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Etiology

Pseudomonas morsprunorum, the Cause of Bacterial Canker of Sour Cherry in Michigan, and its Epiphytic Association with P. syringae. B. A. Latorre, Research associate, Department of Botany and Plant Pathology and Pesticide Research Center, Michigan State University, East Lansing, MI 48824, Present address of senior author: Departamento de Sanidad Vegetal, Facultad de Agronomia, Universidad de Chile, Casilla 1004, Santiago, Chile; A. L. Jones, professor, Department of Botany and Plant Pathology and Pesticide Research Center, Michigan State University, East Lansing, MI 48824. Phytopathology 69:335-339. Accepted for publication 16 October 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-335.

More than 462 Gram-negative, oxidase-negative, green fluorescent, and bacilliform bacterial isolates from diseased and from symptomless Montmorency sour cherry buds, blossoms, leaves, fruits, and 1 yr old wood, and new shoot growth were characterized by four determinative tests. Isolates positive for gelatin liquefaction (G) and aesculin hydrolysis (A) but negative for tyrosinase activity (T) and tartrate utilization (Ta) were referred to as GATTa⁺. Isolates negative for the first two tests and positive for the last two were GATTa^–. The GATTa⁺ isolates utilized lactic acid (L⁺), hydrolyzed arbutin, and produced a yellow supernatant fluid with a cloudy or translucent appearance in sucrose nutrient broth. All isolates from diseased tissue and about 82% of the isolates from symptomless samples were either GATTa⁺ or GATTa^–. The GATTa⁺ and GATTa^– isolates were identified as Pseudomonas syringae and P. morsprunorum, respectively. The hypersensitive reaction on tobacco was not reliable as a criterion for establishing pathogenicity because 15.5% of the isolates induced a reaction on tobacco but failed to infect cherry fruits. Other isolates infected cherry fruits but not tobacco. Syringomycin production also did not correlate well with pathogenicity. P. morsprunorum, rather than P. syringae, was the predominant species isolated from diseased sour cherry trees. Pathogenic P. morsprunorum and P. syringae isolates were recovered from symptomless sour cherry tissues in about a 1:1.4 ratio. Epiphytic populations appear to be an important source of inoculum for bacterial canker of sour cherry.