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Xylella fastidiosa is a xylem-limited plant pathogenic bacterium that is a menace to the agriculture worldwide threating economically relevant crops such as almond. The pathogen presents a dual lifestyle in the plant xylem, consisting of sessile microbial aggregates and mobile independent cells that move by twitching motility. The latter is essential for the systemic colonization of the host and is mediated through type IV pili. In previous reports, it has been demonstrated that peptides can affect different key processes of X. fastidiosa, but their effect on motility has never been assessed. In the present work, peptides previously identified and newly designed analogs were studied for its effect in vitro on the motility of X. fastidiosa and their protective effect against almond leaf scorch was determined. By assessing the twitching fringe width in colonies and using microfluidic chambers, the inhibitory effect of BP100 on twitching motility was demonstrated. Interestingly, type IV pili of BP100-treated cells were similar in frequency and length, and presented no morphological differences when compared to the non-treated control. The application of BP100 by endotherapy in almond plants inoculated with X. fastidiosa under greenhouse conditions significantly reduced population levels and showed less affected xylem vessels, which correlated with decreased disease symptoms. Therefore, BP100 is a promising candidate to manage almond leaf scorch caused by X. fastidiosa.

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Xylella fastidiosa was recently added to the list of threatening pathogens affecting more than 300 plant hosts. Hemipteran hoppers that feed on xylem have been documented as potential transmitters. Hemipteran hoppers, known vectors for plant pathogens via xylem feeding, pose significant risks to agriculture. Despite their role in transmitting diseases, comprehensive data on their species diversity, distribution, and seasonal patterns, particularly in critical agricultural zones, remain sparse. Hence, the current study was carried out at 14 sites (eight olive farms and six vineyards) during the 2021/2022 season to develop a comprehensive checklist of hopper species present on the Egyptian Northwestern Coast, including their seasonal and location distribution, to serve as a real roadmap supporting control strategies if the pathogen breaches Egyptian borders. Utilizing 560 yellow sticky traps, we collected data seasonally, resulting in the identification of 21 hopper species belonging to 14 genera within four families. Olive orchards harbored a higher number of hoppers compared to vineyards, with Empoasca decipiens being the most dominant species. Our findings provide a foundational checklist and highlight the importance of continued monitoring and detailed studies to support proactive control strategies against potential X. fastidiosa outbreaks. We used 560 yellow sticky traps at 10 traps per site (80 traps for olive orchards and 60 traps for the vineyard per season) throughout the study period. Traps were installed at two levels to catch hopper species harboring tree canopies and ground vegetation. Each trap was replaced every 7 days, and the collected trap sheets were sent to the laboratory for segregation and identification. The data revealed 21 hopper species belonging to 14 genera and 4 families, with cicadellid species being the most represented (14 species). Olive orchards harbored a higher number of hoppers than vineyards. Empoasca decipiens exhibited the highest dominance among the remaining species. Although summer sampling yielded the highest number of hopper species and trapped specimens, seasonal variation in the distribution pattern exhibited non-significant differences (F = 1.7 and P = 0.173). Ras El-Hekma had the highest species representation (21 species), whereas El-Negala had the highest species richness. The lowest species representation at the Barrani location had the highest abundance of caught specimens. Although there were fluctuations in the trapped specimens among the examined locations, statistical analysis revealed no significant differences (F = 0.67, P = 0.58). Cluster analysis revealed distinct groupings with different degrees of similarity for both seasonal and location distributions. The impact of trap height on the hopper capture pattern showed a biased tendency towards low traps. Diversity indices showed no significant differences between the examined locations. Although our results offer a foundation for potential control strategies against X. fastidiosa, further detailed studies are required to fill the knowledge gap regarding its suspected vectors. Such research will guide management strategies that can be applied in cases where this infectious bacterium crosses Egyptian borders.

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KEY MESSAGE: New defense elicitor peptides have been identified which control Xylella fastidiosa infections in almond. Xylella fastidiosa is a plant pathogenic bacterium that has been introduced in the European Union (EU), threatening the agricultural economy of relevant Mediterranean crops such as almond (Prunus dulcis). Plant defense elicitor peptides would be promising to manage diseases such as almond leaf scorch, but their effect on the host has not been fully studied. In this work, the response of almond plants to the defense elicitor peptide flg22-NH2 was studied in depth using RNA-seq, confirming the activation of the salicylic acid and abscisic acid pathways. Marker genes related to the response triggered by flg22-NH2 were used to study the effect of the application strategy of the peptide on almond plants and to depict its time course. The application of flg22-NH2 by endotherapy triggered the highest number of upregulated genes, especially at 6 h after the treatment. A library of peptides that includes BP100-flg15, HpaG23, FV7, RIJK2, PIP-1, Pep13, BP16-Pep13, flg15-BP100 and BP16 triggered a stronger defense response in almond plants than flg22-NH2. The best candidate, FV7, when applied by endotherapy on almond plants inoculated with X. fastidiosa, significantly reduced levels of the pathogen and decreased disease symptoms. Therefore, these novel plant defense elicitors are suitable candidates to manage diseases caused by X. fastidiosa, in particular almond leaf scorch.

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This scientific report provides an update of the Xylella spp. host plant database, aiming to provide information and scientific support to risk assessors, risk managers and researchers dealing with Xylella spp. Upon a mandate of the European Commission, EFSA created and regularly updates a database of host plant species of Xylella spp. The current mandate covers the period 2021-2026. This report is related to the 10th version of the database published in Zenodo in the EFSA Knowledge Junction community, covering literature published from 1 July 2023 up to 31 December 2023, and recent Europhyt outbreak notifications. Informative data have been extracted from 39 selected publications. Sixteen new host plants, five genera and one family were identified and added to the database. They were naturally infected by X. fastidiosa subsp. fastidiosa or unknown either in Portugal or the United States. No additional data were retrieved for X. taiwanensis, and no additional multilocus sequence types (STs) were identified worldwide. New information on the tolerant/resistant response of plant species to X. fastidiosa infection were added to the database. The Xylella spp. host plant species were listed in different categories based on the number and type of detection methods applied for each finding. The overall number of Xylella spp. host plants determined with at least two different detection methods or positive with one method either by sequencing or pure culture isolation (category A), reaches now 451 plant species, 204 genera and 70 families. Such numbers rise to 712 plant species, 312 genera and 89 families if considered regardless of the detection methods applied (category E).

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In 2013, an outbreak of Xylella fastidiosa (Xf) was identified for the first time in Europe, in the extreme south of Italy (Apulia, Salento territory). The locally identified subspecies pauca turned out to be lethal for olive trees, starting an unprecedented phytosanitary emergency for one of the most iconic cultivations of the Mediterranean area. Xf pauca (Xfp) is responsible for a severe disease, the olive quick decline syndrome (OQDS), spreading epidemically and with dramatic impact on the agriculture, the landscape, the tourism and the cultural heritage of this region. The bacterium, transmitted by insects that feed on xylem sap, causes rapid wilting in olive trees due to biofilm formation, which obstructs the plant xylematic vessels. The aim of this review is to perform a thorough analysis that offers a general overview of the published work, from 2013 to December 2023, related to the Xfp outbreak in Apulia. This latter hereto has killed millions of olive trees and left a ghostly landscape with more than 8000 square kilometers of infected territory, that is 40% of the region. The majority of the research efforts made to date to combat Xfp in olive plants are listed in the present review, starting with the early attempts to identify the bacterium, the investigations to pinpoint and possibly control the vector, the assessment of specific diagnostic techniques and the pioneered therapeutic approaches. Interestingly, according to the general set criteria for the preliminary examination of the accessible scientific literature related to the Xfp outbreak on Apulian olive trees, fewer than 300 papers can be found over the last decade. Most of them essentially emphasize the importance of developing diagnostic tools that can identify the disease early, even when infected plants are still asymptomatic, in order to reduce the risk of infection for the surrounding plants. On the other hand, in the published work, the diagnostic focus (57%) overwhelmingly encompasses all other possible investigation goals such as vectors, impacts and possible treatments. Notably, between 2013 and 2023, only 6.3% of the literature reports addressing the topic of Xfp in Apulia were concerned with the application of specific treatments against the bacterium. Among them, those reporting field trials on infected plants, including simple pruning indications, were further limited (6%).

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Bacterial plant diseases are difficult to control as the durability of deployed control measures is thwarted by continuous and rapid changing of bacterial populations. Although application of copper compounds to plants is the most widespread and inexpensive control measure, it is often partially efficacious for the frequent appearance of copper-resistant bacterial strains and it is raising concerns for the harmful effects of copper on environment and human health. Consequently, European Community included copper compounds in the list of substances candidates for substitution. Nanotechnologies and the application of nanoparticles seem to respond to the need to find new very effective and durable measures. We believe that Argirium-SUNCs®, silver ultra nanoclusters with an average size of 1.79 nm and characterized by rare oxidative states (Ag2+/3+), represent a valid candidate as a nano-bactericide in the control of plant bacterial diseases. Respect to the many silver nanoparticles described in the literature, Argirium-SUNCs have many strengths due to the reproducibility of the synthesis method, the purity and the stability of the preparation, the very strong (less than 1 ppm) antimicrobial, and anti-biofilm activities. In this mini-review, we provide information on this nanomaterial and on the possible application in agriculture. KEY POINTS: • Argirium-SUNCs have strong antimicrobial activities against phytopathogenic bacteria. • Argirium-SUNCs are a possible plant protection product. • Argirium-SUNCs protect tomato plants against bacterial speck disease.

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Xylella fastidiosa (Xf) is a major phytosanitary threat to global agricultural production. The complexity and difficulty of controlling Xf underscore the pressing need for novel antibacterial agents, i.e., bacteriophages, which are natural predators of bacteria. In this study, a novel lytic bacteriophage of Xf subsp. pauca, namely Xylella phage MATE 2 (MATE 2), was isolated from sewage water in southern Italy. Biological characterization showed that MATE 2 possessed a broad-spectrum of antibacterial activity against various phytobacteria within the family Xanthomonadaceae, a rapid adsorption time (10 min), and high resistance to a broad range of pH (4-10) and temperatures (4-60°C). Most importantly, MATE 2 was able to suppress the growth of Xf subsp. pauca cells in liquid culture for 7 days, demonstrating its potential as an effective antibacterial agent against Xf. The genomic and electron microscopy analyses revealed that MATE 2 is a new species tentatively belonging to the genus Carpasinavirus within the class Caudoviricetes, with an isometric capsid head of 60 ± 5 nm along with a contractile tail of 120 ± 7.5 nm. Furthermore, the high-throughput sequencing and de novo assembly generated a single contig of 63,695 nucleotides in length; representing a complete genome composed of 95 Open Reading Frames. Bioinformatics analysis performed on MATE 2 genome revealed the absence of lysogenic mediated genes, and genes encoding virulence factors, antibiotic resistance, and toxins. This study adds a new phage to the very short list of Xf-infecting lytic phages, whose in-vitro antibacterial activity has been ascertained, while its efficacy on Xf-infected olive trees in the field has yet to be determined.

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Xylella fastidiosa (Xf) is a quarantine plant pathogen capable of colonizing the xylem of a wide range of hosts. Currently, there is no cure able to eliminate the pathogen from a diseased plant, but several integrated strategies have been implemented for containing the spread of Xf. Nanotechnology represents an innovative strategy based on the possibility of maximizing the potential antibacterial activity by increasing the surface-to-volume ratio of nanoscale formulations. Nanoparticles based on chitosan and/or fosetyl-Al have shown different in vitro antibacterial efficacy against Xf subsp. fastidiosa (Xff) and pauca (Xfp). This work demonstrated the uptake of chitosan-coated fosetyl-Al nanocrystals (CH-nanoFos) by roots and their localization in the stems and leaves of Olea europaea plants. Additionally, the antibacterial activity of fosetyl-Al, nano-fosetyl, nano-chitosan, and CH-nanoFos was tested on Nicotiana tabacum cultivar SR1 (Petite Havana) inoculated with Xff, Xfp, or Xf subsp. multiplex (Xfm). The bacterial load was evaluated with qPCR, and the results showed that CH-nanoFos was the only treatment able to reduce the colonization of Xff, Xfm, and Xfp in tobacco plants. Additionally, the area under the disease progress curve, used to assess symptom development in tobacco plants inoculated with Xff, Xfm, and Xfp and treated with CH-nanoFos, showed a reduction in symptom development. Furthermore, the twitching assay and bacterial growth under microfluidic conditions confirmed the antibacterial activity of CH-nanoFos.

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All over the world, from America to the Mediterranean Sea, the plant pathogen Xylella fastidiosa represents one of the most difficult challenges with many implications at ecological, agricultural, and economic levels. X. fastidiosa is a rod-shaped Gram-negative bacterium belonging to the family of Xanthomonadaceae. It grows at very low rates and infects a wide range of plants thanks to different vectors. Insects, through their stylets, suck a sap rich in nutrients and inject bacteria into xylem vessels. Since, until now, no antimicrobial treatment has been successfully applied to kill X. fastidiosa and/or prevent its diffusion, in this study, antimicrobial blue light (aBL) was explored as a potential anti-Xylella tool. Xylella fastidiosa subsp. pauca Salento-1, chosen as a model strain, showed a certain degree of sensitivity to light at 410 nm. The killing effect was light dose dependent and bacterial concentration dependent. These preliminary results support the potential of blue light in decontamination of agricultural equipment and/or plant surface; however, further investigations are needed for in vivo applications.

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Drought and Pierce's disease are common throughout many grapevine-growing regions such as Mexico and the United States. Yet, how ongoing water deficits affect infections of Xylella fastidiosa, the causal agent of Pierce's disease, is poorly understood. Symptoms were observed to be significantly more severe in water-stressed plants one month after X. fastidiosa inoculation, and, in one experiment, titers were significantly lower in water-stressed than well-watered grapevines. Host chemistry examinations revealed overall amino acid and phenolic levels did not statistically differ due to water deficits, but sugar levels were significantly greater in water stressed than well-watered plants. Results highlight the need to especially manage Pierce's disease spread in grapevines experiencing drought.

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The spittlebug Philaenus spumarius (Hemiptera: Aphrophoridae) is the predominant vector of Xylella fastidiosa (Xanthomonadales: Xanthomonadaceae) in Apulia, Italy and the rest of Europe. Current control strategies of the insect vector rely on mechanical management of nymphal stages and insecticide application against adult populations. Entomopathogenic fungi (EPF) are biological control agents naturally attacking spittlebugs and may effectively reduce population levels of host species. Different experimental trials in controlled conditions have been performed to i) identify naturally occurring EPF on P, spumarius in Northwestern Italy, and ii) evaluate the potential for biocontrol of the isolated strains on both nymphal and adult stages of the spittlebug. Four EPF species were isolated from dead P. spumarius collected in semi-field conditions: Beauveria bassiana, Conidiobolus coronatus, Fusarium equiseti and Lecanicillium aphanocladii. All the fungal isolates showed entomopathogenic potential against nymphal stages of P. spumarius (≈ 45 % mortality), except for F. equiseti, in preliminary trials. No induced mortality was observed on adult stage. Lecanicillium aphanocladii was the most promising fungus and its pathogenicity against spittlebug nymphs was further tested in different formulations (conidia vs blastospores) and with natural adjuvants. Blastospore formulation was the most effective in killing nymphal instars and reducing the emergence rate of P, spumarius adults, reaching mortality levels (90%) similar to those of the commercial product Naturalis®, while no or adverse effect of natural adjuvants was recorded. The encouraging results of this study pave way for testing EPF isolates against P, spumarius in field conditions and find new environmentally friendly control strategies against insect vectors of X. fastidiosa.

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Outbreak response to quarantine pathogens and pests in the European Union (EU) is regulated by the EU Plant Health Law, but the performance of outbreak management plans in terms of their effectiveness and efficiency has been quantified only to a limited extent. As a case study, the disease dynamics of almond leaf scorch, caused by Xylella fastidiosa, in the affected area of Alicante, Spain, were approximated using an individual-based spatial epidemiological model. The emergence of this outbreak was dated based on phylogenetic studies, and official surveys were used to delimit the current extent of the disease. Different survey strategies and disease control measures were compared to determine their effectiveness and efficiency for outbreak management in relation to a baseline scenario without interventions. One-step and two-step survey approaches were compared with different confidence levels, buffer zone sizes, and eradication radii, including those set by the EU legislation for X. fastidiosa. The effect of disease control interventions was also considered by decreasing the transmission rate in the buffer zone. All outbreak management plans reduced the number of infected trees (effectiveness), but large differences were observed in the number of susceptible trees not eradicated (efficiency). The two-step survey approach, high confidence level, and the reduction in the transmission rate increased the efficiency. Only the outbreak management plans with the two-step survey approach removed infected trees completely, but they required greater survey efforts. Although control measures reduced disease spread, surveillance was the key factor in the effectiveness and efficiency of the outbreak management plans. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

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Microbial competition within plant tissues affects invading pathogens' fitness. Metabolomics is a great tool for studying their biochemical interactions by identifying accumulated metabolites. Xylella fastidiosa, a Gram-negative bacterium causing Pierce's disease (PD) in grapevines, secretes various virulence factors including cell wall-degrading enzymes, adhesion proteins, and quorum-sensing molecules. These factors, along with outer membrane vesicles, contribute to its pathogenicity. Previous studies demonstrated that co-inoculating X. fastidiosa with the Paraburkholderia phytofirmans strain PsJN suppressed PD symptoms. Here, we further investigated the interaction between the phytopathogen and the endophyte by analyzing the exometabolome of wild-type X. fastidiosa and a diffusible signaling factor (DSF) mutant lacking quorum sensing, cultivated with 20% P. phytofirmans spent media. Liquid chromatography-mass spectrometry (LC-MS) and the Method for Metabolite Annotation and Gene Integration (MAGI) were used to detect and map metabolites to genomes, revealing a total of 121 metabolites, of which 25 were further investigated. These metabolites potentially relate to host adaptation, virulence, and pathogenicity. Notably, this study presents the first comprehensive profile of X. fastidiosa in the presence of a P. phytofirmans spent media. The results highlight that P. phytofirmans and the absence of functional quorum sensing affect the ratios of glutamine to glutamate (Gln:Glu) in X. fastidiosa. Additionally, two compounds with plant metabolism and growth properties, 2-aminoisobutyric acid and gibberellic acid, were downregulated when X. fastidiosa interacted with P. phytofirmans. These findings suggest that P. phytofirmans-mediated disease suppression involves modulation of the exometabolome of X. fastidiosa, impacting plant immunity.

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BACKGROUND AND AIMS: Xylella fastidiosa (Xf) is the xylem-dwelling bacterium associated with Pierce's disease (PD), which causes mortality in agriculturally important species, such as grapevine (Vitis vinifera). The development of PD symptoms in grapevines depends on the ability of Xf to produce cell-wall-degrading enzymes to break up intervessel pit membranes and systematically spread through the xylem vessel network. Our objective here was to investigate whether PD resistance could be mechanistically linked to xylem vessel network local connectivity. METHODS: We used high-resolution X-ray micro-computed tomography (microCT) imaging to identify and describe the type, area and spatial distribution of intervessel connections for six different grapevine genotypes from three genetic backgrounds, with varying resistance to PD (four PD resistant and two PD susceptible). KEY RESULTS: Our results suggest that PD resistance is unlikely to derive from local xylem network connectivity. The intervessel pit area (Ai) varied from 0.07 ±â€…0.01 mm2 mm-3 in Lenoir to 0.17 ±â€…0.03 mm2 mm-3 in Blanc do Bois, both PD resistant. Intervessel contact fraction (Cp) was not statically significant, but the two PD-susceptible genotypes, Syrah (0.056 ±â€…0.015) and Chardonnay (0.041 ±â€…0.013), were among the most highly connected vessel networks. Neither Ai nor Cp explained differences in PD resistance among the six genotypes. Bayesian re-analysis of our data shows moderate evidence against the effects of the traits analysed: Ai (BF01 = 4.88), mean vessel density (4.86), relay diameter (4.30), relay density (3.31) and solitary vessel proportion (3.19). CONCLUSIONS: Our results show that radial and tangential xylem network connectivity is highly conserved within the six different Vitis genotypes we sampled. The way that Xf traverses the vessel network may limit the importance of local network properties to its spread and may confer greater importance on host biochemical responses.

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Xylem-limited bacterial pathogens cause some of the most destructive plant diseases. Though imposed measures to control these pathogens are generally ineffective, even among susceptible taxa, some hosts can limit bacterial loads and symptom expression. Mechanisms by which this resistance is achieved are poorly understood. In particular, it is still unknown how differences in vascular structure may influence biofilm growth and spread within a host. To address this, we developed a novel theoretical framework to describe biofilm behaviour within xylem vessels, adopting a polymer-based modelling approach. We then parameterised the model to investigate the relevance of xylem vessel diameters on Xylella fastidiosa resistance among olive cultivars. The functionality of all vessels was severely reduced under infection, with hydraulic flow reductions of 2-3 orders of magnitude. However, results suggest wider vessels act as biofilm incubators; allowing biofilms to develop over a long time while still transporting them through the vasculature. By contrast, thinner vessels become blocked much earlier, limiting biofilm spread. Using experimental data on vessel diameter distributions, we were able to determine that a mechanism of resistance in the olive cultivar Leccino is a relatively low abundance of the widest vessels, limiting X. fastidiosa spread.

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BACKGROUND: The phytopathogens Xylella fastidiosa and Verticillium dahliae present an unparalleled threat to olive agriculture. However, there is no efficient field treatment available today for either pest. Spore-forming bacteria (i.e., the sporobiota) are known for their extraordinary resistance properties and antimicrobial activity. The aim of this study was thus to identify potential novel sustainable spore-forming biocontrol agents derived from the culturable olive microbiome, termed the sporobiota, in general and in particular against X. fastidiosa and V. dahliae. RESULTS: We demonstrate the wide-ranging antimicrobial profile of 415 isolates from the culturable olive sporobiota towards human and plant pathogens. We further identified five candidates with antagonistic activity against X. fastidiosa and V. dahliae. These belong to the Bacillus subtilis, Bacillus cereus and Peribacillus simplex clade. The activity was related to the species and their relative origin (soil versus leaf endophytic). It is of particular interest that two of these candidates are already naturally present at the site of disease-development that is, plant interior. We further confirmed the presence of lipopeptide genes potentially associated with the reported bioactivity. CONCLUSIONS: The study provides insights into how members of the olive sporobiota may support the olive plant to ward off detrimental pathogens. It further yields five promising candidates for the development of eco-friendly, multi-active biocontrol agents in olive agriculture. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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Phony peach disease (PPD), found predominantly in central and southern Georgia, is a re-emerging disease caused by Xylella fastidiosa (Xf) subsp. multiplex. Accurate detection and rapid removal of symptomatic trees are crucial to effective disease management. Currently, peach producers rely solely on visual identification of symptoms to confirm PPD, which can be ambiguous if early in development. We compared visual assessment to quantitative PCR (qPCR) for detecting Xf in 'Julyprince' in 2019 and 2020 (JP2019 and JP2020) and in 'Scarletprince' in 2020 (SP2020). With no prior knowledge of qPCR results, all trees in each orchard were assessed by a cohort of five experienced and five inexperienced raters in the morning and afternoon. Visual identification accuracy of PPD was variable, but experienced raters were more accurate when identifying PPD trees. In JP2019, the mean rater accuracy for experienced and inexperienced raters was 0.882 and 0.805, respectively. For JP2020, the mean rater accuracy for experienced and inexperienced raters was 0.914 and 0.816, respectively. For SP2020, the mean rater accuracy for experienced and inexperienced raters was 0.898 and 0.807, respectively. All raters had false positive (FP) and false negative (FN) observations, but experienced raters had significantly lower FN rates compared with the inexperienced group. Almost all raters overestimated the incidence of PPD in the orchards. Reliability of visual assessments was demonstrated as moderate to good, regardless of experience. Further research is needed to develop accurate and reliable methods of detection to aid management of PPD as both FPs and FNs are costly to peach production.

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Replicated field studies were conducted to evaluate the factors that could influence the efficacy of Paraburkholderia phytofirmans PsJN for the control of Pierce's disease of grape, as well as to determine the extent to which disease control was systemic within plants. Topical applications of PsJN with an organosilicon surfactant was an effective way to introduce this bacterium under field conditions and provided similar levels of disease control as its mechanical inoculation. Disease incidence in inoculated shoots was often reduced two- to threefold when PsJN was inoculated a single time as much as 3 weeks before Xylella fastidiosa and up to 5 weeks after the pathogen. Inoculation of a shoot with PsJN greatly decreased the probability of any symptoms rather than reducing the severity of disease, suggesting a systemic protective response of individual shoots. Although the likelihood of disease symptoms on shoots inoculated with the pathogen on PsJN-treated plants was lower than on control plants inoculated only with the pathogen, the protection conferred by PsJN was not experienced by all shoots on a given plant. This suggested that any systemic resistance was spatially limited. Whereas the population size of PsJN increased to more than 106 cells/g and spread more than 1 m within 12 weeks after its inoculation alone into grape, its population size subsequently decreased greatly after about 5 weeks, and its distal dispersal in stems was restricted when co-inoculated with X. fastidiosa. PsJN may experience collateral damage from apparent host responses induced when both species are present.

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