DEVELOPMENT OF THE PERITHECIUM IN GNOMONIA COMARI (DIAPORTHACEAE)

Perithecia of Gnomonia comari (Ascomycetes) mature within 14 days on cornmeal agar under continuous fluorescent light at 25 C. The perithecium is initiated by a coiled, multicellular ascogonium. Branches from somatic hyphae surround the ascogonium. This hyphal envelope early differentiates into two regions: a centrum of pseudoparenchymatous cells and a peripheral wall of more elongated, flattened cells. The wall produces a long, ostiolate beak by eruption of a column of hyphae from the inner layers at the apex; the cells gradually become thick-walled and brown from the peripheral layers inward. Proliferations from the ascogonial cells near the center of the perithecium form a bowl-shaped mass of ascogenous hyphae which expands centrifugally until it appears in section as a crescentic layer across the middle of the centrum. The centrum pseudoparenchyma above this incipient hymenium disintegrates, and short abortive paraphyses extend upward from the subhymenial pseudoparenchyma into the resulting cavity. The paraphyses disintegrate as the asci develop among them. The hymenium gradually pushes downward into the disintegrating subhymenial pseudoparenchyma until it rests on the perithecial wall. Maturing asci become detached from the hymenium, fill the perithecial cavity, and pass through the ostiole. At the tip of the beak they discharge their ascospores forcibly. Diaporthaceae with abortive paraphyses may occupy an intermediate position in a series leading from forms (Gaeumannomyces graminis) with long delicate paraphyses resembling those in the Sordariaceae to forms (Stegophora ulmea) in which the centrum is entirely pseudoparenchymatous.     

MORPHOLOGICAL STUDIES IN SORDARIA FIMICOLA AND GELASINOSPORA LONGISPORA

Perithecium development in Sordaria, the type genus of the Sordariaceae, is similar to that reported in other genera of this family. Features that characterize the Sordariaceae include the differentiation of the hyphal envelope that surrounds the ascogonium into peripheral wall layers and a pseudoparenchymatous centrum. Broad paraphyses composed of delicate, multinucleate cells arise from the cells of the centrum and completely fill the perithecium, crushing the remaining pseudoparenchymatous cells against the perithecial wall. Sordaria fimicola differs from other species of Sordariaceae studied in the aggregation of the ascogenous cells to form a placenta-like mass in the base of the centrum. Consequently, the asci arise in a cluster rather than in a uniform wall layer. Incomplete observations on Gelasinospora longispora indicate that its development is typically sordariaceous.     

MORPHOLOGY OF NEURONECTRIA PEZIZA

Hanlin , Richabd T. (Georgia Expt. Sta., Experiment.) Morphology of Neuroneetria peziza . Amer. Jour. Bot. 60(1): 56–66. Illus. 1963.—Swollen tips of vegetative hyphae develop into multicellular, multinucleate ascogonia. Hyphae grow up to form a pseudoparenchymatous ascocarp wall. The ascogonia give rise to ascogenous cells from which croziers and asci form. As the ascocarp develops, an apical meristem produces many cells which are pushed downward and form a compact pseudoparenchyma in the centrum. As the asci form, the cells of the pseudoparenchyma elongate, forming central strands. These disintegrate as the asci grow up among them. Mature asci possess a thickened apical cap but no apical ring; the ascospores have longitudinal striations. The chromosome number is n = 5. The pattern of development resembles the Diapor the type of Luttrell but is unique in the formation of strands from the pseudoparenchyma. Other characters, however, indicate a closer affinity to Nectria.     

MORPHOLOGICAL STUDIES IN PODOSPORA ANSERINA

Perithecium development in Podospora anserina begins with the formation of a coiled ascogonial initial that arises as a lateral branch from a vegetative hypha. Hyphae grow up around the initial, forming an envelope that will become the ascocarp wall. As the ascocarp increases in size, several layers of thin-walled pseudoparenchyma cells form inside the wall, especially at the apex of the ascocarp. Paraphyses arise both from the base of the ascocarp and from the innermost layer of pseudoparenchyma cells and grow inward and upward, completely filling the centrum with tightly packed filaments. During development of the ascocarp the ascogonium proliferates to form ascogenous hyphae along the base of the centrum. Asci arise from the ascogenous hyphae and grow up among the paraphyses. Meristematic growth at the ascocarp apex results in the formation of an ostiole lined with periphyses. Centrum structure in P. anserina could be interpreted as intermediate between the Xylaria and Diaporthe types.     

MORPHOLOGY OF NECTRIA HAEMATOCOCCA

Ascocarp development in Nectria haematoccocca begins with the formation of deeply staining coils as lateral branches of the vegetative hyphae. As these coils develop into multicellular, multi-nucleate ascogonia, they are surrounded by a pseudoparenchymatous envelope. During ascocarp development an apical meristem produces cells that elongate downward into the centrum, forming long, filamentous, apical paraphyses. When fully developed the cells of the apical paraphyses swell, producing a tissue that is pseudoparenchymatous in appearance. The ascogonium proliferates to form a layer of multinucleate ascogenous cells across the base of the ascocarp. Asci form from the ascogenous cells by means of croziers. The asci grow up among the apical paraphyses, which disintegrate as the ascocarp matures. This pattern is typical of the Nectria-type of development, indicating that this species belongs in the Hypocreales.     

Morphology,development and cytology of Taphrina maculans Butler

Morphology, development and nuclear behavior of the ascogenous stroma and asci in the infection spots have been described inTaphrina maculans Butler. The fungus forms subcuticular and intercellular mycelium in the leaf tissues and the ascogenous layers originate through division of the subcuticular hyphal cells in the infection sites. Germination of ascogenous cells starts with their elongation in the uppermost layer forming asci and ascospores without formation of stalk cells. Meiosis of the fusion (diploid) nucleus occurs in the young ascus as in otherTaphrina species devoid of stalk cells. The haploid chromosome complement in this species consists of 3 chromosomes (n=3). All the cells in the stromatic layer are potential ascogenous cells and ascus formation continues, until all of them are exhausted in the infection spot. Eight ascospores are normally formed in each ascus, but multi-plication of ascospores may occurin situ later. Three morphologically distinct types of ascus opening are encountered, which are apparently not correlated with prevalent environment. Multiplication of ascospores after their discharge from mature asci occurs by budding proceded by a mitotic division of the spore nucleus. Blastospores (budded cells) germinate into short hyphae and binucleate condition of cells originates by mitotic division of the nucleus. Occurrence of giant cells containing 2 nuclei is often observed. Possible origin of Uredinales fromTaphrina-like ancestors has been indicated due to their close resemblance.     

MORPHOLOGY OF HYPOMYCES TRICHOTHECOIDES

Large, spirally coiled initials embedded in a subiculum develop into multicellular, multinucleate ascogonia. Hyphae grow up around them to form a prosenchymatous perithecial wall. The ascogonia give rise to multinucleate ascogenous cells from which croziers and asci form. As the ascocarp develops, an apical meristem produces uninucleate cells that elongate downward into long, slender filaments, the apical paraphyses. From a basal layer of ascogenous cells, asci grow up among the apical paraphyses, which disintegrate as the ascocarp matures. Ascospores are verrucose, with obtuse apiculi. This pattern of development is typical of the Nectria-type of Luttrell.     

Studies on the development of perithecium of Ceratocystis stenoceras

The development of the perithecium of Ceratocystis stenoceras was observed by a light microscope and by a scanning electron microscope.The fungus has developed dark brown perithecia on wheat agar medium in three days of incubation. Perithecial primordia appeared as tightly knotted coils. At the center of it an oval ascogonium was observed. The ascogonium was developed from a lateral wall of a hypha, and the hyphae covering the ascogonium branched at the basal part where the ascogonium was attached. These hyphae branched repeatedly in the developmental growth to cover the ascogonium, and it was finally covered tightly. The plasmogamy of this fungus is much probably performed by the gametangial contact. As the stage proceeded, the ascogonium elongated, the terminal and the basal portions of it swelled and cleavage of the ascogonium resulted. Each of the cleaved ascogonia germinated continuously and stretched out the ascogenous hyphae. About that time the cells consisting of perithecia were vacuolated from the center and successively dissolved, so that a space was formed in the center of the body. Ascogenous hyphae continued to develop downwards, and their end were fixed to the inner wall of the body.The upper portion of the hyphae converged to the center of the body and the ascogenous hyphae became the supporting tissue for ascus formation.Hook formation was observed prior to the ascus formation. After completion of karyogamy by hook formation, the fissure appeared on the ascus and the end portion was released. The released portion included eight ascospores. The ascus had a smooth surface and no special structure was seen on the top. As the asci were matured, they evanesced by themselves and concurrently ascospores came out. Finally the body was massively filled with ascospores.     

Perithecium development in Sordaria brevicollis

Microconidia and ascogonial coils were produced by the two strains of Sordaria brevicollis , WTA and WTa. Over 90% of the microconidia, which functioned chiefly for sexual reproduction, germinated producing short–lived germ tubes. Ascogonial coils with conspicuous trichogynes were observed. A hypha was initiated from the base of the ascogonial coil and soon completely surrounded it, giving rise to the protoperithecium. The ascogonial coil became the ascogonium within the proto–perithecium, and it was surrounded by a pseudoparenchymatous centrum. Many paraphyses arose from pseudoparenchymatous cells. The ascogonium followed the Sordariaceous type of development and gave rise to ascogenous hyphae, croziers, unitunicate asci and ascospores. Anomalous perithecia were observed and perithecia reached maturity 9–1 1 days after inoculation.     

THE DEVELOPMENT AND CYTOLOGY OF PYCNIDIOPHORA DISPERSA

Ascocarp development in Pycnidiophora dispersa is similar to that in Phaeotrichum. A stroma originates in an intercalary position on a hypha. It increases in size, and the outer cell layer differentiates to form the wall. The ascogenous system forms from a mass of fertile cells in the center of the centrum. These become enlarged and multinucleate and give rise to ascogenous hyphae which form asci at their tips by means of croziers. In time, most of the cells of the centrum become fertile and give rise to ascogenous hyphae. There are no sterile threads in the centrum and no hymenium is present, the asci being scattered throughout the locule. The haploid chromosome number is n = 6.     

Programmed ascospore death in the homothallic ascomycete Coniochaeta tetraspora

Immature asci of Coniochaeta tetraspora originally contain eight uninucleate ascospores. Two ascospore pairs in each ascus survive and mature, and two die and degenerate. Arrangement of the two ascospore types in individual linear asci is what would be expected if death is controlled by a chromosomal gene segregating at the second meiotic division in about 50% of asci. Cultures originating from single homokaryotic ascospores or from single uninucleate conidia are self-fertile, again producing eight-spored asci in which four spores disintegrate, generation after generation. These observations indicate that differentiation of two nuclear types occurs de novo in each sexual generation, that it involves alteration of a specific chromosome locus, and that the change occurs early in the sexual phase. One, and only one, of the two haploid nuclei entering each functional zygote must carry the altered element, which is segregated into two of the four meiotic products and is eliminated when ascospores that contain it disintegrate. Fusion of nuclei cannot be random-a recognition mechanism must exist. More study will be needed to determine whether the change that is responsible for ascospore death is genetic or epigenetic, whether it occurs just before the formation of each ascus or originates only once in the ascogonium prior to proliferation of ascogenous hyphae, and whether it reflects developmentally triggered alteration at a locus other than mating type or the activation of a silent mating-type gene that has pleiotropic effects. Similar considerations apply to species such as Sclerotinia trifoliorum and Chromocrea spinulosa, in which all ascospores survive but half the spores in each ascus are small and self-sterile. Unlike C. tetraspora, another four-spored species, Coniochaetidium savoryi, is pseudohomothallic, with ascus development resembling that of Podospora anserina.     

MORPHOLOGY OF TRICHOMETASPHAERIA TURCICA

Ascocarps of Trichometasphaeria turcica Luttrell originated in culture as globose parenchymatous stromata within which ascogonia differentiated. As the ascostroma enlarged, stromal cells immediately above the ascogonium produced hyphal outgrowths whose tips grew downward and intertwined beneath the ascogonium. Intercalary growth of these hyphae formed a pseudoparaphysate centrum. Ascogenous hyphae near the base of the centrum produced bitunicate asci which grew upward among the persistent pseudoparaphyses. The ostiole was a broad pore resulting from dissolution of the peripheral stromal cells above the apex of the single locule. Spiny outgrowths from the peripheral cells surrounded the ostiole. The bitunicate asci and ascostromatic ascocarps place this fungus in the subclass Loculoascomycetidae. The pseudoparaphysate centrum and perithecioid ascostroma are characteristic of the Pleosporales. The apparently insignificant character of a protruding conidial hilum was the only essential feature distinguishing Helminthosporium turcicum Pass., the conidial stage of T. turcica, from H. maydis Nisik. & Miyake, a typical representative of species of Helminthosporium with perfect stages in Cochliobolus.     

STUDIES IN THE GENUS NECTRIA. II. MORPHOLOGY OF N. GLIOCLADIOIDES

Hanlin , Richard T. (Georgia Experiment Station, Experiment.) Studies in the genus Nectria. II. Morphology of N. gliocladioides. Amer. Jour. Bot. 48(10): 900–908. Illus. 1961.—Swollen tips of vegetative hyphae develop into multicellular archicarps from which multinucleate ascogonia form. From basal cells of each archicarp arise hyphae which grow up into a prosenchymatous, true perithecial wall; around this wall is formed a thin pseudoparenchymatous stroma of compacted hyphae. The ascogonia give rise to ascogenous cells from which croziers and asci form directly. At the same time, an apical meristem forms cells that grow downward into the centrum. These are pseudoparaphyses. Asci grow up among the pseudoparaphyses, which deliquesce as the ascocarp matures. The ascus tip contains a thick ring with a pore and lateral thickening of the ascus wall. Ascospores are forcibly ejected. The chromosome number is 4. This species conforms to the Nectria Developmental Type of Luttrell.     

PERITHECIAL DEVELOPMENT IN HYPOMYCES AURANTIUS

Perithecia of Hypomyces aurantius are initiated by solitary, symmetrical, hyphal coils. During development of the ascocarp, a locule forms concomitantly with centripetal paraphyses, the uppermost of which elongate downward as a palisade of narrow, septate filaments, the apical paraphyses. The initiating coil retains its integrity in the middle of the primordium and becomes the ascogenous system. Uninucleate, diploid cells are part of the ascogenous system. The ascogenous system proliferates through croziers from which asci develop. The haploid chromosome number is 4. The perithecial papillae are formed of spherical cells. This pattern of development is a modification of the Nectria-type of development and characterizes the genus Hypomyces.     

Perithecial ontogeny in erithecial ontogeny in the fungal genus Epichloe: An examination of the claviciptalean centrum

The structure and development of perithecia in five collections of Epichloe from Europe and North America were studied. Perithecia in early stages of development are oblong to ovate in overall shape. Dichotomously branched paraphyses form on the bottom and sides of the inner walls of the perithecial primordium. As the ovate primordium expands, a mound of ascogenous mycelium develops in its base. As asci develop from the ascogenous mound, paraphyses proximal to asci evanesce and no paraphyses are observable within the cluster of asci. In E. amarillans and E. baconii paraphyses are converted into pseudoparenchyma-like tissues, while in E. typhina paraphyses remain filamentous until they evanesce. Ascospore development is seen to differ among all three species of Epichloe. The development and structure of the Epichloe centrum are compared to those of the Nectria and Xylaria types. It is apparent that a distinct type of centrum is present in Epichloe, and perhaps all of the Clavicipitaceae. It is proposed that the Epichloe type centrum may represent a key feature for distinguishing the Clavicipitaceae from the Hypocreaceae or other groups of pyrenomycetes.     

ULTRASTRUCTURE OF ASCOCARP DEVELOPMENT IN SPORORMIA AUSTRALIS

Thin sections taken from intact ascocarps were examined to trace the developmental sequence of ascocarp formation in Sporormia australis Speg. The ascocarp originated from a uninucleate vegetative hyphal cell which underwent repeated divisions and formed an ascostroma. In the center of the young ascostroma a cavity formed, apparently from cell disintegrations, and enlarged as the ascocarp enlarged. Within the cavity pseudoparaphyses developed from undifferentiated pseudoparenchymatous cells at the apex of the cavity and extended downward. Ascogenous hyphae arose from proliferating uninucleate cells at the base of the cavity. As the ascocarp matured, the pseudoparenchymatous cells differentiated into three layers, none of which were considered homologous to the perithecial wall lining the cavity of pyrenomycetes. The cells of the apex were not differentiated into layers and light microscopy revealed the presence of an ostiole through which bitunicate asci discharged their eight 4-celled ascospores.     

The morphology of Cercophora palmicola (Lasiosphaeriaceae)

A detailed study of ascomal morphology and development in Cercophora palmicola showed that ontogeny is ascohymeniaceous, giving rise to an ostiolate perithecium. Ascomal initials consist of a coiled ascogonium surrounded by several layers of hyphae whose cells become pseudoparenchymatous. The centrum of the young ascoma is composed of a few rows of large, thin-walled pseudoparenchymatous cells that line the ascomal wall, with the central region filled by tightly packed, filamentous paraphyses. The ascogenous system forms along the inside of the layer of pseudoparenchymatous cells at the base of the paraphyses and gives rise to unitunicate asci that grow up among the paraphyses. The wall of the mature perithecium is greatly thickened. It is composed of three regions: a thin outer region of darkly pigmented, angular cells with thickened walls; a broad central region of cells with gelatinized walls; and a thin inner region of flattened cells. Ascomal ontogeny in C. palmicola conforms well to the Sordaria type of development, as defined by Huang.     

CENTRUM DEVELOPMENT IN DIDYMELLA BRYONIAE

Early stages of pseudothecium development consist of small pseudoparenchymatous stromata in which ascogonia differentiate. Deeply staining cells in the apical region of the young pseudothecium elongate to form pseudoparaphyses, which grow down to fill the centrum. Ascogenous hyphae grow out from ascogenous cells, located in the basal plectenchyma, and croziers arise and proliferate from the ascogenous hyphae. Bitunicate asci grow up among the pseudoparaphyses and forcibly discharge two-celled hyaline ascospores at maturity. Because centrum development in Didymella bryoniae (Auersw.) Rehm is pseudoparaphysate, the causal agent of gummy stem blight in watermelon is properly placed in the order Pleosporales. The placement of this species in Didymella on the basis of the Ascochyta cucumis Fautr. et Roum. anamorph is supported by centrum structure.     

New fungal genera, Tectonidula gen. nov. for Calosphaeria-like fungi with holoblastic-denticulate conidiogenesis and Natantiella gen. nov. for three species segregated from Ceratostomella

Two morphologically similar groups of ascomycetes with globose to subglobose perithecia, elongate necks, unitunicate asci floating freely at maturity, and hyaline ascospores currently placed in Calosphaeria s. lat. and Ceratostomella s. lat., respectively, are studied. The Calosphaeria-like fungi have groups of perithecia growing between cortex and wood, arranged in circular groups with converging necks and piercing the cortex in a common point; the asci with a shallow apical ring and U- to horseshoe-shaped hyaline ascospores are compared with Calosphaeria pulchella, the type species of the genus. Conidiogenesis of the investigated Calosphaeria-like fungi is holoblastic-denticulate; ramichloridium-like and sporothrix-like conidiophores and conidia were formed in vitro. Ascospore and ascus morphology, structure of the ascal apex, ascogenous system, mode of conidiogenesis and the large subunit rRNA sequences of this group differ considerably from C. pulchella and both groups are unrelated. Thus a new genus, Tectonidula, is described with two accepted species, T. hippocrepida and T. fagi; they are separated by ascospore and ascus morphology and holoblastic-denticulate conidiogenesis from the core species of Calosphaeria. The placement of Tectonidula among perithecial ascomycetes is discussed. The relationship of Tectonidula with Barbatosphaeria and two ramichloridium-like hyphomycetous genera Rhodoveronaea and Myrmecridium is investigated. Three species formerly attributed to Ceratostomella are studied. The revision of the herbarium type specimen and fresh material of Ceratostomella ligneola revealed that it is conspecific with Ceratostomella ampullasca and Ceratostomella similis. The LSU phylogeny clearly separated C. ligneola from Ceratostomella s. str. and morphologically similar Lentomitella. On the basis of molecular sequence data and detailed comparison of morphology of asci, ascospores and ascogenous system the genus Natantiella is described for C. ligneola with C. ampullasca and C. similis as its synonyms. Natantiella produced sterile mycelium in vitro.     

Morphology and development of Nigrosabulum globosum, a cleistothecial coprophile in the Bionectriaceae (Hypocreales)

Recent DNA sequence analyses indicated that Nigrosabulum globosum is a cleistothecial representative of the Bionectriaceae in the Hypocreales, but morphological characters supporting this relationship are unknown. Using light and electron microscopy we followed the development of the ascomata of this species, from the formation of gametangia through to the development of mature ascospores, and observed a series of characters that confirmed its hypocrealean affinities. These included the formation of a gel-filled centrum during early stages of ascoma development, the subsequent appearance of hyaline peridial tissue enclosed within a layer we interpret as representing a melanized uniloculate stroma, apically derived paraphyses, and an ascogenous system that gives rise to asci that were both cylindrical to clavate and globose. Ascospores, previously reported to be smooth, were ornamented with a honeycomb-like reticulum and were able to germinate within the ascoma. The carbonaceous outer (stromatic) walls of the mature, grit-like cleistothecia indicate possible resistance to UV radiation and desiccation. Furthermore, the complement of germinated ascospores would enable mature ascomata to function as propagules that could quickly initiate new growth when transferred to fresh substrate. Our reexamination of N. globosum also provides data that support the hypothesized close relationship with other bionectriaceous, cleistothecial coprophiles, i.e., species of Hapsidospora, and Bulbithecium in particular.