VIEW ARTICLE

Techniques

The Use of Pathovar-Indicative Bacteriophages for Rapidly Detecting Pseudomonas syringae pv. tomato in Tomato Leaf and Fruit Lesions. D. A. Cuppels, Assistant plant pathologist, Research Centre, Agriculture Canada, University Sub Post Office, London, Ontario N6A 5B7; Phytopathology 74:891-894. Accepted for publication 15 February 1984. Copyright 1984 Department of Agriculture, Government of Canada. DOI: 10.1094/Phyto-74-891.

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 (RTDs) of four Pseudomonas syringae pv. tomato-indicative (PT phages) were spotted onto the agar surface. Phage lysis zones indicating the presence of P. syringae pv. tomato appeared within 18- 36 hr. A minimum of about 8 × 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 × 10⁶ cfu 8 days after inoculation. P. syringae pv. tomato DCT6D1 was detected by the PT phage test 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. Thus, 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.