Virulence of Pectobacterium carotovorum subsp. brasiliense on potato compared with that of other Pectobacterium and Dickeya species under climatic conditions prevailing in the Netherlands

In western Europe, Pectobacterium carotovorum subsp. brasiliense is emerging as a causal agent of blackleg disease. In field experiments in the Netherlands, the virulence of this pathogen was compared with strains of other Dickeya and Pectobacterium species. In 2013 and 2014, seed potato tubers were vacuum infiltrated with high densities of bacteria (10⁶ CFU mL^?1) and planted in clay soil. Inoculation with P. carotovorum subsp. brasiliense and P. atrosepticum resulted in high disease incidences (75–95%), inoculation with D. solani and P. wasabiae led to incidences between 5% and 25%, but no significant disease development was observed in treatments with P. carotovorum subsp. carotovorum, D. dianthicola or the water control. Co‐inoculations of seed potatoes with P. carotovorum subsp. brasiliense and D. solani gave a similar disease incidence to inoculation with only P. carotovorum subsp. brasiliense. However, co‐inoculation of P. carotovorum subsp. brasiliense with P. wasabiae resulted in a decrease in disease incidence compared to inoculation with only P. carotovorum subsp. brasiliense. In 2015, seed potatoes were inoculated with increasing densities of P. carotovorum subsp. brasiliense, D. solani or P. atrosepticum (10³–10⁶ CFU mL^?1). After vacuum infiltration, even a low inoculum density resulted in high disease incidence. However, immersion without vacuum caused disease only at high bacterial densities. Specific TaqMan assays were evaluated and developed for detection of P. carotovorum subsp. brasiliense, P. wasabiae and P. atrosepticum and confirmed the presence of these pathogens in progeny tubers of plants derived from vacuum‐infiltrated seed tubers.     

Distribution of <Emphasis Type="Italic">Dickeya</Emphasis> spp. and <Emphasis Type="Italic">Pectobacterium carotovorum</Emphasis> subsp. <Emphasis Type="Italic">carotovorum</Emphasis> in naturally infected seed potatoes

Detailed studies were conducted on the distribution of Pectobacterium carotovorum subsp. carotovorum and Dickeya spp. in two potato seed lots of different cultivars harvested from blackleg-diseased crops. Composite samples of six different tuber sections (peel, stolon end, and peeled potato tissue 0.5, 1.0, 2.0 and 4.0 cm from the stolon end) were analysed by enrichment PCR, and CVP plating followed by colony PCR on the resulting cavity-forming bacteria. Seed lots were contaminated with Dickeya spp. and P. carotovorum subsp. carotovorum (Pcc), but not with P. atrosepticum. Dickeya spp. and Pcc were found at high concentrations in the stolon ends, whereas relatively low densities were found in the peel and in deeper located potato tissue. Rep-PCR, 16S rDNA sequence analysis and biochemical assays, grouped all the Dickeya spp. isolates from the two potato seed lots as biovar 3. The implications of the results for the control of Pectobacterium and Dickeya spp., and sampling strategies in relation to seed testing, are discussed.     

Assessment of recent outbreaks of <Emphasis Type="Italic">Dickeya</Emphasis> sp. (syn. <Emphasis Type="Italic">Erwinia chrysanthemi</Emphasis>) slow wilt in potato crops in Israel

Suspected Dickeya sp. strains were obtained from potato plants and tubers collected from commercial plots. The disease was observed on crops of various cultivars grown from seed tubers imported from the Netherlands during the spring seasons of 2004–2006, with disease incidence of 2–30% (10% in average). In addition to typical wilting symptoms on the foliage, in cases of severe infection, progeny tubers were rotten in the soil. Six strains were characterised by biochemical, serological and PCR-amplification. All tests verified the strains as Dickeya sp. The rep-PCR and the biochemical assays showed that the strains isolated from blackleg diseased plants in Israel were very similar, if not identical to strains isolated from Dutch seed potatoes, suggesting that the infection in Israel originated from the Dutch seed. The strains were distantly related to D. dianthicola strains, typically found in potatoes in Western Europe, and were similar to biovar 3 D. dadanti or D. zeae. This is the first time that the presence of biovar 3 strains in potato in the Netherlands is described. One of the strains was used for pathogenicity assays on potato cvs Nicola and Mondial. Symptoms appeared 2 to 3 days after stem inoculation, and 7 to 10 days after soil inoculation. The control plants treated with water, or plants inoculated with Pectobacterium carotovorum, did not develop any symptoms with either method of inoculation. The identity of Dickeya sp. and P. carotovorum re-isolated from inoculated plants was confirmed by PCR and ELISA.     

Role of co‐infection by Pectobacterium and Verticillium dahliae in the development of early dying and aerial stem rot of Russet Burbank potato

Potato early dying (PED) is a disease complex primarily caused by the fungus Verticillium dahliae. Pectolytic bacteria in the genus Pectobacterium can also cause PED symptoms as well as aerial stem rot (ASR) of potato. Both pathogens can be present in potato production settings, but it is not entirely clear if additive or synergistic interactions occur during co‐infection of potato. The objective of this study was to determine if co‐infection by V. dahliae and Pectobacterium results in greater PED or ASR severity using a greenhouse assay and quantitative real‐time PCR to quantify pathogen levels in planta. PED symptoms caused by Pectobacterium carotovorum subsp. carotovorum isolate Ec101 or V. dahliae isolate 653 alone included wilt, chlorosis and senescence and were nearly indistinguishable. Pectobacterium wasabiae isolate PwO405 caused ASR symptoms including water‐soaked lesions and necrosis. Greater Pectobacterium levels were detected in plants inoculated with PwO405 compared to Ec101, suggesting that ASR can result in high Pectobacterium populations in potato stems. Significant additive or synergistic effects were not observed following co‐inoculation with these strains of V. dahliae and Pectobacterium. However, infection coefficients of V. dahliae and Ec101 were higher and premature senescence was greater in plants co‐inoculated with both pathogens compared to either pathogen alone in both trials, and V. dahliae levels were greater in basal stems of plants co‐inoculated with either Pectobacterium isolate. Overall, these results indicate that although co‐infection by Pectobacterium and V. dahliae does not always result in significant additive or synergistic interactions in potato, co‐infection can increase PED severity.     

In vitro antibacterial activity of nanoemulsion formulation on biofilm,AHL production,hydrolytic enzyme activity,and pathogenicity of Pectobacterium carotovorum sub sp. carotovorum

In the present investigation the in vitro activity of nanoemulsion (AUSN1) was evaluated against the plant pathogen Pectobacterium carotovorum sub sp. carotovorum causing the soft rot disease in numerous horticultural crops. With AUSN1 nanoemulsion treatment, minimum inhibitory concentration (MIC) of 0.09 mg ml⁻¹, minimum bacteriostatic concentration (MBC) of 1.30 mg ml⁻¹ and zone of inhibition of 2.90 cm was observed against P. carotovorum. This formulation was able to reduce the bacterial population by 32.2–51.6%, under biofilm formation condition and a complete elimination of population under normal cultivation conditions. When subjected AUSN1 treatment, reduction in biofilm formation, swarming and swimming motility was observed in P. carotovorum strain and also inhibited the N-acyl homoserine lactones (AHL) activity by 13.27–62.3% and AHL production by 32.4–76.13%. Reduction in exo polysaccharide (EPS) synthesis and hydrolytic enzymes production in P. carotovorum strain was observed due to AUSN1 treatment. Reduced hydrophobicity (36.9–56.4%) and adhesion to polystyrene (22.9–47.5%) and potato tuber surfaces (19.5–46.8%) was observed with AUSN1 treatment. All these collective evidences clearly show that, under laboratory conditions, AUSN1 treatment was able to inhibit the soft root incidence in potato tubers.     

Characterization of Pectobacterium species from Iran using biochemical and molecular methods

Characteristics of forty strains from macerated potato tubers and water-soaked lesions of some ornamental plants were studied in north parts of Iran. The causal organisms isolated from infected tissues were identified as Pectobacterium spp. based on their physiological and biochemical assays and confirmed by species and subspecies specific PCR and RFLP analysis of 16S–23S intergenic transcribed spacer region. Artificial inoculation of isolates to their related hosts generated the same symptoms on potato and ornamental plants, from which the same bacteria were isolated and identified. We detected two groups of atypical isolates in this study. The first group from potato classified as Pectobacterium carotovorum subsp. carotovorum by phenotypic tests but was unable to elicit HR on tobacco leaves, to grow at 37°C and to amplify the pel gene relevant to this subspecies. The second one from ornamental plants which was again characterized as Pectobacterium carotovorum subsp. carotovorum in biochemical assays, produced a unique ITS-RFLP profile different from all of known Pectobacterium species and subspecies. Our findings based on phylogenetic analysis using concatenated partial sequences of housekeeping genes mdh and gapA, indicated the occurrence of P. wasabiae as a novel species in potato storage in Iran. Furthermore we detected a distinct clade of Pectobacterium spp. from some ornamental plants including Schlumbergera bridgesii, Syngonium podophyllum and Iris spp.     

Characterization of <Emphasis Type="Italic">Dickeya</Emphasis> strains isolated from potato and river water samples in Finland

Plant pathogenic enterobacteria in the genera Pectobacterium and Dickeya (formerly classified as Erwinia) were isolated from diseased potato stems and tubers. The isolated bacteria were identified as P. atrosepticum, P. carotovorum and pathogens in the genus Dickeya with PCR tests. Furthermore, Dickeya strains were isolated from river water samples throughout the country. Phylogenetic analysis with 16S-23S rDNA intergenic spacer sequences suggested that the Dickeya strains could be divided into three groups, two of which were isolated from potato samples. Phylogenetic analysis with 16S rDNA sequences and growth at 39°C suggested that one of the groups corresponds to D. dianthicola, a quarantine pathogen in greenhouse cultivation of ornamentals, while two of the groups did not clearly resemble any of the previously characterised Dickeya species. Field trials with the strains indicated that D. dianthicola-like strains isolated from river samples caused the highest incidence of rotting and necrosis of potato stems, but some of the Dickeya strains isolated from potato samples also caused symptoms. The results showed that although P. atrosepticum is still the major cause of blackleg in Finland, virulent Dickeya strains were commonly present in potato stocks and rivers. This is the first report suggesting that Dickeya, originally known as a pathogen in tropical and warm climates, may cause diseases in potato in northern Europe.     

The genetic characterization of Xanthomonas arboricola pv. juglandis,the causal agent of walnut blight in Poland

Leaves and fruits of walnut trees exhibiting symptoms of bacterial blight were collected from six locations in Poland. Isolations on agar media resulted in 18 bacterial isolates with colony morphology resembling that of the Xanthomonas genus. PCR using X1 and X2 primers specific for Xanthomonas confirmed that all isolates belonged to this genus. In pathogenicity tests on unripe walnut fruits, all isolates caused typical black necrotic lesions covering almost the entire pericarp. Results of selected phenotypic tests indicated that characteristics of all isolates were the same as described for the type strain of Xanthomonas arboricola pv. juglandis. Genetic analyses (PCR MP, ERIC‐, BOX‐PCR and MLSA) showed similarities between the studied isolates and the reference strain of X. arboricola pv. juglandis CFBP 7179 originating from France. However, reference strains I‐391 from Portugal and LMG 746 from the UK were different. MLSA analysis of partial sequences of the fyuA, gyrB and rpoD genes of studied isolates and respective sequences from GenBank of pathotype strains of other pathovars of X. arboricola showed that the X. arboricola pv. juglandis isolates consisted of different phylogenetic lineages. An incongruence among MLSA gene phylogenies and traces of intergenic recombination events were proved. These data suggest that the sequence analysis of several housekeeping genes is necessary for proper identification of X. arboricola pathovars.     

Detection and identification of the crucifer pathogen, <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> pv. <Emphasis Type="Italic">campestris</Emphasis>, by PCR amplification of the conserved Hrp/type III secretion system gene <Emphasis Type="Italic">hrcC</Emphasis>

The development of a rapid detection method for Xanthomonas campestris pv. campestris (Xcc) in crucifer seeds and plants is essential for high-throughput certification purposes. Here we describe a diagnostic protocol for the identification/detection of Xcc by PCR amplification of fragments from the pathogenicity-associated gene hrcC. Under stringent conditions of amplification, a PCR product of 519 bp from hrcC was obtained from a collection of 46 isolates of Xcc, with the exception of two isolates from radish. No amplicons were obtained from 39 pure cultures of the phytopathogenic bacteria Xanthomonas campestris pv. cerealicola, X. campestris pv. juglandis, X. campestris pv. pelargonii, X. campestris pv. vitians, X. arboricola pv. pruni, X. axonopodis pv. phaseoli, X. axonopodis pv. vesicatoria, X. vesicatoria, Pseudomonas syringae pv. phaseolicola, P. syringae pv. syringae, P. syringae pv. tomato, P. fluorescens, P. marginalis, Pectobacterium atrosepticum, P. carotovorum subsp. carotovorum. In addition, PCR reactions were negative for fifty unidentified environmental isolates purified from the surface of crucifers. The PCR fragment was obtained from four strains previously classified as X. campestris pv. aberrans, X. campestris pv. armorociae, X. campestris pv. barbarae and X. campestris pv. incanae using pathogenicity assays. Our PCR protocol specifically detected Xcc in inoculated leaves, seeds and naturally infected leaves of crucifers.     

Rapid phylogenetic identification of members of the Pseudomonas syringae species complex using the rpoD locus

Phylogenies based on four loci confirmed the relatedness of all nine validly published species type strains within the Pseudomonas syringae species complex. To further establish the phylogenetic structure within the complex, all 67 pathovar type strains (with defined host ranges) were sequenced using a 578‐nucleotide rpoD locus. Since this locus encompassed that used in a previous seven‐locus study, it was possible to relate these strains to the existing phylogroup, genomospecies and binomial classifications. All species type strains were distinguished by relatively long branch lengths with all four loci, except for P. savastanoi, P. ficuserectae, P. meliae, P. amygdali and P. tremae, which were attributed to phylogroup 3. The grouping of P. tremae with these genomospecies‐2 species was surprising since this species was previously designated as the sole representative of genomospecies 5. The oat pathogen P. syringae pv. coronafaciens was also distinguished by relatively long branch lengths with all four loci. The rpoD phylogeny grouped all the pathovar type strains into major clades that corresponded to previously defined phylogroups, except for two genomospecies‐7 strains and P. caricapapayae, which were identified as a new phylogroup (6). There was good correlation between phylogroup and genomospecies classifications, except that two genomospecies‐8 strains (P. avellanae and P. syringae pv. theae) were found as a distinct clade within phylogroup 1 along with P. syringae pvs morsprunorum and actinidiae. The rpoD locus will provide a common reference framework to improve monitoring and surveillance of these important pathogens.     

Pathogenicity and molecular phylogenetic analysis reveal a distinct position of the banana fingertip rot pathogen among the Burkholderia cenocepacia genomovars

Banana (Musa spp.) is one of the most widely cultivated subtropical fruits around the globe. Banana cultivation has been extensively increased in southeastern Iran over the last two decades. Recently, banana fruits possessing rotten and blackened fingertip symptoms were observed in Sistan-Baluchestan, Iran. Isolation and characterization of the causal agent showed that the pathogen belongs to the multifaceted bacterial species Burkholderia cenocepacia. Pathogenicity tests and host range assays showed that the strains were pathogenic on banana, as well as carrot, onion and potato. All the strains were resistant to 50 mg L⁻¹ rifampicin and 200 mg L⁻¹ copper sulphate. Phylogenetic analysis of 16S rRNA and recA gene sequences showed that the strains belong to two different genomovars of B. cenocepacia (III-A and III-B), which also include environmental and cystic fibrosis associated strains of the species. The results obtained from recA phylogeny were confirmed using multilocus sequence analysis (MLSA), although MLSA showed that the banana strains were clustered as a novel phylogroup among the members of both genomovars. Banana-pathogenic B. cenocepacia strains isolated in Iran were different from the strains isolated in Taiwan, as the ‘B. cepacia epidemic strain marker’ reported in the Taiwanese strains was absent from Iranian strains. To the authors’ knowledge, this is the first MLSA-based study on the banana-pathogenic strains of B. cenocepacia. However, further in-depth molecular studies are needed to decipher the relationships between the banana fingertip rot pathogen and the clinical strains of B. cenocepacia.     

Multilocus sequence analysis reveals a novel phylogroup of Xanthomonas euvesicatoria pv. perforans causing bacterial spot of tomato in Iran

A multilocus sequence analysis (MLSA) was performed on five housekeeping genes (fusA, gapA, gltA, lacF and lepA) of 22 Xanthomonas euvesicatoria strains recently isolated from alfalfa, pepper and tomato plants in Iran. In addition, 161 strains isolated worldwide from pepper, poinsettia, rose and tomato plants were included in the analysis. All X. euvesicatoria pv. perforans isolates from tomato plants in Iran clustered in a monophyletic group, although five MLSA haplotypes were detected among them. The Iranian tomato strains presented 10 nucleotide differences in the lepA gene sequences compared to the known worldwide population of X. euvesicatoria pv. perforans. Statistical analyses revealed a recombination event that had occurred in the lepA gene of the strains isolated from tomato in Iran. BOX‐PCR analysis confirmed the inclusion of Iranian tomato strains within X. euvesicatoria pv. perforans. Furthermore, X. euvesicatoria pv. euvesicatoria strains isolated from pepper in Iran differed in one nucleotide in the lepA gene sequence from the known worldwide population of the pathovar, and clustered in a group containing strains isolated in Nigeria. The strains isolated from alfalfa in Iran clustered with the type strain of X. euvesicatoria pv. alfalfae. Altogether, the results reveal the existence of a phylogenetically novel population of X. euvesicatoria pv. perforans in Iran which needs further in‐depth analysis to pinpoint the epidemiological impact of these strains.     

Disease protection and growth promotion of potatoes (Solanum tuberosum L.) by Paenibacillus dendritiformis

One of the challenges in developing plant‐beneficial bacterial agents for agricultural application is ensuring that an effective selection and screening procedure is in place. The sporadic success of using bacterial agents in the field is usually due to the inability of added bacteria to compete with the local microorganisms. In the present study, the effectiveness of Paenibacillus dendritiformis, a unique pattern‐forming, Gram‐positive, soil bacterium, to reduce disease indices and increase yield in potato crops was examined. This bacterium was chosen as a potential agent based on genome analysis carried out in previous studies. In vitro laboratory experiments, as well as three greenhouse and one field experiment, were conducted. The results show that, in agreement with the hypothesis, P. dendritiformis significantly reduced the maceration area of tuber slices infected by Pectobacterium carotovorum subsp. carotovorum, significantly reduced disease indices in greenhouse experiments and significantly increased tuber yield of infected plants in the field. This work demonstrates the potential of preliminary screening based on genome analysis to identify effective biocontrol agents.     

A molecular marker for the specific detection of new pathotype 5‐like strains of Plasmodiophora brassicae in canola

Clubroot of crucifers, caused by Plasmodiophora brassicae, is managed in canola (Brassica napus) by the deployment of resistant cultivars. Recently, however, new strains of P. brassicae have been detected in Alberta, Canada, that can overcome this resistance. Some of these strains are classified as pathotype 5 on the differential system of Williams, but are distinguished by their ability to overcome host resistance. In order to expedite the identification of these new pathotype 5‐like strains, three primer sets were developed based on the 18S‐ITS region of the pathogen. With primers P5XF3 and P5XR3, a 127 bp product was amplified from all new pathotype 5‐like strains following optimized PCR analysis. A TaqMan probe‐based quantitative assay was also developed. These protocols could be used to detect as little as 0.5 pg P. brassicae DNA, and as few as 10⁴ mL^?1 pathogen resting spores; infection of host tissues could be detected as soon as 4 days after inoculation. The PCR and qPCR assays described in this study represent useful tools for the rapid and reliable diagnosis and quantification of new pathotype 5‐like strains of P. brassicae.     

Characterization of Pectobacterium carotovorum subsp. carotovorum and brasiliense from diseased potatoes in Kenya

Using a DNA-based typing method, 48 bacterial strains isolated from infected potato (Solanum tuberosum) tubers originating from Kenya were characterized. The pel gene specific primers showed that all the 48 bacterial strains were pectolytic. Subspecies-specific primers EXPCCF/EXPCCR and Br1f/L1r identified 66 % of the strains as Pectobacterium carotovorum subsp. carotovorum while 34 % were identified as Pectobacterium carotovorum subsp. brasiliense based on their characteristic band sizes of 550 and 322 bp, respectively. Amplification of the 16S-23S rDNA (ITS) region did not yield observable differences in banding patterns between the Kenyan strains. However, PCR-RFLP analysis together with partial nucleotide sequences of the housekeeping mdh and gapA genes confirmed the results obtained by the specific primers. Phylogenetic analysis of the concatenated partial gene sequences grouped Pectobacterium carotovorum subsp. carotovorum and Pectobacterium carotovorum subsp. brasiliense Kenyan strains together with those identified in other parts of the world with 90 % and 99 % bootstrap support values, respectively. Pathogenicity assays using representative Kenyan strains demonstrated varied levels of tuber maceration ability. The Pectobacterium carotovorum subsp. carotovorum and Pectobacterium carotovorum subsp. brasiliense Kenyan strains were shown to be less aggressive in causing soft rot when compared to type strains. This study describes for the first time the genetic diversity of pectolytic bacteria causing soft rot disease of potatoes in Kenya.     

Identification and characterization of Xanthomonas albilineans causing sugarcane leaf scald in China using multilocus sequence analysis

Xanthomonas albilineans is the causal agent of leaf scald, a disease that can cause considerable damage to sugarcane industries. This study analysed the phylogenetic relationship of 14 samples of X. albilineans from China and 13 reference strains retrieved from the GenBank database by multilocus sequence analysis (MLSA). To reach this goal, five housekeeping genes of X. albilineans were amplified from diseased leaves and sequenced: gyrB, abc, rpoD, atpD and glnA. Based on the concatenated sequence of these genes (4473 nt), the 14 samples of X. albilineans from China had 99.9–100% sequence identity with one another and with five strains of the pathogen from the French West Indies and the USA (Florida). The 27 samples or strains of X. albilineans were distributed in two distinct clades in the MLSA-based phylogenetic tree. Clade 1 was formed by four strains of the pathogen from Fiji, Papua New Guinea and the USA. All the other strains from worldwide locations, including the 14 samples from China, were grouped in clade 2. This latter clade included all strains of the pathogen that were associated with outbreaks of leaf scald that have occurred over the last two decades, especially in the Caribbean islands and the USA. The very low diversity of X. albilineans in four Chinese provinces suggests recent spread of a single strain (from genetic group PFGE-B) of the leaf scald pathogen within China.     

Occurrence of Pectobacterium wasabiae in potato field samples

During the growing seasons of 1996 and 1997, samples of potato stems and tubers with symptoms of blackleg and soft rot were collected in different regions in Poland. After growing to pure cultures on crystal violet pectate (CVP) medium, isolates of bacteria were identified as Pectobacterium spp. on the basis of their ability to degrade pectate and with the use of biochemical tests. About 43 % strains isolated from 122 different plant samples were identified as Pectobacterium carotovorum subsp. carotovorum, whereas the rest of the pectinolytic bacteria was identified as Pectobacterium atrosepticum. A recent screening of these isolates with recA PCR-RFLP allowed identification of 18 different RFLP groups within the tested P. c. subsp. carotovorum strains. The third largest group of the tested P. c. subsp. carotovorum strains (14 %), which were assigned to the profile 3 recA PCR-RFLP, was re-identified as Pectobacterium wasabiae (formerly Erwinia carotovora subsp. wasabiae) on the basis of recA and 16S rRNA genes sequences. About 50 % of P. wasabiae isolated from potato, in contrast to horseradish isolates of P. wasabiae, have an ability to grow at 37°C and some of them grow on media containing 5 % of NaCl. In a pathogenicity test with 11 strains of P. wasabiae these strains showed a high capacity to rot potato tubers.     

Meloidogyne luci,a new root‐knot nematode parasitizing potato in Portugal

In 2013, during a field survey conducted in Portugal on potato, Solanum tuberosum, an unusual esterase (EST) phenotype was detected in a root‐knot nematode (RKN) from potato roots collected in Coimbra. This Portuguese isolate was purified and maintained on tomato, S. lycopersicum, and morphological, biochemical and molecular characteristics were studied. Perineal pattern morphology was highly variable, similar to Meloidogyne ethiopica and not useful for identification. The EST phenotype, from young egg‐laying females, displayed three bands similar to the Brazilian M. luci (L3) and distinct from M. ethiopica (E3). Phylogenetic analyses of mitochondrial cytochrome oxidase subunit I and the mitochondrial DNA region between COII and 16S rRNA genes revealed that the Portuguese isolate grouped with M. luci isolates close to M. ethiopica isolates. However, considering the ITS1‐5.8S‐ITS2 region, the Portuguese isolate grouped with isolates of M. luci, M. ethiopica and M. hispanica, which limits the confidence of this region for M. luci diagnosis, and its differentiation from other species with morphological similarities. The M. luci pathogenicity to potato was also assessed in 16 commercial cultivars and compared with M. chitwoodi, considered to be a quarantine RKN species by EPPO. All potato cultivars were susceptible to both Meloidogyne species with gall indices of 5 and higher reproduction factor values ranging from 12.5 to 122.3, which suggests that M. luci may constitute a potential threat to potato production. In the present study, M. luci is reported for the first time attacking potato in Portugal.     

Characterization of <Emphasis Type="Italic">Dickeya</Emphasis> and <Emphasis Type="Italic">Pectobacterium</Emphasis> strains obtained from diseased potato plants in different climatic conditions of Norway and Poland

Soft rot and blackleg of potato caused by pectinolytic bacteria lead to severe economic losses in potato production worldwide. To investigate the species composition of bacteria causing soft rot and black leg of potato in Norway and Poland, bacteria were isolated from potato tubers and stems. Forty-one Norwegian strains and 42 Polish strains that formed cavities on pectate medium were selected for potato tuber maceration assays and sequencing of three housekeeping genes (dnaX, icdA and mdh) for species identification and phylogenetic analysis. The distribution of the species causing soft rot and blackleg in Norway and Poland differed: we have demonstrated that mainly P. atrosepticum and P. c. subsp. carotovorum are the causal agents of soft rot and blackleg of potatoes in Norway, while P. wasabiae was identified as one of the most important soft rot pathogens in Poland. In contrast to the other European countries, D. solani seem not to be a major pathogen of potato in Norway and Poland. The Norwegian and Polish P. c. subsp. carotovorum and P. wasabiae strains did not cluster with type strains of the respective species in the phylogenetic analysis, which underlines the taxonomic complexity of the genus Pectobacterium. No correlation between the country of origin and clustering of the strains was observed. All strains tested in this study were able to macerate potato tissue. The ability to macerate potato tissue was significantly greater for the P. c. subsp. carotovorum and Dickeya spp., compared to P. atrosepticum and P. wasabiae.     

Characterization of Pectobacterium carotovorum subsp. odoriferum causing soft rot of stored vegetables

Pectobacterium carotovorum subsp. odoriferum has been generally considered to have a narrow host range and has been isolated most often from chicory. Research was conducted to identify 91 Pectobacterium spp. strains isolated from different vegetables in Europe, North and South America, Asia, and Africa, and to compare their ability to cause disease in chicory and potato. Among the 91 strains, 22 strains from Europe were identified as P. c. subsp. odoriferum. Based on phylogenetic analysis of 16S rDNA, recA, and rpoS gene sequences, strains isolated from stored vegetables clustered together with the type strain of P. c. subsp. odoriferum and clustered separately from the P. c. subsp. carotovorum isolates. Eleven strains previously identified as P. c. subsp. carotovorum were reclassified as P. c. subsp. odoriferum. All P. c. subsp. odoriferum isolates were able to cause soft rot symptoms on chicory and potato. Moreover, the symptoms on potatoes were more severe at temperatures from 15 to 37 °C with P. c. subsp. odoriferum isolates than with P. atrosepticum or P. c. subsp. carotovorum isolates. Tissue maceration by P. c. subsp. odoriferum isolates was highest at 28 °C, and at that temperature tissue maceration was two-times greater for P. c. subsp. odoriferum isolates than for P. c. subsp. carotovorum isolates. Symptoms on inoculated chicory leaves were more severe with P. c. subsp. odoriferum (regardless of origin) than with other subspecies or species. To our knowledge, this is the first report that P. c. subsp. odoriferum occurs on a wide range of vegetables and has the ability to cause soft rot during potato storage.