Fungal Colonization Patterns Research Articles

Spatiotemporal colonization of Scots pine roots by introduced and indigenous ectomycorrhizal fungi in forest humus and nursery Sphagnum peat microcosms

Mycorrhizal and non-mycorrhizal Scots pine (Pinus sylvestris L.) seedling combinations were grown in two-dimensional Perspex® microcosms containing forest humus or nursery Sphagnum peat, without additional fertilization. Spatial and temporal patterns of mycorrhizal fungal colonization of roots were assessed over a 3-month period, through visual morphotyping and polymerase chain reaction assisted rDNA fingerprinting of developed mycorrhizas. Six distinct morphotypes of mycorrhiza developed on non-mycorrhizal seedlings grown in forest humus. Three of the morphotypes (white1-, black-, and brown-type) were, respectively, associated with the fungi Suillus bovinus (L. ex Fr.) O. Kuntze, Cenococcum geophilum Fr., and Thelephora terrestris Ehrh.:Fr. (= Tomentella radiosa (P. Karst.) Rick). A fourth pink-type morphotype displayed features indicating root colonization by Tomentellopsis submollis (Svrcek) Hjortstam, but this could not be confirmed because of a lack of source restriction fragment length polymorphism (RFLP) data. Brown-type mycorrhiza were the first to appear after seedling transplantation and black-type mycorrhizas showed local and dispersed root colonization dynamics. Mycorrhiza development in the unfertilized nursery peat substrate was restricted to a single unidentifiable brown-type morphotype, which appeared after 44 days. Rapid colonization of adjacent non-mycorrhizal seedlings by Tomentellopsis submollis, but not S. bovinus, was detected following the introduction of preinoculated seedlings into the humus or peat microcosms. The biomass of seedlings grown in nursery peat, regardless of mycorrhizal status, was significantly lower than that of mycorrhizal seedlings grown in humus. These findings support and extend previous bait seedling studies, as they provide a primary in situ characterization of distinct root colonization strategies of mycorrhizal species in forest humus and nursery peat.

Fungal biomass and decomposition in Spartina maritima leaves in the Mondego salt marsh (Portugal).

Spartina maritima (Curtis) Fernald is a dominant species in the Mondego salt marsh on the western coast of Portugal, and it plays a significant role in estuarine productivity. In this work, leaf litter production dynamics and fungal importance for leaf decomposition processes in Spartina maritima were studied. Leaf fall was highly seasonal, being significantly higher during dry months. It ranged from 42 g m-2 in June to less than 6 g m-2 during the winter. Fungal biomass, measured as ergosterol content, did not differ significantly between standing-decaying leaves and naturally detached leaves. Fungal biomass increased in wet months, with a maximum of 614 μg g-1 of ergosterol in January in standing-decaying leaves, and 1077 μg g-1 in December, in naturally detached leaves, decreasing greatly in summer. Seasonal pattern of fungal colonization was similar in leaves placed in litterbags on the marsh-sediment surface. However, ergosterol concentrations associated with standing-decaying and naturally detached leaves were always much higher than in litterbagged leaves, suggesting that fungal activity was more important before leaf fall. Dry mass of litterbagged leaves declined rapidly after 1 month (about 50%), mostly due to leaching of soluble organic compounds. After 13 months, Spartina leaves had lost 88% of their original dry weight. The decomposition rate constant (k) for Spartina maritima leaves was 0.151 month-1.

The mycorrhizal colonization of six wetland plant species at sites differing in land use history

Five wetland prairie sites and six native plant species in western Oregon were examined to determine patterns of vesicular-arbuscular mycorrhizal fungal (VAMF) colonization. The sites differed in type and intensity of past land use. VAMF colonization was tested in situ on seedlings from both field-sown seeds and from transplants. Colonization was measured as the percentage of root length with arbuscles or vesicles. All species (Deschampsia cespitosa, Downingia elegans, Eriophyllum lanatum, Hordeum brachyantherum, Microseris laciniata, and Plagiobothrys figuratus) became colonized by VAMF during the study. This is the first report of mycorrhizal colonization of these important native species. All sites supported mycorrhizal colonization of some of the experimental species. Average VAMF colonization ranged from 58% to 92% but was unrelated to subjective rankings of land use intensity. These results suggest that VAMF inoculum at all sites was sufficient to support revegetation by at least some species of native plants.

Effects of biological and chemical treatments against Heterobasidion annosum on the microfungal communities of Picea abies stumps

This study describes the effects of biological treatments with Trichoderma harzianum, Hypholoma fasciculare, Phanerochaete velutina, Verticillium bulbillosum and Vuilleminia comedens and chemical treatment with propiconazole against Heterobasidion annosum, on the microfungal communities of Picea abies stumps in a forest in the Alps of northwestern Italy. Immediately after felling, 20 healthy stumps per treatment were sprayed with the treatment preparations and their surface was protected with an autologous wood disk. The controls were 20 untreated stumps covered with an autologous wood disk. Another 20 untreated stumps were left without a wood disk to evaluate disk effects on the naturally occurring mycoflora. The microfungal populations were evaluated after one yr on 27 shavings from each stump. Fifty-seven fungal taxa were isolated, and most were Deuteromycetes. The number of species was generally significantly lower in the treatments respect to the control; T. harzianum treatment reduced the most species, V. bulbillosum the least. Multivariate analyses differentiated four groups of treatments: one comprising the treatments with the three lignovorous Basidiomycetes, one comprising the treatments with V. bulbillosum and the control, one comprising the treatment with propiconazole and the untreated stumps without the wood disk, and one composed of the treatment with T. harzianum only. These findings provide evidence that the pattern of fungal colonization of Picea abies stumps is influenced, sometimes greatly, by the treatments examined. T. harzianum and V. bulbillosum had the greatest and the least effect, respectively, on the naturally occurring mycocenoses.

Fungal colonists of maize grain conditioned at constant temperatures and humidities

Fungal colonization of shelled maize (Pioneer 3320) harvested from a field near Furman, South Carolina, in 1992 was determined after 348 and 751 days of continuous storage at each of seven temperatures (10, 15, 20, 25, 30, 35, or 40°C) and four constant relative humidities, giving equilibrium grain moisture contents ranging from 9.4% to 17.5% m.c. in 28 grain conditioning environments. Twenty fungal species infected surface sterilized seeds and were recorded from these conditioned grain treatments, including species commonly found in preharvest maize [e.g. Acremonium zeae, Aspergillus flavus, Fusarium moniliforme (syn. F. verticillioides), Penicillium pinophilum (syn. P. funiculosum), etc.]. Eupenicillium cinnamopurpureum and Monascus ruber were recorded only from conditioned grain treatments. Eurotium chevalieri colonized 50–96% of the kernels from grain conditioning treatments with the highest moisture content for each incubation temperature. Grain samples with >33% E. chevalieri infection had a decreased occurrence of F. moniliforme and A. zeae, and no kernels from these samples germinated. No fungi colonized more than 50% of the kernels conditioned at 30–40°C and 9.4–14.2% m.c. The results of this study indicate that individual patterns of fungal colonization during grain conditioning were a function of the survival rates for preharvest fungal colonists and their potential replacement by E. chevalieri.

Mycelial density profiles of fungi on heterogeneous media and their interpretation in terms of nutrient reallocation patterns

The ability to reallocate nutrients by translocation between different parts of the mycelium may have an important influence on patterns of fungal colonization in heterogeneous environments. The shape of colony biomass density profiles of colonies grown on media with opposing gradients of carbon and mineral nutrients was used as an indicator of translocating ability and measured using image analysis for non-coloured mycelia or estimated by eye for coloured mycelia. Three principal types of density profile, with or without autolysis in the older mycelium, were predicted and their occurrence noted in 62 test fungi. Type 1 profiles (26 fungi), characterized by peaks of high biomass densities at the centre of the plates and progressively lower biomass densities in both directions from the centre indicated no translocation, other than diffusion, in any direction. Type 2 profiles (13 fungi), characterized by biomass density profiles similar to control plates (without gradients) on half of the plate and progressively decreasing densities, from the centre of the plates, on the other half of the plates indicated active translocation of carbon (glucose) or minerals in one direction, and diffusive translocation of minerals or carbon in the other direction. Type 3 profiles (21 fungi), characterized by biomass density profiles over the whole plate that were similar to profiles on control plates (without gradients) indicated active translocation of all nutrients in both directions. The profiles of two fungi could only tentatively be assigned to type 3. Some fungi, especially amongst those with type 3 profiles, produced more biomass during the same time of incubation and sometimes also at higher densities on gradient plates than on control plates, but most fungi formed less biomass and at lower densities on these plates. Radial extension rates were expected to decrease during incubation for type 1 fungi on gradient plates but no such tendency was found. Most fungi had constant radial extension rates and, unexpectedly, some showed increasing radial extension rates. Six of the 62 tested fungi even had increasing radial extension rates when grown on control media.

Cytology of infection of 35S‐bean chitinase transgenic canola plants by Rhizoctonia solani: cytochemical aspects of chitin breakdown in vivo

Transgenic canola plants containing high, constitutive levels of bean endochitinase have been shown to be more resistant to infection by the soil‐borne pathogen, Rhizoctonia solani, than are wild‐type plants that lack the chimeric chitinase gene. To determine whether the resistance of the 35S‐chitinase plants to Rhizoctonia infection results from an antimicrobial activity of the bean chitinase in planta, an ultrastructural and cyto‐chemical study was performed on infected control and transgenic canola plants. Analysis of root tissues of infected wild‐type canola plants revealed that R. solani was capable of extensive tissue colonization including the xylem vessels. Pathogen ingress towards the vascular system was associated with marked host cell wall alterations such as disruption of middle lamella matrices that occurred in advance of fungal penetration. Fungal hyphae colonizing these tissues appeared metabolically active as judged by their typical morphological features and their extensive multiplication. In infected transgenic plants, however, the pattern of fungal colonization was different to that observed in wild‐type plants. Penetration of the host cuticle and epidermis was frequently observed, but fungal colonization was usually restricted to the cortex although, in a few cases, some fungal cells could be seen in xylem vessels. In all samples examined, severe hyphal alterations ranging from increased vacuolization to cell lysis were seen. Hyphae occasionally seen in xylem vessels were markedly damaged and often reduced to convoluted wall fragments. Cytochemical labeling of chitin using the WGA/ovomucoid‐gold complex showed that hyphal alterations correlated with extensive chitin degradation. Thus, reduction in fungal biomass, increase in hyphal alterations leading to fungal lysis and chitin breakdown appear to be typical features observed in transgenic canola plants. Because these features were not seen in infected wild‐type plants, it is likely that constitutive expression of the bean endochitinase gene is, at least in part, responsible for the enhanced protection against fungal attack observed in these plants. It is not known, however, if other components of the host defense response contribute to the resistance phenotype.

Micorbial colonization and digestion of feed materials in cattle and buffaloes I. Guinea grass

An experiment was conducted to determine whether there were any apparent differences in the microbial population, colonization pattern and digestion of guinea grass in situ, between cattle and swamp buffalo. Percentage losses in dry matter (DM), nitrogen (N) and neutral detergent fibre (NDF) of guinea grass were significantly (p<0.01) higher when incubated in the rumen of buffalo than in cattle. Buffalo also showed significantly (p<0.05) faster degradation rates than cattle for each grass component (DM, N, DNF). Light microscopy and SEM examination of the incubated grass materials showed that there were no apparent differences in the pattern of bacterial and fungal invasion and colonization of the grass materials between cattle and buffalo. Attachment of bacteria and fungal zoospores on the grass fragments occurred at 15 min after rumen incubation. After 3 h of rumen incubation, dense population of bacteria was observed in the thin-walled mesophyll and parenchyma tissues, whereas root-like fungal rhizoids were observed in both thin-walled and thick-walled cells. By 6 h, eroded zones were apparent in the thin-walled tissues and in thick-walled tissues with profuse rhizoids. After 24, 48 and 72 h of rumen incubation, most thin-walled tissues were degraded leaving mostly the thick-walled tissues. The predominant bacteria were the curved rods resembling Butyrivibrio sp., the thick rods resembling Fibrobacter sp., the diplococcoids resembling Ruminococcus sp. and spirochetes. Fungi were predominantly those with spherical or oval sporangia. Fusiform sporangia with acuminate apices which resembled Ruminomyces sp. were of lesser occurrence. Few protozoa were found on the grass fragments at all incubation times.

Micorbial colonization and digestion of feed materials in cattle and buffaloes II. Rice straw and palm press fibre

Degradation of rice straw was observed to be higher (p<0.01) in the buffaloes than in cattle. At 48 h, the dry matter (DM) loss of straw for buffaloes was 53.6 ± 0.8% and that for cattle was 48.7 ± 2.6%. Palm press fibre (PPF) was poorly degraded in the rumen of both animal species. A loss of about 21% DM was observed in both cattle and buffaloes after 48 h of incubation in the rumen. The pattern of bacterial and fungal colonization of straw and PPF seemed to be similar in both cattle and buffaloes. Microbial colonization was restricted by plant structures like the silica crystals in both straw and PPF. The predominant bacteria colonizing both straw and PPF fragments were the rods. Eroded zones and digestion pits were pronounced in straw fragments after 1 h of incubation. The PPF fragments appeared undergraded even after 6 h of incubation. Fungal colonization of straw was rapid and extensive in both cattle and buffaloes. The sporangia observed in straw were mainly spherical or oval in shape, but fusiform sporangia with acuminate tip were predominantly seen in PPF fragments.

Differential plant response to inoculation with two VA mycorrhizal fungi isolated from a low-pH soil

Sericea lespedaza and ladino clover were inoculated withAcaulospora laevis andGigaspora margarita VA mycorrhizal fungi, both isolated from a local soil having a pH of 4.4. Plants were grown in a greenhouse in fumigated (methyl bromide) soil with four rates of applied P. This soil had a pH of 5.1 for theG. margarita experiment and a 5.8 for theA. laevis experiment. Neither plant species responded to theG. margarita isolate in terms of mycorrhizal infection of roots, top growth, or elemental uptake. TheA. laevis isolate caused increased growth of Ladino clover at the lowest rate of P application and increased growth of sericea lespedeza at the two lowest P application rates. Shoot tissue concentrations of P for both plant species were greater at the two lowest rates of P application when inoculated withA. laevis. Inoculation withA. laevis also resulted in different VAM fungal root colonization patterns between the two plant species as a function of P application rate. Roots of both plants had high infection rates (near 70%) for the two lowest P application rates but sericea lespedeza declined to 40 and 6% at the next two P application rates, respectively, whereas infection in Ladino clover was 74 and 41% at the next two P application rates, respectively. The results of this study support the concept that plant host-VAM fungal endophyte interactions are extremely variable and that characterization of individual combinations must be done if types and magnitudes of responses are to be defined.

Pathological anatomy of black stain root disease of Douglas-fir

Twenty, black stain root disease infected Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) from the Oregon Cascade and Coast ranges were dissected; macroscopic and microscopic patterns of fungal colonization are described. Ceratocystis wageneri Goheen et Cobb colonized secondary xylem, disrupting xylem transport. Histopathological studies revealed that the tracheid-limited pattern of colonization exhibited by this fungus is unique among Ceratocystis wilt pathogens. Axial colonization by hyphae was confined to xylem tracheids and radial development of mycelia in ray tracheids was limited. Parenchyma and cambial necroses did not result from direct hyphal attack. Living host cells, although not invaded, were responsive to hyphal attack of adjacent functional xylem. Secondary phloem was never invaded by hyphae, but some dysfunction was evident. Host responses to infection were unsuccessful in curtailing the spread of the pathogen.

Decay of fire-damaged lodgepole pine in south-central Oregon

About 150 lodgepole pines, Pinus contorta var. murrayana (Grev. and Balf.), growing in topoedaphic climax stands of south-central Oregon, were identified as having survived fires that occurred over a period from 1839 to 1982. All fires were natural wildfires, except for prescribed burns of 1976, 1980 and 1982. The trees were sampled for bole and root damage to investigate fungal colonization patterns, establishment of decay columns, and diameter growth. Fire-damaged roots were the principal entry point for decay fungi in fire damaged trees. White-rot fungal species and fungi imperfecti rapidly colonized fire-killed root tissues within 2 years after a fire. These fungi were later displaced by slower growing brown-rot Basidiomycetes that eventually extended into the boles of infected trees. Trees with butt rot, principally caused by Poria asiatica, grew significantly slower than uninfected trees.

Selective Feeding by Stream Caddisfly (Trichoptera) Detritivores on Leaves with Fungal-Colonized Patches

A leaf in a stream represents a mosaic of fungal-colonized areas or patches. Patches may differ in their fungal composition and stage of processing. They, therefore, represent spatially heterogeneous foods of potentially diverse qualities to detritivores. However, little is known about the ability of detritivores to locate and discriminate among these fungal-colonized patches as food sources. To assess this ability, we manipulated fungal colonization patterns on leaves and fed them to caddisfly (Trichoptera) detritivores. In one experiment, disks were cut from leaves which had been incubated with one of three fungal species for different time periods. Disks from different treatments were randomly fastened to quadrants of uncolonized leaves and fed to caddisfly larvae. In a second experiment, fungal patchiness was produced by incubating leaves with disks attached so that fungi would colonize discrete areas on leaves. Disks were removed before leaves with patches were offered to larvae. Feeding patterns, determined by visual ranking of leaf skeletonization, indicated that larvae fed selectively on fungal-colonized patches in both experiments. Larval choice was affected by fungal species and degree of colonization. Larvae were able to detect fungal hyphae associated with patches before physical changes had occurred in the leaf matrix. Observations of foraging larvae and the feeding patterns they exhibited suggest that these caddiflies view individual leaves as coarse-grained resources.

Patterns of initial saprophytic fungal colonization of grass roots from two severely disturbed soils

Development of the root-surface fungal assemblages of Agropyron trachycaulum grown on amended oil-sands tailings and a subalpine coal-mine spoil from Alberta (Canada) was followed over one growing season. Fungi were isolated, using a root-washing procedure, from the region of main seminal and nodal roots 4 cm from the root–hypocotyl axis. Fungal colonization of the root surfaces was rapid, with equilibrium numbers of species reached 2 weeks after plant emergence. Although the application of either fertilizer, peat, or sewage sludge to these spoils had no effect on the general form of the colonization curve, peat amendation did result in significantly higher numbers of species on the root surfaces. Species turnover within all assemblages was high throughout the growing season. The amount of species replacement ranged from a low of 67% to a high of 91% between consecutive 4-week sampling periods. Thus, although the number of species was relatively constant, species composition changed considerably. The structure of the root-surface fungal assemblages was characterized by a large proportion of rare species. The species abundance distributions were essentially negative exponential. Neither time nor amendation had any significant effect on these distributions. The large incidence of rare species within the assemblages suggests that these root surfaces represent nonequilibrium systems with respect to species occurrences.

Inhibition of aflatoxin accumulation in smoked substrates.

The pattern of fungal colonization on processed (smoked) copra kernels and the levels of aflatoxin detected in copra and in culture of Aspergillus flavus on fresh coconut suggested that aflatoxin accumulation was inhibited by the smoking process. This paper describes the study of the smoking process under laboratory conditions with fresh coconut and potato dextrose broth; aflatoxin accumulation was found to be significantly or totally inhibited in both smoked coconut and in smoked broth. Mycelial growth was inhibited to a lesser degree.On account of the urgent need for simple, cheap and efficent techniques for the processing and safe storage of food substrates especially in poor tropical countries, we suggest that the smoking process deserves study under industrial conditions for the protection of other agricultural food crops (e.g. groundnut) as well.

Some fungi on decaying banana leaves in Jamaica

The pattern of fungal colonization of collapsed leaves is described. Deightoniella torulosa, Gloeosporium musarum, Verticillium theobromae, Nigrospora spp. and Pyricularia musae are the most frequent primary colonists. As the leaf dries out, the primary flora is gradually replaced by many different saprophytes. The infection biology and sporulation of certain primary colonists are discussed. The importance of decaying banana leaves as a source of inoculum of some banana pathogens is pointed out.