Scanning Electron Microscopy of Ascospores of Schwanniomyces

Ascospores of the four recognized species of Schwanniomyces were examined by scanning electron microscopy. Spores of S. alluvius, S. castellii, and S. occidentalis, which were essentially identical, had abundant, long protuberances and wide, thin equatorial rings. The two known strains of S. persoonii differed from the other species as well as from each other. One strain had spores with a wide ring but only a few short protuberances; spores from the second strain were covered with craterlike depressions and had a narrow ring. Also examined were spores of Schwanniomyces hominis (=Saccharomyces rosei) which lacked a ring and were covered with short irregularly shaped protuberances, a finding consistent with the morphology of spores from other strains of S. rosei.     

Homothallism in Sclerotinia minor

Sclerotinia species are sexually reproducing ascomycetes. In the past S. minor and S. sclerotiorum, have been assumed to be homothallic because of the self-fertility of colonies derived from single ascospores. S. trifoliorum has previously been shown to be bipolar heterothallic due to the presence of four self-fertile and four self-sterile ascospores within a single ascus [Uhm, J.Y., Fujii, H., 1983a. Ascospore dimorphism in Sclerotinia trifoliorum and cultural characters of strains from different-sized spores. Phytopathology 73: 565–569]. However, isolates of S. minor and S. sclerotiorum were proven to be homothallic ascomycetes, by self-fertility of all eight ascospores within an ascus. Apothecia were raised from all eight ascospores of a single tetrad from four isolates of S. minor and from an isolate of S. sclerotiorum, indicating that inbreeding may be the predominant breeding mechanism of S. minor. Ascospores from asci of S. minor and S. sclerotiorum were predominantly monomorphic, but rare examples of ascospore dimorphism similar to S. trifoliorum were found.     

Ultrastructure of asci and ascospores of the mangrove ascomyceteDactylospora haliotrepha

Ultrastructure of the marine LoculoascomyceteDactylospora heliotrepha is presented and compared withMarinosphaera mangrovei, Swampomyces armeniacus and other marine species. Ascospores are bi-celled and ridged. The ridges are outgrowths of the outer mesosporial layer and formed later in ascosporogenesis. The exosporial layer fragments to release mucilaginous material present between the spore wall ridges. Asci and pseudoparaphyses are held together by a fibrillar mucilaginous network. The endoascus is thicker than the ectoascus. Comparisons are made of the diameter of ascomata, size of asci and ascospores ofD. heliotrepha collected from mangroves in Hong Kong, Malaysia, the Philippines and Taiwan.     

石蕊属某些地衣共生菌的培养研究

本文对石蕊属15个种子囊孢子进行了培养特性的研究.所有种子囊孢子均在12小时内萌发,并且前7-15天生长迅速,以后逐渐缓慢.随着培养时间增长.分离物可形成有特征性的菌落形态和色素,利用生长型和菌落及培养基中色素产生情况可将不同分离物区分开.对石蕊属的常规培养很有希望成为识别该属成员的有用特征.     

The roles of ascospores and conidia of Pyrenopeziza brassicae in light leaf spot epidemics on winter oilseed rape (Brassica napus) in the UK

Ascospores of Pyrenopeziza brassicae were produced in apothecia (cup‐shaped ascomata) on oilseed rape debris. The conidia, which were morphologically identical to the ascospores, were produced in acervular conidiomata was greater than for lesions caused by ascospores. In June 2000, on the ground under a crop with light on the surface of living oilseed rape tissues. Ascospores were more infective than conidia on oilseed rape leaves. The proportion of lesions caused by conidia located on leaf veins leaf spot, numbers of petioles with apothecia decreased with increasing distance into the crop from the edge of pathways. Air‐borne ascospores of P. brassicae were first collected above debris of oilseed rape affected with light leaf spot on 5 October 1998 and 18 September 1999,12 or 23 days, respectively, after the debris had been exposed outdoors. P. brassicae conidia were first observed on leaves of winter oilseed rape on 6 January 1999 and 15 February 2000, respectively, after plots had been inoculated with debris in November 1998 and October 1999. In 1991/92, numbers of ascospores above a naturally infected crop were small from January to April and increased in June and July. P. brassicae conidia were first observed in February and the percentage plants with leaves, stems or pods with light leaf spot increased greatly in May and June. In 1992/93, in a crop inoculated with debris, numbers of airborne ascospores were small from October to January and increased from April to June. P. brassicae conidia were first observed on leaves in late November and light leaf spot was seen on stems and pods in March and June 1993, respectively.     

Overwintering of Sphaerotheca humuli, the cause of hop powdery mildew

The ability of Sphaerotheca humuli to overwinter as cleistocarps in infected hop cones and leaves and in aerial buds on rootstocks was examined during the winters of 1970-1, 1971-2 and 1972-3. Periodical examination of cleistocarps, collected in October and overwintered in Terylene bags on the soil of a hop garden, consistently revealed two periods of maturation ending in November and in March, when over 50% contained eight, well-defined ascospores. In laboratory tests cleistocarps, kept either in the hop garden or dry at 4, 8 or 18^oC during the winter, could not be encouraged to dehisce earlier than April when naturally dehisced cleistocarps were first detected in the field. More ascospores were discharged from cleistocarps, and germination of ascospores in laboratory tests was greater, at 18 than at 4, 8 or 24^oC. Colonies of S. humuli arose on leaves of potted plants exposed to overwintered cleistocarps in the hop garden and were observed microscopically to originate from ascospores. However, a Burkard spore trap, operated amidst the cleistocarps in this garden in 1972 and 1973, failed to detect ascospores. Ascospores, discharged onto susceptible leaves in the laboratory, germinated but failed to produce colonies. It was demonstrated that S. humuli can perennate in aerial, dormant buds on hop rootstocks. Examination of buds in autumn revealed mycelium external to and between the bud scales. At budburst the mycelium was still present internally. Cleistocarps were occasionally associated with hibernating mycelium. Primarily infected shoots arose from plants bearing infected buds in conditions which precluded chance infection. Some evidence was obtained that conditions during the winter determine the success of survival in buds. The fungus appeared to be incapable of infecting a selection of weeds common to hop gardens and their vicinity.     

Importance of ascospore ornamentation in the taxonomy of Daldinia

Representative specimens of fifteen Daldinia spp. were studied for ultrastructural characteristics of their ascospores by scanning electron microscopy (SEM). The ornamentation of their outermost spore layers was found to be species-consistent, confirming the results of concurrent studies on the morphology of their teleomorphs and anamorphs, secondary metabolite profiles and PCR-based genetic fingerprints. Daldinia spp. may either show smooth or transversally striated ascospores. The spores of the species within the latter group are always ellipsoid-equilateral to ellipsoid-inequilateral with narrowly rounded ends. Smooth, broadly ellipsoid to cylindrical ascospores were observed in all species (D. caldariorum, D. fissa and D. loculata) that are known to produce their stromata on substrates damaged by fire. The ascospores of D. concentrica differed from those of D. childiae (i.e., the cosmopolitan taxon previously regarded as D. concentrica ss. auct.) and other Daldinia spp. in showing a very faint ornamentation, which only became visible at 10000× magnification by SEM. A specimen collected on the isle of Jersey (Channel Islands, UK) showed morphological similarities to the pantropical D. eschscholzii, but its ascospores appeared smooth by SEM, and it may therefore represent a previously undescribed species. Dedicated to Professor Yoshinori Asakawa, Tokushima, Japan, on the occasion of his 60^th birthday PH-R Life Science Center Natural Products     

<Emphasis Type="Italic">Kretzschmaria varians</Emphasis> sp. nov., <Emphasis Type="Italic">Xylaria coremiifera</Emphasis> sp. nov. and <Emphasis Type="Italic">Xylaria umbonata</Emphasis> sp. nov. from Costa Rica

Kretzschmaria varians, a species apparently related to K. micropus, is described as new. It is distinguished primarily by having asci with 2 to 8 ascospores with inconstant germination slit length and remains of synnemata on stromata and surrounding substrate. Xylaria coremiifera, described here as new, bears small fragile coremia on pulvinate stromata and the surrounding substrate. Asci often have fewer than 8 ascospores, most frequently 4. Xylaria umbonata, described here as new, produces perithecia around a central umbo that appears to be the remains of a synnema. Ascospores have long spiralling germination slits.     

Development and dehiscence of the cephalothecoid peridium in Aporothielavia leptoderma shows it belongs in Chaetomidium

The development of the cephalothecoid peridium of Aporothielavia leptoderma was examined using light and electron microscopy. Early stages in ascoma initiation were consistent with previous reports for other species in the Chaetomiaceae. However, as young cleistothecia increased in size, clusters of peridial cells in the outer textura angularis elongated in a radial pattern around a central cell or cell cluster to form rosettes of relatively thick-walled segments that marked the central areas of incipient cephalothecoid plates. The external flank along median portions of the radial cells became thin walled and swelled outwards so that each plate became concave and was separated from adjacent plates by a more or less circular to polygonal ridge of knuckle-shaped swellings. When dry, mature peridia split apart along some of the ridges demarcating individual plates but an internal mechanism for liberating ascospores from the confines of the ascoma was not observed. Physical disturbance of mature cleistothecia by beetles, when enclosed together in a Petri dish, shattered the peridia, liberating the ascospores. Smaller insects were unable to cause disarticulation of the cephalothecoid plates. Because of the presence of an apical germ pore in the ascospores and morphological similarity to Chaetomidium arxii, the new combination Chaetomidium leptoderma (syn. Thielavia leptoderma) comb. nov. is proposed.     

Airborne Ascomycotina on the island of Crete: Seasonal patternsbased on an 8-year volumetric survey

An 8-year study was conducted on the island of Crete in order to identify airborne ascospores and to determine their seasonal pattern. A Burkard 7-day, volumetric spore-trap was continuously operated in the city of Irakleion – located in the center of the island – from 1994 through 2001. Relatively „high” ascospore counts (20 – 48 spores/m ³) were obtained from mid-spring through summer, while the rest of the year exhibited lower activity (8–16 spores/m³). The predominant ascospores identified were those of Leptosphaeria and Chaetomium; their concentrations varied from 1 or 2 spores up to a few dozens of spores/m³. Other spores encountered sporadically were: Ascobolus, Endophragmiella, Didymella, Diatrypaceae, Leptosphaerulina, Massaria, Pleospora, Sporormiella, Xylaria. The mean daily concentration of all identified ascospores was 30/m³ for the entire study period, corresponding to 13.9% of the total fungal load. Ascospores have been recognized as important inhalant allergens and have been implicated as contributing to symptoms of both rhinitis and asthma.     

Observations on gymnoascaceae. IX. A new species of pseudoarachniotus from soil-burial beds

Summary A new species ofPseudoarachniotus P. marginosporus, is described and illustrated. The developmental morphology of this new ascomycete is discussed. On a standard medium such as YpSs,P. marginosporus can be distinguished from other species of the genus by colonial coloration which varies from ochre-rust to very pale yellow at different stages of maturation. The colony ofP. roseus is red, red-orange or orange-yellow;P. citrinus is lemon yellow to brownish yellow in age;P. reticulatus is red orange andP. hyalinosporus is yellowish and usually with a great deal of green pigmentation in the mycelium and in the medium. Furthermore ascospores ofP. marginosporus are oblate, small and thin-walled, measuring 2.2–3.0×4.0–4.4 µ, with a minute elevated rim around the long axis, while ascospores ofP. reticulatus are globose and reticulate, and those ofP. roseus andP. citrinus are large and thick-walled, measuring about 4.4×7.7 µ. Ascospores ofP. hyalinosporus are similar in size and shape to those ofP. marginosporus, but lack a rim or other markings.     

The radiation resistance of ascospores and sclerotia of Pyronema domesticum

The Food and Drug Administration has become aware of several instances where supposedly sterile medical surgical products made of Chinese cotton have been found to contain viable Pyronema domesticum. The aim of this research was to determine the gamma and electron beam radiation resistance values for the two dormant phases (ascospores and sclerotia) of P. domesticum. The resistance values were obtained by developing a standardized system to cultivate, purify, and harvest biological indicators containing sclerotia or ascospores. Ascospores were more resistant to radiation than sclerotia. The D ₁₀ values for sclerotia were 0.79 and 1.09 kGy for strains 32030 and 14881, respectively. The resistance value for wild type ascospores was 2.83 kGy. The current standard for assuring radiation sterilization of medical devices is ISO 11137. This standard was developed to address the propensity for highly radiation-resistant organisms such as P. domesticum. Prior to the standard, biological indicators such as Bacillus pumilus, having a nominal D ₁₀ value or 1.7 kGy, were used to determine the sterility of many medical devices. Journal of Industrial Microbiology & Biotechnology (2002) 29, 51–54 doi:10.1038/sj.jim.7000267 Received 09 October 2001/ Accepted in revised form 08 April 2002     

Fine structures on the surface of nuptial pads of male hylid and rhacophorid frogs

Nuptial pads, secondary sexual characteristics of male frogs, develop on the first digit of the hand of Hyla japonica in the family Hylidae and of Rhacophorus schlegelii in the family Rhacophoridae, and on both the first and second digits of the rhacophorids Buergeria buergeri and B. japonica. By scanning electron microscopy (SEM), it was seen that numerous mounds covered the surface of the pads. Mounds were similarly hemispherical in R. schlegelii and B. buergeri and flat in B. japonica. The mounds of H. japonica were irregular in shape and size and some of them stood in rows. Fine columnar protuberances were present all over the surfaces of the mounds in this species. Numerous peg-like protuberances projected radially upward from the top of the mounds in B. buergeri and B. japonica. Irregular-shaped, leaf-like protuberances bearing knobby or rod-shaped apical protrusions were present on the top of the mounds in R. schlegelii. In pads observed by transmission electron microscopy, the outermost epithelial monolayer of the mounds was generally thick, especially at the top, compared to that of the rest of the skin. Epidermal cells in this layer were well keratinized, devoid of organelles, and contained closely packed, fine filaments within a dense matrix. Apical accessory protuberances projecting from the outermost cells were also packed with dense filamentous materials, showing rigid comb-like structures. © 1994 Wiley-Liss, Inc.     

Comparative studies on the mycorrhization of Larix decidua and Picea abies by Suillus grevillei

Summary Mycorrhization of Picea abies has been achieved, for the first time, with six strains of Suillus grevillei by a new culture method, using activated charcoal paper and liquid medium as a substrate. Mycorrhization of P. abies and Larix decidua was compared, and the process was found to be significantly different in the two tree species. S. grevillei is not incompatible with P. abies, but it forms mycorrhizae more readily with L. decidua. Hyphal growth was clearly stimulated on the surface of roots of Larix but retarded on Picea. A well organized Hartig net was formed with both tree species, but wall protuberances were frequently observed on the outer cell walls of Picea cortex cells when the Hartig net was not fully developed. No conspicuous cell wall reactions occurred in Larix roots. Cell wall protuberances may be comparable to those in transfer cells and are interpreted as an alternative to Hartig net development. Anatomical differences between roots of Larix and Picea, and physiologically active substances such as recognition factors on the root surfaces, are discussed with respect to their responsibility for the different reactions of S. grevillei.     

The meiosis‐specific APC activator FgAMA1 is dispensable for meiosis but important for ascosporogenesis in Fusarium graminearum

Ascospores are the primary inoculum in Fusarium graminearum. Interestingly, 70 of its genes have premature stop codons (PSC) and require A‐to‐I editing during sexual reproduction to encode full‐length proteins, including the ortholog of yeast Ama1, a meiosis‐specific activator of APC/C. In this study, we characterized the function of FgAMA1 and its PSC editing. FgAMA1 was specifically expressed during sexual reproduction. The Fgama1 mutant was normal in growth and perithecium formation but defective in ascospogenesis. Instead of forming four‐celled, uninucleate ascospores, Fgama1 mutant produced oval, single‐celled, binucleated ascospores by selfing. Some mutant ascospores began to bud and underwent additional mitosis inside asci. Expression of the wild‐type or edited FgAMA1 but not the uneditable allele complemented Fgama1. In the Fgama1 x mat‐1‐1 outcross, over 60% of the asci had eight Fgama1 or intermediate (elongated but single‐celled) ascospores, suggesting efficient meiotic silencing of unpaired FgAMA1. Deletion of FgPAL1, one of the genes upregulated in Fgama1 also resulted in defects in ascospore morphology and budding. Overall, our results showed that FgAMA1 is dispensable for meiosis but important for ascospore formation and discharge. In F. graminearum, whereas some of its targets are functional during meiosis, FgAma1 may target other proteins that function after spore delimitation.     

Quantification of Monosporascuscannonballus Ascospores in Muskmelon Fields in Eastern Spain

The populations of Monosporascuscannonballus ascospores in the soils of 14 muskmelon fields throughout muskmelon production areas of Comunidad Valenciana (eastern Spain) were quantified from 2002 to 2003. The fields were surveyed in July, at the end of the cropping season, when plants approached maturity and symptoms of vine decline in the canopy appeared as patches of wilted or dead plants. Ascospores were recovered from all muskmelon fields surveyed. The average soil populations ranged from 1.54 to 6.33 per g of soil and the number of ascospores within a soil sample ranged from 0.50 to 16.20 ascospores/g of soil. This is the first detailed report on ascospore populations of M. cannonballus in muskmelon fields from a cucurbit‐growing area in Spain and the Mediterranean basin.     

CENTRUM DEVELOPMENT IN DIDYMOSPHAERIA SADASIVANII (PLEOSPORALES)

Development of a typical pseudoparaphysate centrum in Didymosphaeria sadasivanii Ramachandra-Reddy indicates that this ascomycete is properly placed in the Pleosporaceae despite the fact that forcible discharge of ascospores from bitunicate asci has not been demonstrated. The relatively thin-walled asci releasing ascospores within the ascocarp in D. sadasivanii, as in Cochliobolus spp., probably were derived by reduction from the bitunicate type. Ascocarps matured on malt agar slants but developed more rapidly and normally on autoclaved alfalfa stems inoculated in medicine bottles and transferred to moist filter paper in large petri dishes when covered by mycelium.     

Proterochampsa barrionuevoi (Archosauriformes: Proterochampsia) from the Late Triassic (Carnian) of Argentina and a phylogenetic analysis of Proterochampsia

Abstract: Restudy of skulls and available postcrania of the proterochampsian archosauriform Proterochampsa barrionuevoi from the Ischigualasto Formation (Upper Triassic, Carnian) in the San Juan Province, Argentina, confirms that the genus is diagnosed by autapomorphies that include dermal sculpturing consisting of prominent ridges and nodular protuberances, a large hook‐like lateral projection on the quadratojugal, an antorbital fossa restricted to a depression along the maxilla, lateral expansion of the premaxilla anterior to the premaxilla–maxilla contact, absence of a supratemporal fossa, exclusion of jugal from suborbital fenestra, basal tubera of parabasisphenoid facing ventrally and reaching laterally beyond the basipterygoid process, and a ventral lamina on the angular. Proterochampsa nodosa is a valid species distinguished from P. barrionuevoi by fewer cranial ridges with larger protuberances, relatively smaller supratemporal fenestrae and width of frontals between orbits less than that of the nasals. A phylogenetic analysis supports the monophyly of Proterochampsia consisting of Proterochampsa, Chanaresuchus bonapartei, Gualosuchus reigi, Tropidosuchus romeri and Cerritosaurus binsfeldi. A temporal separation between the two basal proterochampsians with earliest records in the Late Triassic (Proterochampsa and Cerritosaurus) and Chanaresuchus, Gualosuchus and Tropidosuchus in the Middle Triassic indicates hidden proterochampsian diversity in the Middle Triassic.     

Effects of temperature on germination and hyphal growth from ascospores of A-group and B-group Leptosphaeria maculans (phoma stem canker of oilseed rape)

Ascospores of both A‐group and B‐group Leptosphaeria maculans germinated at temperatures from 5–20°C on distilled water agar or detached oilseed rape leaves. After 2 h of incubation on water agar, some A‐group ascospores had germinated at 10–20°C and some B‐group ascospores had germinated at 5–20°C. The percentages of both A‐group and B‐group ascospores that had germinated after 24 h of incubation increased with increasing temperature from 5–20°C. The observed time (Vo₅₀) which elapsed from inoculation until 50% of the spores had germinated was shorter for B‐group than for A‐group ascospores. Germ tube length increased with increasing temperature from 5–20°C for both ascospore groups. Germ tubes from B‐group ascospores were longer than germ tubes from A‐group ascospores at all temperatures tested, but the mean diameter of germ tubes from A‐group ascospores (1.8 μm) was greater than that of those from B‐group ascospores (1.2μm) at 15°C and 20°C. The average number of germ tubes produced from A‐group ascospores (3.8) was greater than that from B‐group ascospores (3.1) after 24 h of incubation at 20°C, on both water agar and leaf surfaces. Germ tubes originated predominantly from interstitial cells or terminal cells of A‐group or B‐group ascospores, respectively, on both water agar and leaf surfaces. Hyphae from A‐group ascospores grew tortuously with extensive branching, whilst those from B‐group ascospores were predominantly long and straight with little branching, whether the ascospores were produced from oilseed rape debris or from crosses between single ascospore isolates, and whether ascospores were germinating on water agar or leaf surfaces.