The fine structure of developing microsclerotia of Verticillium dahliae Kleb.

Summary Electron micrographs of the early stages in microsclerotial development in v. dahliae Kleb. showed that hyphae became swollen and vacuolate and extruded melanizing particles into the interhyphal spaces of the microsclerotium. Peripheral microsclerotial cells were killed either by a process of autoparasitisation from adjacent hyphae or by autolysis. Variations in the thickness of the melanized material surrounding cells gave the superficial appearance of variations in cell wall thickness between individual cells though actual changes in cell wall thickness were not observed.     

Ringing or colour-banding does not increase predation mortality in redshanksTringa totanus

The use of metal and colour‐rings or bands as a means of measuring survival, movements and behaviour in birds is universal and fundamental to testing ecological and evolutionary theories. The practice rests on the largely untested assumption that the rings do not affect survival. However this assumption may not hold for several reasons, for example because the ‘oddity effect’ predicts predators select prey that appear different to their neighbours in order to avoid the ‘confusion effect’. We compared the foraging behaviour and the death rates of redshanks Tringa totanus conspicuously marked with six colour rings and one metal ring each to unmarked birds in a study system, where routinely up to 50% of the total population are killed by avian predators during a winter. If avian predators selectively target and/or have a higher capture success of ringed birds then we would predict the proportion of colour‐ringed birds in the population to decline through a winter. The proportion of colour‐ringed birds in the population did not change over the course of three separate winters, and in one winter the ratio of marked:unmarked birds found killed by sparrowhawks Accipiter nisus was the same as the ratio of marked birds alive in the population. In the year with largest sample size, power was sufficient to detect a greater than 2.2% difference in predation rate between ringed and unringed groups. The average kill rate difference between ringed and unringed birds across the three winters was less than 1% (0.73±2.2%) suggesting that even if there were differences in predation rate that were not detected because of low statistical power they were extremely small. There were no differences in any foraging measures comparing ringed and unringed birds, suggesting that the rings did not affect the ability of birds to meet their daily energy budgets. The results showed that colour‐ringed birds were not preferentially targeted or killed by avian predators, and suggest that the presence of a metal and even several large colour‐rings is unlikely to affect behaviour and predation mortality even under extreme selection.     

Cytological studies on rust fungi. (vi) fine structures of infection process of Kuehneola japonica (diet.) dietel

The behavior of rust fungi in their host plants has been elucidated by electron microscopy. However, most of the ultrastructural studies on rust fungi have focused on the uredial stage. In order to elucidate the features of the sporidial stage, we studied the fine structure of Kuehneola japonica, a short-cycle rust, in rose leaves. Infection pegs arising from appressoria penetrated the host walls. Papillae formed at the time of penetration against the outer epidermal cell walls. The papillae which had formed at the penetration sites grew extensively and partially surrounded the intracellular hyphae which were connected with the infection pegs. The intracellular hyphae in the epidermal cells developed further and entered adjacent parenchyma cells. Walls of parenchyma cells either invaginated or thin papillae formed at penetration sites and the invaginated walls or papillae surrounded the necks of the intracellular hyphae. Intracellular hyphae in both epidermal and parenchyma cells were not enveloped by the sheath before 20 days after inoculation. In specimens prepared 20 days after inoculation, some of the intracellular hyphae were enveloped by a sheath in both palisade and spongy parenchyma cells. The sheathed hyphae resembled haustoria of other rust fungi which had been described previously. Teliospore initials were formed in mycelial masses in intercellular spaces between the epidermal cells and palisade parenchyma cells 20 days after inoculation. Uninucleate teliospores developed from teliospore initials 30 days after inoculation.Contribution No. 32.     

Knowledge and Experience Predict Indiscriminate Bat‐Killing Intentions among Costa Rican Men

Human–wildlife conflicts create collateral damage when people attempt to control one problematic species and inadvertently kill others. I observed a collateral damage problem in southern Costa where people seeking to control common vampire bats (Desmodus rotundus) indiscriminately killed sympatric, non‐target bat species (e.g., by baiting bats with poisoned bananas). To learn about this phenomenon and its causes, I developed and implemented a questionnaire based on the theory of planned behavior. In a sample of 504 men, 14 percent had individually killed 1–115 bats within the past 5 yr, 68 percent had killed bats as children, and 27 percent said that they would kill bats that they found roosting on their farms, even if they could not identify the species. Men who intended to indiscriminately kill bats thought that it would reduce disease transmission to livestock, whereas men who did not intend to kill bats thought that killing bats would reduce ecosystem functioning and/or damage nature. Ultimately, men were more likely to intend to indiscriminately kill bats if they knew less about bat natural history and/or had previously suffered vampire bats attacking their livestock. Men knew more about bat natural history and were less likely to harbor indiscriminate bat‐killing intentions if they had experienced some form of environmental education. My results suggest that environmental education will be most effective for bat conservation when combined with farmer support to ameliorate perceived livelihood risks associated with vampire bats.     

THE MORPHOGENESIS AND POSSIBLE EVOLUTIONARY ORIGINS OF FUNGAL SCLEROTIA

1. Fungal sclerotia are able to survive adverse conditions for long periods and they are formed by many important plant pathogens. An understanding of the factors involved in their initiation and development may lead to a method of repressing their formation in nature, thereby reducing the chances of survival of fungi that depend on them as persistent resting stages in their life-cycles. Also, data on sclerotial morphogenesis may be applicable to other multihyphal fungal structures. 2. There are three types of sclerotial development. The most primitive and least common is the loose type, which is illustrated by Rhizoctonia solani. The sclerotium forms by irregular branching of the mycelium followed by intercalary septation and hyphal swelling. When mature, it consists of loosely interwoven hyphae that are rich in food reserves and darkly pigmented. The main types of development are terminal and lateral. The former develops from the coalescence of initials that are produced by a well-defined pattern of branching at the tip of a hypha or tips of closely associated hyphae, e.g. Botrytis cinerea. Lateral sclerotia are formed by the interweaving of side branches of one or several main hyphae. When only one main hypha is involved the sclerotium is of the lateral, simple type, e.g. Sclerotinia gladioli. If several main hyphae give rise to a sclerotium, the term strand type has been used. Sclerotium rolfsii is the classical example. 3. There is a considerable literature on the effects of environmental conditions on the initiation, development and maturation of sclerotia but few attempts have been made to interpret the data. Phenolics and/or polyphenol oxidases have been found to be connected with morphogenesis of the protoperithecium of Neurospora crassa, the perithecium of Podospora anserina and of Hypomyces sp. and the basidiocarp of Schixophyllum commune. A close correlation has been shown between melanin synthesis and microsclerotial development by Verticillium but there appears to be no literature on the role of phenolics and polyphenol oxidases in the morphogenesis of sclerotia. Possibly these substances may inhibit growth of the apices of main hyphae by changing the permeability of the membrane, by inducing a thickening of the cell wall at the tip or by reducing the plasticity of the wall. Such a check in growth could trigger-off the formation of initials close to the margin of the colony or elsewhere in the culture. Sulphydryl groups and disulphide bonds are of great significance in morphogenesis of organisms and are probably involved in sclerotial initiation. The formation of a large number of hyphal branches is a prerequisite for sclerotial initiation and mycelial branching is possible only if there is plasticity of hyphal walls. The ability of the wall to be moulded is possibly related to changes in the sulphur linkages of the protein of the protein-carbohydrate complexes of the cell wall and could be influenced by sulphur availability or the activity of specific enzymes. 4. After a sclerotial primordium has been initiated, further increase in size will depend on the continued, active translocation of nutrients to the site of development. Movement of nutrients to sclerotia is through a few translocatory hyphae. Presumably, nutrients will continue to move into the young sclerotium as long as a concentration or pressure gradient is maintained. Energy and substances for the formation of new branches are supplied in this way and as the requirements for hyphal branches are reduced, excess nutrients become available for conversion to inactive or insoluble reserves and for exudation. The exudates are often complex, consisting of proteins, including enzymes, lipids and carbohydrates. Many sclerotia have a mucilaginous matrix in which the medullary hyphae are embedded. Sclerotium-forming, fungal species that are not regarded as having such a matrix appear to secrete a layer of mucilage over the surface of sclerotial hyphae. This mucilage could have a morphogenetic function and serve as an adhesive which loosely binds hyphae together. More permanent unions are by hyphal fusions or anastomoses. 5. The sclerotium matures within a few days of attaining its maximum size. The rind effectively seals off the medullary hyphae from the surroundings and the translocatory hyphae cease to function. Thus the sclerotium is isolated both physiologically and nutritionally. The endogenous reserves enable the structure to exist in the absence of exogenous nutrients and then, when conditions become suitable, to germinate. 6. The sclerotium appears to provide an example of convergent evolution whereby analogous structures, which have become adapted to resist adverse conditions, have evolved. Data are available mainly for Typhula spp. and ScZerotinia spp. Sclerotia may be degenerate sexual reproductive structures, hyphal aggregates that have developed from closely interwoven conidiophores and undifferentiated conidia or they may be modified vegetative structures.     

Barley straw decomposition with varied levels of microbial grazing by Folsomia fimetaria (L.) (Collembola,Isotomidae)

Summary Folsomia fimetaria (L.) were added (0, 5, 10, 20 animals) to 0.100 g barley straw which had been inoculated 10 days (244 h) earlier with a natural soil microflora. Respiration (CO₂ evolution) was monitored continuously. Mass loss, fungal standing crop (total and FDA-active), bacterial and protozoan biomass were estimated 42 days (1,000 h) after microbial inoculation. The degree of surface cover by hyphae was surveyed at regular intervals. No significant differences (P>0.05) were found in respiration, mass loss or microbial biomass, but the density of surface hyphae were reduced by addition of Collembola. Fungal production was low, less than 5% of the estimated microbial production, and could not account for all collembolan growth during incubation. F. fimetaria appeared to consume mainly bacteria and protozoa, and had little impact on carbon mineralization.     

Hyphal contribution to water uptake in mycorrhizal plants as affected by the fungal species and water status

Vesicular-arbuscular mycorrhizae may increase resistance of plants to drought by a number of mechanisms, such as increased root hydraulic conductivity, stomatal regulation, hyphal water uptake and osmotic adjustment. However, a substantial contribution of vesicular-arbuscular mycorrhizal (VAM) hyphae to water uptake has not been demonstrated unequivocally. The objective of this investigation was to examine the contribution of hyphae from two VAM fungi to water uptake and transport by the host plant. Lettuce (Lactuca sativa L.) plants were grown in a container divided by a screen into two compartments. One was occupied by roots, the other only by VAM hyphae, which the screen permitted to pass. Roots were colonized by the VAM fungi Glomus deserticola or Glomus fasciculatum, or were left uninoculated but P-supplemented. Water was supplied to the hyphal compartment at a distance of 10 cm from the screen (root). CO₂ exchange rate, water-use efficiency, transpiration, stomatal conductance and photosynthetic phosphorus-use efficiency of VAM or P-amended control plants were evaluated at three levels of water application in the hyphal compartment. Results indicate that much of the water was taken up by the hyphae in VAM plants. VAM plants, which had access to the hyphal compartment, had higher water and nutrient contents. G. deserticola functioned efficiently under water limitation and mycelium from G. fasciculatum-colonized plants was very sensitive to water in the medium. This discrepancy in VAM behaviour reflects the various abilities of each fungus according to soil water levels. Different abilities of specific mycelia were also expressed in terms of nutritional and leaf gas-exchange parameters. G. fasciculatum caused a significant increase in net photosynthesis and rate of water use efficiency compared to G. deserticola and P-fertilized plants. In contrast, the G. deserticola treatment was the most efficient affecting N, P and K nutrition, leaf conductance and transpiration. Since no differences in the intra- and extra-radical hyphal extension of the two endophytes were found, the results demonstrate that mycorrhizal hyphae can take up water and that there are considerable variations in both the behaviour of these two VAM fungi and in the mechanisms involved in their effects on plant water relations.     

THE ULTRASTRUCTURE OF LICHENS. II. CLADONIA CRISTATELLA: THE LICHEN AND ITS ISOLATED SYMBIONTS1,2,3

A Comparative Study Was Made Of The Fine Structure of Cladonia Cristatella and its algal Symbiont Trebouxia Erici in their lichenized and cultured ( nonlichenized) states. Pyrenoglobuli were produced by the alga in the symbiotic and free conditions. Starch was formed during hydrated conditions. Pyrenoglobbuli migrated to the outer parts of the pyrenoid only during dry periods. Dictyosomes and eyespots were observed for the first time in Trebouxia. The pyrenoid divided by fragmentation. Ellipsoidal bodies were common in the hyphae of the lichenized fungus and absent in cultured hyphae, except for 1 colony which had been induced to form pycnidia. The ellipsoidal bodies were associated closely with the internal membrane system of the mycobiont. Haustoria seemed to penetrate the algal cells by enzymatic digestion. Intrahyphal hyphae were common.     

Electron microscopy of the endophyte ofAlnus glutinosa

Earlier light microscopic investigations have revealed that the endophyte ofAlnus glutinosa presents itself in three different forms. In the present study this is confirmed by electron microscopy; also, new data on the cytology of the endophyte have been obtained.The host cells are primarily infected by the hyphal form of the endophyte. A plant cell nucleus and mitochondria can be found in the infected host cells.In the majority of the infected cells, so-called vesicles develop at the tips of the hyphae. Electron micrographs show that these vesicles, as well as the hyphae, are surrounded by the host-cell cytoplasmic membrane. The endophyte cytoplasm inside the vesicles is divided in all directions by cross walls, many of which are incomplete. Plasmalemmosomes are conspicuous. Some vesicles look vigorous but others shrunken or nearly devoid of cytoplasm as if being digested.A minority of host cells situated between the vesicle-containing ones are completely filled by bacteria-like cells. These host cells, in contrast to the other ones, do not contain a nucleus nor mitochondria, nor are the endophyte cells in them enveloped by a host cell cytoplasmic membrane: these host cells are dead. Vesicles are not found in these cells.It is inferred that a living host cell exerts a stimulus on the endophyte to which the latter responds by forming vesicles at the tips of the hyphae. At a later stage the host cells digest the vesicles and the hyphae. On the other hand, if a host cell does not survive the infection, the hyphae divide into bacteria-like cells, which are not digested owing to the absence of host cytoplasm.According to the cytology of the hyphae, the endophyte is an actinomycete.The cytology of the endophyte needs further elucidation. Its plasmalemmosomes, or membranous bodies connected with the cytoplasmic membrane, are beautifully developed. The striated bodies described on p. 359 under 4) may be a new feature, which may turn up in other actinomycetes or bacteria.     

Enhanced germicidal effects of pulsed UV‐LED irradiation on biofilms

Aims: The major objective of the study was to evaluate the enhanced germicidal effects of low‐frequency pulsed ultraviolet A (UVA)‐light‐emitting diode (LED) on biofilms. Methods and Results: The germicidal effects of UVA‐LED irradiation (365 nm, 0·28 mW cm^?2, in pulsed or continuous mode) on Candida albicans or Escherichia coli biofilms were evaluated by determining colony‐forming units. The morphological change of microbial cells in biofilms was observed using scanning electron microscopy. After 5‐min irradiation, over 90% of viable micro‐organisms in biofilms had been killed, and pulsed irradiation (1–1000 Hz) had significantly greater germicidal ability than continuous irradiation. Pulsed irradiation (100 Hz, 60 min) almost completely killed micro‐organisms in biofilm (>99·9%), and 20‐min irradiation greatly damaged both microbial species. Interestingly, few hyphae were found in irradiated Candida biofilms. Moreover, mannitol treatment, a scavenger of hydroxyl radicals (OH^?), significantly protected viable micro‐organisms in biofilms from UVA‐LED irradiation. Conclusions: The study demonstrated that pulsed UVA‐LED irradiation has a strong germicidal effect (maximum at 100 Hz, over 5‐min irradiation) and causes the disappearance of hyphal forms of Candida. Significance and Impact of the Study: This study can assist in developing a low‐frequency pulsed UVA‐LED system to be applied to pathogenic biofilms for disinfection.     

Structural aspects of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] tuberculate ectomycorrhizae

Summary Tubercles of Pseudotsuga menziesii consisted of clusters of ectomycorrhizae surrounded by a peridiumlike rind. Energy dispersive spectroscopy demonstrated that crystals found in the zone of loose hyphae extending from the inner rind to the mantle of each root probably contain calcium oxalate. Inner mantle and Hartig net hyphae showed a labyrinthine branching pattern and stored carbohydrates and protein. The Hartig net formed up to inner cortical cells which had thickened, darkly stained walls. Bacteria were located either along with hyphae within the rind or as colonies on the surface of the tubercle.     

Hyperparasitism of Streptomyces albus on a Destructive Mycoparasite Nectria inventa

Using scanning electron microscopy, Streptomyces albus was proved to be a hyperparasite of Nectria inventa, itself a well-known mycoparasite on many fungi. The hyperparasite had no apparent antagonistic activity against N. inventa, but did have intense tropic response toward it. Upon contact with the host, the hyperparasite grew along, and formed appressorium-like structures on the host hyphae. The parasitism that led to the eventual collapse of the host cells was not necessarily accompanied by actual hyphal penetration. The hyperparasite could, however, readily penetrate the host hyphae, and its hyphae were frequently found inside the host hyphae.     

Scytinostroma galactinum as a pathogen of woody plants

Scytinostroma galactinum (Fr.)Donk is the fungus commonly known asCorticium galctinum (Fr.)Burt. Although it occurs as a saprobe on woody plants and plant debris, it also has been considered by several authors as an active pathogen that causes a white root and butt or collar rot. During the summer of 1970, it was found near Baltimore and also in Montgomery County, Maryland, under circumstances that seemingly provide additional records of pathogenicity. Several other Maryland records are cited, and many Canadian studies have been reviewed.S. galactinum has a distinctive dextrinoid mycelium, which is characteristic enough to permit a tentative identification even in the absence of other features. Outstanding elements of the basidiocarp are the dextrinoid hyphae and slender gloeocystidia. In culture, dextrinoid fiber hyphae and papillate oil-bearing hyphae with clamp connections are characteristic. These and other features of the basidiocarp and culture serve in the characterization of this fungus, which is economically significant and widely distributed.     

Electron microscope studies on Tomentella

Summary Tomentella bombycina andT. fuscoferruginosa were examined by routine techniques of light and electron microscopy. Special attention was paid to the ultrastructure and inter-relationships of the generative subicular hyphae and subhymenial hyphae. The cell wall consisted of three layers in the generative subicular hyphae and only one layer in the subhymenial hyphae; this corresponded to the inner layer of the first and originated from it. Cells with two nuclei, normal mitochondria, large vacuoles, sparse endoplasmic reticulum and lomasomes were observed. Sometimes the nuclear membrane had unusually large pores and larger open gaps extending over 1/4 of the circumference. Septa with central dolipore-type pores were present. Clamp connections were not frequent. Finally, certain cells of the subhymenial hyphae appeared full of globular material, presumably lipids.     

The effects of a record flood on the aquatic vegetation of the Upper Mississippi River System: some preliminary findings

During 1993 the Upper Mississippi River System experienced floods of exceptional magnitude and duration, especially at its more downstream reaches. The flood had widespread effects on the vegetation. Submerged species such as Potamogeton pectinatus significantly decreased in abundance, especially at sites with more severe flooding. However, many species were able to regenerate in 1994 from seeds or storage organs. Emergent species such as Scirpus fluviatilis were similarly affected, but in the upstream reaches were able to regrow in the autumn following the flood and at many sites showed exceptionally high productivity in the following year, probably due to nutrient-rich sediment deposition by the flood. Many tree species were very severely impacted, although Acer saccharinum and Populus deltoides have shown some seedling regeneration on newly deposited sediment beneath stands of mature trees, which would have out-shaded the seedlings if they had not been killed by the flood.     

Anatomical study on the interaction between the root endophytic fungus <Emphasis Type="Italic">Heteroconium chaetospira</Emphasis> and Chinese cabbage

Chinese cabbage roots colonized by the dematiaceous fungal taxon Heteroconium chaetospira were previously found to become highly resistant to clubroot and Verticillium yellows. The dematiaceous fungus possesses an endophytic nature, but no detailed anatomical studies on endophyte–host plant interactions have so far been provided. Light and electron microscopy revealed that hyphae of H. chaetospira were abundant on and inside the root epidermal cells by 3 weeks following inoculation. The penetration pegs easily breached into epidermal cells, and the infection hyphae penetrated into cortical cells. Some appressorium-like swollen structures formed from intracellular hyphae, but no visible degradation of the host cell walls was evident where the hyphae contacted. No visible signs of host reactions and no invagination of the host plasma membrane around the hyphae were seen in the host cells. By 8 weeks following inoculation, masses of closely packed fungal cells had been formed in some cells of the epidermis and cortical layers, but further hyphal ingress was halted, mostly in the inner cortical cell layer. Thus, root vascular cylinders remained intact.     

The ectomycorrhiza <Emphasis Type="Italic">Piceirhiza internicrassihyphis</Emphasis>: A weak competitor of <Emphasis Type="Italic">Cortinarius obtusus</Emphasis>?

The ectomycorrhiza (ECM) Piceirhiza internicrassihyphis on Picea abies is described in detail. It is yellowish brown to brown with a mantle of a transitional type between plectenchymatous and pseudoparenchymatous. The inner mantle layers show some thick-walled hyphae, often with a few of them growing in parallel. These thick-walled hyphae contain particles which turn brownish in Melzer’s reagent, and their septa and walls are partially amyloid. Rhizomorphs occur infrequently and are undifferentiated, and are composed of rather loosely woven hyphae of uniform diameter. This combination of characteristics has not yet been identified in any other ECM. The lack of cystidia and the presence of amyloidy suggest that this ECM is formed by a species of the family Thelephoraceae. Piceirhiza internicrassihyphis can be found associated with ECM of Cortinarius obtusus, and the hyphae of the latter species often grow on the surface of P. internicrassihyphis and can even cover the whole tip. Although there is a close association and possibly a penetration between these two fungi, it can be excluded that the thick-walled hyphae of the inner mantle layers originate from C. obtusus. Some emanating hyphae of C. obtusus ECM seem to interact with those of P. internicrassihyphis, as indicated by short, hyphal outgrowths which were found attached to the foreign hyphae.     

Structure and histochemistry of mycorrhizae synthesized between Arbutus menziesii (Ericaceae) and two basidiomycetes,Pisolithus tinctorius (Pisolithaceae) and Piloderma bicolor (Corticiaceae)

Arbutoid mycorrhizae were synthesized in growth pouches between Arbutus menziesii Pursch. (Pacific madrone) and two broad host range basidiomycete fungi, Pisolithus tinctorius (Pers.) Coker and Couch and Piloderma bicolor (Peck) Jülich. P. tinctorius induced the formation of dense, pinnate mycorrhizal root clusters enveloped by a thick fungal mantle. P. bicolor mycorrhizae were usually unbranched, and had a thin or non-existent mantle. Both associations had the well-developed para-epidermal Hartig nets and intracellular penetration of host epidermal cells by hyphae typical of arbutoid interactions. A. menziesii roots developed a suberized exodermis which acted as a barrier to cortical cell penetration by the fungi. Ultrastructurally, the suberin appeared non-lamellar, but this may have been due to the imbedding resin. Histochemical analyses indicated that phenolic substances present in epidermal cells may be an important factor in mycorrhiza establishment. Analyses with X-ray energy dispersive spectroscopy showed that some of the granular inclusions present in fungal hyphae of the mantle and Hartig net were polyphosphate. Other inclusions were either protein or polysaccharides.     

An unusual method of development and sporulation of Colletotrichum gloeosporioides on castor leaf – an SEM account

Development and sporogenesis of Colletotrichum gloeosporioides on castor leaf differed from that on other known host plants. C. gloeosporioides had three kinds of hyphae on castor leaf: primary infection hyphae (PIH), runner hyphae (RH) and secondary infection hyphae (SIH). The PIH originated from conidia, grew on leaf surface and entered the leaf by direct penetration of the cuticle without forming appressoria. The RH were sub-cuticular hyphae, the track of which was traceable by the bulgings on the leaf surface, and the SIH were the hyphae that emerged to leaf surface from RH through the cuticle or stomata. Conidia were initiated as small protrusions along the lengths of RH and SIH that got differentiated into distinct conidia, each born on a short stumpy conidiophore without forming any congregation. The protrusions from RH emerged to the leaf surface by piercing the cuticle, and they developed into distinct conidia on the leaf surface. The conidia developed from RH and SIH were identical in size and shape. Even though conidia were occasionally found emerged through stomata, that appeared to be random than a preferred route for the discharge of conidia. The penetration and sporogenesis of C. gloeosporioides on castor leaf differed from that reported on mulberry leaf.     

Time-course study and partial characterization of a protein on hyphae of arbuscular mycorrhizal fungi during active colonization of roots

Material on the surface of hyphal walls of arbuscular mycorrhizal fungi (AMF) during active colonization of plant roots was detected by a monoclonal antibody. Pot-cultured isolates of Glomus, Acaulospora, Gigaspora, Scutellospora, and Entrophospora had immunofluorescent material (IM) on younger, thinner, intact hyphae, but IM was scant to absent on thicker, melanized or lysing hyphae. Colonization of corn (Zea mays L.), Sudangrass (Sorghum sudanense (Piper) Staph.) or red clover (Trifolium pratense L.) was examined during 5 months of plant growth by removing cores and performing an indirect immunoassay on roots with attached hyphae. Fresh spores of some Glomus spp. had IM on the outer layer of the spore wall. Abundant IM was seen on root hairs of plants colonized by some isolates, and some IM was detected on root surfaces of all plants examined even during early colonization. After cultures were dried, hyphae, roots and spores had little to no IM. Uninoculated control roots had very rare, small patches of IM. An immunoreactive protein was extracted from hyphae of Gigaspora and Glomus isolates by using 20mM citrate (pH 7.0) at 121°C for 90 min. Gel electrophoresis profiles indicated that all isolates tested had the same banding patterns. Lectin-binding of extracted protein is suggestive of a glycoprotein. The immunofluorescence assay can be used to examine root sections for active colonization by AMF, and the potential use of the protein to quantify AMF activity in soil is discussed.