Angular Leaf Spot of Iron Wood Incited by a Pathovar of Pseudomonas syringae

A fluorescent pseudomonad inciting brown angular leaf spots on iron wood (Parotia persica) in Mazandaran forest was isolated and identified as a pathovar of Pseudomonas syringae. Strains assimilated adonitol and L-tartrate but not lactate or D-tartrate as carbon sources for growth. The electrophoretic profiles of cell proteins of strains isolated from iron wood were very similar but differred markedly from protein profile of P. syringae pv. syringae.     

Origin of the Outbreak in France of Pseudomonas syringae pv. actinidiae Biovar 3, the Causal Agent of Bacterial Canker of Kiwifruit,Revealed by a Multilocus Variable-Number Tandem-Repeat Analysis

The first outbreaks of bacterial canker of kiwifruit caused by Pseudomonas syringae pv. actinidiae biovar 3 were detected in France in 2010. P. syringae pv. actinidiae causes leaf spots, dieback, and canker that sometimes lead to the death of the vine. P. syringae pv. actinidifoliorum, which is pathogenic on kiwi as well, causes only leaf spots. In order to conduct an epidemiological study to track the spread of the epidemics of these two pathogens in France, we developed a multilocus variable-number tandem-repeat (VNTR) analysis (MLVA). MLVA was conducted on 340 strains of P. syringae pv. actinidiae biovar 3 isolated in Chile, China, France, Italy, and New Zealand and on 39 strains of P. syringae pv. actinidifoliorum isolated in Australia, France, and New Zealand. Eleven polymorphic VNTR loci were identified in the genomes of P. syringae pv. actinidiae biovar 3 ICMP 18744 and of P. syringae pv. actinidifoliorum ICMP 18807. MLVA enabled the structuring of P. syringae pv. actinidiae biovar 3 and P. syringae pv. actinidifoliorum strains in 55 and 16 haplotypes, respectively. MLVA and discriminant analysis of principal components revealed that strains isolated in Chile, China, and New Zealand are genetically distinct from P. syringae pv. actinidiae strains isolated in France and in Italy, which appear to be closely related at the genetic level. In contrast, no structuring was observed for P. syringae pv. actinidifoliorum. We developed an MLVA scheme to explore the diversity within P. syringae pv. actinidiae biovar 3 and to trace the dispersal routes of epidemic P. syringae pv. actinidiae biovar 3 in Europe. We suggest using this MLVA scheme to trace the dispersal routes of P. syringae pv. actinidiae at a global level.     

First Report of Bacterial Leaf Spot of Parsley Caused by Pseudomonas syringae pv. apii in Turkey

Since March, 2011, typical leaf spot symptoms were observed on parsley in several fields inspected in Hatay and Adana provinces of Turkey. Incidence of the disease was 5–15% in the regions. Symptoms were characterized as angular to irregular, initially water soaked later brown to dark black spots. Spots often limited by veins which were visible from both adaxial and abaxial sides of leaves but were not present on stems. Fluorescent bacterial colonies were consistently isolated from typical leaf spots. Biochemical tests, fatty acid methyl ester (FAME) analysis, molecular, pathogenicity tests and sequence of 16S ribosomal DNA of bacterial isolates were performed to identify possible causal disease agent. The causal disease agent was identified as Pseudomonas syringae pv. apii based on symptoms, biochemical, molecular, pathogenicity tests and sequencing. To our knowledge, this is the first report of bacterial leaf spot on parsley caused by Pseudomonas syringae pv. apii in Turkey.     

Angular Leaf Spot of Iron Wood Incited by a Pathovar of Pseudomonas syringae

A fluorescent pseudomonad inciting brown angular leaf spots on iron wood (Parotia persica) in Mazandaran forest was isolated and identified as a pathovar of Pseudomonas syringae. Strains assimilated adonitol and L-tartrate but not lactate or D-tartrate as carbon sources for growth. The electrophoretic profiles of cell proteins of strains isolated from iron wood were very similar but differred markedly from protein profile of P. syringae pv. syringae.     

The Serological Heterogeneity of Pseudomonas syringae pv. atrofaciens Strains and Their Ecological Niches

The paper deals with a comparative analysis of the serological and ecological properties of Pseudomonas syringae pv. atrofaciens strains from the collections of microbial cultures at the Malkov Institute for Plant Genetic Resources and Zabolotny Institute of Microbiology and Virology. All of the strains from the Bulgarian collection, except for one, fall into five serogroups (II through VI) of the classification system of Pastushenko and Simonovich. The P. syringae pv. atrofaciens strains isolated from Bulgarian and Ukrainian wheats belong mainly to serogroups II and IV, respectively. The strains that were isolated from rye plants belong to serogroup I. The strains isolated from sorghum and Sudan grass belong to serogroups II, IV, and VI. Serogroup III includes the P. syringae pv. atrofaciens strains that were isolated from cereals in the United Kingdom but not in Ukraine.     

Homologous Streptomycin Resistance Gene Present among Diverse Gram-Negative Bacteria in New York State Apple Orchards

The streptomycin resistance gene of Pseudomonas syringae pv. papulans Psp36 was cloned into Escherichia coli and used to develop a 500-bp DNA probe that is specific for streptomycin resistance in P. syringae pv. papulans. The probe is a portion of a 1-kb region shared by three different DNA clones of the resistance gene. In Southern hybridizations, the probe hybridized only with DNA isolated from streptomycin-resistant strains of P. syringae pv. papulans and not with the DNA of streptomycin-sensitive strains. Transposon insertions within the region of DNA shared by the three clones resulted in loss of resistance to streptomycin. Colony hybridization of bacteria isolated from apple leaves and orchard soil indicated that 39% of 398 streptomycin-resistant bacteria contained DNA that hybridized to the probe. These included all strains of P. syringae pv. papulans and some other fluorescent pseudomonads and nonfluorescent gram-negative bacteria, but none of the gram-positive bacteria. The same-size restriction fragments hybridized to the probe in P. syringae pv. papulans. Restriction fragment length polymorphism of this region was occasionally observed in strains of other taxonomic groups of bacteria. In bacteria other than P. syringae pv. papulans, the streptomycin resistance probe hybridized to different-sized plasmids and no relationship between plasmid size and taxonomic group or between plasmid size and orchard type, soil association, or leaf association could be detected.     

Hyaluronic acid of Streptococcus sp. as a potent elicitor for induction of systemic resistance against plant diseases

The potential of hyaluronic acid (HA) in inducing systemic resistance to cucumber, tomato and pepper was tested in planta. In the study, HA was found to be a potent agent for suppressing disease caused by Cucumber Mosaic Virus (CMV) (in pepper), Pseudomonas syringae pv. tomato (tomato speck disease), Xanthomonas axonopodis pv. vesicatoria (tomato spot disease), Pseudomonas syringae pv. lachrymans (cucumber angular leaf spot), and Colletotrichum orbiculare (cucumber anthracnose). Disease control was obtained with spraying, injection and drenching of plants with HA. HA did not exhibit direct antimicrobial action against the pathogens tested. Studies carried out in transgenic tobacco indicated that defense genes PR 1a and PDF 1.2 were activated upon treatment with HA, demonstrating salicylic acid (SA) and jasmonic acid (JA) pathways getting activated during defense. Further work is warranted to evaluate the use of HA-mediated disease suppression in crop plants.     

Early detection of bean infection by Pseudomonas syringae in asymptomatic leaf areas using chlorophyll fluorescence imaging

Chlorophyll fluorescence imaging has been used to analyse the response elicited in Phaseolus vulgaris after inoculation with Pseudomonas syringae pv. phaseolicola 1448A (compatible interaction) and P. syringae pv. tomato DC3000 (incompatible interaction). With the aim of modulating timing of symptom development, different cell densities were used to inoculate bean plants and the population dynamics of both bacterial strains was followed within the leaf tissue. Fluorescence quenching analysis was carried out and images of the different chlorophyll fluorescence parameters were obtained for infected as well as control plants at different timepoints post-infection. Among the different parameters analysed, we observed that non-photochemical quenching maximised the differences between the compatible and the incompatible interaction before the appearance of visual symptom. A decrease in non-photochemical quenching, evident in both infiltrated and non-infiltrated leaf areas, was observed in P. syringae pv. phaseolicola-infected plants as compared with corresponding values from controls and P. syringae pv. tomato-infected plants. No photoinhibitory damage was detected, as the maximum photosystem II quantum yield remained stable during the infection period analysed.     

Genetic Characterization of Pseudomonas syringae pv. syringae Strains from Stone Fruits in California

Strains of Pseudomonas syringae pv. syringae were isolated from healthy and diseased stone fruit tissues sampled from 43 orchard sites in California in 1995 and 1996. These strains, together with P. syringae strains from other hosts and pathovars, were tested for pathogenicity and the presence of the syrB and syrC genes and were genetically characterized by using enterobacterial repetitive intergenic consensus (ERIC) primers and PCR. All 89 strains of P. syringae pv. syringae tested were moderately to highly pathogenic on Lovell peach seedlings regardless of the host of origin, while strains of other pathovars exhibited low or no pathogenicity. The 19 strains of P. syringae pv. syringae examined by restriction fragment length polymorphism analysis contained the syrB and syrC genes, whereas no hybridization occurred with 4 strains of other P. syringae pathovars. The P. syringae pv. syringae strains from stone fruit, except for a strain from New Zealand, generated ERIC genomic fingerprints which shared four fragments of similar mobility. Of the P. syringae pv. syringae strains tested from other hosts, only strains from rose, kiwi, and pear generated genomic fingerprints that had the same four fragments as the stone fruit strains. Analysis of the ERIC fingerprints from P. syringae pv. syringae strains showed that the strains isolated from stone fruits formed a distinct cluster separate from most of the strains isolated from other hosts. These results provide evidence of host specialization within the diverse pathovar P. syringae pv. syringae.     

Nutritional Similarity between Leaf-Associated Nonpathogenic Bacteria and the Pathogen Is Not Predictive of Efficacy in Biological Control of Bacterial Spot of Tomato

It has been demonstrated that for a nonpathogenic, leaf-associated bacterium, effectiveness in the control of bacterial speck of tomato is correlated with the similarity in the nutritional needs of the nonpathogenic bacterium and the pathogen Pseudomonas syringae pv. tomato. This relationship was investigated further in this study by using the pathogen Xanthomonas campestris pv. vesicatoria, the causal agent of bacterial spot of tomato, and a collection of nonpathogenic bacteria isolated from tomato foliage. The effects of inoculation of tomato plants with one of 34 nonpathogenic bacteria prior to inoculation with the pathogen X. campestris pv. vesicatoria were quantified by determining (i) the reduction in disease severity (number of lesions per square centimeter) in greenhouse assays and (ii) the reduction in leaf surface pathogen population size (log₁₀ of the number of CFU per leaflet) in growth chamber assays. Nutritional similarity between the nonpathogenic bacteria and X. campestris pv. vesicatoria was quantified by using either niche overlap indices (NOI) or relatedness in cluster analyses based upon in vitro utilization of carbon or nitrogen sources reported to be present in tomato tissues or in Biolog GN plates. In contrast to studies with P. syringae pv. tomato, nutritional similarity between the nonpathogenic bacteria and the pathogen X. campestris pv. vesicatoria was not correlated with reductions in disease severity. Nutritional similarity was also not correlated with reductions in pathogen population size. Further, the percentage of reduction in leaf surface pathogen population size was not correlated with the percentage of reduction in disease severity, suggesting that the epiphytic population size of X. campestris pv. vesicatoria is not related to disease severity and that X. campestris pv. vesicatoria exhibits behavior in the phyllosphere prior to lesion formation that is different from that of P. syringae pv. tomato.     

Construction and Use of a Nonradioactive DNA Hybridization Probe for Detection of Pseudomonas syringae pv. Tomato on Tomato Plants

Pseudomonas syringae pv. tomato, the causal agent for bacterial speck of tomato, produces the phytotoxin coronatine. A 5.3-kilobase XhoI fragment from the chromosomal region controlling toxin production was cloned into the plasmid pGB2, and the resulting recombinant plasmid, pTPR1, was tested for its ability to serve as a diagnostic probe for P. syringae pv. tomato. In a survey of 75 plant-associated bacteria, pTPR1 hybridized exclusively to those strains that produced coronatine. The detection limit for this probe, which was labeled with the Chemiprobe nonradioactive reporter system, was approximately 4 × 10³ CFU of lesion bacteria. During the 1989 growing season, a total of 258 leaf and fruit lesions from nine tomato fields were screened for P. syringae pv. tomato by using pTPR1 and the culture method of detection. The best agreement between the two methods, 90%, occurred early in the season with samples taken from relatively young (5-week-old) plants. Young plants also had a higher percentage of P. syringae pv. tomato-positive lesions. P. syringae pv. tomato was the only coronatine producer recovered from the nine tomato fields. All 244 P. syringae pv. tomato strains isolated during this study reacted strongly with the probe. The P. syringae pv. tomato population of healthy field tomato leaves was determined by a pTPR1 colony hybridization procedure. Every probe-positive colony that was isolated and characterized was identified as P. syringae pv. tomato. The pTPR1 probe should expedite disease diagnosis and facilitate epidemiological studies of this pathogen. It also should aid in screening transplant seedlings for bacterial speck infestation.     

Occurrence of Alfalfa Bacterial Stem Blight Disease in Kurdistan Province, Iran

During spring and summer of 2004 and 2005, a new disease of alfalfa was observed for the first time in some areas of the Kurdistan province in Iran. Symptoms were initially yellowed area on leaves, within which water‐soaked, irregular spots developed. These spots eventually coalesced to produce large necrotic areas. Symptoms on petiole and stem include water‐soaked lesions, which later turned brown. Gram negative and rod‐shaped bacteria were isolated from infected tissues. From the results of LOPAT tests (levan production, oxidase reaction, potato soft rot, arginine dihydrolase and tobacco hypersensitivity) and other phenotypic, biochemical and physiological properties investigated, the causal bacterium have been identified as Pseudomonas syringae pv. syringae. Pathogenicity of selected strains was confirmed by injecting a bacterial suspension into leaf tissue from the underside of leaves.     

Biological control of bacterial spot of tomato under field conditions at several locations in North America

Following the relatively successful biological control of bacterial speck of tomato under field conditions at several locations (Phytopathology 92 (2002) 1284), similar selection and testing strategies were employed in an effort to isolate an effective biological control agent for bacterial spot of tomato. Fifty potential biological control agents were isolated from tomato foliage in Alabama (AL) and Florida (FL) and tested under greenhouse conditions in AL for the ability to reduce the foliar severity of bacterial spot of tomato (Lycopersicon esculentum), which is caused by either Xanthomonas campestris pv. vesicatoria or Xanthomonas vesicatoria. Three pseudomonads that provided protection against bacterial speck also were included in the tests. The strains which were most efficacious (i.e., high mean percentage reduction) and consistent (i.e., low standard deviation) in reducing bacterial spot severity in repeated greenhouse experiments were selected for field experiments conducted over the period 1996–1998. Among these strains were Cellulomonas turbata BT1, which provided the highest mean reduction in disease severity [45.2% (SD = 21.0)], and Pseudomonas syringae Cit7 [36.4% (SD = 12.2)], which was the most consistent. Field experiments were conducted in Shorter, AL; Bradenton and Sanford, FL; Clinton, North Carolina; Wooster, Ohio; and London, Ontario, Canada. The highest mean reductions in severity of bacterial spot on foliage, averaged across all locations, were provided by P. syringae Cit7 [28.9% (SD = 11.6)] and Pseudomonas putida B56 [23.1% (SD = 7.4)]. The efficacy and consistency of P. syringae Cit7 against bacterial spot were very similar to those achieved against bacterial speck [28.3% (SD = 12.7)] (Phytopathology 92 (2002) 1284). Unfortunately, neither the bacterial strains nor the standard copper bactericides consistently reduced disease incidence on fruit.     

The genetic characterization of Pseudomonas syringae pv. tagetis based on the 16S–23S rDNA intergenic spacer regions

Pseudomonas syringae pv. tagetis, a plant pathogen being considered as a biological control agent of Canada thistle (Cirsium arvense), produces tagetitoxin, an inhibitor of RNA polymerase which results in chlorosis of developing shoot tissues. Although the bacterium is known to affect several plant species in the Asteraceae and has been reported in several countries, little is known of its genetic diversity. The genetic relatedness of 24 strains of P. syringae pv. tagetis with respect to each other and to other P. syringae and Pseudomonas savastanoi pathovars was examined using 16S–23S rDNA intergenic spacer (ITS) sequence analysis. The size of the 16S–23S rDNA ITS regions ranged from 508 to 548 bp in length for all 17 P. syringae and P. savastanoi pathovars examined. The size of the 16S–23S rDNA ITS regions for all the P. syringae pv. helianthi and all the P. syringae pv. tagetis strains examined were 526 bp in length. Furthermore, the 16S–23S rDNA ITS regions of both P. syringae pv. tagetis and P. syringae pv. helianthi had DNA signatures at specific nucleotides that distinguished them from the 15 other P. syringae and P. savastanoi pathovars examined. These results provide strong evidence that P. syringae pv. helianthi is a nontoxigenic form of P. syringae pv. tagetis. The results also demonstrated that there is little genetic diversity among the known strains of P. syringae pv. tagetis. The genetic differences that do exist were not correlated with differences in host plant, geographical origin, or the ability to produce toxin.     

The Occurrence of Bacterial Red Streak of Sugarcane Caused by Pseudomonas syringae pv. syringae in Iran

A bacterial leaf streak disease characterized by reddish, narrow (1–2 mm wide) streaks of variable size, and occasionally with bleached centers, was found in sugarcane (Saccharum, interspecific hybrid) fields in northern Iran. The incitant bacterium was identified as Pseudomonas syringae pv. syringae (P. s. syringae). The disease is similar in aetiology to the sugarcane ‘red streak’ disease reported recently from Japan. Cultivardependent variations in symptoms were noted., Difference in pathogenicity as well as in electrophoretic profile of cell proteins between strains of P.s. syringae causing red streak in sugarcane and those causing canker on stone fruit trees, were observed.     

In planta measurements of oxidative bursts elicited by avirulent and virulent bacterial pathogens suggests that H2O2 is insufficient to elicit cell death in tobacco

A rapid and localized programmed cell death – the hypersensitive response (HR) – is a widely utilized plant resistance mechanism against pathogens. Studies have implicated H₂O₂ generation as a key elicitory mechanism in the HR. The causal relationship between the kinetics of the in planta oxidative burst, the HR and certain defence gene expression was examined. H₂O₂ generation following challenge with avirulent strains of Pseudomonas syringae pv. (P. s. pv.) syringae occurred in two phases. The effects of ROS generation were investigated using the H₂O₂-responsive transgene AoPR10-GUS, the dually responsive (H₂O₂ and salicylic acid) PR1a-GUS as well as measures of cell death. Co-application of catalase with P. s. pv. syringae into tobacco leaf panels suppressed AoPR10- and PR1a-GUS expression and cell death. Conversely, varying H₂O₂ generation with glucose: glucose oxidase influenced both defence gene expression and cell death. AoPR10-GUS proved to be primarily responsive to apoplastic not intracellular oxidative stress, suggesting that the apoplasm was a distinctive source of oxidative signals. A biphasic oxidative burst was also observed with virulent P. s. pv. tabaci, which, although delayed compared to that observed during HR, persisted at equivalent levels for a longer period. Taking all these data together we suggest that either (1) additional factors to the apoplastic oxidative burst are required to explain the rapid kinetics of defence signalling and cell death associated with the HR or (2) P. s. pv. tabaci successfully suppresses the effects of H₂O₂ generation by an unknown mechanism.     

Pepper Tree (Schinus terebenthifolius Radii), a New Host Plant for Xanthomonas campestris pv. mangiferaeindicae

Apigmented bacterial colonies were obtained in Reunion Island from angular leaf lesions on Pepper tree (Schinus terebenthifolius Radii), a member of Anacardiaceae. All isolates were identified as Xanthomonas campestris, using physiological and biochemical tests. These strains were reinoculated to Pepper tree leaves, and Koch postulates were verified. Furthermore, they were inoculated to mango leaves and produced lesions identical to those induced by Xanthomonas campestris pv. mangiferaeindicae, the causal agent of bacterial black spot of mangoes. Apigmented and pigmented strains of X. c. pv. mangiferaeindicae from Mango and Ambarella were pathogenic to Pepper tree. Strains isolated from Pepper tree were compared to X. c. pv. mangiferaeindicae, by means of phenotypic features (utilization of 147 carbon sources) and using a serological assay. A high homology among the strains was observed. Thus, It is concluded that strains isolated from Pepper tree belong to pv. mangiferaeindicae, and that Pepper tree is a host species for X. c. pv. mangiferaeindicae.     

Pseudomonas syringae pv. helianthi (Kawamura 1934) Dye, Wilkie et Young 1978, a Pathogen of Sunflower (Helianthus annuus L.)

Among the bacterial strains isolated from diseased sunflower leaves, eight were studied in some detail. A fluorescent pseudomonad isolated from necrotic tissues and its reisolates belong to group Ia of phytopathogenic pseudomonads which includes Pseudomonas syringae bacterium. A study of host range indicated that the pathogen infects only sunflower but not the other plant species. Based on the pathogenicity study and biochemical and physiological tests, it was concluded that the pathogen belongs to the bacterium Pseudomonas syringae pv. helianthi.     

Pathogenicity and identification of the lilac pathogen, Pseudomonas syringae pv. syringae van Hall 1902

Comparative in planta studies with Pseudomonas syringae pv. syringae have established optimum conditions for disease expression in lilac in terms of inoculum concentration, host age and post-inoculation conditions (temperature and day-length). Reproducible disease reactions required an inoculum concentration exceeding the ED⁵⁰, 5 × 10⁶ cfu/ml, and a temperature for post-inoculation incubation not exceeding 19°C. A revised host range of P. syringae pv. syringae, proposed on the basis of confirmation of pathogenicity of strains to lilac, comprises 44 species from monocotyledonous and dicotyledonous plants. Nine new hosts Abelmoschus esculentus, Bromus willdenowii, Camellia sinensis, Centrosema pubescens, Citrullus lanatus, Cotoneaster sp., Cucumis melo, Populus×euramericana and Triticum aestivum, are recorded. A comparative laboratory study was made of strains of P. syringae pv. syringae using more than 30 selected biochemical and nutritional tests. The pathovar could be characterised on the basis of 11 of these which may prove to be useful determinative tests.