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Bacterial blight and leaf spot of geraniums is a destructive disease of cultivated Pelargonium species around the world. During 2020 to 2021, surveys were conducted in seven geranium-growing provinces of Iran to monitor the status of bacterial blight and leaf spot disease. The disease was observed in six surveyed provinces varying in the extent of occurrence and severity. Twenty-two gram-negative pale-yellow bacterial strains resembling members of Xanthomonas were isolated from symptomatic leaves and stems. Pathogenicity and host range assays showed that the bacterial strains were pathogenic on Pelargonium grandiflorum , P. graveolens , P. peltatum , and P. zonale . All strains were positive for a PCR test using the primer pair XcpM1/XcpM2, which is specific for X. hortorum pv. pelargonii . Phylogenetic analysis using the sequences of gyrB and lepA genes showed that the 22 strains clustered in a clade among the sequences of X. hortorum pv. pelargonii strains retrieved from GenBank but were distinct from the other pathovars of X. hortorum . BOX-PCR-based fingerprinting using BOX-A1R primer revealed that the strains isolated in this study were grouped into two clusters, while no distinct correlation was observed between the host/area of isolation and BOX-PCR fingerprinting. None of the strains obtained in this study nor the reference strain of the pathogen produced bacteriocin against each other. Results obtained in this study shed light on the geographic distribution, taxonomic status, and host range of the bacterial blight and leaf spot pathogen of geraniums in Iran, paving the path for further research on disease management., Competing Interests: The author(s) declare no conflict of interest.

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 × 10 2 CFU/ml. The PCR test was capable of detecting the pathogen in extracts of naturally infected wheat seeds at a concentration of 3.5 × 10 4 CFU/g while a culture-plate method was able to detect the pathogen at a concentration of 50 × 10 5 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., Competing Interests: The author(s) declare no conflict of interest.

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 7408 T and X. populina sp. nov. with the type strain CFBP 3123 T . 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 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 FX4 T (=CFBP 8703 T =DSM 112530 T ) as type strain. The name Xanthomonas youngii sp. nov. is proposed for the strains isolated from amaranth with AmX2 T (=CFBP 8902 T =DSM 112529 T ) as type strain.

In summer 2019, widespread occurrence of crown gall disease caused by Agrobacterium spp. was observed on commercially grown ornamental plants in southern Iran. Beside agrobacteria, pale yellow-pigmented Gram-negative strains resembling the members of Xanthomonas were also associated with crown gall tissues on weeping fig (Ficus benjamina) and Amaranthus sp. plants. The purpose of the present study was to characterize the crown gall-associated Xanthomonas strains using plant inoculation assays, molecular-phylogenetic analyses, and comparative genomics approaches. Pathogenicity tests showed that the Xanthomonas strains did not induce disease symptoms on their host of isolation. However, the strains induced hypersensitive reaction on tobacco, geranium, melon, squash, and tomato leaves via leaf infiltration. Multilocus sequence analysis suggested that the strains belong to clade IA of Xanthomonas , phylogenetically close to Xanthomonas translucens, X. theicola, and X. hyacinthi. Average nucleotide identity and digital DNA-DNA hybridization values between the whole-genome sequences of the strains isolated in this study and reference Xanthomonas strains are far below the accepted thresholds for the definition of prokaryotic species, signifying that these strains could be defined as two new species within clade IA of Xanthomonas . Comparative genomics showed that the strains isolated from crown gall tissues are genetically distinct from X. translucens , as almost all the type III secretion system genes and type III effectors are lacking in the former group. The data obtained in this study provide novel insight into the breadth of genetic diversity of crown gall-associated bacteria and pave the way for research on gall-associated Xanthomonas -plant interactions. IMPORTANCE Tumorigenic agrobacteria-members of the bacterial family Rhizobiaceae -cause crown gall and hairy root diseases on a broad range of plant species. These bacteria are responsible for economic losses in nurseries of important fruit trees and ornamental plants. The microclimate of crown gall and their accompanying microorganisms has rarely been studied for the microbial diversity and population dynamics of gall-associated bacteria. Here, we employed a series of biochemical tests, pathogenicity assays, and molecular-phylogenetic analyses, supplemented with comparative genomics, to elucidate the biological features, taxonomic position, and genomic repertories of five crown gall-associated Xanthomonas strains isolated from weeping fig and Amaranthus sp. plants in Iran. The strains investigated in this study induced hypersensitive reactions (HR) on geranium, melon, squash, tobacco, and tomato leaves, while they were nonpathogenic on their host of isolation. Phylogenetic analyses and whole-genome-sequence-based average nucleotide identity (ANI)/digital DNA-DNA hybridization (dDDH) calculations suggested that the Xanthomonas strains isolated from crown gall tissues belong to two taxonomically unique clades closely related to the clade IA species of the genus, i.e., X. translucens , X. hyacinthi , and X. theicola .

Bacterial leaf streak caused by different pathovars of Xanthomonas translucens is the most important seedborne bacterial disease of small grain cereals. However, variations in the virulence-associated genomic areas of the pathogen remain uninvestigated. In this study, the diversity of transcription activator-like effectors (TALE) was investigated using the Southern blotting of Bam HI - digested genomic DNAs in the Iranian strains of X. translucens . All 65 X. translucens strains were assigned into 13 genotypes, where 57 X. translucens pv. undulosa strains were placed in genotypes 1 to 8, and seven X. translucens pv. translucens strains were placed in genotypes 9 to 12. Interestingly, we did not find any TALE genes in the strain XtKm7 (genotype 13), which showed to be pathogenic only on barley. Virulence and aggressiveness of these strains in greenhouse conditions were in agreement with the TALE-based clustering of the strains in the pathovar level, though variations were observed in the aggressiveness of X. translucens pv. undulosa strains. In general, strains containing higher numbers of putative TALE genes were more virulent on wheat and barley than strains containing fewer. This is the first TALE-based genetic diversity analysis on X. translucens strains and provides novel insights into the virulence repertories and genomic characteristics of the pathogen. Further investigations using TALE mutagenesis and complementation analysis are warranted to precisely elucidate the role of each detected X. translucens TALE in bacterial virulence and aggressiveness either on wheat or barley.

This study provides a phylogeographic insight into the population diversity of Xanthomonas translucens strains causing bacterial leaf streak disease of small-grain cereals in Iran. Among the 65 bacterial strains isolated from wheat, barley, and gramineous weeds in eight Iranian provinces, multilocus sequence analysis and typing (MLSA and MLST) of four housekeeping genes ( dnaK , fyuA , gyrB , and rpoD ), identified 57 strains as X. translucens pv. undulosa, while eight strains were identified as X. translucens pv. translucens. Although the pathogenicity patterns on oat and ryegrass weed species varied among the strains, all X. translucens pv. undulosa strains were pathogenic on barley, Harding's grass, rye (except for XtKm35) and wheat, and all X. translucens pv. translucens strains were pathogenic on barley and Harding's grass, while none of the latter group was pathogenic on rye or wheat (except for XtKm18). MLST using the 65 strains isolated in Iran, as well as the sequences of the four genes from 112 strains of worldwide origin retrieved from the GenBank database, revealed higher genetic diversity (i.e., haplotype frequency, haplotype diversity, and percentage of polymorphic sites) among the Iranian population of X. translucens than among the North American strains of the pathogen. High genetic diversity of the BLS pathogen in Iran was in congruence with the fact that the Iranian Plateau is considered the center of origin of cultivated wheat. However, further studies using larger collections of strains are warranted to precisely elucidate the global population diversity and center of origin of the pathogen. IMPORTANCE Bacterial leaf streak (BLS) of small-grain cereals (i.e., wheat and barley) is one of the economically important diseases of gramineous crops worldwide. The disease occurs in many countries across the globe, with particular importance in regions characterized by high levels of precipitation. Two genetically distinct xanthomonads-namely, Xanthomonas translucens pv. undulosa and X. translucens pv. translucens-have been reported to cause BLS disease on small-grain cereals. As seed-borne pathogens, the causal agents are included in the A2 list of quarantine pathogens by the European and Mediterranean Plant Protection Organization (EPPO). Despite its global distribution and high economic importance, the population structure, genetic diversity, and phylogeography of X. translucens remain undetermined. This study, using MLSA and MLST, provides a global-scale phylogeography of X. translucens strains infecting small-grain cereals. Based on the diversity parameters, neutrality indices, and population structure, we observe higher genetic diversity of the BLS pathogen in Iran, which is geographically close to the center of origin of common wheat, than has so far been observed in other areas of the world, including North America. The results obtained in this study provide a novel insight into the genetic diversity and population structure of the BLS pathogen of small-grain cereals on a global scale., (Copyright © 2019 American Society for Microbiology.)

Bacterial leaf streak of small-grain cereals is an economically important disease of wheat and barley crops. The disease occurs in many countries across the globe. with particular importance in regions characterized by high precipitation or areas in which sprinkler irrigation is used. Three genetically distinct lineages of the Gram - negative bacterium Xanthomonas trans! ucens (X. transiticens pv. undulosci. X. Trans lucens pv. trans lucens, and X. transhicens py. cerealis) are responsible for most of the bacterial leaf streak infections on wheat and harley crops. Considering the seedborne nature of the pathogens. they are included in the A2 (high-risk) list of quarantine organisms for some European countries; hence, they are under strict quarantine control and zero tolerance. Due to the taxonomic complexities within X. transhicens. the exact geographic distribution of each pathovar has not yet been determined. In this mini review, we provide an updated overview of the detection and diagnosis of the bacterial leaf streak pathogens. First, a shoi·t history of the leaf streak pathogens is provided, followed by the symptomology and host range of the causal agents. Then, the utility of conventional methods and high-throughput molecular approaches in the precise detection and identification of the pathogens is explained. Finally, we highlight the role of quarantine inspections and early detection of the pathogen in combating the risk of bacterial leaf streak in the 21 st century s small-grains cereals-industry. [ABSTRACT FROM AUTHOR]

Bacterial canker and spot of stone fruits and bacterial blight of walnut, caused by different pathovars of Xanthomonas arboricola, namely X. arboricola pv. pruni and X. arboricola pv. juglandis, respectively, are considered among quarantine or regulated (nonquarantine) agents in different countries. The two pathogens were initially reported in Iran in 2005 and 1977, respectively. However, the precise identity, pathogenicity status and geographic distribution of these pathogens have been questioned. In this study, we have employed a series of comprehensive field surveys and samplings over a course of 5 years (2015–2019) across 16 provinces to reassess and clarify the occurrence and distribution of X. arboricola on fruit and nut trees in Iran. Besides dozens of non‐Xanthomonas and nonpathogenic bacterial strains, 27 X. arboricola strains were isolated from stone fruits (n = 13) and walnut (n = 14). Except for the strains Peh35, Peh78 and Peh79, the stone fruit strains were nonpathogenic on their host of isolation as well as several other plant species, while the walnut strains were pathogenic on their host of isolation. Multilocus sequence analysis (MLSA) of four housekeeping genes, atpD, dnaK, gyrB and rpoD, revealed that among the stone fruit strains only Peh78 and Peh79 could be assigned into X. arboricola pv. pruni, while the walnut strains were identified as X. arboricola pv. juglandis. Based on the results of pathogenicity assays and phylogenetic analyses, we confirm the occurrence of X. arboricola pv. juglandis in Iran, while X. arboricola pv. pruni was absent in the plant samples evaluated in this study. [ABSTRACT FROM AUTHOR]

The Gram-negative bacterium Xanthomonas translucens infects a wide range of gramineous plants with a notable impact on small grain cereals. However, genomics-informed intra-species population structure and virulence repertories of the pathogen have rarely been investigated. In this study, the complete genome sequences of seven X. translucens strains representing an entire set of genetic diversity of two pathovars X. translucens pv. undulosa and X. translucens pv. translucens is provided and compared with those of seven publicly available complete genomes of the pathogen. Organization of the 25 type III secretion system genes in all the 14 X. translucens strains was exactly the same, while TAL effector genes localized singly or in clusters across four loci in X. translucens pv. translucens and five to six loci in X. translucens pv. undulosa. Beside two previously unreported endogenous plasmids in X. translucens pv. undulosa , and variations in repeat variable diresidue (RVD) of the 14 strains, tal1a of X. translucens pv. translucens strain XtKm8 encode the new RVDs HE and YI which have not previously been reported in xanthomonads. Further, a number of truncated tal genes were predicted among the 14 genomes lacking conserved Bam HI site at N-terminus and Sph I site at C-terminus. Our data have doubled the number of complete genomes of X. translucens clarifying the population structure and genomics of the pathogen to pave the way in the small grain cereals industry for disease resistance breeding in the 21st century's agriculture. [ABSTRACT FROM AUTHOR]

The goal of this study was to investigate the role of lipopolysaccharides (LPS) in induction of resistance in tomato against the causal agent of bacterial spot,Xanthomonas perforans. The results showed that pre-treatment with LPS leads to enhancing resistance of tomato againstX. perforans. In addition, expression profiling of β-1,3-glucanase (BGL), Phenylalanine ammonia-lyase (PAL) and catalase (CAT) was examined during the induced resistance by LPS. The effect of LPS on induction ofBGL,PALandCATwas demonstrated in the present study. The data suggest that the effect of LPS on resistance of tomato againstX. perforanscould be through activation of some defence genes such as ofBGL,PALandCATwhich afford defence responses against the pathogen. Our findings might help to better understanding the molecular bases of the induced resistance by LPS. [ABSTRACT FROM PUBLISHER]

We report in this study for the first time the occurrence of bacterial spot of pepper in Iran and both phenotypic and genetic characterization of its causal agent, Xanthomonas euvesicatoria. Pepper plants grown in 15 of 30 surveyed private gardens and commercial fields were infected by the pathogen in Marand County, East Azerbaijan Province, north-western Iran. The obtained strains of X. euvesicatoria had different amylolytic and pectolytic activities compared with those reported for this species elsewhere. Pathogenicity tests showed that strains isolated from diseased pepper are able to infect tomato, in addition to pepper. Host range of the pathogen was assessed on eight annual plant species including crops and weeds by measuring the population dynamics. The host range assessment showed that in addition to pepper and tomato, known hosts of X. euvesicatoria, the Iranian strains were able to colonize a number of new hosts such as nightshade and common bean. In contrast, none of them were able to build up their population on cowpea, eggplant, bindweed and zucchini. All X. euvesicatoria strains obtained in this study were sensitive to copper sulphate and streptomycin at concentrations higher than 20 and 50 mg/l, respectively. Phylogenetic analyses of the strains using the sequences of gyrB and hrpB genes confirmed their species as X. euvesicatoria. Given a direct commercial trade of fresh solanaceous vegetables between Iran and Turkey, it is hypothesized that the pathogen entered north-western Iran from eastern parts of Turkey through infected plant materials. Finally, the role of prevention - based on the use of healthy planting materials and resistant and/or tolerant plant varieties - to contain the potential disease epidemics is discussed. [ABSTRACT FROM AUTHOR]

Bacterial blight of common bean caused by Xanthomonas axonopodis pv. phaseoli (Xap) is one of the most devastating diseases and causes serious yield losses worldwide. To extend our understanding for the efficacy of salicylic acid (SA) as a therapeutic agent against bacterial diseases, we have studied the impact of exogenous SA treatment on disease incidence and development during the course of Xap infection. In this study, an enhanced resistance response induced by SA was detected in common bean infected with Xap. On the other hand, SA did not have direct antibacterial effect in vitro. Additionally, we examined the effects of SA on expression of superoxide dismutase (SOD), malate dehydrogenase (MDH) and phenylalanine ammonia-lyase (PAL). SA-pretreated leaves had higher expression of MDH after Xap infection when compared with their counterparts pretreated with water (control). SA/Xap treatments showed more expression of SOD at 24, 48 and 72 h post-pathogen inoculation (hpi) compared to water/Xap samples, whereas PAL expression was significantly different only at 24 hpi. The results showed the contribution of SA as an effective resistance activator and may provide an additional approach in bacterial blight integrated diseases management programs. [ABSTRACT FROM AUTHOR]