Pythium cryptoirregulare, a new species within the P. irregulare complex

Pythium identification is based on several characteristics with considerable variation, particularly in Pythium irregulare Buis. as currently recognized. Thirty-one isolates of Pythium irregulare Buis. from various hosts and geographic regions were compared by genetic analysis of multiloci DNA fingerprints, sequence analysis of nuclear and mitochondrial genes and morphological and growth rate studies. Previous research indicated two distinct groupings within the species, P. irregulare sensu stricto and a clade referred to here as Pythium sp. Parsimony analyses of 338 AFLP markers divided P. irregulare s.l. into two clades. Comparison of the allele frequencies of 236 polymorphic AFLP loci revealed significant differences between them. The two clades differed in the frequencies of 182 (77%) alleles. P. irregulare s.s. had 122 (52%) polymorphic loci while Pythium sp. had 205 (87%). Pythium sp. had one fixed allele and 79 polymorphic loci absent in P. irregulare s.s. P. irregulare s.s. displayed 16 polymorphic loci absent in Pythium sp. Parsimony and distance analyses of the ribosomal intergenic transcribed spacers (ITS) and the cox II gene sequences support the separation of P. irregulare s.s. and Pythium sp. Amplicon length in P. irregulare s.s. ITS sequences were 936-938 bp and 936-949 bp in Pythium sp. The two clades were separated by two fixed insertion/deletion mutations, nine fixed nucleotide substitutions in the ITS region and three fixed single nucleotide substitutions in the cox II sequences. Average growth rates of the groups differed at 10, 30 and 36 C but not at 15, 21 or 25 C. Statistically significant differences were found in oogonium, oospore and ooplast diameters, antheridial cell length and in ooplast index. We propose that a new species, Pythium cryptoirregulare, be delineated from Pythium irregulare sensu stricto.     

Two pathogenic species of Pythium: P. aphanidermatum and P. diclinum from a wheat field

During a survey of pathogenic and non-pathogenic Pythium spp. in different localities in Egypt, several isolates of Pythia were obtained and maintained on corn meal agar. Among these isolates, Pythium aphanidermatum and Pythium diclinum were obtained from rhizosphere of wheat plants grown in Dear Attia village, Minia, Egypt. Identification was made using morphological and molecular analyses. P. aphanidermatum and P. diclinum were able to cause reductions in emergence and adulating in wheat in laboratory scale. P. aphanidermatum appeared to be the most aggressive parasite under agar and pot experimental conditions.     

Two new Pythium species from China based on the morphology and DNA sequence data

In an investigation of Pythium species in lawn grassland of south China, two new species, Pythium breve and P. baisense, were identified based on morphological characteristics and DNA sequence data. These two new species differ morphologically from the other Pythium species by the oogonia encompassed by many antheridia and with 1?C3 antheridia on the wavy and curved stalks. Furthermore, P. baisense with complexly lobed antheridial stalks differs from P. breve with antheridial stalks entwining the hyphae nearby the oogonia with several turns. Results of phylogenetic analyses showed that these two new species were clearly separated from morphologically similar Pythium species based on the internal transcribed spacer region (ITS1, 5.8S, ITS2) and cytochrome c oxidase subunit I (COXI) gene sequences using maximum parsimony and Bayesian methods. These two new species are described and illustrated in detail.     

Five new species of Pythium (Peronosporomycetidae)

Five new species of Pythium are described, following ecological studies of the genus in the Reading (U.K.) area. Two of the new species were found abundantly, three were rarely isolated. Neither of the abundant species produces sporangia and both have very small oospores. Of the rarer species, two have filamentous sporangia and all three have rather large oospores.     

A new non-zoosporic species of Pythium from Algeria

Pythium ramificatum n.sp. isolated from Algeria is described. It is a non-zoosporic fungus, reproducing asexually be means of hyphal bodies and sexually by oogonia with much branched antheridia. Its morphological and reproductive characters as well as it relationship with other species of Pythium of the same group are described.     

Pythium sukuiense, a new species from undisturbed natural forest in Taiwan

A new species, Pythium sukuiense, was isolated from an undisturbed natural forest in northern Taiwan. The fungus produces sporangia indistinguishable from hyphae and very small oogonia and oospores. Oogonia were smooth and terminal or intercalary and attached with a single antheridium. Oospores were aplerotic, with an average size of only 11 μm.     

Sterols in species of Pythium

Summary Analysis by gas chromatography revealed the presence of small amounts of squalene, but not lanosterol nor ergosterol in Pythium paroecandrum, P. ultimum, P. graminicola, and P. arrhenomonas. However, when acetate-¹⁴C was used as a precursor for sterols, even squalene was not found in P. graminicola. The deficiency in the sterol synthesizing mechanism may therefore be at or before the squalene forming step. Both squalene and ergosterol were present in the mycelium of Rhizoctonia solani, as shown by both gas chromatography and by the incorporation of acetate-¹⁴C into ergosterol. The absence of ergosterol in Pythium and its presence in Rhizoctonia is consistant with the resistance to the antibiotic filipin of Pythium species and the sensitivity of R. solani.     

Comparative photorespiration in Amaranthus,soybean and corn

Summary A tracer technique was used to measure photorespiration in Amaranthus lividus, soybean and corn. Under a light intensity of 40 Wm^-2 (400–700 nm) efflux of tracer carbon dioxide from Amaranthus into air was comparable to that from soybean over a 30-min period and 10 times that from corn. Initial rates of efflux of tracer into air from Amaranthus were higher than from soybean and 9 times that from corn. Efflux of CO₂ from Amaranthus over 30 min in 120 Wm^-2 was only 5 times that of corn and the initial rate was only one third that of soybean. Though total efflux from soybean was similar at the two light intensities, the initial rate was slightly higher under 120 Wm^-2. For Amaranthus and soybean, pure oxygen doubled total efflux of CO₂ and substantially increased the initial rate compared with CO₂-free air whereas there was no effect on corn. A comparison of the light and dark curves suggests that light and dark respiration had different substrates. The results are interpreted in terms of the recycling of photorespiratory CO₂.     

Isolation of Pythium Acanthicum,P. oligandrum,and P. periplocum from Soil and Evaluation of Their Mycoparasitic Activity and Biocontrol Efficacy Against Selected Phytopathogenic Pythium Species

Mycoparasitic Pythium species with spiny oogonia were surveyed in 50 Palestinian agricultural fields subject to different cropping practices using the Sclerotia Bait Technique (SBT) and the Surface-Soil-Dilution-Plate method (SSDP) with the selective VP3 medium. The mycoparasitic Pythium species were obtained from 21 (42%) soils using the SSDP method and from 37 (74%) soils using SBT. Pythium acanthicum and P. oligandrum were isolated by both methods, whereas P. periplocum was isolated only by the SBT. Using a newly modified dual plate culture method (MDPCM), the three mycoparasites showed varying antagonistic performance against several Pythium host species under a range of in vitro conditions. However, P. periplocum and P. oligandrum were found to be active biocontrol agents against P. ultimum, the damping-off organism of cucumber. This pathogen was antagonized, on thin films of water agar, by the three mycoparasites, and was moderately susceptible to P. periplocum while slightly susceptible to P. acanthicum and P. oligandrum. In direct application method in which antagonistic mycoparasites were incorporated into peat/sand mixture artificially infested with P. ultimum under growthroom conditions, Pythium oligandrum and P. periplocum (at 500 CFUg⁻¹) significantly improved seedling emergence and protected seedlings from damping-off. In the seed coating method, biocontrol by two types of seed dressing (homogenate- or oospore coated seeds), was comparable to that achieved by direct application. This revised version was published online in June 2006 with corrections to the Cover Date.     

Two new species in Hyphoderma

Hyphoderma nemorale and H. incrustatum are described. Incompatability between the new species and against related species has been ascertained using confrontations with haploid mycelia.     

Genetic and phenotypic analyses of Pythium isolates from reed suggest the occurrence of a new species,P. phragmiticola,and its involvement in the generation of a natural hybrid

A set of isolates closely related to the reed pathogen Pythium phragmitis was found among Pythium strains obtained from reed (Phragmites australis) soil and plant samples in Germany and Switzerland. These isolates consistently differed from P. phragmitis at 6, 6 and 3 nucleotide positions in the rDNA internal transcribed spacer region, the β-tubulin, and the cytochrome oxidase II gene, respectively. They are formally described here as Pythium phragmiticola sp. nov. An analysis of phenotypic traits like oospore size, growth and aggressiveness to reed showed that P. phragmiticola is almost indiscernible from P. phragmitis, as most features assessed overlapped considerably between species. Phylogenetic analyses provided evidence that P. phragmiticola is the second parent of a previously described Pythium hybrid involving P. phragmitis. The alloploid status of the hybrid, and the parents' reproductive separation was confirmed by molecular evidence and the high ratios of aborted oospores. In natural environments there obviously are two species closely associated with reed, P. phragmitis and P. phragmiticola which are homothallic, but can outcross, resulting in sterile, vegetatively propagated interspecific hybrids. Driving forces leading to the radiation of these two species are unknown, but might be connected with divergent parasitic adaptation to different host tissues or species.     

Two new spider species of the genus Chrysso O. P.-Cambridge, 1882 (Araneae, Theridiidae) in Hainan Island, China

Two new spider species of the genus Chrysso O. P.-Cambridge, 1882 are reported from Hainan Island, China, Chrysso bifurcasp. n. (male, female) and Chrysso bicuspidatasp.n. (male, female). Chrysso bimaculata Yoshida, 1998is recorded from China for the first time.     

Two new species of Keratella (Rotifera: Monogononta: Brachionidae) from Inner Mongolia,P.R. China

The relationship of species abundance to eight environmental variables was tested for 24 common species of crustacean zooplankton collected in the Atchafalaya River Basin during the summer of 1994. Stepwise regressions (α = 0.05) revealed significant relationships between zooplankton abundance and at least one environmental variable for 18 species ( R2 = 0.14-0.61, p < 0.0435-0.0001). The majority of these species' peak abundances were correlated with variables indicative of seasonal changes in floodplain habitat, as the Atchafalaya river receded, water temperature increased, and/or phytoplanktonic photosynthesis increased. Surface water temperature and the percent saturation of dissolved oxygen showed the most significant relationships, but specific conductance, current velocity, and Secchi disk depths were also related to abundance patterns of certain taxa. A principal components analysis of species abundances provided further insight into the partitioning of temporally-distinct zooplanton assemblages, showing that several species ( Bosmina longirostris, Daphnia parvula, Eurytemora affinis, and Ceriodaphnia quadrangula) predominated during early summer, and were supplanted by a distinct late-summer assemblage ( Diaphanosoma birgei, Moina micrura, Mesocyclops edax, and Daphnia lumholtzi) as time progressed. The transitional assemblage was dominated by Simocephalus serrulatus, Macrocyclops albidus, Microcyclops rubellus, and Thermocyclops inversus, all of which were most abundant in the hypoxic conditions characteristic of the latter stages of the Atchafalaya River flood-pulse. This revised version was published online in July 2006 with corrections to the Cover Date.     

Two new species of Cladorrhinum

Two new species of Cladorrhinum, C. flexuosum and C. microsclerotigenum, are described and their sequences of the 5.8S and 28S ribosomal DNA and internal transcribed spacers 1 and 2 of the ribosomal RNA gene cluster analyzed. Cladorrhinum flexuosum, isolated from soil in Spain, forms fast-growing, dull yellow colonies, flexuous conidiophores and globose to dacryoid conidia. Cladorrhinum microsclerotigenum, isolated from Musa sp. in Turkey, strongly resembles Cladorrhinum phialophoroides in the production of abundant terminal phialides, ellipsoid conidia and microsclerotia in culture. It differs from C. phialophoroides in its ability to grow at 36 C and high number of intercalary phialides, which only infrequently occur in C. phialophoroides.     

Two new species of Rhynchosporium

Rhynchosporium consists of two species, R. secalis and R. orthosporum. Both are pathogens of grasses with R. secalis infecting a variety of Poaceae hosts and R. orthosporum infecting Dactylis glomerata. Phylogenetic analyses of multilocus DNA sequence data on R. secalis isolates originating from cultivated barley, rye, triticale and other grasses, including Agropyron spp., Bromus diandrus and Hordeum spp., resolved the monophyletic groups into three species according to their respective hosts. Host specificity according to phylogenetic lineages was confirmed with pathogenicity studies. Because R. secalis was described first on rye this name is retained for Rhynchosporium isolates infecting rye and triticale. Rhynchosporium isolates infecting cultivated barley and other Hordeum spp. and Bromus diandrus belong to a distinct species, R. commune. Similarly isolates infecting Agropyron spp. represent a distinct species of Rhynchosporium, namely R. agropyri. A PCR-RFLP assay was developed as a rapid tool for species identification of R. secalis and R. commune.     

Two species of Stereum,one old,one new

Two species ofStereum are discussed. One,S. macrocystidiatum from Java, is described as new; the other,S. illudens Berk., is redescribed from Mexico-Guatemala collections. Study of this material leads to the conclusion thatXylobolus Karst. emend. Boidin cannot be maintained as distinct fromStereum Hill ex S. F. Gray. Subgeneric distinctions between these two groups of species are also rejected.     

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.