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Xylem‐feeding is apparently the only requirement making an insect a competent vector of the bacterium Xylella fastidiosa, an organism responsible for the devastation of the Southern Italian olive forest and nowadays considered one of the most feared threats to agriculture and landscape in Europe, including vineyards. Here, we used the direct current‐electrical penetration graph (DC‐EPG) technique to compare and describe the feeding behaviour on grapevine of four xylem‐feeding species considered candidate vectors of X. fastidiosa widespread in Europe, namely two spittlebugs (the meadow spittlebug Philaenus spumarius and the spittlebug Neophilaenus campestris) and two sharpshooter leafhoppers (the rhododendron leafhopper Graphocephala fennahi and the green leafhopper Cicadella viridis). We created a standard for the analysis of EPG waveforms recorded with a DC‐EPG device, describing feeding activities performed by these insects from stylet insertion into the plant to withdrawal. This standard, along with freely available software, has been developed to harmonize the calculation of feeding behavioural parameters in xylem‐feeders. The most relevant differences between the two vector taxa were the probing frequency and the dynamics of xylem ingestion. Sharpshooters tended to perform significantly more probes than spittlebugs. In contrast, the latter spent longer times in low‐frequency xylem ingestion, characterized by scattered contractions of the cibarial dilator muscle interspersed with periods of pump inactivity. Cicadella viridis was the species displaying the highest frequency of the electrical pattern found to be associated with X. fastidiosa inoculation in spittlebugs (Xe). Feeding behavioural data presented here represent an important step forward for deepening our knowledge of xylem‐sap feeding insects' interaction with both the host plants and the bacterium they transmit. [ABSTRACT FROM AUTHOR]

The glassy-winged sharpshooter, Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), is an important vector of bacterial Xyllela diseases throughout the southern and southwestern portions of the United States. Strong insect control measures, such that population densities of the insect vector are significantly reduced, are often necessary to limit the spread of Xylella fastidiosa. Glassy-winged sharpshooter populations within the Central Valley of California have developed a high resistance to imidacloprid (resistance ratio greater than 3,200) and tolerance to pyrethroids (ratio of less than 10) due to frequent applications of these materials. The purpose of this study was to determine the potential effects of insecticide resistance upon a variety of sharpshooter life history parameters associated with reproductive fitness. Our results indicate that individuals from susceptible populations of glassy-winged sharpshooters exhibited significantly higher fecundity and longer adult lifespans than those from the resistant populations. Additionally, resistant individuals were on average slightly larger than susceptible individuals. These results provide a strong indication that resistance to neonicotinoids imposes a reproductive fitness cost in an insecticide-free environment. [ABSTRACT FROM AUTHOR]

The activity of Eucalyptus essential oil against eleven strains pertaining to six species of plant pathogenic bacteria was studied using growth inhibition and contact assays. All strains were susceptible to the formulation EGL2, and Xylella fastidiosa subspecies and Xanthomonas fragariae were the most sensitive. The bactericidal effect was strong causing 4.5 to 6.0 log reductions in survival in 30 min at concentrations in the range of 0.75 to 15.0 ml/ml depending on the bacteria tested. Transmission electron microscopy of the formulation EGL2 against the three X. fastidiosa subspecies studied allowed the observation of a strong lytic effect on bacterial cells. In addition, the preventive spray application of EGL2 to potted pear plants subsequently inoculated with Erwinia amylovora significantly decreased the severity of infections. Almond plants treated by endotherapy or soil drenching, and then inoculated with X. fastidiosa showed a significant decrease in disease severity as well as in the levels of the pathogen, depending on the strategy used (endotherapy/soil drenching, preventive/curative). The treatment by endotherapy in almond plants induced the expression of several genes involved in plant defense. It was concluded that the reduction of infections by the Eucalyptus oil treatments was due to the combination of its bactericidal and plant defense induction activities. [ABSTRACT FROM AUTHOR]

For about a decade, olive groves in Apulia (Southern Italy) have been progressively destroyed by Olive Quick Decline Syndrome (OQDS), a disease caused by the bacterium Xylella fastidiosa subsp. pauca (Xfp). Recently, we described an additional wilting syndrome affecting olive trees in that area. The botryosphaeriaceous fungus Neofusicoccum mediterraneum was found associated with the diseased trees, and its high virulence toward olive trees was demonstrated. Given the common features with Branch and Twig Dieback (BTD) of olive tree, occurring in Spain and California, we suggested that the observed syndrome was BTD. During our first survey, we also found a botryosphaeriaceous species other than N. mediterraneum. In the present article, we report the morphological and molecular characterization of this fungal species which we identified as Neofusicoccum stellenboschiana. In the study, we also included for comparison additional N. stellenboschiana isolates obtained from olive trees in Latium and Tuscany region (Central Italy). The occurrence of N. stellenboschiana in olive trees is reported here for the first time in the northern hemisphere. The pathogenicity and virulence were tested in nine inoculation trials, where the Apulian N. stellenboschiana isolate was compared with the isolate from Latium and with the Apulian isolate of N. mediterraneum. Both isolates of N. stellenboschiana proved pathogenic to olive trees. They caused evident bark canker and wood discolouration when inoculated at the base of the stem of two/three-year-old trees and on one-year-old twigs. However, virulence of N. stellenboschiana was significantly lower, though still remarkable, compared with N. mediterraneum in term of necrosis progression in the bark and the wood and capacity of wilting the twigs. Virulence of N. stellenboschiana and N. mediterraneum did not substantially change when inoculations were performed in spring/summer and in autumn, suggesting that these fungal species have the potential to infect and damage olive trees in all seasons. The high thermotolerance of N. stellenboschiana was also revealed with in vitro growth and survival tests. The high virulence of these Botryosphaeriaceae species highlights their contribution in BTD aetiology and the necessity to investigate right away their diffusion and, possibly, the role of additional factors other than Xfp in the general decline of olive groves in Apulia. Hence the importance of assessing the degree of overlap of BTD/Botryosphariaceae with OQDS/Xfp is discussed. [ABSTRACT FROM AUTHOR]

Modeling the potential spread of Xylella fastidiosa can document contingency plans in northern Europe, so far uncolonized by the bacterium. Through mark–release–recapture (MRR) and flight-mill experiments, the flight capacity of two potential vectors for temperate Europe was studied: Philaenus spumarius, the reported southern European vector, and Aphrophora salicina, a xylem-specialist feeding on potential host plants of X. fastidiosa. Aphrophora salicina displayed significantly better flight performances than P. spumarius. In flight-mills, the average distance flown was, respectively, 623 m vs. 102 m and the maximal distance flown was 6.16 km vs. 1.54 km in 2.5 h. In MRRs, A. salicina travelled more than 30 m in a single flight, with a maximal interception distance of 80 m after two days, highlighting that dispersal is driven by connectivity and host plant quality. Philaenus spumarius mainly jumped, with 1 m movements in length and a maximal interception distance of 32 m in 27 days. Models estimated P. spumarius' daily mean dispersal at 1.5 m and A. salicina's at 3.5 m. Although only a small part of the population moves over very long distances, this pool of efficient insects could already be sufficient to effectively spread an epidemic. As Salicaceae have been reported as host plants of the bacterium, the association of Aphrophoridae and Salicaceae in riparian areas could create bacterium reservoirs in corridors allowing for transportation over medium to long distances. [ABSTRACT FROM AUTHOR]

Simple Summary: Cicadomorpha (Hemiptera: Auchenorrhyncha) represent a group of concern in vineyards since they can cause damage directly through feeding or can be vectors for serious pathogens such as grapevine yellows or the bacterium Xylella fastidiosa, the causal agent of Pierce's disease. Therefore, knowing the diversity and abundance of these insects in Portuguese vineyards is the first step for implementing appropriate measures to control these pathogens. Vineyards distributed in mainland Portugal were sampled to investigate species composition, richness, and diversity of the Cicadomorpha community, focusing on vectors and potential vectors of X. fastidiosa. A total of 11,834 individuals belonging to 81 different species/morphospecies were collected. Of these species, only two are confirmed vectors of X. fastidiosa (Philaenus spumarius and Neophilaenus campestris), and three are considered potential vectors (Cicadella viridis, Lepyronia coleoptrata, and N. lineatus). Species that cause direct damage to vines and vectors of grapevine yellows' phytoplasmas were also collected. Cicadomorpha (Hemiptera) insects are currently responsible for a growing negative impact on the agricultural economy due to their ability to directly damage crops or through the capacity to act as vectors for plant pathogens. The phytopathogenic bacterium Xylella fastidiosa, the causal agent of Pierce's disease in vineyards, is exclusively transmitted by insects of this infraorder. Therefore, knowledge of the Cicadomorpha species and understanding their biology and ecology is crucial. In this work, in 2018 and 2019, the canopy and inter-row vegetation of 35 vineyards distributed in mainland Portugal were sampled to investigate species composition, richness, and diversity of the Cicadomorpha community, with a special focus given to vectors and potential vectors of X. fastidiosa. A total of 11,834 individuals were collected, 3003 in 2018 and 8831 in 2019. Of the 81 species/morphospecies identified, only five are considered vectors or potential vectors of this pathogen, namely, Cicadella viridis (Linnaeus, 1758), Philaenus spumarius (Linnaeus, 1758), Neophilaenus campestris (Fallén, 1805), Lepyronia coleoptrata (Linnaeus, 1758), and N. lineatus (Linnaeus, 1758). Cicadella viridis was the most abundant xylem sap feeder, followed by P. spumarius. In addition, Cicadomorpha that cause direct damage to vines and vectors of grapevine yellows' phytoplasmas were also collected and identified in the sampled vineyards. The results suggested that vectors and potential vectors of X. fastidiosa and a large proportion of the population of Cicadomorpha have a positive correction with inter-row vegetation. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa (Xf) is a Gram-negative plant bacterium that causes severe diseases affecting several economically important crops in many countries. To achieve early detection of the pathogen, a droplet digital PCR (ddPCR)-based approach was used to detect the bacterium at low concentrations in different plant species and insect vectors. In this study, we implemented the reaction conditions of a previously developed ddPCR assay, and we validated its use to detect Xf in insect vectors as well as in a broader list of host species. More specifically, the sensitivity and accuracy of the protocol were assessed by testing five plant matrices (Olea europaea, Nerium oleander, Vitis vinifera, Citrus sinensis, and Prunus dulcis), and for the first time, the insect vector (Philaenus spumarius), was either naturally infected or artificially spiked with bacterial suspension at known concentrations. The lowest concentrations detected by ddPCR were 5 ag/µL of bacterial DNA and 1.00 × 102 CFU/mL of bacterial cells. Both techniques showed a high degree of linearity, with R2 values ranging from 0.9905 to 0.9995 and from 0.9726 to 0.9977, respectively, for qPCR and ddPCR. Under our conditions, ddPCR showed greater analytical sensitivity than qPCR for O. europea, C. sinensis, and N. oleander. Overall, the results demonstrated that the validated ddPCR assay enables the absolute quantification of Xf target sequences with high accuracy compared with the qPCR assay, and can support experimental research programs and the official controls, particularly when doubtful or inconclusive results are recorded by qPCR. [ABSTRACT FROM AUTHOR]

Abstract 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 eighth version of the database published in Zenodo in the EFSA Knowledge Junction community, covering literature published from 1 July 2022 up to 31 December 2022, and recent Europhyt outbreak notifications. Informative data have been extracted from 21 selected publications. Twelve new host plants were identified and added to the database. Nine plant species were reported from Portugal and naturally infected by subsp. multiplex or unknown (i.e. not reported). Three plant species were successfully artificially infected by subsp. fastidiosa. No additional data were retrieved for X. taiwanensis, and no additional STs were identified worldwide. New information on the tolerant/resistant response of plant species to X. fastidiosa infection were added to the database. The overall number of Xylella spp. host plants determined with at least two different detection methods or positive with one method (between sequencing and pure culture isolation) reaches now 433 plant species, 197 genera and 68 families. Such numbers rise to 690 plant species, 306 genera and 88 families if considered regardless of the detection methods applied.

Olive trees (Olea europaea L.) are deeply interwoven with the past, present and future of Mediterranean civilizations, both as essential economical as well as cultural valuables. Olive horticulture constitutes one of the primary agroecosystems in the Mediterranean regions of today. Being inhabitant of ecological niches, Olea europaea is prone to a peculiar vulnerability towards climatic and socioeconomical transformations that are briskly reshaping regional and global agroecosystems. Because of climatic changes and the biosafety risks of global agricultural trades, olive plants are highly susceptible to newly emerging diseases and pests, and the traditional olive horticultural crop protection practices are under scrutiny towards reducing their ecological impact. Hence there is an eminent demand for a more nature-positive olive tree crop management. Recent innovations in precision agriculture are raising the prospect for innovative crop protection methods that may provide olive farmers the required agility to respond to present and future agricultural challenges. For instance, endo-therapy, which is the systemic delivery of active ingredients via trunk injection, is a technology that holds promise of a true step-change in sustainable olive crop management. Endo-therapy allows reaching vascular diseases inaccessible to foliar treatments and delivers active ingredients in a precise manner with no risks of off-target drifts. Similarly, progresses in biological precision delivery using controlled release of active ingredients based on innovative formulation technologies are showing an exciting potential for more targeted and sustainable crop protection solutions. This review summarizes the latest innovations on both physical and biological precision deliveries in the realm of olive arboriculture in the Mediterranean regions and gives an outlook how these technologies may help orchestrating innovative olive culture practices soon.

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.

The meadow spittlebug Philaenus spumarius (Hemiptera: Aphrophoridae) is distributed in several habitats worldwide and has been recently recognized as the main vector of Xylella fastidiosa subsp. pauca. This bacterium has been associated with olive quick decline syndrome (OQDS) in the Salento Peninsula (Italy) and is responsible for extensive desiccation and die-off of olive trees. Current OQDS management strategies include the control of P. spumarius populations, mainly through the removal of weed hosts and insecticide treatments. In addition to the mandatory phytosanitary measures, the demand for new strategies compatible with integrated pest management is increasing. In this study, laboratory biological assays were performed to assess the potential toxic effect of vegetal formulations against P. spumarius adults. Two formulations were tested at different concentrations: Form A, an emulsion of 10% hot pepper-infused oil (Capsicum annuum subspecies Cayenna in olive oil) and Arabic gum in an aqueous solution of extracts of Salvia guaranitica, and Form B, an aqueous solution of extracts of Taxus baccata. Both Form A and B showed to be toxic against P. spumarius compared to the water control. The mean percentage of spittlebug mortality obtained with Form A one hour after treatments was dose–dependent; the lethal dose values were 0.13% (LD25), 0.36% (LD50), and 0.85% (LD75). At the same time, no significant differences in mortality rate were observed between the 0.75% treatment and the treatments with deltamethrin (about 90%). The mean percentage of spittlebug mortality obtained with Form B ranged from 21% to 53% one hour after treatment, but these values were significantly lower than those obtained with deltamethrin. The effectiveness of Form A on the P. spumarius population was also evaluated in the field. The averages of captures in the three experimental blocks were 1.8/trap for treated and 7.7/trap for untreated plots, and the spittlebug populations significantly decreased after treatments. Based on these results and the literature data, we hypothesize that the effectiveness of Form A is the result of the synergistic effect of all its components. No symptoms of phytotoxicity were recorded on olive trees treated with Form A, and the number of P. spumarius specimens collected on these plants was much lower than on untreated plants. These results suggest the potential use of Form A in the protection of olive trees. This vegetal formulation can thus be considered as a valid alternative to chemical insecticides for the control of the main vector of X. fastidiosa and could be integrated into a sustainable management system for OQDS.

Xylella fastidiosa is an economically important bacterial plant pathogen. With insights gained from 72 genomes, this study investigated differences among the three main subspecies, which have allopatric origins: X. fastidiosa subsp. fastidiosa, multiplex, and pauca The origin of recombinogenic X. fastidiosa subsp. morus and sandyi was also assessed. The evolutionary rate of the 622 genes of the species core genome was estimated at the scale of an X. fastidiosa subsp. pauca subclade (7.62 × 10-7 substitutions per site per year), which was subsequently used to estimate divergence time for the subspecies and introduction events. The study characterized genes present in the accessory genome of each of the three subspecies and investigated the core genome to detect genes potentially under positive selection. Recombination is recognized to be the major driver of diversity in X. fastidiosa, potentially facilitating shifts to novel plant hosts. The relative effect of recombination in comparison to point mutation was calculated (r/m = 2.259). Evidence of recombination was uncovered in the core genome alignment; X. fastidiosa subsp. fastidiosa in the United States was less prone to recombination, with an average of 3.22 of the 622 core genes identified as recombining regions, whereas a specific clade of X. fastidiosa subsp. multiplex was found to have on average 9.60 recombining genes, 93.2% of which originated from X. fastidiosa subsp. fastidiosa Interestingly, for X. fastidiosa subsp. morus, which was initially thought to be the outcome of genome-wide recombination between X. fastidiosa subsp. fastidiosa and X. fastidiosa subsp. multiplex, intersubspecies homologous recombination levels reached 15.30% in the core genome. Finally, there is evidence of X. fastidiosa subsp. pauca strains from citrus containing genetic elements acquired from strains infecting coffee plants as well as genetic elements from both X. fastidiosa subsp. fastidiosa and X. fastidiosa subsp. multiplex In summary, our data provide new insights into the evolution and epidemiology of this plant pathogen.IMPORTANCEXylella fastidiosa is an important vector-borne plant pathogen. We used a set of 72 genomes that constitutes the largest assembled data set for this bacterial species so far to investigate genetic relationships and the impact of recombination on phylogenetic clades and to compare genome content at the subspecies level, and we used a molecular dating approach to infer the evolutionary rate of X. fastidiosa The results demonstrate that recombination is important in shaping the genomes of X. fastidiosa and that each of the main subspecies is under different selective pressures. We hope insights from this study will improve our understanding of X. fastidiosa evolution and biology.

A field study showed that transgenic grapevine rootstocks can provide trans-graft-mediated protection to a wild type scion against Pierce's disease (PD) development. We individually field-tested two distinct strategies. The first expressed a chimeric antimicrobial protein (CAP) that targeted the functionality of the lipopolysaccharide (LPS) surface of Xylella fastidiosa (Xf), the causative agent of PD. The second expressed a plant polygalacturonase inhibitory protein (PGIP) that prevents PD by inhibiting breakdown of pectin present in primary cell walls. Both proteins are secreted to the apoplast and then into the xylem, where they migrate past the graft union, transiting into the xylem of the grafted scion. Transgenic Vitis vinifera cv. Thompson Seedless (TS) expressing ether CAP or PGIP were tested in the greenhouse and those lines that showed resistance to PD were grafted with wild type TS scions. Grafted grapevines were introduced into the field and tested over 7 years. Here we present data on the field evaluation of trans-graft protection using four CAP and four PGIP independent rootstock lines, compared to an untransformed rootstock. There was 30 to 95% reduction in vine mortality among CAP- and PGIP-expressing lines after three successive yearly infections with virulent Xf. Shoot tissues grafted to either CAP or PGIP transgenic rootstocks supported lower pathogen titers and showed fewer disease symptoms. Grafted plants on transgenic rootstocks also had more spring bud break following infection, more shoots, and more vigorous growth compared to those grafted to wild type rootstocks. No yield penalty was observed in the transgenic lines and some PGIP-expressing vines had enhanced yield potential. Trans-graft protection is an efficient way to protect grape scions against PD while preserving their valuable varietal genotypes and clonal properties.

Plant response to pathogen challenge involves recognition by specific receptors of conserved molecular patterns associated with pathogenic organisms. Understanding a wider range of pathogen detection pathways in different plant species is valuable for identification and development of pathogen-resistant plant material. Xylella fastidiosa is an important bacterial pathogen of several agricultural crops including table and wine grapes. Although some pathogen recognition pathways have been identified for X. fastidiosa in host plants, there are likely several other molecular interactions that could be exploited to increase plant resistance to this pathogen. This study identified a conserved bacterial cold shock protein component (Xfcsp20) as an elicitor of reactive oxygen species production by Vitis vinifera plant tissue, an indication of pathogen recognition response. Characterization of Xfcsp20 as an elicitor of an oxidative burst in grapevine hosts of X. fastidiosa will be useful to continued work in the areas of bacterial-plant interactions and plant resistance. [Figure: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

This article reports the first case of Xylella fastidiosa subsp. sandyi infecting oleander plants in Hawaii. The infected plants displayed symptoms such as stunting, wilt, and leaf scorch. The presence of the pathogen was confirmed through PCR and qPCR testing. A survey of other oleander plants in Hawaii found no evidence of X. fastidiosa infection, except for a few plants with symptoms likely due to insufficient irrigation. The article also mentions that X. fastidiosa subsp. sandyi is known to cause oleander leaf scorch and is transmitted by certain sharpshooter species. The natural host range of the pathogen in Hawaii is still unclear. [Extracted from the article]

BACKGROUND:Arthropod-borne diseases remain a leading cause of human morbidity and mortality and exact an enormous toll on global agriculture. The practice of insecticide-based control is fraught with issues of excessive cost, human and environmental toxicity, unwanted impact on beneficial insects and selection of resistant insects. Efforts to modulate insects to eliminate pathogen transmission have gained some traction and remain future options for disease control. RESULTS:Here, we report a paratransgenic strategy that targets transmission of Xylella fastidiosa, a leading bacterial pathogen of agriculture, by the Glassy-Winged Sharpshooter (GWSS), Homalodisca vitripennis. Earlier, we identified Pantoea agglomerans, a bacterial symbiont of the GWSS as the paratransgenic control agent. We genetically engineered P. agglomerans to express two antimicrobial peptides (AMP)-melittin and scorpine-like molecule (SLM). Melittin and SLM were chosen as the effector molecules based on in vitro studies, which showed that both molecules have anti-Xylella activity at concentrations that did not kill P. agglomerans. Using these AMP-expressing strains of P. agglomerans, we demonstrated disruption of pathogen transmission from insects to grape plants below detectable levels. CONCLUSION:This is the first report of halting pathogen transmission from paratransgenically modified insects. It is also the first demonstration of paratransgenic control in an agriculturally important insect vector.

The activity of Eucalyptus essential oil against eleven strains pertaining to six species of plant pathogenic bacteria was studied using growth inhibition and contact assays. All strains were susceptible to the formulation EGL2, and Xylella fastidiosa subspecies and Xanthomonas fragariae were the most sensitive. The bactericidal effect was strong causing 4.5 to 6.0 log reductions in survival in 30 min at concentrations in the range of 0.75 to 15.0 μl/ml depending on the bacteria tested. Transmission electron microscopy of the formulation EGL2 against the three X. fastidiosa subspecies studied allowed the observation of a strong lytic effect on bacterial cells. In addition, the preventive spray application of EGL2 to potted pear plants subsequently inoculated with Erwinia amylovora significantly decreased the severity of infections. Almond plants treated by endotherapy or soil drenching, and then inoculated with X. fastidiosa showed a significant decrease in disease severity as well as in the levels of the pathogen, depending on the strategy used (endotherapy/soil drenching, preventive/curative). The treatment by endotherapy in almond plants induced the expression of several genes involved in plant defense. It was concluded that the reduction of infections by the Eucalyptus oil treatments was due to the combination of its bactericidal and plant defense induction activities.

Type IV pilus (TFP) is a multifunctional bacterial structure involved in twitching motility, adhesion, biofilm formation, as well as natural competence. Here, by site-directed mutagenesis and functional analysis, we determined the phenotype conferred by each of the 38 genes known to be required for TFP biosynthesis and regulation in the reemergent plant pathogenic fastidious prokaryote Xylella fastidiosa. This pathogen infects > 650 plant species and causes devastating diseases worldwide in olives, grapes, blueberries, and almonds, among others. This xylem-limited, insect-transmitted pathogen lives constantly under flow conditions and therefore is highly dependent on TFP for host colonization. In addition, TFP-mediated natural transformation is a process that impacts genomic diversity and environmental fitness. Phenotypic characterization of the mutants showed that ten genes were essential for both movement and natural competence. Interestingly, seven sets of paralogs exist, and mutations showed opposing phenotypes, indicating evolutionary neofunctionalization of subunits within TFP. The minor pilin FimT3 was the only protein exclusively required for natural competence. By combining approaches of molecular microbiology, structural biology, and biochemistry, we determined that the minor pilin FimT3 (but not the other two FimT paralogs) is the DNA receptor in TFP of X. fastidiosa and constitutes an example of neofunctionalization. FimT3 is conserved among X. fastidiosa strains and binds DNA non-specifically via an electropositive surface identified by homolog modeling. This protein surface includes two arginine residues that were exchanged with alanine and shown to be involved in DNA binding. Among plant pathogens, fimT3 was found in ~ 10% of the available genomes of the plant associated Xanthomonadaceae family, which are yet to be assessed for natural competence (besides X. fastidiosa). Overall, we highlight here the complex regulation of TFP in X. fastidiosa, providing a blueprint to understand TFP in other bacteria living under flow conditions. Author summary: Xylella fastidiosa is a bacterial plant pathogen that lives exclusively inside the xylem vasculature in plants and the food canal of insect vectors. Historically known to cause devastating diseases in the Americas in grapevines and other crops, in the last decade it has expanded to different parts of the world, notably the south of Italy where is killing ancient olive trees. We studied a bacterial structure, type IV pilus (TFP), that is important for cell movement and acquisition of DNA from the environment. During the functional characterization of each one of the 38 proteins involved in TFP formation and regulation, we noticed that multiple copies of the same genes (paralogs) had different functions, indicating that X. fastidiosa allocate several genes for a precise regulation of TFP. This highlights the key role of this structure in the pathogen life cycle. Moreover, we identified a specific protein that attaches DNA and is involved in the internalization of the genetic material used to recombine and generate bacterial variants that could have different virulence levels or host specificity. We hope that our complete phenotypic characterization of TFP genes will inspire others to further understand its role in vascular pathogens. [ABSTRACT FROM AUTHOR]

Olive agro-ecosystems in southern Italy have been heavily damaged due to Xylella fastidiosa subsp. pauca (Xfp). Replacing the Xfp-infected olive-growing areas with economically viable fruit tree species is thought to be a practical control measure. A land suitability analysis can provide an appropriate evaluation of a crop's suitability in these areas. We evaluate the suitability of almond (Prunus dulcis B.), fig (Ficus carica L.), hazelnut (Corylus avellana L.), kiwifruit (Actinidia chinensis P.), pistachio (Pistacia vera L.), and pomegranate (Punica granatum L.) as fruit tree species immune/resistant to Xfp to be planted within the Xfp-infected olive-growing areas in the Apulia region to compensate for economic and environmental losses. Climate and soil data were used to carry out the land suitability analysis. We combined information for each parameter to obtain the overall suitability maps for the six proposed fruit tree crops using GIS (Geographic Information System). The analysis showed that the Xfp-infected olive-growing areas are suitable for the plantation of most of the proposed fruit tree crops, with different suitability levels as the climate and soil conditions vary among the study areas. In particular, large olive-growing areas are suitable for the cultivation of pomegranate (268,886 ha), fig (103,975 ha), and almond (70,537 ha), followed by kiwifruit (43,018 ha) and pistachio (40,583 ha). Hazelnut, with just 2744 ha of suitable land, was the species with fewer suitable areas in these semi-arid environments. This is the first study to provide practical containment measures against the diffusion of Xfp in southern Italy. Our results can help in the selection of the right immune/resistant tree species for replanting in Xfp-infected zones, therefore providing guidelines within the decision-making process to encourage the planting of some underrepresented fruit tree crops with viable economic values as well. [ABSTRACT FROM AUTHOR]

In recent years, the use of Unmanned Aerial Vehicles (UAVs) has been spreading widely, as in plant pest control. The collection of huge amounts of spatial data raises various issues including that of scale. Data from UAVs generally explore multiple scales, so the problem arises in determining which one(s) may be relevant for a given application. The objective of this work was to investigate the potential of UAV images in the fight against the Xylella pest for olive trees. The data were a multiband UAV image collected on one date in an olive grove affected by Xylella. A multivariate geostatistics approach was applied, consisting firstly of estimating the linear coregionalization model to detect the scales from the data; and secondly, of using multiple factor kriging to extract the sets of scale-dependent regionalized factors. One factor was retained for each of the two selected scales. The short-range factor could be used in controlling the bacterium infection while the longer-range factor could be used in partitioning the field into three management zones. The work has shown the UAV data potential in Xylella control, but many problems still need to be solved for the automatic detection of infected plants in the early stages. [ABSTRACT FROM AUTHOR]

Simple Summary: The bacterium Xylella fastidiosa induces many plant diseases causing yield losses and plant death. It is passively delivered into the xylem sap by spittlebugs vectors. These insects are small hemipterans of the Aphrophoridae family mostly ranging from 7 to 9 mm in length. They are quite polyphagous, sucking xylem sap from a multitude food plant species (spontaneous, ornamental and cultivated) present in forest, dry grassland and fruit orchards. Four spittlebug species naturally occur in Tunisia. Two species, Philaenus tesselatus and Neophilaenus campestris, seem to be potential vectors. Consequently, the risk of spreading the bacteria is important because of the exchanges between countries. Knowledge of the vector will enforce the available measures against plant pathogen invasion and help to control plant importations from infected countries. The present study is an update on the situation of potential vectors of Xylella fastidiosa in Tunisia. Investigations in nine Tunisian regions (Nabeul, Bizerte, Béja, Jendouba, Zaghouan, Kairouan, Ben Arous, Tunis and Manouba) from 2018 to 2021 allowed for the observation of 3758 Aphrophoridae among a total of 9702 Auchenorrhyncha individuals collected by sweep net. Four Aphrophoridae species were identified with Philaenus tesselatus as most abundant (62%), followed by Neophilaenus campestris (28%), Neophilaenus lineatus (5%) and Philaenus maghresignus (5%). Aphrophoridae individuals were found to be particularly abundant in both forests of Nabeul and Jendouba, secondarily in olive groves and dry grassland. Furthermore, their distribution on weed hosts was followed in these two regions where nymphs and adults are widely distributed. P. tesselatus appears to be the most abundant species as determined either by conventional sweep netting for adults or by plant sampling on Sonchus, Smyrnium, Cirsium, Rumex, Polygonum and Picris for nymphs. Limited numbers of adults of P. maghresignus were detected by sweep netting, while nymphs of this species were found on Asphodelus microcarpus only. N. campestris was found in high numbers on plants belonging to the Poaceae family in forests, dry grassland and olive groves whereas N. lineatus occurred on herbs under or near olive trees and in dry grasslands. [ABSTRACT FROM AUTHOR]

Infectious diseases of plants present an ongoing and increasing threat to international biosecurity, with wide-ranging implications. An important challenge in plant disease management is achieving early detection of invading pathogens, which requires effective surveillance through the implementation of appropriate monitoring programmes. However, when monitoring relies on visual inspection as a means of detection, surveillance is often hindered by a long incubation period (delay from infection to symptom onset) during which plants may be infectious but not displaying visible symptoms. 'Sentinel' plants–alternative susceptible host species that display visible symptoms of infection more rapidly–could be introduced to at-risk populations and included in monitoring programmes to act as early warning beacons for infection. However, while sentinel hosts exhibit faster disease progression and so allow pathogens to be detected earlier, this often comes at a cost: faster disease progression typically promotes earlier onward transmission. Here, we construct a computational model of pathogen transmission to explore this trade-off and investigate how including sentinel plants in monitoring programmes could facilitate earlier detection of invasive plant pathogens. Using Xylella fastidiosa infection in Olea europaea (European olive) as a current high profile case study, for which Catharanthus roseus (Madagascan periwinkle) is a candidate sentinel host, we apply a Bayesian optimisation algorithm to determine the optimal number of sentinel hosts to introduce for a given sampling effort, as well as the optimal division of limited surveillance resources between crop and sentinel plants. Our results demonstrate that including sentinel plants in monitoring programmes can reduce the expected prevalence of infection upon outbreak detection substantially, increasing the feasibility of local outbreak containment. Author summary: Plant diseases affect the environment and the economy negatively, with implications for biodiversity and food security. Fast detection of invading pathogens is essential to prevent widespread transmission. This is challenging, however, because many plant diseases have a long presymptomatic period (delay from initial infection to symptom onset) in globally important hosts. During this presymptomatic period, infection may spread undetected to other plants. While the presymptomatic period can be long, plant diseases often affect multiple host species, with different epidemiological characteristics. This provides an opportunity for planting sentinel plants, which are alternative host species that display visible symptoms of infection quickly, as early warning beacons for infection. In this research article, we use mathematical modelling to explore the potential for sentinel plants to aid plant disease monitoring programmes. We show that, for a high-profile plant pathogen (Xylella fastidiosa, which is currently devastating olive groves in southern Europe), the use of sentinel plants allows new outbreaks to be identified quickly, reducing the prevalence of infection when outbreaks are detected. Model simulations also indicate that our results apply more generally. Sentinel plants have the potential to assist fast detection of a wide range of invading plant pathogens. [ABSTRACT FROM AUTHOR]

Phlomis viscosa Poiret (an evergreen shrub) represents a valuable source of medicinal compounds. In this study, we discovered compounds with antimicrobial and antiviral properties. The aim of this study was to identify compounds of P. viscosa and estimate the antimicrobial and antiviral activity of its phytochemicals. The volatile compounds were identified using gas chromatography/mass spectrometry (GC/MS) analysis. For the identification of nonvolatile components of the extracts, high-performance liquid chromatography (HPLC), liquid chromatography–electrospray ionization-mass spectrometry (LC-ESI-MS) and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF-MS) were applied. Quercetin 3-O-rutinoside and hesperidin caused a significant decrease in the bacterial concentration of Agrobacterium tumefaciens, Xylella fastidiosa and Pseudomonas syringae (p < 0.001). The growth of drug-resistant microorganisms (Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, Serratia marcescens and Salmonella enteritidis) was inhibited by quercetin 3-O-rutinoside, quercetin 3-O-arabinoside and hesperidin. In addition, these compounds demonstrated antiquorum-sensing properties. Diosmin, hesperidin and quercetin 3-O-arabinoside significantly inhibited varicella zoster virus (VZV) (p < 0.001). Quercetin 3-O-rutinoside and quercetin 3-O-arabinoside were effective against herpes simplex virus 1 (HSV-1), including mutant strains. [ABSTRACT FROM AUTHOR]

Spittlebugs are xylem-sap feeding insects that can exploit a nutrient-poor diet, thanks to mutualistic endosymbionts residing in various organs of their body. Although obligate symbioses in some spittlebug species have been quite well studied, little is known about their facultative endosymbionts, especially those inhabiting the gut. Recently, the role played by spittlebugs as vectors of the phytopathogenetic bacterium Xylella fastidiosa aroused attention to this insect group, boosting investigations aimed at developing effective yet sustainable control strategies. Since spittlebug nymphs are currently the main target of applied control, the composition of gut bacterial community of the juveniles of Philaenus spumarius and Lepyronia coleoptrata was investigated using molecular techniques. Moreover, bacteria associated with their froth, sampled from different host plants, were studied. Results revealed that Sodalis and Rickettsia bacteria are the predominant taxa in the gut of P. spumarius and L. coleoptrata nymphs, respectively, while Rhodococcus was found in both species. Our investigations also highlighted the presence of recurring bacteria in the froth. Furthermore, the foam hosted several bacterial species depending on the host plant, the insect species, or on soil contaminant. Overall, first findings showed that nymphs harbor a large and diverse bacterial community in their gut and froth, providing new accounts to the knowledge on facultative symbionts of spittlebugs. [ABSTRACT FROM AUTHOR]

Background: The meadow spittlebug Philaenus spumarius L. is the vector for the bacterium Xylella fastidiosa subspecies pauca, involved in olive quick decline syndrome (OQDS) in Salento (Italy). Control of P. spumarius is key to limiting transmission of the bacterium, and an innovative approach can be based on effective natural compounds and biocontrol agents. Entomopathogenic fungi are an important source of bioactive natural molecules that play a role in the relationship between microorganisms and insects. Results: Pathogenicity bioassays, performed by dipping adults of P. spumarius in either fungal culture suspension (120 mg mL−1) or cell-free culture supernatant of Trichoderma chlorosporum GJS 91-150, showed, respectively, 97% and 87% death within 24 h. The effect was dose-dependent. In laboratory bioassays, the powdered fungal culture of T. chlorosporum GJS 91-150 did not exhibit pathogenic activity when injected into nymph spittle. Conclusions: T. chlorosporum GJS 91-150 affected the survival of P. spumarius adults. The lethal effect was not associated with the development of mycelium on the cuticle, but seems due, at least partly, to fungal metabolites released in the culture medium. The fungus tested here has good potential for the development of effective low-environmental impact control strategies for P. spumarius and suppression of X. fastidiosa. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa subsp. pauca (Xfp) infects olive trees and other hosts in Southern Apulia (Italy), devastating agriculture and landscape. A containment strategy of the disease requires quick and sensitive detection tools. Therefore, a colorimetric LAMP protocol was developed using as a template a crude alkaline sap obtained from incubation of 50–60 mg of thin slices of olive twigs in a NaOH-containing buffer. This rapid molecular assay can be performed directly in the field, as it needs only a portable isothermal block. Tissues of the same olive trees analysed by this technique were also compared to qPCR (using purified total plant DNA as template) as well as digital droplet PCR (on the same crude alkaline extracts used in cLAMP). A titration of the cLAMP reaction with healthy olive sap, spiked with dilutions of in vitro cultivated Xfp cells and plasmid DNA containing the target sequence, gave positive detection results as low as 102 CFU/mL and up to 169.2 target copies/µL, equivalent to about 0.9 pg of the genomic DNA. A portable, sensitive and target-specific Xfp field test was developed, which has a 40 min sample-to-answer time and does not require any DNA isolation procedure or laboratory equipment. The application of this detection assay could help the monitoring and containment of the disease spread. [ABSTRACT FROM AUTHOR]

Of American origin, a wide diversity of Xylella fastidiosa strains belonging to different subspecies have been reported in Europe since 2013 and its discovery in Italian olive groves. Strains from the subspecies multiplex (ST6 and ST7) were first identified in France in 2015 in urban and natural areas. To trace back the most probable scenario of introduction in France, the molecular evolution rate of this subspecies was estimated at 3.2165 × 10-7 substitutions per site per year, based on heterochronous genome sequences collected worldwide. This rate allowed the dating of the divergence between French and American strains in 1987 for ST6 and in 1971 for ST7. The development of a new VNTR-13 scheme allowed tracing the spread of the bacterium in France, hypothesizing an American origin. Our results suggest that both sequence types were initially introduced and spread in Provence-Alpes-Côte d'Azur (PACA); then they were introduced in Corsica in two waves from the PACA bridgehead populations. A genomic investigation into strains of the plant pathogen, Xylella fastidiosa, in France indicate an American origin with two waves of invasion. [ABSTRACT FROM AUTHOR]

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 seventh version of the database published in Zenodo in the EFSA Knowledge Junction community, covering literature published from 1 January 2022 up to 30 June 2022, and recent Europhyt outbreak notifications. Informative data have been extracted from 30 selected publications. Fifteen new host plants were identified and added to the database. Those plant species were reported from Brazil, France, Italy, Portugal and Spain, and infected by subsp. multiplex, pauca or unknown (i.e. not reported). No additional data were retrieved for X. taiwanensis. Two new STs (namely ST88 and ST89) belonging to subspecies multiplex were identified in host plants in natural conditions, and new information on the tolerant/resistant response of plant species to X. fastidiosa infection were added to the database. The overall number of Xylella spp. host plants determined with at least two different detection methods or positive with one method (between sequencing and pure culture isolation) reaches now 423 plant species, 194 genera and 68 families. Such numbers rise to 679 plant species, 304 genera and 88 families if considered regardless of the detection methods applied. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa subspecies pauca strain De Donno (XfDD) ST53 is the causal agent of olive quick decline syndrome, a severe disease first described in Apulia, Italy. Although the two local cultivars Cellina di Nardò and Ogliarola Salentina showed high susceptibility, traits of resistance to the bacterium were found in the cultivar Leccino. Previous studies in field‐grown olives suggested that vascular occlusions and anatomophysiological properties of the different cultivars played a role in the olive response to XfDD. The present investigation reports observations at the early stage of the infection on artificially inoculated olives. Electron microscope studies showed that XfDD exploits the pit membranes (PMs) of the susceptible cultivar Cellina di Nardò to spread systemically. In this cultivar, PMs were degraded upon XfDD infection, suggesting activity of bacterial cell wall‐degrading enzymes. Moreover, occluded vessels contained an amorphous electrondense matrix resembling gum. Conversely, in Leccino, occluded vessels were mainly filled by callose‐like granules that tightly entrapped XfDD cells. In addition, PMs from Leccino had a compact undegraded structure that was not permeable to XfDD. Our study suggests that exploitation of PMs is a key event in the infection process of X. fastidiosa subsp. pauca ST53 in susceptible olive cultivars. [ABSTRACT FROM AUTHOR]

While most bacteria are unicellular microbes they communicate with each other and with their environments to adapt their behaviors. Quorum sensing (QS) is one of the best-studied cell–cell communication modes. QS signaling is not restricted to bacterial cell-to-cell communication – it also allows communication between bacteria and their eukaryotic hosts. The diffusible signal factor (DSF) family represents an intriguing type of QS signal with multiple roles found in diverse Gram-negative bacteria. Over the last decade, extensive progress has been made in understanding DSF-mediated communication among bacteria, fungi, insects, plants, and zebrafish. This review provides an update on these new developments with the aim of building a more comprehensive picture of DSF-mediated intraspecies, interspecies, and inter-kingdom communication. DSFs are cis -2-unsaturated fatty acids containing fatty acid carbon chains of various lengths and cis double-bond configurations. DSF-producing bacteria are widely distributed in nature. Based on their genomic origins, DSF-mediated intraspecies communication pathways are generally affiliated to three different groups, respectively represented by Xanthomonas campestris pv. campestris (Xcc), Burkholderia cenocepacia (Bcc), and Pseudomonas aeruginosa. DSF-mediated interspecies communication occurs between DSF-producing bacteria and B. cenocepacia, Stenotrophomonas maltophilia , Bacillus , Francisella novicida , Salmonella , and Bdellovibrio bacteriovorus. DSF-mediated inter-kingdom communication occurs between DSF-producing bacteria and Candida albicans. DSF signaling occurs in plant development and defense, Xylella fastidiosa colonization of insects, and the zebrafish inflammatory response. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa is an important bacterial plant pathogen causing high-consequence diseases in agricultural crops around the world. Although as a species X. fastidiosa can infect many host plants, there is significant variability between strains regarding virulence on specific host plant species and other traits. Natural competence and horizontal gene transfer are believed to occur frequently in X. fastidiosa and likely influence the evolution of this pathogen. However, some X. fastidiosa strains are difficult to manipulate genetically using standard transformation techniques. Several type I restriction-modification (R-M) systems are encoded in the X. fastidiosa genome, which may influence horizontal gene transfer and recombination. Type I R-M systems themselves may undergo recombination, exchanging target recognition domains (TRDs) between specificity subunits (hsdS) to generate novel alleles with new target specificities. In this study, several conserved type I R-M systems were compared across 129 X. fastidiosa genome assemblies representing all known subspecies and 32 sequence types. Forty-four unique TRDs were identified among 50 hsdS alleles, which are arrayed in 31 allele profiles that are generally conserved within a monophyletic cluster of strains. Inactivating mutations were identified in type I R-M systems of specific strains, showing heterogeneity in the complements of functional type I RM systems across X. fastidiosa. Genomic DNA methylation patterns were characterized in 20 X. fastidiosa strains and associated with type I R-M system allele profiles. Overall, these data suggest hsdS genes recombine among Xylella strains and/or unknown donors, and the resulting TRD reassortment establishes differential epigenetic modifications across Xylella lineages. [ABSTRACT FROM AUTHOR]

Aim. The modern economic era is riven with issues that significantly affect day-to-day existence. Climate change and its effects are among the most crucial. In this regard, Xylella fastidiosa infection represents one of the most difficult challenges in Italy. The purpose of this study is to propose decision-making insights that, beginning from the emotive information provided by the media, build a foundation for containing the negative economic effects of the Xylella phenomenon by involving the key actors in the agri-food supply chain. Design/methodology. The study was composed in different consequent phases: an indepth historical and literature analysis of the phenomenon; a sentiment analysis on the emotions mostly conveyed by the newspapers that covered the topic; and a PLS-SEM model in a case study of consumers. Measures were detected through a quantitative questionnaire. Findings. The results suggest that the most frequently conveyed emotion was trust. The PLS-SEM mediation model highlighted that trust in farmers could have an indirect impact on willingness to buy olive oil through the perception of safety in the Italian market. Estimates were validated through bootstrap analysis. Novelty. The study aims to investigate a subject that has not yet been addressed, outside of a biological perspective, from a systemic point of view. Complementing the current biological and agronomic viewpoints with a different framework could represent a wellestablished element in assessing the relationship between trust in agri-food supply chain actors and consumer willingness to buy during critical events by offering crucial insights on economic engagement policies. [ABSTRACT FROM AUTHOR]

The vector-borne bacterium Xylella fastidiosa is responsible for Pierce's disease (PD), a lethal grapevine disease that originated in the Americas. The international plant trade is expanding the geographic range of this pathogen, posing a new threat to viticulture worldwide. To assess the potential incidence of PD, we have built a dynamic epidemiological model based on the response of 36 grapevine varieties to the pathogen in inoculation assays and on the vectors' distribution when this information is available. Key temperature-driven epidemiological processes, such as PD symptom development and recovery, are mechanistically modelled. Integrating into the model high-resolution spatiotemporal climatic data from 1981 onward and different infectivity (R0) scenarios, we show how the main wine-producing areas thrive mostly in non-risk, transient, or epidemic-risk zones with potentially low growth rates in PD incidence. Epidemic-risk zones with moderate to high growth rates are currently marginal outside the US. However, a global expansion of epidemic-risk zones coupled with small increments in the disease growth rate is projected for 2050. Our study globally downscales the risk of PD establishment while highlighting the importance of considering climate variability, vector distribution, and an invasive criterion as factors to obtain better PD risk maps. A temperature-driven dynamic epidemiological model provides insights into the risk for Pierce's disease in grapevine. [ABSTRACT FROM AUTHOR]

1.2 Almond leaf scorch The most characteristic symptom associated with I X. fastidiosa i on almond is leaf scorching followed by decreased productivity and general tree decline. EPPO Global Database: Courtesy of M.M. Lopez Instituto Valenciano de Investigaciones Agrarias, Valencia (ES). gl 1.6 Coffee leaf scorch Symptoms of coffee leaf scorch appear on new growth of field plants as large marginal and apical scorched areas on recently developed leaves (Figure 7). The bacterium is the causal agent for Pierce's disease of grapevine, almond leaf scorch, alfalfa dwarf, oak leaf scorch, maple leaf scald, sycamore leaf scorch, mulberry leaf scorch, periwinkle wilt, pecan leaf scorch, elm leaf scorch, oleander leaf scorch, phony peach, plum leaf scald, citrus variegated chlorosis and coffee leaf scorch (Hopkins & Purcell, [28]). Disease symptoms Symptoms depend on the combination of host and I X. fastidiosa i strain and the susceptibility of the host variety. [Extracted from the article]

Coffee leaf scorch Symptoms of coffee leaf scorch appear on new growth of field plants as large marginal and apical scorched areas on recently developed leaves (Figure A7). Almond leaf scorch The most characteristic symptom associated with I X. fastidiosa i on almond is leaf scorching followed by decreased productivity and general decline of the tree. A European Commission database detailing host plants found to be susceptible to I X. fastidiosa i in the European Union is available online.https://ec.europa.eu/food/plants/plant-health-and-biosecurity/legislation/control-measures/xylella-fastidiosa/database-susceptible-host-plants en Plants showing symptoms should be sampled for laboratory testing. Bacterial leaf scorch of shade trees Symptoms of bacterial leaf scorch are similar on different tree hosts such as I Acer i spp., I Cornus florida i , I Celtis occidentalis i , I Liquidambar styraciflua i , I Morus alba i , I Platanus i spp., I Quercus i spp. and I Ulmus americana i (Gould & Lashomb, [28]). [Extracted from the article]

Until today, only Leccino and Fs-17 (=Favolosa®) olive cultivars proved resistant to Xylella fastidiosa subsp. pauca (Xfp) due to a low presence of bacteria in the xylem. Integrated disease management in olive growing areas threatened by the spread of Xfp is crucial to overcoming the environmental, economic and social crisis. Since the EU Decision allows for the plantation of resistant olive cultivars in infected areas, there is a need to define a suitable plantation system for these cultivars. The adoption of new planting systems, such as intensive and super-intensive (SHD), could compensate for the economic losses and restore the olive agroecosystem. The aim is to ascertain the suitability of the available Xfp-resistant cultivars to SHD planting systems that demonstrate the best economic and environmental sustainability. Hence, a five-year study was established in an experimental SHD olive orchard (Southern Italy) in order to analyse the main vegetative and productive traits of Leccino and Fs-17, together with four other Italian cultivars (Cipressino, Coratina, Frantoio and Urano), compared with the well-adapted cultivars to SHD orchards (Arbequina and Arbosana), by means of the von Bertalanffy function. The results indicated that cv. Fs-17 showed sufficient suitability for SHD planting systems, giving the best-accumulated yield despite some canopy growth limitations, whereas cv. Leccino did not show satisfactory results in terms of both vegetative and yield parameters, confirming its suitability for intensive planting systems. These results are useful for optimizing integrated resistance management in Xfp-infected areas by planting resistant host plants. [ABSTRACT FROM AUTHOR]

The Apulia (southern Italy) ornamental sector has been facing regulatory obligations and trade limitations due to a Xylella fastidiosa (Xf) outbreak since 2013. Alternative options to encounter these constraints include the implementation of novel and sustainable ornamental production (NSM) practices. In this context, the purpose of this study is to assess simultaneously the environmental implications and economic viability of these options versus the conventional production options (CMs) among eight ornamental species (Abelia grandiflora, Bougainvillea cv Don Mario, Lantana camara cv Bandana rosa, Jasminum officinalis, Photinia fraseri cv Red Robin, Loropetalum chinense cv Black Pearl, Trachelospermum jasminoides, Viburnum lucidum). Life cycle assessment (LCA) and cost–benefit analysis (CBA) were used for this purpose. LCA revealed that NSM induced relatively less environmental impacts at the nursery level towards agricultural land occupation, climate change, fossil depletion, and water depletion. CBA showed that NSM increases moderately nursery business profitability in an economic sustainable way. An overall annual average gross margin of about EUR 192/1000 plants can be generated using NSM over the CM model. In general, this research provides a useful decision-support, helping nursery growers under the pressure of the threat of quarantine pests such as Xf to adopt NSM practices, which could be useful to produce ornamental and landscape plants with high sanitary quality. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa subsp. pauca (Xfp) is the plant pathogenic bacterium causing the epidemic of olive quick decline syndrome decimating olive trees in the Apulia region (southern Italy). The lack of any effective therapeutic application for the control of this pathogen and its categorization as a regulated quarantine pathogen in many countries worldwide, impose mandatory eradication and containment measures. Based on current EU legislation, containment measures apply in those areas where the bacterium is widely established, such as in the Apulia region, and thus containment strategies to mitigate and cope with the infections are needed. We set up a field trial to assess if pruning interventions could limit and/or recover Xfp-infected trees by reducing the systemic spread of the bacterium and the severity of the desiccation phenomena typically compromising the crown of the highly susceptible cultivars, e.g., cv. Cellina di Nardò. Trees subjected either to major or light pruning interventions, including the removal of all the symptomatic branches, did not demonstrate a reduced bacterial colonization or development of symptoms. After two years of targeted pruning interventions, no significant amelioration of the sanitary status of the infected olive trees was recorded, suggesting that the sole application of these interventions is not effective to counteract the impact of the bacterium in the susceptible olive trees. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa is a major transboundary plant pest, causing severe socioeconomic impacts. Development of preventive strategies and methods for surveillance, early detection, monitoring, and accurate diagnosis of X. fastidiosa and its vectors, are keys to preventing the effects of this plant pathogen, and assist timely eradication or optimisation of containment measures. This review focuses on approaches for early detection of X. fastidiosa in the Mediterranean Basin, including development of climatic suitability risk maps to determine areas of potential establishment, and epidemiological models to assist in outbreak management through optimized surveillance and targeted responses. The usefulness of airborne hyperspectral and thermal images from remote sensing to discriminate X. fastidiosa infections from other biotic- and abioticinduced spectral signatures is also discussed. The most commonly used methods for identifying X. fastidiosa in infected plants and vectors, and the molecular approaches available to genetically characterize X. fastidiosa strains, are described. Each of these approaches has trade-offs, but stepwise or simultaneous combinations of these methods may help to contain X. fastidiosa epidemics in the Mediterranean Basin. [ABSTRACT FROM AUTHOR]

Strengthening Plant Health research is a major challenge for Mediterranean countries. The diversity and fragmentation of the research landscape in this region have weakened the impacts of national efforts. Mediterranean countries can benefit from coordination of research activities to increase efficiency and impacts. The initiative 'Plant health research priorities for the Mediterranean region', led by the International Centre for Advanced Mediterranean Agronomic Studies (CIHEAM Bari)1 and the Euphresco network for phytosanitary research coordination and funding2 can promote convergence of national programmes and optimize the use of the scarce funding available to plant health, thus strengthening international cooperation and increasing the excellence and relevance of research. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa is a fastidious Gram-negative bacterium that is associated with several important plant diseases, and is regulated as a quarantine pest in many countries where strategies are implemented to prevent its introduction and spread. To enact efficient quarantine measures, effective and early detection of the pathogen are essential, especially because global trade of goods increases the risks of introduction of alien pathogens. this study aimed to adapt two qPCR-based diagnostic methods (SYBR Green and Probe based qPCR), already in use to detect X. fastidiosa, for use with a nanoplate based digital PCR assay. Detection of the pathogen using the two digital PCR assays (EvaGreen- and Probe-based) was similar to standard qPCR, giving 100% sensitivity, specificity, and accuracy, while providing accurate absolute quantification of the pathogen when using experimental samples that had low concentrations of host DNA. Using undiluted plant DNA added with low concentrations of X. fastidiosa, only the TaqMan method maintained satisfactory performance and quantification, and is therefore preferred. These results are a first step demonstrating the usefulness of nanoplate-based digital PCR for detection of plant pathogens, which allows greater throughput than qPCR, reducing the time and cost of diagnostic assays. [ABSTRACT FROM AUTHOR]

Early detection of Xylella fastidiosa outbreaks in Apulian olive groves is crucial, especially in buffer zones and pathogen-free areas where olive trees are asymptomatic. Three studies were conducted. Two were on the spatial and temporal progression of X. fastidiosa infections in tree canopies of asymptomatic or mildly symptomatic olive trees of tolerant ('Leccino') and susceptible ('Cellina di Nardò' and 'Ogliarola salentina') cultivars. Despite different trends in pathogen infection rates and concentrations between 'Leccino' and susceptible olive cultivars over the study period, results showed that sampling was most effective in the mid-upper part of tree canopies throughout the year, excluding the warmest and coldest periods. Stem xylem tissues were the most appropriate for detecting the pathogen compared to lower parts of mature leaves with petioles, using serological and molecular assays. Based on these results, a third study was conducted to compare molecular and serological tests (qPCR, real-time LAMP, DAS-ELISA, DTBIA) for detection of X. fastidiosa in the mid-upper part of asymptomatic branches of infected 'Leccino' trees that were sampled in an appropriate collection time, using stem xylem tissue as the most appropriate matrix for testing. The molecular methods showed the greatest sensitivity, with no undetermined results, while among the serological assays, DTBIA was more sensitive than DAS-ELISA. An improved protocol for monitoring asymptomatic olive trees is recommended. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa (Xf) is a vector‐borne plant bacterium native to the Americas, which causes severe diseases to agricultural crops, ornamental plants and forest trees. The bacterium is becoming a source of worldwide health plant concern and disease outbreaks associated with Xf have occurred outside of its native range (in Europe, Asia and the Middle East). Several studies have estimated risks associated with Xf outbreaks in invaded regions under current climate conditions, but future climate change has been seldom addressed. In the present study, we calibrated correlative models of bioclimatic species distribution to forecast the potential range and severity of two economically important Xf‐related diseases (Pierce's disease and the bacterial leaf scorch of shade trees) by the period 2040–2060. Models predict that conditions could become highly favourable for Pierce's disease in economically important wine‐producing regions of the world, highlighting the need to design control strategies. Similarly, models suggest that risk of bacterial leaf scorch of shade trees might increase in temperate regions where it is still apparently absent. However, we note that substantial uncertainty in predictions arises from high levels of correlation among climatic variables in the calibration data set. The inherent lack of knowledge concerning whether the distribution of Xf‐related diseases is at climatic equilibrium or not in Europe may also influence our predictions. The models provide valuable information to identify regions where increased surveillance efforts should be made and where control strategies are required. [ABSTRACT FROM AUTHOR]

Systemic bacteria such as Xylella fastidiosa can be vertically transmitted by using diseased propagative material during nursery tree production. We tested the hypothesis that X. fastidiosa is not transmitted by symptomless olive tree sprouts. In addition, we investigated the distribution of bacteria in olive plants (different parts of canopy and root system) with initial leaf scorch symptoms and with symptoms spread throughout the canopy. In both studies, the presence of bacteria was tested by quantitative real‐time PCR (qPCR). For the first hypothesis, sprouts from a symptomless olive tree were rooted and checked for X. fastidiosa infection 32 months later. A total of 57.7% (41 of 71) of rooted seedlings were positive for X. fastidiosa (Ct from 24.25 to 31.82) but only one plant had scorched leaves. Regarding the distribution of the bacteria in the diseased plants, results based on qPCR showed that X. fastidiosa was systemically distributed through the olive plant canopy (30% to 77% of sampled tissues, with Ct values from 19.56 to 31.59). Samples from trees showing symptoms of olive quick decline syndrome (OQDS), taken 3 m above the lateral branch with symptoms, were positive for the presence of X. fastidiosa, as was the root system. The results demonstrate that vegetative material from olive plants used for rooting must be carefully selected for the absence of X. fastidiosa. Also, based on the qPCR‐positive results, pruning may have a limited effect on eliminating the bacteria from diseased plants, even from the ones showing few OQDS symptoms. [ABSTRACT FROM AUTHOR]

Mycorrhizal plants mediate interactions between their root‐associated fungal symbionts and insect herbivores. Arbuscular mycorrhizal (AM) associations tend to boost phloem sap sucking insects and host specialist chewing insects but depress host generalist chewing insects. In turn, insect herbivores have only small negative effects on the abundance of AM fungi. Ectomycorrhizal (EM) associations, less studied, have no consistent effect on phloem sap‐sucking or chewing insects, but their insect herbivores have strong negative effects on EM fungal abundance.Spittlebugs (Hemiptera: Cercopoidea) feed on xylem sap and are disproportionately associated with EM plants, probably because many EM fungi are especially well equipped to access nitrogen (N) from complex soil organic matter. Assimilated N is transported in host plant xylem sap as amino acids, the primary food source for xylem‐feeding insects.Although EM plants account for only 2% of all vascular plants, about 19% of spittlebugs have EM primary hosts. This compares to 9% of hosts that are rhizobial or actinorhizal N‐fixing plants, alternative modes of root‐associated N acquisition that also attract spittlebugs.Notable spittlebug EM host plants include Pinus and Abies (Pinaceae), Quercus, Alnus and Betula (Fagales), Salix (Salicaceae), Eucalyptus (Myrtaceae) and the gymnosperm Gnetum (Gnetales).Some EM plants, including several Pinus species, host spittlebug pests and some play an important role in the ecology of spittlebug vectors of the bacterial plant pathogen Xylella fastidiosa.The fossil record and dated molecular phylogenies suggest that spittlebugs initially evolved in parallel with EM Pinaceae. [ABSTRACT FROM AUTHOR]

The outbreak of the olive quick decline syndrome caused by Xylella fastidiosa represents one of the main agricultural threats in Italy. Recently, thirty asymptomatic or paucisymptomatic genotypes found in olive groves heavily compromised by the bacterium were identified. HPLC ESI/MS-TOF analyses on leaf petiole extract were carried out to characterize the metabolic profile of selected genotypes. Besides uni- and multi-variate statistical methods differentiated the metabolic profiles of olive genotypes genetically related to the cultivars 'Leccino' and 'Ciciulara', no common metabolic pattern was found among the selected genotypes with respect to susceptible one. In-depth evaluation of seven selected phenolic compounds highlighted quantitative differences between genotypes and the susceptible control cultivar but a resistance-related pattern cannot be yet defind. Nevertheless, an unusually high concentration of quercetin-3-O-rhamnoside characterized a genotype genetically related to Tunisian cultivars which displayed no symptoms besides high bacterial concentration, suggesting how tolerance may be related to peculiar phenolic profiles. [ABSTRACT FROM AUTHOR]

Eradication measures are used when a pest or pathogen invades a free area, the objective being to control its outbreak by eliminating or reducing its population levels in that area, which involves removing all infected plants. Xylella fastidiosa is one of the most notorious plant pathogens presently emerging in Europe. This bacterium is a pathogen of concern for many plants globally, and has a broad range of wild and cultivated hosts common in Europe. Given that there is no effective treatment to reduce the repercussions of this disease, its spread poses a severe risk to European agriculture. The EU has designed mandatory plant health measures for the purposes of implementing an eradication or containment strategy. Since an eradication strategy depends on the actions of farmers, it is vital to adopt measures that encourage behavior that helps reduce the risk of spread. In this paper, we have developed a field-scale economic analysis, which links production costs, revenue, agronomic factors, and mandatory protection measures, and allows us to estimate the losses caused over time by pests or pathogens at the farm level, and the age-dependent payments that farmers should receive. This way a confidence interval for fair compensation can be obtained. This compensation serves to design positive incentives for farmers to inform government authorities about the presence of bacteria on their farms and participate in eradication programmes. We apply our economic modelling to Xylella fastidiosa in vineyards, and on olive and citrus plants, in the Valencian Community of Spain in Europe. [ABSTRACT FROM AUTHOR]

Pierce's disease is a deadly disease of grapevines caused by the bacterial pathogen Xylella fastidiosa (Xf). A Pierce's disease resistance locus from Vitis arizonica/candicans b43-17 segregated as a single dominant gene and mapped as PdR1a and PdR1b in two F1 sibling selections. The physical mapping of the PdR1b allele allowed the identification of five ORFs of the Leucine-Rich Repeat Receptor Kinase gene family. Two ORFs: V.ari-RGA14 and V.ari-RGA18 were used to transform embryogenic callus of V. vinifera Chardonnay (CH) and Thompson Seedless (TS) and V. rupestris St George (SG) via Agrobacterium tumefaciens. Regenerated plants were inoculated with Xf under greenhouse conditions. Genetic transformation with RGA14 and 18 did not generate resistance in CH and TS, although some lines of CH showed significantly lower stem bacterial concentration and/or exhibited reduced symptoms. In transgenic SG14, improved regrowth was accompanied with lower bacterial titers and decreased pectin lyase and ß-1,3-glucanase 3 gene expression. The limited effects of the transgenes on PD resistance could be explained by the lack of suitable partners or the presence of susceptibility factors that could not be overcome under these experimental conditions. The involvement of RGA17 in b43-17 resistance to Xf should not be discarded. Key message: The expression of two candidate genes for Pierce's disease resistance in Vitis arizonica/candicans b43-17 had limited effect in the resistance of susceptible vinifera genotypes to the disease. [ABSTRACT FROM AUTHOR]