Spore Balls Research Articles

Species of Urocystis (Ustilaginomycetes) on Anemone in Japan

Three species ofUrocystis onAnemone (Ranunculaceae) are reported based on comparative morphology with specimens collected in Japan.Urocystis anemones, U. japonica, andU. pseudoanemones sp. nov. are separated by the number of ustilospores and sterile cells surrounding the ustilospores in the spore balls. Morphological characteristics, host plants and geographical distribution of these three species are also reported.

Outbreak of False Smut of Rice in Louisiana.

False smut, caused by Ustilaginoidea virens (Cooke) Takah., has been occurring in Louisiana rice since at least 1906 (4). A color plate (no. 69) of the disease was published in the Compendium of Rice Diseases published by the American Phytopathological Society (3). The slide for this plate was taken by M. C. Rush in 1976 of rice grown at the Rice Research Station at Crowley, LA. Since that time, the disease has been sporadic and light in Louisiana. In 1997, however, incidence was high. False smut was present on many germ plasms at the Rice Research Station in Crowley and was observed on commercial cultivars in several growers' fields in southwestern Louisiana. Incidence ranged from 1 to 15% of tillers infected with at least two to three spore balls per infected panicle. The disease occurred on both long- and medium-grain cultivars. False smut of rice occurs in the field at the hard dough to mature stages of the crop. A few spikelets in a panicle transform into globose, yellowish green, velvety spore balls that are 2 to 5 cm in diameter and covered by a thin orange membrane. The membrane bursts open and releases powdery dark green spores. The chlamydospores formed in the spore balls are spherical to elliptical, warty, olivaceous, and 3 to 5 × 4 to 6 μm in dimension. Some of the spore balls develop one or more sclerotia, which are the overwintering structure, in the center. False smut has been considered a minor disease of rice that occurs sporadically in Louisiana. The recent discovery of ustilotoxin, a phytotoxin and mycotoxin, produced by this pathogen on diseased tissues suggests that the fungus may be of concern as a contaminant on rice products consumed by livestock and humans (1,2). This increases the need to monitor the incidence of this disease.

Spore Liberation and Dispersal in Smut Fungi*

Abstract:Teliospores are the most important diaspores of smut fungi, albeit not the only ones. The role of basidla, basidiospores, secondary spores, yeast cells, and infected parts of the host for dispersal has often been neglected. Many smut species have soral structures like galls, peridia, and elaters, which cause teliospores to be liberated over prolonged periods. This increases the chance that at least some spores are released under favourable wet climatic conditions and while host plants are susceptible.In this review, the diversity of dispersal units as well as vectors of smut fungi are presented. The importance of timing of diaspore liberation, flexibility in dispersal strategies, and the genetic and evolutionary implications of dispersal strategies of smut fungi are discussed.The general considerations are complemented by examples based on original field and laboratory observations: peridia of Farysia corniculata and certain species of Sporisorium expose the spore mass by hygroscopic movement under wet conditions (hygrochasy) favourable for teliospore germination and infection of a host plant. Basidia with firmly attached basidiospores liberated from spore balls of Doassansiopsis deformans, branched basidiospores of Rhamphospora nymphaeae, needle‐shaped basidiospores of species of Entyloma, folded basidiospores of Mycosyrinx cissi, and stellate groups of yeast cells of Trichocintractia utriculicola show enlarged surfaces, which are advantageous for dispersal in water. Galls filled with spore balls of Doassansiopsis limnocharidis and witches' brooms formed by spikelets infected by Cintractia standleyana separate from the host and fall into water where they are dispersed.

First Report of Flag Smut of Wheat Caused by Urocystis agropyri in the United Kingdom.

An isolated occurrence of flag smut of wheat, caused by Urocystis agropyri (G. Preuss) J. Schröt., was confirmed in the county of Essex, UK, in autumn-sown winter wheat (Triticum aestivum L.) cv. Riband grown from certified seed. The origin of the infection is unknown. Symptoms were first observed on 22 May 1998. The presence of U. agropyri was confirmed on the basis of the macroscopic symptoms on the host and the morphology of the pathogen (2). Long gray-black streaks parallel with the veins were observed on leaf blades, especially the flag leaf, and on leaf sheaths. The streaks consisted of lines of fungal sori developing between the leaf veins, giving a striped appearance. Eruption of the sori through the epidermis of the leaves had caused them to fray, exposing dark brown to black powdery spore masses. Microscopic examination revealed spore balls measuring 20 to 28 μm in diameter containing 1 to 3 spores per ball. Spores were dark brown measuring 12 to 17.5 μm in diameter and were surrounded by light brown sterile cells measuring 7 to 7.5 μm. Affected plants were stunted to about half the height of healthy plants. Some affected plants tillered excessively and in some cases the ear failed to emerge from the boot. Some diseased leaves were twisted and, where the host epidermis had ruptured to expose the spore masses, the affected parts had the appearance of being covered in black soot. All of the symptoms are typical of flag smut on wheat. Flag smut has been observed on grasses in every continent except Antartica. However, the distribution of the pathogen on wheat is more limited. Flag smut of wheat is known to occur in at least some of the countries of the European Union as well as (e.g.) the USA and Australia. This finding is significant because it had been considered that U. agropyri on wheat had reached the limits of its ecoclimatic zone, since it requires specific environmental conditions for infection and disease development, particularly a mild winter and an arid summer (1). The climatic conditions in Essex between September 1997 when the affected crop was planted and May 1998 when symptoms were first observed were considerably drier and warmer than normal, thus favoring the pathogen. This is the first report of U. agropyri on wheat in the UK.

Doassinga, a new genus of Doassansiales

In order to examine the systematic position of Entyloma callitrichis Liro, morphological, ultrastructural and molecular characters of E. callitrichis and some species of the Entylomatales and Doassansiales were studied and compared. The results show that E. callitrichis belongs to the Doassansiaceae, occupying a basal position within this family. In contrast with the other species of Doassansiaceae, the teliospores of E. callitrichis are not arranged in spore balls. Therefore, the new genus Doassinga is proposed to accommodate E. callitrichis.

A survey of the spore-ball-forming smut fungi

The 29 spore-ball-forming smut fungus genera (of the total 58 recognized genera) are analysed, grouped, briefly characterized and illustrated. Problems within the genera, similarities, possible relationships and differences between genera are discussed. The following groups and genera are treated: genera with spores in pairs ( Schizonella, Mycosyrinx, Geminago ), genera with permanent spore balls composed of colourless spores and sterile cells and/or modified mycelia ( Burrillia, Doassansia, Doassansiopsis, Heterodoassansia, Nannfeldtiomyces, Narasimhania, Pseudodoassansia, Tracya ), genera with permanent spore balls composed of pigmented spores and sterile cells ( Urocystis, Moesziomyces, Dermatosorus, Testicularia ), and genera with spore balls containing only spores and lacking sterile cells between the spore balls. Within the latter group, the two sub-groups were distinguished: one with light, brownish spores ( Sorosporium, Thecaphora, Glomosporium, Fulvisporium ), and another one with dark, blackish spores ( Tolyposporium, Tolyposporella, Clintamra, Orphanomyces). Heterotolyposporium has small, hyaline spores between the pigmented spore balls. Sporisorium and Macalpinomyces have sterile cells between the true or pseudo spore balls. Odd genera are: Ustacystis, Mundkurella and Uleiella. A key to the spore-ball-forming genera of smut fungi is given. The value of the spore balls in the taxonomy of the Ustilaginales is discussed. The arrangement of the genera in groups is based on the most important characters of the spore balls. It has a practical, didactic purpose and in many case the groups do not reflect natural relationships.

Microscopical observations of the primary zoospores of Spongospora subterranea f.sp. subterranea

A solution culture test system with Spongospora subterranea f.sp. subterranea spore ball inoculum and tomato bait plants was used to create a pulse of primary zoospore production and subsequent host‐root infection. Spore balls and zoospores were examined by light, fluorescence, and transmission and scanning electron microscopy. Most of the resting spores with a developing exit pore did not show any changes in cytoplasmic content typical of zoospore formation. A few empty resting spores and some with developing exit pores were also observed in the absence of host‐root exudates. The average diameter of exit pores of empty resting spores was 1.5 μm and they were often encircled by a ring‐like fusion of wall layers. Mature zoospores were never found inside resting spores. Primary and secondary zoospores are identical in morphology. The infection process is similar to that of other Plasmodiophoromycetes with internal ‘Rohr’‐like structures in encysted zoospores which were attached by an adhesorium to tomato root hairs. Post‐infection papillae and uninucleate plasmodia were observed.

Sorting of the Initial Cell Types inDictyosteliumIs Dependent on thetipAGene

About 8 hr after the initiation of development inDictyostelium discoideum,a few randomly scattered cells express prestalk specific genes and subsequently sort out to the top of the aggregate where they form a tip. The tip elongates and forms the anterior of the migrating slug before differentiating into a stalk which supports the ball of spores in a mature fruiting body. Using REMI mutagenesis we isolated a mutant strain, AK244, in which the initial aggregate subdivides to give a highly papillated surface. This mutant fails to form slugs and appears to have a defect in sorting of prestalk cells. The disrupted gene,tipA,encodes a novel 83-kDa protein and is preferentially expressed in PST-O cells after the cell types have sorted out. Mutant strains that lack TipA express the prestalk-specific geneecmAat reduced levels and form very few spores. These defects cannot be overcome by developing the mutant cells in the presence of wild-type cells. Thus, TipA acts in a cell-autonomous manner at an early stage in development. Using strains carrying reporter constructs, we found that mutant cells expressing a prestalk marker remain dispersed in the aggregates. Prespore cells appear to sort such that the base is free of cells expressing cell-type-specific markers. Even after 20 hr of development, when wild-type cells are undergoing terminal differentiation, prestalk cells intipA−mutants form very small clumps, most of which fail to sort to the periphery or the tops of aggregates. ThetipAgene appears to play an essential role in the sorting of the initial cell types.

Serological detection of spore balls of Spongospora subterranea and quantification in soil

A polyclonal antiserum produced against spore balls of Spongospora subterranca f.sp. subterranea prepared from potato tubers was able to detect as little as 0·02 spore balls in an enzyme‐linked immunosorbent assay (ELISA). In spiked soil samples, the antiserum detected 100 spore balls per g soil. However, the different spore ball contamination levels were discriminated better in ELISA tests al concentrations above 2000 spore balls per g soil than at lower concentrations. In contrast, a bioassay test based on baiting soils with tomato seedlings gave good discrimination of spore ball contamination levels in spiked soils containing <1000 spore balls per g soil and poor discrimination of levels in spiked soils containing >2000 spore balls per g soil. Tests on a limited number of field soils suggested ELISA may be capable of predicting disease levels on tubers group in such soils better than the bioassay. The antiserum did not react with 30 other micro‐organisms tested, including many that are saprophytes or pathogens on potatoes and resting spores of the taxonomically related Plasmodiophora brassicae. It detected spore balls of different cultivar origin equally well. It also detected spores from different geographical origins. An attempt to improve the sensitivity of the serological detection through concentrating spore balls from held soils by sieving was unsuccessful. Cross‐absorption of the antiserum with uncontaminated field soil increased the sensitivity of detection of spore balls in spiked soil samples four‐fold. The ability of the antiserum to discriminate contaminated field soils from an uncontaminated soil was much improved by using the gamma‐globulin fraction or cross‐absorbed serum. Western blot analysis revealed that the antiserum detected a member of different proteins the most distinct of which had a molecular weight of slightly less than 6.5 kDa. A technique was developed to suppress autofluorescence of spore balls, allowing immunofluorescence studies to be carried out. Using this technique in conjunction with indirect FITC immunofluorescence discrete bright fluorescent spots were visualized using the specific serum. With the non‐specific serum, only a very dull background fluorescence was evident.

Doassansia sagittariae . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Doassansia sagittariae . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Sagittaria species, including S. sagittifolia, S. calycinus, S. cuneata, S. graminea, S. heterophylla, S. lancifolia, S. latifolia, S. montevidensis, S. natans . DISEASE: Leaf spot of Sagittaria species. The round or sometimes vein-limited, angular, spots often cover a large proportion of the leaf surface and are then very conspicuous. The disease usually appears on the plants year after year and is present throughout the vegetative season of the host, athough most obvious in the later part of that season. GEOGRAPHICAL DISTRIBUTION: Widespread in north temperate regions (33, 634). Europe: Austria, Belgium, Czechoslovakia, Denmark, Finland, France, Germany, Hungary, Italy, Latvia, Netherlands, Poland, Romania, Russia (European region), Sweden, Switzerland, UK, Ukraine; Asia: Russia (Republic of Georgia, Kazakhstan, Siberia, Yakutskaya ASSR; Ul'yanishchev, 1952); North America: Canada (British Columbia, Manitoba, Ontario, Saskatchewan; 46, 3383), USA (central states, north east states; Arkansas, Connecticut, Delaware, Florida, Illinois, Indiana, Kansas, ME, Missouri, MT, North Dakota, New York, Ohio, South Dakota, Texas, Vermont, Wiskonsin, Wyoming; 69, 2765); South America: Argentina. TRANSMISSION: From the habitat of the host plants water is assumed to be important in dissemination and infection. Germination of ustilospores either before or after release of spore balls by decay of host leaves inevitably results in presence of basidiospores in water. Liro (1938) suggested the probability of a saprophytic, budding phase in water, followed by early stages of host infection under water, but no detailed studies have been reported.

Regulation of Dictyostelium morphogenesis by cAMP-dependent protein kinase.

During formation of the Dictyostelium slug extracellular cAMP signals direct the differentiation of prespore cells and DIF, a chlorinated hexaphenone, induces the differentiation of prestalk cells. At culmination the slug transforms into a fruiting body, composed of a stalk supporting a ball of spores. A dominant inhibitor of cAMP-dependent protein kinase (PKA) expressed under the control of a prestalk-specific promoter blocks the differentiation of prestalk cells into stalk cells. Analysis of a gene specifically expressed in stalk cells suggests that PKA acts to remove a repressor that prevents the premature induction of stalk cell differentiation by DIF during slug migration. PKA is also necessary for the morphogenetic movement of prestalk cells at culmination. Expression of the PKA inhibitor under control of a prespore-specific promoter blocks the accumulation of prespore mRNA sequences and prevents terminal spore cell differentiation. Thus PKA is essential for progression along both pathways of terminal differentiation but with different mechanisms of action. On the stalk cell pathway it acts to regulate the action of DIF while on the spore cell pathway PKA itself seems to act as the inducer of spore cell maturation. Ammonia, the extracellular signal which regulates the entry into culmination, acts by controlling the intracellular concentration of cAMP and thus exerts its effects via PKA. The fact that PKA is necessary for both prespore and spore gene expression leads us to postulate the existence of a signalling mechanism which converts the progressive rise in cAMP concentration during development into discrete, PKA-regulated gene activation events.

Detection of spore balls of Spongospora subterranea on potato tubers by enzyme‐linked immunosorbent assay

A rabbit was immunized with a homogenate of spore balls (cystosori) of Spongospora subterranea which also contained some potato tuber debris. The resultant polyclonal antiserum contained antibodies which reacted against extracts of spore balls and healthy tubers. Antibodies to the tuber debris were removed by incubating the blood serum with an extract from a S. subterranea‐free tuber. In enzyme‐linked immunosorbent assay (ELISA), the γ‐globulin fraction of the absorbed antiserum reacted with dilute tuber extracts containing the equivalent of as little as 0·08 spore balls per ml. The reaction with spore balls was inhibited in high concentrations of tuber sap. Extracts of peel from symptomless tubers which had been stored in contact with scabbed tubers also reacted with the γ‐globulin, presumably because the symptomless tubers became contaminated with spore balls. However, spore balls in soil were only weakly detected when high numbers were present. The γ‐globulin did not react with the plasmodial stage of the pathogen, or with 15 other micro‐organisms tested, including resting spores of Plasmodiophora brassicae.

Ultrastructural changes in the spore and mycelia of Ascosphaera apis after treatment with benomyl (Benlate 50 W)

In Ascosphaera apis, after 8 days growth in darkness at 28° C, numerous sporocysts were observed, within which mature spores were seen aggregated into a spore ball. The mature spore of A. apis had a thick spore wall with an electron-opaque outer layer, a spore membrane with many depressions, and sporoplasm containing numerous ribosomes and mitochondria. In the cytoplasm of the mycelium, mitochondria with well-defined cristae and numerous ribosomes were observed. At a concentration of 1 μg/ml of culture medium, benomyl appeared to inhibit colony growth of A. apis, but some sporocysts containing deformed spores were found. Deformed spores possessed a thick spore wall with a grainy matrix, and depressions were no longer detected in the spore membrane. Ribosomes were lacking in the sporoplasm and mitochondria appeared degenerate. The mycelium from the treated culture contained mitochondria with an electron-lucid matrix and no well defined cristae, while ribosomes were completely depleted. The significance of these observations in relation to the use of benomyl to control chalkbrood disease in the honey bee is discussed.

Urocystis brassicae . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Urocystis brassicae . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Brassica campestris (Indian mustard) and, by inoculation, B. juncea, B. napus, B. nigra, B. oleracea var. capitata , B. rapa var. lorifolia and Raphanus sativus .DISEASE: Root gall smut of Brassica campestris . The plants are stunted, possibly flower early, and have pale leaves, with pods (if formed) empty or with very few, possibly sterile seeds. On careful removal of soil from the roots, galls are found, commonly on the finer roots, and can be readily detached. GEOGRAPHICAL DISTRIBUTION: Asia: India (Pusa), possibly China (as Tuburcinia coralloides var. cantonensis Ciferri). TRANSMISSION: Soil borne: spore balls are released in soil by the breakdown of the galls, and infection occurs when seed of susceptible hosts is sown in the infected soil. Attempts to induce disease by sowing seed dusted with ustilo-spores in uninfested soil were unsuccessful (6, 208).

A new spore cyst fungus from New Zealand

Asosphaera scaccaria sp.nov. is described. The mature ascospores of A. scaccaria in spore balls as perpendicularly arranged bundles of eight, giving the mature spore ball a unique appearance. A. scaccaria is associated with the larvae and prepupae of the sand-nesting, colletid bees, Leioproctus boltoni (Cockerell), L. metallicus (Smith) and two new as yet undescribed species of Leioproctus.

Fine structure of the sporocysts of Ascosphaera apis during development as revealed by the scanning electron microscope

The fine morphology of the sporocysts of Ascosphaera apis (Maassen ex Claussen) Olive & Spiltoir, an entomopathogenic fungus of the immature honey bee has been studied using the scanning electron microscope. During the third day of mycelial growth in the culture medium, numerous short, branched hyphae were formed. The tip of the branch-hypha gradually expanded to form immature sporocysts. The immature sporocysts contained a large number of globules of varying sizes. The walls of the immature sporocysts were finely wrinkled, becoming smooth as the sporocyst matured. Both exterior and interior surfaces of the sporocyst wall possessed numerous papillae. Some globules in the developing sporocyst began to form immature spores which aggregated to form spore balls. The fully formed spore balls were not enveloped by a membrane.

Aspects of spore ball formation in Achlya

Following release from the sporangium, spores of Achlya intricata aggregate at the sporangial apex, round-off within 30 s and encyst. Rounding-off is delayed or prevented by depression of the external osmotic potential with sucrose, suggesting that net uptake of water is necessary for the change in shape to occur. The first spores to be released from the sporangium become bound to the outer surface of the sporangial wall, forming a sub-apical ring upon which other spores become attached. The spherical cluster of encysting spores continues to increase in size until 30 s after complete emptying of the sporangium. The initial aggregation of the spores is dependent upon extracellular Ca2+, though longer-term adhesion between cysts is Ca2+-insensitive.

Life Cycle of the Chalk Brood Fungus, Ascosphaera aggregata, in the Alfalfa Leafcutting Bee, Megachile rotundata, and Its Associated Symptomatology

The life cycle of Ascosphaera aggregata in Megachile rotundata and the symptomatology of the resultant disease are described. The formation of the ascogonium, and the process by which the asci are formed within it, are unlike other Ascomycetes. Variable numbers of asci develop within a membrane-bound “chamber,” which is derived from the ascogenous hyphae within the nutriocyte. Following sporogenesis, the newly developed ascospores are retained within the membrane-bound chambers where they form tightly packed, spore-containing spheres, the spore balls.

Ascospore discharge in the annulate form of Hypoxylon truncatum

Ascospore discharge in the annulate form of Hypoxylon truncatum (Schw.:Fr.) J. H. Mill, is preceded by the loss of the peridial wall covering of the ostiolar region. This is accomplished by way of a specialized mechanism which involves hyaline spongy tissue located between the outer amorphous and inner palisade wall layers of the perithecium. The exposed ostiolar projection becomes concealed by terminal bulbous cells of short hyphae that arise from nearby peridial cells. Disintegration of the ostiolar projection occurs concomitantly with the disappearance of these bulbous cells. By this time a large part of the pseudoparenchyma and most of the paraphyses in the centrum have degenerated to form a transparent gelatinous mass. Asci deliquesce and release mature ascospores within the perithecium just prior to ascospore discharge. The ascospores ooze out of the ostiole mixed with the gelatinous material and form either a massive spore ball or a spore tendril.

The species of Thecaphora on Compositae in North America

Five new species of Thecaphora collected in Mexico are described, some of which are parasitic on genera of Compositae not previously reported as hosts. Species of Thecaphora on Compositae for the North American continent now total 11. New species include Thecaphora denticulata, T. heliopsidis, T. hennenea, T. melampodii, and T. neo-mexicana. New host genera for North America include Bidens, Heliopsis, and Melampodium. Morphological characteristics of Thecaphora species and taxonomic criteria to delimit them are discussed. Keys to the species, interpretations of spore ball morphology and spore sculpturing, and scanning electron and bright-field micrographs are presented.