Mature Sclerotia Research Articles

The ontogeny of the sclerotia of Colletotrichum coccodes

The ontogeny of the sclerotia of Colletotrichum coccodes was investigated by scanning electron microscopy. The sclerotium originated as an acervulus differentiated from a stroma, a mass of tightly interwoven thick-walled hyphal cells. Initially, hyphae at the surface of the stroma differentiated into conidiophores and conidia which resulted in a typical acervulus. Following sporulation, the stroma beneath the acervulus assumed the form of a sclerotium. This sclerotium expanded laterally by repeating the processes of acervulus development. As a result, a large aggregate composed of several small sclerotia was formed.Structurally, a mature sclerotium, regardless of its size and shape, consisted of three zones: the outermost, sclerotized, brown spongy layer; the middle, plectenchymatous layer; and the innermost, prosenchymatous core (medulla). The majority of cells in the spongy layer were empty. The plectenchyma consisted of living, tightly packed, thick-walled cells with little or no intercellular spaces. The prosenchyma consisted of loosely packed, living hyphal cells.

Gas exchanges by Phymatotrichum omnivorum in a closed, axenic system

Gas exchanges byPhymatotrichum omnivorum were studied in a closed, axenic system. The fungus liberated CO2 and ethylene, and appeared to utilize N2. Over a 44-day test period, CO2 increased from 0.1 to 312.8 ml/liter. Oxygen decreased from 211 to 17.8 ml/liter and N2 decreased from 789 to 669.5 ml/liter during the same period. The combined uptake of N2 and O2 was equal to the release of CO2 in the ambient gas. A rapid increase in ethylene was observed 14 to 28 days after the flasks were inoculated (15 to 160 nliter/liter). Mycelial strands and sclerotial initials formed on the flask sides, but mature sclerotia did not develop.

Morphology, development, and cytochemistry of the hyphae and sclerotia of species in the Rhizoctonia complex

A detailed comparison of the gross morphology of hyphae, monilioid cells, and sclerotial formation and structure of 17 isolates of species in seven genera of the Rhizoctonia complex were studied. Cytochemistry of both hyphal and sclerotial cells was also studied. Gross morphology of hyphae was similar in many of the isolates and was considered of limited taxonomic value. Sclerotial formation in species of Thanatephorus, Waitea, Aquathanatephorus, and possibly Ceratobasidium was of the monilioid cell type. That of Athelia was of the hyphal strand type. Although initially similar, mature sclerotia in each of the genera showed great diversity. Most sclerotia of Thanatephorus were constructed of loosely arranged monilioid cells. Those in Ceratobasidium developed a marginal rind; Aquathanatephorus, a pitted surface and hyphal mat; Waitea, a bilaminate condition with elongate marginal and globose medullary cells; and Athelia, a complex tetralaminate structure. Distribution and concentration of carbohydrates, proteins, and lipids differed in the various genera. The strong dextrinoid reaction of the cytoplasm of Thanatephorus and Aquathanatephorus, accompanied by higher total lipids in cell walls and septa, was of significance. Stronger reactions for cellulose were found in species of Ceratobasidium, while cellulose appeared more concentrated in sclerotial cells than in hyphal cells of Thanatephorus. Lipids were deposited more abundantly in sclerotial cells than in hyphal cells.

Ultrastructural basis of sclerotial survival in soil

The ultrastructure of developing and mature sclerotia ofSclerotium rolfsii was studied with a scanning electron microscope. The mature sclerotium is disconnected from the mycelium and well differentiated. The rind is composed of rather thick-walled empty cells. The cortex cells are large and almost completely filled with vesicles, whereas the medullar cells are smaller and some of them are very thickwalled.

Changes in Total Soluble Proteins and in Some Enzymes during Morphogenesis of Sclerotium rolfsii

SUMMARY: Patterns of soluble proteins and enzymes were studied in the normal mycelium of the fungus Sclerotium rolfsii and at three stages of sclerotial formation. Significant changes in total soluble proteins were found during the morphogenetic process, as detected by gel isoelectric focusing. While no changes could be detected in acid phosphatase activity, peroxidase activity was higher in mature sclerotia than at other stages. Polyphenol oxidase activity was demonstrated with dihydroxy-phenylalanine, catechol and tyrosine as substrates. While only one active isozyme of the latter enzyme was found in the mycelium, six different isozymes were detected in the mature sclerotia. Esterase isozymes, on the other hand, decreased significantly during morphogenesis.

The sclerotia of Coprinus lagopus.

Sclerotia of Coprinus lagopus were produced in the laboratory and observed microscopically from initiation to maturity. Isolated bulbous hyphal cells appeared below or on the agar surface as the primary sclerotial initials. Short interhyphal cells had expanded lateral walls and increased in number at their isolated locations, and were surrounded by a thick network of normal mycelium. Increasing in numbers, the bulbous cells developed a tightly compact colony devoid of agar if submerged below the agar surface and lacked normal hyphal filaments. The outer cells thickened formed cell lumina and developed as a protective rind to the mature sclerotium.

Ultrastructure of Sclerotia and Hyphae of Sclerotium rolfsii Sacc.

Summary The ultrastructure of cells of the sclerotia and aerial mycelium of Sclerotium rolfsii Sacc. was studied by electron microscopy. A mature sclerotium of S. rolfsii contains several types of differentiated cells. The thick-walled rind cells which comprise the sclerotial envelope are empty. The underlying cortex cells have thinner walls and contain many vesicles full of reserve materials which appear dark after treatment with osmium tetroxide. Although less reactive to osmium tetroxide, the cells between the cortex and medulla are also rich in reserve materials, some of which are membrane-bound. The inner layer (medulla) is composed of cells with extremely thick walls, of thinner-walled cells full of reserve materials and of empty cells. The walls of the hyphal cells are significantly thinner, and less optically dense than the walls of any of the sclerotial cells. Hyphal cells contain more ribosomes and mitochondria than sclerotial cells. It seems that the resistance of sclerotia to biological degradation depends upon the melanin-rich rind as well as the wall structure and organization of cells comprising the inner layers of the sclerotium.

The role of sclerotial rind in the germinability of sclerotia of Sclerotium rolfsii

Punctured sclerotia of Sclerotium rolfsii Sacc. germinated more rapidly than unpunctured ones, especially on water agar. Discs of agar with mycelium and sclerotia in different stages of development were transferred to medium supplemented with 14C-iodoacetic acid. The radioisotope was not incorporated into mature sclerotia. It was concluded that the sclerotial rind is a mechanical barrier preventing uptake of nutrients from the medium.

The Ontogeny of the Sclerotia of Pyronema domesticum

SUMMARYThe small, dark sclerotia of Pyronema domesticum form in abundance in potato dextrose agar cultures, and originate when certain hyphae undergo the progressive and simultaneous processes of bulging, branching, and coiling. Individual cells are formed by septa delimiting each bulge, and maturation follows. The mature sclerotium consists of three distinct zones, an outer one of partially collapsed cells, the rind or cortex, and the medulla.

The development of sclerotia of certain fungi

The development of sclerotia of six species of fungi was studied and three different methods of formation were distinguished. Sclerotial initials of Rhizoctonia solani develop by the increased branching and septation of the ordinary hyphae. The mature sclerotia are rather loosely constructed of brown barrel-shaped cells with dense contents. Sclerotia of Botrytis allii, B. cinerea and Sclerotium cepivorum develop terminally by the repeated dichotomous branching of a hyphal tip followed by increased septation and fusion of the branches. Mycelial strands of S. rolfsii and Sclerotinia gladioli put out branches which coalesce to form the sclerotia.

STUDIES ON SCLEROTIZATION IN PHYSARUM POLYCEPHALUM

THE RESISTANT STRUCTURE produced by gradual desiccation of a myxomycete plasmodium is usually termed a sclerotium. Since this stage does not appear to be necessary for the completion of the life cycle of the Myxomycetes it has received relatively little attention. Sclerotization has been attributed to desiccation, low temperature, inadequate food supply and . . . unknown (de Bary, 1887), but few critical studies of the causes of sclerotization have been made. A difference of opinion exists among students of the group regarding starvation as a factor, and no information upon the effect of temperature per se appears. Hodapp (1942) observed sclerotia of Physarum polycephalumn formed by desiccation for various time periods and at various temperatures between 70 and 35?C. He noted that gradual death rather than sclerotization took place at 5?-6'C. According to Luyet and Gehenio (1944), death or decreased viability of the sclerotium itself may occur in Physarum polycephalum when desiccation proceeds beyond the amount of water naturally present. Sclerotia appear to be viable for only a few years, in contrast to the longevity of myxomycete spores which in some instances have germinated after 63 years of storage in an herbarium (Elliott, 1949). Jahn (1919) reported his inability to revive sclerotia of Badhamia utricularis after 40 months of storage, and Hodapp (1942) noted a greatly reduced germinating power of the sclerotia of Physarum polycephalum after 8-13 months of storage. A somewhat dubious account by Leveille, cited by de Bary (1887), of the viability of a 20-year-old myxomycete sclerotium of unknown species contrasts with a critical study of over 100 sclerotia of Physarum polycephalum by Gehenio (1944) which indicated that viability was completely lost after 3 years. The microscopic structure of dry, mature sclerotia has been described for Badhamia utricularis by J0rgensen (1925) and for 12 other species of Myxomycetes by Brandza (1928). The latter study did not include Physarum polyceplhalum. The object of this investigation was to study the process of sclerotization and plasmodial reconstitution. Factors inducing sclerotization, and the possible role of the sclerotium in the life history of Physarum polycephalum as well as the applicability of the term sclerotium to the structure in question were also considered. MORPHOLOGY OF SCLEROTIA.-Sclerotia produced by various methods in the laboratory as well as out of doors ranged from a reticulum resembling a typical active plasmodium to a thick irregular mass. Some sclerotia consisted of a thin plaque roughly