ITS region of the rDNA of Pythium longandrum, a new species; its taxonomy and its comparison with related species

Pythium longandrum (F-73.0) was isolated, from soil samples taken in Lille in northern France. Morphologically the fungus resembles closely Pythium rostratum, however its antheridial characters are unique. The oogonia of this species are provided with hypogynous and monoclinous antheridia. The antheridial cells are inflated and are probably the largest and longest for the genus. The internal transcribed spacer region of its nuclear ribosomal DNA indicates that it is entirely different from all other species of Pythium. This new species is characterized by its spherical to elongated sporangia, smooth-walled oogonia and hypogynous to monoclinous antheridia bearing long antheridial cells closely applied to the oogonia. Morphological features of this new species, together with the sequences of the ITS region of its nuclear ribosomal DNA and comparison with related species are discussed here.     

Morphological and molecular taxonomy of Pythium longisporangium sp. nov. isolated from the Burgundian region of France

During the course of an investigation on the Pythiaceous oomycetes occurring in the Burgundian vineyards, some species of Pythium possessing mainly hypogynous antheridia were found. These had been classified as oomycetes belonging to the "Pythium rostratum" group for a long time. Three of these isolates, having similar structures and growth, are very closely related to a recently described species, Pythium bifurcatum Paul. A close look at these, however, underlines some fundamental differences with the latter. Not all of them produce zoospores but have very large sporangia. The type specimen is F-1200 (B 76a) which is a medium-slow growing saprophyte. The sequence of the ITS region of the rDNA also shows a very close relationship with P. bifurcatum. On the basis of morphological and molecular analysis, we now describe this species as Pythium longisporangium sp. nov. Morphological features of this new species, the sequences of the ITS region of its nuclear ribosomal DNA, and its comparison with related species are discussed.     

Pythium root rot of crucifers

A destructive root disease of cabbage (Brassica oleracea L. var. capitata) and cauliflower (Brassica oleracea L. var. botrytis) incited by a species of Pythium Pringsheim is described as occurring in Varanasi, U.P. The pathogen was isolated on potato dextrose and corn meal agar. Pathogenicity and host range of the disease were studied. Cultural characters, morphology and developmental stages and life cycle of the fungus indicated its identity with Pythium middletonii Sparrow.     

Production of a toxic metabolite and pectolytic enzyme by Pythium butleri

Pythium butleri which causes root-rot of Belladonna produced a heat stable toxic metabolitein vitro. The culture filtrate induced wilting when applied to cut shoots. The pathogen produced significant amount of endo-polygalacturonase, endo-polymethylgalacturonase, exo-polygalacturonase, polygalacturonate transeliminase and pectin methyl-trans-eliminase in media containing glucose and pectin as carbon source. The fungus did not produce pectin methyl estrase and was very weakly cellulolytic. The extensive distintegration of host tissue during pathogenesis can be considered due to the pectolytic enzymes produced by the pathogen. The physiology of this fungus differs markedly from other species ofPythium and justifies its taxonomic position as a distinct species.     

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.     

分离自蚊幼虫的腐霉一新种及其rDNA的ITS区段分析

在一次室外蚊虫生物防治实验中,从被病菌感染的蚊幼虫体中分离到一株卵菌。根据其形态特征及其rDNA的ITS区段的碱基系列,鉴定为腐霉属一新种,命名为贵阳腐霉Pythiumguiyangense。对新种作了拉丁文描述。对新种与其近似种卡地腐霉P.carolinianum、奇雄腐霉P.middletonii和多卵腐霉P.multisporum的区别进行了讨论。模式标本(干培养物)保存在中国科学院微生物研究所菌物标本馆(HMAS),活培养物保存在贵阳医学院。     

Pythium vexans Causing Stem Rot of Dendrobium in Yunnan Province,China

Since 2002 a severe root and stem disease of Dendrobium has occurred periodically each year in the plantations of Simao City, Yunnan Province, China. Symptoms included water‐soaked and brown lesions, and rot of tissues. Based on the morphological characteristics and the internal transcribed spacer‐1, 5.8S ribosomal RNA gene, and internal transcribed spacer 2 and β‐tubulin gene sequences, the pathogen was identified as Pythium vexans de Bary. The pathogenicity of the fungus was confirmed by satisfying Koch’s postulates. This is the first world record of stem rot of Dendrobium caused by P. vexans.     

Methods used to study Pythium oligandrum, an aggressive parasite of other fungi

Isolates of Pythium oligandrum Drechsler and P. acanthicum Drechsler behaved similarly in a range of experiments and in a manner consistent with mycoparasitism. They grew on cellulose in association with some fungi - notably Botryotrichum pilulferum Sacc. & March. and Phialophora radicicola Cain var. radicicola (IMI 187786) - and markedly reduced cellulolysis by these species; however, they had little effect on cellulolysis by Gaeumannomyces graminis (Sacc.) Arx & Olivier var. graminis and made little growth on cellulose in the presence or absence of this fungus. Pythium oligandrum and P. acanthicum also grew rapidly across plates of potato-dextrose agar precolonised by Phialophora radicicola var. radicicola, whereas isolates of P. echinulatum Matthews, P. mamillatum Meurs, P. megalacanthum de Bary, P. spinosum Sawada and P. ultimum Trow did not grow under these conditions. Precolonised agar plates were therefore used as a selective medium to isolate Pythium oligandrum and similar fungi from soils. For this, small pieces of soil organic matter were transferred to precolonised agar plates and incubated for 4–6 (-12) days, when the presence of P. oligandrum or similar fungi was assessed by their production of spiny oogonia across the host colony. The technique proved successful in isolating these fungi from a wide range of cultivated soils, even if the soils had been stored air-dry. However, boiled hemp seeds buried in soil and subsequently transferred to precolonised agar plates usually gave rise to phytopathogenic rather than mycoparasitic pythia. Pieces of wheat straw precolonised by P. oligandrum decomposed at the same rate as virgin straws or straws precolonised by P. ultimum or Mucor hiemalis Wehmer, when all were buried in nitrogen-supplemented soil. However, different cellulolytic fungi appeared to colonise straws in these respective treatments, Fusarium spp. being less common and Stachybotrys atra Corda more common in the presence of P. oligandrum than in its absence. When subsequently opposed to P. oligandrum on agar plates, Fusarium spp. appeared to be parasitised by this fungus and made very little growth across the agar, whereas S. atra grew through the colony of P. oligandrum and was clearly unaffected by the presence of this fungus. Our results demonstrate the widespread occurrence of P. oligandrum in cultivated soils in Britain and also suggest that this species might influence the activities of other soil fungi.     

Species-specific PCR primers for Pythium developed from ribosomal ITS1 region

AIMS: To develop a specific method for distinguishing and detecting Pythium species. METHODS AND RESULTS: Twenty PCR primers were designed from the sequences of the rDNA internal transcribed spacer 1 (ITS1) region from 34 Pythium species. The specificity of these forward primers paired with ITS2 or ITS4 and reverse universal primers was tested. Five species-specific primers were obtained, other primers showed different specificity to Pythium species. The specific amplifications enabled nine Pythium species to be differentiated. Specific detection of Pythium aphanidermatum from infested plants and P. dimorphum from soil was demonstrated. CONCLUSIONS: A method for identifying nine Pythium species using specific PCR amplification was achieved. SIGNIFICANCE AND IMPACT OF THE STUDY: Because of its rapidness and ease, the results of PCR amplified with different primers can be a powerful method for identifying Pythium species and detecting or monitoring the target fungus directly from plant material, soil and water samples.     

ITS1 region of the rDNA of Pythium proliferatum, a new species: its taxonomy and its comparison with related species

A new species, Pythium proliferatum (F-382), was isolated from soil samples taken in Genlis in the burgundian region of France. The fungus is unique because of the character combinations of its large, spherical to elongated, proliferating sporangia, and its smooth walled oogonia supplied with different types of antheridia like hypogynous, monoclinous sessile, monoclinous stalked, diclinous and wrapping around the oogonia. Almost all types of antheridia that are found in the genus are present in this new species. Morphological features of this new species, together with the sequences of the ITS1 region of its nuclear ribosomal DNA and its comparison with related species are discussed in this article.     

Molecular analyses of Pythium irregulare isolates from grapevines in South Africa suggest a single variable species

The Pythium irregulare species complex is the most common and widespread Pythium spp. associated with grapevines in South Africa. This species complex has been subdivided into several morphological and phylogenetic species that are all highly similar at the sequence level [internal transcribed spacer (ITS) and cytochrome c oxidase (cox) regions]. The complex includes Pythium regulare and Pythium cylindrosporum, which are morphologically distinct, and P. irregulare sensu stricto (s.s.) and Pythium cryptoirregulare, which are morphologically similar. The aim of the current study was to determine whether 50 South African grapevine P. irregulare isolates represented more than one phylogenetically distinct species. The isolates were characterised using nuclear (ITS and β-tubulin) and mitochondrial (cox1 and cox2) gene region phylogenies and two isozyme loci [glucose-6-phosphate isomerase (Gpi) and malate dehydrogenase (Mdh-1)]. Some of the gene sequence data were difficult to interpret phylogenetically, since some isolates contained two or more polymorphic ITS copies within the same isolate (intra-isolate variation) that clustered into different ITS sub-clades, i.e. the P. irregulare s.s. and P. cryptoirregulare sub-clades. The molecular data furthermore only revealed the presence of one phylogenetic species, P. irregulare. Morphological analyses of a subset of the isolates confirmed that the isolates were P. irregulare, and further showed that the P. cylindrosporum ex-type strain formed typical P. irregulare oogonia, and not the previously reported distinct elongated oogonia. Some of the molecular analyses suggested the occurrence of outcrossing events and possibly the formation of aneuploids or polyploids since (i) the nuclear and mitochondrial gene data sets were incongruent, (ii) polymorphic ITS copies were present within the same isolate, (iii) heterozygosities were observed in the β-tubulin gene and Gpi and Mdh-1 loci in some isolates and (iv) more than two β-tubulin alleles were detected in some isolates. Altogether, the data suggest that P. irregulare, P. cryptoirregulare, P. cylindrosporum, and possibly P. regulare should be synonimised under the name P. irregulare.     

Characterisation of Pythium paroecandrum and its antagonism towards Botrytis cinerea, the causative agent of grey mould disease of grape

Pythium paroecandrum (B-30), an oomycete, was isolated from soil samples taken from a wheat field in Genlis in the Burgundy region of France and was found to check the growth and development of Botrytis cinerea, a serious grapevine pathogen. The oomycete is a fast-growing organism, living on vegetable debris, and can be recognised by its catenulate hyphal swellings, catenulate oogonia, and monoclinous antheridia. When grown together with B. cinerea, the causal agent of the grey mould disease of the grapevine, P. paroecandrum shows a pronounced antagonism and suppresses its growth and its aptitude to provoke the grey mould symptoms. Morphological features of this oomycete, its antagonism to B. cinerea, the sequences of the internal transcribed spacer region of its nuclear ribosomal DNA, and its comparison with related species are discussed in this article.     

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.