The Value of Phage Sensitivity Tests for the Identification of Phytopathogenic Pseudomonas Spp.

Abstract

Summary: To study the value of phage sensitivity tests for the identification of phytopathogenic pseudomonads, 284 isolates from various sources were examined for their sensitivity to 9 phages. Phages came from infected plants (4), meat (2), manure (2) and from a culture of Ps. mors‐prunorum, P27 (1). The main part of the study was concerned with isolates of Ps. syringae from lilac (6), stone fruits (22), pear (46), Ps. mors‐prunorum (17), Ps. phaseolicola (16) and Ps. lachrymans (11), but single isolates of other phytopathogenic Pseudomonas spp. (30) were also examined. Strains of Ps. aeruginosa (5) and pseudomonads from soil, water and chicken meat (151) were included for comparison. Three of the phages 2, 12B and 33 from plant sources showed a high degree of specificity for Ps. phaseolicola, Ps. syringae (pear isolates) and Ps. syringae (lilac isolates), respectively, but in no case was this absolute. Most isolates of the 4 species studied in detail showed characteristic but not specific patterns with phages 12S, 15 and 21. Many of the phytopathogens were sensitive to phage 12S, but pseudomonads from soil, water and chicken meat were not lyzed by this phage. Of this latter group 44% were lyzed by one or more of the phages from meat or manure (14, 15, 20 and 21). Ps. aeruginosa was not lyzed by any of the phages. The ninth phage, P27, lyzed a proportion of Ps. syringae isolates from pear but none of the other pseudomonads tested.Tests for oxidase, sucrose oxidation, gelatinase and lecithinase activity were found useful in conjunction with lesion tests for screening purposes. Many of the phytopathogens, especially those having affinities with Ps. syringae, were oxidase negative.From these results and those of other workers it is concluded that phage sensitivity tests can play a useful part in the identification of phytopathogenic pseudomonads, if used in conjunction with other tests. The importance of the host in connection with phage sensitivity patterns is emphasized; also the fact that isolates from a wide geographical area and saprophytes from the vicinity of the host plant need to be examined if an adequate assessment of the value of a phage is to be obtained.