Cacopsylla Pruni Research Articles

Molecular Characterization of 'Candidatus Phytoplasma prunorum' in the Czech Republic and Susceptibility of Apricot Rootstocks to the Two Most Abundant Haplotypes.

'Candidatus Phytoplasma prunorum' is one of the most destructive pathogens of Prunus species, where susceptible species render unproductive several years after infection. In epidemiology, the molecular characterization of phytoplasmas is based on sequence analysis of variable nonribosomal genes. In this study aceF, pnp, imp and secY genes were used for characterization of the 'Ca. P. prunorum' genotypes present in the Czech Republic. In total, 56 plant and 33 vector (Cacopsylla pruni) samples positive to 'Ca. P. prunorum' collected in seven localities were used in the study. Based on sequence analysis, four aceF, two pnp, six imp, and three secY genotypes were identified in analyzed samples. The most abundant in both plant and insect samples were the A6, P2, I4, and S2 genotypes. Most of the Czech 'Ca. P. prunorum' haplotypes clustered together in the haplotype network analysis. Next, two isolates representing the two most abundant Czech haplotypes (A6-P2-I4-S2 and A5-P2-I4-S2) were used in the susceptibility test of three apricot rootstock types (St. Julien A, M-VA-1, GF-305). Susceptibility was analyzed by phytoplasma quantification using quantitative real-time PCR and evaluation of symptom manifestation. Based on the results, the influence of the rootstock type on the phytoplasma titer and symptom manifestation was greater than of the phytoplasma isolate, while the year of analysis had no influence on the results. The results also showed that the phytoplasma titer is increasing in plant tissues during the vegetation period.

Detection of ‘Candidatus Phythoplasma prunorum’ in Apricot Trees and its Associated Psyllid Samples

‘Candidatus Phytoplasma prunorum’ is causing ever increasing economic losses through the decline of apricot trees in European countries, e.g., Hungary. In this study, the pathogen was identified from plant tissues and insects by nested-PCR. The insect species were identified via morphology and molecular methods. The incidence of the pathogen was 29.6% in randomly selected apricot trees. Most of the infected trees with symptoms died within a year. These results show that phytoplasma is significantly present and causes damage in the investigated plantations. The only known insect vector of this phytoplasma is the plum psyllid, Cacopsylla pruni, which was regularly encountered in the sampled apricot orchards and in their surroundings. In a two-year study, several adults among the sampled specimens were observed to be infected by the pathogen. This observation further confirms the role of the plum psyllid in vectoring the phytoplasma. All the sampled plum psyllid adults belonged to the ‘B’ biotype. Besides C. pruni, Cacopsylla crataegi was abundant in the samples. Several adults of the latter species were also infected by the pathogen ‘Ca. Phytoplasma prunorum’. The rates of occurrence of this phytoplasma in male and female adults of the two psyllid species appeared to be similar. The examined C. crataegi individuals showed genetic differences from each other and from specimens included in a previous investigation.

Cacopsyllapruni (Hemiptera, Psyllidae) in an apricot orchard is more attracted to white sticky traps dependent on host phenology.

The colour preference of the plum psyllid, Cacopsyllapruni (Hemiptera, Psyllidae), is yet poorly studied. This species is the only known vector of the 'Candidatus Phytoplasma prunorum', the agent of European stone fruit yellows (ESFY), a devastating disease of several cultivated Prunus species in Europe. As ESFY is still uncurable, vector control, thus vector monitoring, is pivotal to protect these trees. Cacopsyllapruni is a univoltine, host-shelter-alternating species; overwintered adults migrate from conifer to wild or cultivated Prunus species (family Rosaceae) in late winter-early spring. To select the most effective colour indicating the arrivals of the immigrants, yellow, fluorescent yellow, white, red and transparent sticky traps were deployed in an apricot orchard in Hungary. The two most abundant species in sticky traps were C.pruni and C.melanoneura. Catches of white traps were significantly biased towards C.pruni as compared to C.melanoneura specimens. Moreover, white sticky traps were better at catching plum psyllids than the other colours. Attraction to white was strongest when immigrants from shelter plants kept arriving in the orchard, coinciding with the blooming principal phenophase of apricot trees. When the host flowering growth stage was over, catches of C.pruni in white traps declined sharply to the level of yellow traps that was highest during this post-blooming period. We recommended white sticky traps for promptly monitoring C.pruni in apricot orchards because it is more potent and more selective than yellow ones during the critically important early flowering interval.

Cacopsylla pruni

This datasheet on Cacopsylla pruni covers Identity, Hosts/Species Affected, Further Information.

Occurrence data for the two cryptic species of Cacopsylla pruni (Hemiptera: Psylloidea).

BackgroundCacopsylla pruni is a psyllid that has been known since 1998 as the vector of the bacterium ‘Candidatus Phytoplasma prunorum’, responsible for the European stone fruit yellows (ESFY), a disease that affects species of Prunus. This disease is one of the major limiting factors for the production of stone fruits, most notably apricot (Prunus armeniaca) and Japanese plum (P. salicina), in all EU stone fruit-growing areas. The psyllid vector is widespread in the Western Palearctic and evidence for the presence of the phytoplasma that it transmits to species of Prunus has been found in 15 of the 27 EU countries.Recent studies showed that C. pruni is actually composed of two cryptic species that can be differentiated by molecular markers. A literature review on the distribution of C. pruni was published in 2012, but it only provided presence or absence information at the country level and without distinction between the two cryptic species.Since 2012, numerous new records of the vector in several European countries have been published. We ourselves have acquired a large amount of data from sampling in France and other European countries. We have also carried out a thorough systematic literature review to find additional records, including all the original sources mentioning C. pruni (or its synonyms) since the first description by Scopoli in 1763. Our aim was to create an exhaustive georeferenced occurrence catalogue, in particular in countries that are occasionally mentioned in literature with little detail. Finally, for countries that seem suitable for the proliferation of C. pruni (USA, Canada, Japan, China etc.), we dug deeper into literature and reliable sources (e.g. published checklists) to better substantiate its current absence from those regions.Information on the distribution ranges of these vector psyllids is of crucial interest in order to best predict the vulnerability of stone fruit producing countries to the ESFY threat in the foreseeable future.New informationWe give free access to a unique file of 1975 records of all occurrence data in our possession concerning C. pruni, that we have gathered through more than twenty years of sampling efforts in Europe or through intensive text mining.We have made every effort to retrieve the source information for the records extracted from literature (1201 records). Thus, we always give the title of the original reference, together with the page(s) citing C. pruni and, if possible, the year of sampling. To make the results of this survey publicly available, we give a URL to access the literature sources. In most cases, this link allows free downloads of a PDF file.We also give access to information extracted from GBIF (162 exploitable data points on 245 occurrences found in the database), which we thoroughly checked and often supplemented to make the information more easily exploitable.We give access to our own unpublished georeferenced and genotyped records from 612 samples taken over the last 20 years in several European countries (Switzerland, Belgium, Netherlands, Spain etc.). These include two countries (Portugal and North Macedonia), for which the presence of C. pruni had not been reported before. As our specimens have been genotyped (74 sites with species A solely, 202 with species B solely and 310 with species A+B), our new data enable a better overview of the geographical distribution of the two cryptic species at the Palaearctic scale.

Effect of Daytime and Tree Canopy Height on Sampling of Cacopsylla melanoneura, a 'Candidatus Phytoplasma mali' Vector.

The psyllids Cacopsylla melanoneura and Cacopsylla picta reproduce on apple (Malus × domestica) and transmit the bacterium ‘Candidatus Phytoplasma mali’, the causative agent of apple proliferation. Adult psyllids were collected by the beating-tray method from lower and upper parts of the apple tree canopy in the morning and in the afternoon. There was a trend of catching more emigrant adults of C. melanoneura in the morning and in the lower part of the canopy. For C. melanoneura remigrants, no differences were observed. The findings regarding the distribution of adults were reflected by the number of nymphs collected by wash-down sampling. The density of C. picta was too low for a statistical analysis. The vector monitoring and how it is commonly performed, is suitable for estimating densities of C. melanoneura. Nevertheless, above a certain temperature threshold, prediction of C. melanoneura density might be skewed. No evidence was found that other relatively abundant psyllid species in the orchard, viz. Baeopelma colorata, Cacopsylla breviantennata, Cacopsylla brunneipennis, Cacopsylla pruni and Trioza urticae, were involved in ‘Candidatus Phytoplasma mali’ transmission. The results of our study contribute to an advanced understanding of insect vector behavior and thus have a practical impact for an improved field monitoring.

Multi-scale spatial genetic structure of the vector-borne pathogen \u2018Candidatus Phytoplasma prunorum\u2019 in orchards and in wild habitats

Inferring the dispersal processes of vector-borne plant pathogens is a great challenge because the plausible epidemiological scenarios often involve complex spread patterns at multiple scales. The spatial genetic structure of ‘Candidatus Phytoplasma prunorum’, responsible for European stone fruit yellows disease, was investigated by the application of a combination of statistical approaches to genotype data of the pathogen sampled from cultivated and wild compartments in three French Prunus-growing regions. This work revealed that the prevalence of the different genotypes is highly uneven both between regions and compartments. In addition, we identified a significant clustering of similar genotypes within a radius of 50 km or less, but not between nearby wild and cultivated Prunus. We also provide evidence that infected plants are transferred between production areas, and that both species of the Cacopsylla pruni complex can spread the pathogen. Altogether, this work supports a main epidemiological scenario where ‘Ca. P. prunorum’ is endemic in — and generally acquired from — wild Prunus by its immature psyllid vectors. The latter then migrate to shelter plants that epidemiologically connect sites less than 50 km apart by later providing infectious mature psyllids to their “migration basins”. Such multi-scale studies could be useful for other pathosystems.

Phytoplasma infection status survey in plum psyllid (Cacopsylla pruni) population

European Stone Fruit Yellows (ESFY) phytoplasma disease causes an increasing amount of damage. This is especially true to the Gönci growing region. The insect vector of the disease, which has been shown to have a vector role during transmission experiments, is the plum psyllid (Cacopsylla pruni). In 2018, during the swarming period of plum psyllid, in 3 different settlements (Boldogkőváralja, Nagyvárad and Bekecs) 265 psyllidswere collected, from which 165 were plum psyllid. Molecular biology studies showed 106 individuals infected with phytoplasma, of which 20 were males and 86 were females.

First report of Candidatus Phytoplasma prunorum, the European stone fruit yellows phytoplasma on peach trees on the territory of Canton of Geneva, Switzerland

In recent years, ‘Ca. P. prunorum’, the agent of ESFY was reported from several apricot orchards of Canton of Wallis, the main apricot production region in Switzerland (Genini and Ramel, 2004). The psyllid vector Cacopsylla pruni was also found in several locations in the Lake Geneva area (Ackermann et al., 2006). The presence of the disease and of its proven vector C. pruni at the eastern part of the Lake Geneva area, as well as the existing risk of dissemination of ESFY to other stone fruit orchards along the Lake Geneva are the reasons for which ESFY needs to be studied further. ESFY and its possible dissemination through C. pruni on the territory of Canton of Geneva, bordering France, has never been yet studied. In 2016, visual observations were conducted in several stone fruit orchards near Geneva. Plant material was obtained from peach trees, displaying some of the typical symptoms such premature leaf colouration, leaf-roll, tree decline (Sabaté et al., 2015), in the autumn, when the concentration of the phytoplasma in the upper parts of the trees is the highest. Phloem was prepared from branches and was extracted with a CTAB-based adapted protocol (Lefort and Douglas, 1999). PCR amplification of phytoplasma DNA was achieved with the universal primers: fP1/rP7 (Deng and Hiruki, 1991; Schneider et al., 1995). All positive samples were tested with the ESFY-specific non-ribosomal primers ECA1/ECA2 (Jarausch et al., 1998). Typical symptoms of ESFY, like premature leaf colouration, leaf yellowing with reddish edges, leaf-roll, severe chlorosis, die-back of top branches and partial or, complete decline of the trees (Figure 1) were found in a peach orchard (GPS coordinates: 46°15'17.4"N 6°12'40.7"E) located in the area of Collonge-Bellerive, close to Geneva city. Ten trees were sampled in this orchard. The presence of ‘Ca. P. prunorum’ was confirmed in two of them (Figure 2 and Figure 3). At the beginning of spring 2017, the monitoring of the ESFY symptoms in the infested orchard was resumed. Early bud break was found on the two infected trees and the infection was confirmed again by PCR (Figure 4 and Figure 5). The same symptoms were observed in many trees of this orchard, which correlated with the previous autumn observations. Trapping confirmed the presence of the insect vector Cacopsylla pruni (Bodnár et al., 2018) in the infected area. In order to understand more about the origin and the diversity of ESFY phytoplasma in this area, additional plant and insect samples will be analyzed. The correlation between symptoms and infected plants will be studied further. We report here for the first time on the occurrence of ‘Candidatus Phytoplasma prunorum’ (‘Ca. P. prunorum’) the agent of ESFY on the territory of Canton of Geneva.

Examination of the plum psyllid (Cacopsylla pruni Scopoli), a vector of European Stone Fruit Yellows (ESFY) phytoplasma in the countryside of Boldogkőváralja (Hungary)

European Stone Fruit Yellows(ESFY) phytoplasma disease on apricot was identified by molecular methods for the first time in 1992 in Hungary. Currently, the pathogen is known as’ Ca. Phytoplasma prunorum’. Since, the pathogen become wide-spreaded and manyof the apricot-plantations had to be eliminated. In 2009 and 2010 in the countryside of Boldogkőváralja the infection of the apricot-plantations was about 77%. As the disease spreading and causing large damages, we studied the roleo fpossible vector,the plum psyllid (Cacopsylla pruni Scopoli) in the areas of Boldogkőváralja, North-East-Hungary. Studies were done in the year of 2016, monitoring the behaviour of the psyllids in four different areas, and caught 41 them for further examination. We collected plant samples from those apricot trees, on which the plum psyllids were caught.

Epidemiology of European stone fruit yellows in Germany: the role of wild Prunus spinosa

A nationwide monitoring with regard to the presence and distribution of ‘Candidatus Phytoplasma prunorum’ and its vector, Cacopsylla pruni, has been carried out in Germany between 2013 and 2017. In total, 286 sites with cultivated and wild Prunus species were surveyed. 806 plant samples covering 94 administrative districts in all 13 federal area states and one city-state were analysed by PCR. Furthermore, 3108 C. pruni were caught in 63 districts and tested for ‘Ca. P. prunorum’. European stone fruit yellows was found mainly in symptomatic apricot, plum, almond and peach but also for the first time in Germany in sweet cherry. Non-symptomatic infections were detected in 437 randomly sampled P. spinosa at 104 sites without any stone fruit growing nearby representing a natural infection rate of 14%. The vector C. pruni was found on all P. spinosa plants at 62 sites spread across Germany. The infection rate of C. pruni was 1–2% regardless whether the insects were caught in stone fruit growing areas or at wild habitats. Our results strongly indicate that ‘Ca. P. prunorum’ is widespread in all natural habitats in Germany and that wild P. spinosa represent a major source of infection in stone fruit orchards. A representative sample of 1164 individuals of C. pruni captured at 100 sites was molecularly typed: all but one insect were of B-type, the one which is the proven vector of ‘Ca. P. prunorum’. C. pruni A-type was detected for the first time in Germany near the French border.

A framework for estimating the effects of sequential reproductive barriers: Implementation using Bayesian models with field data from cryptic species.

Determining how reproductive barriers modulate gene flow between populations represents a major step toward understanding the factors shaping the course of speciation. Although many indices quantifying reproductive isolation (RI) have been proposed, they do not permit the quantification of cross-direction-specific RI under varying species frequencies and over arbitrary sequences of barriers. Furthermore, techniques quantifying associated uncertainties are lacking, and statistical methods unrelated to biological process are still preferred for obtaining confidence intervals and P-values. To address these shortcomings, we provide new RI indices that model changes in gene flow for both directions of hybridization, and we implement them in a Bayesian model. We use this model to quantify RI between two species of the psyllid Cacopsylla pruni based on field genotypic data for mating individuals, inseminated spermatophores and progeny. The results showed that preinsemination isolation was strong, mildly asymmetric, and indistinguishably different between study sites despite large differences in species frequencies; that postinsemination isolation strongly affected the more common hybrid type; and that cumulative isolation was close to complete. In the light of these results, we discuss how these developments can strengthen comparative RI studies.

Influence of apricot genotypes and their volatile profiles on their attractiveness to the European stone fruit yellows vector Cacopsylla pruni

Influence of apricot genotypes and their volatile profiles on their attractiveness to the European stone fruit yellows vector <i>Cacopsylla pruni</i>

Review of the biology of plant psyllid (Cacopsylla pruni, Scopoli 1763), and its role in the spreading of European stone fruit yellows, ESFY-phytoplasma with Hungarian data

The European stone fruit yellows (ESFY) phytoplasma disease caused by pathogen ’Ca. Phytoplasma prunorum’ induces serious damages in cherry, sour cherry, peach, and apricot orchards mostly in Europe. Its known vector is the plum psyllid (Cacopsylla pruni). Many articles report on the biology (morphology, taxonomy, life cycle etc.) and the method of transmission of the pathogen by the vector, and the possibilities of their control. This paper reviews our knowledge about the vector, and summarises the results of an inland research carried out in a northeastern Hungarian apricot orchards. Our goal was to show some important data for the farmers or anyone who is interested in this disease and its vector. And give some known method that we can protect our orchards against them to prevent the appearance of the disease. As the psyllid that became infected with the pathogen can hold its infectionous capacity during their lifetime, it is very important to have enough knowledge about their lifecycle, that we can determine the right time and method to control them. We also have to know how to identify them; therefore, this paper lists several important data which can be helpful. The most important keys of identification are their wing color, which dark borwn in the apex and brown is in the remaining part of the forewing. The length of the antennae is also an important factor, since other genuse’s species have longer antennae than twice the width of the head. C. pruni has as long antennae as twice the width of the head. They return to Prunus species in early spring and we have to protect our orhards in this period against them. We have to use preparations with a knock down effect on them to prevent the inoculation of the pathogen into the trees in our orchards.

Cage and field experiments as basis for the development of control strategies against Cacopsylla pruni, the vector of European Stone Fruit Yellows

AbstractThe efficacy and the instant effect of 13 insecticides and antifeedants towards Cacopsylla pruni, the vector of ‘Candidatus Phytoplasma prunorum’ were examined in cage studies (no choice experiments with 10 field‐collected overwintered adults per experiment) on potted apricot trees (budding trees under outdoor conditions in early spring and foliated seedlings kept at 21°C). Cypermethrin caused 100% insect mortality within 2–4 h, thiacloprid 90–100% mortality within 24 h both on foliated and on budding trees. On budding trees spinosad led to 70–90% mortality within 24 h, thixotropic white trunk paint to 90% mortality within 48 h. On foliated seedlings flonicamid gave 70–100% mortality within 1 day, abamectin, spinosad, acetamiprid and spirotetramat 70–100% within 72 h. Field studies monitoring the effects of thiacloprid on remigrants of C. pruni by yellow sticky traps were carried out in two apricot orchards. Additionally the influence of the insecticide on insect dispersal was examined by mark, release and recapture trials. As compared to the control thiacloprid significantly reduced the catches of naturally occurring and released insects, decreased the number of trees on which released insects were recaptured (by 25–100%) and shortened the migration distances of the released insects by more than half. Our results suggest that appropriate insecticide treatments both reduce C. pruni populations and have a direct effect on pathogen transmission. Application of Cypermethrin before bloom and thiacloprid after bloom seem best suited to achieve these objectives. Thixotropic white trunk paint could, a formulation for spray application provided, eventually be a sustainable alternative or complement for treatments before bloom.

Incidence and distribution of ‘Candidatus Phytoplasma prunorum’ and its vector Cacopsylla pruni in Spain: an approach to the epidemiology of the disease and the role of wild Prunus

‘Candidatus Phytoplasma prunorum’ is the causal agent of the European stone fruit yellows (ESFY) disease. This phytoplasma affects wild and cultivated species of Prunus to different degrees, depending on their susceptibility. ‘Candidatus Phytoplasma prunorum’ is present in the four regions of Spain surveyed in this study (Aragon, Catalonia, Extremadura and Valencia) with a variable incidence. Results showed that ‘Ca. Phytoplasma prunorum’ was detected in all of the cultivated Prunus species studied, except P. avium and P. dulcis, and was widespread in Spain. The most affected species was P. salicina, with symptoms including early bud break and blooming, leaf curling and yellowing, collapse, and a major decrease in production. In some plots in the Baix Llobregat area of Barcelona province (Catalonia), the incidence of ESFY on P. salicina was as high as 80%. The insect vector, Cacopsylla pruni, was present in all four of the regions studied, with the highest captures in yellow sticky traps in Catalonia on P. mahaleb and in Extremadura in peach orchards. In Baix Llobregat, large populations of C. pruni were present on infected P. mahaleb bushes, and with high infection rates. This was a key factor in the local pathogenic cycle that caused a major ESFY outbreak in the nearby P. salicina orchards. In the Ebro valley (Lleida and Aragon) and Valencia, the surveys showed very low incidences of the disease and low C. pruni populations.

Ideas on the European stone fruit yellows – as an entomologist can see them

The European stone fruit yellows (ESFY) is an important endemic disease in Europe which causes in both, the Mediterranean countries and Central Europe serious damage. Its pathogen is the ‘Candidatus Phytoplasma prunorum’. The treatment and healing of the diseased trees and plantations with chemicals do not promise success. Thus, prevention may be the only solution. The transmission and spread of the pathogen happen by infected propagation material (grafting) or a vector (the psyllid, Cacopsylla pruni). Mechanism of the pathogen’s transmission and population dynamics of the vector have been extensively investigated in several European countries, which may allow by the control of C. pruni even to hold back the disease. Diseased stone fruit trees and wild Prunus spp. as main host species play an important role in maintaining and spreading the pathogen. C. pruni collects the pathogen by feeding on these plants and it carries persistently ‘Ca. P prunorum’. Researchers in Hungary have been characterized the disease only in terms of plant pathology, but neither the significance of the vector nor the role of wild Prunus spp. have been studied. This summary intends to give clues to these researches, that not only axe and saw should be the instruments of national control, but knowing the role and population dynamics of the vector the stone fruit production should be more successful.

Integrated control of psyllid vectors of European fruit tree phytoplasmas

As there is no applicable means to cure a phytoplasma-infected fruit tree, insecticide treatments are the first measures to control the spread of fruit tree phytoplasma diseases whenever a vector species is identified. Although it is impossible to eliminate all vectors from the environment, well-managed vector control strategies significantly reduce the chance of an epidemic outbreak of phytoplasma diseases. However, important differences exist between the control of univoltine and polyvoltine psyllid vectors. Highly efficient univoltine vectors, e.g. Cacopsylla picta, the vector of apple proliferation disease, might be present in the orchards in very low abundance. An appropriate and efficient insecticides might miss or might not be homologated in all countries. Control of univoltine vectors is not well studied as it is the case for Cacopsylla pruni, the vector of European stone fruit yellows. On the contrary, polyvoltine pear psyllids, vectors of pear decline, are pests on their own and, therefore, control strategies and efficacies of different insecticides are well studied. The present work, focus on recent progress made in integrated control of pear psyllids.

European Stone Fruit Yellows Disease and Its Causal Agent ‘Candidatus Phytoplasma Prunorum’

The European stone fruit yellows (ESFY) caused by ‘Candidatus Phytoplasma prunorum’ (‘Ca. P. prunorum’), is a devastating, quarantine phytoplasma disease. This agent leads to serious damage in apricot and Japanese plum orchards, including decline of infected trees. The consequences are considerable economic losses in production. European plum and cherry are less susceptible to ESFY, although the ‘Ca. P. prunorum’ was also detected in these trees in several countries. ESFY seems to be limited to Europe and the neighboring regions (Asia Minor) as its incidence was reported from most of the southern and central European countries, Turkey, and Azerbaijan. ‘Ca. P. prunorum’ is transmitted by Cacopsylla pruni (Scopoli). The impact of ‘Ca. P. prunorum’ on stone fruit trees, as well as the methods of detection and identification and control management are reviewed.

CANDIDATUS PHYTOPLASMA PRUNORUM, THE CAUSAL AGENT OF EUROPEAN STONE FRUIT YELLOWS: AN OVERVIEW

‘Candidatus Phytoplasma prunorum’ is an important prokaryotic pathogen that infects stone fruits in Europe. It is known to cause several economically relevant disorders of Prunus spp. which are collectively referred to as European stone fruit yellows (ESFY). This organism is phylogenetically closely related to other important fruit trees pathogens such as apple proliferation (AP), pear decline (PD) and peach yellow leaf roll (PYLR) agents. Together they form a distinct phylogenetic cluster, the AP or 16SrX group. Like the other fruit tree phytoplasmas of the AP group, ‘Ca. P. prunorum’ exhibits a high host specificity. In nature, this pathogen has been reported to infect only plants in the genus Prunus and to be transmitted by one insect vector species, the psyllid (Psyllidae) Cacopsylla pruni. Also, ‘Ca. P. prunorum’ includes strains which greatly differ in virulence. This review summarizes the current knowledge of ‘Ca. P. prunorum’ with emphasis on advances that have been made during the last two decades in understanding molecular and epidemiological aspects. Prospects for disease management and future research which could provide insights into the largely unknown mechanisms involved in pathogenicity of ‘Ca. P. prunorum’, are also critically discussed.