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PubMed2006

Intraspecific variability of Pythium myriotylum isolated from cocoyam and other host crops.

Intraspecific variability within 51 isolates of Pythium myriotylum from cocoyam (Xanthosoma sagittifolium) and other host crops was analysed using optimum growth temperature, esterase banding patterns, AFLPs, rDNA-ITS sequencing, and virulence to cocoyam. P. myriotylum isolates virulent to cocoyam could easily be differentiated from other isolates of P. myriotylum by their optimum growth temperature. Isolates from cocoyam grew best at 28 degrees C with no growth at 37 degrees C, while P. myriotylum isolates from other host crops had their optimum growth temperature at 37 degrees C. Esterases produced consistent zymograms with 18 discrete esterase markers, but no monomorphic markers were produced for isolates virulent to cocoyam. Isozyme profiles based on esterase analysis showed that isolates that infect cocoyam plantlets formed a related group, irrespective of their geographic origin. P. myriotylum isolates from other host plants also grouped together, but could clearly be distinguished from the cocoyam cluster. AFLPs produced 189 scorable bands for the cocoyam isolates, of which 77% are monomorphic. Phenetic analysis of AFLP data grouped all isolates originating from cocoyam together except for the isolates C103-04, CMR17, CMR22, and CMR25. These isolates regrouped with isolates of Pythium myriotylum from other host crops or the outgroup and were found not to be pathogenic for cocoyam. ITS sequences of isolates of P. myriotylum from cocoyam were 99.1-99.7% identical to sequences deposited in GenBank. However, alignments of ITS sequences revealed a base transition at position 824 from adenine in typical isolates of P. myriotylum to guanine in isolates that could infect cocoyam plantlets. In a limited pathogenicity test, all isolates from cocoyam having guanine at position 824 were able to infect tissue culture derived cocoyam but not those exhibiting adenine. This study demonstrates for the first time, molecular evidence that isolates of P. myriotylum that infect cocoyam are distinct from P. myriotylum isolates from other crops and have developed a certain degree of host adaptation.

Crops, Agricultural↗

PubMed2003

Pythium carbonicum, a new species isolated from a spoil heap in northern France, the ITS region, taxonomy and comparison with related species.

Pythium carbonicum (F-72) sp. nov. was found in soil samples taken on the top of a spoil heap in northern France. The morphology of this new species resembles that of a recently described species: Pythium megacarpum. However, the antheridial and oogonial characteristics of this new species are unique, and the comparison of its ITS region of the nuclear ribosomal DNA indicates that this species is also related to the genus Phytophthora. The fungus does not sporulate, the sporangia germinate directly into mycelium through germ tubes. The oogonia of P. carbonicum are smooth-walled and also papillated, and are provided with monoclinous and diclinous antheridia that wrap around, forming a complicated knot. Morphological features of this new species, together with the sequences of the ITS region of its nuclear ribosomal DNA and its comparison with related species are discussed here.

Base Sequence↗

PubMed2003

Pythium glomeratum, a new species isolated from agricultural soil taken in north-eastern France, its ITS region and its comparison with related species.

Pythium glomeratum sp. nov. is described here. It was isolated from soil samples taken in the northern France in 1992, was wrongly identified as Pythium heterothallicum and was kept aside. Recently, the ITS region of the rDNA of this oomycete was amplified and sequenced. The differences between the sequence and a more detailed study of the morphological characters of these two species, revealed that both are related but different species. P. glomeratum is characterized by the presence of branched antheridia that wrap around the oogonia, aplerotic to almost plerotic oospores, and the lack of zoosporangia and zoospores. Taxonomical description of this new species, its comparison with related oomycetes, polymerase chain reaction (PCR) amplification of the internal transcribed region (spacers ITS1, ITS2, and the gene 5.8S) of its ribosomal nuclear DNA and the nucleotide sequence of this region are given here.

Base Sequence↗

PubMed2000

Solid formulations of binucleate Rhizoctonia isolates suppress Rhizoctonia solani and Pythium ultimum in potting medium.

Two isolates of binucleate Rhizoctonia spp., previously selected for efficacy in suppression of Rhizoctonia solani and Pythium spp., as well as plant growth promotion, were incorporated into various solid substrate formulations. These formulated products were assayed at three doses in three glass-house experiments for biocontrol of damping-off diseases in Capsicum annuum. R. solani anastomosis group 4 or Pythium ultimum var. sporangiiferum were incorporated into pasteurized potting medium with each formulated binucleate Rhizoctonia product. All formulations were effective against both pathogens in at least two experiments, but some formulations of one isolate of binucleate Rhizoctonia did not give consistent control of R. solani in one experiment. The most consistent formulation, which provided control of both pathogens at all doses of binucleate Rhizoctonia, was the simple substrate of rice hulls. The implications for commercialization of a biocontrol product are discussed.

Capsicum↗

PubMed2002

Biomechanical interaction between hyphae of two Pythium species (Oomycota) and host tissues.

Forces exerted by hyphae of the phytopathogen Pythium graminicola and mammalian pathogen Pythium insidiosum were compared with the mechanical resistance of their hosts' tissues. Hyphal apices of both species exerted a mean force of 2 microN, corresponding to mean pressures of 0.19 microN microm(-2) (or MPa) for P. graminicola, and 0.14 microN microm(-2) for P. insidiosum. Experiments with glass microprobes showed that the epidermis of grass roots resisted penetration until the pressure applied at the probe tip reached 1-12 microN microm(-2). Previously published data show that mammalian skin offers even greater resistance (10-47 microN microm(-2)). Clearly, tissue strength exceeds the pressures exerted by hyphae of these pathogens, verifying that secreted enzymes must play a critical role in reducing the resistance of plant and animal tissues. It is presumed that hyphae are sufficiently powerful to bore through any obstacles remaining after enzyme action.

Biomechanical Phenomena↗

PubMed2004

Pythium attrantheridium sp. nov.: taxonomy and comparison with related species.

Pythium attrantheridium sp. nov. is a new species isolated from cavity spot lesions of carrots as well as apple and cherry seedlings from various locations widely distributed in Canada and the USA. This fungus is closely related to the heterothallic P. intermedium, but is distinguished by: (1) unique molecular characteristics; (2) unique morphological characteristics; and (3) mating incompatibility with P. intermedium. The ITS region of the nuclear rDNA of all strains of P. attrantheridium studied is different from that of all other known Pythium spp. The oogonia attract a large number of antheridia when compatible mating types contact each other. The positive mating type produces zoospores unlike those of P. intermedium. Thus, biological, morphological and molecular data support the recognition of a new species.

Base Sequence↗

PubMed2005

Pythium phragmitis sp. nov., a new species close to P. arrhenomanes as a pathogen of common reed (Phragmites australis).

During a study on the occurrence and pathogenicity of oomycetes in the reed-belt (Phragmites australis) of Lake Constance (Germany), a new Pythium resembling the important cereal pathogen species complex P. arrhenomanes/P. graminicola was consistently isolated from necrotic mature reed leaves and reed rhizosphere samples. The new species proved to be significantly more aggressive towards reed leaves and seedlings in vitro than related species. It is characterised by filamentous, inflated sporangia and plerotic oospores with usually more than one antheridium. ITS and cox II sequence data indicate this new species shares a common ancestor with P. arrhenomanes, but the sequence differences are clearly consistent with a divergence of the two taxa and with P. phragmitis being a distinct species. ITS 1 and 2 of 15 isolates of the taxon consistently differed from P. arrhenomanes by 13 positions. Sequence analyses of the cox II gene confirmed the new species' phylogenetic position. This paper gives a formal description of the taxon as P. phragmitis sp. nov., providing information on morphology, ecology and pathogenicity in comparison to related species. As indicated by the close association to Phragmites australis, the high aggressiveness towards reed leaves and seedlings, and the abundance in the investigated stands, Pythium phragmitis might act as a reed pathogen of considerable importance, in particular under flooding situations.

Cyclooxygenase 2↗

PubMed2002

Biological control of cucumber and sugar beet damping-off caused by Pythium ultimum with bacterial and fungal antagonists.

AIMS: Five bacterial strains belonging to Bacillus subtilis, Pseudomonas fluorescens and Ps. corrugata and two fungal strains belonging to Trichoderma viride and Gliocladium virens were evaluated for their efficacy in controlling sugar beet and cucumber damping-off caused by Pythium ultimum. METHODS AND RESULTS: The in vitro antagonistic activity of bacteria against various Pythium spp. was evaluated with dual cultures in various media. Pseudomonas strains inhibited the pathogen better than Bacillus strains. To identify potentially useful antagonist combinations, dual compatibility of antagonists was also evaluated, based on growth in two liquid media containing substrate previously used by other antagonists. Four pairs of bacteria were selected. Sugar beet damping-off biocontrol was attempted with bacterial seed treatments (individually and in pairs). Cucumber damping-off biocontrol was attempted with bacterial seed treatments and bacterial and fungal compost treatments. In sugar beet, satisfactory biocontrol was only achieved with Pseudomonas antagonists. Antagonist combinations did not show any superior biocontrol ability to individual antagonists and compatibility of bacteria in vitro did not correlate with compatibility in vivo. Bacterial seed treatments and fungal compost treatments failed to control cucumber damping-off. Better biocontrol in cucumber was achieved when bacterial antagonists were applied by drenching or by coating seed with bacteria in a peat carrier. CONCLUSIONS: Pseudomonas antagonists were superior to Bacillus antagonists in controlling damping-off in cucumber and sugar beet. Pseudomonas peat inocula maintained a good shelf-life 2 years after preparation. SIGNIFICANCE AND IMPACT OF THE STUDY: Pseudomonas peat formulations have the potential for development into commercial biopesticides.

Bacillus subtilis↗

PubMedDate not supplied

Genetic variation in homothallic and hyphal swelling isolates of Pythium ultimum var. ultimum and P. utlimum var. sporangiferum.

Genetic variation in a collection of 22 Pythium ultimum isolates was analyzed using restriction fragment length polymorphisms (RFLPs), random amplified polymorphic DNA (RAPD), and sequence characterized amplified regions (SCARs) as genetic markers. Qualitative evidence for the occurrence of sexual outcrossing in the field, asexual mechanisms affecting variation, and differences in aggressiveness between isolates was found. Codominant SCAR and RFLP markers detected multiple alleles in several isolates. Genetic analysis of F1 progeny from a cross indicates that heterozygosity is one cause of multiple alleles and contributes to genetic variation. Segregation analysis of F2 progeny fit diploid expectations and supported the use of the molecular markers for phenetic analysis. One isolate contained three alleles at one locus suggesting that polyploidy, aneuploidy or heterokaryosis may also contribute to genetic variation. Phenetic analysis using UPGMA clustering of Nei's distance calculated from RFLP data, UPGMA clustering of similarity matrixes calculated from RAPD data, and principle component analysis of RAPD data revealed no clustering of the three morphological types of Pythium ultimum (var. ultimum, var. sporangiferum, and group HS). Our results suggest that the three morphological variants of this homothallic oomycete are not genetically distinct.

Base Sequence↗

PubMed1993

Human infectious corneal ulcer caused by Pythium insidiosum.

Pythium insidiosum is a fungus-like organism known to infect a variety of animals. In humans, the few known cases involving Pythium have included arterial infections and cellulitis. We present what we believe to be the first case of P. insidiosum recovered from a human corneal ulcer. The organism is difficult to isolate, causing delays in diagnosis. It is also resistant to the usual antifungal medications, making surgical excision the treatment of choice.

Adult↗

PubMed2000

Oligandrin. A proteinaceous molecule produced by the mycoparasite Pythium oligandrum induces resistance to Phytophthora parasitica infection in tomato plants.

A low-molecular weight protein, termed oligandrin, was purified to homogeneity from the culture filtrate of the mycoparasitic fungus Pythium oligandrum. When applied to decapitated tomato (Lycopersicon esculentum Mill. var. Prisca) plants, this protein displayed the ability to induce plant defense reactions that contributed to restrict stem cell invasion by the pathogenic fungus Phytophthora parasitica. According to its N-terminal sequence, low-molecular weight, acidic isoelectric point, ultraviolet spectrum, and migration profile, the P. oligandrum-produced oligandrin was found to share some similarities with several elicitins from other Phytophthora spp. and Pythium spp. However, oligandrin did not induce hypersensitive reactions. A significant decrease in disease incidence was monitored in oligandrin-treated plants as compared with water-treated plants. Ultrastructural investigations of the infected tomato stem tissues from non-treated plants showed a rapid colonization of all tissues associated with a marked host cell disorganization. In stems from oligandrin-treated plants, restriction of fungal growth to the outermost tissues and decrease in pathogen viability were the main features of the host-pathogen interaction. Invading fungal cells were markedly damaged at a time when the cellulose component of their cell walls was quite well preserved. Host reactions included the plugging of intercellular spaces as well as the occasional formation of wall appositions at sites of potential pathogen entry. In addition, pathogen ingress in the epidermis was associated with the deposition of an electron-opaque material in most invaded intercellular spaces. This material, lining the primary walls, usually extended toward the inside to form deposits that frequently interacted with the wall of invading hyphae. In the absence of fungal challenge, host reactions were not detected.

Algal Proteins↗

PubMed1998

A new species of Pythium isolated from the Burgundy region in France.

Pythium nodosum sp. nov. has been isolated from a soil sample taken in the Burgundy region in France. The fungus has spherical to variously shaped proliferating sporangia, smooth-walled oogonia which are crowded with different antheridial branches making a complicated knot around the former, and aplerotic oospores. Morphological and reproductive aspects of Pythium nodosum as well as the PCR of the internal transcribed spacer (ITS1) of the ribosomal nuclear DNA coupled with restriction fragment length polymorphism analysis are described here. The nucleotide sequences of ITS1 encoding 5.8S rRNA is also given.

Base Sequence↗

PubMed1999

Pythium ornacarpum: a new species with ornamented oogonia isolated from soil in france.

Pythium ornacarpum sp. nov. was isolated from a soil sample taken from Genlis in the Burgundy region of France. This species is unique because of its ornamented oogonia which are completely surrounded by antheridial filaments. The fungus is closely related to Pythium echinulatum Matthews. Morphological and reproductive aspects of this species as well as a study by PCR of the sequence of the internal transcribed spacer (ITS1) of the nuclear ribosomal gene and its comparison with related species are described here. The nucleotide sequence of the ITS1 region flaking the 5.8S rRNA of this species and other related species are also given here.

Base Sequence↗

PubMed1999

Pythium periplocum, an aggressive mycoparasite of Botrytis cinerea causing the gray mould disease of grape-vine.

Pythium periplocum Dreschler has been found to be an aggressive mycoparasite of Botrytis cinerea, the causal agent of the gray mould disease of the grape-vine. When grown together, the former enters the latter's mycelium, branches freely within, coagulates its cytoplasm and finally tears its hyphae apart, bringing about widespread destruction of the grape-vine pathogen. Extensive coiling around the host, as reported in the case of other mycoparasites belonging to the genus Pythium, has not been observed here. The infected mycelium of B. cinerea fails to infect the grape-vine and does not induce the characteristic gray mould symptoms. Since P. periplocum is not a grape-vine parasite, it could be useful for the biological control of B. cinerea. A brief account of this mycoparasitism is discussed in this article.

Botrytis↗

PubMed1999

Pythium prolatum isolated from soil in the Burgundy region: a new record for Europe.

Pythium prolatum Hendrix and Campbell has been isolated from a soil sample taken in the Burgundy region in France. The fungus is easily recognisable by its heavily ornamented oogonia with conical to mammiform spines, elongated sporangia, and its diclinous antheridia forming or originating from a tangled mass of hyphae. Descriptions of the morphological and reproductive aspects of Pythium prolatum, the polymerase chain reaction of the internal transcribed spacer (ITS1) of the ribosomal nuclear DNA as well as the nucleotide sequences of ITS1 coding for 5.8S rRNA are given.

Base Sequence↗

PubMed2000

ITS1 region of the nuclear ribosomal DNA of the mycoparasite Pythium periplocum, its taxonomy, and its comparison with related species.

Pythium periplocum Drechsler was isolated from some soil samples taken in the botanical garden of Tenerife, Canary Islands. This fungus has been found to be an aggressive mycoparasite of Botrytis cinerea. It is unique amongst the members of the genus Pythium because of the character combination of inflated filamentous type of sporangia and ornamented oogonia. The taxonomic description of this fungus and its comparison with related species, together with the polymerase chain reaction of the internal transcribed spacer of its nuclear ribosomal DNA, are discussed in this article.

Base Sequence↗

PubMed2002

Pythium segnitium sp. nov., isolated from the Canary Islands--its taxonomy, ITS region of rDNA, and comparison with related species.

Pythium segnitium (CI-44) was isolated from some soil samples taken in the Canary Islands (Spain). This new species is a slow-growing fungus and is perfectly adapted to terrestrial habitat. It belongs to the group of Pythium that have smooth-walled oogonia, mostly hypogynous antheridia, and plerotic oospores. The fungus lacks sporangia, zoospores, and hyphal bodies are rarely formed. Thus the asexual reproduction, which is so common for fungi and especially for the aquatic ones, is completely lacking in this case. However the fungus reproduces sexually by the formation of oogonia, antheridia and oospores plentifully. The taxonomic description of this fungus, the nucleotide sequence of the internal transcribed region (spacers ITS1, ITS2, and the gene 5.8 S) of its ribosomal nuclear DNA, and its comparison with related species are given here.

Base Sequence↗

PubMed2006

Differences in microbial activity and microbial populations of peat associated with suppression of damping-off disease caused by Pythium sylvaticum.

The microbiological characteristics associated with disease-suppressive peats are unclear. We used a bioassay for Pythium sylvaticum-induced damping-off of cress seedlings to identify conducive and suppressive peats. Microbial activity in unconditioned peats was negatively correlated with the counts of P. sylvaticum at the end of the bioassay. Denaturing gradient gel electrophoresis (DGGE) profiling and clone library analyses of small-subunit rRNA gene sequences from two suppressive and two conducive peats differed in the bacterial profiles generated and the diversity of sequence populations. There were also significant differences between bacterial sequence populations from suppressive and conducive peats. The frequencies of a number of microbial groups, including the Rhizobium-Agrobacterium group (specifically sequences similar to those for the genera Ochrobactrum and Zoogloea) and the Acidobacteria, increased specifically in the suppressive peats, although no single bacterial group was associated with disease suppression. Fungal DGGE profiles varied little over the course of the bioassay; however, two bands associated specifically with suppressive samples were detected. Sequences from these bands corresponded to Basidiomycete yeast genera. Although the DGGE profiles were similar, fungal sequence diversity also increased during the bioassay. Sequences highly similar to those of Cryptococcus increased in relative abundance during the bioassay, particularly in the suppressive samples. This study highlights the importance of using complementary approaches to molecular profiling of complex populations and provides the first report that basidiomycetous yeasts may be associated with the suppression of Pythium-induced diseases in peats.

Basidiomycota↗