A survey of wild cherry (Prunus avium) woodland plantations and nurseries was carried out in 2000/01. Trees with symptoms of bacterial canker were found in 20 of the 24 plantations visited and in three of seven nurseries. Fifty-four Pseudomonas syringae isolates from wild cherry together with 22 representative isolates from sweet cherry and 13 isolates from other Prunus spp., pear and lilac were characterised by physiological, biochemical, serological and pathogenicity tests. Isolates from wild cherry were predominantly P. syringae pv. syringae (Pss), but P. syringae pv. morsprunorum (Psm) races 1 and 2 were also found. Physiological and biochemical tests discriminated Psm races 1 and 2 from other P. syringae isolates. Agglutination and indirect-enzyme-linked immunosorbent assay tests with three different antisera showed that Psm race 1 and race 2 were very uniform and indicated high variability amongst other P. syringae isolates. However, pathogenic Pss isolates could not be distinguished from non-pathogenic isolates of P. syringae on the basis of physiological, biochemical or serological tests. Pathogenicity tests on rooted lilac plants and on micropropagated plantlets of lilac and two wild cherry clones differentiated Pss and Psm isolates and demonstrated a range of aggressiveness amongst Pss isolates. Serological tests could be used as an alternative to the classical physiological and biochemical tests to increase the speed of detection and discrimination of isolates, but pathogenicity tests are still necessary to discriminate the pathogenic Pss isolates.

Identification and Discrimination of Pseudomonas syringae Isolates from Wild Cherry in England

The fire blight pathogen, Erwinia amylovora, commonly infects flowers and shoots of certain rosaceous hosts and systemic (whole-tree) invasion sometimes follows. The bacterium may be found in the parenchyma of bark tissue and/or in mature xylem vessels of stem tissue. Views differ on initial sites of multiplication and the optimal route for systemic migration. This article presents the evidence on which the different views are based. There are limited observations on orchard pear and apple trees; in most experimental studies, young apple shoots on potted plants were used. Tissue maturity at the site of shoot inoculation is of prime importance. If xylem vessels are damaged, inoculum may be sucked into the vessels and the bacteria will multiply there. In younger tissue, there is less suction pressure. The critical stem entry site for the invasion of cortical parenchyma seems to be near or above the most recently unfolded leaf. No one has suggested that migration in bark tissue cannot be a major route. If the xylem route is followed, the pathogen needs a means of escape into bark tissue, where typical symptoms develop; means of escape from mature xylem vessels have not been demonstrated and remain a matter for speculation. Published evidence does not seem to support the idea that fire blight is a vascular wilt disease, nor that the extracellular polysaccharide produced by E. amylovora is a toxin and responsible for the wilting symptom seen in the early stages of the disease.

Fire blight. Why do views on host invasion by Erwinia amylovora differ

Pseudomonas syringae pv. aesculi (Psa) is an emerging bacterial pathogen responsible for a recent epidemic of bleeding canker of European horse chestnut (Aesculus hippocastanum) in northwest Europe. Very little is known about the infection biology of this pathogen, which can cause lethal cankers in the branches and stem of its host. In this study, branches and whole trees of European horse chestnut naturally infected with Psa were subjected to detailed morphological and histological examination to identify the primary infection sites, the time of infection, and the patterns of subsequent lesion expansion within the host. Lesions developed during the host dormant season on the 2003–2009 extension growth increments and were centred mainly on lenticels, leaf scars and nodes. The oldest lesion developed in the 2004/2005 dormant season and the number of new lesions increased in each subsequent year. The lesions developed in the cortex and phloem and extended into the cambium to cause cankers, but there was no evidence of necrosis in the xylem. All lesions on the branches were discrete and apparently contained by a necrophylactic periderm, although there was evidence that Psa could survive within such periderms and subsequently breach them. Examination of two whole 30-year-old trees revealed extensive, continuous cankers in the phloem and cambium which had formed within a single growing season. Thus, the success of Psa as a tree pathogen and the causal agent of a large-scale epidemic may in part reflect an ability to infect the aerial woody parts of its host directly.

Analysis of the natural infection of European horse chestnut (Aesculus hippocastanum) by Pseudomonas syringae pv. aesculi

Bacterial canker of stone-fruits.: V. A comparison of leaf-surface populations of Pseudomonas mors-prunorum in autumn on two cherry varieties

Op grond van een onderzoek van een tiental door ons geisoleerde bacteriestamment uit door bacteriekanker aangetaste kerse-, perzik- en pruimebomen kon worden vastgesteld, dat de in Tabel II samengevatte kenmerken, waarinPseudomonas mors-prunorum
Wormald enPseudomonas syringae
van Hall geacht worden te verschillen, bij aanhouden op peptonagar-2% glycerine of peptonagar allerminst constant zijn Bij inoculatie in kerse-, perzik- en pruimebladeren toonden de stammen geen enkel verschil Aan het soortsonderscheid kan dan ook geen betekenis worden gehecht Bij inoculatieproeven bleken de bacteriekanker veroorzakende organismen naastPrunus-soorten talrijke andere planten te kunnen infecteren EvenalsPseudomonas mors-prunorum kan een groot aantal andere, evenzo weinig specifieke, phytopathogene bacterien identiek geacht worden metPseudomonas syringae Naast deze pathogene bacterie werd in het bijzonder uit gommende kankers een niet-pathogene bacterie geisoleerd, die identiek is gebleken metAerobacter levancium
Hestrin et al De kolonies van deze bacterie blijken op saccharose bevattende agarmedia in morphologish opzicht zeer sterk met de bacteriekanker veroorzakende organismen overreen te stemmen Het is, vooral ook bij herisolaties, niet voldoende gebleken de bacterien naar het uiterlijk der kolonies te determineren A number of bacterial strains were isolated from cherry, peach and plum trees attacked by bacterial canker The two species,Pseudomonas mors-prunorum
Wormald andPseudomonas syringae
van Hall, could not consistently be distinguished by cultural characteristics All but one of these strains at first might have been identified asPseudomonas mors-prunorum However, after a number of serial transfers on peptone agar or peptone agar plus 2% glycerine it was impossible to separate them fromPseudomonas syringae by some differentiating characters presented byWormald (1932) andCrosse (1953) Thus, these characters such as longevity on sucrose-containing agar media, colour change on Difco nutrient agar plus 2% lactose and bromcresol purple (see Table III), fluorescent green pigment production, and pH change in a basic mineral medium plus lactose and the same basic medium plus maltose varied in a completely inconstant manner Not only in these differentiating characteristics but also in others the isolated strains showed a great diversity Thus, no great reliability may be placed on such inconstant characters, in which according toWormald, the two species differ After being inoculated into the leaves of cherry, peach and plum trees all strains caused identical symptoms Therefore, it is impossible to separate the two species after prolonged cultivation on peptone agar media either by biochemical or by pathogenic characteristics The bacterial canker organism could be inoculated successfully in many plants unrelated toPrunus spp; e g balsamine, bean, lemon, lilac, lupine, pear and red clover Thus, the bacterial canker organism proved to be rather unspecific in its ability to infect higher plants In these respects too it shows a certain relationship with many other bacteria, now generally included in the speciesPseudomonas syringae (Bergey, 6th ed, 1948) From data in the literature it can be concluded, that the speciesPseudomonas matthiolae, Pseudomonas nectarophila, Pseudomonas barkeri andPseudomonas rimaefaciens can also be grouped in this spcies Therefore, it seems warranted to apply the name ofPseudomonas syringae to all these bacteria, includingPseudomonas morsprunorum In addition to this pathogenic bacterium another one has been isolated which could be identified asAerobacter levanicum
Hestrin et al; this bacterium which is a common saprophyte, found on cherry and plum gum, has some morphological characteristics very similar to those shown by the bacterial canker organism: both organisms, if grown on sucrose-containing agar media, are characterized by slimy, hemispherical colonies with a distinct radial structure It was possible to enrich forAerobacter levanicum in a medium containing 1% cherry gum and small amounts of inorganic salts from soil, ditch water, etc After enrichment on the cherry gum medium, the organisms were isolated on peptone agar+5% sucrose It is noteworthy that although the cherry gum medium was good for enrichment, it did not support the growth of any of the strains thus isolated in pure culture Morphological characters of the colonies such as radial structure and slime production proved to be insufficient for determination of the isolated bacterial strains

Bacteriekanker bij Steenvruchten

The entrance of phytopathogenic bacteria into host tissues is a comparatively simple process. Unlike many pathogenic fungi they are incapable of active penetration of protective surfaces and gain a...

Bacterial Canker of Stone-Fruits: I. Field Observations on the Avenues of Autumnal Infection of Cherry

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Bacterial Canker of Stone-Fruits: I. Field Observations on the Avenues of Autumnal Infection of Cherry