demonstrates that the disease is caused by a pathogen known to cause disease on celery. Previously the celery pathogen was thought to only cause disease on celery but recently was shown to cause disease on parsley. Growers should refrain from planting celery, fennel or parsley directly after an occurrence of these diseases on any of these crops. Thus this information is essential to help growers prevent the disease in subsequent plantings after an outbreak.

Technical Abstract: A new bacterial streak disease appeared on fennel leaves, stems and bulbs grown in Salinas California production fields. Initial symptoms consisted of small black lesions on stems that spread down the stem to the bulbs and up the stem to leaves as the disease progressed. The disease rendered the plants unmarketable. Eighteen Gram-negative, fluorescent bacteria were isolated. The isolates tentatively identified as Pseudomonas syringae using physiological tests. The fennel isolates were compared to P. syringae pathovars known to be pathogens of the Apiaceae. The fennel isolates were identified as P. syringae pv. apii using molecular identification methods. In pathogenicity experiments, fennel isolates and known strains of P. syringae pv. apii were shown to cause disease on fennel and Koch’s postulates were fulfilled. Previously, the host range of P. syringae pv. apii was reported to be restricted to celery. This research expands the host range of P. syringae pv. apii and is the first report of this novel disease.