Summary Vein clearing of zucchini (VCZ) and bacterial leaf spot (BLS) are caused by various strains of the Pseudomonas syringae species complex that infect zucchini ( Cucurbita pepo ) seeds. VCZ strains have a narrow host range of cucurbits and affect only seedlings, whereas BLS strains have a broader host range and cause symptoms on adult plants. A multiplex qPCR test showed that VCZ strains predominated in infected seed lots produced in different countries. We surveyed hybrid seed crops grown in parallel in two French regions to address inoculum sources. According to DNA-based approach, parental seed lots were positive to BLS strains, although no culturable bacteria were recovered. Hybrid seed lots produced in the Rhone Valley (southeastern France) showed higher infection rates than those produced in Limagne (central France), and VCZ strains were recovered only from the Rhone Valley. Two representative strains of VCZ and BLS colonized seeds through the vascular and floral pathways, whereas only the BLS strain was transmitted through the pericarp. These findings suggest that floral transmission, potentially mediated by pollinators, could explain the predominance of VCZ strains under favorable regional conditions, and that pericarp transmission in BLS strains could be linked to their capacity to cause disease on adult plants. Furthermore, some infections undetected in seeds became apparent after germination, indicating that testing germinated seeds rather than seeds could help seed industry to take in account only bacterial infections transmitted to the seedling. Together, these results provide valuable insights into the epidemiology of P. syringae transmission to zucchini seeds.

Plants have evolved a complex cell wall (CW) providing support and protection against environmental constraints, including constant attacks from pests and pathogens. Indeed, the plant CW serves as both a physical barrier and a sophisticated monitoring and signalling system, making it a central component of plant immunity. The Xanthomonas genus encompasses a large diversity of plant-pathogenic bacteria that, together, can infect a wide range of more than 400 plant species including monocots and dicots. Remarkably, Xanthomonas species are subdivided into highly specialized pathovars infecting a narrow range of plant species and/or tissues, each possessing a distinct CW structure and composition. This diversity makes Xanthomonas a perfect case for studying the interactions between bacterial pathogens and the plant CW. In this review, we provide an overview of the intricate interactions between Xanthomonas and the plant CW during the infection process. During infection, Xanthomonas degrades the plant CW both directly by using CW degrading enzymes and indirectly by reprogramming the plant transcriptome to enhance the expression of plant CW modifying enzymes. This degradation of the plant CW plays a central role during infection. On the plant side, it triggers immune responses, while on the Xanthomonas side, it facilitates bacterial invasion and access to nutrients, and activates a signalling hub that primes the pathogen for host colonization.

During 2020-2024, 25 Gram-positive actinobacterial strains were isolated from small-grain cereals in Iran. Colony morphology, phenotypic characteristics and multilocus sequence analyses showed that the strains belonged to the coryneform genus Clavibacter (family Microbacteriaceae). The Clavibacter strains isolated from small-grain cereals in Iran were distributed within five distinct phylogenetic clades. Two of those clades included Clavibacter tessellarius and Clavibacter zhangzhiyongii, while the other three groups of Clavibacter strains were taxonomically undetermined and phylogenetically distinct from all validly described species in the genus. Whole-genome sequence-based indices, i.e. average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH), showed that the latter three phylogenetic clades differed from all validly described Clavibacter species, with ANI/dDDH values <94% and <70%, respectively. Analyses of KEGG pathways and pathogenicity-associated genes revealed substantial differences among the five Clavibacter groups associated with small-grain cereals. All Clavibacter strains were capable of infecting their hosts of isolation, i.e. wheat, barley and oat. Thus, based on both phenotypic features, i.e. differences in colony morphology, biolog microbial identification microplate data and polar lipid repertoires, as well as DNA similarity indices, the three clades could represent three new species within Clavibacter. In this study, we provide formal species descriptions for three Clavibacter clades isolated from small-grain cereals. These three species include Clavibacter vidaverae sp. nov. (type strain Sh2088ᵀ=CFBP 9070ᵀ=ICMP 24732ᵀ), Clavibacter rahimiani sp. nov. (type strain Sh2141ᵀ=CFBP 9069ᵀ=ICMP 24735ᵀ) and Clavibacter davisi sp. nov. (type strain Sh2036ᵀ=CFBP 9071ᵀ=ICMP 24729ᵀ).

Xylella fastidiosa is a Gram-negative bacterium native to the Americas and classified as a priority pest under EU regulations. This xylem-limited plant pathogenic bacterium has a wide host range and is transmitted by insect vectors. Since 2013, X. fastidiosa has been identified in several European countries including Italy, France, Spain and Portugal, with different subspecies and sequence types (ST) detected. Since 2015, most strains identified in France are of the subspecies multiplex, specifically ST6 and ST7. Two new STs of X. fastidiosa subsp. multiplex, ST88 and ST89, were recently detected in the region Provence-Alpes-Côte d’Azur (PACA), and one strain of each ST has been isolated from infected plants. To investigate the phylogenetic relationships between the four STs present in France, a complete circular genome and a single-contig genome were assembled for the ST89 and ST88 strains, respectively, by combining PacBio and Illumina sequencing data. A phylogenomic analysis was performed to investigate the phylogenetic position and potential origin of these new strains. This data article contributes to improve our knowledge of the diversity and origin of X. fastidiosa subsp. multiplex in France and Europe.

Bacterial canker of tomato caused by the gram-positive corynebacterial species Clavibacter michiganensis is one of the most destructive seedborne diseases in both open-air and greenhouse tomatoes. The pathogen is a regulated agent in all tomato-producing countries, as translocation of infected tomato materials transports the bacterium into new areas. C. michiganensis is generally known to have yellow-pigmented colonies on culture media, which is a key differentiative phenotypic feature in standard diagnostic guidelines. During 2020 and 2021, pink-pigmented corynebacterial strains were isolated from tomato seeds (cultivar Sun 6189F1) and plants showing severe canker symptoms in Southern Iran. The six pink-pigmented strains were pathogenic on tomato and pepper seedlings under greenhouse conditions and yielded positive results with C. michiganensis-specific primers pairs described in the literature. Phylogenomics and DNA similarity calculations showed that the pink-pigmented strains were highly similar to the authentic yellow-pigmented members of the pathogen. Thus, they were identified as a new phenotypic variant of tomato bacterial canker pathogen. Whole-genome screenings accomplished with PCR-based assays showed that the pink strains contain all pathogenicity-determinant genes described in C. michiganensis. Further, orthologous gene clusters in the pink-pigmented strains were more similar to the pathogenic members of C. michiganensis than to those of nonpathogenic tomato-associated Clavibacter species. The results obtained in this study demonstrate the emergence of a new pink-pigmented variant of C. michiganensis and highlight the importance of colony pigmentation/morphology in culture-based detection of the bacterium. The need for updating diagnostic guidelines on the colony variants of the pathogen is further discussed.

Common bacterial blight (CBB) is a devastating seed-transmitted disease of common bean (Phaseolus vulgaris L.), caused by Xanthomonas phaseoli pv. phaseoli and Xanthomonas citri pv. fuscans. The genes responsible for CBB resistance are largely unknown. Moreover, the lack of a reproducible and universal transformation protocol limits the study of genetic traits in common bean. We produced X. phaseoli pv. phaseoli strains expressing artificially designed transcription-activator like effectors (dTALEs) to target 14 candidate genes for resistance to CBB based on previous transcriptomic data. In planta assays in a susceptible common bean genotype showed that induction of PvOFP7, PvAP2-ERF71, or PvExpansinA17 expression by dTALEs resulted in CBB symptom reduction. After PvOFP7 induction, in planta bacterial growth was reduced at early colonization stages, and RNA-seq analysis revealed up-regulation of cell wall formation and primary metabolism, together with major down-regulation of heat shock proteins. Our results demonstrated that PvOFP7 contributes to CBB resistance, and underlined the usefulness of dTALEs for functional validation of genes whose induction impacts Xanthomonas-plant interactions.

OBJECTIVE:Bacterial wilt and canker of tomato caused by the gram-positive corynebacterial species Clavibacter michiganensis is an economically important disease threatening the tomato industry in both open-air and greenhouse productions around the world. The disease occurs in many countries, with a particular importance in regions characterised by high temperature and water scarcity. Management of bacterial canker has been a major problem since its original description in 1909. This is due in part to the seedborne nature of the pathogen, allowing the bacterium to be transmitted over long distances via infected seeds, as well as a lack of effective treatment to clean seeds. Detection of the pathogen from seeds is difficult due to high competition on culture media with diverse members of the seed-associated microbiota. Identification of the pathogen can also be difficult owing to the presence of different colony variants on culture media. In this review, we provide a historical perspective and an updated overview on the aetiology, epidemiology and management strategies of the bacterial canker disease. We also gathered recent molecular findings in the pathogenicity mechanisms and bioecology of C. michiganensis to boost management of the bacterial canker disease in the 21st century tomato industry. TAXONOMY:Class: Actinobacteria; Order: Micrococcales; Family: Microbacteriaceae; Genus: Clavibacter; Species: Clavibacter michiganensis. DISEASE SYMPTOMS:Interveinal leaf chlorosis leading to necrotic areas. Canker on stems and lateral branches of the plant. Discolouration of vascular and pith tissues to dark yellow or brown. Small and early ripened fruits or discolouration of the placenta from white to yellow in the interior part of the ripening fruits. HOST RANGE:Tomato (Solanum lycopersicum) is the main host of the pathogen while natural infection has also been reported on eggplant, pepper and wild nightshade plants. SYNONYMS (HISTORICAL/NON-PREFERRED SCIENTIFIC NAMES):Aplanobacter michiganensis; Pseudomonas michiganense; Pseudomonas michiganensis; Bacterium michiganense; Phytomonas michiganensis; Mycobacterium michiganense; Erwinia michiganensis (=michiganense); Corynebacterium michiganense; Corynebacterium michiganense pv. michiganense; Corynebacterium michiganense subsp. michiganense; Clavibacter michiganensis subsp. michiganensis. MICROBIOLOGICAL PROPERTIES:The bacterium produces domed, round and shiny mucoid colonies on general culture media. Colonies are usually yellow-pigmented, while pink-pigmented strains are occasionally observed. Cells are gram-positive, aerobic, non-motile, non-spore-producing curved rods (coryneform). DISTRIBUTION:Present in all continents. PHYTOSANITARY CATEGORIZATION:EPPO A2 List no. 50, EU 2019/2072 RNQP Annex IV. See EPPO (https://gd.eppo.int/taxon/CORBMI/categorization) and CABI (https://www.cabidigitallibrary.org/doi/10.1079/cabicompendium.15338) databases for further country-specific categorisations. EPPO code: CORBMI.

New crop disease outbreaks can occur when phytopathogenic bacterial pathogens acquire new traits, switch to a new host plant, or are introduced into new geographic areas. Therefore, the rapid detection of a pathogen in a new environment and/or in a new host plant is essential to mitigate disease outbreaks. However, bacteria with a wide plant host range, many asymptomatic hosts, and slow symptom development can sometimes remain unnoticed for years. This is the case for the vector-borne xylem-inhabiting bacterium Xylella fastidiosa known to infect hundreds of plant species worldwide and its sister species X. taiwanensis, currently thought to be restricted to Taiwan. To investigate whether the two Xylella species are already present in other parts of the world, potentially in unrecognized host species, we performed an in-depth data mining of raw sequence data available in the NCBI Sequence Read Archive. This led to the identification of 62 datasets from diverse plant and insect samples from around the world. Furthermore, nine draft and one circular Xylella genome could be assembled from these datasets. Our results reveal several potential new host plants and previously unrecognized infected areas in the Americas, Africa, and Southeast Asia. Moreover, the newly assembled genomes represent several new strains of both X. fastidiosa and X. taiwanensis as well as an additional Xylella species infecting wild rice. Taken together, our work extends our knowledge on the genetic diversity, host range, and global distribution of the genus Xylella and can orient surveillance programs towards new regions and host plants.IMPORTANCEThe rapid detection of a pathogen in a new environment and/or in a new host plant is essential to mitigate disease outbreaks. However, bacteria with a wide plant host range, many asymptomatic hosts, and slow symptom development can sometimes remain unnoticed for years. In this work, we used an in-depth screening of publicly available raw sequencing data as an alternative approach to investigate the distribution of the xylem-inhabiting bacteria Xylella fastidiosa and X. taiwanensis across the world. Our results reveal several potential new host plants and previously unrecognized infected areas in the Americas, Africa, and Southeast Asia. Moreover, we provide evidence, including a complete genome sequence, for a third Xylella species infecting wild rice. This work extends our knowledge of the genetic diversity, plant host range, and global distribution of the genus Xylella in natural environments and motivates surveillance programs in so-far-neglected biomes, regions, and host plants.

Microbial plant pathogens possess higher diversity in the center of domestication of their host plants than in the introduced geographic area of the corresponding crops. In this study, the center of wheat, barley, and oat domestication in the Iranian Plateau was surveyed to shed light on the population structure, taxonomic diversity, and biology of Clavibacter species associated with these crops. Comprehensive field surveys completed with pathological assays and molecular-phylogenetic analyses showed that phylogenetically diverse groups of Clavibacter strains were associated with bacterial mosaic symptoms on small grain cereals in this domestication center. Besides the two previously described species, Clavibacter tessellarius and Clavibacter zhangzhiyongii, three clades of atypical Clavibacter strains, phylogenetically distinct from all described Clavibacter species, were isolated from wheat, barley, and oat in this study. Thus, Clavibacter strains associated with small grain cereals in the center of domestication of these crops belong to at least five taxonomically distinct clades, whereas simultaneous occurrence of multitaxa Clavibacter strains on small grain cereals has never been reported outside the Iranian Plateau. All five phylogenetic Clavibacter clades were capable of inducing mosaic and chlorosis on their host of isolation. Whole genome sequence-based comparative investigations showed that most virulence-associated genomic contents of the five Clavibacter clades isolated in this study were somewhat similar. Data obtained in this study suggest a correlation between the center of wheat, barley, and oat domestication and the high taxonomic diversity of the accompanying Clavibacter pathogens. Additional phylogeographic investigations in the area would strengthen this co-evolutionary hypothesis. IMPORTANCE:Members of the gram-positive corynebacterial genus Clavibacter sp. (family Microbacteriaceae) are seed-borne plant pathogens causing economically important plant diseases on annual crops and vegetables. While comprehensive global-scale studies have been conducted to study the population structure of Clavibacter species infecting tomato, potato, and pepper, phylogenomics investigations have not yet been conducted to monitor the taxonomic diversity, pathogenicity, and origin of Clavibacter strains pathogenic to small grain cereals. Archaeobotanical investigations suggested that human agriculture was established ≈11,000 years ago in the foothills of the Zagros Mountains in Northwestern Iran, while wheat and barley were among the very first crops domesticated in these areas. Thus, the analyses of taxonomic diversity and population structure of Clavibacter strains in the Iranian Plateau would shed light on the correlation between the center of domestication of these crops and the center of diversity of accompanying bacterial pathogens. Our findings showed that most of the Clavibacter strains isolated from small grain cereals in Iran belonged to the two previously described species Clavibacter tessellarius and Clavibacter zhangzhiyongii, while several strains were grouped in three distinct clades, all representing hypothetical novel species in the genus.

In the original publication [...].

Vein clearing of zucchini (VCZ) is a disease caused by seedborne bacteria that affects young plants of Cucurbita pepo subsp. pepo. VCZ agents are distributed into four phylogenetic clusters within clades 2a and 2ba of phylogroup 2 of the Pseudomonas syringae species complex. All these strains are pathogenic to squash, but only certain strains can also attack melon and cucumber. Strains belonging to clades 2b and 2d are sometimes isolated from zucchini seeds but have not been associated with VCZ epidemics. Identification tools for VCZ agents are required to improve disease control. Primers were designed to implement a seven-gene multilocus sequence analysis (MLSA) scheme for a collection of 60 strains isolated from zucchini seeds. The MLSA showed a clear predominance of strains of cluster 2ba-A and the presence of VCZ strains in a fifth cluster (2ba-C). PCR tests were designed to characterize strains in the VCZ clusters, and a multiplex qPCR test was proposed to distinguish strains with a cucurbit host range extended to melon and cucumber, harboring hopZ5 and sylC, from other strains harboring avrRpt2 and sylC. Additional qPCR tests were also designed to gain insights into clade-2b and -2d strains that can be isolated from cucurbits. These tools evaluated in silico with the NCBI database and experimentally with a collection of 112 strains detected all target strains, except for the test dedicated to clade-2b strains, and excluded 96.7 to 100% of nontarget strains. These tools are intended to serve phylogenetic studies, epidemiological monitoring, and seed testing. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

Background Bacteria of the genus Xanthomonas cause economically significant diseases in various crops. Their virulence is dependent on the translocation of type III effectors (T3Es) into plant cells by the type III secretion system (T3SS), a process regulated by the master response regulator HrpG. Although HrpG has been studied for over two decades, its regulon across diverse Xanthomonas species, particularly beyond type III secretion, remains understudied. Results In this study, we conducted transcriptome sequencing to explore the HrpG regulons of 17 Xanthomonas strains, encompassing six species and nine pathovars, each exhibiting distinct host and tissue specificities. We employed constitutive expression of plasmid-borne hrpG*, which encodes a constitutively active form of HrpG, to induce the regulon. Our findings reveal substantial inter- and intra-specific diversity in the HrpG* regulons across the strains. Besides 21 genes directly involved in the biosynthesis of the T3SS, the core HrpG* regulon is limited to only five additional genes encoding the transcriptional activator HrpX, the two T3E proteins XopR and XopL, a major facility superfamily (MFS) transporter, and the phosphatase PhoC. Interestingly, genes involved in chemotaxis and genes encoding enzymes with carbohydrate-active and proteolytic activities are variably regulated by HrpG*. Conclusions The diversity in the HrpG* regulon suggests that HrpG-dependent virulence in Xanthomonas might be achieved through several distinct strain-specific strategies, potentially reflecting adaptation to diverse ecological niches. These findings enhance our understanding of the complex role of HrpG in regulating various virulence and adaptive pathways, extending beyond T3Es and the T3SS.

In this Opinion paper, members of the French Network on Xanthomonads give their personal view on what they consider to be some of the groundbreaking discoveries in the field of molecular plant pathology over the past 20 years. By celebrating the 20th anniversary of the first Xanthomonas genome sequences, they explain how genomics revolutionized taxonomy, provided insight into the emergence of pathogenic bacteria, enabled new fundamental discoveries and contributed to the development of novel control measures. Collectively, such new, genomics-enabled perspective will help to ensure sustainable agriculture and conservation of our environment in the future.

ABSTRACT Common bacterial blight of bean (CBB) is a devastating seed-transmitted disease caused by Xanthomonas phaseoli pv. phaseoli and Xanthomonas citri pv. fuscans on common bean ( Phaseolus vulgaris L.). The genes responsible for CBB resistance are largely unknown. moreover, the lack of reproducible and universal transformation protocol limits the study and improvement of genetic traits in common bean. We produced X. phaseoli pv. phaseoli strains expressing artificially-designed Transcription-Activator Like Effectors (dTALEs) to target 14 candidate genes and performed in planta assays in a susceptible common bean genotype to analyse if the transcriptional induction of these genes could confer resistance to CBB. Induction of PvOFP7 , PvAP2-ERF71 and PvExpansinA17 resulted in CBB symptom reduction. In particular, PvOFP7 induction led to strong symptom reduction, linked to reduced bacterial growth in planta at early colonisation stages. RNA-Seq analysis revealed up-regulation of cell wall formation and primary metabolism, and major down-regulation of Heat Shock Proteins. Our results demonstrate that PvOFP7 is contributes to CBB resistance, and underline the usefulness of dTALEs for highlighting genes of quantitative activity.

ABSTRACTThe classical lineage of Mycobacterium ulcerans is the most prevalent clonal group associated with Buruli ulcer in humans. Its reservoir is strongly associated with the environment. We analyzed together 1,045 isolates collected from 13 countries on two continents to define the evolutionary history and population dynamics of this lineage. We confirm that this lineage spread over 7,000 years from Australia to Africa with the emergence of outbreaks in distinct waves in the 18th and 19th centuries. In sharp contrast with its global spread over the last century, transmission chains are now mostly local, with little or no dissemination between endemic areas. This study provides new insights into the phylogeography and population dynamics of M. ulcerans, highlighting the importance of comparative genomic analyses to improve our understanding of pathogen transmission.IMPORTANCEMycobacterium ulcerans is an environmental mycobacterial pathogen that can cause Buruli ulcer, a severe cutaneous infection, mostly spread in Africa and Australia. We conducted a large genomic study of M. ulcerans, combining genomic and evolutionary approaches to decipher its evolutionary history and pattern of spread at different geographic scales. At the scale of villages in an endemic area of Benin, the circulating genotypes have been introduced in recent decades and are not randomly distributed along the river. On a global scale, M. ulcerans has been spreading for much longer, resulting in distinct and compartmentalized endemic foci across Africa and Australia.

Mixed infections caused by multiple pathogenic and weakly pathogenic strains inhabiting the same host plants are common in nature and may modify pathogen dynamics. However, traditional plant pathogen studies have mostly focused on the binary interaction between a single host and a single pathogen. In this study, we have looked beyond this binary interaction and evaluated the impact of coinfection on disease dynamics on tomato using the bacterial spot pathogen Xanthomonas perforans (Xp), the co-occurring weakly pathogenic strain of X. arboricola (Xa), and the co-occurring potential weak pathogenic strain of Pseudomonas capsici (Pc). Time-series coinfection experiments monitoring disease severity and within-host population dynamics revealed higher disease severity in coinfection by three species compared with infection by Xp alone. However, coinfection by dual species, Xp and Pc, or Xa resulted in lower disease severity compared with Xp alone. Thus, coinfection outcomes depend on interacting species. Weak pathogens could exploit Xp to colonize the host plant as indicated by their higher populations in coinfection. However, Xp population dynamics were dependent on the coinfecting partner. While resource competition might be a possible explanation for lower Xp population in dual coinfection, interaction of Pc with the host was found to influence Xp population. Interestingly, Xp population was higher in the presence of three-species interaction compared with Xp and Xa coinfection, suggesting potential modulation of cooperative interactions among Xp and Xa in three-species coinfection rather than competitive interactions. Humidity played a significant role in population dynamics of the three species. Overall, this study highlighted the importance of coinfection dynamics in studying plant disease outbreaks.

A survey of common bacterial blight (CBB) was conducted in common bean fields in Brazil, in the state of Goiás and in the Federal District. Isolation from symptomatic leaves on a semi-selective medium yielded yellow, mucoid colonies typical of Xanthomonas, and 161 pure cultures were obtained. PCR with specific primers for X. phaseoli pv. phaseoli and X. citri pv. fuscans was performed and confirmed the presence of both fuscans and GL2 strains of X. citri pv. fuscans and the presence of X. phaseoli pv. phaseoli. However, for 81 isolates, PCR results were negative. Housekeeping genes gyrB and rpoD sequences placed these strains in the provisionally named X. cannabis species clade, clustering pv. zinniae, pv. esculenti, and the strain Nyagatare, isolated from beans in Rwanda in 2013. The identification of a subset of 20 strains was complemented by a positive PCR with Xanthomonas-specific primers that amplify a portion of the gumD gene and the induction of hypersensitive reaction in tomato leaves within 24-48 hours. Pathogenicity was confirmed by inoculation on the French common bean cv. Flavert and the Brazilian common bean cv. BRS Ártico. Symptoms such as white spots along the leaf blade, leaf curling, and wilting developed in inoculated plants. Partial gyrB and rpoD sequences analyses revealed identity values ranging from 98.3 to 100

The genus Xanthomonas has been primarily studied for pathogenic interactions with plants. However, besides host and tissue-specific pathogenic strains, this genus also comprises nonpathogenic strains isolated from a broad range of hosts, sometimes in association with pathogenic strains, and other environments, including rainwater. Based on their incapacity or limited capacity to cause symptoms on the host of isolation, nonpathogenic xanthomonads can be further characterized as commensal and weakly pathogenic. This study aimed to understand the diversity and evolution of nonpathogenic xanthomonads compared to their pathogenic counterparts based on their cooccurrence and phylogenetic relationship and to identify genomic traits that form the basis of a life history framework that groups xanthomonads by ecological strategies. We sequenced genomes of 83 strains spanning the genus phylogeny and identified eight novel species, indicating unexplored diversity. While some nonpathogenic species have experienced a recent loss of a type III secretion system, specifically the hrp2 cluster, we observed an apparent lack of association of the hrp2 cluster with lifestyles of diverse species. We performed association analysis on a large data set of 337 Xanthomonas strains to explain how xanthomonads may have established association with the plants across the continuum of lifestyles from commensals to weak pathogens to pathogens. Presence of distinct transcriptional regulators, distinct nutrient utilization and assimilation genes, transcriptional regulators, and chemotaxis genes may explain lifestyle-specific adaptations of xanthomonads.

In an era marked by rapid global changes, the reinforcement and modernization of plant health surveillance systems have become imperative. Sixty-five scientists present here a research agenda for an enhanced and modernized plant health surveillance to anticipate and mitigate disease and pest emergence. Our approach integrates a wide range of scientific fields (from life, social, physical and engineering sciences) and identifies the key knowledge gaps, focusing on anticipation, risk assessment, early detection, and multi-actor collaboration. The research directions we propose are organized around four complementary thematic axes. The first axis is the anticipation of pest emergence, encompassing innovative forecasting, adaptive potential, and the effects of climatic and cropping system changes. The second axis addresses the use of versatile broad-spectrum surveillance tools, including molecular or imaging diagnostics supported by artificial intelligence, and monitoring generic matrices such as air and water. The third axis focuses on surveillance of known pests from new perspectives, i.e., using novel approaches to detect known species but also anticipating and detecting, within a species, the populations or genotypes that pose a higher risk. The fourth axis advocates the management of plant health as a commons through the establishment of multi-actor and cooperative surveillance systems for long-term data-driven alert systems and information dissemination. We stress the importance of integrating data and information from multiple sources through open science databases and metadata, alongside developing methods for interpolating and extrapolating incomplete data. Finally, we advocate an Integrated Health Surveillance approach in the One Health context, favoring tailored and versatile solutions to plant health problems and recognizing the interconnected risks to the health of plants, humans, animals and the environment, including food insecurity, pesticide residues, environmental pollution and alterations of ecosystem services.

In October 2022, v-shaped necrotic lesions were observed on the leaf margins of field-grown winter oilseed rape (WOSR), Brassica napus L., in western France (Ille-et-Vilaine (35) and Maine-et-Loire (49) departments). Disease incidence on volunteers and cultivated WOSR was generally low (5-10 %) but occasionally up to 80% on some fields. Leaf sections sampled from the margin of necrotic leaf tissue were dilacerated in sterile deionized water and the extract was spread onto tryptone soya agar (TSA) with cycloheximide (100 mg.L-1) and Polyflor (Syngenta, France) (2ml.L-1, containing 5 mg.L-1 propiconazole) then incubated at 28°C for 2 days. Colonies were yellow-pigmented, mucoid, and convex, which are morphological characteristics of Xanthomonas spp. colonies. The partial fyuA and gyrB gene sequences were amplified for eight isolated strains (CFBP 9155, CFBP 9156, CFBP 9157, CFBP 9158, CFBP 9159, CFBP 9161, CFBP 9162, and CFBP 9163) using primers of Fargier et al. (2011), and sequenced (Genoscreen, France). The sequences were deposited under numbers OR232891 to OR232898 for fyuA and OR634932 to OR634939 for gyrB. BLASTN analysis of the sequenced fyuA amplicon showed 100% identity and query coverage with the fyuA fragment of Xanthomonas campestris pv. campestris (Xcc) CFBP 6865R (Bellenot et al., 2022). BLASTN analysis of the sequenced gyrB amplicon showed two allelic forms: one showed 100% identity and query coverage with the gyrB fragment of Xcc strain CFBP 6865R (Bellenot et al., 2022), the other one showed 100% identity and query coverage with the type strain Xcc CFBP 5241 (ATCC33913) (Vorhölter et al., 2003). Moreover, two qPCR tools were used to identify the strains successfully as Xcc (Köhl et al., 2011; Rezki et al., 2016) which target the same gene encoding a hypothetical protein and whose primers overlap. The pathogenicity of the eight isolated strains was validated using a bacterial suspension (108 CFU.ml-1) for i) leaf spraying until runoff onto the leaf surfaces of WOSR plants previously maintained at saturated humidity for 48 hours, ii) wound-leaf inoculation of the two youngest true leaves with scissors that had been dipped into the bacterial suspension. Both tests were performed on 3-week-old WOSR plants of the Aviso (INRAE) genotype. Deionized water was used as negative control. Strains CFBP 5241 and the strain CFBP 4954 (Fargier et al., 2007) were used as positive controls for disease expression. Tested plants (seven for spray inoculation and four for wound-leaf inoculation per strain and control condition) were incubated in a greenhouse at 20°C/24°C (night/day). Isolated strains and the strain CFBP 4954 caused yellow lesions with both inoculation methods that necrotized starting about 10 days post inoculation (dpi). The spots coalesced within 14 dpi to form necrotic areas. The type strain CFBP 5241 caused mild symptoms, with only yellow lesions that did not coalesce. Plants inoculated with water remained symptomless. To complete Koch's postulate, re-isolations were achieved. Re-isolated strains on TSA showed the same colony morphology as described above. All re-isolated strains were identified as Xcc based on partial gyrB sequencing and Xcc specific qPCR test (Rezki et al., 2016). This first report in France and the recent identification in Serbia (Popović et al., 2013) may illustrate the emergence of the disease on this crop in Europe. The prevalence and consequences of this disease should be evaluated over a wider geographic area.