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At least 73 records · Page 4Linked to original sources

PubMed2003

Differential inactivation of seed exudate stimulation of Pythium ultimum sporangium germination by Enterobacter cloacae influences biological control efficacy on different plant species.

This study was initiated to understand whether differential biological control efficacy of Enterobacter cloacae on various plant species is due to differences in the ability of E. cloacae to inactivate the stimulatory activity of seed exudates to Pythium ultimum sporangium germination. In biological control assays, E. cloacae was effective in controlling Pythium damping-off when placed on the seeds of carrot, cotton, cucumber, lettuce, radish, tomato, and wheat but failed to protect corn and pea from damping-off. Seeds from plants such as corn and pea had high rates of exudation, whereas cotton and cucumber seeds had much lower rates of exudation. Patterns of seed exudation and the release of P. ultimum sporangium germination stimulants varied among the plants tested. Seed exudates of plants such as carrot, corn, lettuce, pea, radish, and wheat were generally more stimulatory to P. ultimum than were the exudates of cotton, cucumber, sunflower, and tomato. However, this was not directly related to the ability of E. cloacae to inactivate the stimulatory activity of the exudate and reduce P. ultimum sporangium germination. In the spermosphere, E. cloacae readily reduced the stimulatory activity of seed exudates from all plant species except corn and pea. Our data have shown that the inability of E. cloacae to protect corn and pea seeds from Pythium damping-off is directly related to its ability to inactivate the stimulatory activity of seed exudates. On all other plants tested, E. cloacae was effective in suppressing damping-off and inactivating the stimulatory activity of seed exudates.

Crops, Agricultural↗

PubMed2004

Development of a species-specific probe for Pythium insidiosum and the diagnosis of pythiosis.

Pythium insidiosum, the only species in the genus that infects mammals, is the etiological agent of pythiosis, a granulomatous disease characterized by cutaneous and subcutaneous lesions and vascular diseases. Accurate diagnosis of pythiosis and identification of its causal agent are often inconsistent with current immunological diagnostic methods. A species-specific DNA probe was constructed by using a 530-bp HinfI fragment from the ribosomal DNA intergenic spacer of P. insidiosum. When the probe was incubated with dot blots of genomic DNA from 104 Pythium species, it hybridized only to the DNA of P. insidiosum and P. destruens-two species that have been considered conspecific. The probe also hybridized to DNA from 22 P. insidiosum isolates in this study, regardless of their geographic origin or animal host. When tested against genomic DNA from other pathogenic organisms (Aspergillus fumigatus, Basidiobolus ranarum, Conidiobolus coronatus, Lagenidium giganteum, Paracoccidioides brasiliensis, and Prototheca wickerhamii), no cross-hybridization of the probe was detected. The specificity of the probe to hybridize to genomic DNA from all isolates of P. insidiosum and not cross-react with DNA from other Pythium species or pathogens that cause symptoms similar to pythiosis in their hosts makes it a powerful tool for the accurate diagnosis of pythiosis. In addition, the probe has the potential for pathological and environmental diagnostic applications.

DNA Probes↗

PubMed1975

Differential uptake and metabolism of sitosterol and cholesterol by Achlya, Pythium, and Phytophthora species.

The relative ability of isolates of Achlya bisexualis and A. ambisexualis and isolates of Pythium and Phytophthora to take up and metabolize sitosterol and cholesterol was studied. Species of Pythium and Phytophthora took up cholesterol and sitosterol efficiently, whereas Achlya species took up booth sterols inefficiently. Species of Pythium and Phytophthora produced a polar metabolite and esters from sitosterol as they did from cholesterol. Achlya species did not produce the polar metabolite from either sterol. In these experiments Achlya species produced esters only from cholesterol; however, their failure to produce esters from sitosterol may have been due to the higher sitosterol than cholesterol concentration.

Cholesterol↗

PubMed2001

Disinfection of Pythium-infested recirculation water by UV-oxidation technology.

Selective disinfection against Pythium aphanidermatum in recirculation water was tested with UV-irradiation and with UV-oxidation technology with the objective to reduce the electrical energy consumption per cubic meter treated water. UV-oxidation technology is based on injection of hydrogen peroxide in recirculation water, just before passage along a UV-lamp, thus creating hydroxyl radicals. Pythium aphanidermatum was applied artificially to recirculation water from tomatoes, grown, in rockwool and coconut fibre. Other parameters in this study were pH and transmission value (T10) of the infested recirculation water. Results indicated that the recommended UV-C dose of 100 mJ/cm2 for elimination of fungal pathogens in general can be lowered in case recirculation water is infected with Pythium aphanidermatum only. When UV-oxidation technology was applied with 1 mmol hydrogen peroxide per litre recirculation water, the UV-C dose could be reduced even more in comparison with merely UV irradiation.

Disinfection↗

PubMed2003

Pythium corneal ulcer in Ramathibodi Hospital.

This is a retrospective study of corneal ulcers caused by Pythium insidiosum in Ramathibodi Hospital from 1988 to 1998. The clinical data was from the medical records of 10 patients, of which 8 had complete information. Mean age of the patients was 49.8 years old and seven were farmers. Initial visual acuity was mostly below finger counts. All manifested as fungal corneal ulcers, diagnosis of Pythium insidiosum was confirmed by histology. After failed medication, penetrating keratoplasty (PKP) was performed in order to remove the infected tissue. One patient had only anterior lamella keratectomy performed and was completely cured. Seven other patients had to have their eyes removed (evisceration or enucleation) to be cured. The study shows that Pythium corneal ulcer is rare but devastating. Patients with an agricultural occupation are most at risk. Antibiotics and antifungals could not control or cure this disease, so education for people at high risk is advocated.

Adult↗

PubMed1996

Diverged 5s rRNA sequences adjacent to 5s rRNA genes in the rDNA of Pythium pachycaule.

The non-transcribed spacer of the ribosomal DNA repeat of Pythium pachycaule was found to exist in two versions, one about 200 bp longer than the other. Both versions contained a conserved 5s rRNA gene in inverted orientation and a diverged copy of the 5s sequence as a tandem repeat, with a spacer of about 180 bp between them. This is the first report of multiple 5s-like sequences in the non-transcribed spacer of the rDNA of any organism. The two diverged 5s sequences differ from each other at nine positions in the 5' half of the sequence, but they have the same central 10-bp deletion and their 3' halves are identical. The diverged sequences, 5s' and 5s'', when aligned with the 5s sequence, have the same base at 63.9 and 58.8% of the positions respectively. The spacers between 5s sequences in both versions were highly conserved. The secondary structures of potential rRNA products of the diverged 5s sequences indicate that they may be pseudogenes. The relationships between the functional 5s gene and the diverged gene copies suggest that the 5s sequence family of P. pachycaule originated by duplication of an ancestral gene, followed by divergence and the introduction of heterogeneity. This work shows the potential for tandemization of 5s genes in the NTS, and may shed light on the evolutionary events that led to the transition from the rDNA-linked 5s genes found in Pythium species with filamentous zoosporangia to the unlinked tandem arrays found in Pythium species with globose zoosporangia.

Base Sequence↗

PubMed1998

Identification of Pythium carolinianum causing 'root rot' of cotton in Egypt and its possible biological control by Pseudomonas fluorescens.

A severe root rot disease of cotton caused by Pythium carolinianum was diagnosed in a cotton field in Beni-Musa village, 20 km southwest of El-Minia city, Egypt, during the summer of 1996. This was the first reported isolation of this fungus in Egypt. In the light of the importance of the cotton industry in Egypt, research was initiated to develop a biocontrol agent against Pythium carolinianum. In vitro agar plate technique identified a Pseudomonas fluorescens strain that was highly antagonist to Pythium carolinianum. Subsequent plant growth experiments establish that substantial disease control could be obtained by applying Pseudomonas fluorescens to the soil. Optimal control was obtained by mixing the bacteria with the soil rather than by dipping the cotton roots in the bacterial suspension immediately before planting. Disease was more severe in autoclaved soil than in nonsterile soil.

Journal Article↗

PubMed2000

Viscosinamide-producing Pseudomonas fluorescens DR54 exerts a biocontrol effect on Pythium ultimum in sugar beet rhizosphere.

Growth inhibition of the root pathogen Pythium ultimum by the biocontrol agent Pseudomonas fluorescens DR54 inoculated on sugar beet seeds was studied in a soil microcosm. Plant emergence was followed, together with bacterial rhizosphere colonization, antibiotic production and effects on fungal growth. P. fluorescens DR54 inoculation of the P. ultimum-challenged seeds improved plant emergence after 7 days compared to a control without the biocontrol strain. At this time, P. fluorescens DR54 was the dominating colony-forming pseudomonad in rhizosphere soil samples from inoculated seedlings as shown by immuno-staining with a strain specific antibody. Viscosinamide, a cyclic lipopeptide, which has previously been identified as a major antagonistic determinant produced by P. fluorescens DR54 and shown to induce physiological changes in P. ultimum in vitro, could be detected in the rhizosphere samples. The impact of P. fluorescens DR54 on the growth and activity of P. ultimum was studied by direct microscopy after staining with the vital fluorescent dyes Calcofluor white and fluorescein diacetate. P. fluorescens DR54 caused reduction in P. ultimum mycelial density, oospore formation and intracellular activity. Further, Pythium oospore formation was absent in the presence of P. fluorescens DR54. A striking effect on zoospore-forming indigenous fungi was also observed in microcosms with P. fluorescens DR54 and, thus, where viscosinamide could be detected; a large number of encysted zoospores were seen in such microcosms both with and without P. ultimum infections. In vitro studies confirmed that purified viscosinamide induced encystment of Pythium zoospores.

Journal Article↗

PubMed1997

Cellular and Molecular Mechanisms Involved in the Interaction between Trichoderma harzianum and Pythium ultimum.

The interaction between Trichoderma harzianum and the soilborne plant pathogen Pythium ultimum was studied by electron microscopy and further investigated by gold cytochemistry. Early contact between the two fungi was accompanied by the abnormal deposition of a cellulose-enriched material at sites of potential antagonist penetration. The antagonist displayed the ability to penetrate this barrier, indicating that cellulolytic enzymes were produced. However, the presence of cellulose in the walls of severely damaged Pythium hyphae indicated that cellulolytic enzymes were not the only critical traits involved in the antagonistic process. The marked alteration of the (beta)-1,3-glucan component of the Pythium cell wall suggested that (beta)-1,3-glucanases played a key role in the process.

Journal Article↗

PubMed1966

Sterols and the sensitivity of Pythium species to filipin.

Schlosser, Eckart (University of Illinois, Urbana), and David Gottlieb. Sterols and the sensitivity of Pythium species to filipin. J. Bacteriol. 91:1080-1084. 1966.-The growth of several Pythium species was not affected by filipin. No leakage of inorganic phosphate was observed after treatment with the antibiotic. No sterol could be detected in 1 g (dry weight) of mycelium. Thus, the insensitivity of these fungi to the antibiotic may be explained by the lack of sterols, the postulated reaction site for filipin in the cell membrane. Though not capable of synthesizing sterols, Pythium species can incorporate exogeneous sterols, which renders them sensitive to filipin; such treatment causes a lag in growth and leakage of inorganic phosphate. The leakage after filipin treatment is indirect evidence that the sterols have been incorporated into the cell membrane. Induced sensitivity to filipin was reversible; it was lost when the sterols were diluted out by one transfer through a medium free from sterols. The hypothesis that the primary site of interaction of filipin is the sterol located in the cell membrane was strengthened by these studies. The experiments further demonstrated a change in sensitivity of a fungus to a toxic agent due to nutritional conditions.

Anti-Bacterial Agents↗

PubMed1968

Structure of the cell wall of Pythium debaryanum.

The structure of hyphal walls of Pythium debaryanum was investigated by electron microscopy of shadowed replicas and thin sections, before and after digestion by snail gut enzymes or by 1 n HCl at 100 C for 1 hr, and by X-ray diffraction. We found that the wall had two phases, one composed of microfibrils of unknown composition and a second consisting of an amorphous matrix, part of which stained like protein with potassium permanganate and part of which was removed by snail-gut enzymes. In the microfibrillar phase, there were two layers; an outer, thicker layer of randomly disposed microfibrils and an inner, thin layer of microfibrils oriented parallel to the hyphal axis. As in Neurospora crassa, the amorphous phase included a branching system of pores, 40-80 A in diameter. Unlike N. crassa, the cytoplasm of Pythium showed Golgi bodies frequently, and many lomasomes were observed between the cytoplasmic membrane and the wall. The relations between these organelles and the mechanism of wall formation in Pythium are not understood.

Cell Wall↗

PubMed1976

Effect of inhibitors of sterol biosynthesis on growth and sexuality of Pythium and Zygorhynchus.

Seven commercial inhibitors of sterol biosynthesis were tested for their effect upon vegatative growth and sexuality in Pythium acanthicum and Zygorhynchus moelleri. Five compounds (SKF 525, Chlorpropamide, Tolbutamide, Benzmalacene, AY 9944) inhibited both growth and sexuality of both fungi and two (SKF 7732 and SKF 7997) were ineffective. Pythium was more sensitive to the activity of the inhibitors than was Zygorhynchus. None of the compounds tested inhibited sexuality without similarly reducing vegetative growth.

Chlorpropamide↗

PubMed2002

Effectiveness of municipal waste compost and its humic fraction in suppressing Pythium ultimum.

The effect of addition of a municipal solid waste (MSW) compost and its water-soluble and humic fraction to suppress the effect of Pythium ultimum on pea plants was studied and compared with that of a chemical pesticide (metalaxyl). The biotic and abiotic characteristics of compost involved in the biocontrol effects of these materials were also evaluated. The addition into soil of whole composts and their humic fractions reduced the effect of the pathogen on pea plants, significantly reducing the number of root lesions and Pythium populations and avoiding reductions of plant growth. The greatest pathogen suppression was achieved with the chemical pesticide. However, it also caused a significant decrease in the number of nontarget bacteria and fungi and on beneficial soil microorganisms such as Trichoderma and Pseudomonas. Addition of organic amendments increased population size of nontarget and specific biocontrol microorganisms. The humic fraction showed similar results to compost. All this suggests that metalaxyl has a nonspecific effect, producing adverse effects on aspects of soil quality. This was avoided if the chemical pesticide was reduced and replaced by organic amendments such as an MSW compost or its humic fraction.

Agriculture↗

PubMed2006

Pythium rhizo-oryzae sp. nov. isolated from paddy fields: taxonomy, ITS region of rDNA, and comparison with related species.

Pythium rhizo-oryzae sp. nov. was isolated from some soil samples taken in paddy fields in northeastern India. For quite a long time it was wrongly identified as Pythium catenulatum Mathews, because of the presence of numerous catenulate hyphal bodies. The sequencing of the ITS region of its nuclear ribosomal DNA and a close look at its morphological characters have now enabled us to describe it as a new species. This species is characterized by the absence of zoospores and sporangia, rarely formed aritheridia and oogonia, and the presence of chained and terminal hyphal bodies. The ITS region of its rDNA comprises 774 bases. This oomycete is closely related to the members producing a filamentous inflated type of sporangia like P. catenulatum Mathews, P. torulosum Coker & Paterson, and P. inflatum Mathews. The closest of all these is P. catenulatum. Taxonomic description of this new species and its comparison with related oomycetes, together with the sequence of the PCR amplified internal transcribed region (spacers ITS1, ITS2, and the gene 5.8S) of its rDNA are given here.

Base Sequence↗

PubMed2004

Single-strand conformational polymorphism analysis of the ribosomal internal transcribed spacer 1 for rapid species identification within the genus Pythium.

Single-strand conformational polymorphism (SSCP) of the ribosomal internal transcribed spacer 1 (ITS-1) was characterized for 58 isolates of Pythium, representing 41 species from the five groups of Plaats-Niterink. Thirty-one species each produced a distinct SSCP pattern. Three species produced more than one unique pattern, corresponding to morphological subgrouping. The remaining seven species produced three distinct patterns with two or three morphologically similar species sharing a pattern. A successful blind test with four samples and the identification of eight previously unknown isolates from irrigation water demonstrated the reliability of this technique for species identification. Each SSCP pattern was defined and described by the positions of the top and bottom bands and the number of bands in between, which allows laboratories to use this technique without need to access the type isolates of Pythium species.

DNA, Algal↗

PubMed2004

Antifungal activity of Tagetes patula extracts on some phytopathogenic fungi: ultrastructural evidence on Pythium ultimum.

Methanol extract, obtained from Tagetes patula plant, was assayed against three phytopathogenic fungi: Botrytis cinerea, Fusarium moniliforme and Pythium ultimum. The antifungal activity was tested both in the dark and in the light, using two different lighting systems. The data showed that the extract proved to have a dose-dependent activity on all the fungi with a marked difference between treatments in the light than in the dark. Good growth inhibition was observed in fungi only when these were treated with the highest dose of the extract and irradiated, whereas the same dose gave only a modest inhibition when the experiment was conducted in the dark. At 5 and 10 microg/ml in the dark, growth increased. The results indicated that the presence of a luminous source enhances the antifungal activity, with small differences between UV-A and solar spectrum light. SEM and TEM observations on Pythium ultimum revealed that the Tagetes patula extract induced alterations on cell fungal membranes with a photoactivation mechanism possibly involving the production of free radicals and leading to a premature aging of the mycelium.

Antifungal Agents↗

PubMed2005

Zoospore encystment and pathogenicity of Phytophthora and Pythium species on plant roots.

Seven plant species (lucerne, maize, oat, sugarbeet, sorghum, tomato, wheat) and 12 Pythium and Phytophthora species were used in a comparative study designed to investigate the effects of plant and oomycete inter-specific variation on zoospore encystment density and pathogenicity. Zoospores showed differential encystment behaviour and they encysted more on dicotyledonous than on monocotyledonous plants. Pythium aphanidermatum, P. deliense, and Phytophthora nicotianae were the most aggressive species. Sugarbeet was the most severely attacked plant species followed by tomato while oat plants were relatively unaffected. The relationship between zoospore encystment on roots and disease severity depended on the oomycete-plant combination. Correlation analysis between zoospore encystment density and disease severity indicated low and no significant levels (p.05) of association for most plant-oomycete combinations.

Avena↗

PubMed2005

Diversity and evolution of 5S rRNA gene family organization in Pythium.

The 5S rRNA gene family organization among 87 species and varieties of Pythium was investigated to assess evolutionary stability of the two patterns detected and to determine which pattern is likely the ancestral state in the genus. Species with filamentous sporangia (Groups A-C according to the ITS phylogenetic tree for Pythium) had 5S genes linked to the rDNA repeat that were predominantly coded for on the DNA strand opposite to the one with the other rRNA genes ('inverted' orientation). A small group of species with contiguous sporangia (Group D) is related to Groups A-C but had unlinked 5S genes. The main group of species with spherical zoosporangia (Groups E-J) generally had unlinked 5S genes in tandem arrays. The six species in Group K, although they also have spherical sporangia, had linked genes on the same strand as the other rRNA genes 'non-inverted' and most of them had pairs of tandem 5S genes. The evolutionary stability of 5S sequence organization was compared with the stability of morphological characters as interpreted from a phylogeny based on ITS sequence analysis. Features of 5S sequence organization were found to be just as consistent within groups as were the morphological characters. To determine the ancestral type of 5S family organization, a survey of Phytophthora strains was conducted to supply an outgroup reference. The most parsimonious interpretation of the data in this survey yielded the tentative conclusion that the linked condition of the 5S sequences was ancestral.

DNA, Ribosomal↗