Mature Asci Research Articles

The Use of Mycoendophyte-Based Bioformulations to Control Apple Diseases: Toward an Organic Apple Production System in the Aurès (Algeria)

The present study aims to investigate the effectiveness of bioformulations based on endophytic fungi to control apple scab and Valsa canker disease in two orchards in the Aurès region (Algeria). In both orchards, the results showed that the treatment of senescent apple leaves by invert emulsions containing Trichoderma longibrachiatum and Chaetomium globosum harmed the ascogenesis of winter forms of Venturia inaequalis by reducing the number of ascospore-ejecting asci, the number of morphologically mature asci, and a considerable increase in the immature asci number. This antifungal activity was more essential in soil-incorporated leaves, showing the importance of the combination of treatments with cultural practices to efficiently control the apple scab disease. Furthermore, the disease incidence decreased by 52.63% and 50.68% in R'haouat and Bouhmama orchards, respectively. Moreover, the treatment of Valsa ceratosperma cankers with a biogel containing the endophytic yeast Metschnikowia sp. led to wound healing varying from 43.52% and 87.97% after 120 days but remained more considerable than conventional treatment with Folicur (tebuconazol). The current results open real opportunities concerning the implementation of eco-friendly and potent apple protection systems.

Methods for observing, culturing, and studying living ascospores

Ascospore morphologies provide important characters with which to diagnose and describe taxa in Ascomycota. Ascospore features such as size, shape, color, septation, wall thickness, and guttulation, among others, are provided in identification manuals and descriptions of new species. Yet, by tradition, ascospores are usually described from dead fungarium material, and unfortunately, occasionally from immature or overmature ones. However, living, mature ascospores display a wealth of taxonomically informative morphological features that are lost or obscured when they die. Examples of the severe morphological changes that ascospores undergo when they die are provided here. Data from living ascospores may not be observed and recorded by mycologists because field and laboratory practices do not prioritize the study of freshly collected specimens. In this review, we discuss how to assess ascospore maturity and describe methods to produce an ascospore deposit for the purpose of obtaining living, mature ascospores. Ascospores are ejected from living, mature asci onto a cover glass or growth medium. The ascospores collected on these surfaces can be used in microscopy and culture studies. Notes on a method for isolating conidia on growth medium are also provided. This guide is aimed at those who have a basic understanding of ascomycetes, including the various types of ascomata and mechanisms of ascospore liberation. Methods given in this paper are primarily applied to ascomycete fungi that have active ascospore discharge. Some methods may be adapted for use with other groups that have passive discharge. Our purpose is to promote standardized, accurate, and thorough morphological characterization of living ascospores, as well as to encourage the routine employment of culture-based methods.

Clypeococcum hemiamyloideum (Polycoccaceae, Ascomycota), a novel lichenicolous fungus on Verrucaria latebrosa

Shivarov, V. V. 2019. Clypeococcum hemiamyloideum (Polycoccaceae, Ascomycota), a novel lichenicolous fungus on Verrucaria latebrosa. - Herzogia 32: 438–443.Clypeococcum hemiamyloideum is described as a novel lichenicolous fungus on Verrucaria latebrosa from the Malyovitsa River, Bulgaria. It is characterized by two types of hymenial gels: lower gel predominant, hemiamyloid (1+ red), upper gel only in the ostiolar region, euamyloid (1+ blue), a variable spore number in the mature asci (1–8), pseudothecia 100–175 µm diam., black, and ascospores 17.8–20.3 x 6.6–7.6 µm, brown, thick-walled, warted, 1-sep-tate. The reactions of the hymenial gels in C. hemiamyloideum and V. latebrosa were tested with different concentrations of IKI in order to identify their types and thresholds.

Molecular manipulation of the mating-type system and development of a new approach for characterizing pathogen virulence in Pyrenophora tritici-repentis

The ascomycete Pyrenophora tritici-repentis (Ptr) is an important fungal pathogen worldwide that causes tan spot of wheat. The fungus is self-fertile because each isolate contains both mating type (MAT) idiomorphs. In this work, we developed knockouts of the MAT genes in Ptr and tested fertility of the knockout strains and outcrossing between the knockout strains carrying the opposite mating type. The fungal strains with deletions of either MAT1-1-1 or MAT1-2-1 did not form mature pseudothecia making them functionally heterothallic. The cross between the heterothallic strains of the same isolate (86–124) was fully fertile with the only difference compared to the homothallic wild type strain being the slightly lower percentage of pseudothecium formation. However, the cross between 86–124 (race 2, ToxA-containing isolate) and DW5 (race 5, ToxB-containing isolate) was partially fertile and had fewer mature pseudothecia. Furthermore, most mature asci produced only two or four instead of eight functional ascospores. A collection of ascospores from this cross was obtained and genotyped for the presence of the ToxA, ToxB and MAT genes as well as simple sequence repeat markers. The segregation of these genes and markers and recombination of different allele types at these loci was observed. This work clearly demonstrates that the fungus requires both MAT genes for sexual production and can undergo outcrossing and sexual recombination. It also establishes a new and practical way for further characterizing fungal virulence in Ptr through the development of segregating fungal populations and subsequent genetic analysis.

FIRST REPORT OF TALAROMYCES ALBOBIVERTICILLIUS CAUSING POSTHARVEST FRUIT ROT ON POMEGRANATE IN ITALY

In 2016, circular brownish lesions and stamens both covered by greenish sporification, were observed on two month-stored Punica granatum L. fruits (cvs Wonderful One and Acco). Soft rotting originating from wounds on the rind, without nesting or connection with stamen colonization, was recorded on 18% of infected fruit. Surface-sterilized rotted portions were plated on potato dextrose agar (PDA), containing streptomycin and ampicillin (250 mg/l each), incubated at 24oC in the dark and sub-cultured on Malt Extract Agar (MEA). Colonies were velvety, 26.5±1.5 mm in size after 7 day-incubation. The 3-8 acerose phialides (10.5±2.5×2.5±0.5 µm) were slender aculeate or lanceolate, highlighting the symmetrical, biverticillate conidiophores; interlaced hyphae constituted the layers of the typical soft ascomatal wall; mature asci were chain-like. Pinkish-white conidia, from globose to sub-globose, measured 3±1×2±0.5 µm. The divergent metulae (10.5±2.5×3±1.5 µm, each) varied between 3 and 8. Stipes were 300±100×3.25±0.75 µm with smooth surface. These traits, together with the production of intense red soluble pigments, identified the fungus as Talaromyces albobiverticillius Samson et al. (Yilmaz et al., 2014). For confirmation, fungal DNA was amplified using primers Bt2a/Bt2b (Glass and Donaldson, 1995). The amplicon (GenBank accession No. KY563698) showed 99% identity with other T. albobiverticillius sequences. For pathogenicity tests, surface-sterilized fruit of cvs Wonderful One and Acco were wounded, inoculated with a mycelial plug and incubated as above. Sterile plugs were used as controls. Typical symptoms developed only on infected fruits. The re-isolated fungus corresponded to T. albobiverticillius, fulfilling Koch’s postulates. To our knowledge, this is the first report of T. albobiverticillius causing postharvest rot of pomegranate. This fungus is a Penicillium sensu latu (Samson et al., 2011) which may be mistaken for a Penicillium sensu strictu.

Metschnikowia drakensbergensis sp. nov. and Metschnikowia caudata sp. nov., endemic yeasts associated with Protea flowers in South Africa.

In a taxonomic study of yeasts recovered from nectar of flowers and associated insects in South Africa, 11 strains were found to represent two novel species. Morphological and physiological characteristics and sequence analyses of the large-subunit rRNA gene D1/D2 region, as well as the actin, RNA polymerase II and elongation factor 2 genes, showed that the two novel species belonged to the genus Metschnikowia. Metschnikowia drakensbergensis sp. nov. (type strain EBD-CdVSA09-2(T) =CBS 13649(T) =NRRL Y-63721(T); MycoBank no. MB809688; allotype EBD-CdVSA10-2(A) =CBS13650(A) =NRRL Y-63720(A)) was recovered from nectar of Protea roupelliae and the beetle Heterochelus sp. This species belongs to the large-spored Metschnikowia clade and is closely related to Metschnikowia proteae, with which mating reactions and single-spored asci were observed. Metschnikowia caudata sp. nov. (type strain EBD-CdVSA08-1(T) =CBS 13651(T) =NRRL Y-63722(T); MycoBank no. MB809689; allotype EBD-CdVSA57-2(A) =CBS 13729(A) =NRRL Y-63723(A)) was isolated from nectar of Protea dracomontana, P. roupelliae and P. subvestita and a honeybee, and is a sister species to Candida hainanensis and Metschnikowia lopburiensis. Analyses of the four sequences demonstrated the existence of three separate phylotypes. Intraspecies matings led to the production of mature asci of unprecedented morphology, with a long, flexuous tail. A single ascospore was produced in all compatible crosses, regardless of sequence phylotype. The two species appear to be endemic to South Africa. The ecology and habitat specificity of these novel species are discussed in terms of host plant and insect host species.

Taxonomic placement of Epichloë poae sp. nov. and horizontal dissemination to seedlings via conidia

A new Epichloe species distributed in Africa, Europe, North America and South America on host genera Bromus, Festuca, Lolium and Poa is described. Stromata, characteristic of the genus, frequently occurred on the reproductive tillers of Poa secunda subsp. juncifolia, but neither perithecia nor mature asci were observed. Conidiogenous cells and conidial characteristics were in the range of Epichloe typhina. Regions of the genes encoding β-tubulin (tub2) and translation elongation factor 1-α (tef1) were amplified and sequenced. Phylogenetic analyses of these sequences grouped the Poa secunda subsp. juncifolia endophyte into one group within a non-hybrid Epichloe species complex. On the basis of morphology, host range and evolutionary history we propose that this endophyte represents a new species of Epichloe. The name Epichloe poae is proposed for this endophyte. The infectivity of the conidia produced on plants was evaluated. In the first experiment, using conidia of Epichloe poae from leaves and endophyte-free seeds of Poa secunda subsp. juncifolia we show that when germinating seeds and developing seedlings of the plant were exposed to conidia, 28–57 % of seedlings became infected by the endophyte. The non-inoculated control plants showed no colonization by the endophyte. In the following spring after vernalization, colonized plants on flowering culms produced stromata with conidia. In the second experiment, using stromal conidia and the same procedure, 19–42 % of seedlings of Poa secunda subsp. juncifolia became colonized by the endophyte. Our results demonstrate that Epichloe poae may spread to uninfected grass hosts by conidia frequently formed on the surfaces of plant leaves as well as by conidia formed on stromata.

Ribosomal DNA sequence polymorphism and the delineation of two ascosporic yeast species: Metschnikowia agaves and Starmerella bombicola

The relationship between mating success and sequence divergence in the internal transcribed spacer (ITS)/5.8S-D1/D2 rDNA region was examined in isolates tentatively assigned to Metschnikowia agaves and Starmerella bombicola. Both species are haplontic and heterothallic, such that the formation of mature asci can be used as a measure of genetic compatibility. Parsimony haplotype network analysis and mating success confirmed that all known isolates of M. agaves are conspecific. The previously reported D1/D2 polymorphism of five substitutions was not corroborated; the maximum divergence observed between any two strains was three substitutions, four with ITS. Of 39 putative S. bombicola strains, 36 formed an ITS-D1/D2 haplotype network using the 95% criterion. Thirty-five strains could mate with one or more compatible partner. The excluded strains did not mate. Mature asci arose from crosses between individuals differing by as many as five, but not six or seven substitutions in the D1/D2 domain. All strains capable of mating formed mature asci with at least one partner and all network members could be linked to another member by three or fewer substitutions. These results support the use of sequence divergence as a criterion for species delineation, but caution against describing poorly sampled species solely on the basis of that criterion.

A new stromata-producing Neotyphodium species symbiotic with clonal grass Calamagrostis epigeios (L.) Roth. grown in China

We describe a new stromata-producing Neotyphodium species symbiotic with clonal Calamagrostis epigeios (L.) Roth. Stromata on the grass, 47.5–186 mm long, occurred frequently, but neither perithecium nor mature ascus was observed. Morphology of fungal isolates obtained from symptomatic and asymptomatic tillers were identical to each other and similar to those of epichloë endophytes. In phylogenetic analysis all selected five fungal isolates clustered into a significantly distinct clade based on sequences of β-tubulin gene (tubB) introns and translation elongation factor 1-α gene (tefA) introns with bootstrap values of 99%, supporting erection of a new species. Concerning the production of extremely long stromata on the host plants and absence of sexual spores, we propose the name Neotyphodium stromatolongum Y. Ji, L. Zhan et Z. Wang, sp. nov.

Kurtzmaniella gen. nov. and description of the heterothallic, haplontic yeast species Kurtzmaniella cleridarum sp. nov., the teleomorph of Candida cleridarum

The teleomorph of Candida cleridarum was discovered through the detection of conjugation between isolates of a large collection from the nitidulid beetles of the genus Carpophilus found in the flowers of various cacti in Arizona, USA. The previous oversight of the sexual cycle of this yeast is attributed to the inequality (ca. 5 : 1) of the two mating types. Extensive conjugation between compatible mating types is observed after overnight incubation on 5 % malt agar, followed after 3-5 days by the formation of mature asci. The hat-shaped ascospores are reminiscent of those seen in Kodamaea species, which are members of the same guild. However, published analyses of D1/D2 large subunit rDNA sequences indicate an affinity with the genus Debaryomyces. As the latter is polyphyletic and morphologically heterogeneous, and in view of the distinct life cycle of the new teleomorph, the new genus Kurtzmaniella is described with a novel species, Kurtzmaniella cleridarum sp. nov. Given the close relatedness of Kurtzmaniella cleridarum sp. nov. to Candida quercitrusa, Candida oleophila and Candida railenensis, for which several natural isolates were available, strains of these species were mixed in pairs under the conditions found favourable for the former. Conjugation was not detected in those species. The type strain of Kurtzmaniella cleridarum sp. nov. is UWOPS 99-101.1(T) (=CBS 8793(T)=NRRL Y-48386(T), h(+)), type of Candida cleridarum. The allotype is UWOPS 07-123.1 (=CBS 10688=NRRL Y-48387, h(-)).

Incubation of excised apothecia enhances ascus maturation of Sclerotinia sclerotiorum

Synchronized maturation of ascospores of Sclerotinia sclerotiorum is desirable for establishing a transformation system, conducting genetic analyses of the pathogen, defining the precise epidemiological roles of ascospores and screening plant germplasm for resistance. In general, fresh apothecia collected from germinated sclerotia contained primarily immature or discharged asci. This study was undertaken to investigate whether maturation of asci and ascospores could be enhanced by incubation of excised apothecia and to determine the effects of factors such as temperature, excision time, light and ventilation on maturation of asci and ascospores in excised apothecia. Maturation of asci was compared between intact and excised apothecia that were incubated under similar conditions. Results demonstrated that temperature was an important factor affecting ascus maturation of S. sclerotiorum during incubation of excised apothecia, and the optimum temperature was around 21 C. After incubation at 21 C for 30 h, the percentage of undischarged mature asci in excised apothecia increased up to 70–80%. This increase was accompanied by a significant increase in ascospore production of up to 5 × 105 ascospores per apothecium. Detailed time course studies indicated that mature asci peaked at 30–36 h of postexcision incubation. Mature asci and the number of ascospores were higher in open incubation than in closed incubation, suggesting that accumulation of volatile substances was not required for ascus/ascospore maturation during postexcision incubation and ventilation could enhance the maturation process. Light also did not affect the maturation of asci during the incubation of excised apothecia. Germination rates for ascospores from excised apothecia under various treatments were similar to those from untreated apothecia but declined slightly with time postexcision. The incubation of excised apothecia promoted ascus maturation compared with intact apothecia.

Incubation of excised apothecia enhances ascus maturation of Sclerotinia sclerotiorum

Synchronized maturation of ascospores of Sclerotinia sclerotiorum is desirable for establishing a transformation system, conducting genetic analyses of the pathogen, defining the precise epidemiological roles of ascospores and screening plant germplasm for resistance. In general, fresh apothecia collected from germinated sclerotia contained primarily immature or discharged asci. This study was undertaken to investigate whether maturation of asci and ascospores could be enhanced by incubation of excised apothecia and to determine the effects of factors such as temperature, excision time, light and ventilation on maturation of asci and ascospores in excised apothecia. Maturation of asci was compared between intact and excised apothecia that were incubated under similar conditions. Results demonstrated that temperature was an important factor affecting ascus maturation of S. sclerotiorum during incubation of excised apothecia, and the optimum temperature was around 21 C. After incubation at 21 C for 30 h, the percentage of undischarged mature asci in excised apothecia increased up to 70-80%. This increase was accompanied by a significant increase in ascospore production of up to 5 x 10(5) ascospores per apothecium. Detailed time course studies indicated that mature asci peaked at 30-36 h of postexcision incubation. Mature asci and the number of ascospores were higher in open incubation than in closed incubation, suggesting that accumulation of volatile substances was not required for ascus/ascospore maturation during postexcision incubation and ventilation could enhance the maturation process. Light also did not affect the maturation of asci during the incubation of excised apothecia. Germination rates for ascospores from excised apothecia under various treatments were similar to those from untreated apothecia but declined slightly with time postexcision. The incubation of excised apothecia promoted ascus maturation compared with intact apothecia.

CRR1, a gene encoding a putative transglycosidase, is required for proper spore wall assembly in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, sporulation is a developmental process that converts a single cell into four haploid spores. The four haploid nuclei are encapsulated within multilayered spore walls that protect them against stressful conditions. The formation of the spore-specific cell wall is a highly coordinated process that requires the participation of enzymic activities for biosynthesis, degradation, and cross-linking between components. Here the sporulation-specific gene CRR1, encoding a putative transglycosidase that is required for proper spore wall assembly, is described. Both the transcription of CRR1 and the synthesis of Crr1p were induced biphasically under sporulating conditions, with a first expression peak displaying kinetics similar to those of the middle to middle-late sporulation-specific genes, and a second late peak after 24 h under these conditions. Localization studies revealed that Crr1p localized to the spore wall that surrounds each of the four ascospores within the mature asci. Mutation of this gene had no effect on the efficiency of spore formation. However, crr1 mutant spores were sensitive to hydrolytic enzymes such as glusulase and to heat-shock treatments, underscoring the importance of this gene in the proper formation and assembly of the ascospore wall. Moreover, the deletion of CRR1 had additive effects with respect to the sensitivity of cda1 cda2 mutants to these treatments. Interestingly, overexpression of CRR1 not only complemented the phenotype of the crr1 strain but also rendered spores more resistant to the stress conditions than the wild-type. Like other mutants impaired in the formation of the spore outer layer, crr1 mutants were permeable to Calcofluor White. Finally, detailed analysis by electron microscopy of the spore walls in the crr1 mutants revealed a defect in the assembly of the spore wall components, suggesting a role for Crr1p in the cross-linking between the inner (glucan/mannoprotein) and the outer (chitosan/dityrosine) spore layers.

RSC Nucleosome-remodeling complex plays prominent roles in transcriptional regulation throughout budding yeast gametogenesis.

RSC is a nucleosome-remodeling complex of Saccharomyces cerevisiae essential for growth that can alter histone-DNA interaction by using the energy of ATP hydrolysis. Nps1p/Sth1p is an ATPase subunit of RSC. A mutation in the conserved ATPase domain of Nps1p causes a sporulation defect with decreased expression of early meiotic genes, especially IME2. This defect is partially suppressed by the overexpression of either IME1 or IME2. A homozygous diploid of a novel temperature-sensitive nps1 mutation, nps1-13, harboring amino acid substitutions within the bromodomain, was unable to sporulate. Overexpression of IME, IME2, or both of these genes allowed the completion of meiosis I and meiosis II in nps1-13 but not the formation of mature asci. In nps1-13 carrying YEpIME1, the expression of a group of sporulation-specific genes, which express at the middle stages of sporulation and are required for spore-wall formation, notably diminished, and several late sporulation genes expressed at the early stages of sporulation. These results suggest that Nps1p/RSC plays important roles during the spore development process by controlling gene expression for initiating both meiosis and spore morphogenesis, and ensures proper expression timing of late meiotic genes.

Ultrastructure of the ascus apical apparatus and ascospore wall in Ombrophila hemiamyloidea (Helotiales, Ascomycota)

The ultrastructure of the ascus apical apparatus, lateral ascus wall and ascospore wall of Ombrophila hemiamyloidea was studied with TEM. The apical apparatus is composed of a well-developed apical thickening that surrounds an apical chamber and is fully occupied by a broad annulus. This annulus initially consists of a homogeneous matrix, but, due to changes in ultrastructure and PA-TCH-SP reactivity, two annular subregions become distinguishable as the ascus matures. These features do not correlate with the hemiamyloid properties of the annulus in Lugol' s iodine solution, which imparts a distinct and homogeneous red colour to both of these subregions in mature asci. After dehiscence, the annulus is everted over an angle of about 90° . The mature ascospore wall is composed of an endospore covered by an epispore. The endospore is lined by an inner wall layer which is continuous with the septal walls. Comparison with ultrastructure of the ascus and ascospores of Ombrophila violacea , the type species of the genus Ombrophila, indicates that O. hemiamyloidea does not belong in this genus. The general morphology of the apical apparatus and the structure and reactivity of the annulus agree with the Pezicula ascus type. The results indicate that O. hemiamyloidea is more closely related to Pezicula and related genera of the family Dermateaceae than to the Vibrisseaceae or the Mollisiaceae as previously been suggested.

Meiosis and ascospore development in nonlinear asci of Neurospora pannonica

Neurospora pannonica is homothallic, with 8-spored asci. Immature asci are usually swollen and noncylindrical while the mature asci are narrow and cylindrical. The two meiotic divisions resemble those of other Neurospora species. However, the orientation of third-division mitotic spindles and the distribution of nuclei in the swollen asci are irregular. Ascospores are arranged irregularly at first, but as the ascospores enlarge and mature the asci gradually become cylindrical, with the ascospores aligned in single file. The asci cannot be considered ordered tetrads, because ascospore order does not reliably reflect the assortment of chromosomes at the first and second meiotic divisions. Contrary to the original species description, ascospores require heat shock for germination and hyphae are sent out at both ends of germinating ascospores.

Genetic variability in the endophytic fungus Guignardia citricarpa isolated from citrus plants

During some phases of of their life-cycle endophytic fungi colonize plants asymptomatically being found most frequently inside the aerial part of plant tissues. After surface disinfection of apparently healthy leaves from three varieties of mandarin orange and one tangor, and after incubation on appropriate culture medium, 407 fungal isolates were obtained, giving a total infection frequency of 81%. No fungal growth was observed from disinfected seeds, indicating that fungi are probably not transmitted via seeds. Of the fungal isolates, 27% belonged to the genus Guignardia, with 12 isolates being identified as Guignardia citricarpa Kiely, which is described as a citrus pathogen. The isolates were variable in respect to the presence of sexual structures and growth rates. Most of the isolates produces mature asci, supporting the hypothesis that they are nonpathogenic endophytes, which recently were identified as G. mangiferae. High intraspecific genetic variability (an average similarity coefficient of 0.6) was detected using random amplified polymorphic DNA (RAPD) markers generated by seven different primers. The highest similarity coefficient (0.9) was between isolates P15 and M86 and the smallest (0.22) between isolates P15 and C145. These results did not allow us to establish an association between genetic similarity of the fungal isolates and the citrus varieties from which they were obtained.

Analysis of Host Species Specificity of Magnaporthe grisea Toward Wheat Using a Genetic Cross Between Isolates from Wheat and Foxtail Millet

ABSTRACT A genetic cross was performed between a Setaria isolate (pathogenic on foxtail millet) and a Triticum isolate (pathogenic on wheat) of Magnaporthe grisea to elucidate genetic mechanisms of its specific parasitism toward wheat. A total of 80 F(1) progenies were obtained from 10 mature asci containing 8 ascospores. Lesions on wheat leaves produced by the F(1) progenies were classified into four types, which segregated in a 1:1:1:1 ratio. This result suggested that the pathogenicity of the F(1) population on wheat was controlled by two genes located at different loci. This idea was supported by backcross analyses. We designated these loci as Pwt1 and Pwt2. Cytological analyses revealed that Pwt1 and Pwt2 were mainly associated with the hypersensitive reaction and papilla formation, respectively.

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.