Biphasic diurnal cycle of ascus development of Taphrina maculans Butler

Taphrina maculans Butler inciting the brown leaf spot disease of turmeric (Curcuma longa L.) produces cuboid ascogenous cells several layers in depth in the subcuticular interspaces of the epidermis. The ascogenous cells germinate to produce asci centrifugally maturing toward the periphery of the stroma, expelling octosporous microcolonies of asco-blastospores on the leaf surface inciting secondary infection in favorable environment. Occurrence of a rhythmic cycle of ascus development and ascospore discharge giving 2 peaks of ascospore discharge each day has been demonstrated in Taphrina maculans. The cycle is directly affected by atmospheric temperature, availability of free moisture on the leaf surface and sunlight. Free moisture on a leaf surface appropriately soaks the infection spots (ascogenous cells) and induces ascus elongation and ascospore discharge, when a suitable atmospheric temperature is reached. Sunlight may adversely affect the cycle by increasing the temperature and lowering humidity in the atmosphere.     

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.     

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.     

印度块菌子囊果内部解剖结构的扫描电镜观察

利用扫描电镜对成熟印度块菌子囊果的内部结构进行了观察,以系统揭示其子囊果内部组织特征,为块菌属的分类以及块菌属真菌子囊果的生理研究奠定基础。观察结果进一步证明,成熟印度块菌子囊果横切面上的白色迷宫状脉络是由不育的侧丝构成,而暗脉则是被侧丝缠绕并包裹着的可育的菌丝组织,即产孢组织,这些白色脉络和暗脉就构成了印度块菌子囊果横切面上迷宫状的纹脉;产孢组织中,可观察到正在发育的大大小小的子囊被缠绕在一起的大量产囊丝与侧丝包裹着,形成密密麻麻微小的类似蜂巢状结构;子囊孢子游离于子囊中,成熟子囊孢子表面有刺状纹饰,刺的顶端有小弯钩。单个子囊内含的子囊孢子大小与其内含的子囊孢子数目有关,子囊内所含的子囊孢子越多,子囊孢子就越小。     

STRUCTURE AND DEVELOPMENT OF CLEISTOIODOPHANUS CONGLUTINATUS GEN. & SP. N. (ASCOBOLACEAE)

Cleistoiodophanus represents a new coprophilous genus of the tribe Iodophaneae in the Ascobolaceae (Pezizales). The only species thus far discovered, C. conglutinatus, is described and illustrated. Aspects of its cytological development are described from cultures obtained from apothecia found on sheep dung near Gainesville, Florida. Plasmogamy occurs in acogonial coils, two or three cells of which give rise to ascogenous hyphae. Ascogonia are quickly enclosed by vegetative hyphae and the ascocarp continues in a cleistohymenial development. Unlike Iodophanus and related genera, the excipulum remains intact even after spore maturation and the asci push through the epihymenial regions to release spores. The asci are characteristically thickened at their apices, diffusely amyloid, and somewhat saccate. The asci are predominantly 8-spored, but have been found with four or 16 spores per ascus. A previously undescribed Oedocephalum imperfect stage was induced in culture.     

Ascospore linearity in the four-spored ascus ofNeurospora tetrasperma

The four-spored ascus ofNeurospora tetrasperma is linearly ordered, i.e. the order of the ascospores within the linear ascus directly reflects preceding meiotic events. This conclusion is based upon the finding of only two types of arrangements of homokaryotic ascospores in asci showing second division segregation and the failure to find any of the other four theoretically possible types of homokaryotic arrangements. The data are also consistent with the regular occurrence of nuclear passing at both the second and third meiotic divisions during ascus development. This work was supported by Public Health Service Grant GM 10672. Supported in part by Public Health Service Training Grant 5-T1-GM-767-05.     

MORPHOLOGY OF CHAETOMIUM ERRATICUM

Development of perithecia from single, uninucleate ascospores disclosed a homothallic condition for Chaetomium erraticum. This species was found to produce sessile ascogonial coil initials from uninucleate vegetative cells that become enveloped by hyphae formed at the base of the ascogonium. The ascogonium consists of several cells that are uninucleate or binucleate. A perithecium forms from numerous divisions and enlargement of the surrounding uninucleate cells. Differentiation of the perithecial cells results in the formation of a carbonaceous wall, perithecial hairs, and an ostiole lined with periphyses. A convex hymenial cluster of ascogenous cells forms in the lower half of the centrum from which typical croziers develop. Asci push up into the pseudoparenchyma cells of the centrum. The growth of the ascogenous system is in part responsible for increase in perithecial size. The breakdown of the pseudoparenchyma cells around the developing asci results in the formation of a central cavity in which ascospores are released when the asci deliquesce. No paraphyses are present. The type of development and features of the centrum of C. erraticum and other species of Chaetomium indicate a distinct Xylaria-type centrum.     

CYTOLOGY OF HELMINTHOSPORIUM TURCICUM AND ITS ASCIGEROUS STAGE,TRICHOMETASPHAERIA TURCICA

Knox- Davies , P. S., and J. G. Dickson . (U. Wisconsin, Madison.) Cytology of Helmintho sporium turcicum and its ascigerous stage, Trichometasphaeria turcica . Amer. Jour. Bot. 47(5) : 328—339. Illus. 1960.–The cells of the vegetative hyphae were generally multinucleate. Interphase nuclei resembled those of higher organisms, with a matrix of thread-like chromatin material surrounding a spherical nucleolus. “Beaked” nuclei frequently associated with anastomosing hyphae were interpreted as migrating nuclei. Nuclear division in the vegetative hyphae was rapid. Various division stages were distinguished but it was difficult to make accurate chromosome counts. The nucleoli were discarded at prophase or prometaphase and were reorganized in daughter nuclei at telophase. An outstanding feature of nuclear division was that all the nuclei in a cell divided simultaneously. Conidiophores and conidia were occasionally joined by wide cytoplasmic connections. They were multinucleate throughout their development. Mechanisms therefore exist for the perpetuation of heterokaryons through the conidium. Ascus development was studied in a hybrid between a dark and an albino isolate. Crozier formation was typical and nuclear fusion occurred in the young ascus. Four nuclear divisions were completed in the ascus before there was evidence of ascospore delimitation. Further nuclear division took place in the ascospores whose cells were multinucleate. The occurrence of less than 8 ascospores in an ascus appeared to follow degeneration of nuclei rather than the incorporation of a number of division-Ill nuclei in a single ascopore. Chromosome counts and irregularities in the appearance and behavior of nuclei and chromosomes in the asci indicate that aneuploidy occurs in Trichometasphaeria turcica. It is suggested that aneuploidy is a common phenomenon in the conidial stage of the fungus H. turcicum, and possibly also in other imperfect fungi.     

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.     

Saitoella coloradoensis sp. nov., a new species of the Ascomycota, subphylum Taphrinomycotina

Saitoella coloradoensis sp. nov. (NRRL YB-2330, CBS 12360, type strain, MycoBank accession number 563858) is described. This new member of the phylum Ascomycota, subphylum Taphrinomycotina was isolated from insect frass occurring in an Engelmann spruce (Picea engelmannii) that was growing in Colorado, USA. Multigene sequence analysis showed that S. coloradoensis is distinct from Saitoella complicata, the only other known species of Saitoella. The two species may be separated phenotypically from growth reactions on d-xylose, ribitol and methyl-α-d-glucoside. Asexual reproduction is by budding and both species produce thick-walled, spherical cells that appear morphologically similar to the ascogenous cells formed in plant host tissue by species of Protomyces and some species of Taphrina. The thick-walled cells did not form ascospores but did produce buds when placed on fresh growth media.     

The Ascogenous Hyphae of Pyronema confluens

The ascogenous hyphae arise from the oogonium, opposite groupsof nuclei, as minute, enucleate papillae. Nuclei pass into themsingly, rarely two at a time, and a knob-like swelling is formed,containing several nuclei and later growing out into one ormore branches. The nuclei are in single file in the branchesand irregularly arranged in the bulbous base. There are frequentlytwo nuclei in a leading position at the tip of the young branch,but the nuclei may become more evenly spaced as the hypha elongates.The nuclei undergo a simultaneous mitosis. The spindles of thedividing nuclei in the branches are not parallel and this is,therefore, not a conjugate division. Walls are formed as ingrowingrings across the spindles so that the ascogenous hypha, whenseptate, has a uninucleate end cell followed by one, or usuallymore, binucleate cells and a basal bulb containing a variablenumber of nuclei. Croziers are formed as lateral, hooked outgrowths from the binucleatecells. After a simultaneous mitosis of the two nuclei a uninucleateend cell, a binucleate penultimate cell, and a uninucleate stalkcell are formed. Thus, the division in the crozier and thatin the ascogenous hypha are alike. The binucleate cell of the crozier may proliferate to form anothercrozier, or it may form an ascus after the fusion of its twonuclei. The stalk and terminal cell of the crozier may anastomoseand grow out to form a lateral crozier. The chromosome number in the mitosis in the ascogenous hyphais twelve and there are twelve bivalents at the first divisionof meiosis in the ascus. The effect of increasing the illumination of the cultures withan electric lamp in addition to diffuse daylight is to ensurethe further development of all early formed sexual organs, tomake the ascogenous hyphae develop rapidly, to make the lattershort and curved in form with few binucleate cells, and to increasethe tendency towards a period of erect proliferation beforethe formation of the asci and lateral proliferation begin. The bearing of the results on current theories of sexualityin the Ascomycetes is discussed.     

Anatomy and cytology of Taphrina entomospora during infection of Nothofagus

Taphrina entomospora is one of the few species of the genus described on native plants of the Southern Hemisphere and also one of the few leaf pathogens known on Nothofagus species. The anatomical changes it produces on N. pumilio leaves, and its morphology, cytology, and sporogenesis were studied. The fungus is a perennial species that overwinters as mycelium in the foliar buds and infects the developing leaves, so the whole blade develops the disease symptoms. Interveinal areas of the leaves become chlorotic, thickened and rounded. Palisade parenchyma fails to develop, with spongy parenchyma developing as packed, rounded, isodiametric cells with little intercellular space. The mycelium is subcuticular, dikaryotic, and produces ascogenous hyphae, asci, and ascospores as described for other species in the genus. Before ascus discharge, ascospores bud in a regular, unique way. The life-cycle of T. entomospora is compared with other representative taxa in the genus and the distribution of this pathogen is discussed.     

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.     

Use of Neurospora spore killer strains to obtain centromere linkage data without dissecting asci

Use of a centromere-linked Spore killer gene Sk reduces manyfold the labor involved in obtaining tetrad data that would otherwise require ordered dissection of intact linear eight-spored asci. Heterozygous crosses are made for Spore killer (SkK X SkS) and for markers to be tested. In such crosses only SkK ascospores survive. The four viable (SkK) and four aborted (SkS) ascospores of each ascus are ejected from the perithecium as a physically disordered group. The four surviving SkK ascospores of individual asci are germinated and scored. SkK segregates from SkS at the first meiotic division. If both marker alleles are represented in the surviving products, they must therefore have segregated from one another at the second division. Four-spore (Fsp) genes have been used to eliminate one postmeiotic nuclear division, so that only two ascospores per ascus need to be scored. The Spore killer method has been useful for mapping closely linked genes in centromere regions, for identifying genes that are far out on chromosome arms, for obtaining information on meiotic crossing-over, and for comparing linkages in different species.     

The ultrastructure of septal pores and associated structures in the ascogenous hyphae and asci ofSordaria humana

Summary Septal pores and associated structures have been studied in ascogenous hyphae, croziers and asci ofSordaria humana by means of electron microscopy of serial and random sections. Pores exhibit variable structures from relatively simple pore caps to complex swollen rims with associated membrane cisternae. The simple types are found at the base of the ascogenous hyphae while the complex forms occur at the apex, in the croziers and in very young, presporulation asci. Post-sporulation asci contain a relatively simple type of pore structure. Cells which subtend the ascogenous hyphae exhibit both open and capped pores in their cross walls. Pore structures may be asymmetric in which case they show greater complexity on the side of the cross wall nearest to the apex or crozier. Membranous components of the complex pores are continuous with the endomembrane systems of the two adjacent cells and thus with the outer membranes of the nuclear envelopes. Membrane continuities may connect prefusion nuclei or fusion nuclei in penultimate cells, with nuclei of the stalk and terminal cells of croziers. Some speculation is presented as to the implication and possible roles of these structures in relation to cell differentiation within the ascogenous hyphae and croziers.     

A Putative Rhamnogalacturonase Required for Sexual Development of Neurospora Crassa

In previous work, the asd-1 (ascus development) gene of the filamentous fungus Neurospora crassa was identified as a gene expressed preferentially during the sexual cycle and shown to be essential for normal sexual development. The asd-1 gene has been sequenced and further characterized. It contains two introns, the first of which is in-frame and inefficiently or differentially spliced. The predicted ASD-1 protein has extensive homology with rhamnogalacturonase B of Aspergillus aculeatus, which cleaves the backbone within the ramified hairy regions of pectin. In homozygous asd-1 crosses, sexual development is initiated and large numbers of normal-sized asci are formed. Ascospore delineation does not occur, however, and no sexual progeny are produced. As most asd-1 asci contain eight nuclei, the two meiotic divisions and subsequent mitotic division typical of normal crosses seem to occur, but the haploid nuclei are not partitioned into ascospores. In wild-type crosses, the ASD-1 protein is present in large amounts in croziers and young asci, but it is only faintly detectable in more mature asci containing developing ascospores. Models to explain the possible role of a rhamnogalacturonase in sexual development are presented.     

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.     

Four new species and a new Chinese record of the nectrioid fungi

Four new species belonging to Bionectria, Calonectria, Haematonectria and Neonectria on plant substrates collected from nature reserves in southern and central China are described. Bionectria truncata has smooth perithecia of a flattened to shallow discoid apex, clavate asci with an apical ring, and ellipsoid, smooth to spinulose ascospores. Calonectria dicephalospora is characterized by pyriform perithecia with a warted surface, clavate asci with a simple apex and long, narrow stalk, and fusoid ascospores with a cap-like appendage at each end. Haematonectria lushanensis possesses warted perithecia which are laterally collapsing when dry, cylindrical asci with a simple apex, and ellipsoid, spinulose ascospores. Neonectria dinghushanica is distinguishable by subglobose perithecia with a warted surface, clavate asci, and striate ascospores. Morphological features of these new species are described comprehensively and compared with their related fungi. Neonectria castaneicola is recorded as new to China.     

CHROMOSOME NUMBERS IN THE HYPOCREALES. II. ASCUS DEVELOPMENT IN NECTRIA CINNABARINA

The cytology of ascus development in Nectria cinnabarina was investigated with the orceinsmear technique, from crozier formation to ascospore maturation. At prophase I synapsis occurs while the chromosomes are still contracted, and the nucleus passes through dictyotene, a diffuse stage rarely seen in plants. A haploid complement of five chromosomes has been precisely determined. The first two divisions in the ascus constitute meiosis, and the third (mitotic) is followed by ascospore delimitation. A fourth division takes place in the ascospore, which is subsequently divided by a septum into two uninucleate cells. Of all species of Nectria thus far investigated N. cinnabarina is the only species in which additional nuclear divisions in the ascus do occur, accounting for the multinucleate condition in the ascospore cells. The bearing that this distinctive nuclear condition has on phylogeny and evolution in the Hypocreales is discussed.     

Ascospore formation and morphology in two species of the genusErysiphe remaining immature on the living host plant

Erysiphe cumminsiana andE. galeopsidis, which have immature asci in the current season, have been recorded from Japan, but the ascospores of both fungi have not been described. In the present experiments, some observations before and after overwintering were made on the cleistothecia ofE. cumminsiana on three species ofCacalia and two species ofLigularia, andE. galeopsidis onGeranium thunbergii. After overwintering, the former fungus developed six to eight, rarely four spores in an ascus and the latter fungus always four spores in an ascus. Their teleomorphic characteristics including those of ascospores are also described.