The effect of vesicular arbuscular mycorrhizal associations on growth of cereals

The growth of wheat seedlings which were already mycorrhizal when transplanted to a field deficient in phosphorus was improved compared with non-mycorrhizal controls, and grain yield was increased three-fold by the fungus, indicating that Endogone stimulated growth and increased yield. Differences between mycorrhizal and non-mycorrhizal wheat were eliminated by the application of phosphate fertilizer, indicating that the fungus does not enhance wheat growth in soils containing enough available phosphate. It is probable that the mycorrhizal effect is primarily to improve the supply of phosphate. There were clear relationships between spore number in the soil and mycorrhizal development and between the extent of root infection and increased growth. The extent of root infection was greatest in mycorrhizal plants in soil not supplemented with phosphate and it decreased in inoculated plants in the plot supplemented with superphosphate. The non-centrospermous and non-zygophyllaceous weeds growing on the experimental field had typical vesicular arbuscular infection and indigenous Endogone spores in their rhizospheres. The centrospermous plants were non-mycorrhizal and had no Endogone spores in their rhizospheres.     

Myrothecium: A new indoor contaminant?

In the natural environmentMyrothecium species occur as soil or leaf surface saprobes or as weak plant pathogens. In addition, some species ofMyrothecium are known to produce trichothecene mycotoxins. During a previous aerobiological investigation at two Las Vegas elementary schools,Myrothecium conidia were found to be the second most abundant spore type identified indoors from Burkard personal spore trap samples. The present study was undertaken to re-examine the schools to locate the source ofMyrothecium spores and to examine the ability ofMyrothecium to grow on indoor substrates. There were no obvious signs of contamination in the classrooms; however,Myrothecium spores occurred on about 30% of the Burkard samples. Two colonies ofMyrothecium were identified from subcultures of the Andersen samples, and three colonies were identified from carpet dust samples. Culture studies showed that a strain ofMyrothecium cinctum was able to grow on various culture media as well as on various indoor substrates including paper, cardboard, wallpaper, ceiling tiles, dry wall, carpets and cotton rug. Although there was no attempt to estimate any human health risks, these investigations are believed to be the first to document abundantMyrothecium spores from indoor air samples.     

Recovery of Pseudocercosporella herpotrichoides Spores from Rain-Splash Samples

Methods for recovery of P. herpotrichoides spores from rain-splash were tested, initially with pure spore suspensions and then with field samples. Provided surfactant was added and samples were processed immediately, centrifugation gave good recovery or spores from field samples which contained few soil particles. Foam-flotation, glycerol and sucrose methods for separation of spores from soil particles were not satisfactory for P. herpotrichoides spores. A paraffin oil method proved to be the most reliable because it gave good recovery of P. herpotrichoides spores from field samples containing many soil particles.     

Honey-coloured,sessile Endogone spores: II. Changes in fine structure during spore development

Summary The fine structure of honey-coloured, sessile Endogone spores is described from initiation of the mother spore to dormancy of the resting spore. Three unusual organelles occur viz. pigment granules, large crystals and selfduplicating bacteria-like organisms. The first two are very numerous, and are specifically associated with spore formation. The pigment granules are involved in the deposition of the honey-coloured wall, and change into myelin-like figures when cytoplasm moves from the mother into the resting spore. The crystals, whose function is not known, are most conspicuous just before the resting spore reaches dormancy. The bacteria-like organisms, which may be actinomycete spores living symbiotically in the fungus, multiphy greatly as the spore enters dormancy. The dormant spore contains very little cytoplasm compressed into a fine network between very large polygonal oil globules and large round bodies thought to contain a storage polysaccharide.     

Scanning electron microscopic observation of resting spore clusters ofPolymyxa spp.

Resting spore clusters ofPolymyxa graminis andP. betae, fungal vectors of virus diseases, were observed using the scanning electron microscope. The spore clusters in host plant cells were uncovered using the styrene resin cracking method. Resting spores ofP. graminis were found to be spherical, whileP. betae spores were more irregular in shape.     

Seasonal variation in the spore bank of ferns in grasslands on dolomite rock

Composition and seasonal patterns of the fern spore bank were compared to the surface vegetation of grasslands on dolomite rock in Hungary. Viability and potential dormancy of spores were tested through storage experiments. Although Asplenium ruta-muraria L. was the only species found at the study sites, five others, probably originating from air-borne spores from nearby areas, emerged from the soil samples. Considerable seasonal variability was detected in the number of prothallia emerging from soil samples from different sampling dates, with a peak after spore dispersal. The increased number of emerging prothallia after 1 year of storage suggests that a part of the spores stored in the soil samples were presumably dormant. Investigations on the dormancy of fern spores might be of great interest, especially in species adapted to seasonally unfavourable habitats.     

Honey-coloured,sessile Endogone spores

Summary Wall structure is described in the parent and resting spores of an Endogone sp. with honey-coloured, sessile spores. Wall thickness increases in the parent spore and subtending hypha by passage of material through the plasmalemma, or by formation of an apparently separate inner wall and degeneration of the trapped cytoplasm. Structure and development of the multi-layered wall of the mature resting spore are described. Unusual features are: 1. the incorporation of many pigment granules into the coloured outer wall, 2. the presence between the outer coloured and inner transparent walls of a tripartite membrane and adjacent layer with a regular periodicity and 3. a sectored layer with a crystalline component. The structure of the wall is discussed with reference to that of other mucoraceous fungi, to spore germination and to the mechanism of wall formation.     

Daily and seasonal variations ofAlternaria andCladosporium airborne spores in León (North-West, Spain)

The spores ofAlternaria andCladosporium are present throughout the year in the atmosphere of León (NW Spain), although they show an important seasonal variation. To understand the relationship between the number of spores and climatic factors,Alternaria andCladosporium spores counts for January 1994 to December 1995 were examined by means of correlation analyses. The results of weekly samples of both years showed that the spores concentration of two taxa are significantly and positively correlated with maximum and minimum temperature and sunshine hours and negatively with relative humidity. The statistical analysis of daily samples generally showed the same results. In the hourly distribution of spore concentrations we can see a similar behaviour ofAlternaria andCladosporium, with most spores collected in the 12–14 h period.     

Airborne fungal spores in 80 homes in the Latrobe Valley, Australia: levels, seasonality and indoor-outdoor relationship

Airborne viable and total fungal spores were sampled inside and outside 80 houses in the Latrobe Valley, Victoria, Australia as part of a larger indoor environmental study. Each residence was visited six times over a period of 1 year for sample collection, and fungal spore samples were collected from at least three indoor sites and from an outdoor site. Viable spores were sampled using an Andersen sampler, while total spores were assessed using a Burkard spore trap. Identification of fungal colonies to genera level was performed in two seasons; winter and late spring. The most common fungal genera/groups wereCladosporium, Penicillium, and yeasts, both indoors and outdoors in winter and late spring. Outdoor levels were higher than those indoors throughout the year, and a significant seasonal variation in spore levels was seen both indoors and outdoors with overall maxima in summer. Contrary to this trend, the levels ofAspergillus, yeasts,Cephalosporium andGliocladium were higher in winter. Most fungal genera were found in greater concentrations outdoors compared to indoors, butPenicillium was more common indoors. Outdoor spore levels were a significant influence on indoor levels, but seasonal differences suggest that other influences are important.     

Resting spore formation ofLeptocylindrus danicus (Bacillariophyceae) during short time-scale upwelling and its significance as predicted by a simple model

Resting spore formation during short time-scale upwelling and its significance were investigated in the field and by a simple theoretical model. Field observations of spore formation ofLeptocylindrus danicus were made off Izu Peninsula, Japan. A rapid increase in ratio of resting spore to vegetative cell numbers indicated thatL. danicus formed resting spores quickly as a response to nutrient depletion in the upwelled water, although only a very low number of resting spores was found in the upwelling. A simple model was constructed to investigate the possible advantages of spore formation during short time-scale upwelling. This showed that there is a critical time-scale for resting spore formation to be advantageous. The nutrient depletion period of the upwelling off Izu was shorter than the critical time-scale determined by the model. Rapid-sinking of resting spores may increase further the critical time-scale, unless spores return with upwelling water. For short time-scale upwelling, the vegetative cell may be better suited than the resting spore for enduring a short period of nutrient depletion. Contribution from Shimoda Marine Research Center, University of Tsukuba, No. 475.     

Effect of volatile substances fromOriganum majorana andOcimum basilicum on spore respiration and germination of some soil fungi

Oxygen uptake by the spores ofFusarium moniliforme, F. oxysporum, F. semitectum, F. solani, Mucor racemosus andTrichoderma viride was increased in the presence of volatile substances extracted, fromOriganum majorana andOcimum basilicum. This increase was greater in the presence of volatile substances fromO. basilicum thanO. majorana, except in the case ofF. semitectum where the reverse was true. A drop in the RQ of all the germinating spores was observed in the presence of these substances. Volatile substances fromO. majorana reduced the spore germination ofM. racemosus whereas the spores ofT. viride were stimulated to germinate. Volatile substances fromO. basilicum stimulated the spore germination ofM. racemosus whereasT. viride spores were not affected.     

Impact of long-term conventional and organic farming on the diversity of arbuscular mycorrhizal fungi

Previous work has shown considerably enhanced soil fertility in agroecosystems managed by organic farming as compared to conventional farming. Arbuscular mycorrhizal fungi (AMF) play a crucial role in nutrient acquisition and soil fertility. The objective of this study was to investigate the diversity of AMF in the context of a long-term study in which replicated field plots, at a single site in Central Europe, had been cultivated for 22 years according to two organic and two conventional farming systems. In the 23rd year, the field plots, carrying an 18-month-old grass-clover stand, were examined in two ways with respect to AMF diversity. Firstly, AMF spores were isolated and morphologically identified from soil samples. The study revealed that the AMF spore abundance and species diversity was significantly higher in the organic than in the conventional systems. Furthermore, the AMF community differed in the conventional and organic systems: Glomus species were similarly abundant in all systems but spores of Acaulospora and Scutellospora species were more abundant in the organic systems. Secondly, the soils were used to establish AMF-trap cultures using a consortium of Plantago lanceolata, Trifolium pratense and Lolium perenne as host plants. The AMF spore community developing in the trap cultures differed: after 12 months, two species of the Acaulosporaceae (A. paulinae and A. longula) were consistently found to account for a large part of the spore community in the trap cultures from the organic systems but were found rarely in the ones from the conventional systems. The findings show that some AMF species present in natural ecosystems are maintained under organic farming but severely depressed under conventional farming, indicating a potentially severe loss of ecosystem function under conventional farming.     

Hydrogen gas accelerates thermal inactivation ofClostridium botulinum 113B spores

Summary Heat inactivation ofClostridium botulinum spores was accelerated in atmospheres containing hydrogen gas. Hydrogen gas also moderately increased the thermal destruction ofBacillus spores. Hydrogen gas may react with components inC. botulinum spores such as transition metals producing hydrogen ions or hydrides, which destroy essential spore components. Thermal processing in modified atmospheres may have applications in food processing and in sterilization of medical supplies.     

Dispersal of Spores of Mycorrhizal Fungi in Scats of Native Mammals in Tropical Forests of Northeastern Australia

One hundred and thirty-eight scat (faecal) samples from 17 mammal species native to forests of northeastern Queensland were examined for the presence of spores of both ectomycorrhizal and arbuscular mycorrhizal fungi. Spores of mycorrhizal fungi were found in 57 percent of scat samples representing 12 animal species (Aepyprymnus rufescens, Antechinus godmani, Bettongia tropica, Hypsiprymnodon moschatus, Isoodon macrourus, Melomys ceruinipes, Perameles nasuta, Rattus fuscipes, R. tunneyi, Thylogale stigmatica, Trichourur uulperula, Uromys caudimaculatus). Spores were absent in scats of Antechinus stuartii, Dasyurus hallucatus, Dendrolagus lumholtzi, Petaurus australis and Mesembriomys gouldii. Spores of ectomycorrhizal fungi occurred in 38 percent of scats, and all but one of these samples were from Eucalyptus-dominated sclerophyll forests. Based on the frequency and abundance of spores in scats, five mammals were considered active consumers of hypogeous mycorrhizal sporocarps in sclerophyll forests (A. rufescens, B. tropica, I. macrourus, P. nasuta, and U. caudimaculatus). Individual scats of these animals generally contained a range of distinctive spore types. Spores of arbuscular mycorrhizal fungi were found in low abundance in almost 40 percent of scat samples collected, from both sclerophyll forest and rainforest habitats. We suggest that the majoriry of these spores were acquired incidentally through ingestion of soil during foraging activities on the forest floor. Glasshouse inoculation experiments in which seedlings of Eucalyptus grandis and Sorghum bicolor were inoculated with scat material from several species of mammal demonstrated that the spores of ectomycorrhizal and arbuscular mycorrhizal fungi retained some viability and colonized the roots of host-plant seedlings. Insufficient information is known of the ecology of mycorrhizal fungi in Australia's tropical forests to speculate as to the implications of these findings for forest conservation and rehabilitation.     

Survival of Bacillus thuringiensis Spores in Soil

Bacillus thuringiensis spores and parasporal crystals were incubated in natural soil, both in the laboratory and in nature. During the first 2 weeks, the spore count decreased by approximately 1 log. Thereafter, the number of spore CFU remained constant for at least 8 months. B. thuringiensis did not lose its ability to make the parasporal crystals during its residence in soil. Spore survival was similar for a commercial spore-crystal preparation (the insecticide) and for laboratory-grown spores. In contrast to these results, spores that were produced in situ in soil through multiplication of added vegetative cells survived for only a short time. For spore additions to soil, variations in soil pH had little effect on survival for those spores that survived the first 2 weeks of incubation. Also without effect were various pretreatments of the spores before incubation in soil or nutritional amendment or desiccation of the soil. Remoistening of a desiccated soil, however, caused a decrease in spore numbers. Spores incubated in soil in the field did not show this, but the degree of soil desiccation in nature probably never reached that for the laboratory samples. The good survival of B. thuringiensis spores after the first 2 weeks in soil seemed to be a result of their inability to germinate in soil. We found no evidence for the hypothesis that rapid germination ability for spores in soil conferred a survival advantage.     

Possible involvement of Ca<Superscript>2+</Superscript>-dependent protein kinases in spore germination of the fern<Emphasis Type="Italic">Osmunda Japonica</Emphasis>

Fern gametophyte is a good model system to investigate signal transduction in plant cells. In this work, we examined whether CDPKs are involved in the mechanisms of spore germination of the fernOsmunda japonica. A protein extract from the spores included four CDPK isoforms with relative molecular weights of 56, 53, 49, and 47 kDa, as detected by immunoblot analysis, and they showed CDPK-like activities, as detected by in-gel protein-kinase assay. It was also found that the inhibitors effective on CDPKs, such as a general protein kinase inhibitor, K252a, and a calmodulin antagonist, W-7, largely suppressed the spore germination, and that many proteins of the spores were phosphorylated in vivo in a calcium dependent manner in the period when the spores require external Ca²⁺ for the germination. Furthermore, we showed that Sr²⁺ and Mn²⁺, which could substitute for Ca²⁺ in the spore germination, were also able to activate theOsmunda CDPKs. From these results, we concluded that CDPKs would participate in the spore germination ofO. japonica.     

THE “HYSTRICHOSPHAERID” RESTING SPORE OF THE DINOFLAGELLATE PYRODINIUM BAHAMENSE,PLATF, 19062

Germination experiments demonstrate that the “hystrichosphere” called Hemicystodinium zoharyi, which previously has been found only as a microfossil organism, is the resting spore stage in the life history of Pyrodinium bahamense, a modern bioluminescent, thecate dinoflagellate. The morphology of this spore, together with new details of the thecal structure and ontogeny of P. bahamense, is described, and it is concluded that Pyrodinium is closely related to Gonyaulax but worthy of retention as a discrete genus. The geological history of P. bahamense is traceable to the Eocene through fossil occurrences of its spore, and it is suggested that additional pyrodinioid dinoflagellates which now are extinct were represented in Lower Tertiary seas by another hystrichosphere genus, called Homotryblium. Selected aspects of the physiology and ecology of modern dinoflagellate resting spores are discussed briefly with special reference to Pyrodinium.     

Colonization capacity of the soil micro-organisms in relation to fungistasis

Summary Evans' tube and cellophane agar-disc techniques were used to evaluate the colonization capacity of the soil microbes and fungistasis, respectively. Spore germination ofAlternaria tenuis, Curvularia geniculata, Helminthosporium rostratum andPestalotia sp. was studied on a natural soil. Aspergillus fumigatus was the pioneer colonizer, followed in the order of decreasing colonizing capacity by,A. flavus, A. niger, A. terreus andPenicillium nigricans. Sensitivity of test spores to soil fungistasis declined in the order,C. geniculata → Pestalotia sp. →A. tenuis → H. rostratum. The fungistatic level of the soil samples decreased gradually from side arms 1 to 7 of the Evans tube, inoculated with unsterilized soil from one end. Studies conducted with an inoculum of four soil fungi (A. fumigatus, A. flavus, A. niger, andP. nigricans) as well as those involving fumigation of Evans tube by CS₂ also proved the greater colonizing capacity ofA. fumigatus. The level of fungistasis followed closely the colonization pattern of this fungus. When added individually to the soil, all fungi were able to inhibit spore germination of test fungi to some degree or other.     

Spore productivity in Cladosporium

The high incidence ofCladosporia in the airspora indicates a prolific production of spores. Six species ofCladosporium were sampled over a period of 9 weeks, using dry and wet (mist-laden) air, and over a period of 4 weeks using humid air. Many more spores were released in wet air than in dry air: numbers released in humid air were generally intermediate between those of wet and dry samples. None of the cultures was exhausted of spores at the end of the sampling periods although samples generally decreased in size from the fifth or sixth week onwards. Removal of spores would seem to be conducive to further sporulation provided the substrate is not exhausted. Maximum productivities recorded for the six species (all in mist-laden air) ranged from 730 to 26 100 spores per mg dry weight of mycelium. Differences in the levels of spore production in culture by the six species do not correlate with their individual frequencies in the airspora, indicating that the latter are more dependent on the distribution and substrate relationships of each species.     

Arbuscular fungi and mycorrhizae (Glomales) of the Hel Peninsula,Poland

In the years 1985–1989, the occurrence of arbuscular fungi and mycorrhizae on the Hel Peninsula (Poland) was investigated with the help of 45 soil and root samples collected under 20 plant species of eight families. Except for Zea mays, the other plant species were from uncultivated sites. All soil samples contained spores of arbuscular fungi, of which about 45% were of the genus Glomus. Acaulospora spp. preferred members of the Cupressaceae. Spores of Gigaspora occurred rarely and only in two plant families. Glomus spp. were most frequently associated with plants of the Rosaceae, and species of Scutellospora were found at markedly higher frequencies among roots of plants of the Gramineae and Cupressaceae. A total of 29 spore-forming species and Glomus tenue (a fungus recognizable by its distinctive infections) were found. The most frequently recovered fungus, Glomus tenue, was present in roots of 56.8% of examined plants. Of the spore-forming fungi, the most frequently isolated spores were those of Scutellospora dipurpurascens, then Glomus constrictum, Acaulospora 61, and Glomus microcarpum. The overall spore density in examined samples averaged 99.8 in 100 g dry soil in the range 1 to 547, and was highest in a sample taken from around roots of Festuca arundinacea. The dominant fungi forming spores in sampled soils were Glomus constrictum, Glomus microcarpum, and Scutellospora dipurpurascens. The average species density was 3.9 in 100 g dry soil in the range 1 to 10, and was highest in Corynephorus canescens, Rosa canina, and Thuja occidentalis. Levels of colonization by arbuscular fungi ranged from 0.0 to94.0% (mean 23.3%) of the root length and were highest in Festuca arundinaceae and Zea mays.