Volatiles produced by soil-borne endophytic bacteria increase plant pathogen resistance and affect tritrophic interactions

Volatile organic compounds (VOCs) released by soil microorganisms influence plant growth and pathogen resistance. Yet, very little is known about their influence on herbivores and higher trophic levels. We studied the origin and role of a major bacterial VOC, 2,3-butanediol (2,3-BD), on plant growth, pathogen and herbivore resistance, and the attraction of natural enemies in maize. One of the major contributors to 2,3-BD in the headspace of soil-grown maize seedlings was identified as Enterobacter aerogenes, an endophytic bacterium that colonizes the plants. The production of 2,3-BD by E. aerogenes rendered maize plants more resistant against the Northern corn leaf blight fungus Setosphaeria turcica. On the contrary, E. aerogenes-inoculated plants were less resistant against the caterpillar Spodoptera littoralis. The effect of 2,3-BD on the attraction of the parasitoid Cotesia marginiventris was more variable: 2,3-BD application to the headspace of the plants had no effect on the parasitoids, but application to the soil increased parasitoid attraction. Furthermore, inoculation of seeds with E. aerogenes decreased plant attractiveness, whereas inoculation of soil with a total extract of soil microbes increased parasitoid attraction, suggesting that the effect of 2,3-BD on the parasitoid is indirect and depends on the composition of the microbial community.

Occupational exposure to blood borne pathogens among healthcare workers and preventative strategies

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Interactions between nematodes, potato and soil-borne micro-organisms and their effect on the management of potato cyst nematodes

Potato cyst nematodes (PCN) cause significant damage to the potato crop worldwide and growers experience economic losses related to yield loss and the cost of control measures. Experiments were set up to further elucidate the complex tritrophic PCNpotato-soil bacteria relationship. Bacterial strains isolated from the sugar beet rhizosphere were shown to be hatch active towards Globodera pallida and to be capable of successfully colonising the sugar beet rhizosphere when applied exogenously. A trap-crop system, based on these isolates, was proposed. Ridge and bulk soil taken from a commercial potato field were incubated with sterile potato root leachate (sPRL) and subsequent in vitro hatching assays showed that PCN hatch was influenced by microorganisms present in the ridge, but not in the bulk soil. Community level physiological profiling (CLPP) of ridge and bulk soil, using BIOLOG EcoplatesTM, demonstrated differences in bacterial functional diversity between the two soil types. An investigation of the inter-species competition between G. pallida and G. rostochiensis showed that G. pallida performed significantly better, in terms of multiplication rate, in competition with G. rostochiensis compared to its multiplication rate in single-species populations. Effectively removing the early hatch of G. rostochiensis in pot trials led to the removal of this competitive advantage of G. pallida suggesting that this advantage was due, at least in part, to morphological changes to the root caused by the early hatching of G. rostochiensis.

Molecular survey and genetic characterization of tick-borne pathogens in dogs in metropolitan Recife (north-eastern Brazil).

To identify DNA of the main tick-borne pathogens in dogs from Recife (Brazil), polymerase chain reactions were carried out on blood samples of dogs treated at the Veterinary Hospital of the Universidade Federal Rural de Pernambuco from March 2007 to June 2008. The detection of DNA was performed using specific primers. Amplicons were analyzed through electrophoresis and sequencing. A phylogenetic tree was constructed using the UPGMA method, revealing that the sequences were closely related to those of strains from other geographic regions. Among the 205 blood samples analyzed, 48.78% was positive for Anaplasma platys; 38.04% was positive for Ehrlichia canis; 7.31% was positive for Babesia canis vogeli; and 0.49% was positive for Hepatozoon canis and Mycoplasma haemocanis. Coinfection of two or three pathogens was found in 23.9% (49/205) of the dogs. The subspecies B. canis vogeli was identified. Infection by H. canis and M. haemocanis is reported for the first time in dogs in the state of Pernambuco (Brazil). The data indicate that the main tick-borne pathogens in dogs in this region are E. canis and/or A. platys, followed by B. canis vogeli.

Use of fluorescent proteins to monitor the regulation of antifungal activity in root-associated Pseudomonas fluorescens CHA0

SUMMARY Roots of crop plants are the target of soil-borne pathogens, mainly fungi that cause considerable damage to plant health. By antagonizing these pathogens, some root-colonizing pseudomonads provide plants with efficient biological protection from disease. Pseudomonas fluorescens CHAO is a soil bacterium with the ability to suppress a considerable range of root diseases. A major characteristic conferring biocontrol capacity to this strain is the production of antifungal compounds, in particular 2,4-diacetyphloroglucinol (DAPG) and pyoluteorin (PLT). The regulation of the biosyntheses of these metabolites is complex and involves several regulatory systems responding to multiple environmental signals. In the present work, we have developed reporter systems based on green (GFP) and red fluorescent (DsRed) proteins to monitor regulation of antifungal gene expression in vitro and on plant roots. Stable and unstable GFP-based reporter fusions to the DAPG and PLT biosynthetic genes allowed us to demonstrate that P. fluorescens CHAO keeps the two antifungal compounds at a fine-tuned balance that can be affected by environmental signals. A GFP-based screening technique helped us to identify two novel regulators of balanced antibiotic production, i.e. MvaT and MvaV that are functionally and structurally related to the nucleoid-binding protein H-NS. They act in concert as global regulators of DAPG and PLT production and other biocontrol-related traits in P. fluorescens CHAO, and are essential for the bacterium's capacity to control a root disease caused by Pythium. The combined use of autofluorescent reporters, flow cytometry, and epifluorescence microscopy permitted us to visualize and quantify the expression of DAPG and PLT biosynthetic genes on roots. A GFP- and DsRed-based two-color approach was then developed to further improve the sensitivity of the flow cytometric quantitation method. The findings of this study shed more light on the complex regulatory mechanisms controlling antifungal activity of P. filuorescens in the rhizosphere. RESUME 4 e Les racines de plantes de culture sont la cible de divers pathogènes, principalement des champignons, qui nuisent gravement à la santé des plantes. Certains pseudomonades colonisant les racines peuvent avoir un effet antagoniste sur les pathogènes et protéger ainsi les plantes de manière efficace. Pseudomonas fluorescens CHAO est une bactérie du sol ayant la capacité de supprimer une gamme considérable de maladies racinaires. Une des caractéristiques principales conférant la capacité de biocontrôle à cette souche, est la production de composés antifongiques, en particulier le 2,4-diacétyphloroglucinol (DAPG) et la pyolutéorine (PLT). La régulation de la biosynthèse de ces métabolites est complexe et implique plusieurs systèmes régulateurs répondant à de multiples signaux environnementaux. Dans ce travail, nous avons développé des systèmes rapporteurs basés sur des protéines fluorescentes verte (GFP) et rouge (DsRed), afin d'étudier la régulation de l'expression des gènes d'antifongiques in vitro et sur les racines des plantes. Des fusions GFP stables et instables rapportrices de l'expression des gènes de biosynthèse du DAPG et de la PLT nous ont permis de démontrer que P. fluorescens CHAO gère les deux antifongiques dans une balance finement régulée pouvant être affectée par des signaux environnementaux. Une technique de criblage basée sur la GFP nous a permis d'identifier deux nouveaux régulateurs de la production d'antibiotiques, MvaT et MvaV, apparentés à la protéine H-NS liant l'ADN, Elles agissent de concert en tant que régulateurs globaux sur la production de DAPG et de PLT, ainsi que sur d'autres éléments relatifs au biocontrôle chez P. fluorescens CHAO. De plus, elles sont essentielles à la bactérie pour contrôler une maladie racinaire causée par Pythium. L'utilisation combinée de rapporteurs autofluorescents, de cytométrie de flux et de microscopie à épifluorescence nous a permis de visualiser et de quantifier l'expression des gènes de biosynthèse du DAPG et de la PLT sur les racines. Une approche utilisant simultanément la GFP et la DsRed a ensuite été développée afin d'améliorer la sensibilité de la méthode de quantification par cytométrie de flux. Les résultats de cette étude ont apporté plus de lumière sur les mécanismes régulateurs complexes contrôlant l'activité antifongique de P. fluorescens dans la rizosphère.

The endodermis.

A Casparian strip-bearing endodermis is a feature that has been invariably present in the roots of ferns and angiosperms for approximately 400 million years. As the innermost cortical layer that surrounds the central vasculature of roots, the endodermis acts as a barrier to the free diffusion of solutes from the soil into the stele. Based on an enormous body of anatomical and physiological work, the protective endodermal diffusion barrier is thought to be of major importance for many aspects of root biology, reaching from efficient water and nutrient transport to defense against soil-borne pathogens. Until recently, however, we were ignorant about the genes and mechanisms that drive the differentiation of this intricately structured barrier. Recent work in Arabidopsis has now identified the first major players in Casparian strip formation. A mechanistic understanding of endodermal differentiation will finally allow us to specifically interfere with endodermal barrier function and study the effects on plant growth and survival under various stress conditions. Here, I critically review the major findings and models related to endodermal structure and function from other plant species and assess them in light of recent molecular data from Arabidopsis, pointing out where the older, descriptive work can provide a framework and inspiration for further molecular dissection.

Pea-barley intercropping and short-term subsequent crop effects across European organic cropping conditions

Grain legumes are known to increase the soil mineral nitrogen (N) content, reduce the infection pressure of soil borne pathogens, and hence enhance subsequent cereals yields. Replicated field experiments were performed throughout W. Europe (Denmark, United Kingdom, France, Germany and Italy) to asses the effect of intercropping pea and barley on the N supply to subsequent wheat in organic cropping systems. Pea and barley were grown either as sole crops at the recommended plant density (P100 and B100, respectively) or in replacement (P50B50) or additive (P100B50) intercropping designs. In the replacement design the total relative plant density is kept constant, while the additive design uses the optimal sole crop density for pea supplementing with 'extra' barley plants. The pea and barley crops were followed by winter wheat with and without N application. Additional experiments in Denmark and the United Kingdom included subsequent spring wheat with grass-clover as catch crops. The experiment was repeated over the three cropping seasons of 2003, 2004 and 2005. Irrespective of sites and intercrop design pea-barley intercropping improved the plant resource utilization (water, light, nutrients) to grain N yield with 25-30% using the Land Equivalent ratio. In terms of absolute quantities, sole cropped pea accumulated more N in the grains as compared to the additive design followed by the replacement design and then sole cropped barley. The post harvest soil mineral N content was unaffected by the preceding crops. Under the following winter wheat, the lowest mineral N content was generally found in early spring. Variation in soil mineral N content under the winter wheat between sites and seasons indicated a greater influence of regional climatic conditions and long-term cropping history than annual preceding crop and residue quality. Just as with the soil mineral N, the subsequent crop response to preceding crop was negligible. Soil N balances showed general negative values in the 2-year period, indicating depletion of N independent of preceding crop and cropping strategy. It is recommended to develop more rotational approaches to determine subsequent crop effects in organic cropping systems, since preceding crop effects, especially when including legumes, can occur over several years of cropping.

Involvement of phenazine-1-carboxylic acid, siderophores and hydrogen cyanide in suppression of Rhizoetonia solani and Pythium spp. damping-off by Pseudomonas oryzihabitans and Xenorhabdus nematophila

Entomopathogenic bacterial strains Pseudomonas (Flavimonas) oryzihabitans and Xenorhabdus nematophilus, both bacterial symbionts of the entomopathogenic nematodes Steinernema abbasi and S. carpocapsae have been recently used for suppression of soil-borne pathogens. Bacterial biocontrol agents (P. oryzihabitans and X nematophila) have been tested for production of secondary metabolites in vitro and their fungistatic effect,on mycelium and spore development of soil-borne pathogens. Isolates of Pythium spp. and Rhizoctonia solani, the causal agent of cotton damping-off, varied in sensitivity in vitro to the antibiotics phenazine-I-carboxylic acid (PCA), cyanide (HCN) and siderophores produced by bacterial strains shown previously to have potential for biological control of those pathogens. These findings affirm the role of the antibiotics PCA, HCN and siderophores in the biocontrol activity of these entomopathogenic strains and support earlier evidence that mechanisms of secondary metabolites are responsible for suppression of damping-off diseases. In the present studies colonies of R oryzihabitans showed production of PCA with presence of crystalline deposits after six days development and positive production where found as well in the siderophore's assay when X nematophila strain indicated HCN production in the in vitro assays. In vitro antifungal activity showed that bacteria densities of 101 to 10(6)cells/ml have antifungal activity in different media cultures. The results show further that isolates of Pythium spp. and R. solani insensitive to PCA, HCN and siderophores are present in the pathogen population and provide additional justification for the use of mixtures of entomopathogenic strains that employ different mechanisms of pathogen suppression to manage damping-off.

Water, irrigation and plant diseases

Irrigation is a major husbandry tool, vital for world food production and security. The purpose of this review is twofold:- firstly drawing attention to the beneficial and deleterious aspects of irrigation resulting from interactions with the microbial world; secondly, forming a basis for encouraging further research and development. Irrigation is for example, a valuable component in the control of some soil borne pathogens such as Streptomyces scabies, the cause of potato common scab and Fusarium cubense, a cause of banana wilt. By contrast, applying irrigation encourages some foliar pathogens and factors such as splash dispersal of propagules and the retention of leaf wetness are important elements in the successful establishment of disease foci. Irrigation applied at low levels in the canopy directly towards the stem bases and root zones of plants also provides means encouraging disease development. Irrigation also offers means for the direct spread of microbes such as water borne moulds, Oomycetes, and plasmodial pathogens coming from populations present in the water supply. The presence of plant disease causing microbes in sources of irrigation has been associated with outbreaks of diseases such as clubroot (Plasmodiophora brassicae). Irrigation can be utilised as a means for applying agrochemicals, fungigation. The developing technologies of water restriction and root zone drying also have an impact on the success of disease causing organisms. This is an emerging technology and its interactions with benign and pathogenic microbes require consideration.

Enxertia e podridão de raízes e colo em cucurbitáceas

Pós-graduação em Agronomia (Produção Vegetal) - FCAV

Induction of suppressiveness to Fusarium wilt of chrysanthemum with composted sewage sludge

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Optimization of aeroponic technology for future integration in quality potato seed production systems in tropical environments

Virus and soil borne pathogens negatively impact on the production of potatoes in tropical highland and sub-tropical environments, limiting supply of an increasingly popular and important vegetable in these regions. It is common for latent disease infected seed tubers or field grown cuttings to be used as potato planting material. We utilised an International Potato Centre technique, using aeroponic technology, to produce low cost mini-tubers in tropical areas. The system has been optimised for increased effectiveness in tropical areas. High numbers of seed tubers of cultivar Sebago (630) and Nicola per m2 (>900) were obtained in the first generation, and the system is capable of producing five crops of standard cultivars in every two years. Initial results indicate that quality seed could be produced by nurseries and farmers, therefore contributing to the minimisation of soil borne diseases in an integrated management plan. This technology reduces seed production costs, benefiting seed and potato growers. © ISHS.