Garlic Bulb Decay and Soft Rot Caused by the Cross-Kingdom Pathogen Burkholderia gladioli.

In 2021, two gram-negative bacterial strains were isolated from garlic (Allium sativum) bulbs showing decay and soft rot symptoms in Central Iran. The bacterial strains were aggressively pathogenic on cactus, garlic, gladiolus, onion, potato, and saffron plants and induced soft rot symptoms on carrot, cucumber, potato, and radish discs. Furthermore, they were pathogenic on sporophores of cultivated and wild mushrooms. Phylogenetic analyses revealed that the bacterial strains belong to Burkholderia gladioli. Garlic bulb rot caused by B. gladioli has rarely been reported in the literature. Historically, B. gladioli strains had been assigned to four pathovars, namely, B. gladioli pv. alliicola, B. gladioli pv. gladioli, B. gladioli pv. agaricicola, and B. gladioli pv. cocovenenans, infecting onion, Gladiolus sp., and mushrooms and poisoning foods, respectively. Multilocus (i.e., 16S rRNA, atpD, gyrB, and lepA genes) sequence-based phylogenetic investigations including reference strains of B. gladioli pathovars showed that the two garlic strains belong to phylogenomic clade 2 of the species, which includes the pathotype strain of B. gladioli pv. alliicola. Although the garlic strains were phylogenetically closely related to the B. gladioli pv. alliicola reference strains, they possessed pathogenicity characteristics that overlapped with three of the four historical pathovars, including the ability to rot onion (pv. alliicola), gladiolus (pv. gladioli), and mushrooms (pv. agaricicola). Furthermore, the pathotype of each pathovar could infect the hosts of other pathovars, undermining the utility of the pathovar concept in this species. Overall, using phenotypic pathovar-oriented assays to classify B. gladioli strains should be replaced by phylogenetic or phylogenomic analysis.

Clavibacter lycopersici sp. nov.: a peach-colored actinobacterium isolated from symptomless tomato plant.

In 2015, Gram-positive peach-coloured actinobacterial strains were isolated from symptomless tomato phyllosphere in Iran. Biochemical and physiological characteristics, as well as 16S rRNA phylogeny showed that the strains belong to Clavibacter sp., while they were non-pathogenic on the host of isolation, and morphologically distinct from the tomato pathogen C. michiganensis and other plant-associated bacteria. Multilocus sequence analysis of five housekeeping genes showed that the two peach-coloured strains CFBP 8615T (Tom532T) and CFBP 8616 (Tom495) were phylogenetically distinct from all validly described Clavibacter species. Whole genome sequence-based indices, i.e. average nucleotide identity (orthoANI) and digital DNA-DNA hybridization (dDDH), showed that the two peach-colored strains share nearly 100 % orthoANI value with one another, while they differ from all validly described Clavibacter species with the orthoANI/dDDH values <93 % and <50 %, respectively. Thus, based on both phenotypic features and orthoANI/dDDH indices the peach-coloured strains could belong to a new species within Clavibacter. In this study, we provide a formal species description for the peach-coloured tomato-associated Clavibacter strains. Clavibacter lycopersici sp. nov. is proposed for the new species with Tom532T = CFBP 8615T = ICMP 22100T as type strain.

Complete Genome Sequencing of Three Clade-1 Xanthomonads Reveals Genetic Determinants for a Lateral Flagellin and the Biosynthesis of Coronatine-Like Molecules in Xanthomonas.

Evolutionarily, early-branching xanthomonads, also referred to as clade-1 xanthomonads, include major plant pathogens, most of which colonize monocotyledonous plants. Seven species have been validly described, among them the two sugarcane pathogens Xanthomonas albilineans and Xanthomonas sacchari, as well as Xanthomonas translucens, which infects small-grain cereals and diverse grasses but also asparagus and pistachio trees. Single-gene sequencing and genomic approaches have indicated that this clade likely contains more, yet-undescribed species. In this study, we sequenced representative strains of three novel species using long-read sequencing technology. Xanthomonas campestris pv. phormiicola strain CFBP 8444 causes bacterial streak on New Zealand flax, another monocotyledonous plant. Xanthomonas sp. strain CFBP 8443 has been isolated from common bean, and Xanthomonas sp. strain CFBP 8445 originated from banana. Complete assemblies of the chromosomes confirmed their unique phylogenetic position within clade 1 of Xanthomonas. Genome mining revealed novel genetic features, hitherto undescribed in other members of the Xanthomonas genus. In strain CFBP 8444, we identified genes related to the synthesis of coronatine-like compounds, a phytotoxin produced by several pseudomonads, which raises interesting questions about the evolution and pathogenicity of this pathogen. Furthermore, strain CFBP 8444 was found to contain a second, atypical flagellar gene cluster in addition to the canonical flagellar gene cluster. Overall, this research represents an important step toward better understanding the evolutionary history and biology of early-branching xanthomonads.

Pathovar-Specific PCR Method for Detection and Identification of Xanthomonas translucens pv. undulosa.

Bacterial leaf streak disease caused by Xanthomonas translucens pv. undulosa is an economically important disease threatening wheat and barley crops around the globe. Thus far, specific PCR-based detection and identification tests for X. translucens pathovars are not available. In this study, we used comparative genomics approach to design a pathovar-specific primer pair for detection of X. translucens pv. undulosa in naturally infected seeds and its differentiation from other pathovars of the species. For this aim, complete genome sequences of strains of different X. translucens pathovars were compared and the specific PCR primer pair XtuF/XtuR was designed. These primers were strictly specific to X. translucens pv. undulosa because the expected 229-bp DNA fragment was not amplified in the closely related pathovars or in other xanthomonads, wheat-pathogenic bacteria, and other plant-pathogenic bacteria. High sensitivity of the primer pair XtuF/XtuR allowed detection of pure DNA of the pathogen in a concentration as low as 4.5 pg/µl. The pathogen was also detected in water suspension at a concentration of 8.6 × 102 CFU/ml. The PCR test was capable of detecting the pathogen in extracts of naturally infected wheat seeds at a concentration of 3.5 × 104 CFU/g while a culture-plate method was able to detect the pathogen at a concentration of 50 × 105 CFU/g of the same seeds. The PCR test developed in this study is a step forward for precise detection and identification of X. translucens pv. undulosa to prevent outbreaks of the bacterial leaf streak disease.

Clonality and Diversity in the Soft Rot Dickeya solani Phytopathogen.

Bacterial diversity analyses often suffer from a bias due to sampling only from a limited number of hosts or narrow geographic locations. This was the case for the phytopathogenic species Dickeya solani, whose members were mainly isolated from a few hosts-potato and ornamentals-and from the same geographical area-Europe and Israel, which are connected by seed trade. Most D. solani members were clonal with the notable exception of the potato isolate RNS05.1.2A and two related strains that are clearly distinct from other D. solani genomes. To investigate if D. solani genomic diversity might be broadened by analysis of strains isolated from other environments, we analysed new strains isolated from ornamentals and from river water as well as strain CFBP 5647 isolated from tomato in the Caribbean island Guadeloupe. While water strains were clonal to RNS05.1.2A, the Caribbean tomato strain formed a third clade. The genomes of the three clades are highly syntenic; they shared almost 3900 protein families, and clade-specific genes were mainly included in genomic islands of extrachromosomal origin. Our study thus revealed both broader D. solani diversity with the characterisation of a third clade isolated in Latin America and a very high genomic conservation between clade members.

Xanthomonas bonasiae sp. nov. and Xanthomonas youngii sp. nov., isolated from crown gall tissues.

The genus Xanthomonas contains a set of diverse bacterial strains, most of which are known for their pathogenicity on annual crops and fruit trees causing economically important plant diseases. Recently, five Xanthomonas strains were isolated from Agrobacterium-induced crown gall tissues of amaranth (Amaranthus sp.) and weeping fig (Ficus benjamina) plants in Iran. Phenotypic characteristics (i.e. biochemical tests and pathogenicity features) and whole genome sequence-based core-genome phylogeny followed by average nucleotide identity and digital DNA-DNA hybridization calculations suggested that these gall-associated strains belong to two new species within the genus Xanthomonas. In this study, we provide a formal species description for these new species where Xanthomonas bonasiae sp. nov. is proposed for the strains isolated from weeping fig with FX4T (=CFBP 8703T=DSM 112530T) as type strain. The name Xanthomonas youngii sp. nov. is proposed for the strains isolated from amaranth with AmX2T (=CFBP 8902T=DSM 112529T) as type strain.

Taxonomic Refinement of Xanthomonas arboricola.

Xanthomonas arboricola comprises a number of economically important fruit tree pathogens classified within different pathovars. Dozens of nonpathogenic and taxonomically unvalidated strains are also designated as X. arboricola, leading to a complicated taxonomic status in the species. In this study, we have evaluated the whole-genome resources of all available Xanthomonas spp. strains designated as X. arboricola in the public databases to refine the members of the species based on DNA similarity indexes and core genome-based phylogeny. Our results show that, of the nine validly described pathovars within X. arboricola, pathotype strains of seven pathovars are taxonomically genuine, belonging to the core clade of the species regardless of their pathogenicity on the host of isolation (thus the validity of pathovar status). However, strains of X. arboricola pv. guizotiae and X. arboricola pv. populi do not belong to X. arboricola because of the low DNA similarities between the type strain of the species and the pathotype strains of these two pathovars. Thus, we propose to elevate the two pathovars to the rank of a species as X. guizotiae sp. nov. with the type strain CFBP 7408T and X. populina sp. nov. with the type strain CFBP 3123T. In addition, other mislabeled strains of X. arboricola were scattered within Xanthomonas spp. that belong to previously described species or represent novel species that await formal description.

The Complete Genome Sequence of Xanthomonas theicola, the Causal Agent of Canker on Tea Plants, Reveals Novel Secretion Systems in Clade-1 Xanthomonads.

Xanthomonas theicola is the causal agent of bacterial canker on tea plants. There is no complete genome sequence available for X. theicola, a close relative of the species X. translucens and X. hyacinthi, thus limiting basic research for this group of pathogens. Here, we release a high-quality complete genome sequence for the X. theicola type strain, CFBP 4691T. Single-molecule real-time sequencing with a mean coverage of 264× revealed two contigs of 4,744,641 bp (chromosome) and 40,955 bp (plasmid) in size. Genome mining revealed the presence of nonribosomal peptide synthases, two CRISPR systems, the Xps type 2 secretion system, and the Hrp type 3 secretion system. Surprisingly, this strain encodes an additional type 2 secretion system and a novel type 3 secretion system with enigmatic function, hitherto undescribed for xanthomonads. Four type 3 effector genes were found on complete or partial transposons, suggesting a role of transposons in effector gene evolution and spread. This genome sequence fills an important gap to better understand the biology and evolution of the early-branching xanthomonads, also known as clade-1 xanthomonads.

Comparative Genomics and Phylogenetic Analyses Suggest Several Novel Species within the Genus Clavibacter, Including Nonpathogenic Tomato-Associated Strains.

Members of the genus Clavibacter are economically important bacterial plant pathogens infecting a set of diverse agricultural crops (e.g., alfalfa, corn, potato, tomato, and wheat). Tomato-associated Clavibacter sp. strains account for a great portion of the genetic diversity of the genus, and C. michiganensissensu stricto (formerly C. michiganensis subsp. michiganensis), causing bacterial canker disease, is considered one of the most destructive seed-borne agents for the crop worldwide. However, current taxonomic descriptions of the genus do not reflect the existing diversity of the strains, resulting in unsatisfactory results in quarantine surveys for the pathogens. In this study, we used all the available genome sequences of Clavibacter sp. strains, including the type strains of newly described subspecies, to provide precise insight into the diversity of tomato-associated members of the genus and further clarify the taxonomic status of the strains using genotypic and phenotypic features. The results of phylogenetic analyses revealed the existence of nine hypothetical new species among the investigated strains. None of the three new subspecies (i.e., C. michiganensis subsp. californiensis, C. michiganensis subsp. chilensis, and C. michiganensis subsp. phaseoli) is included within the tomato-pathogenic C. michiganensissensu stricto lineage. Although comparative genomics revealed the lack of chp and tomA pathogenicity determinant gene clusters in the nonpathogenic strains, a number of pathogenicity-related genes were noted to be present in all the strains regardless of their pathogenicity characteristics. Altogether, our results indicate a need for a formal taxonomic reconsideration of tomato-associated Clavibacter sp. strains to facilitate differentiation of the lineages in quarantine inspections.IMPORTANCEClavibacter spp. are economically important bacterial plant pathogens infecting a set of diverse agricultural crops, such as alfalfa, corn, pepper, potato, tomato, and wheat. A number of plant-pathogenic members of the genus (e.g., C. michiganensissensu stricto and C. sepedonicus, infecting tomato and potato plants, respectively) are included in the A2 (high-risk) list of quarantine pathogens by the European and Mediterranean Plant Protection Organization (EPPO). Although tomato-associated members of Clavibacter spp. account for a significant portion of the genetic diversity in the genus, only the strains belonging to C. michiganensissensu stricto (formerly C. michiganensis subsp. michiganensis) cause bacterial canker disease of tomato and are subjected to the quarantine inspections. Hence, discrimination between the pathogenic and nonpathogenic Clavibacter sp. strains associated with tomato seeds and transplants plays a pivotal role in the accurate detection and cost-efficient management of the disease. On the other hand, detailed information on the genetic contents of different lineages of the genus would lead to the development of genome-informed specific detection techniques. In this study, we have provided an overview of the phylogenetic and genomic differences between the pathogenic and nonpathogenic tomato-associated Clavibacter sp. strains. We also noted that the taxonomic status of newly introduced subspecies of C. michiganensis (i.e., C. michiganensis subsp. californiensis, C. michiganensis subsp. chilensis, and C. michiganensis subsp. phaseoli) should be reconsidered.

High-Quality Genome Resource of Xanthomonas hyacinthi Generated via Long-Read Sequencing.

The bacterial plant pathogen Xanthomonas hyacinthi is the causal agent of yellow disease of Hyacinthus and other ornamental plant genera. There is no available complete genome for X. hyacinthi, limiting basic research for this pathogen. Here, we release a high-quality complete genome sequence for the X. hyacinthi type strain, CFBP 1156. Single-molecule real-time (SMRT) sequencing with a mean coverage of 306× revealed two contigs of 4,918,645 and 44,381 bp in size. This was the first characterized plant-disease-causing species of Xanthomonas and this genome provides a resource to better understand the biology of yellow disease of hyacinth.

Pectobacterium aquaticum sp. nov., isolated from waterways.

This work aimed to establish the taxonomic status of six strains (A212-S19-A16T, A127-S21-F16, A105-S21-F16, A104-S21-F16, A101-S19-F16 and A35-S23-M15) isolated from three different waterways in 2015 and 2016 in south-east France. Amplification and sequencing of the gapA housekeeping gene clustered these six strains together inside the genus Pectobacterium outside of already described or proposed Pectobacterium species and supspecies. Phenotypic analysis, using GENIII Biolog plates performed with strains A212-S19-A16T, A105-S21-F16, A101-S19-F16 and the closely related Pectobacterium polaris(CFBP 1403), Pectobacterium carotovorum subsp. odoriferum (CFBP 1878T), 'Pectobacteriumcarotovorum subsp. actinidiae' (CFBP 7370), Pectobacterium carotovorum subsp. carotovorum (CFBP 2046T), 'Pectobacterium carotovorum subsp. brasiliense' (CFBP 6617) or the most distantly related Pectobacteriumaroidearum (CFBP 8168T) failed to identify specific compounds metabolized by these three strains, but weak activity was specifically observed at pH 5 with these three strains. Illumina sequencing was used to sequence these six strains. Based on phylogenetic data, average nucleotide identity values and in silico DNA-DNA hybridization results, strains A212-S19-A16T, A127-S21-F16, A105-S21-F16, A101-S19-F16, A35-S23-M15 and A104-S21-F16 are suggested to represent a novel species of the genus Pectobacterium, for which the name Pectobacterium aquaticum sp. nov. is proposed. The type strain is A212-S19-A16 T (=CFBP 8637T=NCPPB 4640T).

Elevation of Pectobacterium carotovorum subsp. odoriferum to species level as Pectobacterium odoriferum sp. nov., proposal of Pectobacterium brasiliense sp. nov. and Pectobacterium actinidiae sp. nov., emended description of Pectobacterium carotovorum and description of Pectobacterium versatile sp. nov., isolated from streams and symptoms on diverse plants.

The Pectobacteriumcarotovorum species corresponds to a complex, including two subspecies with validly published names, two proposed subspecies and two new species, Pectobacterium polaris and Pectobacterium aquaticum. Recent studies suggested that this complex needed revision. We examined the taxonomic status of 144 Pectobacterium strains isolated from a wide range of plant species, various geographical origins and waterways. Sequences of the leuS, dnaX and recA housekeeping genes clustered 114 of these Pectobacterium strains together within a not yet described clade. We sequenced eight strains of this clade and analysed them together with the 102 Pectobacterium genomes available in the NCBI database. Phylogenetic analysis, average nucleotide identity calculation and in silico DNA-DNA hybridization allowed us to differentiate seven clades. This led us to propose the elevation of Pectobacterium carotovorumsubsp. odoriferum to species level as Pectobacteriumodoriferum sp. nov. (type strain CFBP 1878T=LMG 5863T=NCPPB 3839T=ICMP 11533T), the proposal of Pectobacteriumactinidiae sp. nov. (type strain KKH3=LMG 26003 T=KCTC 23131T) and Pectobacteriumbrasiliense sp. nov. (type strain CFBP 6617T= LMG 21371T=NCPPB 4609T), to emend the description of Pectobacterium carotovorum (type strain CFBP 2046T=LMG 2404T=NCPPB 312T=ICMP 5702T), and to propose a novel species, Pectobacterium versatile sp. nov (type strain CFBP6051T= NCPPB 3387T=ICMP 9168T) which includes the strains previously described as 'Candidatus Pectobacterium maceratum'. Phenotypic analysis performed using Biolog GENIII plates on eight strains of P. versatile sp. nov. and related strains completed our analysis.

Xanthomonas prunicola sp. nov., a novel pathogen that affects nectarine (Prunus persica var. nectarina) trees.

Three isolates obtained from symptomatic nectarine trees (Prunus persica var. nectarina) cultivated in Murcia, Spain, which showed yellow and mucoid colonies similar to Xanthomonas arboricola pv. pruni, were negative after serological and real-time PCR analyses for this pathogen. For that reason, these isolates were characterized following a polyphasic approach that included both phenotypic and genomic methods. By sequence analysis of the 16S rRNA gene, these novel strains were identified as members of the genus Xanthomonas, and by multilocus sequence analysis (MLSA) they were clustered together in a distinct group that showed similarity values below 95 % with the rest of the species of this genus. Whole-genome comparisons of the average nucleotide identity (ANI) of genomes of the strains showed less than 91 % average nucleotide identity with all other species of the genus Xanthomonas. Additionally, phenotypic characterization based on API 20 NE, API 50 CH and BIOLOG tests differentiated the strains from the species of the genus Xanthomonas described previously. Moreover, the three strains were confirmed to be pathogenic on peach (Prunus persica), causing necrotic lesions on leaves. On the basis of these results, the novel strains represent a novel species of the genus Xanthomonas, for which the name Xanthomonas prunicola is proposed. The type strain is CFBP 8353 (=CECT 9404=IVIA 3287.1).

Ancestral acquisitions, gene flow and multiple evolutionary trajectories of the type three secretion system and effectors in Xanthomonas plant pathogens.

Deciphering the evolutionary history and transmission patterns of virulence determinants is necessary to understand the emergence of novel pathogens. The main virulence determinant of most pathogenic proteobacteria is the type three secretion system (T3SS). The Xanthomonas genus includes bacteria responsible for numerous epidemics in agroecosystems worldwide and represents a major threat to plant health. The main virulence factor of Xanthomonas is the Hrp2 family T3SS; however, this system is not conserved in all strains and it has not been previously determined whether the distribution of T3SS in this bacterial genus has resulted from losses or independent acquisitions. Based on comparative genomics of 82 genome sequences representing the diversity of the genus, we have inferred three ancestral acquisitions of the Hrp2 cluster during Xanthomonas evolution followed by subsequent losses in some commensal strains and re-acquisition in some species. While mutation was the main force driving polymorphism at the gene level, interspecies homologous recombination of large fragments expanding through several genes shaped Hrp2 cluster polymorphism. Horizontal gene transfer of the entire Hrp2 cluster also occurred. A reduced core effectome composed of xopF1, xopM, avrBs2 and xopR was identified that may allow commensal strains overcoming plant basal immunity. In contrast, stepwise accumulation of numerous type 3 effector genes was shown in successful pathogens responsible for epidemics. Our data suggest that capacity to intimately interact with plants through T3SS would be an ancestral trait of xanthomonads. Since its acquisition, T3SS has experienced a highly dynamic evolutionary history characterized by intense gene flux between species that may reflect its role in host adaptation.

Genomics and transcriptomics of Xanthomonas campestris species challenge the concept of core type III effectome.

BACKGROUND: The bacterial species Xanthomonas campestris infects a wide range of Brassicaceae. Specific pathovars of this species cause black rot (pv. campestris), bacterial blight of stock (pv. incanae) or bacterial leaf spot (pv. raphani). RESULTS: In this study, we extended the genomic coverage of the species by sequencing and annotating the genomes of strains from pathovar incanae (CFBP 1606R and CFBP 2527R), pathovar raphani (CFBP 5828R) and a pathovar formerly named barbareae (CFBP 5825R). While comparative analyses identified a large core ORFeome at the species level, the core type III effectome was limited to only three putative type III effectors (XopP, XopF1 and XopAL1). In Xanthomonas, these effector proteins are injected inside the plant cells by the type III secretion system and contribute collectively to virulence. A deep and strand-specific RNA sequencing strategy was adopted in order to experimentally refine genome annotation for strain CFBP 5828R. This approach also allowed the experimental definition of novel ORFs and non-coding RNA transcripts. Using a constitutively active allele of hrpG, a master regulator of the type III secretion system, a HrpG-dependent regulon of 141 genes co-regulated with the type III secretion system was identified. Importantly, all these genes but seven are positively regulated by HrpG and 56 of those encode components of the Hrp type III secretion system and putative effector proteins. CONCLUSIONS: This dataset is an important resource to mine for novel type III effector proteins as well as for bacterial genes which could contribute to pathogenicity of X. campestris.

New Coffee Plant-Infecting Xylella fastidiosa Variants Derived via Homologous Recombination.

Xylella fastidiosa is a xylem-limited phytopathogenic bacterium endemic to the Americas that has recently emerged in Asia and Europe. Although this bacterium is classified as a quarantine organism in the European Union, importation of plant material from contaminated areas and latent infection in asymptomatic plants have engendered its inevitable introduction. In 2012, four coffee plants (Coffea arabica and Coffea canephora) with leaf scorch symptoms growing in a confined greenhouse were detected and intercepted in France. After identification of the causal agent, this outbreak was eradicated. Three X. fastidiosa strains were isolated from these plants, confirming a preliminary identification based on immunology. The strains were characterized by multiplex PCR and by multilocus sequence analysis/typing (MLSA-MLST) based on seven housekeeping genes. One strain, CFBP 8073, isolated from C. canephora imported from Mexico, was assigned to X. fastidiosa subsp. fastidiosa/X. fastidiosa subsp. sandyi. This strain harbors a novel sequence type (ST) with novel alleles at two loci. The two other strains, CFBP 8072 and CFBP 8074, isolated from Coffea arabica imported from Ecuador, were allocated to X. fastidiosa subsp. pauca. These two strains shared a novel ST with novel alleles at two loci. These MLST profiles showed evidence of recombination events. We provide genome sequences for CFBP 8072 and CFBP 8073 strains. Comparative genomic analyses of these two genome sequences with publicly available X. fastidiosa genomes, including the Italian strain CoDiRO, confirmed these phylogenetic positions and provided candidate alleles for coffee plant adaptation. This study demonstrates the global diversity of X. fastidiosa and highlights the diversity of strains isolated from coffee plants.

Erwinia iniecta sp. nov., isolated from Russian wheat aphid (Diuraphis noxia).

Short, Gram-negative-staining, rod-shaped bacteria were isolated from crushed bodies of Russian wheat aphid [Diuraphis noxia (Kurdjumov)] and artificial diets after Russian wheat aphid feeding. Based on multilocus sequence analysis involving the 16S rRNA, atpD, infB, gyrB and rpoB genes, these bacterial isolates constitute a novel clade in the genus Erwinia, and were most closely related to Erwinia toletana. Representative distinct strains within this clade were used for comparisons with related species of Erwinia. Phenotypic comparisons using four distinct strains and average nucleotide identity (ANI) measurements using two distinct draft genomes revealed that these strains form a novel species within the genus Erwinia. The name Erwinia iniecta sp. nov. is proposed, and strain B120T ( = CFBP 8182T = NCCB 100485T) was designated the type strain. Erwinia iniecta sp. nov. was not pathogenic to plants. However, virulence to the Russian wheat aphid was observed.

Wild mushrooms as potential reservoirs of plant pathogenic bacteria: a case study on Burkholderia gladioli.

Fruit bodies (sporocarps) of wild mushrooms growing in natural environments play a substantial role in the preservation of microbial communities, for example, clinical and food-poisoning bacteria. However, the role of wild mushrooms as natural reservoirs of plant pathogenic bacteria remains almost entirely unknown. Furthermore, bacterial transmission from a mushroom species to agricultural plants has rarely been recorded in the literature. In September 2021, a creamy-white Gram-negative bacterial strain was isolated from the sporocarp of Suillus luteus (slippery jack) growing in Bermuda grass (Cynodon dactylon) lawn in Southern Iran. A similar strain was isolated from the same fungus in the same area in September 2022. Both strains were identified as Burkholderia gladioli based on phenotypic features as well as phylogeny of 16S rRNA and three housekeeping genes. The strains were not only pathogenic on white button mushrooms (Agaricus bisporus) but also induced hypersensitive reaction (HR) on tobacco and common bean leaves and caused soft rot on a set of diverse plant species, that is, chili pepper, common bean pod, cucumber, eggplant, garlic, gladiolus, narcissus, onion, potato, spring onion, okra, kohlrabi, mango, and watermelon. Isolation of plant pathogenic B. gladioli strains from sporocarp of S. luteus in two consecutive years in the same area could be indicative of the role of this fungus in the preservation of the bacterium in the natural environment. B. gladioli associated with naturally growing S. luteus could potentially invade neighboring agricultural crops, for example, vegetables and ornamentals. The potential role of wild mushrooms as natural reservoirs of phytopathogenic bacteria is further discussed.IMPORTANCEThe bacterial genus Burkholderia contains biologically heterogeneous strains that can be isolated from diverse habitats, that is, soil, water, diseased plant material, and clinical specimens. In this study, two Gram-negative pectinolytic bacterial strains were isolated from the sporocarps of Suillus luteus in September 2021 and 2022. Molecular phylogenetic analyses revealed that both strains belonged to the complex species Burkholderia gladioli, while the pathovar status of the strains remained undetermined. Biological investigations accomplished with pathogenicity and host range assays showed that B. gladioli strains isolated from S. luteus in two consecutive years were pathogenic on a set of diverse plant species ranging from ornamentals to both monocotyledonous and dicotyledonous vegetables. Thus, B. gladioli could be considered an infectious pathogen capable of being transmitted from wild mushrooms to annual crops. Our results raise a hypothesis that wild mushrooms could be considered as potential reservoirs for phytopathogenic B. gladioli.