Characteristics of a <Emphasis Type="Italic">Plasmopara angustiterminalis</Emphasis> isolate from <Emphasis Type="Italic">Xanthium strumarium</Emphasis>

Leaves of Xanthium strumarium infected with downy mildew were collected in the vicinity of a sunflower field in southern Hungary in 2003. Based on phenotypic characteristics of sporangiophores, sporangia and oospores as well as host preference the pathogen was classified as Plasmopara angustiterminalis. Additional phenotypic characters were investigated such as the size of sporangia, the number of zoospores per sporangium and the time-course of their release. Infection studies revealed infectivity of the P. angustiterminalis isolate to both X. strumarium and Helianthus annuus. Inoculation of the sunflower inbred line, HA-335 with resistance to all known P. halstedii pathotypes, resulted in profuse sporulation on cotyledons and formation of oospores in the bases of hypocotyls. Infections of sunflower differential lines often led to damping-off. Molecular genetic analysis using simple sequence repeat primers and nuclear rDNA sequences revealed clear differences to Plasmopara halstedii, the downy mildew pathogen of sunflower.     

Immunisation strategies against prion diseases: prime-boost immunisation with a PrP DNA vaccine containing foreign helper T-cell epitopes does not prevent mouse scrapie

Vaccination against prion diseases constitutes a promising approach for the treatment and prevention of the disease. Passive immunisation with antibodies binding to the cellular prion protein (PrP(C)) can protect against prion disease. However, immunotherapeutic strategies with active immunisation are limited due to the immune tolerance against the self-antigen. In order to develop an anti-prion vaccine, we designed a novel DNA fusion vaccine composed of mouse PrP and immune stimulatory helper T-cell epitopes of the tetanus toxin that have previously been reported to break tolerance to other self-antigens. This approach provoked a strong PrP(C)-specific humoral and cellular immune response in PrP null mice, but only low antibody titres were found in vaccinated wild-type mice. Furthermore, prime-boost immunisation with the DNA vaccine and recombinant PrP protein increased antibody titres in PrP null mice, but failed to protect wild-type mice from mouse scrapie.     

A potential perennial host for <Emphasis Type="Italic">Pseudoperonospora cubensis</Emphasis> in temperate regions

Pseudoperonospora cubensis causes great losses in cucurbitaceous crops worldwide. In cool temperate climates of northern Europe or North America overwintering as active mycelium is not possible, because all hosts so far reported there are summer annuals. Oospores have not yet been found in these regions under field conditions. The only perennial member of the Cucurbitaceae found naturally in central and northern Europe is Bryonia dioica. To date this plant has not been recorded as a host for downy mildews, but our infection trials demonstrate that P. cubensis is able to infest this plant. Amplification and sequencing of the ITS rDNA confirmed the observed downy mildew disease on B. dioica as P. cubensis. From these findings, the possibility that P. cubensis may be able to overwinter on this perennial host cannot be excluded. Whether or not B. dioica plays a part in the epidemology of P. cubensis in Europe requires evaluation by further studies.     

Towards a classification and an understanding of developmental relationships of vertebral body malformations in Atlantic salmon (Salmo salar L.)

Vertebral column malformations in Atlantic salmon occur under farming conditions and in wild specimens and are commonly diagnosed by X-ray. The literature uses varied terms to describe malformations, and often, different terms refer to similar phenomena or similar terms describe unrelated pathologies. A coherent classification of spine defects is lacking. This shortcoming complicates the comparison of studies, makes it difficult to link particular malformations to particular causes and hampers the assessment of the prevalence of spinal deformities.Expanding available systems to categorise skeletal malformations in different teleost species, we propose 20 types of salmon vertebral column malformations that are repetitively observed under farming conditions. As vertebral column deformities are usually diagnosed by X-ray, the classification of deformity types is based on radiological observations that have been obtained over the past 10 years from more than 5000 specimens. The proposed deformity types should be identifiable independent from the type (analogue, digital) and the quality of radiographs. We propose nine types of compression and fusion-related deformities, four types of abnormal radiotranslucent or radiopaque vertebral bodies, three types of spine curvatures, three types of symmetry deviations and displacement of vertebral bodies and one type of severe multiple malformations. Based on the suggested categories we discuss the relationships between types of vertebral body malformations. Several types of malformations involve the development of heterotopic cartilage, a pathology that is possibly linked to mechanical overload and accelerated growth. Refined categories for vertebral body malformations should help link particular types of malformations to particular causes. It should also help find out which deformities represent final stages and which deformities represent transitory stages.     

EFFECT OF THE ECTOMYCORRHIZAL FUNGUS PAXILLUS INVOLUTUS ON GROWTH AND CATION (POTASSIUM,CALCIUM, AND MAGNESIUM) NUTRITION OF PINUS SYLVESTRIS L. IN SEMI-HYDROPONIC CULTURE

A semi-hydroponic culture was used to compare growth and cation nutrition of mycorrhizal (Paxillus involutus) and non-mycorrhizal Scots pine seedlings. When roots and hyphae grew together, concentrations and contents of macronutrients in needles and roots were not significantly different between mycorrhizal and non-mycorrhizal plants. When grown in two separate compartments, root potassium (K) concentrations, concentrations and contents of calcium (Ca) in needles and roots, needle nitrogen (N) concentrations, total N content and contents of root K and Mg were significantly reduced in mycorrhizal plants. Whereas ¹⁵N abundance increased in roots of mycorrhizal plants. The results indicated that the extraradical mycelium of the fungus strain used was able to transport N to the plant but did not contribute to long-term cation uptake and growth of host plants. An insufficient supply of macro-elements [N, phosphorus (P)] may account for the reduced growth of mycorrhizal plants and the differences in cation uptake between mycorrhizal and non-mycorrhizal plants.     

Selection of bacteria and fungi for control of soilborne seedling diseases of maize

Journal of Plant Diseases and Protection - Plant-based screening experiments were conducted with the aim of identifying biocontrol bacteria and fungi for seed treatment of maize. Candidate...     

Das Platzen von Weinbeeren (Vitis vinifera) bei Befall mit Grauschimmel (Botrytis cinerea)

Rain-cracking of post-veraison grape berries (Vitis vinifera L.) reduces yield and quality of must and wine. Under vineyard conditions, cracking is often associated with bunch rots. The objective of the present study was to identify the role of Botrytis cinerea Pers.: Fr. as the dominant bunch rot fungus in cracking of Riesling berries. For these experiments grape berries with characteristic symptoms of Botrytis infections were selected in the vineyard. Berries infected by Botrytis always cracked in those regions of the berry where symptoms of the infections (brownish purple colour of the fruit skin) were present. In 55 % of these berries, cracks were orientated perpendicularly to the pedicel/stylar scar axis. Microscopic cracks referred to as microcracks were often present in the stylar scar region and occasionally in the vicinity of lenticels. These cracks allowed penetration of the fluorescent tracer acridine orange. The area infiltrated by the dye was positively related to crack length (r²?=#x003D;?0.43*). Water uptake of detached berries increased with time. Rates of uptake were highly variable and higher for infected berries as compared to berries without infections. Rates of water uptake into infected berries were positively related to cumulative crack length (number of cracks multiplied with average crack length) per berry (r²?=#x003D;?0.45*). Exposing the outer surface of the strained grape berry exocarp to water increased the frequency of microcracks. The increase was larger in infected berries than in those without symptoms. Our data demonstrate that Botrytis infections increase the cracking susceptibility of Riesling grape berries by weakening the grape berry exocarp, increasing crack length per berry which in turn resulted in increased water uptake.     

Natural durability of Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) heartwood grown in southern Germany

Abstract

The natural durability of timber is an important property in order to assess its performance in service. For numerous species grown in primary forests, this property has already been determined. As plantation-grown timber becomes more and more important, detailed information on its properties is needed, because increasing amounts of this material are coming to the market. The majority of planted Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) in Germany is around 40 years old. In the present study, representative material of totally ten trees from two different sites in the south of Germany was investigated with regard to natural durability. In laboratory tests based on European standard DIN EN 350-1, inner and outer heartwood zones were exposed to basidiomycetes. Density measurements were additionally used for further characterisation of this material. Results showed a lower durability of the plantation-grown Douglas fir wood as compared with wood from natural sites. Significant differences for both durability and density were found between inner and outer heartwood, even though no correlation between the parameters was recognised. Data illustrate that for a better understanding of durability variations, chemical, topochemical and electron microscopic studies are needed.     

Effects of bovine serum albumin and estrous cow serum on development and ultrastructure of in vitro-produced porcine embryos

This study evaluated the effects of bovine serum albumin (BSA; 4 mg/ml) and estrous cow serum (ECS; 10%) in North Carolina State University (NCSU) 23 medium on the development of in vitro-matured and in vitro-fertilized porcine oocytes. Early cleavage rate was significantly (P < 0.05) higher in NCSU/ECS (71.3 +/- 14.7%) vs. NCSU/BSA (60.6 +/- 4.7%). Cleavage beyond the four-cell stage was not different between the two culture media (43.5 +/- 9.5% and 41.4 +/- 17.7%, respectively). The proportion of development to blastocysts was--with borderline significance (P = 0.05)--higher in NCSU/BSA (28.0 +/- 4.4%) than in NCSU/ECS (20.4 +/- 7.3%). Blastocysts produced in NCSU/BSA had significantly (P < 0.001) higher cell numbers than those cultured in NCSU/ECS (29.5 +/- 20.1 vs. 16.9 +/- 10.8). The ultrastructure of in vitro-produced blastocysts from both culture systems was compared vs. in vivo-derived blastocysts. The latter showed a clear differentiation between trophectoderm (TE) and inner cell mass (ICM) cells. The TE cells were anchored to other TE cells or ICM cells by long, well-developed junctional complexes. The apical membrane of trophoblast cells was covered with numerous microvilli. Mitochondria were abundant, round to elongated in shape, and showed clear transverse cristae. The ultrastructure of blastocysts cultured in NCSU/BSA mimicked that of in vivo-derived embryos closely. In contrast, blastocysts from the NCSU/ECS culture system displayed an irregular ultrastructure with reduced numbers of organelles and numerous cytoplasmic inclusions, such as lipid-yolk-vacuoles and vacuoles with lipid content. In some sections of these embryos, cellular debris was detected in cytoplasm. The shape of mitochondria was more ovoid and cristae were not visible. In summary, our results demonstrate a beneficial influence of ECS in the culture medium on initial cleavage of in vitro-produced porcine embryos. Clearly negative effects of ECS in the subsequent culture period are associated with marked ultrastructural changes of embryonic cells.     

Transient expression of gfp in the obligate biotrophic oomycete Plasmopara halstedii using electroporation and a mechanoperforation method

Studying plant biotrophic oomycetes is difficult, because they depend on living plant cells for nutrition, which necessitates investigations in planta . Internal optical labelling is a powerful tool for analysing intra- and interspecific interactions. Different approaches are described for establishing a gfp -transformation system for Plasmopara halstedii , the causal agent of sunflower downy mildew. A vector containing gfp and the oomycete-specific ham34 regulators from Bremia lactucae was constructed for transformation experiments. Particle bombardment of infected sunflower cotyledons during different developmental stages of the pathogen did not result in successful transformation. In contrast, transient gfp expression in sporangia was achieved using electroporation. However, gfp expression was lost during the subsequent round of infection. A novel transformation method for biotrophic organisms in planta employing mechanoperforation – so-called Löchern–resulted in sporangiophores of P. halstedii transiently expressing gfp and emerging distant from the site of transformation. The new technique is advantageous compared with others as the transformed hyphae can recover during their vegetative growth, before reproductive structures occur. This first step lays an important foundation for further investigations of obligate biotrophic organisms.