Strains Of Xanthomonas Campestris Pv Research Articles

Preharvest UV-C Hormesis Induces Key Genes Associated With Homeostasis, Growth and Defense in Lettuce Inoculated With Xanthomonas campestris pv. vitians.

Preharvest application of hormetic doses of ultraviolet-C (UV-C) generates beneficial effects in plants. In this study, within 1 week, four UV-C treatments of 0.4 kJ/m2 were applied to 3-week-old lettuce seedlings. The leaves were inoculated with a virulent strain of Xanthomonas campestris pv. vitians (Xcv) 48 h after the last UV-C application. The extent of the disease was tracked over time and a transcriptomic analysis was performed on lettuce leaf samples. Samples of lettuce leaves, from both control and treated groups, were taken at two different times corresponding to T2, 48 h after the last UV-C treatment and T3, 24 h after inoculation (i.e., 72 h after the last UV-C treatment). A significant decrease in disease severity between the UV-C treated lettuce and the control was observed on days 4, 8, and 14 after pathogen inoculation. Data from the transcriptomic study revealed, that in response to the effect of UV-C alone and/or UV-C + Xcv, a total of 3828 genes were differentially regulated with fold change (|log2-FC|) > 1.5 and false discovery rate (FDR) < 0.05. Among these, of the 2270 genes of known function 1556 were upregulated and 714 were downregulated. A total of 10 candidate genes were verified by qPCR and were generally consistent with the transcriptomic results. The differentially expressed genes observed in lettuce under the conditions of the present study were associated with 14 different biological processes in the plant. These genes are involved in a series of metabolic pathways associated with the ability of lettuce treated with hormetic doses of UV-C to resume normal growth and to defend themselves against potential stressors. The results indicate that the hormetic dose of UV-C applied preharvest on lettuce in this study, can be considered as an eustress that does not interfere with the ability of the treated plants to carry on a set of key physiological processes namely: homeostasis, growth and defense.

Reaction of biofortified lettuce genotypes to different strains of Xanthomonas campestris pv. vitians

Lettuce bacterial leaf spot caused by Xanthomonas campestris pv. vitians is an aggressive disease that is difficult to control. So far there are no reports of the reaction of biofortified lettuce genotypes to different isolates of the bacteria. Thus, the objective was to evaluate the aggressiveness of X. campestris pv. vitians, as well as the reaction of biofortified lettuce genotypes to bacterial spot. Two experiments were performed in two distinct seasons (winter and summer), in greenhouse at the Vegetable Experimental Station of the Federal University of Uberlândia (UFU). The experimental design in both experiments was a randomized block design, in a factor scheme of 5 × 4 (five genotypes and four strains), with four repetitions. Were evaluated the severity and the area under the disease progress curve. In general, the biofortified lettuce ‘Uberlândia 10000’ was more resistant to most bacterial strains in the summer cultivation, and in the winter period UFU ‘Crespa 206’. The commercial cultivar Robusta was the most susceptible to the strains during both seasons. The UFU E125 strain was the most aggressive for most genotypes in both seasons.

Complete Genome Sequences of Two Strains of Xanthomonas campestris pv. campestris Isolated in Japan

Here, we report the complete genome sequences of two strains of Xanthomonas campestris pv. campestris (MAFF106712 and MAFF302021), which cause black rot in crucifer crops, isolated from Chinese cabbage and cauliflower, respectively, in Japan. The MAFF106712 chromosome was 5,002,720 bp, with a G+C content of 65.2%, and harbored one plasmid of 78,747 bp. The MAFF302021 chromosome was 5,048,651 bp, with a G+C content of 65.1%.

LbDSF, the Lysobacter brunescens Quorum-Sensing System Diffusible Signaling Factor, Regulates Anti- Xanthomonas XSAC Biosynthesis, Colony Morphology, and Surface Motility.

Lysobacter species are emerging as novel sources of antibiotics, but the regulation of these antibiotics has not been thoroughly elucidated to date. In this work, we identified a small diffusible signaling factor (DSF) molecule (LbDSF) that regulates the biosynthesis of a novel Xanthomonas-specific antibiotic compound (XSAC) in Lysobacter brunescens OH23. LbDSF was isolated from the culture broth of L. brunescens OH23, and the chemical structure of the molecule was determined by NMR and MS. The LbDSF compound induced GUS expression in a reporter strain of Xanthomonas campestris pv. campestris FE58, which contained the gus gene under the control of a DSF-inducible engXCA promoter. LbDSF production was found to be linked to the enoyl-CoA hydratase RpfF and dependent on the two-component regulatory system RpfC (hybrid sensor histidine kinase)/RpfG (response regulator), and LbDSF production was increased 6.72 times in the ΔrpfC compared to wild-type OH23. LbDSF-regulated XSAC production was dramatically decreased in ΔrpfF, ΔrpfC, and ΔrpfG. Additionally, a significant reduction in surface motility and a number of changes in colony morphology was observed in the ΔrpfF, ΔrpfC, and ΔrpfG compared to the wild-type OH23. The exogenous LbDSF significantly increased XSAC production in wild-type OH23 and recovered the XSAC biosynthetic ability in ΔrpfF. Taken together, these results showed that LbDSF is a fatty-acid-derived DSF that positively regulates XSAC biosynthesis, cell morphology, and surface motility. Moreover, the RpfC/RpfG quorum-sensing signal transduction pathway mediates XSAC biosynthesis. These findings may facilitate antibiotic production through genetic engineering in Lysobacter spp.

Preparation and In Vitro Characterization of Chitosan Nanoparticles and Their Broad-Spectrum Antifungal Action Compared to Antibacterial Activities against Phytopathogens of Tomato

The present study was to prepare chitosan nanoparticles (CNPs) from chitosan (CS) to evaluate their in vitro antimicrobial activities against phytopathogens of tomato. We prepared and characterized CNPs for their particle size, polydispersity index, and structures. The antifungal properties of CS and CNPs against phytopathogenic fungi namely Colletotrichum gelosporidies, Phytophthora capsici, Sclerotinia sclerotiorum, Fusarium oxysporum, Gibberella fujikuori were investigated. CNPs showed the maximum growth inhibitory effects on mycelial growth of F. oxysporum followed by P. capsici. We also studied antibacterial activities against phytopathogenic bacteria, such as three strains of Erwinia carotovora subsp. carotovora and one strain of Xanthomonas campestris pv. vesicatoria. Our results showed that both CS and CNPs markedly inhibited the growth of the both Xanthomonas and Erwinia strains. From our study, it is evident that both CS and CNPs have tremendous potential against phytopathogens of tomato for further field screening towards crop protection.

Characterization of a unique copper resistance gene cluster in Xanthomonas campestris pv. campestris isolated in Trinidad, West Indies

Whole genome sequencing of a copper resistant (CuR) black rot strain of Xanthomonas campestris pv. campestris (Xcc) isolated from a broccoli plant in Trinidad revealed a unique operon for copper resistance. The cop genes of strain Xcc-BrA1 were determined to be present on a 160 to 180 kb plasmid shown to be non-conjugative with other xanthomonads. While nucleotide comparison of a putative 8.0 Kbp copLABMGF gene cluster identified in Xcc-BrA1 genome did not reveal any homologous region with other known CuR Xanthomonas strains from diverse origins, the comparison of the translated amino acid sequence indicated similarity with X. citri, X. c. pv. citrumelonis and X. vesicatoria Cop proteins. Cloning of the copLAB gene cluster from Xcc-BrA1 conferred copper resistance to other copper-sensitive xanthomonads. Although Xcc-BrA1 harbors copLAB genes with similar sizes and organization and is able to grow on Cu-amended medium as other CuR xanthomonads, the phylogenetic analysis of nucleotide sequences indicates that the cop cluster in Xcc-BrA1 is unique and distantly related to other copLAB genes from Xanthomonas and Stenotrophomonas. The origin of copper resistance genes in Xcc-BrA1 is likely a result of horizontal gene acquisition from a still unknown phylloplane cohabitant. The findings of this study have implications for the management of crop diseases caused by CuR xanthomonads. Future studies could focus on and determining the distribution, overall importance and appropriate control measures for strains harbouring these unique genes.

Expression and Functional Roles of the Pepper Pathogen-Induced bZIP Transcription Factor CabZIP2 in Enhanced Disease Resistance to Bacterial Pathogen Infection.

A pepper bZIP transcription factor gene, CabZIP2, was isolated from pepper leaves infected with a virulent strain of Xanthomonas campestris pv. vesicatoria. Transient expression analysis of the CabZIP2-GFP fusion protein in Nicotiana benthamiana revealed that the CabZIP2 protein is localized in the cytoplasm as well as the nucleus. The acidic domain in the N-terminal region of CabZIP2 that is fused to the GAL4 DNA-binding domain is required to activate the transcription of reporter genes in yeast. Transcription of CabZIP2 is induced in pepper plants inoculated with virulent or avirulent strains of X. campestris pv. vesicatoria. The CabZIP2 gene is also induced by defense-related hormones such as salicylic acid, methyl jasmonate, and ethylene. To elucidate the in vivo function of the CabZIP2 gene in plant defense, virus-induced gene silencing in pepper and overexpression in Arabidopsis were used. CabZIP2-silenced pepper plants were susceptible to infection by the virulent strain of X. campestris pv. vesicatoria, which was accompanied by reduced expression of defense-related genes such as CaBPR1 and CaAMP1. CabZIP2 overexpression in transgenic Arabidopsis plants conferred enhanced resistance to Pseudomonas syringae pv. tomato DC3000. Together, these results suggest that CabZIP2 is involved in bacterial disease resistance.

Lactose consuming strains of Xanthomonas citri subsp. citri (Xcc) insight into the emergence of natural field resources for xanthan gum production

Xanthomonas genus possesses a low level of β-galactosidase gene expression and is therefore unable to produce xanthan gum in lactose-based media. In this study, we report the emergence of some natural field strains of Xanthomonas citri subsp. citri (Xcc) capable to use lactose as a sole carbon source to produce xanthan gum. From 210 Xcc strains isolated from key lime (C. aurantifolia), 27 showed the capacity to grow on lactose containing medium. Xcc lactose consuming strains demonstrated a good level of xanthan production. Amongst all, NIGEBK37 produced the greatest (14.62g/l) amount of xanthan gum in experimental laboratory conditions. By evaluating the viscosity of the biopolymer at 25°C, it was demonstrated that xanthan synthesized by strain NIGEBK37 has the highest viscosity (44,170.66cP). Our results were indicative for the weakness of a commercial strain of Xanthomonas campestris pv. Campestris DSM1706 (Xcc/DSM1706) to produce xanthan in lactose containing medium.

Phenotypic and genotypic characterization of Xanthomonas campestris strains isolated from cabbage, kale and broccoli

Thirty-six strains of Xanthomonas campestris pv. campestris (Xcc) isolated from cabbage, kale and broccoli were identified according to their pathogenicity, phenotypic and genotypic characterization. Pathogenicity was confirmed by the injection method with a hypodermic syringe into the mesophilic tissue of cabbage leaves. All strains were Gramnegative, aerobic, catalase-positive, oxidase-negative, grew at 35?C, produced levan, H2S and indole, did not reduce nitrate, hydrolyzed Tween 80, starch, gelatin and esculin and did not show tolerance to 0.1 and 0.02% TTC. The strains produced acid from d-arabinose, arginine, dulcitol, galactose, d-glucose, maltose, mannose, sorbitol, sucrose and xylose. The genetic characterization was based on the sequence analyses of 16S rDNA and ERIC and BOX PCR. Strains of different pathovars were also used to compare PCR resulting patterns. BOX-PCR of the strains from kale and broccoli, obtained using (GTG)5 primer, yielded patterns with a high similarity level to pathovar reference strain Xcc. The strains from cabbage yielded BOX and ERIC product patterns, distinguishing them from the other tested strains and reference strains. 16S rDNA of the representative strains was closely related to Xcc strain ATCC 33913. ERIC PCR and BOX using (GTG)5 primer generated different Xcc patterns and were effective in distinguishing strains from different plant hosts.

Copper resistance in Xanthomonas campestris pv. campestris affecting crucifers in Trinidad

Fifty-six native isolates collected in 12 farming districts of Trinidad and seven reference strains of Xanthomonas campestris pv. campestris were evaluated for resistance to copper in buffered (pH 7.0) and unbuffered (pH 5.6) nutrient agar media. All isolates and reference strains were pathogenic and elicited typical black rot symptoms on a susceptible variety of Brassica olearceae, ‘Copenhagen Market’. Thirty-four and thirty-three native isolates were highly resistant to copper (growth on ≥ 200 ppm copper) in buffered and unbuffered media, respectively; however, all the reference strains were highly susceptible to copper. The mean minimum inhibition concentration for the 56 native isolates was 224.6 ppm copper indicating that high levels of copper resistance are present in X. campestris pv. campestris in Trinidad. The association between growth of the 56 isolates and seven reference stains on buffered and unbuffered media was strong (Pearson’s and Spearman’s r = 0.93; P < 0.01) suggesting that either medium can be used to evaluate resistance to copper in X. campestris pv. campestris. There was also a strong association between length of time of continuous applications of copper formulations to treat black rot disease and proportion of the native X. campestris pv. campestris with resistance to copper (Pearson’s r = 0.96; Spearman’s r = 0.93); however, there was no association between resistance to copper and aggressiveness at 10 days after inoculation.

Host and Non-Host Disease Resistances of Kimchi Cabbage Against Different Xanthomonas campestris Pathovars

Department of Horticultural Sciences, Gyeongnam National University of Science and Technology (GNTech), Jinju 660-758,Korea(Received on April 1, 2012; Revised on May 31, 2012; Accepted on May 31, 2012)This study was conducted to investigate host and non-host disease resistances of kimchi cabbage plants tobacterial infection. Kimchi cabbage leaves respondeddifferently to infections with a virulent strain of Xanth-omonas campestris pv. campestris (Xcc) 8004 and twostrains (85-10 and Bv5-4a.1) of non-host bacteria X.campestris pv. vesicatoria (Xcv). Non-host bacteriatriggered a rapid tissue collapse of the leaves showing asbrown coloration at the infected sites, highly increasedion leakage, lipid peroxidation and accumulation of UV-stimulated autofluorescence materials at the inoculatedsites. During the observed interactions, bacterial pro-liferations within the leaf tissues were significantlydifferent. Bacterial number of Xcc 8004 progressivelyincreased within the inoculated leaf tissues over time,while growths of two non-host bacteria Xcv strains weredistinctly limited. Expressions of pathogenesis-relatedgenes, such as GST1, PR1, BGL2, VSP2, PR4 and LOX2,were differentially induced by host and non-host bacterialinfections of X. campestris pathovars. These resultsindicated that rapid host cellular responses to the non-host bacterial infections may contribute to an array ofdefense reactions to the non-host bacterial invasion.Keywords : kimchi cabbage, non-host disease resistance,programmed cell death, Xanthomonas campestris pathovarsPlants protect themselves actively against non-host patho-gens via an array of defense reactions, which are sometimessimilar to those against host pathogen infections. So far,non-host disease resistance have been classified into twotypes in diverse plant species (Mysore and Ryu, 2004; Ohet al., 2006). Type I and type II non-host disease resistanceis differentiated by appearance of visible cell death inresponse to infections by non-host fungal and bacterialpathogens. Hypersensitive cell death was not found in typeI non-host resistance, while rapid cell death usually observedin incompatible interactions between hosts and avirulentstrains appear in type II non-host resistance. During celldeath-mediated non-host disease resistance, host plantslaunched sophisticated defense mechanisms i.e. oxidativeburst, kinase cascades and accumulation of antimicrobialproteins usually found during incompatible interactions ofhost plant-pathogen (Dixon et al., 1994).Non-host disease resistance of kimchi cabbage plantswere previously reported against infection by Pseudomonassyringae pv. tomato (Pst) (Park et al., 2005). Hypersensitivecell death and accumulation of H

Bacterial Leaf Spot of Zinnia Caused by Xanthomonas campestris pv. zinniae, a New Disease in Korea.

In September 2011, bacterial leaf spot was observed on zinnia plants (Zinnia elegans L.) grown in a garden in Suwon, Korea. Leaf symptoms included angular lesions that were yellow or brown-to-reddish brown in the center. Bacterial isolates (BC3293 to BC3299) were recovered on trypticase soy agar from lesions surface-sterilized in 70% ethyl alcohol for 1 min. Pathogenicity of the isolates was confirmed by spray inoculation with a bacterial suspension (106 CFU/ml) prepared in sterile distilled water and applied to zinnia plants at the four- to five-leaf growth stage (two plants per isolate). Sterile distilled water was used as the negative control. The inoculated plants were incubated in a greenhouse at 26 to 30°C and 95% relative humidity. Characteristic leaf spot symptoms developed on inoculated zinnia plants 5 days after inoculation. No symptoms were observed on the negative control plants. The bacterium reisolated from the inoculated leaves was confirmed through gyrB gene sequence analysis (3). All isolates were gram-negative, aerobic rods, each with a single flagellum. Isolates were positive for catalase and negative for oxidase. The biochemical and physiological tests for differentiation of Xanthomonas were performed using methods described by Shaad et al. (2). The isolates were positive for mucoid growth on yeast extract-dextrose-calcium carbonate agar, growth at 35°C, hydrolysis of starch and esculin, protein digestion, acid production from arabitol, and utilization of glycerol and melibiose. Colonies were negative for ice nucleation, and alkaline in litmus milk. The gyrB gene (870 bp) and the 16S-23S rRNA internal transcribed spacer (ITS) regions (884 bp) were sequenced to aid in identification of the original field isolates using published PCR primer sets Xgyr1BF/Xgyr1BR (3) and A1/B1 (1), respectively. Sequence of the gyrB gene (GenBank Accession Nos. JQ665732 to JQ665738) from the zinnia field isolates shared 100% sequence identity with the reference strain of Xanthomonas campestris pv. zinniae (GenBank Accession No. EU285210), and the ITS sequences (GenBank Accession Nos. JQ665725 to JQ665731) had 99.9% sequence identity with X. campestris pv. zinnia XCZ-1 (GenBank Accession No. EF514223). On the basis of the pathogenicity assays, biochemical and physiological tests, and sequence analyses, the isolates were identified as X. campestris pv. zinniae. To our knowledge, this is the first report of bacterial leaf spot of zinnia caused by X. campestris pv. zinniae in Korea. The disease is expected to result in economic and aesthetic losses to plants in Korean landscapes. Thus, seed treatment with bactericides will be required to control the bacterial leaf spot of zinnia before planting.

Origin of hydrogen peroxide during the cowpea- Xanthomonas interaction

To assay hydrogen peroxide (H2O2) production by phytopathogenic bacteria in vivo, cowpea seedlings were inoculated using wild-type Xanthomonas campestris pv. phaseoli and its mutant strain on ahpC (with attenuated H2O2 production). Antibiotic rifampicin (Rif) was used to kill off the Xanthomonas campestris pv. phaseoli in cowpea leaves. The optimal concentration of Rif to eradicate the bacteria was 500 μg mL–1, and duration of the Rif treatment to eradicate the bacteria in the cowpea tissues was 48 h. This level of Rif did not significantly affect chloroplast and mitochondrial function in cowpea leaves. The concentration of H2O2 in cowpea inoculated with wild-type or mutant strain of Xanthomonas campestris pv. phaseoli following Rif treatment was measured. Increased H2O2 accumulation was observed in cowpea leaves respectively inoculated with wild-type and mutant strain. The accumulation of excess H2O2 was significantly decreased by the Rif treatment on cowpea wild-type bacteria systems. However, the level of H2O2 in cowpea leaves inoculated with mutant strains following Rif treatment was at the same level as in plant leaves without Rif treatment. The results demonstrate that the change in H2O2 concentration observed in vivo was caused by wild-type bacteria.

New Zealand strains of plant pathogenic bacteria classified by multi‐locus sequence analysis; proposal of Xanthomonas dyei sp. nov.

Strains of Xanthomonas isolated in New Zealand from diseased endemic and introduced plants, investigated in a multi‐locus sequence analysis (MLSA), were distributed primarily in two species. Strains from Dysoxylum, Hardenbergia, Liquidambar, Magnolia and Mahonia were members of Xanthomonas arboricola. Strains of Xanthomonas campestris pv. laureliae, X. campestris pv. eucalypti and strains from Aralia, Diospyros, Dysoxylum, Eriostemon, Eucalyptus, Metrosideros and Olea formed a population distinct from all known Xanthomonas spp. These latter strains have a unique fatty acid methyl ester profile and are considered to be members of a new Xanthomonas species, for which the name Xanthomonas dyei is proposed. Xanthomonas campestris pv. eucalypti and X. campestris pv. laureliae are considered to be pathovars of the new species and their reclassification as X. dyei pv. eucalypti and X. dyei pv. laureliae, respectively, is proposed. Strains previously identified as Pseudomonas syringae pv. dysoxyli from Dysoxylum spectabile, including the pathotype strain, were examined and found not to represent the pathogen originally described as P. dysoxyli. Other strains (proved to be pathogenic) from diseased D. spectabile, corresponding to the original description of P. dysoxyli, are members of X. dyei and the new combination X. dyei pv. dysoxyli is proposed. The geographic and evolutionary origins of X. dyei, apparently endemic to Australasia, and the adaptation of strains to the introduced host plants Aralia, Diospyros, Eriostemon, Metrosideros and Olea, are discussed. The origins of the X. arboricola strains isolated from Dysoxylum, Hardenbergia, Liquidambar, Magnolia and Mahonia pose a conundrum.

Diversity of effector genes in plant pathogenic bacteria of genus Xanthomonas

Gram-negative plant pathogenic bacteria are secreting into plant cell a special type of pathogeni city-related proteins called effectors. They are capable of suppressing plant innate immunity or stimulating synthesis and export of metabolites desired by the pathogen. We identified a number of effector-coding genes typical of xanthomonads analyzing 8 completely sequenced genomes of genus Xanthomonas. Using representative collection provided by Russian Research Institute of Phytopathology we identified genetic diversity of effector gene loci in population of Xanthomonas bacteria. Patterns of effector genes were identified for individual strains and statistic linkage between particular genes and race of the pathogen was established. For the first time several untypical effector genes were found in strains of Xanthomonas campestris pv. campestris.

Caracterização de isolados de Xanthomonas campestris pv campestris de sistemas de produção orgânico e reação de brássicas à podridão-negra

Noventa isolados de Xanthomonas campestris pv. campestris (Xcc) de brássicas oriundas de sistemas de produção orgânico das Zonas da Mata e Agreste de Pernambuco foram caracterizados com base na sensibilidade a antibióticos e sulfato de cobre e atividade de esterase. A maioria apresentou alta sensibilidade à tetraciclina (76,6%), eritromicina (63,3%) e estreptomicina (63,3%), resistência à amoxicilina (70%), gentamicina (40,0%) e norfloxacin (45,5%) e média sensibilidade (44,4%) ou resistência (44,4%) à neomicina. Cinqüenta e cinco isolados de Xcc foram resistentes ao sulfato de cobre na concentração de 50 mg/mL e todos foram sensíveis ao produto na concentração de 200 mg/mL. Atividade de esterase foi apresentada por 92,22% dos isolados. A análise Euclidiana por ligação simples evidenciou variabilidade entre os isolados separando-os em sete grupos de similaridade. Foi estudada também a reação de 14 cultivares de brássicas à podridão-negra, utilizando o isolado "B21" de Xcc. As cultivares diferiram significativamente entre si em relação ao período de incubação, incidência e severidade final da doença. Os maiores valores de severidade final da doença foram verificados em brócolos "Ramoso", couve-flor "Bola de Neve" e "Piracicaba de Verão", e repolho "Chato de Quintal". Os híbridos de couve-chinesa "AF 70", "AF 72", "AF 69" e "AF 66" mostraram-se altamente resistentes à doença, enquanto que brócolos "Ramoso" e "Precoce Piracicaba", couve-flor "Piracicaba de Verão" e "Híbrido Cindy" e repolho "60 Dias" foram medianamente resistentes.

Detection of genetic diversity among Indian strains of Xanthomonas campestris pv. mangiferaeindicae using PCR-RAPD

AbstractThe randomly amplified polymorphic DNA (RAPD) technique was used to investigate the genetic diversity in 6 strains of Xanthomonas campestris pv. mangiferaeindicae (Xcmi), the causal pathogen of mango bacterial canker disease (MBCD). The RAPD analysis was also intended to identify molecular markers, specific to the species to develop PCR-based markers for detection of Xcmi in mango field and planting materials. Twenty RAPD primers (CP 1-CP 20) were evaluated to establish molecular characters and genetic variability in the genome of Xcmi. Among these, only 4 were found efficient for development of reproducible banding pattern. It has been observed that the largest and smallest amplified RAPD products were of 2.036 and 0.201 kbp. A total of 136 bands were scored against 6 strains of Xcmi. There was 7.66 per cent polymorphism in individual isolates which indicates significant polymorphism among the evaluated strains, with mean difference of 0.33 (Xcmi 2 vs. Xcmi 8) and 0.29 (Xcmi 10 vs. Xcmi 12). However, the single linkage euclidean distances were statistically significant (P&gt;0.05), i.e., 0.58. The markers CP 5, 10, 16 and 19 were amplified in all the strains with polymorphic alleles, which indicates that these markers could be used for rapid detection of genetic variability in Xcmi strains.

CHARACTERIZATION OF ITALIAN POPULATIONS OF XANTHOMONAS CAMPESTRIS pv. CAMPESTRIS USING PRIMERS BASED ON DNA REPETITIVE SEQUENCES

One-hundred and forty-one strains of Xanthomonas campestris pv. campestris (Xcc), the causal agent of vascular blackening of crucifers were isolated from different crucifer plants in central and southern Italian regions and characterized for DNA polymorphism by PCR, using primers based on repetitive sequences. By M13-PCR, all strains, except for two, were distributed in three main clusters: a, with similarity index (SI) 0.78, containing 70 strains grouped in 19 haplotypes; b (SI = 0.80) containing 54 strains in 17 haplotypes; g (SI = 0.75) containing 15 strains in 6 haplotypes. By BOX-PCR, all strains were distributed in three main clusters: a (SI = 0.58) containing 102 strains distributed in 9 haplotypes; b (SI = 0.45), including 24 strains distributed in 9 haplotypes; g (SI = 0.37), including 15 strains distributed in 3 haplotypes. A very large variability was observed in these Italian populations of Xcc especially using M13-PCR. No obvious relationships were observed between the strains comprised in each cluster, sub-cluster or haplotype and their geographic origin or host plant.

Reappearance of bacterial leaf and flower spot onZinnia eleganscaused byXanthomonas campestrispv.zinniaein Europe

During the years 2006 and 2007, serious outbreaks of bacterial leaf and flower spot disease were observed on zinnia ( Zinnia elegans Jaqc. cv. Mondo and Capricio) plants grown in several parks in Budapest, Hungary. Five strains of Xanthomonas campestris pv. zinniae isolated from diseased zinnia plants were identified based on morphological, physiological, biochemical and pathogenicity tests, as well as sequence analysis of the bacterial 16S–23S rDNA spacer region.

Sensitive real‐time PCR detection of Xanthomonas fragariae in strawberry plants

Xanthomonas fragariae, the causal agent of angular leaf spot on strawberry, is a quarantine organism in strawberry propagation material in the European Union. For the reliable screening of planting material for latent infections, a real‐time PCR assay based on Taqman® chemistry for the detection of X. fragariae was developed. Primers and probe sequences were based on a DNA fragment amplified by a previously reported X. fragariae‐specific technique. The sequence of this genomic fragment had no significant similarity with any published GenBank sequence. Specificity of the designed assay was tested with an extended range of X. fragariae collection strains and isolates, with other Xanthomonas spp. and with unidentified bacterial isolates from strawberry plants. A nested PCR, which until now was the reference method for sensitive detection in planta, cross‐reacted with the reference strain of Xanthomonas campestris pv. campestris. In combination with an elaborated DNA extraction procedure, the Taqman® PCR enabled reliable detection down to 300 colony forming units in a 100 mg strawberry leaf sample. The assay offers a new tool for epidemiological research and for sanitary control of plant material with low level or latent infections of X. fragariae.