The Use of Pathovar-Indicative Bacteriophages for Rapidly DetectingPseudomonas syringaepv.tomatoin Tomato Leaf and Fruit Lesions

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Abstract
A suspension of macerated tomato leaf or fruit lesions was added to molten nutrient broth yeast extract (NBY) soft agar and the soft agar was poured over the surface of an NBY agar plate. Once the agar had hardened the routine test dilutions (RTD) of 4 P. syringae pv. [pathover] tomato-indicative (PT phages) were spotted onto the agar surface. Phage lysis zones indicating the presence of P. syringae pv. tomato [the causal agent of tomato bacterial speck] appeared within 18-36 h. A minimum of about 8 .times. 104 colony-forming units (cfu) of P. syringae pv. tomato per lesion was required for clear zones to appear. Lesions on leaves inoculated with strain DCT6D1 contained an average of 2.9 .times. 106 cfu 8 days after inoculation. P. syringae pv. tomato DCT6D1 was detected by the PT phage test at 43 days after inoculation. Thirty-eight tomato fields and five fresh-produce markets were surveyed for the bacterial speck pathogen by the PT phage method of detection and by the isolation-physiological characterization (IPC) method. Identical results were obtained with both methods for all 34 leaf samples and 68 of 100 fruit samples. Thirty of the fruit samples were positive by the IPC method only. The PT phage test was a better detection method for leaf lesions than for fruit lesions. All 77 isolates of P. syringae pv. tomato obtained from the tomato fields were sensitive to the PT phages and pathogenic for tomato. The predominant bacteria in fruit lesions negative for P. syringae pv. tomato were identified as saprophytic fluorescent pseudomonads.