Pseudomonas morsprunorum,the Cause of Bacterial Canker of Sour Cherry in Michigan, and its Epiphytic Association withP. syringae

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Abstract
More than 462 Gram-negative, oxidase-negative, green fluorescent and bacilliform bacterial isolates from diseased and from symptomless Montmorency sour cherry [Prunus cerasus] buds, blossoms, leaves, fruits and 1 yr old wood, and new shoot growth were characterized by 4 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 2 GATTa+. Isolates negative for the first 2 tests and positive for the last 2 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 disease tissue and about 82% of the isolates from symptomless samples were either GATTa+ or GATTa-. The GATTa+ and GATTa- isolates were identified as P. syringae and P. mors-prunorum, 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. mors-prunorum, rather than P. syringae, was the predominant species isolated from diseased sour cherry trees. Pathogenic P. mors-prunorum and P. syringae isolates were recovered from symptomless sour cherry tissues in about a 1:1.4 ratio. Epiphytic populations apparently are an important source of inoculum for bacterial canker of sour cherry.