Plant Pathogen Research Papers - Academia.edu (original) (raw)

Conventional methods to detect and assess the viability of plant pathogenic bacteria are usually based on plating assays or serological techniques. Plating assays provide information about the number of viable cells, expressed as... more

Conventional methods to detect and assess the viability of plant pathogenic bacteria are usually based on plating assays or serological techniques. Plating assays provide information about the number of viable cells, expressed as colony-forming units, but are time-consuming and laborious. Serological methods, such as the enzyme-linked immunosorbent assay (ELISA) and immunofluorescence microscopy (IF), can be performed in a shorter timespan than most plating assays, but they do not discriminate between live and dead cells. Flow cytometry (FCM) in combination with fluorescent probe technology is a rapid, sensitive, and quantitative technique to detect microorganisms and assess their viability. Quantitative information on the presence and viability of plant pathogenic microorganisms is valuable for risk assessment regarding disease transmission and disease development. FCM has been applied successfully in the fields of food microbiology, veterinary science, and medical research to dete...

An overview is given of rapid methods for the detection of plant-related organisms in plant material, soil, compost, water, etc. Protein-based detection assays such as isozyme analysis, ELISA, immunofluorescence colony-staining and future... more

An overview is given of rapid methods for the detection of plant-related organisms in plant material, soil, compost, water, etc. Protein-based detection assays such as isozyme analysis, ELISA, immunofluorescence colony-staining and future applications of immunological tests are described as well as nucleic acid-based tests. Examples of RNA amplification tests, such as RT-PCR, NASBA and AmpliDet RNA are given, and numerous DNA-based tests using PCR, either with or without the use of probes, are illustrated. Most tests described are directed towards the detection of plant pathogens such as viruses, bacteria, fungi and nematodes. A test for the detection of mRNA of a mycotoxin producing fungus is also shown in this review. This illustrates that the technology of many of the tests described can equally well be used for the development of assays to detect harmful organisms in food, feed, water, air or any other environment in the agrofood production chain. The latest development in detection are in the field of multiplex detection using microarrays is presented as the pUMA technology.

We have previously reported the identification of a small, basic and cysteine-rich antifungal peptide (AcAFP) secreted by Aspergillus clavatus and shown its ability to prevent growth of various human-and plant-pathogenic filamentous... more

We have previously reported the identification of a small, basic and cysteine-rich antifungal peptide (AcAFP) secreted by Aspergillus clavatus and shown its ability to prevent growth of various human-and plant-pathogenic filamentous fungi. In this study, we sought to determine the physiological/microbiological requirements to enhance the AcAFP production and the conditions influencing its stability. The maximum of AcAFP production was obtained when A. clavatus was grown on 2% glycerol as sole carbon source and 100 mM NaCl. The AcAFP expression was shown to be influenced by pH, being suppressed under acidic (pH 5) and strongly induced under alkaline conditions. The activity of the purified AcAFP was not affected by temperature; it loosed approximately 20% of its activity after 3 h at 100°C and was efficient through a large pH range (pH 5-12) with an optimum at pH 8. AcAFP activity decreased at high ionic strength and in the presence of 10 mM of divalent cations (Mn 2+ , Fe 2+ and Ca 2+ ).

Hypersensitive response and pathogenicity (hrp) genes control the ability of major groups of plant pathogenic bacteria to elicit the hypersensitive response (HR) in resistant plants and to cause disease in susceptible plants. A number of... more

Hypersensitive response and pathogenicity (hrp) genes control the ability of major groups of plant pathogenic bacteria to elicit the hypersensitive response (HR) in resistant plants and to cause disease in susceptible plants. A number of Hrp proteins share significant similarities with components of the type III secretion apparatus and f lagellar assembly apparatus in animal pathogenic bacteria. Here we report that Pseudomonas syringae pv. tomato strain DC3000 (race 0) produces a filamentous surface appendage (Hrp pilus) of 6-8 nm in diameter in a solid minimal medium that induces hrp genes. Formation of the Hrp pilus is dependent on at least two hrp genes, hrpS and hrpH (recently renamed hrcC), which are involved in gene regulation and protein secretion, respectively. Our finding of the Hrp pilus, together with recent reports of Salmonella typhimurium surface appendages that are involved in bacterial invasion into the animal cell and of the Agrobacterium tumefaciens virB-dependent pilus that is involved in the transfer of T-DNA into plant cells, suggests that surface appendage formation is a common feature of animal and plant pathogenic bacteria in the infection of eukaryotic cells. Furthermore, we have identified HrpA as a major structural protein of the Hrp pilus. Finally, we show that a nonpolar hrpA mutant of P. syringae pv. tomato DC3000 is unable to form the Hrp pilus or to cause either an HR or disease in plants. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked ''advertisement'' in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Plant pathogens emerge in agro-ecosystems following different evolutionary mechanisms over different time scales. Previous analyses based on sequence variation at six nuclear loci indicated that Mycosphaerella graminicola diverged from an... more

Plant pathogens emerge in agro-ecosystems following different evolutionary mechanisms over different time scales. Previous analyses based on sequence variation at six nuclear loci indicated that Mycosphaerella graminicola diverged from an ancestral population adapted to wild grasses during the process of wheat domestication approximately 10,500 years ago. We tested this hypothesis by conducting coalescence analyses based on four mitochondrial loci using 143 isolates that included four closely related pathogen species originating from four continents. Pathogen isolates from bread and durum wheat were included to evaluate the emergence of specificity towards these hosts in M. graminicola. Although mitochondrial and nuclear genomes differed greatly in degree of genetic variability, their coalescence was remarkably congruent, supporting the proposed origin of M. graminicola through host tracking. The coalescence analysis was unable to trace M. graminicola host specificity through recent evolutionary time, indicating that the specificity towards durum or bread wheat emerged following the domestication of the pathogen on wheat.

Erwinia chrysanthemi causes soft-rot diseases of many plants by secreting a battery of enzymes which degrade the plant cell walls. We initiated a proteomic analysis to create a reference map of the E. chrysanthemi secretome. Extracellular... more

Erwinia chrysanthemi causes soft-rot diseases of many plants by secreting a battery of enzymes which degrade the plant cell walls. We initiated a proteomic analysis to create a reference map of the E. chrysanthemi secretome. Extracellular proteins were isolated from E. chrysanthemi culture supernatants and resolved by two-dimensional electrophoresis. By analysis of mutants, Western blotting, and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) 55 spots representing 25 unique proteins were identified. In uninduced conditions, we identified spots corresponding to the cellulase Cel5, the proteases PrtA, PrtB, and PrtC, the flagellin FliC, and some intracellular proteins whose presence probably resulted from spontaneous cell lysis. We identified another secreted protein, AvrL, homologous to an avirulence protein of Xanthomonas campestris. After culture in conditions inducing pectinase production, i.e., in the presence of galacturonate and plant extract, we identified spots corresponding to the endopectate lyases PelA, PelB, PelC, PelD, PelE, PelI, PelL, and PelZ, the pectin acetylesterases PaeX and PaeY, the pectin methylesterase PemA, and the polygalacturonase PehX. In the presence of other inducing compounds, we detected the rhamnogalacturonate lyase RhiE and the esterase FaeD. Analysis of mutants, altered for one type of secretion system, was performed to determine the targets of each system. The type I system Prt was necessary for the secretion of three proteases. No proteins secreted by the type III Hrp system could be detected in E. chrysanthemi supernatants. In addition to the already known substrates (eleven pectinases and one cellulase), this analysis revealed that the type II Out system mediates secretion of the esterase FaeD and of the Avr-like protein AvrL.

Soil microbial biomass plays important roles in nutrient cycling, plant-pathogen suppression, decomposition of residues and degradation of pollutants; therefore, it is often regarded as a good indicator of soil quality. We reviewed more... more

Soil microbial biomass plays important roles in nutrient cycling, plant-pathogen suppression, decomposition of residues and degradation of pollutants; therefore, it is often regarded as a good indicator of soil quality. We reviewed more than a hundred studies in which microbial biomass-C (MB-C), microbial quotient (MB-C/TSOC, total soil organic carbon) and metabolic quotient (qCO 2 ) were evaluated with the objective of understanding MB-C responses to various soil-management practices in Brazilian ecosystems. These practices included tillage systems, crop rotations, pastures, organic farming, inputs of industrial residues and urban sewage sludge, applications of agrochemicals and burning. With a metaanalysis of 233 data points, we confirmed the benefits of no-tillage in preserving MB-C and reducing qCO 2 in comparison to conventional tillage. A large number of studies described increases in MB-C and MB-C/TSOC due to permanent organic farming, also benefits from crop rotations particularly with several species involved, whereas application of agrochemicals and burning severely disturbed soil microbial communities. The MB-C decreased in overgrazed pastures, but increased in pastures rotated with wellmanaged crops. Responses of MB-C, MB-C/TSOC and qCO 2 to amendment with organic industrial residues varied with residue type, dose applied and soil texture. In conclusion, MB-C and related parameters were, indeed, useful indicators of soil quality in various Brazilian ecosystems. However, direct relationships between MB-C and nutrient-cycling dynamics, microbial diversity and functionality are still unclear. Further studies are needed to develop strategies to maximize beneficial effects of microbial communities on soil fertility and crop productivity.

Plant pathogen resistance is mediated by a large repertoire of resistance (R) genes, which are often clustered in the genome and show a high degree of genetic variation. Here, we show that anArabidopsis thaliana R-gene cluster is also... more

Plant pathogen resistance is mediated by a large repertoire of resistance (R) genes, which are often clustered in the genome and show a high degree of genetic variation. Here, we show that anArabidopsis thaliana R-gene cluster is also subject to epigenetic variation. We describe a heritable but metastable epigenetic variant bal that overexpresses the R-like geneAt4g16890 from a gene cluster on Chromosome 4. The balvariant and Arabidopsis transgenics overexpressing theAt4g16890 gene are dwarfed and constitutively activate the salicylic acid (SA)-dependent defense response pathway. Overexpression of a related R-like gene also occurs in the ssi1(suppressor of SA insensitivity1) background, suggesting that ssi1 is mechanistically related to bal.

The utility of polymorphism analysis was determined for differentiation of the following subspecies of the Gram-positive plant pathogenic bacterium, Clavibacter michiganensis: C. m. subsp. michiganensis, C. m. subsp. sepedonicus, C. m.... more

The utility of polymorphism analysis was determined for differentiation of the following subspecies of the Gram-positive plant pathogenic bacterium, Clavibacter michiganensis: C. m. subsp. michiganensis, C. m. subsp. sepedonicus, C. m. subsp. insidiosus C. m. subsp. nebraskensis, and C. m. subsp. tessellarius. Specific primers designed for amplification of the housekeeping genes recA, rpoB, and rpoD generated 827-, 1037-, and 862-bp DNA fragments, respectively. PCR products obtained from 40 C. michiganensis strains were analysed using RFLP with four restriction endonucleases, and those PCR products with specific RFLP patterns were sequenced. The genotypes discriminated after PCR–RFLP were specific for each subspecies and also allowed for differentiation of C. m. subsp. michiganensis strains. Sequence analysis of the recA, rpoB, and rpoD gene fragments also distinguished C. michiganensis subspecies and was useful for phylogenetic analysis of all subspecies. For rapid, inexpensive, and effective differentiation of the five subspecies in this research, we recommend the amplification of recA and/or rpoD gene fragments and digestion of the PCR products with the restriction endonuclease FnuDII.

The aspects of the antifungal activity of essential oil of laurel (Laurus nobilis) obtained by means of a supercritical carbon dioxide (SFE-CO 2 ) technique against post harvest spoilage fungi, have been studied in this research work by... more

The aspects of the antifungal activity of essential oil of laurel (Laurus nobilis) obtained by means of a supercritical carbon dioxide (SFE-CO 2 ) technique against post harvest spoilage fungi, have been studied in this research work by tests performed under in vitro and in vivo conditions. The measurement of antifungal activity of the oil, for its potential application as botanical fungicide, is very useful to find alternatives to synthetic fungicides. The present paper reports, for the first time, the results about the antifungal activity of laurel oil, obtained by a semi-industrial process that utilize a SFE-CO 2 technique, against three plant pathogenic fungi. The determination of the main active substances was carried out by gas chromatography analysis: laurel oil was characterized by high content (!10%) of 1.8-cineole, linalool, terpineol acetate, methyl eugenol and a low content (<10%) of linalyl acetate, eugenol, sabinene, b-pinene, a-terpineol. The inhibition of the mycelial growth of Botrytis cinerea, Monilinia laxa and Penicillium digitatum was evaluated in vitro at the concentration range of 200, 400, 600, 800 and 1000 mg/ mL. M. laxa was totally inhibited by application of the oil at the lowest concentration, B. cinerea was completely inhibited at the highest concentration, and a fungistatic action was observed in both cases. P. digitatum was only partially inhibited at all the concentration ranges. The activity of the oil, placed in the form of spray on the fruit skin at the concentration range of 1, 2 and 3 mg/mL, was studied by biological tests. Both curative and protective activities of the oil have been evaluated on peaches, kiwifruits, oranges and lemons artificially inoculated with M. laxa, B. cinerea and P. digitatum, respectively. A very good antifungal activity has been found on kiwifruits and peaches when the oil was placed before the inoculation at a concentration of 3 mg/mL (68 and 91% of decay inhibition respectively). The same activity has been found on peaches when the oil was placed after the infection (76% of decay inhibition). The application of the oil did not caused any phytotoxic effect and kept any fruit flavour, fragrance or taste. This study has demonstrated that the essential oil of L. nobilis extracted by a SFE-CO 2 technique, is one potential and promising antifungal agent which could be used as botanical fungicide in the postharvest protection of peaches and kiwifruits against M. laxa and B. cinerea.

Oomycete Pythiosis Pythium insidiosum a b s t r a c t Oomycetes are unique eukaryotic microorganisms that share a mycelial morphology with fungi. Many oomycetes are pathogenic to plants, and a more limited number are pathogenic to... more

Oomycete Pythiosis Pythium insidiosum a b s t r a c t Oomycetes are unique eukaryotic microorganisms that share a mycelial morphology with fungi. Many oomycetes are pathogenic to plants, and a more limited number are pathogenic to animals. Pythium insidiosum is the only oomycete that is capable of infecting both humans and animals, and causes a life-threatening infectious disease, called "pythiosis". In the majority of pythiosis patients life-long handicaps result from the inevitable radical excision of infected organs, and many die from advanced infection. Better understanding P. insidiosum pathogenesis at molecular levels could lead to new forms of treatment. Genetic and genomic information is lacking for P. insidiosum, so we have undertaken an expressed sequence tag (EST) study, and report on the first dataset of 486 ESTs, assembled into 217 unigenes. Of these, 144 had significant sequence similarity with known genes, including 47 with ribosomal protein homology. Potential virulence factors included genes involved in antioxidation, thermal adaptation, immunomodulation, and iron and sterol binding. Effectors resembling pathogenicity factors of plant-pathogenic oomycetes were also discovered, such as, a CBEL-like protein (possible involvement in host cell adhesion and hemagglutination), a putative RXLR effector (possibly involved in host cell modulation) and elicitin-like (ELL) proteins. Phylogenetic analysis mapped P. insidiosum ELLs to several novel clades of oomycete elicitins (ELIs), and homology modeling predicted that P. insidiosum ELLs should bind sterols. Most of the P. insidiosum ESTs showed homology to sequences in the genome or EST databases of other oomycetes, but one putative gene, with unknown function, was found to be unique to P. insidiosum. The EST dataset reported here represents the first steps in identifying genes of P. insidiosum and beginning transcriptome analysis. This genetic information will facilitate understanding of pathogenic mechanisms of this devastating pathogen.

The bacterial strain E1R-j, isolated as an endophyte from wheat roots, exhibited high antifungal activity to Gaeumannomyces graminis var. tritici (Ggt). Strain E1R-j was identified as Bacillus subtilis based on morphological,... more

The bacterial strain E1R-j, isolated as an endophyte from wheat roots, exhibited high antifungal activity to Gaeumannomyces graminis var. tritici (Ggt). Strain E1R-j was identified as Bacillus subtilis based on morphological, physiological and biochemical methods as well as on 16S rDNA analysis. This strain inhibited mycelium growth in vitro of numerous plant pathogenic fungi, especially of Ggt, Coniothyrium diplodiella, Phomopsis sp. and Sclerotinia sclerotiorum. In greenhouse experiments, soil drenches with cell densities of 10 6 , 10 9 and 10 12 CFU ml À1 E1R-j reduced significantly take-all disease, caused by Ggt, in wheat seedling by 62.6%, 68.6% and 70.7%, respectively, compared to the inoculated control, 4 weeks after sowing. Growth parameters such as lengths and fresh weights of roots and shoots of Ggt-inoculated control plants were significantly lower compared to Ggt-inoculated and E1R-j treated plants. Field experiments in the season 2006/2007, heights of wheat plants in the Ggt inoculated plots were significantly reduced compared to the non inoculated treatments. Yield parameters such as kernels per head and thousand kernel weight (TKW) in inoculated control plants were lower compared to the other treatments. In the experimental year 2007/2008, independent treatments with the bacterial strain E1R-j and the fungicide Triadimefon reduced take-all disease in wheat roots by 55.3% and 61.9%, compared to the inoculated control plants. In this season plant height in inoculated control was significantly lower and also the yield parameters seeds per head and especially TKW were drastically reduced compared to the other treatments. E1R-j treatment alleviated the detrimental effects of take-all on grain yield parameters to a similar extent as Triadimefon application. SEM studies revealed that in the presence of E1R-j, hyphae of Ggt showed leakage, appeared ruptured, swollen and shriveled. Following root drench, strain E1R-j was able to colonize endophytically roots and leaves of wheat seedlings. While the population of the bacterial strain in wheat roots steadily increased from the second to the fourth leaf stage, in the leaf tissue the population of the strain rapidly declined. TEM studies also showed that cells of E1R-j were present in roots of wheat seedlings and effectively retarded infection and colonization of Ggt in root tissue; suppression of Ggt by E1R-j was accompanied by disintegration of hyphal cytoplasm. In addition, in the presence of E1R-j cells in Ggt-infected root tissue morphological defense reactions were triggered such as formation of wall appositions and papillae. The results presented indicate that the endophytic strain E1R-j of B. subtilis meets demands required for biocontrol of take-all.

The main theme of the book is sustainable disease management in a European context. Some of the questions addressed are: How does society benefit from plant pathology research? How can new molecular approaches solve relevant problems in... more

The main theme of the book is sustainable disease management in a European context. Some of the questions addressed are: How does society benefit from plant pathology research? How can new molecular approaches solve relevant problems in disease management? What other fields can we exploit in plant pathology research? What challenges are associated with free trade across the new borders? How can we contribute to solving problems of developing countries? How does plant pathology contribute to food quality and safety? How does globalisation/internationalisation affect teaching and extension in plant pathology?

Colletotrichum musae is an important pathogen causing banana anthracnose. The type material (K) had no conidia or sclerotia, and DNA could not be extracted from a darkened area of the herbarium sample. This sample thus provides few... more

Colletotrichum musae is an important pathogen causing banana anthracnose. The type material (K) had no conidia or sclerotia, and DNA could not be extracted from a darkened area of the herbarium sample. This sample thus provides few characters to delimit this species from other closely related taxa in the “gloeosporioides” species complex. An epitype is therefore designated for C. musae

investigate phenomena. The use of the site in large-enrollment classes for 6-plus years affords a well-documented case of Web-enhanced instruction. Qualitative and quantitative data on student perceptions of the site, their learning, and... more

investigate phenomena. The use of the site in large-enrollment classes for 6-plus years affords a well-documented case of Web-enhanced instruction. Qualitative and quantitative data on student perceptions of the site, their learning, and the relation of the Web site to the course as a whole provide insights into both the benefits and the challenges of Web-based teaching and learning. Students rate the site as an enhancement to their learning, but there are differential responses to various components of the site, which provide a fuller picture of how students see Web-based learning relating to their overall educational experience. Plants, Pathogens, and People 1731 related to the course through the Web; and they freely use e-mail to contact other students or the professor regarding the course (Bruce, 1997).

Background: Pseudomonas syringae pv. phaseolicola is a Gram-negative plant-pathogenic bacterium that causes "halo blight" disease of beans (Phaseolus vulgaris L.). This disease affects both foliage and pods, and is a major problem in... more

Background: Pseudomonas syringae pv. phaseolicola is a Gram-negative plant-pathogenic bacterium that causes "halo blight" disease of beans (Phaseolus vulgaris L.). This disease affects both foliage and pods, and is a major problem in temperate areas of the world. Although several bacterial genes have been determined as participants in pathogenesis, the overall process still remains poorly understood, mainly because the identity and function of many of the genes are largely unknown. In this work, a genomic library of P. syringae pv. phaseolicola NPS3121 was constructed and PCR amplification of individual fragments was carried out in order to print a DNA microarray. This microarray was used to identify genes that are differentially expressed when bean leaf extracts, pod extracts or apoplastic fluid were added to the growth medium.

Trichoderma isolates are known for their ability to control plant pathogens. It has been shown that various isolates of Trichoderma, including T. harzianum isolate T-39 from the commercial biological control product TRICHODEX, were... more

Trichoderma isolates are known for their ability to control plant pathogens. It has been shown that various isolates of Trichoderma, including T. harzianum isolate T-39 from the commercial biological control product TRICHODEX, were effective in controlling anthracnose (Colletotrichum acutatum) and grey mould (Botrytis cinerea) in strawberry, under controlled and greenhouse conditions. Three selected Trichoderma strains, namely T-39, T-161 and T-166, were evaluated in large-scale experiments using different timing application and dosage rates for reduction of strawberry anthracnose and grey mould. All possible combinations of single, double or triple mixtures of Trichoderma strains, applied at 0.4% and 0.8% concentrations, and at 7 or 10 day intervals, resulted in reduction of anthracnose severity; the higher concentration (0.8%) was superior in control whether used with single isolates or as a result of combined application of two isolates, each at 0.4%. Only a few treatments resulted in significant control of grey mould. Isolates T-39 applied at 0.4% at 2 day intervals, T-166 at 0.4%, or T-161 combined with T-39 at 0.4% were as effective as the chemical fungicide fenhexamide. The survival dynamics of populations of the Trichoderma isolates (T-39, T-105, T-161 and T-166) applied separately was determined by dilution plating and isolates in the mixtures calculated according to the polymerase chain reaction (PCR) using repeat motif primers. The biocontrol isolates were identified to the respective species T. harzianum (T-39), T. hamatum (T-105), T. atroviride (T-161) and T. longibrachiatum (T-166), according to internal transcribed spacer sequence analysis.

Abstract: Wilt is an important disease of brinjal crop causing significant reduction in yield. In present study, the pathogenic fungus was isolated from infected plant parts and identified based on morphological and cultural characters as... more

Abstract: Wilt is an important disease of brinjal crop causing significant reduction in yield. In present study, the pathogenic fungus was isolated from infected plant parts and identified based on morphological and cultural characters as Fusarium solani f. sp. melongenae. ...

Twenty-two microsatellite loci were characterized in the soilborne plant pathogenic 8 fungus Verticillium dahliae by analysis of the genome sequence. All loci were 9 polymorphic in at least two of three populations of V. dahliae from... more

Twenty-two microsatellite loci were characterized in the soilborne plant pathogenic 8 fungus Verticillium dahliae by analysis of the genome sequence. All loci were 9 polymorphic in at least two of three populations of V. dahliae from lettuce, spinach and 10 tomato. These loci were useful in genotyping isolates and highlighting differences in 11 genetic diversity among the three tested populations.

Plant pathogens in irrigation water were recognized early in the last century as a significant crop health issue. This issue has increased greatly in scope and degree of impact since that time and it will continue to be a problem as... more

Plant pathogens in irrigation water were recognized early in the last century as a significant crop health issue. This issue has increased greatly in scope and degree of impact since that time and it will continue to be a problem as agriculture increasingly depends on the use of recycled water. Plant pathogens detected from water resources include 17 species of Phytophthora, 26 of Pythium, 27 genera of fungi, 8 species of bacteria, 10 viruses, and 13 species of plant parasitic nematodes. There is substantial evidence demonstrating that contaminated irrigation water is a primary, if not the sole, source of inoculum for Phytophthora diseases of numerous nursery, fruit, and vegetable crops. These findings pose great challenges and opportunities to the plant pathology community. A variety of water treatment methods are available but few have been assessed for agricultural purposes under commercial conditions. Investigations into their technical feasibility and economics are urgently needed. Aquatic ecology of plant pathogens is an emerging field of research that holds great promise for developing ecologically based water decontamination and other strategies of pathogen mitigation. Pathogen detection and monitoring as well as biological and economic thresholds are much-needed IPM tools and should be priorities of future research. Teaming with hydrologists, agricultural engineers, ecologists, geneticists, economists, statisticians, and farmers is essential to effectively attack such a complex issue of growing global importance. Research should proceed in conjunction with nutrient and pesticide management studies in a coordinated and comprehensive approach as they are interrelated components of water resource conservation and protection.

Hemileia vastatrix is a biotrophic fungus, causing coffee leaf rust in all coffee growing countries, leading to serious social and economic problems. Gene expression studies may have a key role unravelling the transcriptomics of this... more

Hemileia vastatrix is a biotrophic fungus, causing coffee leaf rust in all coffee growing countries, leading to serious social and economic problems. Gene expression studies may have a key role unravelling the transcriptomics of this pathogen during interaction with the plant host. Reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) is currently the golden standard for gene expression analysis, although an accurate normalisation is essential for adequate conclusions. Reference genes are often used for this purpose, but the stability of their expression levels requires validation under experimental conditions. Moreover, pathogenic fungi undergo important biomass variations along their infection process in planta, which raises the need for an adequate method to further normalise the proportion of fungal cDNA in the total plant and fungus cDNA pool. In this work, the expression profiles of seven reference genes [glyceraldehyde-3-phosphate dehydrogenase (GADPH), elongation factor (EF-1), Beta tubulin (β-tubulin), cytochrome c oxidase subunit III (Cyt III), cytochrome b (Cyt b), Hv00099, and 40S ribosomal protein (40S_Rib)] were analysed across 28 samples, obtained in vitro (germinated uredospores and appressoria) and in planta (post-penetration fungal growth phases). Gene stability was assessed using the statistical algorithms incorporated in geNorm and NormFinder tools. Cyt b, 40S_Rib, and Hv00099 were the most stable genes for the in vitro dataset, while 40S_Rib, GADPH, and Cyt III were the most stable in planta. For the combined datasets (in vitro and in planta), 40S_Rib, GADPH, and Hv00099 were selected as the most stable. Subsequent expression analysis for a gene encoding an alpha subunit of a heterotrimeric G-protein showed that the reference genes selected for the combined dataset do not differ significantly from those selected specifically for the in vitro and in planta datasets. Our study provides tools for correct validation of reference genes in obligate biotrophic plant pathogens, as well as the basis for RT-qPCR studies in H. vastatrix.► Reference genes were selected for Hemileia vastatrix in planta RT-qPCR studies. ► Gene stability was assessed using geNorm and NormFinder programmes. ► 40S_Rib, GADPH, and Hv00099 were the most stable reference genes. ► An extra correction step enabled normalisation of fungal biomass in planta.

creo que esto se ha ido provocando a falta del interés del docente, como de la familia, ya que esas habilidades que mencionas son de nivel básico o al menos ahí se desarrollan las bases, las cuales no están bien cimentadas es muy difícil... more

creo que esto se ha ido provocando a falta del interés del docente, como de la familia, ya que esas habilidades que mencionas son de nivel básico o al menos ahí se desarrollan las bases, las cuales no están bien cimentadas es muy difícil que se vayan mejorando, por lo cual creo que de importancias la relación padresmaestro para hacerle saber que se necesita apoyo también de ellos.

Since the introduction and subsequent naturalisation of five species of Berberis into New Zealand, two species, B. glaucocarpa and B. darwinii have become aggressive invaders of both agricultural and native ecosystems throughout many... more

Since the introduction and subsequent naturalisation of five species of Berberis into New Zealand, two species, B. glaucocarpa and B. darwinii have become aggressive invaders of both agricultural and native ecosystems throughout many regions. Both are now targets for a biological control program. A survey for pathogens to be used as potential classical or inundative biocontrol agents was initiated on weed infestations in New Zealand. Five species of primary plant pathogens were found to be associated with systemic leaf, flower and/or fruit disease symptoms, Colletotrichum gloeosporioides, C. acutatum, Pestalotiopsis sp., Phomopsis sp., and Sclerotinia sclerotiorum. The aecial stage of a barberry rust, Puccinia graminis, was recorded from the flowers of B. glaucocarpa, which is a new host record for New Zealand.

Hiking, horse riding and mountain biking are popular in protected areas in Australia and the United States of America. To help inform the often contentious deliberations about use of protected areas for these three types of activities, we... more

Hiking, horse riding and mountain biking are popular in protected areas in Australia and the United States of America. To help inform the often contentious deliberations about use of protected areas for these three types of activities, we review recreation ecology research in both countries. Many impacts on vegetation, soils and trails are similar for the three activities, although there can be differences in severity. Impacts include damage to existing trails, soil erosion, compaction and nutrification, changes in hydrology, trail widening, exposure of roots, rocks and bedrock. There can be damage to plants including reduction in vegetation height and biomass, changes in species composition, creation of informal trails and the spread of weeds and plant pathogens. Due to differences in evolutionary history, impacts on soil and vegetation can be greater in Australia than in the USA. There are specific social and biophysical impacts of horses such as those associated with manure and urine, grazing and the construction and use of tethering yards and fences. Mountain bike specific impacts include soil and vegetation damage from skidding and the construction of unauthorised trails, jumps, bridges and other trail technical features. There are gaps in the current research that should be filled by additional research: (1) on horse and mountain bike impacts to complement those on hiking. The methods used need to reflect patterns of actual usage and be suitable for robust statistical analysis; (2) that directly compares types and severity of impacts among activities; and (3) on the potential for each activity to contribute to the spread of weeds and plant pathogens. Additional research will assist managers and users of protected areas in understanding the relative impacts of these activities, and better ways to manage them. It may not quell the debates among users, managers and conservationists, but it will help put it on a more scientific footing.

A conventional PCR and a SYBR Green real-time PCR assays for the detection and quantification of Phytophthora cryptogea, an economically important pathogen, have been developed and tested. A conventional primer set (Cryp1 and Cryp2) was... more

A conventional PCR and a SYBR Green real-time PCR assays for the detection and quantification of Phytophthora cryptogea, an economically important pathogen, have been developed and tested. A conventional primer set (Cryp1 and Cryp2) was designed from the Ypt1 gene of P. cryptogea. A 369 bp product was amplified on DNA from 17 isolates of P. cryptogea. No product was amplified on DNA from 34 other Phytophthora spp., water moulds, true fungi and bacteria. In addition, Cryp1/Cryp2 primers were successfully adapted to real-time PCR. The conventional PCR and real-time PCR assays were compared. The PCR was able to detect the pathogen on naturally infected gerbera plants and on symptomatic artificially infected plants collected 21 days after pathogen inoculation. The detection limit was 5 × 103 P. cryptogea zoospores and 16 fg of DNA. Real-time PCR showed a detection limit 100 times lower (50 zoospores, 160 ag of DNA) and the possibility of detecting the pathogen in symptomless artificially infected plants and in the re-circulating nutrient solution of closed soilless cultivation systems.

Siderophores produced by rhizosphere bacteria may enhance plant growth by increasing the availability of Fe near the root or by inhibiting the colonization of roots by plant pathogens or other harmful bacteria. To examine the populations... more

Siderophores produced by rhizosphere bacteria may enhance plant growth by increasing the availability of Fe near the root or by inhibiting the colonization of roots by plant pathogens or other harmful bacteria. To examine the populations of siderophore-producing bacteria colonizing the roots of two grass species that differed in their susceptibility to Fe deficiency, we inoculated serial dilutions of root samples onto chrome azurol S (CAS) agar and several other selective and non-selective culture meida. CAS agar effectively differentiated bacteria that were capable of excreting large amounts of siderophore, but the composition of the medium limited its usefulness for ecological studies. A large proportion (71–79%) of the bacterial population that grew on a non-selective medium (tryptic soy agar) failed to grow on CAS agar, and several isolates that showed no sign of siderophore production on CAS agar produced siderophore in liquid culture. Similar populations of siderophore-producing bacteria were observed on roots of St. Augustine grass, which frequently exhibits Fe chlorosis, and bermuda grass, which does not. Roots of both grasses were colonized by bacteria that produced siderophore in vitro at concentrations ranging from 100 to 230 μM. The CAS assay solution was also used to compare siderophore production by Pseudomonas fluorescens Q6, an isolate from bermuda grass, and by P. putida B 10, a plant growth-promoting pseudomonad. P. fluorescens Q6 produced 2.4 times more siderophore in vitro than P. putida B 10.

The biopesticidal potential of six plant-derived essential oils mint [Mentha arvensis], ajwain [Carum capticum], lemongrass [Cymbopogon citrates], clove [Eugenia caryophyllata], cedarwood [Cedrus deodara], and eucalyptus [Eucalyptus... more

The biopesticidal potential of six plant-derived essential oils mint [Mentha arvensis], ajwain [Carum capticum], lemongrass [Cymbopogon citrates], clove [Eugenia caryophyllata], cedarwood [Cedrus deodara], and eucalyptus [Eucalyptus globulas]) was evaluated against Odontotermes obesus (termites), Fusarium oxysporum (plant pathogenic fungi)

Although Aspergillus species are not usually considered as serious plant pathogens, Aspergilli are frequently encountered in plant products. The most important consequence of their presence is mycotoxin contamination. The main mycotoxins... more

Although Aspergillus species are not usually considered as serious plant pathogens, Aspergilli are frequently encountered in plant products. The most important consequence of their presence is mycotoxin contamination. The main mycotoxins produced by Aspergilli are the aflatoxins, ochratoxin A and patulin, which are produced by a variety of Aspergillus species in different plant commodities. Phylogenetic analysis of sequences of the ribosomal RNA gene cluster is useful for clarifying taxonomic relationships among toxigenic Aspergilli causing pre-and postharvest contamination of agricultural products. Molecular data has enabled us to clarify the taxonomy of black Aspergilli, A. flavus and its relatives, and sections Circumdati and Clavati, which include ochratoxin and patulin-producing species. Phylogenetically unrelated species were found to produce the same mycotoxins, indicating that mycotoxin-producing abilities of the isolates have been lost (or gained) several times during the evolution of the genus. The data also indicate that biosynthetic gene-based probes are necessary for molecular detection of these mycotoxin-producing organisms. The organisation of the biosynthetic genes of patulin and ochratoxins is unknown, although experiments are in progress in several laboratories to clarify the genetic background of biosynthesis of these mycotoxins. Identification of biosynthetic genes responsible for mycotoxin production is essential for clarifying the evolution of mycotoxin biosynthesis in Aspergilli, and to develop specific gene probes for the detection of mycotoxin-producing Aspergilli in agricultural products.

Arbuscular Mycorhizal (AM) fungi are ubiquitous and form symbiotic relationships with roots of most terrestrial plants. Their associations benefit plant nutrition, growth and survival due to their enhanced exploitation of soil nutrients.... more

Arbuscular Mycorhizal (AM) fungi are ubiquitous and form symbiotic relationships with roots of most terrestrial plants. Their associations benefit plant nutrition, growth and survival due to their enhanced exploitation of soil nutrients. These fungi play a key role in nutrient cycling and also protect plants against environmental and cultural stresses. The establishment of AM fungi in the plant root has been shown to reduce the damage caused by soil-borne plant pathogens with the enhancement of resistance in mycorrhizal plants. The effectiveness of AM fungi in biocontrol is dependent on the AM fungus involved, as well as the substrate and host plant. However, protection offered by AM fungi is not effective against all the plant pathogens and is modulated by soil and other environmental conditions. AM fungi generally reduce the severity of plant diseases to various crops suggesting that they may be used as potential tool in disease management. AM fungi modify the quality and abundance of rhizosphere microflora and alter overall rhizosphere microbial activity. These fungi induce changes in the host root exudation pattern following host colonization which alters the microbial equilibrium in the mycorrhizosphere. Given the high cost of inorganic fertilizers and health hazards associated with chemical pesticides, AM fungi may be most suitable for sustainable agriculture and also for increasing the yield of several crops through biocontrol of plant pathogens. This chapter provides an overview of mechanisms of interaction which take place between soil-borne plant pathogens and AM fungi on different plants. The availability of new tools and techniques for the study of microbial interactions in the rhizosphere may provide a greater understanding of biocontrol processes in the near-future.

Over the years, many bacterial isolates have been evaluated as potential biocontrol agents against soilborne fungal phytopathogens. However, few of them were ultimately successful after evaluation in field trials. One of the major reasons... more

Over the years, many bacterial isolates have been evaluated as potential biocontrol agents against soilborne fungal phytopathogens. However, few of them were ultimately successful after evaluation in field trials. One of the major reasons for this failure is the lack of appropriate screening procedures to select the most suitable microorganisms for disease control in diverse soil environments. For this reason, the study of bacterial screening has a future that is characterised by many technical and conceptual challenges. In this review, we summarise and discuss the convenience of use of the main screening methods currently applied to select bacterial candidates for biocontrol of fungal and oomycete soilborne phytopathogens. Also, a comparative case study of the application of different screening methods applied to an experimental pathosystem is shown, revealing the success of bacterial candidates selected by different strategies for biocontrol of the phytopathogenic fungus Rosellinia necatrix in avocado plants. Screening for antagonism against this fungal pathogen, one of the more straightforward methods used for the selection of bacterial biocontrol agents, was proven to be a valid strategy for this experimental system.

The rhizosphere is the soil-plant root interphase and in practice consists of the soil adhering to the root besides the loose soil surrounding it. Plant growth-promoting rhizobacteria (PGPR) are potential agents for the biological control... more

The rhizosphere is the soil-plant root interphase and in practice consists of the soil adhering to the root besides the loose soil surrounding it. Plant growth-promoting rhizobacteria (PGPR) are potential agents for the biological control of plant pathogens. A biocontrol strain should be able to protect the host plant from pathogens and fulfill the requirement for strong colonization. Numerous compounds that are toxic to pathogens, such as HCN, phenazines, pyrrolnitrin, and pyoluteorin as well as, other enzymes, antibiotics, metabolites and phytohormones are the means by which PGPR act, just as quorum sensing and chemotaxis which are vital for rhizosphere competence and colonization. The presence of root exudates has a pronounced effect on the rhizosphere where they serve as an energy source, promoting growth and influencing the root system for the rhizobacteria. In certain instances they have products that inhibit the growth of soil-borne pathogens to the advantage of the plant root. A major source of concern is reproducibility in the field due to the complex interaction between the plant (plant species), microbe and the environment (soil fertility and moisture, day length, light intensity, length of growing season, and temperature). This review listed most of the documented PGPR genera and discussed their exploitation.

Pseudomycin A is a cyclic lipodepsinonapeptide phytotoxin produced by a strain of the plant pathogenic bacterium Pseudomonas syringae. Like other members of this family of bacterial metabolites, it is characterised by a fatty acylated... more

Pseudomycin A is a cyclic lipodepsinonapeptide phytotoxin produced by a strain of the plant pathogenic bacterium Pseudomonas syringae. Like other members of this family of bacterial metabolites, it is characterised by a fatty acylated cyclic peptide with mixed chirality and lactonic closure. Several biological activities of Pseudomycin A are lower than those found for some of its congeners, a difference which might depend on the diverse number and distribution of charged residues in the peptide moiety. Hence, it was of interest to investigate its conformation in solution. After the complete interpretation of the two-dimensional NMR spectra, NOE data were obtained and the structure was determined by computer simulations, applying distance geometry and molecular dynamics procedures. The conformation of the large ring of Pseudomycin A in solution includes three rigid structural regions interrupted by three short flexible regions that act as hinges. The overall three-dimensional structure of the cyclic moiety is similar to that of previously studied bioactive lipodepsinonapeptides produced by other pseudomonads.

Plant growth promoting rhizobacteria (PGPR) belonging to Pseudomonas spp. are being exploited commercially for plant protection to induce systemic resistance against various pests and diseases. Mixtures of di!erent PGPR strains have... more

Plant growth promoting rhizobacteria (PGPR) belonging to Pseudomonas spp. are being exploited commercially for plant protection to induce systemic resistance against various pests and diseases. Mixtures of di!erent PGPR strains have resulted in increased e$cacy by inducing systemic resistance against several pathogens attacking the same crop. Seed-treatment with PGPR causes cell wall structural modi"cations and biochemical/physiological changes leading to the synthesis of proteins and chemicals involved in plant defense mechanisms. Lipopolysaccharides, siderophores and salicylic acid are the major determinants of PGPRmediated ISR. The performance of PGPR has been successful against certain pathogens, insect and nematode pests under "eld conditions.

We have identified a family of dispersed repetitive DNA sequences in the genome ofMagnaporthegrisea, the fungus that causes rice blast disease. We have named this family of DNA sequences "MGR" for M. grisea repeat. Analysis of five MGR... more

We have identified a family of dispersed repetitive DNA sequences in the genome ofMagnaporthegrisea, the fungus that causes rice blast disease. We have named this family of DNA sequences "MGR" for M. grisea repeat. Analysis of five MGR clones demonstrates that MGR sequences are highly polymorphic. The segregation of MGR sequences in genetic crosses and hybridization of MGR probes to separated, chromosome-size DNA molecules of M. grisea shows that this family of sequences is distributed among the M. grisea chromosomes. MGR sequences also hybridize to discrete poly(A)I RNAs. Southern blot analysis using a MGR probe can distinguish rice pathogens from various sources. However, MGR sequences are not highly conserved in the genomes of M. grisea field isolates that do not infect rice. These results suggest that host selection for a specific pathogen genotype has occurred during the breeding and cultivation of rice. Abbreviations: MGR, M. grisea repeat; CHEF, contour-clamped homogeneous electric field.

Hypocrea/Trichoderma is a genus of soil-borne or wood-decaying fungi containing members important to mankind as producers of industrial enzymes and biocontrol agents against plant pathogens, but also as opportunistic pathogens of... more

Hypocrea/Trichoderma is a genus of soil-borne or wood-decaying fungi containing members important to mankind as producers of industrial enzymes and biocontrol agents against plant pathogens, but also as opportunistic pathogens of immunocompromised humans and animals, while others can cause damage to cultivated mushroom. With the recent advent of a reliable, BarCode-aided identification system for all known taxa of Trichoderma and Hypocrea, it became now possible to study some of the biological fundamentals of the diversity in this fungal genus in more detail. In this article, we will therefore review recent progress in (1) the understanding of the geographic distribution of individual taxa; (2) mechanisms of speciation leading to development of mushroom diseases and facultative human mycoses; and (3) the possible correlation of specific traits of secondary metabolism and molecular phylogeny.

Entomopathogenic nematode-bacterium complex research is being conducted in many parts of the world, and initially, a global assessment of this research was the goal of this paper. However, this was deemed impossible because there are so... more

Entomopathogenic nematode-bacterium complex research is being conducted in many parts of the world, and initially, a global assessment of this research was the goal of this paper. However, this was deemed impossible because there are so many researchers in many countries and regions working on these important biological control agents of soil pests. Accordingly, research activities from selected countries or regions are presented. In North America and Europe, emphasis was placed on the status of commercially available nematodes, whereas with other countries and regions, the emphasis was placed on the research activities with the nematode-bacterium complexes. The one exception was with Japan where the development of commercial nematodes was emphasized. In China, Korea, and India, research activities in the use of the nematode for controlling insect pests or soil plant pathogens was stressed. In Turkey where the research is in its initial stages, we report on the Turkish nematodes and their associated bacteria. In Central America, initial attempts to control insect pests and mass production research are reported, whereas in South America, the emphasis is on biological control of some insect pests and on some basic research with some of their native nematodes. The research is still in its early stages or non-existent in most African countries, but considerable research progress has been made in Egypt with these nematodes. Overall, the intensity of research varies by country or regions. In most cases, the research in developing countries shows that the emphasis is to demonstrate the usefulness of the entomopathogenic nematodes or their symbiotic bacteria against various pests. The ultimate goal of these research activities is to use them as biological control agents of soil pests.

The survival of Sclerotinia sclerotiorum, to a large extent depends on the production and viabilty of sclerotia. Reduction in the production of sclerotia is essential in the control of the pathogen. A local Trichoderma harzianum isolate... more

The survival of Sclerotinia sclerotiorum, to a large extent depends on the production and viabilty of sclerotia. Reduction in the production of sclerotia is essential in the control of the pathogen. A local Trichoderma harzianum isolate and two Bacillus amyloliquefaciens isolates were evaluated in vitro and in vivo as potential biological control agents (BCAs) against S. sclerotiorum. The study showed that T. harzianum and B. amyloliquefaciens inhibited the growth and production of mycelia and sclerotia. The local isolates, T. harzianum and B. amyloliquefaciens appeared to exhibit mycoparasitism and antibiosis, respectively, in the in vitro study. As antagonists, these isolates protected over 80% of tomato, squash and eggplant seedlings inoculated with S. sclerotiorum. The efficacy of T. harzianum and B. amyloliquefaciens compared with two commercial products, PlantShield and SoilGard in the control of S. sclerotiorum was similar or slightly lower depending on the crop plant.

The highly divergent characters of morphology, ecology, and biology in the Helotiales make it one of the most problematic groups in traditional classification and molecular phylogeny. Sequences of three rDNA regions, SSU, LSU, and 5.8S... more

The highly divergent characters of morphology, ecology, and biology in the Helotiales make it one of the most problematic groups in traditional classification and molecular phylogeny. Sequences of three rDNA regions, SSU, LSU, and 5.8S rDNA, were generated for 50 helotialean fungi, representing 11 out of 13 families in the current classification. Data sets with different compositions were assembled, and parsimony and Bayesian analyses were performed. The phylogenetic distribution of lifestyle and ecological factors was assessed. Plant endophytism is distributed across multiple clades in the Leotiomycetes. Our results suggest that (1) the inclusion of LSU rDNA and a wider taxon sampling greatly improves resolution of the Helotiales phylogeny, however, the usefulness of rDNA in resolving the deep relationships within the Leotiomycetes is limited; (2) a new class Geoglossomycetes, including Geoglossum, Trichoglossum, and Sarcoleotia, is the basal lineage of the Leotiomyceta; (3) the Le...

Roots serve a multitude of functions in plants including anchorage, acquisition of nutrients and water, and production of exudates with growth regulatory properties. The root–soil interface, or rhizosphere, is the site of greatest... more

Roots serve a multitude of functions in plants including anchorage, acquisition of nutrients and water, and production of exudates with growth regulatory properties. The root–soil interface, or rhizosphere, is the site of greatest biological and chemical activity within the soil matrix. Plant growth-promoting rhizobacteria (PGPR) are known to influence plant health by controlling plant pathogens or via direct enhancement of plant development in the laboratory and in greenhouse experiments. Unfortunately, however, results in the field have been less consistent. The colonization of roots by inoculated bacteria is an important step in the interaction between beneficial bacteria and the host plant. However, colonization is a complex phenomenon influenced by many biotic and abiotic parameters, some of which are only now apparent. Monitoring fate and metabolic activity of microbial inoculants as well as their impact on rhizosphere and soil microbial communities are needed to guarantee safe and reliable application, independent of whether they are genetically modified or not. The first and most crucial prerequisite for effective use of PGPRs is that strain identity and activity are continuously confirmed. A combination of both classical and molecular techniques must be perfected for more effective monitoring of inoculants strain (both genetically modified and unmodified) after release into the soil. Recent developments in techniques for studying rhizobacterial communities and detection and tracking systems of inoculated bacteria are important in future application and assessment of effectiveness and consistent performance of microbial inoculants in crop production and protection.

Pathogenicity of Xanthomonas campestris pathovar (pv.) vesicatoria and most other Gram-negative bacterial plant pathogens largely depends on a type III secretion (TTS) system which is encoded by hypersensitive response and pathogenicity... more

Pathogenicity of Xanthomonas campestris pathovar (pv.) vesicatoria and most other Gram-negative bacterial plant pathogens largely depends on a type III secretion (TTS) system which is encoded by hypersensitive response and pathogenicity (hrp) genes. These genes are induced in the plant and are essential for the bacterium to be virulent in susceptible hosts and for the induction of the hypersensitive response (HR) in resistant host and non-host plants. The TTS machinery secretes proteins into the extracellular milieu and effector proteins into the plant cell cytosol. In the plant, the effectors presumably interfere with cellular processes to the benefit of the pathogen or have an avirulence activity that betrays the bacterium to the plant surveillance system. Type III effectors were identified by their avirulence activity, co-regulation with the TTS system and homology to known effectors. A number of effector proteins are members of families, e.g., the AvrBs3 family in Xanthomonas. AvrBs3 localizes to the nucleus of the plant cell where it modulates plant gene expression. Another family that is also present in Xanthomonas is the YopJ/AvrRxv family. The latter proteins appear to act as SUMO cysteine proteases in the host. Here, we will present an overview about the regulation of the TTS system and its substrates and discuss the function of the AvrRxv and AvrBs3 family members in more detail.

The family Xanthomonadaceae is a wide-spread family of bacteria belonging to the gamma subdivision of the Gram-negative proteobacteria, including the two plant-pathogenic genera Xanthomonas and Xylella, and the related genus... more

The family Xanthomonadaceae is a wide-spread family of bacteria belonging to the gamma subdivision of the Gram-negative proteobacteria, including the two plant-pathogenic genera Xanthomonas and Xylella, and the related genus Stenotrophomonas. Adhesion is a widely conserved virulence mechanism among Gram-negative bacteria, no matter whether they are human, animal or plant pathogens, since attachment to the host tissue is one of the key early steps of the bacterial infection process. Bacterial attachment to surfaces is mediated by surface structures that are anchored in the bacterial outer membrane and cover a broad group of fimbrial and non-fimbrial structures, commonly known as adhesins. In this chapter, we discuss recent findings on candidate adhesins of plant-pathogenic Xanthomonadaceae, including polysaccharidic (lipopolysaccharides, exopolysaccharides) and proteineous structures (chaperone/usher pili, type IV pili, autotransporters, two-partner-secreted and other outer membrane adhesins), their involvement in the formation of biofilms and their mode of regulation via quorum sensing. We then compare the arsenals of adhesins among different Xanthomonas strains and evaluate their mode of selection. Finally, we summarize the sparse knowledge on specific adhesin receptors in plants and the possible role of RGD motifs in binding to integrin-like plant molecules.