<Emphasis Type="Italic">Pseudomonas syringae</Emphasis> pv. <Emphasis Type="Italic">alliifistulosi</Emphasis> pv. nov., the causal agent of bacterial leaf spot of onions

In 1972, bacterial leaf spot of onion (BLSO) was first recorded in Japan by Goto. The pathogen was considered as a pathovar of Pseudomonas syringae specifically causing disease on onion and Welsh onion, but it has not been taxonomically investigated in detail. In 2012 and 2014, a disease suspected as BLSO re-emerged on onion in Shizuoka and Hyogo Prefectures, Japan, respectively. A pathogenic bacterium isolated from the infected onions was thought to be the BLSO agent after preliminary examinations. Strains isolated from BLSO in 1969, 1986, 1987, 2012 and 2014 were characterized and compared with the causal agent of bacterial blight of leek (P. syringae pv. porri), which causes similar symptoms on Allium plants. The result of rep-PCR distinguished the BLSO agent from P. syringae pv. porri. Multilocus sequence analysis on housekeeping genes and hrp genes encoding the type-III secretion system revealed that the strains of the BLSO agent clustered independently of P. syringae pv. porri. The BLSO agent and P. syringae pv. porri also differed in utilization of erythritol, dl-homoserine, glutaric acid and other bacteriological characteristics and caused different reactions on onion, Welsh onions, chives, shallot, rakkyo, leek, garlic and Chinese chive. Thus, the BLSO agent clearly differs from P. syringae pv. porri and is considered to be a new pathovar of P. syringae. The name P. syringae pv. alliifistulosi is proposed with pathotype strain ICMP3414.     

Genetic variation among <Emphasis Type="Italic">Fusarium</Emphasis> isolates from onion,and resistance to <Emphasis Type="Italic">Fusarium</Emphasis> basal rot in related <Emphasis Type="Italic">Allium</Emphasis> species

The aim of this research was to study levels of resistance to Fusarium basal rot in onion cultivars and related Allium species, by using genetically different Fusarium isolates. In order to select genetically different isolates for disease testing, a collection of 61 Fusarium isolates, 43 of them from onion (Allium cepa), was analysed using amplified fragment length polymorphism (AFLP) markers. Onion isolates were collected in The Netherlands (15 isolates) and Uruguay (9 isolates), and received from other countries and fungal collections (19 isolates). From these isolates, 29 were identified as F. oxysporum, 10 as F. proliferatum, whereas the remaining four isolates belonged to F. avenaceum and F. culmorum. The taxonomic status of the species was confirmed by morphological examination, by DNA sequencing of the elongation factor 1-α gene, and by the use of species-specific primers for Fusarium oxysporum, F. proliferatum, and F. culmorum. Within F. oxysporum, isolates clustered in two clades suggesting different origins of F. oxysporum forms pathogenic to onion. These clades were present in each sampled region. Onion and six related Allium species were screened for resistance to Fusarium basal rot using one F. oxysporum isolate from each clade, and one F. proliferatum isolate. High levels of resistance to each isolate were found in Allium fistulosum and A. schoenoprasum accessions, whereas A. pskemense, A. roylei and A. galanthum showed intermediate levels of resistance. Among five A. cepa cultivars, ‘Rossa Savonese’ was also intermediately resistant. Regarding the current feasibility for introgression, A. fistulosum, A. roylei and A. galanthum were identified as potential sources for the transfer of resistance to Fusarium into onion.     

A new pathovar of <Emphasis Type="Italic">Pseudomonas syringae</Emphasis>, pathovar <Emphasis Type="Italic">allii,</Emphasis> isolated from onion plants exhibiting symptoms of blight

Bacterial pathogens of onion (Allium cepa) plants and their undetected presence in seed can cause substantial losses to onion producers. In this study, 23 Pseudomonas syringae strains were isolated from five onion plants and 18 onion seeds. The symptoms on leaves and seed stalks were irregular lesions with necrotic centres and water soaked margins. The aim of the study was to characterize these P. syringae strains using Biolog GN III carbon source utilization, multilocus sequence typing (MLST) based on partial sequences of four housekeeping genes (cts, gapA, gyrB and rpoD), and to determine whether or not the strains were pathogenic on onion (cv. Granex 33), chive (Allium schoenoprasum cv. Grasiue), leek (Allium porrum cv. Giant Italian) and spring onion (Allium fistulosum cv. Salotte) plants. Both Biolog analysis and MLST analysis separated onion strains into two clusters, one supporting the existence of a new pathovar of P. syringae, and the other corresponding to P. syringae pv. porri. Pseudomonas syringae strains belonging to the new pathovar we pathogenic only on onion plants of the Allium spp. tested. The results of this study revealed that bacterial blight of onion in South Africa is caused by two pathovars of P. syringae sensu lato, namely, the newly described pathovar, allii, and P. syringae pv. porri. The symptoms caused by these two pathovars in the field were indistinguishable.     

Real-time detection of <Emphasis Type="Italic">Phytophthora nicotianae</Emphasis> and <Emphasis Type="Italic">P. citrophthora</Emphasis>in citrus roots and soil

Two primers, specific for Phytophthora nicotianae (Pn6) and P. citrophthora (Pc2B), were modified to obtain Scorpion primers for real-time identification and detection of both pathogens in citrus nursery soils and roots. Multiplex PCR with dual-labelled fluorogenic probes allowed concurrent identification of both species ofPhytophthora among 150 fungal isolates, including 14 species of Phytophthora. Using P. nicotianaespecific primers a delayed and lower fluorescence increase was also obtained from P. cactorumDNA. However, in separate real-time amplifications, the aspecific increase of fluorescence from P. cactorum was avoided by increasing the annealing temperature. In multiplex PCR, with a series of 10-fold DNA dilutions, the detection limit was 10 pg l^-1 for P. nicotianaeand 100 pg l^–1 for P. citrophthora, whereas in separate reaction DNA up to 1 pg l^-1 was detected for both pathogens.Simple and rapid procedures for direct DNA extraction from soil and roots were utilised to yield DNA whose purity and quality was suitable for PCR assays. By combining these protocols with a double amplification (nested Scorpion-PCR) using primers Ph2-ITS4 amplifying DNA from the main Phytophthora species (first round) and PnB5-Pn6 Scorpion and Pc2B Scorpion-Pc7 (second round), it was possible to achieve real-time detection of P. nicotianaeand P. citrophthora from roots and soil. The degree of sensitivity was similar to that of traditional detection methods based on the use of selective media. The analyses of artificially and naturally infested soil showed a high and significant correlation between the concentration of pathogen propagules and the real-time PCR cycle threshold.     

<Emphasis Type="Italic">Eutypa lata</Emphasis>, the causal agent of dieback in red currant (<Emphasis Type="Italic">Ribes rubrum</Emphasis>) and gooseberry (<Emphasis Type="Italic">R. uva-crispa</Emphasis>) in the Netherlands

Dieback of red currant (Ribes rubrum) and gooseberry (Ribes uva-crispa) is an increasing problem in commercial fields in the Netherlands. Field surveys were done in 2006–2007 and samples with dieback symptoms were analysed. In this study the causal agent was diagnosed as Eutypa lata, based on morphological characteristics and rDNA-ITS sequence data. The field surveys revealed the presence of the anamorph and teleomorph states of the fungus produced on dead infected currant wood. Eutypa lata is a vascular pathogen of many woody plants. Related fungi from the same family Diatrypaceae are difficult to distinguish from E. lata based on morphological features. The genetic variability of E. lata was compared by rDNA-ITS sequencing of isolates from different hosts and origins. Within the E. lata isolates little variability in the ITS sequences was observed. Phylogenetic analysis showed no clear subdivisions within the species. Eutypa lata strains isolated from the different hosts were closely related, indicating that there is no direct evidence for host specificity.     

Reaction of <Emphasis Type="Italic">Leersia</Emphasis> grasses to <Emphasis Type="Italic">Xanthomonas oryzae</Emphasis> pv. <Emphasis Type="Italic">oryzae</Emphasis> collected from Japan and Asian countries

The present study was conducted to determine if there is specificity in the host-pathogen relationship between the isolates of Xanthomonas oryzae pv. oryzae, the causal bacterium for rice blight and Leersia grasses, the alternative weed hosts of the disease. Plants of three species of Leersia, namely, L. sayanuka, L. oryzoides and L. japonica, were collected from various parts of Japan and were inoculated with the X. oryzae pv. oryzae isolates obtained from various locations in Japan and from 11 Asian countries. Four L. sayanuka plants were found susceptible to all Race II isolates and some Race I isolates, but were resistant to all Race III isolates. Race III is known to have a wider range pathogenicity to rice cultivar groups compared with Race I and II. Although the reactions of two L. oryzoides plants to Race I and II isolates were similar to that of L. sayanuka, the L. oryzoides plant collected from Niigata Prefecture showed a susceptible reaction to some Race III isolates. On the other hand, L. japonica plants gave reactions different those of L. sayanuka and L. oryzoides, with two plants of L. japonica found to be resistant to all test isolates collected from Japan. The Asian isolates exhibited a wide host range against the international differential rice cultivars, but almost all of them were avirulent to Leersia plants. These results indicate that the relationship between the pathogenicity of the causal bacterium and the resistance of host plants is very complex, and suggest that pathogenic diversity of X. oryzae pv. oryzae might be related to the resistance of Leersia spp.     

Occurrence and distribution of <Emphasis Type="Italic">Phytophthora</Emphasis> species in European chestnut stands,and their association with Ink Disease and crown decline

The Phytophthora complex associated with Castanea sativa Mill. was investigated in five European countries in 35 regions and with respect to various domestication levels. Annual precipitation and length of drought season were the main parameters that regulated the presence of Phytophthora species in the chestnut stands. Seven species of Phytophthora were detected; three of these, P. megasperma, P. cryptogea and P. syringae had not been previously reported on sweet chestnut. P. cinnamomi. P. cambivora and P. citricola were most frequently isolated. P. cinnamomi and P. cambivora were the species significantly associated with declining trees with symptoms of Ink Disease. P. cinnamomirequired distinct ecological conditions compared to the other species. P. cinnamomi was never detected in sites characterized by minimum temperatures below 1.4 °C, maximum temperature above 28 °C, or soil pH below 5.4. The results obtained provide useful information for modeling the probability of Ink Disease, crown decline and associated Phytophthora species in chestnut groves in global climatic change scenarios.     

Germination of <Emphasis Type="Italic">Plasmodiophora brassicae</Emphasis> resting spores stimulated by a non-host plant

Plant-induced germination of Plasmodiophora brassicae resting spores was studied in a laboratory experiment. Spore reaction was analysed in nutrient solution with exudates from growing roots of different plant species – one host plant (Brassica rapa var. pekinensis) and four non-host plants (Lolium perenne, Allium porrum, Secale cereale and Trifolium pratense) – and in controls with distilled water and nutrient solution. It was found that root exudates from L. perenne stimulated spore germination more than exudates from the other plants, including those from the host plant. The effect could not be explained by differences in the nutritional composition of the solutions due to differential uptake of the plant species, or by differences in root activity, measured as exudation of soluble sugars. This is the first time such a separation of factors has been done in analysing the influence of plants on P. brassicae germination. Although stimulation of P. brassicae resting spore germination is not restricted to the presence of host plants, it seems to vary depending on the plant species.     

Phylogenetic investigations in the genus <Emphasis Type="Italic">Pseudoperonospora</Emphasis> reveal overlooked species and cryptic diversity in the <Emphasis Type="Italic">P. cubensis</Emphasis> species cluster

Pseudoperonospora cubensis is one of the most devastating diseases of cucurbitaceous crops. The pathogen has a worldwide distribution and occurs in all major cucurbit growing areas. It had been noticed for the first time at the end of the 19th century, but it became a globally severe disease as recently as 1984 in Europe and 2004 in North America. Despite its economic importance, species concepts in Pseudoperonospora are debated. Here, we report that the genus Pseudoperonospora contains cryptic species distinct from the currently accepted ones. Pseudoperonospora on Celtis is split into two phylogenetic lineages and Pseudoperonospora humuli is confirmed as a species distinct from the Cucurbitaceae-infecting lineages. A cryptic species occupying a basal position within the Pseudoperonospora cubensis complex is revealed to be present on Humulus japonicus, thus providing evidence that the host jump that gave rise to Pseudoperonospora cubensis likely occurred from hops. Notably, Cucurbitaceae infecting pathogens are present in two cryptic sister species or subspecies. Clade 1 contains primarily specimens from North America and likely represents Pseudoperonospora cubensis s.str.. Pre-epidemic isolates in clade 2 originate from Japan and Korea, suggesting this cryptic species or subspecies is indigenous to East Asia. Recent samples of this lineage from epidemics in Europe and the United States cluster together with clade 2. It thus seems possible that this lineage is associated with the recent severe epidemics of cucurbit downy mildew and is now naturalised in North America and Europe.     

Spread of levan-positive populations of <Emphasis Type="Italic">Pseudomonas savastanoi</Emphasis> pv. <Emphasis Type="Italic">savastanoi</Emphasis>, the causal agent of olive knot,in central Italy

Mixtures of wet vegetable wastes (Brassica, carrot or onion) and dry onion waste were composted at 50 °C for 7 days. The incorporation of the raw or composted vegetable waste mixtures into sandy loam, silt and peat soils reduced the viability of sclerotia of S. cepivorum in glasshouse pot bioassays. The reduction in viability was dependent on waste type, rate of incorporation, duration of exposure and soil type. Onion waste was the most effective waste type in reducing sclerotia viability in all three soils. The Brassica and carrot wastes were as effective as the onion waste in silt soil but less effective in sandy loam and peat soil. A 50% w/w incorporation rate of the wastes gave the largest reduction in viability, with an increase in reduction over time. Composted onion waste reduced sclerotia viability under glasshouse and field conditions although the effect was smaller in the field. Composted onion waste incorporated into soil at 50% w/w reduced the incidence of Allium white rot on onion seedlings in glasshouse pot tests. Incidence and control of the disease differed with soil type. The most consistent control was achieved in peat soil whereas no control was observed in silt soil. Incorporation of the waste 2 months prior to sowing or transplanting reduced seedling emergence in sandy loam soil and growth in all three soil types. The potential for field application of composted vegetable wastes as a sustainable method for control of Allium white rot and waste disposal is discussed.     

Characterization of <Emphasis Type="Italic">Inago1</Emphasis> and <Emphasis Type="Italic">Inago2</Emphasis> retrotransposons in <Emphasis Type="Italic">Magnaporthe oryzae</Emphasis>

From the genome of a Japanese field isolate of the rice blast fungus, Magnaporthe oryzae, we newly identified Inago1 and Inago2 LTR retrotransposons. Both elements were found to be Ty3/gypsy-like elements whose copies were dispersed within the genome of Magnaporthe spp. isolates infecting rice and other monocot plants. Southern hybridization patterns of nine re-isolates derived from conidia of the strain Ina168 produced after a methyl viologen treatment were not changed, indicating that the insertion pattern of Inago elements is relatively stable.     

Conventional PCR and real time quantitative PCR detection of <Emphasis Type="Italic">Phytophthora cryptogea</Emphasis> on <Emphasis Type="Italic">Gerbera jamesonii</Emphasis>

A conventional PCR and a SYBR Green real-time PCR assays for the detection and quantification of Phytophthora cryptogea, an economically important pathogen, have been developed and tested. A conventional primer set (Cryp1 and Cryp2) was designed from the Ypt1 gene of P. cryptogea. A 369 bp product was amplified on DNA from 17 isolates of P. cryptogea. No product was amplified on DNA from 34 other Phytophthora spp., water moulds, true fungi and bacteria. In addition, Cryp1/Cryp2 primers were successfully adapted to real-time PCR. The conventional PCR and real-time PCR assays were compared. The PCR was able to detect the pathogen on naturally infected gerbera plants and on symptomatic artificially infected plants collected 21 days after pathogen inoculation. The detection limit was 5 × 10³ P. cryptogea zoospores and 16 fg of DNA. Real-time PCR showed a detection limit 100 times lower (50 zoospores, 160 ag of DNA) and the possibility of detecting the pathogen in symptomless artificially infected plants and in the re-circulating nutrient solution of closed soilless cultivation systems.     

<Emphasis Type="Italic">Fusarium ershadii</Emphasis> sp. nov., a Pathogen on <Emphasis Type="Italic">Asparagus officinalis</Emphasis> and <Emphasis Type="Italic">Musa acuminata</Emphasis>

Two Fusarium strains, isolated from Asparagus in Italy and Musa in Vietnam respectively, proved to be members of an undescribed clade within the Fusarium solani species complex based on phylogenetic species recognition on ITS, partial RPB2 and EF-1α gene fragments. Macro- and micro-morphological investigations followed with physiological studies done on this new species: Fusarium ershadii sp. nov can be distinguished by its conidial morphology. Both isolates of Fusarium ershadii were shown to be pathogenic to the monocot Asparagus officinalis when inoculated on roots and induced hollow root symptoms within two weeks in Asparagus officinalis seedlings. In comparison mild disease symptoms were observed by the same strains on Musa acuminata seedlings.     

Epidemiology of <Emphasis Type="Italic">Pseudomonas syringae</Emphasis> pv. <Emphasis Type="Italic">syringae</Emphasis> on tomato

Leaf spot of tomato, incited by Pseudomonas syringae pv. syringae, has been reported recently in Italy on grafted and non-grafted tomato plants (scion Cuore di Bue, rootstock Solanum lycopersicum x Solanum hirsutum cv. Beaufort). In some greenhouses, more than 80% of plants were affected, with a marked reduction in yield. This work was undertaken in order to understand the effect of the number of hours of incubation at high relative humidity (r.h.) and temperature as well as the effect of the presence of wounds at infection time on the development of leaf spot. A difference in sensitivity to leaf spot was observed in the various cultivars tested, in terms of severity of P. syringae pv. syringae, with “Cuore di Bue” being the most susceptible of these cultivars. The development of leaf spot is mostly favored by the presence of wounds, at temperatures between 15 and 20°C. The severity of the disease is lower at 10 and 25°C and very low at 30°C. Under the most favorable temperature conditions, the presence of wounds is sufficient to allow the development of the pathogen immediately upon incubation at high r.h. The effect of wounds and the relatively low requirement of hours of incubation at high r.h. suggest the need for careful management and handling of plants when temperatures range between 15 and 25°C, and particularly within 15 and 20°C. All operations carried out, particularly at transplant and immediately after, should avoid the creation of wounds.     

Multigene phylogenetic analysis of inter- and intraspecific relationships in <Emphasis Type="Italic">Venturia nashicola</Emphasis> and <Emphasis Type="Italic">V. pirina</Emphasis>

Isolates of Venturia species isolated from pear in Japan, China, Taiwan and Israel were used in this study to analyze their molecular phylogenetic relationship. The nucleotides of rDNA-ITS, partial β-tubulin and elongation factor 1α genes were sequenced directly after PCR. Based on these sequence data two phylogenetic groups could be distinguished. Isolates collected from Asian pears such as Japanese and Chinese pears formed a distinct evolutionary lineage from those derived from European and Syrian pears. This result corroborated the early taxonomic separation of V. nashicola from V. pirina. In addition, trees from single-locus data sets and the combined data set showed that all isolates of V. nashicola were included in a monophyletic group and representative isolates of five pathological races originating from different locations and cultivars formed a single lineage. In contrast, two distinct evolutionary lineages were revealed in V. pirina and isolates of five races were scattered in two lineages. Israeli isolates of race 2 as well as two Japanese isolates of V. pirina formed a distinct lineage from other isolates of this species, while other Israeli isolates belonging to races 1, 3, 4, and 5 were closely related to each other and formed another lineage. It was indicated that the evolution of pathological races in V. nashicola might have occurred relatively recently as compared with V. pirina.     

Pathogenicity,colony morphology and diversity of isolates of <Emphasis Type="Italic">Guignardia citricarpa</Emphasis> and <Emphasis Type="Italic">G. mangiferae</Emphasis> isolated from <Emphasis Type="Italic">Citrus</Emphasis> spp.

In the present study, the pathogenicity of 36 isolates of Guignardia species isolated from asymptomatic ‘Tahiti’ acid lime fruit peels and leaves, ‘Pêra-Rio’ sweet orange leaves and fruit peel lesions, and a banana leaf were characterized. For pathogenicity testing, discs of citrus leaves colonized by Phyllosticta citricarpa under controlled laboratory conditions were kept in contact with the peels of fruit that were in susceptible states. In addition, pathogenicity was related to morphological characteristics of colonies on oatmeal (OA) and potato dextrose agar (PDA). This allowed the morphological differentiation between G. citricarpa and G. mangiferae. Polymerase chain reactions (PCRs) were also used to identify non-pathogenic isolates based on primers specific to G. citricarpa. A total of 14 pathogenic isolates were detected during pathogenicity tests. Five of these were obtained from leaf and fruit tissues of the ‘Tahiti’, which until this time had been considered resistant to the pathogen. Given that the G. citricarpa obtained from this host was pathogenic, it would be more appropriate to use the term insensitive rather than resistant to categorize G. citricarpa. A non-pathogenic isolate was obtained from lesions characteristic of citrus black spot (CBS), indicating that isolation of Guignardia spp. under these conditions does not necessarily imply isolation of pathogenic strains. This also applied to Guignardia spp. isolates from asymptomatic citrus tissues. Using fluorescent amplified fragment length polymorphism (fAFLP) markers, typically pathogenic isolates were shown to be more closely related to one another than to the non-pathogenic forms, indicating that the non-pathogenic isolates display higher levels of genetic diversity.     

Monitoring of <Emphasis Type="Italic">Phytophthora</Emphasis> species on fruit trees in Bulgaria

Disease on fruit trees in Bulgaria caused by Phytopthora cactorum and P. citrophthora was found in the period 1998–1999. Leaves of some trees become reddish during July, and later in the season fall off. Infected trees die during the same season, or the next season. Observations on symptom development and spread of Phytophthora root and crown rot of fruit trees was undertaken from 1999 to 2009. Disease incidence is between 2% and 14% in some gardens and nurseries. The disease was registered in the regions of Plovdiv, Kjustendil, Sliven, Yambol, Karnobat, Bourgas and Svishtov. Samples from infected plant tissues were taken and isolations were done on selective PARP media, or by applying a baiting bioassay. Based on morphological and cultural characteristics and temperature requirements the following Phytophthora species have been identified: Phytophthora cactorum, P. citrophthora, P. drechsleri, P. cryptogea, hybrid and Pythium. Pathogenicity of the isolates was tested on green apple fruits or one-year-old apple rootstocks. Laboratory studies of the effect of temperature on mycelia growth showed that most isolates can grow from 5° up to 30°C, with an optimum from 18° to 25°C. Only three strains grew at 35–36°C, two developed slowly, one grew well. The optimal pH for mycelia development was tested. Aiming at control of disease, in vivo pot trials have been carried out for studying resistance of rootstocks to P. cactorum. At the end of the growing season a good level of resistance has been shown in the rootstocks M29C, Gizela 6, and MAXMA 14.     

Pathogenic variation and molecular characterization of <Emphasis Type="Italic">Fusarium</Emphasis> species isolated from wilted Welsh onion in Japan

Thirty-two isolates of Fusarium species were obtained from wilted Welsh onion (Allium fistulosum) grown on nine farms from six regions in Japan and identified as F. oxysporum (18 isolates), F. verticillioides (7 isolates), and F. solani (7 isolates). The pathogenicity of 32 isolates was tested on five commercial cultivars of Welsh onion and two cultivars of bulb onion in a seedling assay in a greenhouse. The Fusarium isolates varied in the degree of disease severity on the cultivars. Five F. oxysporum isolates (08, 15, 17, 22, and 30) had a higher virulence on the cultivars than the other isolates. The host range of these five isolates was limited to Allium species. Molecular characterization of Fusarium isolates was performed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of the internal transcribed spacer (ITS) regions of ribosomal DNA. The 32 isolates were grouped into eight types (four types for F. oxysporum, one for F. verticillioides, and three for F. solani). Restriction patterns of the ITS region were not related to pathogenicity. However, the haplotypes obtained with five enzymes (RsaI, HinfI, HaeIII, ScrFI, and MspI) and the phylogenetic analysis permitted the discernment of the three Fusarium species. The PCR-RFLP analysis should provide a rapid, simple method for differentiating Fusaruim species isolated from wilted Welsh onion in Japan.     

Population features of <Emphasis Type="Italic">Xanthomonas arboricola</Emphasis> pv. <Emphasis Type="Italic">pruni</Emphasis> from <Emphasis Type="Italic">Prunus spp.</Emphasis> orchards in northern Italy

Bacterial leaf/fruit spot and canker of stone fruits, caused by Xanthomonas arboricola pv. pruni, is a recurrent disease in Italy. A set of 23 strains has been isolated in peach and plum orchards in an intensively stone fruit cultivated area located in north-eastern Italy. They were all identified as X. arboricola pv. pruni by means of phytopathological and serological features: hypersensitive reaction on bean pods, pathogenicity test on immature peach or plum fruitlets, identification by immunofluorescence assay and conventional PCR. Phylogenetic analysis based on sequencing of the gyrB housekeeping gene of the isolates showed that they formed a unique clade, well characterised and separated from other xanthomonads. An insight into the genetic population features was attempted by rep-PCR analysis, using the ERIC, REP and BOX primers. The combined rep-PCR fingerprints showed a slight intra-pathovar variation within our isolates, which grouped in five close clusters. Copper resistance has been assessed in vitro for our whole X. arboricola pv. pruni collection, highlighting that two isolates show a level of resistance in vitro up to 200 ppm of copper. Nonetheless, the copLAB gene cluster, present in many other species of Xanthomonads, was not detected in any isolate, confirming the presence of a still unknown mechanism of copper detoxification in our Xanthomonads arboricola pv. pruni tolerant/resistant strains.