A study of populations of Pseudomonas syringae pv. syringae on stonefruits in Victoria

In a survey of the major stonefruit nurseries in Victoria during winter 1978 and 1979, Pseudomonas syringae pv. syringae , the causal organism of bacterial canker, was found to be present on most of the stonefruit material in all nurseries but was detected most frequently on apricot.
The epiphytic populations of P.s. pv. syringae on leaves, buds and shoots of apricot and cherry were assessed periodically between 1979 and 1983 by determining the proportion of trees bearing the bacterium or by counting numbers of bacteria. Populations consistently reached peak levels during spring and late autumn, with highest levels in spring. Populations were lowest during mid- to late summer. High proportions of tree contamination and high populations coincided with periods when maximum temperatures ranged from 19° to 25°C, and when rainfall was moderately high. The significance of these findings in the light of information from other studies on the seasonal variability of host susceptibility, and in relation to chemical control, is discussed.
There was no evidence of occurrence of P.s. pv. morsprunorum in Victoria.     

Comparison of ethylene-producing Pseudomonas syringae strains isolated from kudzu (Pueraria lobata) with Pseudomonas syringae pv. phaseolicola and Pseudomonas syringae pv. glycinea

The relationships among strains of Pseudomonas syringae pv. glycinea (Psg) and Pseudomonas syringae pv. phaseolicola (Psp) isolated from kudzu ( Pueraria lobata) and bean ( Phaseolus vulgaris) were investigated. All strains tested showed a close phenotypic similarity, with the exception of the utilization of inositol and mannitol as well as the production of toxins. On this basis the strains could be divided into three groups. Group 1 consists of all strains of pathovar glycinea, group 2 includes all Psp strains isolated from kudzu, and all Psp strains isolated from bean belong to group 3. This grouping was also reflected in the genetic fingerprints using the polymerase chain reaction (PCR) with primers that anneal to dispersed repetitive bacterial sequences (rep-PCR). The rep-PCR generated fingerprints were unique for each of the three groups. The strains of group 2, Psp strains isolated from kudzu, possess certain characteristics of group 1 (ethylene production) and group 2 (phaseolotoxin production). The Psp strains from kudzu can be clearly differentiated from Psp strains isolated from bean. They utilize mannitol, produce ethylene, and are strongly pathogenic to kudzu, bean, and soybean. The results obtained show that the Psp strains from kudzu should be separated from the pathovar phaseolicola and should represent their own pathovar.     

Spatial and temporal changes in chlorophyll fluorescence images of Nicotiana benthamiana leaves following inoculation with Pseudomonas syringae pv. tabaci

Inoculation of Nicotiana benthamiana leaves with virulent and avirulent strains of Pseudomonas syringae pv. tabaci resulted in increasing changes in F_v/F_m, and NPQ over time. Images of these chlorophyll a fluorescence measurements revealed different changes in different zones of the leaf. For the virulent strain, the infiltrated zone and zone directly surrounding it showed decreased F_v/F_m, and NPQ before the appearance of visible symptoms, and these decreases corresponded with increasing bacterial populations and putative tabtoxin activity. Another distinct zone of reduced F_v/F_m and NPQ extended several centimetres from the lesion to the nearest leaf margin, but only very low bacterial populations and no putative tabtoxin activity were detected in this zone. For the avirulent strain, a hypersensitive response occurred, bacterial populations remained low, and there was little detectable putative tabtoxin activity. Decreased F_v/F_m and NPQ, but not , were observed in the infiltrated zone prior to the hypersensitive response, followed by decreased values in a zone directly surrounding it. Following that, no further changes were observed. These results demonstrate that in addition to detecting pre‐symptomatic impacts of bacteria, chlorophyll a fluorescence imaging can also show that there are highly distinct regions of affected tissue that can extend considerably beyond the area of bacterial colonization. This should be considered in selecting leaf tissues for examining the effects of pathogens on plants, such as altered host gene expression or protein levels.     

Induction of pear blossom blast caused by Pseudomonas syringae pv. syringae

Conditions were established for inducing pear blossom blast caused by Pseudomonas syringae pv. syringae on both attached and detached shoots. The incidence of blossom blast was proportional to the logarithm of the P.s. pv. syringae population under optimal temperature, moisture, and bloom developmental stage. Highest incidence of blossom infection followed occurrence of a major exotherm (an increase in temperature caused by the heat of fusion from ice formation within blossom tissue) in the presence of P. s. pv. syringae. The exotherm was detected inside ovary tissue at temperatures ranging from –1.8 to –3.5 C. Wetness duration following the thawing process was less important than wetness during and immediately after the freeze event. Blossoms inoculated, then air-dried or removed from low-temperature treatment prior to occurrence of an exotherm, had a low incidence of infection, The full bloom stage of blossom development was more susceptible to blossom blast than either the open cluster or tight cluster stages of development.     

Bacterial inflorescence rot of grapevine caused by Pseudomonas syringae pv. syringae

Molecular sequencing (rpoB) and standard pathological and microbiological methods identified Pseudomonas syringae pv. syringae (Pss) as the causal agent of bacterial inflorescence rot of grapevines (Vitis vinifera) in three vineyards in Tumbarumba, NSW, Australia in 2006 and 2007. Pss strains from shrivelled berries and necrotic inflorescences of diseased grapevines were used to inoculate leaves and inflorescences of potted cv. Semillon grapevines. Pss caused disease symptoms similar to those experienced in the field, including angular leaf lesions, longitudinal lesions in shoot tissues and rotting of inflorescences from before flowering until shortly after fruit set. High humidity promoted symptom severity. The necrotic bunch stem and leaf lesions were susceptible to the development of Botrytis cinerea infections. Cryo‐scanning electron microscopy (cryoSEM) indicated that Pss entered leaves and inflorescence tissues via distorted, open, raised stomata surrounded by folds of tissue that appeared as ‘star‐shaped’ callose‐rich complexes when viewed by UV light microscopy. In necrotic tissues, cryoSEM revealed Pss within petiole parenchyma cells and air‐filled rachis xylem vessels. This is the first report of inflorescence and hence fruit loss caused by Pss in grapevines. The disease is described as ‘bacterial inflorescence rot’ and regarded as one that expands the previously reported pathology of grapevines caused by P. syringae. This study also indicated that infection by Pss might promote destructive B. cinerea infections when the fungus is already present but latent, although further experimentation is needed to prove such an interaction.     

Occurrence of Pseudomonas syringae pv. actinidiae on kiwifruit in Italy

Pseudomonas syringae pv. actinidiae has been isolated from kiwifruit plants for the first time in Italy. Biochemical tests were consistent with those characterizing the type-strain; pathogenicity tests yielded severe blights in the inoculated kiwifruit plants and no symptoms on lilac, pear and peach. Nutritional tests as well as whole-cell protein profiles revealed slight differences between the strains isolated in Japan and those of the present study. The main symptoms observed in the field are a red-rusty exudation covering the bark of twigs and trunks, blight of young canes and plants, angular leaf spots surrounded by chlorotic haloes and tiny cankers along the twigs.     

Weed community interference in burley oriental tobacco (Nicotiana tabacum)

The effects of interference from natural weed communities for varying periods were examined on growth, yield, and chemical composition of tobacco in field conditions at three locations and years in Greece. Tobacco yield increased significantly with weed-free periods of 3 or 4 weeks and decreased with weed interference greater than 3 to 4 weeks after transplanting. The results were similar for tobacco growth as fresh weight in both burley and oriental and as plant height and leaf number only in burley tobacco. When yield was affected there were also changes in chemical composition of tobacco. Tobacco growth was decreased in soils in which weeds had previously grown, even with adequate nutrition provided. The presence of Amaranthus retroflexus L. shoot residues allowed to decay in soil for more than 1 month were also harmful. L'influence d'une communauté de mauvaises herbes en culture de tabac burley et oriental (Nicotiana tabacum L.) L'influence exercée par la présence pendant diverses périodes de communautés spontanées de mauvaises herbes sur la croissance, le rendement et la composition chimique du tabac a fait l'objet d'une étude durant trois ans dans des conditions de plein champ à trois emplacements en Grèce. Le rendement du tabac a augmenté de façon significative lorsque la culture est restée indemne de mauvaises herbes pendant 3 ou 4 semaines après le repiquage; par contre, il a diminué lors d'un enherbement de trois ou quatre semaines après le repiquage. Pour ce qui est du poids frais du tabac, l'influence sur le développement végétal était semblable chez les deux sortes mais seul le tabac burley a subi une réduction dans la hauteur des plantes et le nombre de feuilles/plante, L'influence sur le rendement a été accompagnée de modifications dans la composition chimique du tabac. Dans des sols envahis antérieurement par des mauvaises herbes, la croissance du tabac a diminué, même en présence d'une alimentation convenable. La présence de résidus de pousses d'Amaranthus retroflexus L. qu'on avait laissé s'altérer pendant plus de 1 mois dans le sol, a également exercé une influence néfaste. Unkrautkonkurrenz bei Burley- und Orient-Tabak (Nicotiana tabacum L.) Der Einfluss natürlicher Verunkrautung unterschiedlich langer Perioden auf Wachstum, Ertrag und Inhaltsstoffe von Tabak wurde über 3 Jahre und an 3 Orten in Griechenland untersucht. Eine signifikante Ertragssteigerung konnte beobachtet werden, wenn die Tabakpflanzen für 3 oder 4 Wochen nach der Pflanzung unkrautfrei gehalten wurden; wenn die Konkurrenz der Unkräuter länger anhielt, kam es zu Ertragsminderungen. Ähnliche Ergebnisse wurden für das Frischgewicht bei beiden Tabakarten, für Pflanzenhöhe und Blattzahl aber nur beim Burley-Tabak festgestellt. Die chemische Zusammensetzung des Tabaks, der Asche) änderte sich in gleicher Weise wie der Ertrag. In Gewächshausversuchen nahm das Pflanzenwachstum in den Böden ab, wo vorher Unkrauter gewachsen waren, auch wenn eine entsprechende Düngung erfolgte. Wurden Pflanzenreste von Amaranthus retroflexus L. über mehr als einen Monat im Boden gelassen, um zu verrotten, so sank das Trockengewicht anschlies-send gepflanzten Tabaks.     

Pathogenicity and virulence factors of Pseudomonas syringae

In 1994, Oku reported that plant pathogens, mainly fungal pathogens, require three essential abilities to infect plants: to enter plants, to overcome host resistance, and to evoke disease. Because the infectious process of phytopathogenic bacteria differs from that of fungal pathogens, we have attempted to characterize pathogenicity, the ability of a pathogen to cause disease, using the phytopathogenic bacterium Pseudomonas syringae as a representative pathogen. To establish infection and incite disease development, bacteria first have to enter a plant. This process requires flagella- and type IV pili-mediated motility, and active taxis is probably necessary for effective infection. After bacteria enter a plant’s apoplastic spaces, they need to overcome host plant resistance. To do this, they secrete a wide variety of hypersensitive response and pathogenicity (Hrp) effector proteins into the plant cytoplasm to interfere with pathogen/microbe-associated molecular pattern- and effector-triggered immunity, produce phytohormones and/or phytotoxins to suppress plant defense responses and extracellular polysaccharides to prevent access by antibiotics and to chelate Ca²⁺, and activate the multidrug resistance efflux pump to extrude antimicrobial compounds for successful colonization. Furthermore, to evoke disease, bacteria produce toxins and Hrp effectors that compromise a plant’s homeostasis and injure plant cells. The expression of these virulence factors depends on the infection processes and environmental conditions. Thus, the expression and function of virulence factors interact with each other, creating complex networks in the regulation of bacterial virulence-related genes.     

Specificity of polyclonal antibodies to different antigenic preparations of Pseudomonas syringae pv. pisi strain UQM551 and Pseudomonas syringae pv. syringae strain L

Polyclonal antibodies were produced against sonicated and heat-killed cells of Pseudomonas syringae pv. pisi strain UQM551 and Pseudomonas syringae pv. syringae strain L, and their specificities were compared. Evidence is presented that the serological specificity between these two pathovars lies in surface antigens. Of the surface antigens purified and tested, only flagella and lipopolysaccharide from the cell wall showed no cross-reactivity with heterologous antisera. Antisera to glutaraldehyde-fixed flagella of the two strains showed a high level of specificity. At a species or genus level, antisera prepared from heat-killed cells of P. syringae distinguished this species from all other bacterial species and genera tested, including strains of Pseudomonas fluorescens, Escherichia coli, Agrobacterium and Rhizobium.     

Syringopeptins, Pseudomonas syringae pv. syringae phytotoxins, resemble syringomycin in closing stomata

The recent finding that syringomycin (SR) and syringotoxin (ST)-producing isolates of Pseudomonas syringae pv. syringae also synthesize syringopeptins (SPs), another class of phytotoxic lipodepsipeptides, prompted studies of the biological properties and comparisons of the activities of the two groups of metabolites. The present paper reports the effects of two forms of SP on stomatal movement in detached leaves of Xanthium strumarium and in epidermal strips of Vicia faba and shows that these phytotoxins, as does the previously investigated SR, promote stomatal closure. SPs are at least 10-fold more efficient than SR in both tissues. In epidermal strips, the toxin-induced closure was not reversed by fusicoccin, a fungal metabolite that reversed the closing effects of abscisic acid. As reported in previous papers, these amphiphilic toxins affect several functions of biological membranes. A marked decrease in the rate of photosynthesis recorded in X. strumarium leaves treated with SPs is consistent with effects on biological membranes.     

Effects of para-aminobenzoic acid on bacterial speck symptom development and Pseudomonas syringae pv. tomato populations in tomato leaves

Para-aminobenzoic (PABA) is reported to induce resistance against a range of plant pathogens in different crops in a salicylic acid-dependent manner. However, factors affecting its efficacy are not well understood. Foliar PABA applications on tomato seedlings reduced lesion incidence caused by Pseudomonas syringae pv. tomato (Pst) in a dose-dependent manner in distal leaves up to 18 mM under controlled environment conditions, but only three out of six commercial processing tomato cultivars tested showed a response to PABA. Leaves in direct contact with 9 and 18 mM PABA of both PABA-responsive and PABA-nonresponsive cultivars showed phytotoxicity. In a PABA-responsive cultivar, one, two and three PABA applications were equally effective at reducing lesion incidence in distal leaves, but the duration of control only persisted for approximately 7 days. Although PABA application reduced lesion incidence in distal leaves, the Pst population in leaves was unaffected. Lesions on PABA-treated plants were larger than nontreated plants, and thus the proportion of leaf surface area with lesions was unaffected by PABA treatment. In in vitro assays, 18 and 72 mM PABA produced zones of inhibition against Pst 15 and 50% larger than the ethanol control, demonstrating direct antimicrobial effects of PABA. PABA application did not affect symptom development in a mixed infection of Pst or Xanthomonas spp. in one field experiment with a PABA-responsive cultivar. Further research is needed to understand why PABA was unsuccessful in the field before it is to be used as a practical disease management tool for foliar bacterial diseases of tomato.

     

Identification of Pseudomonas syringae pv. syringae causing bacterial leaf blight of Miscanthus sinensis

Journal of Plant Diseases and Protection - In the late summer of 2015, severe leaf blight occurred on Miscanthus sinensis grown on natural riverside lands of the Han River in Seoul, South Korea....     

Factors that Affect Spread of Pseudomonas syringae in the Phyllosphere

ABSTRACT Successful spread of an organism to a new habitat requires both immigration to and growth on that habitat. Field experiments were conducted to determine the relative roles of dispersal (i.e., immigration) and bacterial multiplication in spread of Pseudomonas syringae pv. syringae in the phyllosphere. To study spread, individual plots consisted of three nested concentric squares with the inner 6 m(2) planted to snap beans serving as the sink. Each sink, in turn, was surrounded by a barrier zone, usually 6 m wide, which was surrounded by a 6-m-wide source area. The source areas were planted with snap bean seeds inoculated with doubly marked strains derived from wild-type P. syringae pv. syringae B728a. The treatments were designed to test the effects of the nature and width of the barrier zone and suitability of the habitat in the sinks on spread of P. syringae pv. syringae. The marked strains introduced into the source areas at the time of planting were consistently detected in sink areas within a day or two after emergence of bean seedlings in the sources as assessed by leaf imprinting and dilution plating. The amounts of spread (population sizes of the marked strain in sinks) across barrier zones planted to snap bean (a suitable habitat for growth of P. syringae pv. syringae), soybean (not a favorable habitat for P. syringae pv. syringae), and bare ground were not significantly different. Thus, the nature of the barrier had no measurable effect on spread. Similarly, spread across bare-ground barriers 20 m wide was not significantly different from that across barriers 6 m wide, indicating that distance on this scale was not a major factor in determining the amount of spread. The suitability of the sink for colonization by P. syringae pv. syringae had a measurable effect on spread. Spread to sinks planted to clean seed was greater than that to sinks planted with bean seeds inoculated with a slurry of pulverized brown spot diseased bean leaves, sinks planted 3 weeks before sources, and sinks planted to a snap bean cultivar that does not support large numbers of P. syringae pv. syringae. Based of these results, we conclude that the small amount of dispersal that occurred on the scale studied was sufficient to support extensive spread, and suitability of the habitat for multiplication of P. syringae pv. syringae strongly influenced the amount of spread.     

Factors affecting the severity of bacterial canker of pear caused by Pseudomonas syringae pv. syringae

Several factors affecting the severity of bacterial canker of pear were studied. In the orchard, infection of shoots by Pseudomonas syringae pv. syringae occurred only when the inoculum dose exceeded 10⁶ colony-forming units/shoot. However, under favourable conditions in a growth chamber, cankers formed on detached shoots inoculated with 5 cfu/shoot. A second-order polynomial relationship was established between log₁₀ transformed canker length and log₁₀ transformed inoculum dose. In orchard and growth chamber experiments, shoots were susceptible from the time of bud swell until after fruit harvest. The severity of Pseudomonas canker of detached shoots increased if they were frozen at – 10°C for 24 h before inoculation. Shoots were most susceptible when inoculated immediately after wounding, and no cankers developed in the orchard when 3-day-old wounds were inoculated. Additionally, no cankers resulted from inoculation of leaf scars at leaf drop. Actively growing, current-season shoots were more susceptible than shoots that had set a terminal bud. The practical implications of these results are discussed as a basis for control of bacterial canker of pear.     

Occurrence of specific reactions induced by Pseudomonas syringae pv. syringae on bean pods, lilac and pear plants

A study on the pathogenicity of 81 strains of Pseudomonas syringae pv. syringae (PSS) isolated from 16 different hosts was conducted on lilac plants, bean pods and pear seedlings, using artificial inoculation.
Only 55 among the 81 strains induced a necrotic lesion when inoculated on lilac leaves. On bean pods, all but one of the bean isolates, and only eight strains among the 52 strains isolated from other hosts, induced typical green water-soaked lesions. On pear leaves, only pear isolates incited a typical progressive necrotic reaction, the isolates from other origins inducing no symptoms or a weak reaction limited to the inoculation point. This study indicates that in addition to the large variability observed in aggressiveness of PSS strains, host specificity occurred on bean and pear.     

Evaluation of drench treatments with phosphonate derivatives against Pseudomonas syringae pv. syringae on pear under controlled environment conditions

Several phosphonate derivatives including theoomycetic antifungal agents phosphonate andtris-o-ethylphosphonate (fosetyl), theethylene-releasing compound 2-chloroethylphosphonate(ethephon), and the antibiotic2-epoxypropylphosphonate (phosphomycin) were evaluatedfor in vitro and in planta activityagainst Pseudomonas syringae pv. syringae.Inhibition of colony growth in CYE agar byphosphonate, fosetyl and etephon was very slight(minimal inhibitory concentrations MIC= 0.31–;0.62 gHP /l). Also, survival of P. syringae pv. syringae in aqueous solutions ofphosphonate or fosetyl was high. Only phosphomycinshowed significant antibacterial activity invitro (MIC=10-20 µg HP /ml) comparedto streptomycin (1-2 µg a.i./ml). Potted pearplants irrigated with these chemicals and inoculatedwith Pseudomonas syringae pv. syringae had significantly less disease than non-treatedcontrols ( P<0.001). Phosphomycin was the mostactive compound with a median effective dose(ED₅₀) of less than 0.62 g HP /l.Activities of the other phosphonates were weak butconsistent between experiments. The ED₅₀s on wholeplants were 2.1, 3.3, and 6.9 g HP /l for ethephon, phosphonate and fosetyl, respectively. TheED₅₀of P. syringae pv. syringaeincreased from 6.5 in non-treated controls to 7.7-8.8log₁₀ cfu/ml on plants treated with phosphonatesat 1.86 g HP /l. It was concluded thatdrench treatment with fosetyl is not a practicaloption for control of P. syringae pv. syringae on pear.