Pathogenicity of Pseudomonas morsprunorum in Relation to Host Specificity

Abstract

S U M M A R YDifferences in phage type between plum and cherry strains of Pseudomonas morspruiiorum were stable during passage through the homologous and heterologous hosts. In experiments controlled by phage typing reisolates from lesions, both strains were specific for the homologous plant when inoculated into leaves at low concentrations (< 105/ml.) but not at high concentrations (> io6/ml.). No specificity was observed in wound inoculations of branches made during the winter.Autumn inoculation of cherry leaf scars with cherry strains resulted in severe disease, with a dose response type of relationship between inoculum concentration and infection. Plum strains were ineffective through cherry leaf scars and inhibited infection by cherry strains when present in the same inoculum. The inhibitory effect was not observed with plum strains killed by heat or streptomycin, or with plum strains inoculated live in the presence of bacteriostatic levels of streptomycin.

Relations between Phage Sensitivity and Virulence in Pseudomonas morsprunorum

“…In previous work with indigenous plum and cherry strains of Pseudomonas morsprunorum, only those sensitive to phage A7 (all cherry strains and very rare plum strains such as ~1 7 ) were infective through cherry leaf scars, suggesting a possible link between phage sensitivity and the pathological characters responsible for host specificity in these organisms (Crosse & Garrett, 1970). This is not supported by the present experiments with phage-resistant mutants and non-indigenous cherry strains.…”

“…Comparison with the controls suggests on the contrary that it reduced natural infection from 'wild' cherry strains present on the leaf surfaces of the experimental trees. This agreed with previous results (Crosse & Garrett, 1970).…”

“…Table 2). The phage reactions of c9, c12, c22 and c46 were typical of English cherry strains; all those so far examined were sensitive to phages A3 and A7 and most of them sensitive to the related phages A9 and A32 Crosse & Garrett, 1970). The reactions of DIO, insensitive to A3, A7, A9 and A32 but sensitive to A15 S5 and S6, were similarly characteristic of most English plum strains (Lazar & Crosse, 1969;Crosse & Garrett, 1970).…”

“…Cankers were graded on an arbitrary rating scale of I to 5 inclusive and rate of leaf scar infection, a measure of the infectivity of the bacteria via this route, was calculated as the product (percentage of diseased spurs) x (mean Virulence in Pseudomonas rnorsprunorum 477 canker size) (Crosse & Garrett, 1970). Results were compared by analysis of variance using an angular transformation for percentage of diseased spurs and a square root transformation for rate of leaf scar infection.…”

“…Thus cherry isolates that are sensitive to A7 and related phages will readily infect cherry trees through leaf scars. Plum isolates, with rare exceptions insensitive to these phages, are non-virulent through cherry leaf scars ; furthermore, when mixed in the same inoculum they inhibit infection by the homologous cherry isolates Crosse & Garrett, 1970). In this paper we examine the relationship between phage sensitivity and virulence in a selection of non-indigenous P. morsprunorum cherry isolates from widely separated geographical localities and describe the effects of mutation to phage resistance on the virulence of indigenous cherry isolates.…”