Perithecial Initials Research Articles

Observations on the Biology of Ophiodothella angustissima

Ophiodothella augustissima causes a leafspot disease on shrubs of Vaccinium arboreum . In autumn, diseased leaves bearing lesions fall to the ground where they overwinter. These lesions contain perithecial initials that mature with the advent of warm temperatures and spring rains, conditions that also favor the development of new leaves on the host. Mature perithecia contain asci with ascospores that are forcibly ejected upward onto young host leaves, which they infect. These new lesions grow and produce an acervular stage that forms numerous conidia that spread the disease throughout the plant during the summer. The timing of these events is determined by weather conditions, especially rainfall. As infected leaves dehisce in autumn, they remain beneath the shrubs, where they overwinter, ready to begin the cycle again the following spring.

Perithecial Development by Gibberella zeae: A Light Microscopy Study

Gibberella zeae (anamorph Fusarium graminearum) is the causal agent of head blight, and foot and crown rots of wheat, corn, oats and barley. The developmental sequence of perithecia from homothallic Group II isolates of G. zeae was traced by light microscopy. Cultures induced to form perithecia produced wide hyphae with two or more nuclei per cell that gave rise to perithecial initials composed of undifferentiated, uninucleate cells. Neither ascogonia nor antheridia were observed. The ascogenous system arose from cells in the inner wall of the young perithecium and as the perithecium matured, formed a hymenium at the base of the centrum. Apical paraphyses, differentiated from cells in the upper periderm, grew downward and became attached to the hymenium. In the central axis of the perithecium, the ostiole formed from small, darkly-staining, uninucleate cells that differentiated into the periphyses. Once the apical paraphyses were completely developed, typical croziers formed in the hymenium. As the asci elongated, the apical paraphyses collapsed, although their walls remained intact between the asci. Mature asci contained eight, four-celled ascospores in a biseriate arrangement. The ascus walls were simple with a slight thickening at the tip.

Perithecial development by Gibberella zeae: a light microscopy study

Gibberella zeae (anamorph Fusarium graminearum) is the causal agent of head blight, and foot and crown rots of wheat, corn, oats and barley. The developmental sequence of perithecia from homothallic Group II isolates of G. zeae was traced by light microscopy. Cultures induced to form perithecia produced wide hyphae with two or more nuclei per cell that gave rise to perithecial initials composed of undifferentiated, uninucleate cells. Neither ascogonia nor antheridia were observed. The ascogenous system arose from cells in the inner wall of the young perithecium and as the perithecium matured, formed a hymenium at the base of the centrum. Apical paraphyses, differentiated from cells in the upper periderm, grew downward and became attached to the hymenium. In the central axis of the perithecium, the ostiole formed from small, darkly-staining, uninucleate cells that differentiated into the periphyses. Once the apical paraphyses were completely developed, typical croziers formed in the hymenium. As the asci elongated, the apical paraphyses collapsed, although their walls remained intact between the asci. Mature asci contained eight, four-celled ascospores in a biseriate arrangement. The ascus walls were simple with a slight thickening at the tip.

Economic importance and cycle of Polystigma ochraceum, causing red leaf blotch disease of almond, in Lebanon

The red leaf blotch disease, incited by the pathogen Polystigma ochraceum, is a major disease of almonds in Lebanon. An investigation was conducted to study the severity of the disease in almond‐growing areas of Lebanon and the cycle and developmental stages of the pathogen in an almond orchard in the coastal area. The disease was found to be widespread and severe in the coastal and mountainous areas, moderate in the north, and mild in the interior Bekaa plain. Ascospore discharge began in early February, just before flowering, and continued until mid‐May. Maximum ascospore discharge occurred about one month after flowering. Pycnidia started to form in the stromata when turning red in colour and acquiring a crusty appearance. Perithecial initials appeared later during the month of July, but continued their development and maturation during autumn and winter to start discharging their ascospores in February. The pathogen could not be grown in vitro on culture media. No secondary infections by pycnidiopores were noticed.

The Development of Diaporthe phaseolorum Variety Sojae in Culture

The development of the Phomopsis state of Diaporthephaseolorum var. sojae is described briefly. Both a and J conidia are produced from similar phialides. The isolate studied is homothallic but has trichogynes or trichogyne-like hyphae in early developmental stages. Perithecia develop from initials that include an ascogonial coil surrounded by enveloping hyphae. Perithecial initials ultimately differentiate into an outer peridium, a prominent centrum pseudoparenchyma layer, and paraphyses. Peridial and centrum hyphae in the apical region proliferate early in development to produce an elongate, periphysis-lined neck. The ascogenous system develops from the terminal portion of the ascogonial coil by septation of coil cells and subsequent production of short, ascogenous hyphae. The ascogenous hyphae proliferate to form a hemispherical basal hymenium. Asci are produced from croziers. The asci become detached from the hymenium and fill the centrum, compressing paraphyses and pseudoparenchyma. Development of D. phaseolorum var. sojae is believed to be a variation of the basic developmental pattern known in some other Pyrenomycetes. Data obtained from developmental studies of perithecia play an important role in current systematic concepts of pyrenomycetous fungi. The major source of this emphasis comes from Luttrell's comprehensive review (26) of perithecial development where developmental patterns were conceived as centrum types characteristic of various taxonomic groups. The present study is the third in a series of investigations of perithecial development in representative Pyrenomycetes. Previous studies on Hypoxylon serpens (Pers. : Fr.) Kickx (17) and Gelasinospora reticulospora (Greis & Greis-Dengler) Moreau & Moreau (18) revealed that perithecial development in these fungi could be viewed as a variation on the same basic ontogenetic pattern. Nonetheless, these two fungi belong to different families and represent the Xylaria and Sordaria perithecial centrum types, respectively. An additional centrum type believed to represent the Diaporthales has received little detailed study. The Diaporthe type centrum has traditionally been depicted as lacking paraphyses in the perithecium, although Luttrell himself has questioned the universality of this concept (27). More recently, studies in the genus Gnomonia by Fayret and Parguey-Leduc (10) and Huang and Luttrell (16) have provided evidence that paraphyses exist in fungi that are unquestionably members of the Diaporthales. There have been, however, no comprehensive developmental studies on Diaporthe, the type genus of the Diaporthales. The present study was therefore undertaken.

The developmental morphology of Hypoxylon serpens in culture

The perithecial development of Hypoxylon serpens (Pers. ex Fr.) Kickx in artificial culture is described. Perithecia develop from initials formed within the vegetative mycelium. Perithecial initials include an ascogonium and surrounding envelope. The ascogonium gives rise to ascogenous elements and eventually asci. The envelope gives rise to all sterile structures, including paraphyses and pseudoparenchyma. Features ofHypoxylon serpens perithecia are representative of the Xylaria-type centrum. The relationship of the Xylaria-type centrum with some other centra is discussed.

Development of perithecia and pycnidia of Didymella applanata (causing spur blight) on raspberry canes

The development of perithecia and pycnidia of Didymella applanata (Niessl) Sacc. was studied microscopically in whole mounts and tissue sections. Perithecia and pycnidia occurred together on the same stems. Perithecial initials were first seen in mid-August; development continued throughout the winter, and perithecia reached maturity by early April. Pycnidia were initiated from November onwards, and reached maturity between April and mid-November. Pycnidiospores were apparently released over a long period, with a peak in July and August.

Perithecial formation in Gelasinospora reticulispora

When hyphae in the basal region of 72-hold, dark-grown mycelium of G. reticulispora (Greis et Greis-Dengler) C. et M. Moreau (Sordariaceae) were exposed to a microbeam of monochromatic blue light, perithecial initials were induced only in hyphae located within or in the vicinity of the light spot. The average distance from the periphery of the microbeam spot to perithecial initials produced outside the spots was 100-200 μm, regardless of the beam diameter or the incident light energy. The maximum distance of a perithecium formed outside a microbeam spot was ca. 700 μm. The inductive effect of blue light became detectable at 100 J m(-2) and reached a maximum at 1000 J m(-2), regardless of beam diameter. A microphotographic examination showed that the microbeam irradiation was effective only in hyphae rich in protoplasm.

Promotion of Perithecial Initials in Monacrosporium doedycoides by 6-Methyl Purine

The promotion of perithecial initials in the imperfect fungus Monacrosporium doedycoides is enhanced by the addition of the RNA synthesis inhibitor 6-methyl purine (6-MP). The addition of two other RNA inhibitors (8-azaguanine and actinomycin-D) causes the promotion of initials but not at the magnitude observed with 6-MP. Application of a protein synthesis inhibitor (cycloheximide), a base analog (5-fluorouracil), or an amino acid analog (p-fluorophenyl-alanine) are not promotive on initial formation and can be inhibitory. The apparent cause for the promotion of perithecial initials in the imperfect fungus is that sexual structures are inhibited by mRNA's synthesized by the organism and the addition of 6-MP prohibits their synthesis.

PROMOTION OF PERITHECIAL INITIALS IN MONACROSPORIUM DOEDYCOIDES BY 6–METHYL PURINE

The promotion of perithecial initials in the imperfect fungus Monacrosporium doedycoides is enhanced by the addition of the RNA synthesis inhibitor 6‐methyl purine (6‐MP). The addition of two other RNA inhibitors (8‐azaguanine and actinomycin‐D) causes the promotion of initials but not at the magnitude observed with 6‐MP. Application of a protein synthesis inhibitor (cycloheximide), a base analog (5‐fluorouracil), or an amino acid analog (p‐fluorophenyl‐alanine) are not promotive on initial formation and can be inhibitory. The apparent cause for the promotion of perithecial initials in the imperfect fungus is that sexual structures are inhibited by mRNA's synthesized by the organism and the addition of 6‐MP prohibits their synthesis.

Ascocarp development of Eutypella parasitica

Perithecial initials of Eutypella parasitica were found during the spring in bark phellem of cankered sugar maples. These initials were commonly intermingled with mature perithecia probably produced in the current year. One or several ascogonial coils appeared in these initials, but no trichogyne-like hyphae were seen in the archicarp. Asci developed rapidly from croziers formed on ascogenous hyphae and enlarged almost to their mature size before the diploid fusion nucleus divided to form the eight ascospores. The perithecium of E. parasitica has a Xylaria-type centrum as defined by Luttrell in 1951.

Tripospermum camelopardus sp.nov.

Tripospermum camelopardus sp.nov. is described. It was grown in culture from a spore from river foam. In addition to spores characteristic of the genus, minute spherical phialospores and structures which are possibly perithecial initials with trichogynes are produced. The temperature optimum for growth is low (around 15–20°C).

Some observations on the growth and sporulation of Chaetomium globosum in media containing ammonium tartrate

Chaetomium globosum , grown at 30°C. on media in which the source of nitrogen is ammonium tartrate, produces no mature perithecia, although perithecial initials appear freely. Maturation of initials occurs at 26°, or in the presence of certain other fungi. Organic phosphates, biotin and other substances also affect the development of perithecia. These results are taken to indicate that different stages in the production of mature perithecia call for different physical or chemical environments.

ASCOCARPIC DEVELOPMENT IN DIPOROTHECA RHIZOPHILA

In Diporotheca rhizophila Gordon & Shaw upright unicellular perithecial initials are produced on the superficial mycelium covering the host's roots. By septation the initial becomes a three-celled primordium. Two cells, produced laterally from the penultimate cell of the primordium, by division in two planes, form the perithecial wall. During final maturation two to three divisions in the third plane make the wall three to five cells thick. The centrum originates from the apical cell of the primordium. Dikaryotization of an immature perithecium involves the production of one to many hyaline receptive hyphae from the dark, pigmented, peridial cells. These receptive hyphae fuse with superficial vegetative hyphae, and a nucleus from a cell of the vegetative hypha apparently migrates into the centrum. No structure within the centrum of the perithecium could be interpreted as an ascogonium. The same hyaline, pseudoparenchymatous filaments which form the ascal generative cells in the basal and central areas of the centrum give rise to periphyses within the perithecial neck.

THE EFFECT OF CERTAIN ELEMENTS, WITH EMPHASIS ON NITROGEN, ON THE PRODUCTION OF PERITHECIA OF VENTURIA INAEQUALIS (CKE.) WINT.

Various elements were tested for their effect on the formation of perithecia of Venturia inaequalis. Apart from nitrogen the elements tested had little effect on the formation of perithecia except at relatively high concentrations. Perithecia did not form in media containing low concentrations of nitrogen and this was influenced by the source of nitrogen and by the cation present in nitrate salts. Perithecial initials developed in higher nitrogen concentrations than perithecia. Nitrogen added 9 weeks after mating of two lines of the fungus prevented the formation of perithecia.Results were difficult to reproduce in a potato-dextrose apple leaf decoction medium but reproducible results were obtained in a synthetic medium.

Plasmogamy and Ascocarp Development in Gelasinospora calospora

(WITH 23 FIGURES) Sun (1953) was able to observe the development of perithecial initials of the homothallic strain of Gelasinospora calospora (Mouton) Moreau & Moreau in living cultures. She seemingly observed plasmogamy but was not able to follow development between the formation of a pseudoparenchymatous ball of cells and crozier formation. Most of the reported descriptions of the Pyrenomycetes state that development proceeds in the usual manner between these latter two stages. Meyer (1957) attempted to fill this gap in our knowledge of G. calospora; however, he made observations from only stained, sectioned material. The purpose of the present investigation was twofold: firstly, to follow and record plasmogamy as it occurs in the homothallic strain of G. calospora; and secondly, to discover the origins of the various tissues and structures found in the protoperithecium and to follow their

Perithecial Initials of Chaetomium

Perithecial Initials of Chaetomium

Perithecial Initials of Chaetomium

Perithecial Initials of Chaetomium

Contributions to the life History of certain coprophilous fungi

Summary 1. Species of Sordaria, Podospora, Philocopra, Sporormia and Chaetomium were grown in culture and their development studied. 2. In all genera examined except Sporormia the perithecium originates from a coiled hypha about which the peridium grows up. 3. The perithecial initials of the two investigated species of Sporormia resemble each other and differ from those of the same family in a very striking manner, since septation occurs in three dimensions. 4. Micro-conidia were observed in Podospora anserina and Podosporaminuta. They vary greatly in number according to the medium onwhich the fungus is grown. Further work on their function andbehaviour is much to be desired.