[Possible aggravation of a Henoch Schoenlein purpura by isotretinoin]

We report on a 16 year old patient with a hemorrhagic bullous form of a Henoch-Schönlein purpura. The cause for the event could not be determined, but the patient recovered without complications. Since he had begun a therapy with isotretinoin due to an acne inversa 3 weeks before, a possible association between the event and the treatment could not be excluded, and the case was reported to Swissmedic. In the comment, we discuss the pharmacology of isotretinoin, drug-induced vasculitis, and its pathomechanisms. As a general reminder, the criteria for the causality assessment of adverse drug reactions as well as the reporting system of adverse drug reactions in Switzerland are discussed.

Saprophytic Activity and Sporulation of Cryphonectria parasitica on Dead Chestnut Wood in Forests with Naturally Established Hypovirulence

ABSTRACT Sustainable biological control of the chestnut blight fungus Crypho-nectria parasitica with hypovirulence depends on the production and dissemination of hypovirus-infected propagules of the pathogen. We investigated the ability of C. parasitica to sporulate and produce hypo-virus-infected spores on recently dead chestnut wood in coppice stands in southern Switzerland where hypovirulence has been naturally established. The number and type (active, inactive, or none) of cankers was assessed on experimentally cut and stacked stems, firewood stacks, and natural dead wood. Hypovirus-free and hypovirus-infected strains readily survived for more than 1 year in the chestnut blight cankers of the stacked stems. Sporulation of C. parasitica was observed on the surface of preexisting inactive and active cankers, as well as on newly colonized bark areas and was significantly more abundant than on comparable cankers on living stems. On all types of dead wood, we observed more stromata with perithecia than with pycnidia; however, a large proportion of the stromata was not differentiated. All perithecia examined yielded only hypovirus-free ascospores. The incidence of pycnidia that produced hypovirus-infected conidia ranged from 5% on natural dead wood to 41% on the experimental stacks. The mean virus transmission rate into conidia was 69%. Our study demonstrates a considerable saprophytic activity of C. parasitica on recently dead chestnut wood and supports the hypothesis of a role of this saprophytic phase in the epidemiology of hypovirulence.

Sequence variation and evolution of Cryphonectria hypovirus 1 (CHV-1) in Europe

Cryphonectria hypovirus 1 (CHV-1) acts as a naturally occurring biological control agent for chestnut blight, a destructive fungal disease of chestnut trees, which has been introduced into Europe in the 1930s. We have determined partial nucleotide and deduced amino acid sequences of the ORF A of 47 CHV-1 isolates collected in Europe over a period of 28 years. Phylogenetic analysis revealed the presence of four groups or single viruses, which showed sequence divergences ranging from 11 to 19%. These results confirm the previous subtype classification based on RFLP markers, with the exception of the two CHV-1 subtypes E and D, which appear to be related closer than anticipated previously. Dates of divergences between CHV-1 subtypes, calculated from nucleotide substitution rates, indicate that the CHV-1 subtypes diverged several hundreds years ago. Our results suggest that the genetic variation among CHV-1 subtypes did not evolve in Europe and support the hypothesis of multiple introductions of CHV-1 into Europe.

Differential transfer and dissemination of hypovirus and nuclear and mitochondrial genomes of a hypovirus-infected Cryphonectria parasitica strain after introduction into a natural population

Biological control of plant diseases generally requires release of living organisms into the environment. Cryphonectria hypoviruses function as biological control agents for the chestnut blight fungus, Cryphonectria parasitica, and hypovirus-infected C. parasitica strains can be used to treat infected trees. We used naturally occurring molecular marker polymorphisms to examine the persistence and dissemination of the three genomes of a hypovirus-infected C. parasitica strain, namely, the double-stranded RNA genome of Cryphonectria hypovirus 1 (CHV1) and the nuclear and mitochondrial genomes of its fungal host. The hypovirus-infected strain was experimentally introduced into a blight-infested chestnut coppice forest by treating 73 of 246 chestnut blight cankers. Two years after introduction, the hypovirus had disseminated to 36% of the untreated cankers and to 35% of the newly established cankers. Spread of the hypovirus was more frequent within treated sprout clusters than between sprout clusters. Mitochondrial DNA of the introduced fungus also was transferred into the resident C. parasitica population. Concomitant transfer of both the introduced hypovirus and mitochondrial DNA was detected in almost one-half of the treated cankers analyzed. The introduced mitochondrial DNA haplotype also was found in three resident isolates from newly established cankers. The nuclear genome of the introduced strain persisted in the treated cankers but did not spread beyond them.

Cryphonectria radicalis: rediscovery of a lost fungus

In an attempt to isolate the ascomycete Cryphonectria parasitica (Diaporthales, Valsaceae) from dead chestnut stems, we obtained three C. radicalis strains. All three strains were isolated in areas of Switzerland with high chestnut blight incidence. To confirm our species designation, we compared the three C. radicalis strains to hypovirus (hv)-free and hv-infected C. parasitica strains. The comparison revealed several distinctive characteristics. On potato dextrose agar in the dark, the C. radicalis strains produced a fluffy mycelium and small droplets of a purple exudate giving the mycelium a light pinkish appearance. On corn meal medium in the dark, the C. radicalis strains caused a color change of the medium to purple, whereas the C. parasitica strains did not cause any color change. Ascospores from C. radicalis were significantly smaller than C. parasitica ascospores and their dimensions fit within other published size ranges. Southern hybridization analysis of the two species using nuclear and mitochondrial probes support their taxonomic separation. This separation is further supported by the lack of successful interspecific crosses. In virulence tests on chestnut trees, the C. radicalis strains exhibited very low virulence, comparable to highly hypovirulent hv-infected C. parasitica strains. Our results suggest that C. radicalis still coexists with C. parasitica although at a low frequency.

Genetic variation of Cryphonectria hypoviruses (CHV1) in Europe, assessed using restriction fragment length polymorphism (RFLP) markers

A total of 72 hypovirus-infected isolates of the chestnut blight fungus Cryphonectria parasitica were sampled from nine European countries between 1975 and 1997. The double-stranded RNA of the Cryphonectria hypoviruses (CHV1) was isolated and reverse transcription (RT)-PCR products were obtained for two different regions of the viral genome (ORF A and ORF B) using primer sequences of the type species CHV1-EP713. Both PCR products of each viral isolate were digested with four restriction endonucleases recognizing sequences of four nucleotides. The restriction fragment length polymorphism (RFLP) analysis revealed 41 genetically distinct RFLP types of CHV1 with 10 types occurring more than once. Identical RFLP types were detected nine times among viruses collected in the same location. Cluster analysis based on the RFLP banding patterns separated the viral isolates into five CHV1 clusters or subtypes. Most viral isolates (64 out of 72) grouped into one large cluster which comprised all viruses from Italy (including CHV1-EP747), Switzerland, Crotia, Bosnia, Hungary, Greece, and the French island Corsica, as well as five out of 11 isolates from continental France. Two additional subtypes of CHV1 were found in France (one related to CHV1-EP713) and one each in Spain and Germany. The Swiss samples collected over a period of 20 years showed that very little RFLP variation has evolved during this time. The results of this study are consistent with the hypothesis of multiple introductions of CHV1 into Europe.

Population Structure and Disease Development of Cryphonectria parasitica in European Chestnut Forests in the Presence of Natural Hypovirulence

ABSTRACT The Cryphonectria parasitica populations in two 6-year-old European chestnut (Castanea sativa) coppices were investigated in southern Switzerland over a period of 4 years. Occurrence of white isolates indicating an infection with Cryphonectria hypovirus, vegetative compatibility groups (VCGs), hypovirulence conversion capacity, and mating types were used to characterize the populations. Sampling of randomly chosen cankers in the first year yielded 59% white isolates in one and 40% in the other population. The distribution of the VCGs and mating types was similar among white and orange isolates, indicating a homogeneous infection of the two populations by the hypovirus. Fourteen VCGs were found in the first population, 16 VCGs in the second. Altogether, 21 VCGs were determined. The same three VCGs dominated in both populations, comprising more than 60% of all isolates. Several VCGs were represented only by white isolates. Five of the six most common VCGs were clustered in two hypovirulence conversion groups, with almost 100% hypovirus transmission within each cluster. Repeated sampling of the same cankers in 1990, 1992, and 1994 did not reveal an increase of white isolates. The portion of blighted stems rose from 37% to about 60% in both plots within 4 years. In this time, chestnut blight killed 15% and competition an additional 21% of the sprouts. Predominantly, sprouts with low diameters at breast height were killed. The growth rate of new cankers was high in their first year and decreased gradually in the following years. A role of hypovirulence in the decline of disease severity was evident since (i) cankers yielding white isolates grew slower and killed considerably fewer sprouts than cankers with orange isolates; and (ii) the majority of the cankers yielded white isolates at least once during the 4-year observation period.

Gremmeniella abietina and G. laricina in Europe: characterization and identification of isolates and laboratory strains by soluble protein electrophoresis

Forty-four isolates of Gremmeniella abietina from different European regions and laboratory strains of G. abietina and Ascocalyx abietis, which originated from regenerated protoplasts, were characterized morphologically and by protein electrophoresis. On the basis of the electrophoretic profiles of all isolates tested, the North American race of G. abietina is not present in Europe. Isolates from Pinus cembra and two Finnish isolates differed slightly from the tester strain for the European race; their electromorphs were very similar to that of the European race on other hosts but differences were noticed that would support the maintenance of the variety cembrae. Gremmeniella abietina var. balsamea, common on Abies balsamea and Picea spp. in Quebec, Canada, seems to be absent from the European counterparts Abies alba and Picea abies. The isolates from P. abies belong unequivocally to the European race of G. abietina. European isolates of G. laricina were morphologically and electrophoretically indistinguishable from the North American ones. The P. cembra and Larix decidua endophytes showed the same electrophoretic profile as the isolates from diseased pines identified as Brunchorstia pinea var. cembrae. No changes in the electrophoretic patterns of laboratory strains derived from regenerated protoplasts, compared with those of the original isolates, were observed. Two isolates from Abies do not belong to any known species of Brunchorstia; on the basis of morphological, electrophoretic, and immunological evidence they belong to a taxon taxonomically close to G. abietina. Key words: Gremmeniella abietina, protein electrophoresis, Pinus cembra, Picea abies, European isolates.

Extracellular enzymes of Phytophthora infestans: endo-cellulase, β-glucosidases, and 1,3-β-glucanases

An endo-cellulase, two β-glucosidases, and two 1,3-β-glucanases from Phytophthora infestans were partially purified from the culture filtrate and their biochemical properties determined. The molecular weights were estimated by chromatography on Sephacryl S-200 and were 21 000 (endo-cellulase), 160 000 – 230 000 and 32 000 (β-glucosidases I and II), 160 000 – 230 000 and 21 000 (β-glucanases I and II). The optimal pH of the endocellulase was 6.0. The other enzymes showed the following optimal pH and temperature values: β-glucosidase 1,5.5 and 48 °C; β-glucosidase II, 5.25 and 30 °C; 1,3-β-glucanase 1, 7.0and40 °C; and 1,3-β-glucanase II, 4.5 and 45 °C. The β-glucosidase II was unstable above 30 °C, while the other enzymes remained stable to 43 °C. The β-glucosidase I did not show Michaelis–Menten kinetics for p-nitrophenyl-glucopyranoside (pNPG) and gentiobiose as substrates. The extrapolated Km value for pNPG was 1.1 mmol/L and the Km value for cellobiose was 280 mmol/L. The Km values of the β-glucosidase II were 34 mmol/L for pNPG, 340 mmol/L for cellobiose, and 42 mmol/L for gentiobiose. Finally, the Km value of the 1,3-β-glucanase II for laminarin was 0.29 g/L. The isoelectric point of the enzymes were 3.2 (endo-cellulase), 3.3 (β-glucosidase I), 4.7 (β-glucosidase II), and 3.4 (the two 1,3-β-glucanases). At 10 mmol/L, Cu2+ inhibited the β-glucosidase I by 90%, and the β-glucosidase II by about 50%. The 1,3-(3-glucanase II was inhibited 75% by Mn2+ and 35% by Cu2+.

UDP-glucose: Glucan Synthetase in Developing Cotton Fibers: I. Kinetic and Physiological Properties

A uridine diphosphate(UDP)-glucose:glucan synthetase can be demonstrated in detached cotton fibers (Gossypium hirsutum L.) and in an isolated particulate fraction from such fibers. When assayed with detached fibers, the kinetics of the glucan synthetase activity with respect to variation in substrate concentration is complex and indicates activation of the enzyme by the substrate. Activity is stimulated by Ca(2+) or Mg(2+) and beta-linked glucosides; the effect of the beta-linked glucosides is to shift the range in which substrate activation occurs to lower concentrations of UDP-glucose. At concentrations of UDP-glucose below 50 mum, addition of uridine triphosphate, in addition to beta-linked glucoside, results in significant stimulation of activity. This effect can be explained by the conversion of uridine triphosphate to UDP-glucose by UDP-glucose pyrophosphorylase, thereby raising substrate concentration to the activating range. In detached fibers, glucan synthetase activity is high at all stages of fiber development. The properties of the glucan synthetase of the isolated particulate fraction closely resemble those of the enzyme assayed in detached fibers; however, in contrast to detached fibers, the ability to detect enzyme activity is more dependent on fiber age, showing maximal activity between 16 and 18 days postanthesis, coincident with the time of rapid onset of secondary wall cellulose deposition.

UDP-glucose: Glucan Synthetase in Developing Cotton Fibers: II. Structure of the Reaction Product

The solubility properties, composition, and structure of the radioactive product synthesized from UDP-[(14)C]glucose by a highly active cotton fiber glucan synthetase have been determined. Product obtained under the following three different conditions was analyzed: at high and low substrate concentrations by detached fibers, and at high substrate concentrations with an isolated particulate preparation. The results of acetic and nitric acid digestion, enzyme digestion, total acid hydrolyses, periodate oxidation, partial acid hydrolyses, and methylation analyses all support the conclusion that the product of the glucan synthetase produced under all three assay conditions is a linear beta-(1-->3)-glucan.