Genetic diversity of Pseudomonas syringae pv. lachrymans strains isolated from cucumber leaves collected in Poland

Several strains of Pseudomonas syringae pathovar (pv.) lachrymans and related bacterial pathogens were isolated from cucumber ( Cucumis sativus ) leaves collected in central and southern Poland in 2001 and 2002. Twenty five original strains, together with five reference strains of P. syringae pv. lachrymans , pv. syringae and pv. tomato , were genetically characterized by PCR-RFLP (polymerase chain reaction − restriction fragment length polymorphism), ADSRRS (amplification of DNA fragments surrounding rare restriction sites), and PCR-MP (PCR − melting profiles) fingerprinting techniques. Genetic similarity analyses of the PCR-RFLP and ADSRRS fingerprints showed that strains of P. syringae pv. lachrymans form distinct clusters. The results also indicated that the ADSRRS and the PCR-MP fingerprinting techniques may serve as more efficient tools for evaluating genetic similarity among pathovars and strains of P. syringae than PCR-RFLP. The 25 strains showed diverse pathogenicity to cucumber seedlings and biochemical tests were varied. The syrB gene was identified in four cucumber strains, characterized as P. syringae pv. syringae .     

Identification and origin of races of Pseudomonas syringae pv. phaseolicola from Africa and other bean growing areas

Isolates of Pseudomonas syringae pv. phaseolicola from Africa and other bean growing areas were categorized into nine races on the basis of their reactions to eight differential cultivars following artificial inoculation. Eight hundred and ninety-three isolates representing 303 disease occurrences were initially identified as P.s. pv. phaseolicola by their pathogenicity to bean, cultural and serological characteristics and phage sensitivity. These tests also served to distinguish P.s. pv. phaseolicola from the closely related pathovars P.s . pv. glycinea and P.s. pv. syringae . Detailed race determinations were carried out on 175 selected isolates of p.s. pv. phaseolicola representative of the different geographical regions and hosts in which the pathogen was found and nine races were identified. A number of races (1,2,5,6 and 7) were distributed worldwide with race 6 predominant. Other races were found mainly in Africa; races 3 and 4 in East/Central Africa and races 8 and 9 in Southern Africa. Most isolates were obtained from the major host, Phaseolus vulgaris . Alternative natural hosts included 10 legume species representative of seven different genera ( Cajanus cajan, Desmodium sp., Lablab purpureus, Macroptilium atropurpureum, Neonotonia wightii, Phaseolus acutifolius, P. coccineus, P. lunatus, Vigna angularis and V. radiata ). Of these, Desmodium sp. constitutes a new host record.     

Evaluation of physiological and serological profiles of Pseudomonas syringae pv. pisi for pea blight identification

Phenotypic variability of the pea blight bacterium, Pseudomonas syringae pv. pisi, was studied on a large collection of strains isolated in France, as well as those obtained from foreign collections. Some other pseudomonads encountered on peas, particularly P.s. pv. syringae, were included in the study to evaluate differential tests for identification purposes. All the isolates that induced watersoaking on the pea cultivar Kelvedon Wonder after inoculation were considered to be P.s. pv. pisi. The other pseudomonads gave either no reaction or a hypersensitive reaction. When they corresponded to P. syringae according to the LOPAT test, they were referred to as P.s. pv. syringae.
P.s. pv. pisi did not show a single uniform phenotype. The variation of the different tests was estimated (fluorescence+ 93%; esculin-86%; dl-lactate-85%; homoserine + 75%; INA + 97%). Three O-sero-groups contained P.s. pv. pisi strains: APT-PIS (88.5%), HEL2 (11.4%) and RIB (0.1%). When the main criteria were combined, eight profiles were encountered within P.s. pv. pisi. This diversity was not linked to race structure or geographical origin of the strains. Profile PI was the most frequent (72.8%), and it was specific to the pathovar pisi . The strains belonging to the other profiles could be confused with some P.s. pv. syringae strains because of the serological heterogeneity of that pathovar. For instance, the pv. pisi strains belonging to profiles P2 and P4 resembled some of the P.s. pv. syringae found on peas and required pathogenicity tests on pea for their identification. The confusing pea isolates represented 12.8% of the total 4740 strains studied.     

Phylogenetic Relationships Among Global Populations of Pseudomonas syringae pv. actinidiae

ABSTRACT Pseudomonas syringae pv. actinidiae, the causal agent of canker in kiwifruit (Actinidia spp.) vines, was first detected in Japan in 1984, followed by detections in Korea and Italy in the early 1990s. Isolates causing more severe disease symptoms have recently been detected in several countries with a wide global distribution, including Italy, New Zealand, and China. In order to characterize P. syringae pv. actinidiae populations globally, a representative set of 40 isolates from New Zealand, Italy, Japan, South Korea, Australia, and Chile were selected for extensive genetic analysis. Multilocus sequence analysis (MLSA) of housekeeping, type III effector and phytotoxin genes was used to elucidate the phylogenetic relationships between P. syringae pv. actinidiae isolates worldwide. Four additional isolates, including one from China, for which shotgun sequence of the whole genome was available, were included in phylogenetic analyses. It is shown that at least four P. syringae pv. actinidiae MLSA groups are present globally, and that marker sets with differing evolutionary trajectories (conserved housekeeping and rapidly evolving effector genes) readily differentiate all four groups. The MLSA group designated here as Psa3 is the strain causing secondary symptoms such as formation of cankers, production of exudates, and cane and shoot dieback on some kiwifruit orchards in Italy and New Zealand. It is shown that isolates from Chile also belong to this MLSA group. MLSA group Psa4, detected in isolates collected in New Zealand and Australia, has not been previously described. P. syringae pv. actinidiae has an extensive global distribution yet the isolates causing widespread losses to the kiwifruit industry can all be traced to a single MLSA group, Psa3.     

Multilocus sequence typing of Pseudomonas syringae sensu lato confirms previously described genomospecies and permits rapid identification of P. syringae pv. coriandricola and P. syringae pv. apii causing bacterial leaf spot on parsley

Since 2002, severe leaf spotting on parsley (Petroselinum crispum) has occurred in Monterey County, CA. Either of two different pathovars of Pseudomonas syringae sensu lato were isolated from diseased leaves from eight distinct outbreaks and once from the same outbreak. Fragment analysis of DNA amplified between repetitive sequence polymerase chain reaction; 16S rDNA sequence analysis; and biochemical, physiological, and host range tests identified the pathogens as Pseudomonas syringae pv. apii and P. syringae pv. coriandricola. Koch's postulates were completed for the isolates from parsley, and host range tests with parsley isolates and pathotype strains demonstrated that P. syringae pv. apii and P. syringae pv. coriandricola cause leaf spot diseases on parsley, celery, and coriander or cilantro. In a multilocus sequence typing (MLST) approach, four housekeeping gene fragments were sequenced from 10 strains isolated from parsley and 56 pathotype strains of P. syringae. Allele sequences were uploaded to the Plant-Associated Microbes Database and a phylogenetic tree was built based on concatenated sequences. Tree topology directly corresponded to P. syringae genomospecies and P. syringae pv. apii was allocated appropriately to genomospecies 3. This is the first demonstration that MLST can accurately allocate new pathogens directly to P. syringae sensu lato genomospecies. According to MLST, P. syringae pv. coriandricola is a member of genomospecies 9, P. cannabina. In a blind test, both P. syringae pv. coriandricola and P. syringae pv. apii isolates from parsley were correctly identified to pathovar. In both cases, MLST described diversity within each pathovar that was previously unknown.     

Infection of horse chestnut (Aesculus hippocastanum) by Pseudomonas syringae pv. aesculi and its detection by quantitative real-time PCR

Pseudomonas syringae pv. aesculi is a pathogenic bacterium causing bleeding canker disease of horse chestnut ( Aesculus hippocastanum ). This is a serious disease which has been affecting horse chestnut in several European countries over the last five years; however, very little is known about the biology of the causal agent. One of the obstacles to studying this pathogen is the lengthy procedure associated with confirming its presence on the host. In this study, P. syringae pv. aesculi was isolated from lesions on different parts of horse chestnut and its pathogenicity confirmed on horse chestnut saplings using two inoculation techniques. Real-time PCR primers were developed based on gyrase B gene sequence data for the specific detection of P. syringae pv. aesculi . Primer specificity was tested on isolates of the target pathogen as well as on a broad range of related non-target bacteria and other bacterial spp. which inhabit horse chestnut. The real-time primers reliably amplified P. syringae pv. aesculi down to 1 pg of extracted DNA, with and without the presence of host DNA, and also amplified unextracted DNA in whole cells of the bacterium down to at least 160 colony forming units. Detection and quantification of the target pathogen in phloem and xylem of both naturally infected and inoculated horse chestnut tissues was also demonstrated. This quantitative real-time PCR assay provides the facility to study several important aspects of the biology of P. syringae pv. aesculi on horse chestnut including its potential for dissemination in different substrates.     

Patterns of interaction between isolates of three pathovars of Pseudomonas syringae and accessions of a range of host and nonhost legume species

Isolates of three pathovars of Pseudomonas syringae were tested against 10 legume species. Some isolates of all pathovars showed cultivar-specific interactions with at least one legume species outside the expected host range. Lablab purpureus and Phaseolus lunatus were found to be hosts to isolates of both P. syringae pv. glycinea and P. syringae pv. phaseolicola, while Lathyrus latifolius was host to isolates of P. syringae pv. pisi and P. syringae pv. glycinea . Lens culinaris showed patterns of interaction with isolates of all three pathovars. Gene models based on mathematical estimates of minimum gene numbers agreed with those previously published for the interactions of P. syringae pv. pisi with Pisum sativum and P. syringae pv. phaseolicola with Phaseolus vulgaris. Two different gene-for-gene models based on five resistance/avirulence gene pairs were proposed to explain observed interactions between Glycine max and P. syringae pv . glycinea . Pathogen isolates which contained no known avirulences defined on their respective host species were found to carry cryptic avirulences recognized by other plant species. Estimates of minimum gene numbers required to explain the interactions of a plant species with all pathogen isolates or to explain the interactions of the isolates of one pathovar with all plant accessions were consistently lower than the sum of the minimum gene numbers required to explain the interactions of each individual component.     

Genetic diversity, presence of the syrB gene, host preference and virulence of Pseudomonas syringae pv. syringae strains from woody and herbaceous host plants

A total of 101 Pseudomonas syringae pv. syringae strains, obtained from international culture collections or isolated from diseased tissues of herbaceous and woody plant species, were assessed by repetitive PCR using the BOX primer, and for the presence of the syrB gene. Representative strains were also tested for pathogenicity to lilac, pear, peach, corn and bean, as well as for virulence to lemon and zucchini fruits. The unweighted pair-group method using arithmethic averages analysis (UPGMA) of genomic fingerprints revealed 17 different patterns which grouped into three major clusters, A, B and C. Most of the strains (52·4%) were included in patterns 1–4 of group A. These patterns comprised strains obtained from either herbaceous or woody species, and showed four fragments of similar mobility. Genetic variability was ascertained for strains isolated from apple, pear, apricot, Citrus spp. and cereals. No clear relationship was observed between host plant and bacterial genomic fingerprint. Variability was also observed in pathogenicity and virulence tests. The inoculation of pear leaves discriminated strains isolated from pear as well as the very aggressive strains, whereas inoculation of lilac, peach and corn did not discriminate the host plant from which the strains were originally isolated. Lemon fruit inoculation proved very effective for P. syringae pv. syringae virulence assessment. The syrB gene was present in almost all strains.     

Nontoxigenic Strains of Pseudomonas syringae pv. phaseolicola Are a Main Cause of Halo Blight of Beans in Spain and Escape Current Detection Methods

ABSTRACT From a collection of 152 pseudomonads isolated from diseased beans in Spain, 138 (91%) of the strains were identified as Pseudomonas syringae pv. phaseolicola and the rest as P. syringae pv. syringae. The P. syringae pv. phaseolicola strains produced typical water-soaked lesions on bean pods, although 95 of them did not produce phaseolotoxin in vitro. Ninety-four of these isolates did not produce the expected 0.5-kb product after polymerase chain reaction (PCR) amplification using primers specific for open reading frame (ORF) 6 of the phaseolotoxin (tox) gene cluster and did not contain DNA homologous to ORF 6 in Southern hybridization experiments. To our knowledge, this is the first report of the widespread occurrence in the field of strains of P. syringae pv. phaseolicola lacking the tox cluster, which contrasts sharply with the general belief that Tox(+) isolates are the only ones with epidemiological importance. Additionally, the tox(-) isolates were not specifically detected by a commercial polyclonal antisera in an enzyme-linked immunosorbent assay. Accordingly, it is possible that the certification of seed lots as free of the pathogen cannot be reliably done in Spain, or in any other country where tox(-) strains might occur frequently, using current PCR or serological protocols. The amplification of three avirulence genes by PCR allowed us to make predictions of the P. syringae pv. phaseolicola race structure, as confirmed by plant assays. Six races (races 1, 2, 5, 6, 7, and 9) were identified, with race 7 being the most prevalent (46.1%) followed by races 6 (21.3%) and 1 (9.0%). All the tox(-) isolates contained gene avrPphF, typical of races 1, 5, 7, and 9.     

广东南瓜细菌性叶枯病及其病原鉴定

 在广东省雷州市发生一种南瓜(Cucurbita moschata)叶枯病,病株叶片边缘开始出现水渍状病斑,逐步发展成大病斑,后期病斑焦枯;在叶片上也可形成近圆形水渍状病斑,伴有黄色晕圈,后期病斑联合形成不规则大枯斑;叶柄和匍匐茎被侵染后呈水渍状腐烂。从病斑上分离到一种细菌,在KB培养基上,菌落为椭圆形,乳白色,半透明,边缘参差不齐,紫外灯照射下产生荧光反应。致病性测定结果表明,该病原细菌可侵染6个南瓜品种引起与田间症状相同的叶枯病。生理生化试验结果表明,该病原细菌与丁香假单胞丁香致病变种(Pseudomonas syringae pv. syringae)的特性一致。应用假单胞菌属特异引物Ps-for/Ps-rev和丁香假单胞丁香致病变种组群特异性引物Group III-F/Group III-R,可从该病原细菌中扩增出预期大小分别为1 018 bp和750 bp的目的片段。应用丁香致病变种syrB基因特异性引物B1/B2,可从该病原菌中扩增出预期大小为750 bp的丁香霉素基因片段。基于16S rDNA与gyrB基因序列系统进化分析均表明,南瓜叶枯病菌株与已报道的P. syringae pv. syringae菌株HS191(CP006256)亲缘关系最近,二者聚类在一起形成一个小分支。人工接种条件下,该病原细菌还可侵染西葫芦、丝瓜、茄子、番茄、菜豆、扁豆等植物。这些结果表明,引起广东省南瓜叶枯病的病原为丁香假单胞丁香致病变种(Pseudomonas syringae pv. syringae)。这是首次在中国发现丁香假单胞丁香致病变种引起南瓜叶枯病。     

Biochemical and pathogenic differences between Kenyan and Brazilian isolates of pseudomonas syringae pv. garcae

Isolates of Pseudomonas syringae pv. garcae from Kenya and Brazil differed in pathogenic and biochemical characters. In inoculations on Coffea arabica var. SL28 from Kenya, only the Kenyan isolates were virulent. The Kenyan isolates were not bacteriocin producers while the Brazilian isolates were active producers comparable to P. s. syringae from lilac ( Syringa vulgaris ). Pigment production separated the two types of P. s. garcae isolates distinctly. The Kenyan isolates produced the UV fluorescent yellow-green siderophore while the Brazilian isolates produced a nonfluorescent brown diffusible pigment on King's B medium. API-20NE diagnostic kits were largely ineffective in distinguishing between biochemical reactions of P. s. garcae isolates from Kenya and Brazil or between these and P. s. syringae . Syringomycin activity on lemon and Geotrichum candidum distinguished P. s. syringae from P. s. garcae isolates. It is concluded that P. s. garcae (as represented by the seven cultures from the National Collection of Plant Pathogenic Bacteria, Harpenden, UK) exists in at least two strains, the Kenyan isolates comprising one strain while the Brazilian isolates comprise one or more distinct strains.     

Pseudomonas syringae pv. syringae on pepper seedlings in Italy

Pseudomonas syringae pv. syringae causing leaf spot on pepper seedlings grown in a plant bed is reported in Italy for the first time. The pathogen was identified by means of biochemical, physiological and pathogenicity tests as well as by SDS-polyacrylamide gel electrophoresis of whole-cell proteins. The bacterial isolates showed positive for ice nucleation and biocide production.     

进境油菜籽中十字花科黑斑病菌的检测

 利用MT选择性培养基从加拿大进境油菜籽样品中分离到2株细菌分离物2305-1和5309-1,对分离物进行致病性测定、LOPAT测试、Biolog测试、hrpZ和cfl基因序列分析,以及多位点序列分析。结果表明:2株分离物人工接种油菜、花椰菜和番茄幼苗都能引起典型黑斑症状;LOPAT测试和Biolog测试结果与丁香假单胞菌(Pseudomonas syringae)的各项生理指标一致;hrpZ基因序列与十字花科黑斑病菌(P. syringae pv. maculicola)和番茄细菌性叶斑病菌(P. syringae pv.tomato)的序列相似性均为99.18%～100%;cfl基因序列分析表明分离物2305-1和5309-1基因组中存在冠毒素合成基因;选择gyrB、ropD、gltA、 gap1、 acnB和pgi 6个看家基因进行多位点序列分析,系统发育树显示分离物2305-1和5309-1均与P. syringae pv. ma-culicola聚在一起。根据试验结果将分离物2305-1和5309-1鉴定为十字花科黑斑病菌P. syringae pv. maculicola。     

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.     

Selective detection of Pseudomonas syringae pv. tomato using dot blot hybridization and real-time PCR

Two rapid detection methods based on dot blot hybridization with a nonradioactive DNA probe and molecular beacon-PCR were developed for the specific detection of Pseudomonas syringae pv . tomato , the causal agent of bacterial speck of tomato. A 1378 bp DNA fragment (Acc. No. AM039892), obtained from the extension of a 255 bp fragment generated by a RAPD protocol, was used to find a suitable combination of primers specific for the tomato pathovar. A 138 bp fragment from the genome of P. syringae pv. tomato DC 3000 was used as DNA probe. In dot blots of DNA extracted from either pure cultures or artificially contaminated seeds washes, the probe recognized specifically the tomato pathovar. A molecular beacon was designed from the same region for the specific detection and quantification of P. syringae pv . tomato by real-time PCR. A highly significant correlation was observed between the amount of target DNA and the cycle threshold (Ct). Using a fast protocol for DNA extraction, from pure cultures and from washes of artificially contaminated seeds, the limit of detection was about 1 × 10² CFU. The diagnostic tools developed proved highly specific for P. syringae pv. tomato and simple to use. They can therefore be applied to large-scale testing of tomato seeds and seedlings for the assessment of their phytosanitary condition in nurseries.     

Genetic relationship between races of Pseudomonas syringae pv.pisi and cultivars of Pisum sativum

Isolates of Pseudomonas syringae pv. pisi from the UK and overseas were categorized into six races on the basis of their reactions to a range of differential pea (Pisum sativum) cultivars. Race 2 was predominant among the isolates examined and this probably reflects its relative international importance. A previously uncharacterized race (race 6) was virulent on all cultivars tested. Resistance to races 1-5 was widespread in commercial cultivars and breeding lines with more than 75% showing resistance to one or more races. A preliminary study of the inheritance of resistance indicated that for races 1, 2 and 3, resistance was controlled by different dominant genes. The genetic basis for the relationship between races of P. syringae pv. pisi and pea cultivars was explained in terms of a gene-for-gene relationship involving five matching gene pairs. With further clarification of the genetics of resistance this host-pathogen association will meet most of the requirements of a model system for the study of the genetic and molecular basis of pathogenicity and host specificity.     

Diagnostic methods for phytopathogenic bacteria of stone fruits and nuts in COST 873

Different diagnostic methods used or developed in the EU-COST ² 873 project 'Bacterial diseases of stone fruits and nuts' are presented. The methods concern detection and identification of the plant pathogenic bacteria Xylella fastidiosa (EPPO A1 list), Xanthomonas arboricola pv corylina , X.a . pv. pruni , Pseudomonas syringae pv. persicae (A2 list pathogens), Agrobacterium tumefaciens , Brenneria nigrifluens and B. rubrifaciens , P. amygdali , P. avellanae , P.s. pv . avii , P.s. pv. morsprunorum , P.s . pv. syringae , X.a . pv. juglandis . Furthermore, a recently described xanthomonas species (proposed name X. translucens pv . pistachiae ), causing a new disease on pistachio, viz. Pistachio decline, in Australia and the recently renamed Xanthomonas citri pv. mangiferaeindicae on mango are included. The methods range from classical ones such as nutritional tests, use of (semi-)selective media, PCR, fatty acid analysis, serology and pathogenicity tests as well as (more) modern ones such as free flow capillary electrophoresis, real-time PCR, rep-PCR, fAFLP and sequencing of open reading frames (ORFs) and/or housekeeping genes such as gyrB and rpoD . The usefulness of these methods are outlined and reference made to publications where they were successfully used. Development of useful (molecular) tools are also indicated. Whole genome sequencing has been performed for Pantoea agglomerans (a relevant biocontrol agent) by the Swiss laboratory and initiated for X. a . pv. pruni by the French laboratory in cooperation with the Swiss and Italian laboratories and development of a microarray test has been initiated by the Swiss laboratory, Details of meetings and training programmes throughout the region are elaborated.     

Pseudomonas syringae pv. solidagae pv. nov., the Causal Agent of Bacterial Leaf Spot of Tall Goldenrod Solidago altissima L.

A new bacterial disease of tall goldenrod (Solidago altissima L., “Seitaka-awadachiso” in Japanese), one of the most serious weeds in non-agricultural land, was discovered in Ibaraki Prefecture, Japan. Characterized by angular or round, dark brown necrotic spots on leaves, this disease resulted in defoliation and terminal dieback of the plants in severe cases. The disease was named “bacterial leaf spot”. The causal bacterium was identified as Pseudomonas syringae based on its bacteriological properties including those determined by LOPAT tests. The present bacterium was pathogenic to tall goldenrod alone but not to many other tested plants including weeds, flowers, trees and crops. In addition, P. syringae pv. syringae and other pathovars did not show any pathogenicity to tall goldenrod. Because no pathovars of P. syringae pathogenic to tall goldenrod have been reported, the present bacterium was concluded to be a new pathovar of P. syringae. We propose the name P. syringae pv. solidagae pv. nov. , and strain Sei 1 (MAFF 810063) is designated as the pathotype strain and has been deposited in the MAFF collection with two reference strains (MAFF 810064 and MAFF81066). Received 9 May 2001/ Accepted in revised form 18 June 2001     

Pseudomonas syringae pv. coryli, the Causal Agent of Bacterial Twig Dieback of Corylus avellana

ABSTRACT Thirty-eight bacterial strains isolated from hazelnut (Corylus avellana) cv. Tonda Gentile delle Langhe showing a twig dieback in Piedmont and Sardinia, Italy, were studied by a polyphasic approach. All strains were assessed by fatty acids analysis and repetitive sequence-based polymerase chain reaction (PCR) fingerprinting using BOX and ERIC primer sets. Representative strains also were assessed by sequencing the 16S rDNA and hrpL genes, determining the presence of the syrB gene, testing their biochemical and nutritional characteristics, and determining their pathogenicity to hazelnut and other plants species or plant organs. Moreover, they were compared with reference strains of other phytopathogenic pseudomonads. The strains from hazelnut belong to Pseudomonas syringae (sensu latu), LOPAT group Ia. Both fatty acids and repetitive-sequence-based PCR clearly discriminate such strains from other Pseudomonas spp., including P. avellanae and other P. syringae pathovars as well as P. syringae pv. syringae strains from hazelnut. Also, the sequencing of 16S rDNA and hrpL genes differentiated them from P. avellanae and from P. syringae pv. syringae. They did not possess the syrB gene. Some nutritional tests also differentiated them from related P. syringae pathovars. Upon artificial inoculation, these strains incited severe twig diebacks only on hazelnut. Our results justify the creation of a new pathovar because the strains from hazelnut constitute a homogeneous group and a discrete phenon. The name of P. syringae pv. coryli is proposed and criteria for routine identification are presented.