Sequence variation of intergenic mitochondrial DNA spacers (mtDNA‐IGS) of Phytophthora infestans (Oomycetes) and related species

The potato late‐blight disease is caused by the pseudofungus Phytophthora infestans (Oomycetes). This pathogen was of historical importance as it caused the Irish Potato Famine. There is currently a worldwide resurgence of the disease. Following worldwide migrations as well as being able to discriminate P. infestans from related species are key issues. We present sequence variation of five inter‐genic mitochondrial DNA spacers (mtDNA‐IGS) for P. infestans and four related taxa. Intra and inter‐taxon variation was observed showing potential for both molecular ecology and molecular systematic.     

Cytology of oomycetes

Evidence is presented for gametangial meiosis in six Oomycetes. Particular attention is drawn to late meiotic prophase stages (pachytene-diplotene) in which chromomeres and paired homologues can be seen. One of these Oomycetes has been shown to have an abortive meiosis. Multiple chromosome associations (quadrivalent configurations, with some trivalent and univalent configurations) at first metaphase with unequal divisions at first telophase or second metaphase suggest that autopolyploidy is to be found in several species. Allopolyploidy is suspected at intermediate levels of ploidy. Basic chromosome numbers of n=3 for Achlya and n=10 for Pythium are proposed.     

How modern systematics relates to the rumen fungi

The zoosporic fungi comprise a polyphyletic grouping of four classes, the Plasmodiophoromycetes, Oomycetes, Hyphochytriomycetes and Chytridiomycetes. Apart from their absorptive mode of nutrition and the presence of zoospores in some stage of their life cycle, there is little these classes have in common. The zoosporic species of rumen fungi are classified in the Class Chytridiomycetes which is a monophyletic group with extreme diversity in thallus morphology, reproduction and zoospore cytology. The rumen fungi have many characteristics in common with the Spizellomycetaceae but have been given their own family, the Neocallimasticaceae. There are arguments for reducing this family to synonymy with the Spizellomycetaceae, or elevating it to a new order, but before a rational decision can be made, more rumen fungi require detailed examination, especially their zoospore ultrastructure.     

Microsatellite DNA markers for Plasmopara viticola,the causal agent of downy mildew of grapes

Microsatellite loci were isolated from Plasmopara viticola (Oomycetes), the causal agent of downy mildew of grape, one of the most damaging fungal diseases of grapevine worldwide. Seven polymorphic loci were obtained from an enriched partial genomic library. A low genetic diversity was observed at all loci, with a mean observed allele number of 3.75 and an observed heterozygosity ranging from 0.074 to 0.547. Cross‐amplification tests on three closely related taxa indicated that two loci could be used in other Oomycetes species. These microsatellite loci were proved to be useful for population genetic analysis.     

Comparative biochemistry of oxygen toxicity in lactic acid-forming aquatic fungi

Taxonomically diverse aquatic fungi ranging in oxidative capabilities from obligate aerobes to aerotolerant anaerobes were examined for growth under hyperbaric (0.9 atm) O₂, and for the ability to degrade H₂O₂ and O ₂ ^- . The results support the presumption that several Oomycetes and Chytridiomycetes are biochemically adapted to environments low in O₂. Results further indicate significant differences between Oomycetes and Chytridiomycetes in the enzymatic means of dealing with O ₂ ^- and H₂O₂, supporting the recent concept of a great evolutionary divergence between the groups. In general, facultative anaerobes and aerotolerant anaerobes were more severely inhibited by hyperbaric O₂, and they exhibited lower superoxide dismutase (SOD), catalase and peroxidase activities than did strongly-oxidative species. SOD activity, which was detected in all isolates, was insensitive to cyanide in Oomycetes but cyanide sensitive in the Blastocladiales (Chytridiomycetes). All strongly-oxidative Oomycetes exhibited readily-detectable catalase and peroxidase activities, while activities were very low or absent in strongly-fermentative species. As with the Oomycetes, peroxidase activities among the Blastocladiales were high in aerobes and low in strong fermenters. Surprisingly, however, none of the Blastocladiales, including strongly-oxidative species, exhibited substantial catalase activity. Catalase and SOD activities in faculatively anaerobic Oomycetes increased with increasing O₂ concentration; but even in hyperbaric (0.5 atm) O₂, activities for both enzymes in the aerotolerant anaerobe Aqualinderella fermentans were very low compared with activities in aerobes.Abbreviation SOD Superoxide dismutase     

Pathogenicity and oxidative stress in Nile tilapia caused by Aphanomyces laevis and Phoma herbarum isolated from farmed fish

Identified (n = 17) and unidentified (n = 1) fish-pathogenic fungal species from 10 genera of Oomycetes and soil fungi were isolated from 40 infected freshwater fish samples of the species Oreochromis niloticus niloticus (Nile tilapia) and Clarias gariepinus (African catfish). Samples were collected from various fish farms in the Nile Delta, Egypt. Nile tilapia were tested in aquaria for their susceptibility to the commonest Oomycetes species, Aphanomyces laevis and Achlya klebsiana, and also against the 2 most prevalent pathogenic soil fungi, Paecilomyces lilacinus and Phoma herbarum. Two techniques were used: water bath exposure and intramuscular (subcutaneous) injection. Water bath exposure to the 2 species of Oomycetes caused greater mortalities of O. niloticus niloticus than intramuscular injection, but the reverse was true of the soil fungal species. Regardless of the infection method, the 2 Oomycetes species were more potent pathogens than the soil fungal species. In both gills and mytomal muscles of fish infected by A. laevis and P. herbarum, we measured and compared with controls the oxidative stress parameters total peroxide (TP), lipid peroxidation (LPO) and nitric oxide (NO), as well as levels of the antioxidants vitamin E and glutathione (GSH), and superoxide dismutase (SOD) and catalase (CAT) activities. Infection by these 2 fungal species through either spore suspension or spore injection significantly increased oxidative damage in gills and induced marked decrease in most studied antioxidants. In addition, both routes showed similar effects and A. laevis depressed the antioxidants CAT, vitamin E and GSH more than P. herbarum.     

Obligate biotrophic pathogens of the genus Albugo are widespread as asymptomatic endophytes in natural populations of Brassicaceae

Mutualistic interactions of plants with true fungi are a well‐known and widespread phenomenon, which includes mycorrhiza and non‐mycorrhizal endophytes like species of Epichloë. Despite the fact that these organisms intrude into plants, neither strong defence reactions nor the onset of symptoms of disease can be observed in most or even all infested plants, in contrast to endophytic pathogens. Oomycetes are fungal‐like organisms belonging to the kingdom Straminipila, which includes diatoms and seaweeds. Although having evolved many convergent traits with true fungi and occupying similar evolutionary niches, widespread oomycete endophytes are not known to date, although more than 500 endophytic pathogens, including species of the obligate biotrophic genus Albugo, have been described. Here, we report that oomycetes of the genus Albugo are widespread in siliques of natural host populations. A total of 759 plants, encompassing four genera with rare reports of white blister incidents and one with common incidents, were collected from 25 sites in Germany. Nested PCR with species‐specific primers revealed that 5–27% of the hosts with rare disease incidence carried asymptomatic Albugo in their siliques, although only on a single plant of 583 individuals, an isolated pustule on a single leaf could be observed. Control experiments confirmed that these results were not because of attached spores, but because of endophytic mycelium. Vertical inheritance of oomycete infections has been reported for several plant pathogens, and it seems likely that in nature this way of transmission plays an important role in the persistence of asymptomatic endophytic Albugo species.     

The occurrence of species of semi-aquatic Enchytraeidae (Oligochaeta) in Ireland

The Enchytraeidae are essentially terrestrial oligochaetes but many species have marked aquatic tendencies. Over two thirds of recorded Irish species were found in soils which were submerged or frequently flooded and 35% showed a distinct preference for these conditions. Relatively few species were living in soils subject to drought. Red blood was present in 28 species, all but one from soils with more than 55% water. Cognettia sphagnetorum and C. glandulosa developed red blood in very wet conditions. In a survey of Irish wetlands, samples were taken from bog, heath, marsh, fen, margins of lakes and rivers, and saltmarsh. The influence of various environmental parameters was determined using ordination techniques. Magnesium and pH were found to be the most important factors. A high level of magnesium distinguished coastal sites and pH 5.2 separated two clusters representing acid peat and marsh-fen-aquatic sites. Groups of indicator species characterized each of the three clusters. The ecological distribution of the indicator species is described, and their usefulness in classifying enchytraeid communities is discussed.     

THE DEVELOPMENT OF CYTOLOGICAL THEORY IN THE OOMYCETES

1. Meiosis in the Oomycetes is gametangial. 2. The life-cycle of the Oomycetes is therefore haplobiontic, type B. 3. The gametangia are multinucleate prior to septation. Vegetative nuclear divisions may occur in the hyphae subtending the gametangia, but there is no evidence for such divisions occurring in the gametangial primordia nor is there any indication that nuclei may move out of the primordium against any cytoplasmic flow. 4. Some abortion of supernumerary nuclei probably occurs after the gametangium is cut off from the vegetative thallus by the septum. Meiosis then takes place. 5. The spindle of the first metaphase is almost certainly within a persistent nuclear membrane, but there remains some doubt as to whether this membrane persists to the second telophase in all Oomycetes. 6. In the higher Peronosporales, and possibly the Rhipidiaceae, meiosis is accompanied or preceded by zonation into the periplasm and ooplasm. Spindle orientation and the timing of zonation movements probably account for the differences in the number of presumptive oosphere nuclei recorded between many Peronosporales. In some Albuginaceae, at least, it is possible that only one nucleus completes the meiotic division, but this needs confirmation. 7. A smaller number of nuclei enter the male gametangium and undergo a more or less simultaneous meiosis. 8. Some variation in the pattern and degree of synchrony of meiotic division within and between gametangia occurs in different species. 9. Nuclear abortions may precede, accompany or follow meiosis, but only in a few instances (Pythium debaryanum, P. deliense, Phytophthora himalayensis, Aphanomyces laevis) does the male gametangium finally contain only a single gamete nucleus. 10. Cytoplasmic cleavage, involving the tonoplast and central vacuole of the oogonium, occurs after meiosis in the Saprolegniales, thus offering an alternative mechanism to zonation movements for the production of uninucleate oospheres. The presence (Edson, 1915; Patterson, 1927b; Murphy, 1918) or absence (Trow, 1901; Saskena, 1936) or an homologous central vacuole in the Pythiaceae is disputed. 11. Karyogamy must follow antheridial penetration in those species which are not agamospermous, but the degree of facultative agamospermy is unknown. The timing of karyogamy, as opposed to somatogamy, is apparently variable between and within species (Wager, 1899; Arens, 1929, Moreau & Moreau, 1935; McDonough, 1937; Flanagan, 1970; Win-Tin, 1972). There are a few indications that karyogamy may be precocious and other evidence that it may be considerably delayed, even after the oospore has achieved morphological maturity, and exceptionally until germination. 12. It would appear that the majority of the oospores of most Oomycetes eventually contain only one fusion or diploid nucleus, but there are exceptions (Albugo bliti, A. platensis, A. portulacae and Aplanopsis terrestris respectively) and without further study it would be unwise to assume that this is necessarily true even for closely related species. 13. Mitosis immediately following karyogamy is reported as occurring in some species of Albugo, but in most Oomycetes it is delayed until the period immediately preceding any cytoplasmic or morphological change at the start of germination. 14. The nuclear divisions of the germinating oospore are mitotic, but they may differ in the detailed morphology of the spindle apparatus or the degree of condensation of the chromosomes. 15. Interpretations of the cytology of the small nuclei of the Oomycetes have been profoundly influenced by the prevailing climates of scientific opinion. In particular, the development of studies of meiosis and the science of genetics on the one hand, and the appreciation of the polyphyletic origin of the fungi, especially the algal origins of the Oomycetes on the other hand, have necessitated a re-evaluation of much of the older literature.     

Range-edge effects promote clonal growth in peripheral populations of the one-sided wintergreen Orthilia secunda

Existing in suboptimal conditions is a frequent occurrence for species inhabiting the cusp of their ecological range. In range‐edge populations of plants, the scarcity of suitable habitat may be reflected in small population sizes which may result in increased self‐pollination and/or inbreeding and an increase in the incidence of clonal reproduction. These factors may result in a decrease in levels of genetic diversity and a loss of potential adaptive variation that may compromise species’ ability to cope with changes in their environment, an issue that is particularly relevant today with the current concern surrounding global climate change and its effect on species’ distributional ranges. In the present study, we have compared the levels of clonal reproduction in the one‐sided wintergreen Orthilia secunda (L.) House in (1) populations from its main continuous distribution range, (2) populations occurring on the limits of the continuous range, and (3) peripheral populations outwith the species’ continuous distribution range. Range‐edge populations in Scotland and Sweden displayed significantly lower genotypic richness and diversity than those from the main area of the species’ distribution in these countries. Populations from Ireland, which occur in the temperate zone rather than the boreal conditions that are the preferred habitat for the species, and which represent relict populations left over from cooler periods in the Earth's history, displayed no within‐population genetic diversity, suggesting a complete lack of sexual reproduction. Furthermore, the genetic distinctiveness of the Irish populations, which contained alleles not found in either the Scottish or the Swedish populations, highlights the value of ‘trailing edge’ populations and supports the concept of ‘parochial conservation’, namely the conservation of species that are locally rare but globally common.     

Microbody-like organelles as taxonomic markers among Oomycetes

Zoospores of Oomycetes contain a variety of microbody-like organelles with highly structured matrices. Although in general their function is unknown, the appearance of similar organelles in related taxa suggests the ultrastructural differences could be used as taxonomic characters. This study surveys microbody-like organelles of oomycetous zoospores to determine if this is an additional criterion by which the phylogeny of these fungi can be evaluated. In zoospores of the order Saprolegniales, kinetosome-associated organelles (K-bodies) are found which typically consist of tubular and/or granular matrices. K-bodies are not found associated with kinetosomes in zoospores of the Peronosporales, but microbodies containing tubules, and in some genera marginal plates, are located near the kinetosomes, along the groove, and in other peripheral areas. K-bodies have been reported in only one member of the order Lagenidiales. These K-bodies lack a granular matrix, but contain a single curved plate from which tubules arise, forming a cone. In the one genus of the Leptomitales examined, a similar K-body contains a plate and scattered tubules. Organisms with similar microbody-like organelles are probably more closely related than those with different types of microbody-like organelles. The presence of an organelle resembling K-bodies in zoospores of an alga in the Tribophyceae supports the phylogenetic association between algae and Oomycetes. A complete survey of Oomycete genera may well reveal intermediates between the structurally different types of microbody-like organelles, allowing the reconstruction of the phylogenetic history of an organelle.     

Museum samples provide novel insights into the taxonomy and genetic diversity of Irish red grouse

The taxonomic status of red grouse in Ireland has been the subject of considerable debate over the past century. Irish red grouse are usually classified as Lagopus lagopus scoticus, which is the same subspecies as that found in Britain, but some ornithologists believe that native Irish red grouse constitute an endemic subspecies, namely L. lagopus hibernicus. The considerable decline of Irish red grouse over the past century, along with possible hybridization with introduced grouse from Britain, have highlighted the need to resolve their taxonomic status as part of a biodiversity management plan. However, genetic analysis of samples from a single point in time will provide limited insight into potentially confounding historical events such as hybridization and introgression. We therefore compared mtDNA sequences from both current and historical samples of the two putative subspecies, scoticus and hibernicus, to see if they are or were genetically distinct. Red grouse from Britain and Ireland shared mitochondrial haplotypes, and our historical data suggest that this is unlikely to be the result of recent hybridization and introgression. These findings, combined with a general lack of documented differences in behaviour and ecology, suggest that Irish red grouse should remain classified as L. lagopus scoticus. At the same time, we found evidence that a significant amount of genetic diversity has been lost from Irish red grouse over the past century, presumably as a result of diminishing population sizes and fragmentation of extant populations. A loss of habitat, combined with the declining numbers and genetic diversity of Irish red grouse, justify their designation as an All-Ireland Priority (Red List) species and a Northern Ireland Priority Species for conservation.     

Gypsies,Celts and tinkers: Colonial antecedents of anti‐traveller racism in Ireland

Post‐colonial nationalist ideologies and practices construct an Irish Republic free of ‘ethnicity’ and ‘racism’. The ethnicization of the Irish Travelling People ('itinerants’, ‘tinkers') and the existence of anti‐traveller racism, however, reveal the limitations of this construction. This article focuses upon the antecedents of anti‐traveller ideologies by concentrating on the period that preceded Irish independence in 1922. The history of Irish itinerancy from the middle ages to the mid‐nineteenth century is first described and located within the context of British colonialism. This is followed by a consideration of scholarly, literary and popular representations of ‘tinkers’ during the late nineteenth century. Three interelated discourses, those of the British Gypsylorists, the Anglo‐Irish Celtic Literary Revivalists, and the folklore of the Irish peasantry, are described and linked to British imperialism, Irish cultural nationalism, and agrarian class relations respectively. It is argued that an analysis of these discourses, grounded in political economy, provides a useful historical context for analyses of more recent constructions of Travellers that have arisen in the course of struggles over a state settlement programme initiated in the 1960s. Through documentation and analysis of historical constructions of Travelling People, especially constructions of their origins, this article aims to challenge contemporary essentialist constructions of both ethnic identity and racism by redirecting attention instead towards the economic and political processes and relations of power that produce difference and inequality within the Irish context. Such analysis can also raise broader issues regarding the existence and specificity of racism in the Irish Republic.     

腐霉属分类性状评价及其中国的种

本文对腐霉属Pythium Pringsheim的研究历史作了简单的回顾,对该属的分类性状和系统进行了论述和评价,最后对中国已发现的55种腐霉,以检索表的方式进行了分类、检索。     

An ecomorphological framework for the coexistence of two cyprinid fish and their hybrids in a novel environment

Niche variation between hybrid taxa and their parental species has been deemed imperative to the persistence of hybrid populations in nature. However, the ecological factors promoting hybrid establishment remain poorly understood. Through the application of a multidisciplinary approach integrating genetics, morphometry, life‐history, and trophic ecology, we studied the hybrids of roach (Rutilus rutilus L.) and bream (Abramis brama L.), and their parental species inhabiting an Irish lake. The roach × bream hybrid exhibited a body shape intermediate of that of the parental species. Diet analyses depicted the hybrid as a generalist, feeding on all prey items consumed by either parental species. Stable isotope data confirm the trophic niche breadth of hybrids. A significant correlation between body shape and diet was detected, suggesting that the intermediate phenotype of hybrids might play a role in their feeding abilities, resulting in the utilization of a broader trophic spectrum than the parental species. Growth and age class structure analyses also yielded a scenario that is consistent with the ecological success of hybrids. Genetic analyses suggest that the majority of hybrids result from first‐generation crosses between the parental species; however, a potentially significant proportion of back‐crosses with bream were also detected. The recent introduction of roach and bream into Irish waters, as well as the climatic and ecological features of the colonized habitats, can explain the remarkable success of the roach × bream hybrid in Ireland. The adaptive significance of hybridization and its demographic consequences for the parental species are discussed. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 768–783.     

Zoospore interspecific signaling promotes plant infection by <Emphasis Type="Italic">Phytophthora</Emphasis>

Background  

Oomycetes attack a huge variety of economically and ecologically important plants. These pathogens release, detect and respond to signal molecules to coordinate their communal behaviors including the infection process. When signal molecules are present at or above threshold level, single zoospores can infect plants. However, at the beginning of a growing season population densities of individual species are likely below those required to reach a quorum and produce threshold levels of signal molecules to trigger infection. It is unclear whether these molecules are shared among related species and what their chemistries are.     

Genetic study reveals close link between Irish and Northern Spanish specimens of the protected Lusitanian slug Geomalacus maculosus

The slug Geomalacus maculosus is a prominent member of the Lusitanian fauna. As its global distribution is restricted to western Ireland and northern Iberia, it is protected under EU legislation. Nothing is known about the genetic variability and population structure of this species, so, with a special view to shedding light on the origin of the Irish G. maculosus, tissue samples from 78 specimens were collected from 13 locations within Ireland and ten locations within Iberia and partial sequences of the mitochondrial 16S rRNA and cytochrome oxidase subunit 1 (COI) and from the nuclear internal transcribed spacer 1 region (ITS‐1) were compared. The genetic diversity of the Irish G. maculosus was found to be greatly reduced compared with the Iberian populations, with only one (16S rRNA) and two (COI) mitochondrial haplotypes identified respectively. No private Irish ITS‐1 haplotype was found. Based on the COI sequences, the Irish specimens clustered closest to Spanish specimens from Northern Asturias and Cantabria, and the bGMYC analysis identified five further Iberian clades that were highly genetically differentiated suggesting long‐term allopatric divergence.     

Notes on helminth parasites of the whiting Odontogadus m. merlangus (L.) from the northern Irish Sea

In an examination of 1352 whiting from the Irish Sea 13 helminth species were discovered. One species, Scolex polymorphus Rudolphi, was a new species associated with whiting and 7 other species were new species for whiting from the Northern Irish Sea. The species of the digenean genus Podocotyle found in whiting is probably an ecotype of P. atomon. It was concluded that the bothridial structure of 5. polymorphus cannot be used for diagnostic purposes nor to determine early and late stages of the larvae. The number of Diclidophora merlangi Kuhn (Monogenea) from each monthly sample with eggs in the uterus is directly proportional to temperature, but egg production under experimental conditions was greatest at 6° C. Several theories are proposed to explain these apparently contradictory observations. The life-history of the digenean Stephanostomum pristis Looss, appears to be unusual in that the 2nd intermediate host may be planktonic. The nematode Contra caecum clavatum Rudolphi is found both as larvae and adults but larvae comprise the greater part of the worm population. The discovery of small stage II larvae in the stomach of whiting supports the theory that only one intermediate host is necessary for the development of Contmcaecum . There were significantly more female C. clavatum than male but a 1: 1 sex ratio is demonstrated by the acanthocephalan Echinorhynchus gadi Muller. Early and late forms of the plerocercoid of Grillotia erinaceus Van Beneden are identified. The early form occurred predominantly in the young whiting.     

Invasibility or invasiveness? Effects of habitat, genotype, and their interaction on invasive Rhododendron ponticum populations

The extent and nature of biological invasions are mainly influenced by either the genotype of the invading species, the suitability of the new habitat or by genotype-habitat interactions expressed in adaptations to the new environment. The relevance of these factors was assessed for the invasive evergreen shrub Rhododendron ponticum. Habitat characteristics of soil, climate and community properties were analysed in six native populations in both Georgia (Caucasus) and Spain and in six invasive ones in Ireland. Growth variables of rhododendron individuals and seedling occurrences in the field served as response variables. We performed a reciprocal transplant experiment with rhododendron cuttings and determined survival of transplants in all countries. Due to low survival rates in Georgia and Spain, vegetative increase was only analysed for Ireland. The Irish sites benefited from significantly higher nutrient supply than the Spanish and Georgian sites. We found both strong positive correlations of nutrient supply and negative correlations of seasonal temperature amplitude with growth variables of shoots and seedling density. Origin, target site and interaction effects were significant in the survival of transplanted rhododendron individuals. The Irish site was more favorable for all genotypes, but the invasive genotypes did not perform better than the native ones. The total increase in shoot length of transplants in Ireland was highest in the Irish genotypes, which might suggest adaptation of the Irish populations to their new area. In conclusion, we found evidence for invasiveness of Irish Rhododendron ponticum populations, but only in the invaded habitat. Nonetheless, habitats in the new range also seem to be well suited to native Spanish populations, supporting the idea that invasibility of these new sites also contributes to rhododendron invasion success.     

Zoospore development in the oomycetes

Oomycetes cause destructive diseases on both animals and plants. The epidemic spread of oomycete diseases is primarily based on rapid dispersal from host to host by free swimming zoospores. These single-nucleated spores are formed in sporangia and are only released in aqueous environments. Oomycetes are classified in the Kingdom of the Stramenopiles or Chromista, which is comprised of several organisms, including the golden brown algae. The unique shared attribute found in most Stramenopiles is the morphology of the zoospores and especially the structure of their two flagella. They have one tinsel flagellum, and one whiplash flagellum. Only the tinsel flagellum has distinctive flagellar hairs. Zoospore formation can occur within minutes and it is considered one of the fastest developmental processes in any biological system. Once released from the sporangium they are able to exhibit chemotactic responses, electrotaxis, and autotaxis or autoaggregation to target new hosts for infection. Here we discuss the latest discoveries in the development and biology of the oomycete zoospore.