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Causal Agent (causal + agent)
Selected AbstractsDetection and Identification of Brenneria nigrifluens, the Causal Agent of the Shallow Bark Canker of Walnut by, PCR AmplificationJOURNAL OF PHYTOPATHOLOGY, Issue 7-8 2008S. Loreti Abstract A 1 kb DNA band from strains of Brenneria nigrifluens, as shown by amplification of their genomic DNA by polymerase chain reaction (PCR) using minisatellite primer designed on the minisatellite sequence of the M13 phage, was isolated, cloned and sequenced. Specific oligonucleotides (F1,C3) were selected into this 1 kb DNA sequence and used in a PCR assay to detect and identify strains of B. nigrifluens. Several strains of B. nigrifluens were assessed with F1,C3 primers producing a specific band of approximately 250 bp pairs in length. This target was successfully amplified from purified genomic DNA, from bacterial culture and directly from infected walnut bark tissue. No amplification was obtained when the PCR assay was performed on other plant-pathogenic species from the following genera Brenneria, Erwinia, Agrobacterium, Pseudomonas, Ralstonia, Pectobacterium, Xanthomonas and from walnut-associated bacteria, indicating the specificity of these primers. The PCR assay with the primers described here provides a rapid, specific and sensitive diagnostic method for B. nigrifluens and a useful tool for epidemiological studies. [source] Heritability of Phenols in the Resistance of Theobroma cacao against Phytophthora megakarya, the Causal Agent of Black Pod DiseaseJOURNAL OF PHYTOPATHOLOGY, Issue 9 2007P. F. Djocgoue Abstract The black pod disease caused by Phytophthora megakarya is responsible for 80% of the cocoa production loss in Cameroon. To assess the resistance of cocoa plants against this pathogen, necrotic lesions, phenolic content and qualitative alteration of phenolics were conducted in ICS84 and ICS95 clones (two Trinitario introduced from Trinidad) and their hybrids (families F30 and F25) derived from reciprocal cross breeding between these two parental clones after inoculation. The existence of strong hybrid vigour has been shown. Ninety percentage of the hybrid's genotypes manifested a positive heterosis effect for the development of lesion size. This suggests the existence of hybrid vigour with a genetic additive effect. F3086, F2509, F2552 and F2586 hybrids were characterized by localized lesions. Those hybrids genotypes can be considered as elite clones. In relation to analysis of total phenolics and lesion size, no maternal effect was detected in the transmission of these characters. A significant and negative correlation (r = ,0.683) (P < 0.01) has been observed between necrosis evolution and phenolics accumulation. The values of the heritability of lesion size and the total phenolic content in offsprings did not permit to show the maternal effect. Qualitative analyses of phenolics showed high flavonones content in cocoa leaves. Qualitative analyses of phenolics in ICS84, ICS95 clones and their hybrids showed a modification of the phenolics profiles, notably concerning apigenin and luteolin derivatives due to the inoculation. These compounds, along with others that were not identified, could have a role in the reaction and mechanism of defence of cocoa against P. megakarya. [source] Pathogenic Variation among Isolates of Pyrenophora teres, the Causal Agent of Barley Net BlotchJOURNAL OF PHYTOPATHOLOGY, Issue 7-8 2003M. I. E. Arabi Abstract Isolates of Pyrenophora teres, the causal agent of net blotch of barley (Hordeum vulgare L.) has been collected from France and Syria. Their virulence spectra were evaluated using 11 barley genotypes as differential hosts. The genotypes exhibited a continuous range of response from highly susceptible to moderately resistant. A mean disease rating of 3.7 is considered as the separation point between avirulent and virulent reactions. The frequency of virulence was highest for isolates S5, R5 and S6-2 and lowest for R-ICA31 and R-HAS-6. A cluster analysis indicated that the isolates exhibited distinct differential virulence patterns and they were identified into five groups. The French isolates S5, R5 and S6-2 had a higher mean virulence and a low variance across all genotypes. None of the tested genotypes was highly resistant to all investigated isolates. [source] Physiological and Biochemical Characteristics of Iranian Strains of Xanthomonas axonopodis pv. citri, the Causal Agent of Citrus bacterial Canker DiseaseJOURNAL OF PHYTOPATHOLOGY, Issue 2 2001M. Mohammadi Twenty-four strains of Xanthomonas axonopodis pv. citri (Xac), the causal agent of bacterial canker of citrus, isolated from Mexican lime (Citrus aurantifolia) and lemon (Citrus limon) in southern Iran, were characterized phenotypically. Strains were all pathogenic on C. aurantifolia. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis revealed slight differences in soluble protein profiles among the strains. Based on host range specificity and phenotypic characteristics, representative strains were differentiated into two groups of Asiatic (A) and atypical Asiatic (aA) forms. DNA fingerprinting analysis using EcoRI as the restriction endonuclease showed a negligible difference in restriction pattern between the two groups. On the basis of isozymic analysis, the two groups were distinct with respect to superoxide dismutase (SOD) and esterase (EST) banding patterns. Plasmid DNA profile analysis showed that the bacterial strains were different from each other in terms of plasmid number and molecular weight. Phage typing study revealed that most of group A strains were susceptible to Cp1 and/or Cp2 and some were resistant to both phage types including the strain in aA group. Bacteriocin production test indicated that there was a variation among Xac strains using different indicators for each bacteriocin producer. It is concluded that the Iranian strains of Xac are heterogeneous and constitute a subgroup(s) within the pathotype A. Physiologische und biochemische Merkmale iranischer Stämme von Xanthomonas axonopodis pv. citri, dem Erreger des bakteriellen Zitruskrebses Vierundzwanzig Stämme von Xanthomonas axonopodis pv. citri, dem Erreger des bakteriellen Zitruskrebses, wurden von mexikanischen Sauren Limetten (Citrus aurantifolia) und Zitronen (Citrus limon) im Südiran isoliert und phänotypisch charakterisiert. Alle Stämme waren für C. aurantifolia pathogen. Eine SDS-PAGE-Analyse zeigte, daß zwischen den Stämmen geringfügige Unterschiede bei den Profilen der löslichen Proteine bestanden. Auf Grundlage der Spezifität des Wirtsspektrums und phänotypischer Merkmale wurden repräsentative Stämme in die zwei Gruppen asiatische (A) und atypische asiatische (aA) Formen eingeteilt. Eine Analyse mit DNA-Fingerabdrücken, wobei EcoRI als Restriktionsendonuclease diente, zeigte einen vernachlässigbar kleinen Unterschied bei den Restriktionsmustern der beiden Gruppen. Die Isoenzymanalyse ergab Unterschiede zwischen beiden Gruppen bezüglich der Bandenmuster von Superoxiddismutase (SOD) und Esterase (EST). Eine Analyse der Plasmid-DNA-Profile zeigte, daß die Bakterienstämme unterschiedliche Plasmidzahlen und verschiedene Molekülmassen aufwiesen. Eine Phagentypisierung ergab, daß die meisten Stämme der Gruppe A anfällig für Cp1 und/oder Cp2 waren; einige waren resistent gegen beide Phagentypen, darunter der Stamm in der aA-Gruppe. Ein Test der Bacteriocinproduktion ergab, daß die Xac -Stämme variierten; hier wurden verschiedene Indikatoren für jeden Bakteriocinbildner verwendet. Es wird gefolgert, daß die iranischen Stämme von Xac heterogen sind und eine oder mehrere Untergruppen innerhalb des Pathotyps A bilden. [source] Xanthomonas axonopodis pv. citri: factors affecting successful eradication of citrus cankerMOLECULAR PLANT PATHOLOGY, Issue 1 2004James H. Graham SUMMARY Taxonomic status:, Bacteria, Proteobacteria, gamma subdivision, Xanthomodales, Xanthomonas group, axonopodis DNA homology group, X. axonopodis pv. citri (Hasse) Vauterin et al. Microbiological properties:, Gram negative, slender, rod-shaped, aerobic, motile by a single polar flagellum, produces slow growing, non-mucoid colonies in culture, ecologically obligate plant parasite. Host range:, Causal agent of Asiatic citrus canker on most Citrus spp. and close relatives of Citrus in the family Rutaceae. Disease symptoms:, Distinctively raised, necrotic lesions on fruits, stems and leaves. Epidemiology:, Bacteria exude from lesions during wet weather and are disseminated by splash dispersal at short range, windblown rain at medium to long range and human assisted movement at all ranges. Crop loss:, Severe infections cause defoliation, blemished fruit, premature fruit drop, die-back of twigs and general debilitation of the tree. Distribution:, Citrus canker is not present in all subtropical to tropical regions of citriculture in the world, so considerable regulatory efforts are expended to prevent the introduction and spread of X. axonopodis pv. citri into areas in the Americas, Australia and elsewhere, with climates conducive to the disease. Importance:, Limited strategies exist for suppression of citrus canker on more susceptible cultivars. Blemished fruit are unmarketable and exposed fruit are restricted in market access. The economic impact of loss of markets is much greater than that from yield and quality reductions of the crop. Useful websites:,http://doacs.state.fl.us/canker , http://www.apsnet.org/education/lessonsplantpath/citruscanker/top.htm , http://www.apsnet.org/online/feature/citruscanker/ , http://www.plantmanagementnetwork.org/pub/php/review/citruscanker/ , http://www.abecitrus.com.br/fundecitrus.html , http://www.biotech.ufl.edu/PlantContainment/canker.htm , http://www.aphis.usda.gov/oa/ccanker/ . [source] Two similar enhanced root-colonizing Pseudomonas strains differ largely in their colonization strategies of avocado roots and Rosellinia necatrix hyphaeENVIRONMENTAL MICROBIOLOGY, Issue 12 2008Clara Pliego Summary Pseudomonas alcaligenes AVO73 and Pseudomonas pseudoalcaligenes AVO110 were selected previously as efficient avocado root tip colonizers, displaying in vitro antagonism towards Rosellinia necatrix, causal agent of avocado white root rot. Despite the higher number of antagonistic properties shown in vitro by AVO73, only AVO110 demonstrated significant protection against avocado white root rot. As both strains are enhanced root colonizers, and as colonization is crucial for the most likely biocontrol mechanisms used by these strains, namely production of non-antibiotic antifungal compounds and competition for nutrients and niches, we decided to compare the interactions of the bacterial strains with avocado roots as well as with R. necatrix hyphae. The results indicate that strain AVO110 is superior in biocontrol trait swimming motility and establishes on the root tip of avocado plants faster than AVO73. Visualization studies, using Gfp-labelled derivatives of these strains, showed that AVO110, in contrast to AVO73, colonizes intercellular crevices between neighbouring plant root epidermal cells, a microhabitat of enhanced exudation. Moreover, AVO110, but not AVO73, also colonizes root wounds, described to be preferential penetration sites for R. necatrix infection. This result strongly suggests that AVO110 meets, and can attack, the pathogen on the root. Finally, when co-inoculated with the pathogen, AVO110 utilizes hyphal exudates more efficiently for proliferation than AVO73 does, and colonizes the hyphae more abundantly than AVO73. We conclude that the differences between the strains in colonization levels and strategies are likely to contribute to, and even can explain, the difference in disease-controlling abilities between the strains. This is the first report that shows that two similar bacterial strains, selected by their ability to colonize avocado root, use strongly different root colonization strategies and suggests that in addition to the total bacterial root colonization level, the sites occupied on the root are important for biocontrol. [source] A field validation of two sediment-amphipod toxicity testsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2002Steven P. Perraro Abstract A field validation study of two sediment-amphipod toxicity tests was conducted using sediment samples collected subtidally in the vicinity of a polycyclic aromatic hydrocarbon (PAH)-contaminated Superfund site in Elliott Bay (WA, USA). Sediment samples were collected at 30 stations with a 0.1 m2 grab from which subsamples were taken for sediment toxicity testing and geochemical and macrofaunal analyses. Standard 10-d sediment-amphipod toxicity tests were conducted with Rhepoxynius abronius and Leptocheirus plumulosus. Sediments were analyzed for 33 PAHs, pentachlorophenol, polychlorinated biphenyls, acid-volatile sulfide, simultaneously extracted metals (Cd, Cu, Zn, Pb, Ni), total organic carbon, and grain size. Sediment temperature, oxygen-reduction potential, water depth, and interstitial water salinity were also measured. Polycyclic aromatic hydrocarbons, quantified as total PAH toxic units (TUPAH), were confirmed to be an important common causal agent of the changes in the two toxicity test (% survival R. abronius, % survival L. plumulosus) and five macrofaunal community (number of species, S; numerical abundance, A; total biomass, B; Swartz's dominance index, SDI; Brillouin's index, H) endpoints. Two other macrofaunal community metrics (the complement of Simpson's index, 1 , SI, and McIntosh's index, MI) were less sensitive to TUPAH than the two toxicity test endpoints. The sensitivities of R. abronius and L. plumulosus to TUPAH were statistically indistinguishable. Field validations were conducted by testing the association between or among each toxicity test endpoint, each of seven macrofaunal community metrics (S, A, B, SDI, H, 1 , SI, MI), and TUPAH by (1) Spearman's coefficient of rank correlation, (2) Kendall's coefficient of concordance, (3) G tests of independence, and (4) regression analysis. Some field validations based on multivariable tests of association (e.g., points 2 and 3) among toxicity test, field, and stressor endpoints produced false positive results. Both toxicity test endpoints were validated as indicators of changes in S, A, SDI, and H by all the methods tested. The resolution power of the relationships between the laboratory toxicity test and macrofaunal field endpoints was low (, three classes) but sufficient to discriminate ecologically important effects. We conclude that standard sediment-amphipod toxicity tests are ecologically relevant and that, under the proper conditions, their results can be used for lab-to-field extrapolation. [source] Identification and characterization of Pepino mosaic potexvirus in tomatoEPPO BULLETIN, Issue 3 2002R. A. A. Van Der Vlugt At the beginning of 1999, a new virus disease occurred in protected tomato crops in The Netherlands. Initial diagnostic tests revealed the presence of a potexvirus but serological tests ruled out the presence of Potato X potexvirus (PVX). Tests for other potexviruses reported from solanaceous crops provisionally identified the virus as Pepino mosaic potexvirus (PepMV). The virus was purified, and an antiserum was produced, which showed strong reactions with both the type isolate of PepMV from pepino and two other isolates from tomato. Host range and symptomatology of the pepino and tomato isolates of PepMV revealed clear differences from PVX. However, differences were also observed between the pepino and tomato isolates of PepMV. Sequence alignment of DNA fragments of 584 bp derived from the RNA polymerase cistron showed almost 95% identity with the pepino isolate, whereas the identity with PVX appeared to be < 60%. Together, these results identified PepMV as the causal agent of the new virus disease in tomato. Based on the differences from the type isolate from pepino (Solanum muricatum), the isolates from tomato should be considered as a distinct strain of PepMV for which the name tomato strain is proposed. [source] CAN INTRASPECIFIC COMPETITION DRIVE DISRUPTIVE SELECTION?EVOLUTION, Issue 3 2004AN EXPERIMENTAL TEST IN NATURAL POPULATIONS OF STICKLEBACKS Abstract Theory suggests that frequency-dependent resource competition will disproportionately impact the most common phenotypes in a population. The resulting disruptive selection forms the driving force behind evolutionary models of niche diversification, character release, ecological sexual dimorphism, resource polymorphism, and sympatric speciation. However, there is little empirical support for the idea that intraspecific competition generates disruptive selection. This paper presents a test of this theory, using natural populations of the three-spine stickleback, Gasterosteus aculeatus. Sticklebacks exhibit substantial individual specialization associated with phenotypic variation and so are likely to experience frequency-dependent competition and hence disruptive selection. Using body size and relative gonad mass as indirect measures of potential fecundity and hence fitness, I show that an important aspect of trophic morphology, gill raker length, is subject to disruptive selection in one of two natural lake populations. To test whether this apparent disruptive selection could have been caused by competition, I manipulated population densities in pairs of large enclosures in each of five lakes. In each lake I removed fish from one enclosure and added them to the other to create paired low- and high-population-density treatments with natural phenotype distributions. Again using indirect measures of fitness, disruptive selection was consistently stronger in high-density than low-density enclosures. These results support long-standing theoretical arguments that intraspecific competition drives disruptive selection and thus may be an important causal agent in the evolution of ecological variation. [source] Structural studies of the capsular polysaccharide and lipopolysaccharide O-antigen of Aeromonas salmonicida strain 80204-1 produced under in vitro and in vivo growth conditionsFEBS JOURNAL, Issue 22 2004Zhan Wang Aeromonas salmonicida is a pathogenic aquatic bacterium and the causal agent of furunculosis in salmon. In the course of this study, it was found that when grown in vitro on tryptic soy agar, A. salmonicida strain 80204-1 produced a capsular polysaccharide with the identical structure to that of the lipopolysaccharide O-chain polysaccharide. A combination of 1D and 2D NMR methods, including a series of 1D analogues of 3D experiments, together with capillary electrophoresis-electrospray MS (CE-ES-MS), compositional and methylation analyses and specific modifications was used to determine the structure of these polysaccharides. Both polymers were shown to be composed of linear trisaccharide repeating units consisting of 2-acetamido-2-deoxy- d -galacturonic acid (GalNAcA), 3-[(N -acetyl-L-alanyl)amido]-3,6-dideoxy- d -glucose{3-[(N -acetyl- l -alanyl)amido]-3-deoxy- d -quinovose, Qui3NAlaNAc} and 2-acetamido-2,6-dideoxy- d -glucose (2-acetamido-2-deoxy- d -quinovose, QuiNAc) and having the following structure: [,3)- , - d -GalpNAcA-(1,3)- , - d -QuipNAc-(1,4)- , - d -Quip3NAlaNAc-(1-]n, where GalNAcA is partly presented as an amide and AlaNAc represents N -acetyl- l -alanyl group. CE-ES-MS analysis of CPS and O-chain polysaccharide confirmed that 40% of GalNAcA was present in the amide form. Direct CE-ES-MS/MS analysis of in vivo cultured cells confirmed the formation of a novel polysaccharide, a structure also formed in vitro, which was previously undetectable in bacterial cells grown within implants in fish, and in which GalNAcA was fully amidated. [source] Subcellular localization of proteins labeled with GFP in Xanthomonas citri ssp. citri: targeting the division septumFEMS MICROBIOLOGY LETTERS, Issue 1 2010Paula M.M. Martins Abstract Xanthomonas citri ssp. citri (Xac) is the causal agent of citrus canker, an economically important disease that affects citrus worldwide. To initiate the characterization of essential biological processes of Xac, we constructed integrative plasmids for the ectopic expression of green fluorescent protein (GFP)-labeled proteins within this bacterium. Here, we show that the disruption of the ,-amylase gene (amy), the site of plasmid integration into the bacterial chromosome, does not alter its pathogenesis while abolishing completely the ability of Xac to degrade starch. Furthermore, our GFP expression system was used to characterize ORF XAC3408, a hypothetical protein encoded by Xac that shares significant homology to the FtsZ-stabilizing factor ZapA from Bacillus subtilis (ZapABsu). GFP-XAC3408 expressed in Xac exhibited a septal localization pattern typical of GFP-ZapABsu, which indicates that XAC3408 is the Xac orthologue of the cell division protein ZapABsu. The results demonstrate the potential of GFP labeling for protein functional characterizations in Xac, and, in addition, the Xac mutant strain labeled at the septum constitutes a biological model for the exploration of antibacterial compounds able to inhibit cell division in this plant pathogen. [source] Xanthomonas albilineans HtpG is required for biosynthesis of the antibiotic and phytotoxin albicidinFEMS MICROBIOLOGY LETTERS, Issue 1 2005Eric Vivien Abstract Xanthomonas albilineans, the causal agent of leaf scald disease of sugarcane, produces a highly potent polyketide-peptide antibiotic and phytotoxin called albicidin. Previous studies established the involvement of a large cluster of genes in the biosynthesis of this toxin. We report here the sub-cloning and sequencing of an additional gene outside of the main cluster and essential for albicidin biosynthesis. This gene encodes a 634-amino-acid protein that shows high identity with the Escherichia coli heat shock protein HtpG. Complementation studies of X. albilineans Tox, mutants confirmed the requirement of htpG for albicidin biosynthesis and revealed functional interchangeability between E. coli and X. albilineans htpG genes. HtpG was co-localised with albicidin in the cellular membrane, i.e., the cellular fraction where the toxin is most probably biosynthesised. Here we show the requirement of an HtpG protein for the biosynthesis of a polyketide-peptide antibiotic. [source] Molecular mechanisms of pathogenicity: how do pathogenic microorganisms develop cross-kingdom host jumps?FEMS MICROBIOLOGY REVIEWS, Issue 3 2007Peter Van Baarlen Abstract It is common knowledge that pathogenic viruses can change hosts, with avian influenza, the HIV, and the causal agent of variant Creutzfeldt,Jacob encephalitis as well-known examples. Less well known, however, is that host jumps also occur with more complex pathogenic microorganisms such as bacteria and fungi. In extreme cases, these host jumps even cross kingdom of life barriers. A number of requirements need to be met to enable a microorganism to cross such kingdom barriers. Potential cross-kingdom pathogenic microorganisms must be able to come into close and frequent contact with potential hosts, and must be able to overcome or evade host defences. Reproduction on, in, or near the new host will ensure the transmission or release of successful genotypes. An unexpectedly high number of cross-kingdom host shifts of bacterial and fungal pathogens are described in the literature. Interestingly, the molecular mechanisms underlying these shifts show commonalities. The evolution of pathogenicity towards novel hosts may be based on traits that were originally developed to ensure survival in the microorganism's original habitat, including former hosts. [source] Vegetative compatibility types of Cryphonectria parasitica, causal agent of chestnut blight, in the Black Sea region of TurkeyFOREST PATHOLOGY, Issue 6 2009S. Akilli Summary Vegetative compatibility types (vc types) of 296 isolates of the chestnut blight fungus, Cryphonectria parasitica, were determined. The isolates had been obtained from 32 localities in 11 provinces in the Black Sea region of Turkey. Five vc types were detected: EU-1, EU-12, EU-14, EU-2 and EU-5. The number of vc types found in single provinces varied between one and five. All of the five vc types were present only in the Kastamonu province. Vc type EU-1 was detected in all the provinces. EU-1 accounted for 90.8% of all isolates. Vc type EU-12 was present in eight provinces and accounted for 6.8% of the isolates, whereas one or two isolates each of EU-14, EU-2 and EU-5 were found in one or two provinces. Isolates possessing the white colony phenotype were considered to be hypovirulent. Hypovirulent isolates of each vc type were found, and they were detected in nine of 11 provinces. [source] The teleomorph of Chalara fraxinea, the causal agent of ash diebackFOREST PATHOLOGY, Issue 5 2009T. Kowalski Summary Ash dieback, caused by the pathogen Chalara fraxinea, is an emerging lethal disease of Fraxinus excelsior, threatening the host species in large parts of Europe. The ascomycete Hymenoscyphus albidus (Helotiaceae, Helotiales) was identified as the teleomorph of C. fraxinea by culturing from ascospores, morphological comparison and nuclear ribosomal internal transcribed spacer (ITS) sequencing. [source] Methods for inoculum production and inoculation of Cistella japonica, the causal agent of resinous stem canker in Chamaecyparis obtusaFOREST PATHOLOGY, Issue 1 2008T. Yamanobe Summary The ascomycete Cistella japonica was cultured on potato dextrose agar medium (PDA) for inoculation into Chamaecyparis obtusa, enabling the development of an inoculation method suitable for use in a breeding programme aimed at selecting for families of Ch. obtusa resistant to resinous stem canker. Using PDA to generate the inoculum resolved the problems encountered with the previously used mixed medium of rice bran and wheat bran, including unfavourable characteristics, uncertain growth of Ci. japonica mycelia, and a complex culturing operation. The inoculation test induced resin exudation similar to that observed in natural infections, and reproduced clonal differences with regard to damage severity. [source] Rubber tree (Hevea brasiliensis) trunk phloem necrosis: aetiological investigations failed to confirm any biotic causal agentFOREST PATHOLOGY, Issue 1 2007F. Pellegrin Summary Trunk phloem necrosis (TPN) is currently a main constraint in rubber (Hevea brasiliensis) plantations. The apparent spread of the disease, from tree to tree along the planting line, strongly supported the implication of a pathogen that could be transmitted mechanically via the tapping knife. In order to detect a causal agent of the disease, studies focusing on characterization of the known mechanically transmitted pathogens (e.g. viroids, cryptic viruses or phytoplasma) were initiated. RNA strands of low molecular weight (200,400 and >500 bp) displaying structural similarities with viroids and viral dsRNAs were observed in various tested samples. However, attempts to show the potential role of these RNA molecules in the spread of the disease failed. First of all, there was no significant or reproducible correlation between the health status of the rubber trees sampled and these RNA molecules. Moreover, no sequence homology with known pathogens could be found when randomly amplified cDNA fragments isolated from trees presenting the disease symptoms were sequenced. In conclusion, the aetiological investigations, in order to show the presence of a pathogen responsible of the TPN disease, were non-conclusive, which tends to disprove the hypothesis of a biotic causal agent. [source] Dothistroma rhabdoclinis sp. nov. associated with Rhabdocline pseudotsugae on Douglas firFOREST PATHOLOGY, Issue 4 2000H. Butin Dothistroma rhabdoclinis, a new coelomycete on needles of Pseudotsuga menziesii is described. The fungus is associated, possibly as a hyperparasite, with Rhabdocline pseudotsugae, the causal agent of Rhabdocline needle-cast of Douglas fir. The presence of D. rhabdoclinis interferes with and sometimes completely inhibits the production of ascomata of R. pseudotsugae. The cultural and morphological characters of the new fungus are compared with the only other known member of the genus, Dothistroma septospora. [source] Isolation and Characterization of a Porin-Like Outer Membrane Protein from Xanthomonas campestris pv. campestrisIUBMB LIFE, Issue 1 2002Lingyun Wang Abstract Xanthomonas campestris pv. campestris, a plant-associated pathogenic bacterium, is the causal agent of foliar spots and blights in crucifers. The major outer membrane protein, Omp37, of 37 kDa, has been identified, purified to homogeneity, and its characterization has also been carried out. Native Omp37 behaved as a trimer, as revealed by gel filtration and SDS-PAGE. FTIR measurements revealed a high ,-structure content. The pore-forming ability of the purified Omp37 was studied by the liposome swelling assay. Omp37, to our knowledge, is the first porin that has been isolated from Xanthomonas . This study clearly demonstrates that Omp37 is related to the family of trimeric bacterial porins. [source] Comparative genomics-guided loop-mediated isothermal amplification for characterization of Pseudomonas syringae pv. phaseolicolaJOURNAL OF APPLIED MICROBIOLOGY, Issue 3 2009X. Li Abstract Aims:, To design and evaluate a loop-mediated isothermal amplification (LAMP) protocol by combining comparative genomics and bioinformatics for characterization of Pseudomonas syringae pv. phaseolicola (PSP), the causal agent of halo blight disease of bean (Phaseolus vulgaris L.). Methods and Results:, Genomic sequences of Pseudomonas syringae pathovars, P. fluorescens and P. aeruginosa were analysed using multiple sequence alignment. A pathovar-specific region encoding pathogenicity-related secondary metabolites in the PSP genome was targeted for developing a LAMP assay. The final assay targeted a polyketide synthase gene, and readily differentiated PSP strains from other Pseudomonas syringae pathovars and other Pseudomonas species, as well as other plant pathogenic bacteria, e.g. species of Pectobacterium, Erwinia and Pantoea. Conclusion:, A LAMP assay has been developed for rapid and specific characterization and identification of PSP from other pathovars of P. syringae and other plant-associated bacteria. Significance and Impact of the Study:, This paper describes an approach combining a bioinformatic data mining strategy and comparative genomics with the LAMP technology for characterization and identification of a plant pathogenic bacterium. The LAMP assay could serve as a rapid protocol for microbial identification and detection with significant applications in agriculture and environmental sciences. [source] Serological detection and immunogold localization of cross-reactive antigens shared by Camellia sinensis and Exobasidium vexansJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2007B.N. Chakraborty Abstract Aims:, Pathogenicity of Exobasidium vexans, causal agent of blister blight of tea, was studied in 30 commercially cultivated tea varieties by analysing the antigenic patterns of host and pathogen using immunological techniques. Methods and Results:, Whole plant inoculation of tea varieties with E. vexans showed that T-78 and T-17/1/54 were most susceptible and most resistant respectively. Antigen preparations from tea varieties, pathogen, nonpathogen (Fusarium oxysporum) and of nonhosts (Glycine max, Leucaena leucocephala and Oryza sativa) were compared by indirect enzyme-linked immunosorbent assay and dot-immunobinding assay using polyclonal antibodies raised against the pathogen, nonpathogen, susceptible and resistant tea varieties. Cross-reactive antigens (CRA) were found among susceptible varieties and E. vexans isolates but not in resistant varieties, nonhosts or nonpathogen. Indirect staining of antibodies using fluorescein isothiocyanate indicated CRA were concentrated mainly around epidermal and mesophyll cells in compatible host (T-78). This was substantiated by ultrastructural studies using gold-labelled antibodies through transmission electron microscopy which showed specific localization in the chloroplasts and host cytoplasm. Conclusion:, Pathogenicity of E. vexans to different tea varieties is therefore related to the level of antigenic similarity between host and pathogen. Significance and Impact of the Study:, Immunological methods proved to be valuable in screening commercially cultivated tea varieties against E. vexans. [source] Response surface methodology study of the combined effects of temperature, pH, and aw on the growth rate of Trichoderma asperellumJOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2007B.A.D. Begoude Abstract Aims:, To evaluate the influence of environmental parameters (water activity aw, temperature, and pH) on the radial growth rate of Trichoderma asperellum (strains PR10, PR11, PR12, and 659-7), an antagonist of Phytophthora megakarya, the causal agent of cocoa black pod disease. Methods and Results:, The radial growth of four strains of T. asperellum was monitored for 30 days on modified PDA medium. Six levels of aw (0·995, 0·980, 0·960, 0·930, 0·910, and 0·880) were combined with three values of pH (4·5, 6·5, and 8·5) and three incubation temperatures (20, 25, and 30°C). Whatever the strain, mycelial growth rate was optimal at aw between 0·995 and 0·980, independently of the temperature and pH. Each strain appeared to be very sensitive to aw reduction. In addition, all four strains were able to grow at all temperatures and pH values (4·5,8·5) tested, highest growth rate being observed at 30°C and at pH 4·5,6·5. The use of response surface methodology to model the combined effects of aw, temperature, and pH on the radial growth rate of the T. asperellum strains confirmed the observed results. In our model, growth of the T. asperellum strains showed a greater dependence on aw than on temperature or pH under in vitro conditions. Conclusion:,aw is a crucial environmental factor. Low aw can prevent growth of T. asperellum strains under some conditions. The observed and predicted radial growth rate of strain PR11 showed its greater capacity to support low aw (0·93) as compared with other tested strains at 20°C. This is in agreement with its better protective level when applied in medium-scale trials on cocoa plantations. Significance and Impact of the Study:, This study should contribute towards improving the biocontrol efficacy of T. asperellum strains used against P. megakarya. Integrated into a broader study of the impact of environmental factors on the biocontrol agent,pathogen system, this work should help to build a more rational control strategy, possibly involving the use of a compatible adjuvant protecting T. asperellum against desiccation. [source] New media for the semiselective isolation and enumeration of Xanthomonas campestris pv. mangiferaeindicae, the causal agent of mango bacterial black spotJOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2005O. Pruvost Abstract Aims:, Mango bacterial black spot, caused by Xanthomonas campestris pv. mangiferaeindicae, is a potentially severe disease in several tropical and subtropical areas. Data describing the life cycle of the pathogen are needed for improving integrated pest management strategies. Because of the important bacterial microflora associated with mango leaves, isolation of the pathogen is often difficult using nonselective agar media. Methods and Results:, A previously developed medium, BVGA, failed to inhibit several Gram-negative saprophytic bacteria, especially those belonging to Enterobacteriaceae. Two new semiselective media were developed. The selectivity of KC and NCTM3 media was achieved using cephalexin 40 mg l,1, kasugamycin 20 mg l,1 and neomycin 1 mg l,1, cephalexin 100 mg l,1, trimethoprime 5 mg l,1, pivmecillinam 100 mg l,1 respectively. Plating efficiencies ranged from 76 to 104% and from 78 to 132% for KC and NCTM3 respectively. Conclusions:, The new media allowed the growth of X. campestris pv. mangiferaeindicae whatever its country of isolation. The pathogen was repeatedly isolated with these media from asymptomatic leaves sampled in growth chamber experiments. Significance and Impact of the Study:, This work provides a description of new semiselective media, which should be valuable tools to study the ecology and epidemiology of X. campestris pv. mangiferaeindicae. [source] Relevance of incubation temperature for Vibrio salmonicida vaccine productionJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2002D.J. Colquhoun Aims:,To investigate the relationships between water temperature, bacterial growth, virulence and antigen expression in Vibrio salmonicida, the causal agent of cold water vibriosis in Atlantic salmon (Salmo salar L.). Methods and Results:,The significance of sea temperature was investigated using historical clinical and oceanographic data. An upper threshold for disease of approx. 10°C was established. The effects of culture temperature and media type on bacterial growth were studied on solid and in liquid media. The highest rates of cell division were identified at 15°C on solid media and 10°C in liquid media. Outer membrane protein (OMP) expression and serological response in Atlantic salmon were studied using sodium dodecyl sulphate-polyacrylamide gel electrophoresis, Western blotting and enzyme-linked immunosorbent assay. A novel 76-kDa OMP produced in unshaken cultures at 10°C was not found to stimulate a specific humoral response. Conclusions:,Diagnostic agar plate-based incubation of suspected V. salmonicida should be carried out at 15°C. High yield broth cultures for vaccine production should be incubated at 10°C or lower. Significance and Impact of the Study:,This study is, to the best of our knowledge, the first to identify different optimal temperatures in a bacterial species cultured on physically different types of media. The evidence presented suggests that V. salmonicida and possibly other bacteria destined for vaccine use in poikilothermic organisms should be cultured at temperatures consistent with that at which disease occurs. [source] First description of non-motile Yersinia ruckeri serovar I strains causing disease in rainbow trout, Oncorhynchus mykiss (Walbaum), cultured in SpainJOURNAL OF FISH DISEASES, Issue 6 2006B Fouz Abstract Yersinia ruckeri, the causal agent of enteric redmouth (ERM) disease, was isolated from epizootics that occurred in different Spanish rainbow trout, Oncorhynchus mykiss (Walbaum), farms in which vaccination against ERM had been performed. In all episodes, the most pronounced clinical signs exhibited by affected fish were severe haemorrhages in the mouth, eyes and around the vent. The isolates were identified as Y. ruckeri serovar I by 16S rRNA sequencing together with serological tests. They lacked motility and lipase activity and thus belonged to biotype 2, and were highly virulent for juvenile rainbow trout, both by intraperitoneal injection (from 3.1 × 102 to 6.3 × 103 cfu per fish) and bath challenge (5.1,7.3 × 106 cfu mL,1). This is the first description of Y. ruckeri serovar I biotype 2 causing disease in cultured trout in Spain vaccinated with commercial ERM vaccines. The occurrence of this emergent pathogen in Spanish continental aquaculture from its first isolation in 2001 to date is also documented. [source] Identification of Three Strains of a Virus Associated with Cassava Plants Affected by Frogskin DiseaseJOURNAL OF PHYTOPATHOLOGY, Issue 11-12 2008L. A. Calvert Abstract Cassava Frogskin Disease (CFSD) can cause severe damage to cassava roots and is one of the most important diseases of cassava in Latin America. The principal objective of this study was to identify the causal agent of CFSD. Electron microscopy, viral purifications, double-stranded RNA (dsRNA) analysis, cloning, sequencing, rtPCR and hybridizations were carried out to characterize and associate a novel virus with the disease. Virus-like particles of 70 and 45 nm in diameter were found in affected cassava plants and partially purified preparations respectively. Nine species of dsRNA were associated with this disease and cDNA clones to six genomic segments were synthesized from the purified dsRNAs. The putative proteins predicted from the sequence of the cassava virus cDNA clones have similarity with the P1, P2, P3, P4, P5 and P10 proteins of Rice ragged stunt virus (RRSV). Phylogenic analysis confirmed that this virus is a member of the family Reoviridae and is most closed related to RRSV. Hybridization analyses of dsRNA identified S1, S2, S3, S4, S5 and S10 genomic segments in the CFSD-affected plants, but not in healthy controls. Additionally, 26 isolates were compared using a portion of the putative polymerase gene. The virus was detected in all 26 isolates, and they were classified into three distinct races. The association of this virus with CFSD was strengthened by the detection of this virus in diseased plants collected from different locations throughout Colombia. [source] Use of RAPD and ISSR Markers in Detection of Genetic Variation and Population Structure among Fusarium oxysporum f. sp. ciceris Isolates on Chickpea in TurkeyJOURNAL OF PHYTOPATHOLOGY, Issue 3 2008H. Bayraktar Abstract Genetic variation among the isolates of Fusarium oxysporum f. sp. ciceris, the causal agent of chickpea wilt worldwide, was analysed using pathogenicity tests and molecular markers , random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) polymorphism. Hundred and eight isolates were obtained from diseased chickpea plants in 13 different provinces of Turkey, out of which 74 isolates were assessed using 30 arbitrary decamer primers and 20 ISSR primers. Unweighted pair-grouped method by arithmetic average cluster analysis of RAPD, ISSR and RAPD + ISSR datasets provided a substantially similar discrimination among Turkish isolates and divided into three major groups. Group 1, 2 and 3 consisted of 41, 18 and 15 isolates, respectively. These methods revealed a considerable genetic variation among Turkish isolates, but no correlation with regard to the clustering of isolates from different geographic regions. Analysis of molecular variance confirmed that most genetic variability resulted from the differences among isolates within regions. Our results also indicated that the low-genetic differentiation (FST) and high gene flow (Nm) among populations had a significant effect on the emergence and evolutionary development of F. oxysporum f. sp. ciceris. This is the first report on genetic diversity and population structure of F. oxysporum isolates on chickpea in Turkey. [source] Measurement of Horizontal and Vertical Movement of Ralstonia solanacearum in SoilJOURNAL OF PHYTOPATHOLOGY, Issue 10 2006M. Satou Abstract Two model systems were constructed to measure horizontal and vertical movement of bacteria in soil. These systems were applied to measuring movement of Ralstonia solanacearum (race 1, biovar 3), a causal agent of bacterial wilt of tomato, in andosol and sand at 28°C. The first system was used to measure horizontal movement of the bacteria in soil packed in a narrow horizontal frame. Suspension of the pathogen was applied to soil at one end of the frame, and bacterial number per gram of soil was measured over distance from the inoculation point after 4 days. Horizontal movement of R. solanacearum in supersaturated soil, but without flow, was possibly due to diffusion and the front advanced at 2.2 cm/day in andosol, and at 8.1 cm/day in sand. Using the same experimental system, but applying water inflow to one end of the frame only, the bacterium was detected at the front of water in andosol and sand. The front of the distribution advanced at 20.4 cm/h in andosol and 66.3 cm/h in sand. In the second experimental system, a cylinder of soil packed in a short tube was soaked with water, and soil at the top of the tube was inoculated with bacterial suspension. Immediately, soil cylinders were turned upward, and the bacterial number per gram of soil was measured along vertical distance from the inoculation point after 7 days. Using the system with andosol, the capillary water front rose to 32.5 cm over 7 days after inoculation, and R. solanacearum reached to 18.8 cm height. In sand, capillary water rose to 20.0 cm and the bacteria reached to 16.3 cm height. [source] Two Genetically Distinct Populations of Colletotrichum gloeosporioides Penz.JOURNAL OF PHYTOPATHOLOGY, Issue 3 2005Causing Anthracnose Disease of Yam (Dioscorea spp.) Abstract Variation within Colletotrichum gloeosporioides, the causal agent of yam anthracnose disease, is still poorly defined and this hinders breeding for resistance. Two morphotypes of C. gloeosporioides, designated slow-growing grey (SGG) and fast-growing salmon (FGS), are associated with anthracnose disease of yam in Nigeria. The morphotypes are distinguishable based on colony and conidial morphology, growth rate, virulence, as well as vegetative compatibility, but molecular differentiation of SGG and FGS strains is needed to facilitate epidemiological studies. Denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)-amplified small subunit (18S) rDNA fragments, and microsatellite-primed PCR (MP-PCR) genomic fingerprinting were employed to provide a basis for molecular differentiation of the morphotypes. DGGE analysis revealed patterns that clearly differentiated isolates of the aggressive defoliating SGG from the moderately virulent non-defoliating FGS strains. Genetic analysis based on 52 MP-PCR markers revealed highly significant differentiation between the SGG and FGS populations on yam (GST = 0.22; Nei's genetic identity = 0.85; , = 0.28, P < 0.001), indicating that the SGG and FGS morphotypes represent genetically differentiated populations. The results of the molecular typing using DGGE and MP-PCR analyses were consistent with the disease phenotype caused by the two morphotypes. Consequently, these molecular techniques might be used, at least partly, to replace time-consuming virulence studies on yam. [source] Yield Responses of Barley to Leaf Stripe (Pyrenophora graminea) under Experimental Conditions in Southern SyriaJOURNAL OF PHYTOPATHOLOGY, Issue 8-9 2004M. I. E. Arabi Abstract The seed-borne pathogen, Pyrenophora graminea is the causal agent of barley leaf stripe disease. Field trials were undertaken to investigate the impact of leaf stripe on barley yield in two growing seasons in Southern Syria, by comparing plots with and without artificial inoculation. Ten barley cultivars originating from widely dispersed areas were used. The overall response to leaf stripe differed with the differences in susceptibility levels of the cultivars. Grain yield, the number of tillers, kernel weight and plant biomass decreased as disease severity increased. Diseased plants had fewer tillers, and as a consequence a reduced grain yield per plant. High yield losses resulted from leaf stripe in susceptible cultivars in Arrivate, Furat 1, WI2291 and Arabi Abiad with 44%, 50%, 73% and 92%, respectively. The cultivar Banteng had the best level of resistance to the disease, and is a candidate donor for resistance in future breeding programmes. As leaf stripe can dramatically reduce barley yields under favourable conditions, the disease should be considered by crop improvement programmes in Mediterranean and similar environments. [source] | |||||||||||||||||||||||||||||||||||||