The initial events involved in basidiospore germination and infection of dyer's woad by Puccinia thlaspeos were studied using scanning electron microscopy and the polymerase chain reaction. The presence of dew was shown to promote infection but was not necessary. Under the conditions of this study, infection of leaf tissue could sometimes be detected using the polymerase chain reaction as quickly as 3 h after inoculation, but 6 h was usually required. Basidiospores and germ tubes were both attached to the leaf surface by an extracellular matrix, and the germ tubes produced appressoria before penetration into the leaf tissue. Penetration was direct rather than through the stomates, and colonization occurred via the growth of intercellular hyphae and haustoria.Key words: biological control, mycoherbicide, noxious weed, Puccinia, dyer's woad.

Dyers Woad (Isatis tinctoria) is an introduced noxious weed of crop and rangeland in northern Utah. A native rust fungus (tentatively identified as Puccinia thlaspeos) is being investigated as a possible biological control agent of the weed. In order to effectively use the rust in a bio-control program, it is necessary to understand its epidemiology and characteristics.Weeds were inoculated by suspending previously infected weed leaf fragments over test plants. Teliospores on these fragments produced basidiospores which dropped onto the weed seedling leaf surfaces. Inoculated leaves were prepared for SEM by fixation in 2% cacodylate buffered glutaraldehyde, post fixed in 2% buffered osmium tetroxide and dehydrated through ethyl alcohol and critical point dried. Mounted specimens were sputter-coated with gold. Some tissues were freeze fractured in 100% alcohol and fragments were critical point dried, coated and mounted for SEM.

This study addressed the differences in microsporogenesis between male sterile and fertile lines of Chinese pink. The microsporogenesis processes of male sterile and fertile lines were histologically examined in squashed pollen grains and in paraffin embedded sections. A stable male-sterile line (H-37B) was obtained following six generations of inbreeding in a self-fertile line, followed by two generations of backcrossing. In the corresponding fertile line, development of the mature pollen grains was followed through the initiation of the sporogenous cell, microsporocyte formation, and the tetrad developmental period. In the male-sterile line, abortion of the developing pollen grains was observed to take place at various stages, namely, sporogenous cell growth, mother cell meiosis, and tetrad transformation to the uninuclear state. The pollen grains of the fertile line were spheroid, turgid, and viable. By contrast, the male-sterile line produced pollen that was irregular in shape, empty, and nonviable. The abortion of the microspore in the male-sterile line appeared to relate to abnormal growth of the tapetum layer.

SUMMARYFruit bodies of Nidularia pulvinata were grown in the laboratory on a special nutrient-supplemented straw medium. Fruit bodies were cryo-sectioned, fixed, dehydrated, critical-point dried, and observed in a scanning-electron microscope. Young fruit bodies were clearly differentiated into an upper portion and a lower portion where peridiole formation began. The peridium of young fruit bodies was composed of dense spinose skeletal hyphae which differentiated into three layers as they matured. The peridioles were formed from spherical aggregations of hyphae. They eventually developed a three-layered cortex. The peridioles gradually became oval with a central cavity in which basidiospores were produced. Four basidiospores on long sterigmata were formed on each basidium. Distribution of gelatinous material appeared to be correlated with development. Some similarities in ultrastructure between Nidularia and Cyathus were noted.

ABSTRACT Interactions between fungal and algal components of Usnea cavernosa Tuck, were demonstrated with transmission and scanning electron microscopy. Cells were observed in very close associations, and both intrawall and intracellular haustoria were evident. In addition, a previously unreported type of interaction was discovered which consisted of an extracellular hyphal sheath with distinctive protuberances which penetrated into the algal cell wall. Internal environmental factors which may bear on the types of cellular interactions were evaluated by dividing the lichen thalius into three artificial regions using spatial and temporal criteria. Fungal hyphae in the various internal anatomical zones (e.g., cortex, medulla, central cord) demonstrated differences in cell wall structure and extracellular material produced.

SUMMARYSUMMARYFruit bodies of Mutinus caninus were grown in the laboratory on a special nutrient-supplemented straw medium. Fruit bodies were cryosectioned, fixed, dehydrated, critical-point dried, and observed using scanning-electron microscopy and photography. Young fruit bodies were differentiated into a peridium and an inner core from which the gleba and pseudostem differentiated. A gelatinous layer developed between the peridium and inner core and gradually increased in thickness during fruit body development. Hymenial differentiation began as a cluster of indistinct chambers. Pseudostem formation occurred after hymenial differentiation. Eight basidiospores were produced on each basidium. Numerous cells, formed in folds in the wall of the pseudostem early in development, increased in size as development proceeded. Their expansion apparently caused the elongation of the pseudostem.

Examination of cooked pre-rigor muscle by TEM (transmission electron microscopy) and SEM (scanning electron microscopy) revealed that all cookery methods resulted in the development of supercontraction bands alternating with areas showing tissue fragmentation and tearing. Microwave cookery produced smaller and less dense supercontraction nodes in pre-rigor muscle with less tearing and fragmentation but more fibre separation. Although cold-shortened pre-rigor muscle cooked by all methods also exhibited supercontraction bands with some tearing and fragmentation in adjacent sarcomeres, the samples cooked by microwaves showed a more uniform repeating pattern of small stretched areas alternating with dense contracted areas. Cooking of muscle in full rigor resulted in myofibrillar protein coagulation and shrinkage but supercontraction nodes were absent. Cold-shortened bicarbonate treated muscle was relatively intact after cooking, exhibiting fusion of the myofibrils and an absence of intermyofibrillar spaces. Results are discussed in relation to possible effects upon tenderness.

Polysaccharides (1,2-glycols), identified by a cytochemical stain at the ultrastructural level, were found in storage droplets of algal cells and cytoplasm of both the medullary hyphae and hyphae of the chondroid central cord of Usnea cavernosa Tuck. The intercellular matrix of the chondroid cen- tral cord contained no polysaccharides stainable with the method employed. High concentration of 1,2-glycol polysaccharides noted in the hyphal cyto- plasm of the chondroid central cord may suggest a possible function of the cord as a storage tissue for a readily converted energy source.

Zygosporangium and zygospore formation in Phycomyces nitens was followed by correlative light microscopy and scanning and transmission electron microscopy. Compatible multibranched zygophores became interlocked by the interdigitation of their lobes. Progametangia grew up from the substratum in pairs and then differentiated into gametangia and tongs-shaped suspensors. Plasmogamy was deferred until the gametangia were delimited. Development of rings of hyaline appendages on the suspensors was concomitant with plasmogamy. The appendages originated from the tertiary suspensor wall layer and ruptured the outer primary and secondary wall layers prior to development of their terminal thornlike processes.Developing zygosporangia contained a large central vacuole and some organelle zonation; however, these features were not discernible in more mature zygosporangia. A reticulum of electron-opaque fluted warts developed within the secondary zygosporangial wall layer. Cryofractured zygosporangia revealed a smooth hyaline zygospore with truncate ends. Wall layer relations of mature zygosporangia and zygospores were presented. Information obtained was correlated with existing ultrastructural observations on zygosporangiogenesis in the Mucorales.

SUMMARYCyathus stercoreus was grown in the laboratory and basidiocarps produced in culture were prepared for study with the scanning and transmission electron microscopes. The peridium consisted of three morphologically distinct layers. The funiculus consisted of three regions. The hyphae in these regions, the funicular cord and hapteron showed a special modification in the clamp connections. The peridioles had a wall consisting of three layers. The spores were surrounded by special nurse hyphae. Cyathus stercoreus structure is far more complex than light microscopy has revealed in the past. Ultrastructural study shows the nature of some previously described structures to be in error.

Abstract UHF Electromagnetic energy (2450 MHz) is lethal at dosages from 100-200 J/cm 2 to seeds of several weed species. Seeds were exposed to uniform energies by placing them in a quartz tube and inserting the tube in a waveguide. Seeds of barnyard grass, ( Echinochlea crusgalli (L.) Beauv.), large crabgrass ( Digitaria sauginalis (L.) and common purslane ( Portulaca oleracea L.) showed no visible external damage when viewed in the scanning electron microscope at up to 5,000 × after treatment. No discernible internal damage was visible when tissues were immediately fixed and viewed by transmission electron microscopy after receiving minimum lethal dosages of UHF energy. At higher UHF dosages, membrane breakage and loss of integrity of organelles was observed. ATPase activity in treated seeds was monitored by transmission electron microscopy as an indicator of possible UHF destruction of enzymes. ATPase activity of tissues was absent after minimal or higher dosages of microwaves. Cells receiving minimal UHF treatment otherwise appeared normal. Toxicity from microwaves may occur as a result of selective heating of cells which results in partial protein denaturization and inactivation of key enzymes.

Apothecial ontogeny in Pulvinula tetraspora, an operculate Discomycete (Pezizales, Pyronemataceae), was followed by correlative light microscopy and scanning electron microscopy. Hymenial development was paragymnohymenial; opening occurred in the prohymenial phase. A functional ascogonium gave rise to ascogenous hyphae which by sympodial and centrifugal growth, produced typical croziers. Developmental aspects of the sterile and fertile portions of the apothecia were described and illustrated.

Transmission and scanning electron microscopy were used to study the development of Syncephalis sphaerica (Piptocephalidaceae, Mucorales) merosporangia. Merosporangia were initiated as simple evaginations of the ampulla wall. Three spores were cleaved out of each merosporangial protoplast by invaginations of the merosporangial plasmalemma. An abscission zone was formed in each cleavage zone. A fibrillar spore wall was laid down between the spore plasmalemma and the inner lining layer of the merosporangial wall. Portions of the outer merosporangial wall remained attached to the spore at the time of detachment. During late cleavage, a wall was laid down on the surface of the ampulla at the base of each merosporangium forming a scar. Mature spores remained associated with the ampulla as a spore drop.

SUMMARYSyncephalis sphaerica (PiptocephaUdaceae, Mucorales) is a biotrophic, haustorial mycoparasite. Fifty genera of fungi, representing four classes, were tested as potential hosts for the parasite. Twenty genera of Mucorales supported growth and sporulation of S. sphaerica. A single ascomycete (a yeast) and two members of the Deuteromycetes were also parasitized by S. sphaerica. None of the Basidiomycetes tested supported growth of the parasite.Axenic culture of S. sphaerica was partially successful, with dense mycelial growth and some sporulation on certain media. The use of certain filtrates with host exudates as well as the use of killed mycelium to support growth was unsuccessful. The host range and axenic culture of S. sphaerica are compared to S. californica and species of Piptocephalis.

SUMMARYWhen freeze-fractured fungal structures are critical point dried and then examined in the scanning electron microscope a number of structures are evident that are obscured by other techniques. A comparison of freeze-fracture to the techniques of razor blade sectioning and microtomy of wax-embedded or plastic-embedded material was carried out or reviewed from the literature. In most cases superior results can be obtained with the cryofracture technique followed by critical point drying.