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Effective disease management hinges on an accurate understanding of the ecological and epidemiological underpinnings of the pathosystem. New epidemics may prompt consideration of whether knowledge gaps or changes to the pathosystem warrant revision of management strategies. Pierce's disease of grapevines is highly episodic in coastal Northern California vineyards, with modest incidence in most years punctuated by occasionally severe epidemics.To better understand what was driving a developing epidemic in the region, we revaluated what is known about the ecology and epidemiological role of the dominant vector, the blue-green sharpshooter Graphocephala atropunctata. We monitored vector spatiotemporal dynamics at 32 vineyards over three years, surveyed plant community composition in the adjacent habitat to understand its link to vector recruitment, and quantified patterns of natural infectivity for the pathogen Xylella fastidiosa. Overall, the results were consistent with past studies of G. atropunctata ecology. For example, the scale of dispersal from source habitat and seasonal patterns in activity were generally similar to those documented in prior studies. The results also confirmed the influence of adjacent plant community composition on G. atropunctata activity in vineyards, and the role of riparian habitat and select plant taxa as vector sources. Nonetheless, further consideration of the epidemiological significance of certain features of the pathosystem may be warranted, especially those related to seasonality in X. fastidiosa infection in vectors. A marked increase in infected G. atropunctata late in the season likely reflects pathogen acquisition from infected grapevines, which may have implications for disease management strategies. [ABSTRACT FROM AUTHOR]

The study of Auchenorrhyncha species composition in Greek olive orchards is crucial due to the potential threat of Xylella fastidiosa invading the region. Recent studies have begun exploring agricultural landscapes, particularly olive and citrus orchards. From 2016 to 2022, biodiversity surveys were conducted in thirteen olive orchards across three regions of Greece: Peloponnese, Sterea Ellada, and the Northeast Aegean. Malaise traps were installed in each orchard and monitored monthly, supplemented by sweep net sampling in two orchards to capture less mobile species and assess their association with host plants. A total of 14,771 specimens were collected, representing 125 species predominantly feeding on weeds. The dominant species were the Typhlocybinae Hebata decipiens and Zyginidia pullula, while Euscelis lineolata was the most common Deltocephalinae. Aphrophoridae, including Philaenus spumarius and Neophilaenus campestris, were more effectively collected with sweep nets, primarily from Avena sterilis L. This study offers a detailed overview of the Auchenorrhyncha fauna in Greek olive orchards, providing essential insights for developing strategies to prevent the invasion of Xylella fastidiosa. [ABSTRACT FROM AUTHOR]

The dynamics of virulence evolution in vector‐borne plant pathogens can be complex. Here, we use individual‐based, quantitative‐genetic simulations to investigate how virulence evolution depends on genetic trade‐offs and population structure. Although quite generic, the model is inspired by the ecology of the plant‐pathogenic bacterium Xylella fastidiosa, and we use it to gain insights into possible modes of virulence evolution in that group. In particular, we aim to sharpen our intuition about how virulence may evolve over short time scales via antagonistically pleiotropic alleles affecting pathogen performance within hosts and vectors. We find that even when pathogens find themselves much more often in hosts than vectors, selection in the vector environment can cause correlational and potentially non‐adaptive changes in virulence in the host. The extent of such correlational virulence evolution depends on many system parameters, including the pathogen transmission rate, the proportion of the pathogen population occurring in hosts, the strengths of selection in host and vector environments, and the functional relationship between pathogen load and virulence. But there is a statistical interaction between the strength of selection in vectors and the proportion of the pathogen population in hosts, such that if within‐vector selection is strong enough, over the short term, it can dominate virulence evolution, even when the host environment predominates. [ABSTRACT FROM AUTHOR]

Bacterial tree diseases have been mainly studied in agriculture and horticulture. For forest trees, damage due to bacterial diseases is understudied. Moreover, bacterial tree diseases often appear in the context of so‐called complex diseases, which are dependent on other factors, such as multiple microorganisms, insects or abiotic factors which weaken the host. In recent years, outbreaks of bacterial tree diseases, such as Xylella fastidiosa in the Mediterranean region or acute oak decline (AOD) in the United Kingdom, raised the awareness of bacterial diseases on forest trees. In this review, we aim to summarise the current issues and available knowledge about bacterial diseases of forest trees in Central Europe. Furthermore, we identify potential bacterial pathogens that could gain importance in the future for central European forests. The methods used were a systematic literature search and the analysis of the data collected over the last 10 years on bacterial diseases by the Swiss forest protection service. We conclude that, on one side, complex bacterial diseases could increase in importance, especially considering ongoing climate change. Therefore, the bacterial community of diseased trees (the pathobiome) needs to be studied more in depth to understand the emergence of complex bacterial diseases. On the other side, host ranges of highly pathogenic invasive genera and species, such as Xylella, need to be investigated experimentally for common central European tree species and varieties, to implement proactive risk management strategies against bacterial diseases in forest trees. Finally, urban trees and green spaces should be monitored more closely, as they could serve as starting points for bacterial disease outbreaks in forests, similarly to other emerging diseases and pathogens. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa is a destructive bacterial plant pathogen affecting hundreds of plant families, including important crops such as olive and citrus trees and vines. The pathogenicity of this bacterium rests in a group of genes that encode toxins, enzymes, fimbrial/afimbrial adhesins, cell–cell aggregation proteins and other virulence factors. We investigated the contribution of mobile genetic elements (MGEs) to the pathogenicity of X. fastidiosa. Using computational tools, we analysed 94 X. fastidiosa genomes corresponding to the three most important subspecies to identify insertion sequences (ISs) and prophages. Results indicate that the distribution and diversity of ISs are modest, with a few families widespread throughout the subspecies of X. fastidiosa. The prophages are abundant, and play a more significant role in the pathogenicity of X. fastidiosa. Prophages are common in the subspecies of X. fastidiosa and contribute to numerous genes related to pathogenicity. The phylogenetic analyses suggest that prophages are recently acquired and that the rearranging of pathogenicity genes triggered by them could generate strains with new pathogenic capacities. Finally, the contribution of MGEs to the pathogenesis of X. fastidiosa was evidenced by determining their association with virulence genes using a Bayesian framework for phylogenetic analysis of character evolution. [ABSTRACT FROM AUTHOR]

The spread of Xylella fastidiosa since 2013 in the Mediterranean olive groves of the Apulia region has modified the landscape. The aims of this research are focused on the analysis of its effects on the following: (1) Landscape multifunctionality supported by olive groves in terms of landscape service provision; (2) The functional relations among the main Mediterranean land covers in terms of landscape service supply and demand. (3) The landscape fragmentation at different spatial scales. The landscape has completely changed, mainly in those land covers that, in the past, acted as stabilizing factors (croplands and olive groves), which has been replaced by grasslands in 2021. The main effects of Xylella fastidiosa were on the multifunctionality of olive grove landscape in terms of food production, water regulation, carbon sequestration, and pollination, as well as on landscape cultural value. Ecosystem service supply is mainly related to olive groves, tree covers, shrublands, and wetlands. The province of Lecce showed the highest fragmentation, as demonstrated by the number of patches, the mean patch area, and the DIVISION metric, while the province of Brindisi was the least fragmented, with a DIVISION metric similar in 2011 and in 2021. The multiscale assessment of "olive groves" fragmentation has helped in better analyzing the effect of its spatial configuration on the provision of landscape services and in identifying the right spatial scale for each landscape service provision. It is essential to analyze landscape service flow to enlarge the understanding of the ways in which their supply is maintained through a landscape regeneration policy toward the socio-economic–ecological recovery. [ABSTRACT FROM AUTHOR]

Since recently, a decline of holm oak (Quercus ilex L.) is observed in Salento (South Italy), this caused concern regarding the protection of native biodiversity and local forests. Symptomatic trees show browning of leaves, thinning of canopy, and loss of branches. The aim of this study was to understand the biotic factors involved in the observed decline. During the monitoring activity, the use of phenotypic descriptors highlighted the presence of two types of decline with distinct symptoms among oaks in rural and urban areas, which could be classified as Acute Oak Decline (AOD) and Chronic Oak Decline (COD), respectively. Following this, diagnostic analyses were carried out to assess the presence of various holm oak pathogens on twigs, trunk, and soil. These analyses revealed the presence of several Botryosphaeriaceae oak pathogens, present ubiquitously between the two environmental contexts, with Diplodia seriata being overall the most prevalent. Contrarily, bacteria associated with AOD were only present in the rural areas and included: Brenneria goodwinii , Gibbsiella quercinecans , and Rahnella victoriana. As far as known to the authors, this is the first time these pathogens have been found in the Mediterranean coastal regions. Lastly, soil analyses performed to detect the presence of Phytophthora cinnamomi were negative. Our results highlight the presence of several pathogens, which indicates that oak decline is a multifactorial phenomenon for which the predisposing, initial, and contributing factors are not yet known particularly for the recently described AOD and COD. Finally, the identification of AOD-related bacteria in Salento is a cause of concern for the need of urgent management actions aimed to contain their spread and to preserve the forest heritage of the region. [ABSTRACT FROM AUTHOR]

This study describes the antibacterial activity of pomegranate peel extract on the development of the Olive Quick Decline Syndrome (OQDS) caused by Xylella fastidiosa subsp. pauca strain De Donno. Xylella fastidiosa subsp. pauca is a systemic bacterium that colonizes the xylem tissue of olive trees by blocking them and limiting the correct sap flow of the plant. For six years, from 2016 to 2021, olive trees affected by X. fastidiosa subsp. pauca were treated with a hydroalcoholic extract obtained from Punica granatum fruit peel. High-Performance Liquid Chromatography–Diode Array Detection–Electro-Spray Ionization Mass Spectrometry (HPLC–DAD-ESI/MS) analysis was carried out to identify punicalagins and ellagic acid which are the main antifungal and antibacterial compounds. The research was carried out on a farm in Trepuzzi (Lecce) located in Salento (Italy). Both in vitro and in vivo tests show the effectiveness of the extract tested. Symptom severity was lower on the canopy of treated plants vs untreated olive trees. Molecular biology tests to assess the presence of X. fastidiosa in treated and untreated plants confirm the effectiveness of Pomegranate Peel Aqueous + Ethanol Extract (PPAEE). [ABSTRACT FROM AUTHOR]

Xylella fastidiosa is an aerobic, Gram-negative bacterium that is responsible for many plant diseases. The bacterium is the causal agent of Pierce's disease in grapes and is also responsible for citrus variegated chlorosis, peach phony disease, olive quick decline syndrome and leaf scorches of various species. The production of biofilm is intrinsically linked with persistence and transmission in X. fastidiosa. Biofilm formation is regulated by members of the Diffusible Signal Factor (DSF) quorum sensing signalling family which are comprised of a series of long chain cis-unsaturated fatty acids. This article describes the evaluation of a library of N-acyl sulfonamide bioisosteric analogues of BDSF, XfDSF1 and XfDSF2 for their ability to control biofilm production in X. fastidiosa. The compounds were screened against both the wild-type strain Temecula and an rpfF* mutant which can perceive but not produce XfDSF. Planktonic cell abundance was measured via OD600 while standard crystal violet assays were used to determine biofilm biomass. Several compounds were found to be effective biofilm inhibitors depending on the nature of the sulfonamide substituent. The findings reported here may provide future opportunities for biocontrol of this important plant pathogen. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa is one of the most dangerous plant‐pathogenic bacteria globally, affecting various host species. Plum leaf scald (PLS) is the primary disease affecting plum trees in Brazil, with plant eradication efforts significantly increasing in recent years. This study aims to elucidate the disease dynamics and its vector in three monitored orchards from 2010 to 2015 and associate the pattern of pathogen dispersal with mechanical pruning. The incidence was lower in Porto Amazonas, starting at 0% and reaching 14% after 5 years. In contrast, the orchards in Araucaria and Palmeira showed an initial incidence around 5% in the first year, exceeding 80% by the end of the study. Sharpshooter leafhoppers, the vectors, were collected at ground and plant canopy level during the last 3 years. In 2013, more leafhoppers were found near the ground, but their numbers equalized across heights in the following years. Kernel smoothing revealed spatial dependence, and an autologistic model indicated an aggregated infection pattern with increased PLS risk for neighbouring plants. The border effect at the epidemic's onset was linked to pathogen entry via external vectors. The disease's progression along rows was attributed to effective mechanical pathogen transmission through pruning. Therefore, in regions with several summer prunings, it is recommended to sanitize pruning shears to prevent pathogen transmission. Constant monitoring and control of the vector are essential for effective disease management. [ABSTRACT FROM AUTHOR]

Background: In the context of pathogen surveillance, it is crucial to ensure interoperability and harmonized data. Several surveillance systems are designed to compare bacteria and identify outbreak clusters based on core genome MultiLocus Sequence Typing (cgMLST). Among the different approaches available to generate bacterial cgMLST, our research used an assembly-based approach (chewBBACA tool). Methods: Simulations of short-read sequencing were conducted for 5 genomes of 27 pathogens of interest in animal, plant, and human health to evaluate the repeatability and reproducibility of cgMLST. Various quality parameters, such as read quality and depth of sequencing were applied, and several read simulations and genome assemblies were repeated using three tools: SPAdes, Unicycler and Shovill. In vitro sequencing were also used to evaluate assembly impact on cgMLST results, for six bacterial species: Bacillus thuringiensis, Listeria monocytogenes, Salmonella enterica, Staphylococcus aureus, Vibrio parahaemolyticus and Xylella fastidiosa. Results: The results highlighted variability in cgMLST, which not only related to the assembly tools, but also induced by the intrinsic composition of the genomes themselves. This variability observed in simulated sequencing was further validated with real data for six of the bacterial pathogens studied. Conclusion: This highlights that the intrinsic genome composition affects assembly and resulting cgMLST profiles, and that variability in bioinformatics tools can induce a bias in cgMLST profiles. In conclusion, we propose that the completeness of cgMLST schemes should be considered when clustering strains. [ABSTRACT FROM AUTHOR]

Introduction: The epidemic spread of the harmful bacterium Xylella fastidiosa causing the "olive quick decline syndrome", decimating olive trees in southern Italy, in the region of Apulia, prompted investigations to search for olive genotypes harbouring traits of resistance. Methods: A prospecting survey was carried out to identify, in the heavily infected area of Apulia, olive genotypes bearing resistance. Given the limited genetic diversity in the commercial olive groves with few cultivars widely cultivated, surveys targeted predominantly spontaneous olive genotypes in natural and uncultivated areas. Trees, selected for the absence of symptoms, were subjected to diagnostic tests and parentage analysis to disclose their genetic background. Transcriptomic analyses were also employed to decipher the molecular pathways in resistant genotypes. Artificial inoculations were carried out to confirm the resistant phenotypes of four open-pollinated seedlings of the cultivar Leccino. Results: Among the 171 olive collected genotypes, 139 had unique simple sequence repeat (SSR) profiles, with the cultivars Leccino, Cellina di Nardò, and Ogliarola salentina being the most frequent candidate parents. Among the Leccino progeny (n. 61), 67% showed a highly resistant (HR), resistant (R), or tolerant (T) phenotype to infection by X. fastidiosa. The occurrence of such phenotypes among those deriving from Cellina di Nardò and Ogliarola salentina was 32% and 49%, respectively. Analyses of the transcriptomic profiles of three Leccino-bearing genotypes, naturally infected and not showing symptoms, unravelled that a total of 17,227, 13,031, and 4,513 genes were found altered in the expression, including genes involved in photosynthesis, cell wall, or primary and secondary metabolism. Discussion: Indeed, transcriptomic analyses showed that one of these genotypes (S105) was more resilient to changes induced by the natural bacterial infection than the remaining two (S215 and S234). This study consolidates the evidence on the presence and heritage of resistance traits associated with the cv. Leccino. Moreover, valuable insights were gathered when analysing their transcriptomic profiles, i.e., genes involved in mechanisms of response to the bacterium, which can be used in functional genetic approaches to introduce resistance in susceptible cultivars and initiate strategies in olive-breeding programs through marker-assisted selection. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa (Xf) bacteria form biofilm on the cuticular surfaces of the functional foregut (precibarium and cibarium) of its vectors, xylem fluid-ingesting sharpshooter leafhoppers and spittlebugs. While much is known about Xf biofilm development and maturation in vitro, little is known about these processes in vectors. Real-time (RT)-PCR was used to quantify Xf genomes daily in the functional foreguts of blue-green sharpshooters, Graphocephala atropunctata, over 7 days of exposure to infected grapevines. Scanning electron microscopy (SEM) was used to examine Xf biofilm formation at 4 and 7 days of that time course. PCR showed populations building and reducing over a 4-day cycle. SEM revealed that foreguts at 4 days showed variability in quantity and location of bacterial attachment. Only early-stage biofilm formation occurred in low-turbulence areas of the cibarium, while high-turbulence areas of the cibarium and precibarium had rare but older, more developed macro-colonies. Biofilm was almost absent at 7 days but left behind adhesive material and remnants of prior colonization. Evidence supports the hypothesis that bacterial colonization was repeatedly interrupted and constrained by the vector. Behaviors such as egestion and enzymatic salivation likely can loosen and eject Xf biofilm, perhaps when profuse biofilm interferes with ingestion. Thus, vector acquisition of Xf is a dynamic and stochastic process of interactions between bacteria and insects. We further hypothesize for future testing that the insect can regulate this interaction. A deep understanding of Xf acquisition will aid the ongoing development of grapevine resistance to vector transmission of xylellae diseases. IMPORTANCE Xylella fastidiosa (Xf) is one of the most destructive invasive plant pathogens in the world, able to hijack new vectors when it invades a region; yet the temporal interplay of bacterial colonization and insect behavior is unknown. This paper describes important findings about the process of Xf biofilm formation and maturation in a vector, contrasting similarities and differences with such formation in vitro. Results support the hypothesis that the behavior of the vector constrains and may regulate Xf biofilm formation, in dynamic competition with the bacterium. The data from this paper partly explain why Xf is so successful at invasion. Because the bacterium can be acquired and inoculated very quickly, it can move readily from old to new vectors and host plants in all-new environments. Our findings are relevant to biosecurity decisions because they demonstrate the importance of identifying potential vector species in the Xylella invasion front. [ABSTRACT FROM AUTHOR]

Strains of Xylella fastidiosa subspecies pauca can infect olive trees, and an introduction of this pathogen has caused significant damage to the olive industry in Europe. Although this subspecies is not known to be present in North America, the environment, plant hosts, and insect vectors in the United States olive-growing regions (mainly California) are conducive to X. fastidiosa spread and disease damage. This study evaluated several risk factors for X. fastidiosa disease in the California olive industry, including infection of the common cultivars and acquisition by insect vectors. Olive cultivars Manzanillo, Sevillano, and Mission all exhibited disease symptoms after inoculation with X. fastidiosa strain De Donno obtained from the olive disease outbreak in southern Italy. Glassy-winged sharpshooters were able to acquire X. fastidiosa De Donno from infected olive plants as soon as 30 days after plant inoculation. This information is valuable for risk assessment and disease management planning in the event of a future introduction of olive-pathogenic strains of X. fastidiosa to the United States. [Figure: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

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.

Xylella fastidiosa ssp. fastidiosa (Xff) is the causal agent of Pierce's disease of grapevine, a management-intensive and potentially deadly disease. However, different stains and other subspecies, such as Xylella fastidiosa ssp. multiplex (Xfm), exist in the same regions and vary in capacity to cause disease. All strains differ in the fatty acids that comprise cell membranes, as these allow adaptations to specific host microenvironments. Therefore, studies were initiated to observe the fatty acid profiles of different Californian Xf isolates via fatty acid methyl ester (FAME) analysis. Observations revealed that the four Xff strains had similar FAME profiles that were distinct from those of the three Xfm strains, even in isolates that originated from the same host plant species. These data show consistent differences between Xff and Xfm strains and demonstrate the potential that FAME profiling has for Xylella subspecies identification of novel isolates. [Figure: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

Xylella fastidiosa is a xylem‐limited bacterial plant pathogen transmitted by insect vectors. It infects a wide range of plant species and causes devastating diseases. Botanical gardens are global repositories of plant diversity exposed to local biotic and abiotic stresses. We used molecular diagnostic tools for the detection of X. fastidiosa in a collection of New Zealand indigenous plants grown in a X. fastidiosa‐infected Californian area to determine if any species were infected with this bacterial pathogen and to help inform biosecurity responses. To this end, 130 New Zealand indigenous plant species comprising 72 genera, growing in the University of California Botanical Garden at Berkeley, California, were screened for X. fastidiosa. Multiple PCR‐based methods were used to detect the pathogen at the subspecies and sequence‐type levels directly from plant material; nine plant species tested positive by at least two PCR‐based methods. All nine infections were identified as X. fastidiosa subsp. multiplex sequence types 6 or 7 by the amplification of seven housekeeping genes. Three strains were cultured in vitro and their whole genome sequences were obtained; these strains belonged to three distinct clades within subspecies multiplex, indicating that the infections were not transmitted among these New Zealand indigenous plant species. The information gathered in this study will help to assess the risk of X. fastidiosa to New Zealand indigenous flora and the potential spillover to crops of agricultural importance. The work also shows the applied value of botanical garden collections as sentinels for international plant pathogen biosecurity risk assessment. [ABSTRACT FROM AUTHOR]

Spittlebugs and froghoppers (Hemiptera: Cercopoidea) are insects feeding on xylem, which potentially can cause significant economic damage worldwide by transmitting plant pathogenic bacteria such as Xylella fastidiosa. Australia and New Zealand are currently free from X. fastidiosa, but they are home to at least 45 native spittlebug species. Among these, the Australian natives Bathyllus albicinctus (Erichson, 1842) and Philagra parva (Donovan, 1805) are particularly widespread and can be found across southern and eastern Australia, with B. albicinctus also in New Zealand. The potential that both species might be capable of vectoring Xylella fastidiosa poses a substantial biosecurity risk if the bacterium were to invade these regions. In this study, we examined 87 spittlebug nymphs collected across 12 different host plant species, in five locations in Victoria, Australia. Our objective was to explore the factors influencing bacterial communities within and between these widespread spittlebug species, considering geographic location, insect phylogenetics, and host plant associations. We employed COI barcoding to assess insect genetic variation and 16S high throughput sequencing (HTS) metabarcoding to analyse bacterial microbiome diversity across various host plants. Our findings revealed minimal genetic divergence among spittlebug individuals in the same species, highlighting conspecificity despite conspicuous morphological divergences. On the other hand, we recorded significant variation in bacterial communities harboured by Bathyllus albicinctus nymphs feeding on different plants, even when these were collected within close proximity to each other. Therefore, host plant association appeared to shape the bacterial communities of spittlebugs more than insect genetic divergence or geographical location. These diverse bacterial communities could potentially facilitate transmission of plant pathogenic bacteria, underscoring the risk of widespread transmission among numerous plant hosts through insect-plant interactions. This study emphasizes the critical need to understand these complex interactions, particularly in the context of biosecurity. [ABSTRACT FROM AUTHOR]

Global change is believed to be a major driver of the emergence of invasive pathogens. Yet, there are few documented examples that illustrate the processes that hinder or trigger their geographic spread. Here, we present phylogenetic, epidemiological and historical evidence to explain how European vineyards escaped Xylella fastidiosa (Xf), the vector-borne bacterium responsible for Pierce's disease (PD). Using Bayesian temporal reconstruction, we show that the export of American grapevines to France as rootstocks to combat phylloxera (~1872–1895) preceded the spread of the Xf grapevine lineage in the USA. We found that the time of the most recent common ancestor in California dates to around 1875, which agrees with the emergence of the first PD outbreak and the expansion into the southeastern US around 1895. We also show that between 1870 and 1990, climatic conditions in continental Europe were mostly below the threshold for the development of PD epidemics. However, our model indicates an inadvertent expansion of risk in southern Europe since the 1990s, which is accelerating with global warming. Our temporal approach identifies the biogeographical conditions that have so far prevented PD in southern European wine-producing areas and predicts that disease risk will increase substantially with increasing temperatures. [ABSTRACT FROM AUTHOR]

Sharpshooters are known vectors of Plum Leaf Scald, caused by Xylella fastidiosa. The present study assessed diversity, population fluctuation and faunistic analysis in two plum orchards in Santa Catarina – Brazil, from January 2011 to December 2012. Traps were installed at 10 equidistant points in each orchard: two traps, high and low, at each sampling point. Cicadellini were the most abundant tribe, with 15 species, seven of them potential vectors (Bucephalogonia xanthophis, Dilobopterus costalimai, Hortensia similis, Macugonalia cavifrons, Macugonalia leucomelas, Pawiloma gratiosa, and Sibovia sagata) and a total of 759 specimens. In Proconiini, six species were captured, including two potential vectors (Homalodisca ignorata and Oncometopia facialis), and a total of 226 specimens. Dominant species were Erythrogonia dorsalis, M. cavifrons, O. fusca, B. xanthophis, and O. facialis. Constant species were E. dorsalis, M. cavifrons, S. sagata, O. facilis, and O. fusca. In Cicadellini, 104 specimens were caught on high traps (11 species) and 655 on low traps (15). In Proconiini, 59 specimens on high traps (6) and 167 on low traps (4). The composition and community diversity were distinct when comparing the sampled orchards, according to Shannon and Equitability Indexes, Effective Number of Species, and Hutcheson t-Test. Cicadellinae population peak was in April for 2011, 2012 altogether. Dominant species population peaks were in February (E. dorsalis), April (M. cavifrons), July (B. xanthophis), September (O. facialis), and October (O. fusca). Population fluctuation is likely affected by biotic and abiotic factors, especially human activity, and plant phenology. [ABSTRACT FROM AUTHOR]

This study investigated the phenology and population dynamics of potential insect vectors of Xylella fastidiosa Wells et al. and other Auchenorrhyncha species in olive and citrus groves of Chania province, Crete, Greece. Although X. fastidiosa has not been reported in Greece, its introduction could cause serious diseases in many crops, including olives and citrus. Olive groves of Olea europaea L. 'Koroneiki' were sampled systematically using sweep net and Malaise traps over 24 months. One citrus grove was sampled for one year using a Malaise trap. Sweep net samples were taken from the herbaceous cover, tree canopy, and field borders of olive groves. Auchenorrhyncha were more abundant on the herbaceous cover compared to the canopy and field margins. Aphrophoridae species were mostly found on the herbaceous cover and in low numbers during fall (October–December) and spring (April–May). Cicadellidae species, such as Euscelis spp., were frequently found on the herbaceous cover of both olive and citrus groves. One Aphrophoridae and several Cicadellidae species were recorded in the citrus grove. Altitude was found to influence the population abundance of some Auchenorrhyncha species in olive groves. These results provide information for effective integrated management of insect vectors and their vector-borne pathogens. [ABSTRACT FROM AUTHOR]

Spiroplasma citri, the causal agent of citrus stubborn disease (CSD), causes significant losses in citrus crops. An efficient pathogen detection system is critical for epidemiology studies, particularly when a large sample size is involved. In this study, we report the development of an immunomolecular assay, immunocapture real-time polymerase chain reaction (IC-qPCR), targeting the spiralin gene for direct detection of S. citri without DNA isolation. This method can use either plant sample extracts or media in which S. citri was cultivated. The IC-qPCR protocol demonstrated a limit of detection for pure S. citri culture at a Ct value of 36.523 with a 103-fold dilution factor, making it equally sensitive as qPCR, which exhibited signal disappearance at a 10–3 dilution (Ct value of 37.484). In contrast, the immunological double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) test produced positive results up to a 10–2 dilution only. For S. citri-infected citrus samples, the established IC-qPCR protocol had a limit of detection at 36.46 Ct with a 1/64-fold dilution factor, matching the sensitivity of qPCR, where signal disappearance occurred at a 1/64 dilution (Ct value of 37.21). On the other hand, the immunological DAS-ELISA test yielded positive results only up to a 1/16 dilution, with optical density (OD) values of 0.364 and 0.113 for 1/16 and 1/32 dilutions, respectively. The IC-qPCR assay shows no cross-reaction for any other highly related spiroplasma species and bacteria affecting citrus trees including Candidatus liberibacter, Xylella fastidiosa, and Xanthomonas campestris pv. citri. Therefore, IC-qPCR assay provides an alternative quick and very sensitive method to screening S. citri, with the advantage of not requiring any concentration or DNA purification steps while still allowing an accurate diagnosis of CSD. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa subsp. pauca (Xfp) is a significant threat to Mediterranean agriculture, particularly impacting olive trees in southern Italy, causing Olive Quick Decline Syndrome. Resistant olive cultivars, such as 'Leccino' and 'Fs-17', have been identified as alternatives to restore the oliviculture within the infected areas. 'Frantoio' and 'Cipressino' are included in ongoing studies on genetic resistance to Xfp. The mechanization of olive harvesting is essential for reducing production costs in the olive oil sector. Two systems, trunk shakers and over-the-row machines, are used depending on the tree density and canopy structure, with super-high-density systems offering advantages in terms of cost and efficiency. This study investigates the feasibility of using simple and non-destructive indices to assess the optimal mechanical harvesting time. Different physical ripening indices, including detachment force, fresh weight, pigmentation, and firmness, were measured on four olive cultivars ('Fs-17', 'Leccino', 'Frantoio', 'Cipressino') in southern Italy over two years. The study found that the pigmentation index had a strong relationship with the detachment index, particularly for 'Fs-17', and 'Leccino', providing a reliable non-destructive measure for optimal harvesting time. The results indicate that the optimal harvesting times for mechanical harvesting are early September for 'Cipressino', early October for 'Fs-17', and mid-October for 'Frantoio' and 'Leccino'. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa (Xf), a gram-negative bacterium, is a notorious, world-wide plant pathogen with an extended latent period that presents a challenge for early disease detection and control interventions. We used thermal imaging of tissue-cultured, experimentally Xf-infected blueberry plants to identify visually pre-symptomatic leaves and compared the minimum force required to dislodge symptomatic leaves from infected plants to leaves on uninfected (control) blueberry plants. For two different blueberry cultivars and one pathogenic isolate of X. fastidiosa, we found no statistical difference between the mean downward force for leaf dislodgement, regardless of symptom category, on Xf-infected blueberry plants. That force was about 50% to 30% of the mean force to remove leaves from uninfected blueberry plants depending on the cultivar. These results indicate that visually pre-symptomatic leaves may be just as readily lost under field conditions as visually symptomatic leaves, both of which are important for early disease detection. Second, some thermally symptomatic and visually symptomatic leaves appeared to self-prune (abscise) and this may be an unrecognized early symptom of Xf-caused disease in blueberries. Last, it is possible that the self-pruning of visually asymptomatic leaves may occur in other agriculturally and culturally important plants infected by X. fastidiosa, but this remains an unrecognized early disease symptom. [ABSTRACT FROM AUTHOR]

Pistachio (Pistacia vera L.) is a dioecious, anemophilous, and drought-resistant fruit tree species. It is cultivated in new Mediterranean areas, including the regions of southern Italy (Apulia and Basilicata). It has been estimated that over 40,000 ha are suitable for pistachio cultivation in areas infected by Xylella fastidiosa subsp. pauca. As a newly introduced species, knowledge of its biological reproductive behaviors in its new areas of spreading is essential for appropriate agronomic planning and management. This two-year study (2022 and 2023), carried out in the countryside of Stigliano (MT, Italy), had the objective of evaluating the flowering phenograms, pollen production, and assessing protocols for the conservation and extension of pollen viability, of the most widespread cultivars. A slight delay was observed in the blooming phenograms, compared to other cultivation Mediterranean areas, such as Spain or Sicily. Furthermore, the overlap between female and male phenograms was partial. No significant differences were observed in the polliniferous aptitude of the two male cultivars. Among the different protocols tested, the pollen storage at 33% relative humidity and a temperature of −80 °C maintained the pollen germinability above 50% for up to three weeks. These findings highlight the importance of controlled environmental conditions in preserving pollen viability over extended periods, providing valuable insights for agricultural and botanical research that relies on maintaining pollen viability for breeding and genetic studies. [ABSTRACT FROM AUTHOR]

Site selection analysis is a fundamental methodology for the regeneration of Xylella fastidiosa subsp. pauca (Xfp) infected areas, with the introduction of Xfp immune/resistant tree crop species. The diffusion of these species could be assessed by combining ecological optima data, climate and soil attributes of the study area, and GIS tools. The study aimed to evaluate the potential suitability of eight Xfp immune tree crops, including Neglected and Underutilized Species (NUS) drought-resistant and new species, as follows: carob, hawthorn, prickly pear, mulberry, loquat, walnut, persimmon, and avocado. The use of GIS tools allowed the integration of different layers, such as climate and soil, to contribute to the identification of suitable areas for the cultivation of these tree crops helping the policy-makers to define plans for land use at a regional scale. Following the ecological optima, which represents the ideal environmental conditions for each species, this analysis provided valuable insights into the compatibility of the selected tree crops with the prevailing environmental factors in the affected area. Carob revealed its remarkable adaptability and drought resistance, presenting the broadest suitability. Hawthorn and Loquat also exhibited high adaptability, indicating their potential contribution to agricultural diversification and ecological balance. Conversely, crops like Avocado, Prickly pear, and Walnut, despite their economic value, demonstrated limited adaptability due to their specific soil and climate requirements. These findings can potentially contribute to the development of strategies for the policymakers, aimed at diversifying and enhancing the resilience of agricultural systems, facing the problem of emerging quarantine pathogens and the incoming climate change, and highlighting the possibility of opening new cultivation scenarios in the zones affected by Xfp. [ABSTRACT FROM AUTHOR]

One of the factors stalling studies on the transmission biology of Xylella fastidiosa by spittlebugs is the lack of model host plant species for transmission trials. Here, we performed transmission and Electropenetrography (EPG) trials with Philaenus spumarius and X. fastidiosa pauca ST53 on eight candidate model host plant species, namely alfalfa, basil, common amaranth, lavender, periwinkle, rosemary, sunflower, and tobacco. Spittlebugs transmitted the bacterium to alfalfa, periwinkle, rosemary, tobacco and basil, with periwinkle and tobacco showing the highest inoculation rates. In a significant number of alfalfa and basil plants, inoculation was not followed by persistent systemic infection. Tobacco (lowest spittlebugs survival), and basil and sunflower (shortest xylem ingestion), were the least suitable for the spittlebug among the plant species tested. Xylella fastidiosa-positive spittlebugs performed egestion (the inoculation behavior) more frequently than negative individuals, and far later in the probe (ca. 60 min after the first stylets insertion) than previously reported for sharpshooters (ca. 5 min). Overall, periwinkle was the best model host among the ones tested. Besides fundamental research, this plant species could be used for insect vectors infectivity screening in large-scale surveys aimed at determining X. fastidiosa presence in a given area. [ABSTRACT FROM AUTHOR]

This scientometric study reviews the scientific literature and CABI distribution records published in 2022 to find evidence of major disease outbreaks and first reports of pathogens in new locations or on new hosts. This is the second time we have done this, and this study builds on our work documenting and analyzing reports from 2021. Pathogens with three or more articles identified in 2022 literature were Xylella fastidiosa, Bursaphelenchus xylophilus, Meloidogyne species complexes, 'Candidatus Liberibacter asiaticus', Raffaelea lauricola, Fusarium oxysporum formae specialis, and Puccinia graminis f. sp. tritici. Our review of CABI distribution records found 29 pathogens with confirmed first reports in 2022. Pathogens with four or more first reports were Meloidogyne species complexes, Pantoea ananatis, grapevine red globe virus, and Thekopsora minima. Analysis of the proportion of new distribution records from 2022 indicated that grapevine red globe virus, sweet potato chlorotic stunt virus, and 'Ca. Phytoplasma vitis' may have been actively spreading. As we saw last year, there was little overlap between the pathogens identified by reviewing scientific literature versus distribution records. We hypothesize that this lack of concordance is because of the unavoidable lag between first reports of the type reported in the CABI database of a pathogen in a new location and any subsequent major disease outbreaks being reported in the scientific literature, particularly because the latter depends on the journal policy on types of papers to be considered, whether the affected crop is major or minor, and whether the pathogen is of current scientific interest. Strikingly, too, there was also no overlap between species assessed to be actively spreading in this year's study and those identified last year. We hypothesize that this is because of inconsistencies in sampling coverage and effort over time and delays between the first arrival of a pathogen in a new location and its first report, particularly for certain classes of pathogens causing only minor or non-economically damaging symptoms, which may have been endemic for some time before being reported. In general, introduction of new pathogens and outbreaks of extant pathogens threaten food security and ecosystem services. Continued monitoring of these threats is essential to support phytosanitary measures intended to prevent pathogen introductions and management of threats within a country. [ABSTRACT FROM AUTHOR]

Olive Quick Decline Syndrome (OQDS) associated with Xylella fastidiosa subsp. pauca is one of the most destructive diseases of olive trees in the Salento Peninsula (Southern Italy), particularly on the cultivars Cellina di Nardò and Ogliarola Salentina. This study proposes the NuovOlivo protocol as a management strategy to permit coexistence between X. fastidiosa subsp. pauca and olive drupes and extra-virgin oil production. Thirty-two private olive orchards affected by OQDS and cultivated following the standard agronomic techniques in use in the area were surveyed during the 2019–2023 olive-growing seasons. Tested cultivars included Cellina di Nardò, Ogliarola Salentina, Coratina, Ascolana Tenera, Nociara, Leccino, and Bella di Cerignola. At the beginning of the protocol application, the susceptible plants showed OQDS symptom severity of 40–80% and did not produce olives or oil, while the resistant(?)/tolerant cultivars exhibited a 2–8% leaf scorch and a drupe production less than 1–2 kg/plant. After the removal of dry branches in January–February, plants were sprayed two times per year (preferably in March and October) with NuovOlivo®, a mixture of aqueous botanical extracts esterified in the presence of sodium hydroxide with vegetable oils and activated at the time of use with sodium bicarbonate. In all the orchards, a slow-release fertilizer was distributed, and weeds were controlled by mowing or chopping. Upon eventual appearance, the dry twigs were removed. Treated olive trees produced new vegetation, rebuilt their foliage, reduced OQDS symptoms, and turned out cluster inflorescence and drupes. The drupes yield was 6.67–51.36 kg per plant, with an average of 13.19% in extra-virgin olive oil (free acidity 0.01–0.2%). Plants used as controls showed OQDS symptoms and were unproductive, and newly formed shoots were desiccated. The proposed protocol promotes, supports, and restores new vegetation, flowers, fruits, and oil production of the treated olive plants affected by OQDS without losing susceptible olive plants. The Apulian landscape and economy, based on olive presence and production, could be also safeguarded. [ABSTRACT FROM AUTHOR]

The initial outbreak of Xylella fastidiosa subsp. pauca (Xfp) on olive groves in Salento (Apulia, Italy) dates back to the years 2008 and 2009 when extensive twig and branch diebacks were observed in the area of Gallipoli area (province of Lecce). Subsequently, the bacterium also spread northwards to other areas of Apulia. In many cases, entire olive groves, also including the centennial ones, died. After the crown collapse, in many cases, it has been observed that the suckers are resprouting at the base of the trunk. After two to three years, such suckers usually died as well. However, during the last four to five years, in the first Xfp outbreak area, a complete restoration of the crown of the Xfp-susceptible cultivars Ogliarola salentina and Cellina di Nardò has been noticed. Such trees or olive groves also started to yield again. To monitor this tree resilience phenomenon, together with local non-profit organizations, a survey in the province of Lecce has been carried out to find olive groves for which any curative or agronomical practices have been applied since the bacterium outbreak. Resilient olive groves are scattered in many municipalities all over the province of Lecce. The phenomenon regards both young and adult olive groves and also includes some centennial trees. In many cases, the trees are yielding fruits, and farmers started to cultivate them again. Olive resilience in Salento is already being studied and can represent a significant opportunity to restore the local and valuable olive germplasm. [ABSTRACT FROM AUTHOR]

Simple Summary: In our research conducted in seven citrus orchards in Amazonas State, Brazil, we recorded the presence of eight sharpshooter species. One of the identified species is known to transmit the bacterium Xylella fastidiosa, which is responsible for causing citrus variegated chlorosis (CVC). Among the eight species found, five were newly recorded in citrus plants within the State, and three were entirely new to the northern region. This research emphasizes the importance of mapping the locations of these insects to gain insights into their behavior. Doing so will enable the development of strategies to effectively manage the threat of CVC in local citrus crops. This research study reports new records of eight species of Cicadellini (Hemiptera, Cicadellidae, Cicadellinae) across seven municipalities in Amazonas State, Brazil. Among these species, one is known as a vector of CVC (Provancherana corniculata). Additionally, five species are being reported for the first time in citrus for the State (Erythrogonia sexguttata, Hortensia similis, Provancherana corniculata, Scopogonalia amazonensis, and Scoposcartula oculata), and three species (Diedrocephala variegata, Macugonalia moesta and Xyphon reticulatum) are reported for the first time in the northern region. This research highlights the lack of information on sharpshooter occurrence in the Amazonas region, emphasizing the need for further investigations in this area. [ABSTRACT FROM AUTHOR]

The detection of Xylella fastidiosa in Portugal occurred through prospection in 2019 in Vila Nova de Gaia, Porto, in plants of Lavandula dentata L. Currently, in Portugal, there are 18 Xylella fastidiosa Demarcated Zones (DZs). The main objective of this study is to gain a comprehensive understanding of this problem within the defined Demarcated Zones in the North Region of Portugal from 2019 to June 2023. This work comprised two phases: the prospection phase (inspecting plants, sampling, and submission of samples to the laboratory) and the research phase (collecting and organizing data and statistical treatment). Our findings provide essential insights, suggesting that the Northern Region of Portugal is highly conducive to Xylella fastidiosa. Portugal has Xf-preferred hosts such as the olive tree, orange tree, Laurus nobilis, Rosa spp., Nerium oleander L., Pelargonium sp., Hedera helix L., and Lavandula dentata L. Portugal's favorable environmental factors such as temperature and humidity can have an important role in influencing the interaction between bacteria and hosts. Nevertheless, it is crucial to consider variations in the behavior of insect vectors, as these variations can limit the prevalence of the disease. Activities like the transport of infected planting materials from the first Demarcated Zone of the Area Metropolitana do Porto could be associated with the introduction and spread of Xylella fastidiosa, potentially triggering new disease outbreaks in the country. Our findings confirm the alarming spread of Xylella fastidiosa across Portugal. Factors such as the presence of insect vectors, abundance of host plants, and climate suitability play pivotal roles in Xylella fastidiosa dispersal. We recommend that countries identified with relatively high risk, like Portugal, undertake thorough individual risk analyses. The implementation of preventive measures and, if necessary, the enhancement of surveillance systems for early detection of Xylella fastidiosa in plants and insect vectors are crucial steps. [ABSTRACT FROM AUTHOR]

Abundance on and access time to the host plant are the pivotal factors in Xylella fastidiosa transmission to olive by the meadow spittlebug Philaenus spumarius. Therefore, olive varieties suitable for the vectors, i.e., plants providing all the necessary cues to the insect for their location, settling and acceptance, and devoid of antixenotic defenses, could be more susceptible to infection than varieties non- or less suitable for the vector. Here we evaluated whether a bacterium-susceptible olive variety, Ogliarola Salentina, could be a more suitable host for P. spumarius than the two resistant varieties Leccino and FS-17. We carried out: (i) an evaluation of between-hosts and within-host preference; (ii) an insect survival analysis; (iii) an Electrical Penetration Graph (EPG)-assisted analysis of the probing behavior; (iv) light microscopy of the tissues the spittlebugs had access to; (v) an analysis of the xylem sap primary metabolites. In choice tests, the insect exhibited a significant preference for Ogliarola Salentina. In addition, spittlebugs displayed longer xylem sap ingestion bouts on the bacterium-susceptible variety compared to resistant genotypes, possibly because of differences in the xylem sap chemical profile rather than xylem anatomy. Spittlebugs preference for Ogliarola over both Leccino and FS-17 could be a relevant and so far overlooked component of the low disease prevalence in these two olive varieties reported in Southern Italian olive orchards. Overall, our data point toward the importance of incorporating studies on vector-plant interaction and host traits of resistance to the vector in research on genotypes resistant to X. fastidiosa. [ABSTRACT FROM AUTHOR]

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BACKGROUND: Xylella fastidiosa is an important causative agent of Olive Quick Decline Syndrome in the Apulia region of Italy. The current study evaluated the bioefficacy of three entomopathogenic fungal strains: Beauveria bassiana SGB7004, Metarhizium robertsii SGB1K, and Akanthomyces lecanii SGB4711 against Philaenus spumarius the main vector of this pathogen, under laboratory conditions. Pathogenicity bioassays were performed by dipping nymphs and adults of P. spumarius in an aqueous suspension of powdered fungal culture (PFC) or conidial suspension (CS) of the three fungal strains. RESULTS: Both B. bassiana SGB7004 and M. robertsii SGB1K affected the viability of nymphs, resulting in more than 80% mortality at 48 h post treatment, while the effect of A. lecanii SGB4711 was not statistically significant. On adults, all three biocontrol strains were effective in a time‐ and concentration‐dependent manner. The PFCs of B. bassiana SGB7004, M. robertsii SGB1K, and A. lecanii SGB4711 at the highest concentration tested (120 mg mL−1) resulted in 97%, 83% and 27% mortality at the trial endpoint (120 h), respectively. Mycelial growth was observed on 38.5%, 37.0% and 61.5% of dead insects treated with B. bassiana SGB7004 (2.3 × 108 CFU mL−1), M. robertsii SGB1K (3.8 × 106 CFU mL−1) and A. lecanii SGB4711 (5.4 × 108 CFU mL−1), respectively. None of the PFCs of the tested strains was pathogenic when injected into nymph spittle. CONCLUSIONS: Beauveria bassiana SGB7004 and M. robertsii SGB1K significantly affected the survival of P. spumarius nymphs and adults, while A. lecanii SGB4711 was not effective on nymphs and only slightly effective against adults. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

BACKGROUND: Xylella fastidiosa is a multi‐host bacterium that can be detected in hundreds of plant species including several crops. Diseases caused by X. fastidiosa are considered a threat to global food production. The primary method for managing diseases caused by X. fastidiosa involves using insecticides to control the vector. Hence, it is necessary to adopt new and sustainable disease management technologies to control not only the insect but also the bacteria and plant health. We demonstrated that N‐acetylcysteine (NAC), a low‐cost cysteine analogue, is a sustainable molecule that can be used in agriculture to decrease the damage caused by X. fastidiosa and improve plant health. RESULTS: Using 15N‐NAC we proved that this analogue was absorbed by the roots and transported to different parts of the plant. Inside the plant, NAC reduced the bacterial population by 60‐fold and the number of xylem vessels blocked by bacterial biofilms. This reflected in a recovery of 0.28‐fold of the daily sap flow compared to health plants. In addition, NAC‐treated citrus variegated chlorosis (CVC) plants decreased the oxidative stress by improving the activity of detoxifying enzymes. Moreover, the use of NAC in field conditions positively contributed to the increase in fruit yield of CVC‐diseased plants. CONCLUSION: Our research not only advances the understanding of NAC absorption in plants, but also indicates its dual effect as an antimicrobial and antioxidant molecule. This, in turn, negatively affects bacterial survival while improving plant health by decreasing oxidative stress. Overall, the positive field‐based evidence supports the viability of NAC as a sustainable agricultural application. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

After the Xylella fastidiosa outbreak, the Salento area (Southern Italy) needs a strategic plan aimed at disclosing the potentials of rurality. The study aim is to establish empirical evidence regarding the importance of the cultural, heritage and territorial components in acting as drivers for tourism flows. Using weighted least squares (WLS) regression models, the study analyses the 145 municipalities within the provinces of Taranto, Brindisi and Lecce. The proposed models estimate the relationship between tourist arrivals and numbers and territorial independent variables. Results demonstrate that rurality is a driver of tourist demand and reveal some specific components which allow for an increase in tourism growth, particularly agritourism locations as places where agricultural multifunctionality is realised. Policymakers may benefit from the results, which can be considered foundational for the development of territorial strategies aimed at creating alternative income for the local communities and restoring damages caused by the Xylella fastidiosa outbreak. [ABSTRACT FROM AUTHOR]

The fungi Botryosphaeriaceae are involved in olive declines in both the world hemispheres and in all continents where this species is cultivated. In Salento (Apulia, Italy), the Botryosphaeriaceae Neofusicoccum mediterraneum and N. stellenboschiana have been reported as the agents of a branch and twig dieback that overlaps with olive quick decline syndrome caused by Xylella fastidiosa subsp. pauca. In this study, we report the finding of Diplodia seriata, another Botryosphaeriaceae species, in Salento in Xylella fastidiosa-infected olive trees affected by symptoms of branch and twig dieback. Given that its presence was also reported in olive in the Americas and in Europe (Croatia) with different degrees of virulence, we were prompted to assess its role in the Apulian decline. We identified representative isolates based on morphological features and a multilocus phylogeny. In vitro tests showed that the optimum growth temperature of the isolates is around 25–30 °C, and that they are highly thermo-tolerant. In pathogenicity trials conducted over eleven months, D. seriata expressed a very low virulence. Nonetheless, when we imposed severe water stress before the inoculation, D. seriata significatively necrotized bark and wood in a time frame of 35 days. Moreover, the symptoms which resulted were much more severe in the trial performed in summer compared with that in autumn. In osmolyte-supplemented media with a water potential from −1 to −3 Mpa, the isolates increased or maintained their growth rate compared with non-supplemented media, and they also grew, albeit to a lesser extent, on media with a water potential as low as −7 Mpa. This suggests that olives with a low water potential, namely those subjected to drought, may offer a suitable environment for the fungus' development. The analysis of the meteorological parameters, temperatures and rainfall, in Salento in the timeframe 1989–2023, showed that this area is subjected to a progressive increase of temperature and drought during the summer. Thus, overall, D. seriata has to be considered a contributor to the manifestation of branch and twig dieback of olive in Salento. Coherently with the spiral decline concept of trees, our results suggest that heat and drought act as predisposing/inciting factors facilitating D. seriata as a contributor. The fact that several adverse factors, biotic and abiotic, are simultaneously burdening olive trees in Salento offers a cue to discuss the possible complex nature of the olive decline in Salento. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa subsp. pauca ST53 (XFP), the causal agent of olive quick decline syndrome (OQDS), was thoroughly investigated after a 2013 outbreak in the Salento region of Southern Italy. Some trees from Ogliarola Salentina and Cellina di Nardò, susceptible cultivars in the Gallipoli area, the first XFP infection hotspot in Italy, have resprouted crowns and are starting to flower and yield fruits. Satellite imagery and Normalized Difference Vegetation Index analyses revealed a significant improvement in vegetation health and productivity from 2018 to 2022 of these trees. Lipid molecules have long been recognized as plant defense modulators, and recently, we investigated their role in XFP-positive hosts and in XFP-resistant as well as in XFP-susceptible cultivars of olive trees. Here, we present a case study regarding 36 olive trees (12 XFP-positive resprouting, 12 XFP-positive OQDS-symptomatic, and 12 XFP-negative trees) harvested in 2022 within the area where XFP struck first, killing millions of trees in a decade. These trees were analyzed for some free fatty acid, oxylipin, and plant hormones, in particular jasmonic and salicylic acid, by targeted LC-MS/MS. Multivariate analysis revealed that lipid markers of resistance (e.g., 13-HpOTrE), along with jasmonic and salicylic acid, were accumulated differently in the XFP-positive resprouting trees from both cultivars with respect to XFP-positive OQDS symptomatic and XFP-negative trees, suggesting a correlation of lipid metabolism with the resprouting, which can be an indication of the resiliency of these trees to OQDS. This is the first report concerning the resprouting of OQDS-infected olive trees in the Salento area. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa has been identified as the causal agent of several horticultural plant diseases that have resulted in major economic and cultural heritage losses. In the last decade, X. fastidiosa emerged as a destructive phytopathogen on olive trees in the Apulia region, Italy, prompting widespread surveillance throughout the Mediterranean basin. The present paper reports monitoring efforts for X. fastidiosa in Palestine on olive for 5 years (2017–2022) and 1 year (2022) on stone fruit trees, as a result of international collaboration projects. No signs of olive quick decline syndrome were observed on olive trees in all the Palestinian olive‐growing lands. This observation was confirmed by molecular tests using LAMP technology and PCR. In addition, 500 leaf samples from stone fruit trees (almond, apricot, peach, nectarine and plum) were tested using LAMP and PCR. All of these samples were negative for X. fastidiosa, even though few of the samples from almond trees in Idna (Hebron governorate) and apricot trees in Bal'a (Tulkarm governorate) showed leaf scorch‐like symptoms. This study provides confirmation that these important horticultural crops in Palestine (olive and stone fruits) are still free of X. fastidiosa. Preventive measures and surveillance of these and other horticultural crops such as grapevine and citrus trees are strongly recommended. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Simple Summary: Zelus renardii Kolenati (Hemiptera, Reduviidae, Harpactorinae), the Leafhopper Assassin Bug (LAB), first appeared in Europe in 2011 and is now well-acclimatized. The LAB is a promising mass-rearing candidate for the inundative biocontrol strategy of Xylella fastidiosa pauca ST53 vectors. We reared LABs for two subsequent years, using live adult Drosophila melanogaster Meigen (Diptera, Drosophilidae) (Dm) as living prey versus several artificial diet formulations (D0, D1, D2, D3, and D4), to identify the best formulation. An artificial medium can minimize rearing costs and make the process sustainable and safer. The rearing of LAB is feasible with live prey, oligidic, meridic, and holidic artificial formulations. All diets, except for D2, showed a favorable trend according to the species' reproductive potential. Scoring accumulated degree days in LAB's rearing made it possible to predict the time required to complete post-embryonic development as a function of temperature. Mass production is a prerequisite for using natural enemies in integrated pest management and organic farming. Natural enemies in agroecosystems include predators that prey on insects, which they can subdue while maintaining adequate pest population densities. The Leafhopper Assassin Bug (LAB), Zelus renardii, can be a natural enemy in agroecosystems, selecting its prey for size and mobility. Some of LAB's prey include Philaenus spumarius (L.), Bactrocera oleae (Rossi), Drosophila suzukii (Matsumura), and Macrohomotoma gladiata Kuwayama, suggesting this reduviid for biocontrol agent in various contexts. We reared LABs for two subsequent broods offering living prey and artificial diets. Our data show that the rearing of Z. renardii is feasible with oligidic, meridic, and holidic artificial formulations. Four artificial diets allowed the complete post-embryonic development of LABs in captivity for two successive generations. The accumulated degree-days (ADDs) accurately predict the growth of LABs based on heat accumulation, estimating that up to three generations could grow per year in captivity at the experimented T°C. [ABSTRACT FROM AUTHOR]

The pathogen Xylella fastidiosa subsp. fastidiosa has circulated through California's vineyards since its introduction from Central America in the 1800s. This pathogen is responsible for a bacterial disease called Pierce's disease (PD) of grapevine. With no known cure, PD has had devastating effects on some vineyards. Important factors that impact disease severity and persistence include: the presence of insect vectors, grapevine cultivar, management, ecology, and winter temperatures. Removal of infected vines is critical for reducing pathogen spread but relies on accurate and rapid pathogen detection. In this study, we foster a greater understanding of disease symptom emergence by way of a 3-year field inoculation project in Napa Valley. Although PD emergence and symptom progression have been studied in greenhouse and experimental plots, there is a large knowledge gap in quantifying disease progression under commercial conditions. After inoculating 80 mature Vitis vinifera vines in April 2017, we measured bacterial populations and six symptom types at four locations within each plant throughout the subsequent three growing seasons. The main foci of the project were understanding X. fastidiosa movement through the plants, infection, overwinter curing, and symptom development. We observed greater winter recovery than expected, and shriveled grape clusters proved to be a more reliable early indication of infection than other more commonly used symptoms. Although there were differences among wine grape cultivars, this work suggests that disease progression in the field may not fit the paradigm of predominant leaf scorch and low recovery rates as neatly as has been previously believed.

While there are documented host shifts in many bacterial plant pathogens, the genetic foundation of host shifts is largely unknown. Xylella fastidiosa is a bacterial pathogen found in over 600 host plant species. Two parallel host shifts occurred-in Brazil and Italy-in which X. fastidiosa adapted to infect olive trees, whereas related strains infected coffee. Using 10 novel whole-genome sequences from an olive-infecting population in Brazil, we investigated whether these olive-infecting strains diverged from closely related coffee-infecting strains. Several single-nucleotide polymorphisms, many derived from recombination events, and gene gain and loss events separated olive-infecting strains from coffee-infecting strains in this clade. The olive-specific variation suggests that this event was a host jump with genetic isolation between coffee- and olive-infecting X. fastidiosa populations. Next, we investigated the hypothesis of genetic convergence in the host shift from coffee to olive in both populations (Brazil and Italy). Each clade had multiple mutations and gene gain and loss events unique to olive, yet no overlap between clades. Using a genome-wide association study technique, we did not find any plausible candidates for convergence. Overall, this work suggests that the two populations adapted to infect olive trees through independent genetic solutions.

Homologous recombination plays a key function in the evolution of bacterial genomes. Within Xylella fastidiosa, an emerging plant pathogen with increasing host and geographic ranges, it has been suggested that homologous recombination facilitates host switching, speciation, and the development of virulence. We used 340 whole-genome sequences to study the relationship between inter- and intrasubspecific homologous recombination, random mutation, and natural selection across individual X. fastidiosa genes. Individual gene orthologs were identified and aligned, and a maximum likelihood (ML) gene tree was generated. Each gene alignment and tree pair were then used to calculate gene-wide and branch-specific r/m values (relative effect of recombination to mutation), gene-wide and branch-site nonsynonymous over synonymous substitution rates (dN/dS values; episodic selection), and branch length (as a proxy for mutation rate). The relationships between these variables were evaluated at the global level (i.e., for all genes among and within a subspecies), among specific functional classes (i.e., COGs), and between pangenome components (i.e., accessory versus core genes). Our analysis showed that r/m varied widely among genes as well as across X. fastidiosa subspecies. While r/m and dN/dS values were positively correlated in some instances (e.g., core genes in X. fastidiosa subsp. fastidiosa and both core and accessory genes in X. fastidiosa subsp. multiplex), low correlation coefficients suggested no clear biological significance. Overall, our results indicate that, in addition to its adaptive role in certain genes, homologous recombination acts as a homogenizing and a neutral force across phylogenetic clades, gene functional groups, and pangenome components. IMPORTANCE There is ample evidence that homologous recombination occurs frequently in the economically important plant pathogen Xylella fastidiosa. Homologous recombination has been known to occur among sympatric subspecies and is associated with host-switching events and virulence-linked genes. As a consequence, is it generally assumed that recombinant events in X. fastidiosa are adaptive. This mindset influences expectations of how homologous recombination acts as an evolutionary force as well as how management strategies for X. fastidiosa diseases are determined. Yet, homologous recombination plays roles beyond that of a source for diversification and adaptation. Homologous recombination can act as a DNA repair mechanism, as a means to facilitate nucleotide compositional change, as a homogenization mechanism within populations, or even as a neutral force. Here, we provide a first assessment of long-held beliefs regarding the general role of recombination in adaptation for X. fastidiosa. We evaluate gene-specific variations in homologous recombination rate across three X. fastidiosa subspecies and its relationship to other evolutionary forces (e.g., natural selection, mutation, etc.). These data were used to assess the role of homologous recombination in X. fastidiosa evolution.

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). [ABSTRACT FROM AUTHOR]