Ascoma Development Research Articles

Taitaia, a novel lichenicolous fungus in tropical montane forests in Kenya (East Africa)

AbstractDuring lichenological explorations of tropical montane forests in Kenya, a remarkable new lichenicolous fungus was repeatedly found growing on thalli of the epiphytic tripartite cyanolichen Crocodia cf. clathrata. Molecular phylogenetic analyses placed the fungus within Gomphillaceae (Ostropales, Lecanoromycetes), a family mainly of lichen-symbiotic species in the tropics. The anatomical features (unitunicate, non-amyloid asci and simple, septate paraphyses) as well as the hemiangiocarpic ascoma development confirm its taxonomic affinity. DNA sequence data showed the closest relationship was with Gyalidea fritzei, followed by Corticifraga peltigerae. A monotypic genus, Taitaia, is introduced to incorporate a single species, T. aurea. The new fungus is characterized by aggregated ascomata with yellow margins and salmon red discs developing from a single base.

Repeated evolution of closed fruiting bodies is linked to ascoma development in the largest group of lichenized fungi (Lecanoromycetes, Ascomycota)

Fruiting bodies are responsible for the effective dispersal of meiospores in ascomycetes. Different fruiting body types include open (apothecia) or closed (perithecia, cleistothecia) forms, which have traditionally been used as key paradigms for ascomycete classification. Molecular phylogenies show that most fruiting body types have multiple phylogenetic origins within the phylum, and are not suitable for the circumscription of classes. One exception are perithecia that are restricted in non-lichenized fungi to the monophyletic class Sordariomycetes. However, lichenized fungi with perithecioid fruiting bodies were found to belong to three other classes unrelated to Sordariomycetes. One of these is Lecanoromycetes, which includes the bulk of lichenized fungi. To understand the evolution of perithecioid fruiting bodies in the mostly apotheciate Lecanoromycetes, we assembled a combined data set of nuclear and mitochondrial ribosomal, and RPB1 DNA sequences, and traced the evolution of two morphological characters (fruiting body type and fruiting body development). We reconstructed ancestral character states using maximum likelihood and Bayesian methods. Additionally, we tested for correlation of character changes in a combined Bayesian/maximum likelihood framework. The results suggest that perithecia have evolved in unrelated groups of lichen-forming fungi. Within Lecanoromycetes they have evolved independently several times from apotheciate ancestors. Further, our analyses support a correlation between the type of fruiting body and the type of ascoma ontogeny. The evolution of angiocarpous ascoma development in Lecanoromycetes is a pre-adaptation for the repeated gain of perithecia. This finding is consistent with the hypothesis of a neotenic origin of perithecioid fruiting bodies in Lecanoromycetes.

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.

Evidence that the gemmae of Papulaspora sepedonioides are neotenous perithecia in the Melanosporales

Papulaspora sepedonioides produces large multicellular gemmae with several, thick-walled central cells enclosed within a sheath of smaller thin-walled cells. Phylogenetic analysis of the large subunit rDNA indicates P. sepedonioides has affinities to the Melanosporales (Hypocreomycetidae). The development of gemmae in P. sepedonioides was characterized by light and scanning and transmission electron microscopy and was similar to previous ontogenetic studies of ascoma development in the Melanosporales. However instead of giving rise to ascogenous tissues the central cells of the incipient gemma became darkly pigmented, thick walled and filled with lipid globules while the contents of the sheath cells autolysed, leaving them empty and deflated at maturity. Both central cells and pre-autolytic sheath cells produced both germ tubes and new gemmae primordia, suggesting microcyclic conidiogenesis occurs in this species. Mature gemmae were non-deciduous or seceded by schizolytic secession and appear to have both perennating and disseminative potential. The evolution of these neotenous perithecial propagules may be driven by life-history and ecological factors selecting for functional versatility.

Phylogenetic analysis of nuclear and mitochondrial rDNA sequences supports the view that loculoascomycetes ( Ascomycota) are not monophyletic

The loculoascomycetes are defined by the initiation of ascoma development prior to dikaryotisation and functionally bitunicate asci. Previous molecular studies suggested non-monophyly of loculoascomycetes and consequently, Chaetothyriomycetes and Dothideomycetes were distinguished. We have used sequences of nu SSU rDNA, nu LSU rDNA, and mt SSU rDNA to re-evaluate the monophyly of loculoascomycetes. 13 new sequences of these regions from 10 species, including two representatives of Pezizomycetes used as outgroup, were aligned with sequences obtained from GenBank. A combined data set was analysed phylogenetically using maximum parsimony. The Chaetothyriomycetes and Eurotiomycetes form a sister-group, supported by a bootstrap value of 97%, suggesting that loculoascomycetes are not monophyletic. A topology constrained to loculoascomycete monophyly can be rejected as being significantly worse using parametric bootstrapping. Our results also indicate that mt SSU rDNA sequence data are useful as additional characters to elucidate the phylogeny of ascomycetes at the rank of different classes. Additional data from more representatives of these groups and other ascomycetes are required to clarify whether the loculoascomycetes are a paraphyletic or polyphyletic assemblage.

Phylogeny of filamentous ascomycetes.

Phylogenetic studies of higher ascomycetes are enhanced by the introduction of molecular markers. Most studies employed sequences of the SSU rRNA gene, but recently data from additional genes (RPB2, LSU rRNA) have become available. Several groups defined by their ascoma-type, such as Pyrenomycetes, are supported while others, like the Discomycetes, appear to be paraphyletic. The Pezizales with operculate asci are basal to other eu-ascomycetes, while other Discomycetes appear to be derived eu-ascomycetes. The reevaluation of classical characters using molecular data is discussed using three examples. Ascus types are often regarded as being of major importance in ascomycete systematics, but prototunicate asci were found to be of poor taxonomic value, since ascomycetes with prototunicate asci are polyphyletic. The independence of the Agyriales, assumed from their morphological characters, is supported by sequence data but the relationship to supposed sister groups remains dubious. The phylogeny of ascolocularous fungi and their circumscription requires further study. While a circumscription based on bitunicate asci can be rejected, it remains unclear whether fungi with ascolocularous ascoma development represent a monophyletic entity.

ASCOMA ONTOGENY: IS THIS CHARACTER SET OF ANY USE IN THE SYSTEMATICS OF LICHENIZED ASCOMYCETES?

The use of ascoma ontogeny in the systematics of lichenized asco-mycetes is reviewed briefly. Two recently studied examples are discussed to illustrate the use of ontogenetic studies to discover phylogenetic relationships. As one example, theAgyriaceaewas mainly circumscribed by the ascus type and included diverse genera.Xylographais characterized by lirelliform apothecia. However, the ascoma development shares the ontogenetic pattern observed inTrapeliaand its placement in the family was confirmed. In contrast,Anamylopsoraexhibited a substantially different apothecial development and was separated as a family of its own. As a second example, theCandelariaceaeis based on chemical characters. With the detection of pulvinic acid derivatives also in the genusLecanora, the distinction of theCandelariaceaeandLecanoraceaebecame doubtful. Therefore, the ascoma ontogeny was employed to evaluate this classification and is illustrated here in detail forCandelaria fibrosa. The substantial similarity of the ascoma development found in both families suggests that both might be better united. Finally, a general discussion of the significance of ontogenetic characters in lichen taxonomy is included.

A Comparison of Ascoma Ontogeny Supports the Inclusion of the Eigleraceae in the Hymeneliaceae (Lecanorales)

A Comparison of Ascoma Ontogeny Supports the Inclusion of the Eigleraceae in the Hymeneliaceae (Lecanorales)

Anatomical and Ontogenetic Studies on the Lichen Family Schaereriaceae (Agyriineae, Lecanorales)

The systematic position of the lichen family Schaereriaceae, formerly included in the Pezizales or incertae sedis, is evaluated. Since the genus shares a number of characters with the Agyriaceae, including the hemiangiocarpous ascoma development, zeorine apothecia, and similar chemistry, it is best placed in the Agyriineae. The ascus of Schaereria is interpreted as a reduction of the Trapelia-type. Since some differences occur between Schaereria and the Agyriaceae, namely the different paraphyses, ascus structure, and pycnidia, it is proposed to maintain the family Schaer- eriaceae within the Agyriineae. The genus Ach. in the traditional sense was a most diverse assemblage of lichenized asco- mycetes. Hertel and Rambold (1985) listed 54 gen- era that were formerly placed in this collective ge- nus. The genus Schaereria was one of these. It was originally described by Kibrber (1855) and recog- nized by Th. Fries (1860), but was subsequently placed in synonymy with under Nylander's influence. More recently, Poelt and Vezda (1977) resurrected the genus to accommodate S. cinereo- rufa (Schaerer) Th. Fr. Five species of Schaereria were accepted by Clauzade and Roux (1985), name- ly S. cinereorufa, S. endocyanea (Stirton) Hertel & Schneider, S. fuscocinerea (Nyl.) Clauzade & Roux, Lecidea pissodes Stirton, and S. tenebrosa (Flo- tow) Hertel & Poelt. According to Rambold (1989), S. endocyanea and S. tenebrosa are synonyms of S. fuscocinerea, while Lecidea pissodes is regarded as a synonym of Clauzadeana macula (Taylor) Cop- pins & Rambold (Purvis et al. 1992). In the mean- time, three further species--S. corticola Muhr & Tonsberg, S. fabispora Hertel & Ziirn, and S. xe- rophila Rambold & Mayrhofer-have been de- scribed (Hertel & Ziirn 1986; Rambold 1989; Tens- berg 1992), so that five species are currently ac- cepted in the genus. No material ofS. fabispora and S. xerophila was available and these two species are not considered here.

Genetics and systematics of North American populations ofMorchella

Our knowledge of the genetics and systematics of the genus Morchella in North America has increased greatly because of many recent field and laboratory studies. Field studies have expanded distribution records and provided insights on ascoma development. More detailed morphological studies have improved species descriptions and simplified species identification. Mating studies between monosporous strains and the formation of presumptive heterokaryons have given evidence for species delimitation. The isolation of chemical products and antigen comparisons using ELISA have provided additional support for species concepts. Electrophoretic studies of allelic variation have given insights into the genetic structure of morels from different geographical areas. Sequence data from the nuclear large rDNA (28S) have been used to infer phylogenetic relationships among species. Additional insights have been obtained from physiological and environmental studies on sclerotium formation that have enabled the production of ascoma in culture. This has led to the filing of patents, commercial production, and the availability of growing kits. Key words: Morchella, systematics, genetics, North America, review.

Anamylopsoraceae ? a new family of lichenized ascomycetes with stipitate apothecia (Lecanorales: Agyriineae)

The anatomy, chemistry and developmental morphology ofAnamylopsora pulcherrima is investigated. Some characters, including the ascus structure, suggest a close affinity with theAgyriaceae. However, the chemistry and the pycnidial structure differ as well as the ascoma ontogeny.Anamylopsora has a gymnocarpous ascoma development and the ascogonia are produced in stipes.Trapelia coarctata, as a typical member of theAgyriaceae, shows a hemiangiocarpous ascoma ontogeny. The anatomical, chemical and ontogenetical characters of several families are compared withAnamylopsora and it is shown that the genus is best placed in a monotypic familyAnamylopsoraceaeLumbsch & Lunke, fam. nova, which is placed in theAgyriineae (Lecanorales).

Ultrastructural study of ascoma and ascospore development in Ophiostoma distortum and Ophiostoma minus

The development of the ascoma, ascus, and elongated ascospores in Ophiostoma distortum and Ophiostoma minus was studied at the ultrastructural level and compared with that of other related Ascomycetes. The organization of the centra in O. distortum and O. minus differed considerably. In O. distortum, asci were irregularly arranged in clusters that occurred in the lower half along the periphery of the ascoma. In O. minus, asci developed from a central cluster at the base of the ascoma. The asci extended upwards and outwards from the base. Ascospore development in both fungi commenced with the formation of double, delimiting membranes in the ascus. Between these membranes ascospore walls developed, consisting of the primary and secondary wall. In comparison with other species having similar ascospores, differences were found between the number of wall layers of the ascospores and formation of the outer wall layers. The secondary wall and perisporic sac of O. minus were smooth and of uniform thickness, whereas the inner layer of the secondary wall in O. distortum was thickened and distorted in certain areas. It is suggested that additional ultrastructural studies should be undertaken to provide a better understanding of the development and evolution of ascospore sheaths in Ceratocystis sensu lato. Key words: Ceratocystis, elongated ascospores, centrum.

A Scanning Electron Microscopic Study of Ascoma Development in Chaetomium Malaysiense

Ascocarp ontogeny of Chaetomium malaysiense was studied by means of scanning electron microscopy (SEM). Ascoma development begins when a side branch of a vegetative hypha coils about itself spirall...

Ascoma Morphology of Pseudopeziza Trifolii Forma Specialis Medicaginis-Sativae (Dermateaceae) on Alfalfa

Ascomatal initials of Pseudopeziza trifolii f. sp. medicaginis-sativae consist of ascogonial coils forming on intracellular hyphae in parenchyma cells of living alfalfa leaflets. In some young ascomata, the ascogonial coils are surrounded by an aggregation of hyphae, while in other initials, such hyphae are sparse. Ascogenous hyphae and paraphyses develop and grow through the surrounding mycelium toward the host epidermis. Croziers proliferate from the binucleate ascogenous cells. Asci are eventually produced, with each mature ascus containing eight uninucleate ascospores. Ascosporogenesis is similar to that described in a number of Ascomycetes. Until the time of ascospore discharge, the hymenium of an ascoma is covered by hyphae in and under the infected host epidermis, and by periphysoids arising from these hyphae. The host epidermis ruptures when the ascoma is mature. A pseudoparenchymatous excipulum is present. Vegetative mycelium generally fills most of the host cells under the ascoma, and somatic hyphae appear to radiate outward from the ascoma to surrounding host cells. Septa in the hyphae have pores, with Woronin bodies in close proximity to the pores. Some pores have electron-dense plugs. The aggregation of hyphae observed throughout ascoma development is often referred to as a stroma; however, this aggregation is not always well developed, and it is not known whether or not it arises as a result of a sexual stimulus. Ascomata of this fungus can therefore be interpreted as either stromatic or nonstromatic.