Population performance of collembolans feeding on soil fungi from different ecological niches

The potential reproductive value of arbuscular mycorrhizal fungi (Glomus intraradices and Glomus invermaium), root pathogenic fungi (Rhizoctonia solani and Fusarium culmorum) and saprotrophic fungi (Penicillium hordei and Trichoderma harzianum) were examined for the collembolans Folsomia candida Willem and Folsomia fimetaria L. Dried baker's yeast (Saccharomyces cerevisiae) was used as a reference standard food in laboratory cultures. Collembolan performance was determined as final size, fecundity and population growth rate after when fed the fungal food sources for 31 days. The mycorrhizal fungi gave the least growth and fecundity compared with the other fungi, but G. intraradices gave good fecundity for F. candida. In terms of growth, Baker's yeast was a high-quality food for both adults and juveniles of both species, but it was a poorer food in terms of fecundity of F. candida. Preference of the fungi in all possible pairwise combinations showed that although F. fimetaria did not perform well on Glomus spp. and F. candida did not grow well on Glomus spp. their preference for these fungi did not reflect this. The highest fecundity was seen with the root pathogen F. culmorum. Different quality indicators such as the C:N ratio of the fungal food sources as well as other biological parameters are discussed in relation to their reproductive value and Collembola preferential feeding.     

Species-specific impacts of collembola grazing on fungal foraging ecology

Fungi are primary agents of organic matter decomposition in forests. Although invertebrate grazing affects fungal biomass and morphology, the species-specific consequences of these interactions are little understood. Using three collembola species (Folsomia candida, Protaphorura armata, Proisotoma minuta) we employed a multi-trophic approach to investigate the individual effects of invertebrate grazing on four species of saprotrophic basidiomycete fungi growing in two species (one fungus: one collembola) soil microcosms. We studied these effects at three trophic levels: the rate of wood decay brought about by the fungi was assessed; fungal growth was characterized across multiple time points using a range of image analysis parameters (radial extension, hyphal coverage, fractal dimension); and collembola abundance was determined at the end of the experiment. Collembola species had different impacts both within and across fungal species; F. candida had the greatest effect on fungal mycelia whereas P. armata often had little impact. Fungal species varied in their resilience to grazing; all collembola species modified Phanerochaete velutina and Hypholoma fasciculare morphology, that of Resinicium bicolor was only markedly affected by F. candida, and effects on Phallus impudicus were negligible. In the case of H. fasciculare, these grazing effects translated into effects on the rate of fungus-induced wood decay: F. candida and P. armata, but not P. minuta, reduced wood decay rate compared to ungrazed controls. Rate of wood decay was unaffected in the other three fungal species. Changes in collembola population size were generally consistent across fungal species, with each species achieving a greater abundance on P. velutina than on H. fasciculare and P. impudicus. The collembola species did, however, respond differently to R. bicolor, with F. candida being more successful than P. armata. Our study suggests that a wide range of impacts can occur during fungus–collembola interactions, and that caution should be exercised when treating saprotrophic fungi and mycophagous collembola as uniform functional components.     

Effects of temperature and life stage on the fatty acid composition of Collembola

Fatty acid (FA) analysis is used as a promising tool to investigate trophic interactions in soil food webs. The FA profile of neutral lipids in consumers is affected by the diet, and the occurrence and amount of certain FAs can reflect feeding strategies. We investigated the lipid composition of the Collembola Folsomia candida, Heteromurus nitidus and Protaphorura fimata with the fungus Chaetomium globosum as food source. The impact of environmental temperature and life stage was assessed, with special respect to linoleic acid (18:2ω6,9) as a marker FA for fungal feeding. In all Collembola species the ratio of C16/C18 in neutral lipid fatty acids (NLFAs) increased with decreasing temperature. In the NLFAs of F. candida and H. nitidus the Unsaturation Index and the amount of 18:2ω6,9 decreased with temperature, whereas in P. fimata effects were the opposite. The composition of phospholipid fatty acids (PLFAs) differed between species, but was little affected by temperature. The degree of unsaturation in NLFAs increased with the age of Collembola, mainly due to higher amounts of 18:2ω6,9 and a lower proportion of 18:1ω9. The biomarker linoleic acid represented over 20% of FAs in all fungal feeding Collembola. Despite considerable influence of temperature and life stage on its proportion, the amount was always higher than in individuals reared on other diets. This suggests that linoleic acid can serve as marker for fungal feeding independent of such physiological variations in Collembola.     

Inter- and intraspecific feeding selectivity of Folsomia candida (Willem) (Collembola,Isotomidae) on fungi

Summary Selective grazing of fungi by soil microarthropods may affect decomposition rates of litter materials and the structure of microarthropod and fungal communities. We developed laboratory methods to assay feeding selectivity and investigated the preferences of the collembolan Folsomia candida on three fungi: Acremonium sp., Paecilomyces varioti, and Penicillium citrinum. F. candida showed stronger preference for Acremonium sp. than for P. varioti and P. citrinum. Oviposition site selection followed the same pattern. Actively metabolizing hyphae of Acremonium sp. and P. varioti were preferred over senescent hyphae, while spores of P. citrinum were preferred over active hyphae. If microarthropod preference for active hyphae is extensive, microarthropod regulation of decomposition could be more important than their biomass indicates. Furthermore, as the P. citrinum results indicate, mechanisms of microbial dissemination may include selective grazing.Contribution in part to International Symposium on Faunal Influences on Soil Structure, Edmonton, Alberta, Canada (11–13 June 1984), organized by W. B. McGill; and the annual meeting of the Ecological Society of America, Minneapolis, Minnesota (17–21 June 1985)     

Effects of Cd and Pb on the survival and juvenile production of Sinella coeca and Folsomia candida

Degradation factors can cause both quantitative and qualitative changes in fauna and thus affect soil functioning. The use of bio-indicators may help to detect environmental changes. The aim of this study was to evaluate the effects of lead and cadmium on the biology (mortality, reproduction, egg hatching) of two euedaphic collembolans, Sinella coeca and Folsomia candida and to evaluate sensitivity differences between the two species. The results showed that low concentrations of lead did not cause dramatic effects on the survival and reproduction of both species. Reproduction of both species was reduced when the soil contained a nominal concentration of Pb at 1000 μg g^–1. S. coeca and F. candida showed a high sensitivity to cadmium and both their reproduction and survival were significantly reduced on exposure to 50 μg g^–1. Moreover, egg hatching of F. candida was affected by the cadmium concentrations in the soil, and by the amount of time that the eggs stayed in contact with cadmium. This study showed that the inhibition determined by Cd on F. candida juvenile production was caused in part by inhibition of deposition and, in part, by reduction of egg viability.     

Olfactory cues associated with fungal grazing intensity and secondary metabolite pathway modulate Collembola foraging behaviour

Fungal secondary compounds play an important role for springtail food choice and fitness. Little is known, however, on the role of olfactory cues for Collembola foraging behaviour and whether Collembola can olfactorily perceive volatiles associated with fungal secondary metabolite pathways. We investigated the ability of three species of Collembola (Folsomia candida, Heteromurus nitidus and Supraphorura furcifera) to use olfactory cues for discriminating between fungi of different phylogenetic affiliation (Aspergillus nidulans, Cladosporium cladosporioides, Ascomycota; Laccaria bicolor, Basidiomycota) and toxicity using fungal strains of A. nidulans with reduced secondary metabolite production. Furthermore, we studied if olfactory cues from hyphae injured by grazing affect the foraging behaviour of Collembola. We hypothesized that (i) Collembola are able to olfactorily perceive and respond to fungal species/strains with different secondary metabolite pathways and that (ii) Collembola are able to sense fungal mycelia injured by grazing. Each of the Collembola species studied preferentially oriented their foraging towards fungal strains of A. nidulans with suppressed secondary metabolites, and in particular towards the mutant where the global regulator for secondary metabolites (ΔlaeA) has been silenced. Two of the three Collembola species (H. nitidus and S. furcifera) sensed olfactory cues of previously grazed fungi and moved towards ungrazed fungi, however, the response of S. furcifera was restricted to fungi extensively exposed to grazing (5 days) suggesting that the response varies between Collembola species.Overall, the results support the first and second hypothesis indicating that Collembola (1) are able to olfactorily differentiate fungi of different toxicity and move towards more palatable fungi, and (2) showed a lesser preference for fungi previously exposed to grazing.     

Density-dependent grazing on the extraradical hyphal network of the arbuscular mycorrhizal fungus, Glomus intraradices, by the collembolan, Folsomia candida

The effect of microarthropod density on the relative palatibility of selected microfungi and on the integrity of extraradical arbuscular-mycorrhizal (AM) hyphal networks was examined. A series of microcosm experiments were conducted using two conidial fungi (Alternaria alternata and Trichoderma harzianum), one AM fungus (Glomus intraradices) and the microarthropod Folsomia candida (Collembola). We did not detect a significant effect of athropod density on food preference. Food preferences for conidial over mycorrhizal hyphae were consistent across a wide range of collembolan densities. Collembolan density did, however, have a significant effect on the numbers of extraradical AM hyphae which were severed from the plant root in vitro. Even in the presence of a preferred food source, numbers of severed AM hyphal networks increased with increasing collembolan density. Also, the fecundity of Folsomia candida increased in the presence of preferred food sources. We conclude that microarthropod population densities are influenced by the fungal species available and that the potential of microarthropods to impair the efficacy of AM symbioses is density-dependent. Received: 16 May 1997     

Palatability of microfungi to soil arthropods in relation to the functioning of arbuscular mycorrhizae

We investigated the feeding preferences of six species of mites and collembolans for three fungi commonly associated with roots of Acer saccharum (Glomus macrocarpum, Alternaria alternata and Trichoderma harzianum), from a maple-forest soil in southern Ontario, Canada. Experiments were also conducted in vitro to determine animal feeding responses to (1) increasing quantities of hyphal biomass, (2) the presence of root vs. litter fungal substrates, and (3) hyphae of different widths of Glomus macrocarpum. The results indicate that arthropods prefer to graze in the litter region rather than in the deeper soil layers. Under ideal moisture/temperature conditions, animals are forced to the lower regions by interspecific interactions. They prefer to graze on hyphae of conidial fungi rather than on those of arbuscular mycorrhizal fungi. When arbuscular mycorrhizal fungal hyphae are grazed, there is a clear preference for the narrower hyphae, which are those further away from the root. The thicker hyphal segments, commonly found connecting absorptive hyphal fans to roots, were less preferred. These data are not consistent with the hypothesis that microarthropods are detrimental to arbuscular mycorrhizal associations, and suggest that Glomalean fungi may have evolved mechanisms to deter grazing by microarthropods.     

Use of an avoidance test for the assessment of microbial degradation of PAHs

An avoidance test using the soil springtail Folsomia candida was used to assess changes in contamination levels at low doses of PAHs following incubation with indigenous microflora. A soil from a former coke site was diluted to 1% in an unpolluted soil from the same site, which was used as a control, then both substrates were remoistened to 80% field capacity. The diluted soil was previously shown to be strongly repellent to F. candida, although not toxic. After 2-month incubation at 20 °C, the mixture lost its repellence capacity and became attractive to the test animal, while the global 16 PAHs content had decreased to a great extent (50%). PAH disappearance was linked to the occurrence of indigenous microbiota able to degrade hydrocarbons.     

Fungal-feeding habits of six nematode isolates in the genus Filenchus

The family Tylenchidae is a large group of soil nematodes but their feeding habits are not fully known. We studied the fungal-feeding abilities of nematodes in the genus Filenchus. We measured population growth rates (PGRs) of six nematode isolates, representing three Filenchus species, when feeding on seven fungal species on two types of culture media. On Potato Dextrose Agar (PDA) Filenchus misellus, Filenchus discrepans and an unidentified Filenchus sp. generally showed moderate to large PGRs on saprophytic fungi (Rhizoctonia solani, Chaetomium globosum, Coprinus cinereus, Flammulina velutipes) and low PGRs on plant-pathogenic fungi (Fusarium oxysporum, Pythium ultimum). In soil medium amended with chopped soybean plant material or wheat bran, the status of most of the fungi as food for the nematodes was similar to that on PDA, although PGRs tended to be lower in the soil medium. However, C. globosum, a good food on PDA, only supported low PGR in soil for each of the three nematodes. The PGRs of F. misellus on C. globosum in soil were still low even when types and amounts of organic matter amendments were varied. A nematophagous fungus, Pleurotus ostreatus (oyster mushroom), was determined to be a food for Filenchus on PDA or in soil, based on PGR measurements corrected for extraction efficiency. To determine whether fungal species and culture media affected nematode extraction efficiencies and, consequently, the apparent PGRs, we compared efficiencies between R. solani, C. globosum and C. cinereus, and between PDA and soil. The relatively low extraction efficiencies across fungal species in soil seemed responsible for the lower nematode PGRs in soil than on PDA. On PDA generally, fungal species did not affect the assessment. In soil, effects of fungal species on extraction were significant, but not consistent, across nematode species. Nevertheless, the extraction efficiency differences in soil were considered not to affect assessment of the three fungi as food for the nematodes. The confirmation that three Filenchus species reproduce by feeding on fungi in soil suggests that fungal-feeding is not an unusual habit in the field, in this genus. We believe that in community studies, nematodes in the genus Filenchus should be considered fungal feeders or root and fungal feeders, rather than only plant feeders. Our confirmation of fungal-feeding habits in the genus Filenchus supports the hypotheses that plant-feeding nematodes evolved from those feeding on fungi.     

Food choice and reproductive success of Folsomia candida feeding on copper-contaminated mycelium of the soil fungus Alternaria alternata

We examined collembolan food preference for fungal mycelium grown on copper-contaminated medium, and the relationship between copper content, food selectivity and collembolan fitness when fed contaminated mycelium.To clarify whether collembolan food selectivity is related to fitness parameters, Folsomia candida were fed mycelium of the dark-pigmented fungus Alternaria alternata grown on medium with different copper concentrations. Copper-contaminated food (fungus grown on 50, 125, 250 and 500 μg Cu g⁻¹ medium, fresh wt.) was offered together with untreated food for 4 weeks. F. candida fed selectively on the provided mycelium and discriminated clearly between mycelium grown on high and low levels of contamination, distinctly preferring fungus grown on medium with a total copper concentration of 50 and 125 μg g⁻¹. In contrast, fungus grown on highly contaminated medium (250 and 500 μg g⁻¹) was avoided. Collembolan food preference generally matched fitness parameters. Reproduction was significantly affected by the total copper concentration of the fungal growth medium. When fed their preferred mycelium, collembolan reproduction was enhanced, whereas a diet of highly contaminated mycelium (250 or 500 μg g⁻¹) resulted in a strong decrease in reproduction. Adult survival was affected only marginally. Even though heavy metal contamination is a potential stress factor for many soil microarthropods, F. candida is able to discriminate between high and low quality food sources, and even benefits from moderately elevated copper concentrations.     

Organic acid exudation by mycorrhizal Andropogon virginicus L. (broomsedge) roots in response to aluminum

Elevated aluminum (Al) availability limits plant growth on acidic soils. Although this element is found naturally in soils, acidic conditions create an environment where Al solubility increases and toxic forms of Al impact plant function. Plant resistance to Al is often attributed to organic acid exudation from plant roots and the chelation of cationic Al in the rhizosphere. The association of arbuscular mycorrhizal (AM) fungi with the roots of plants may alleviate Al toxicity by altering soil Al availability or plant exposure through the binding of Al to fungal structures or through the influence of fungi on exudation from roots. Diverse communities of AM fungi are found in soil ecosystems and research suggests that AM fungi exhibit functional diversity that may influence plant performance under varying edaphic environments. In the present study, we evaluated acidic isolates of six AM species in their responses to Al. Andropogon virginicus (broomsedge), a warm-season grass that commonly grows in a range of stressful environments including acidic soils, was used as a plant host for Acaulospora morrowiae, Glomus claroideum, Glomus clarum, Glomus etunicatum, Paraglomus brasilianum, and Scutellospora heterogama. Fungal spores were germinated and exposed to 0 or 100 μM Al on filter paper in sand culture or were grown and exposed to Al in sand culture in association with A. virginicus. Short- and long-term responses to Al were evaluated using direct measurements of fungal spore germination, hyphal elongation, and measurements of A. virginicus colonization and plant growth as a phytometer of AM function in symbio. Spore germination and hyphal elongation varied among AM species in response to Al, but patterns were not consistent with the influences of these AM species on A. virginicus under Al exposure. Exposure to Al did not influence colonization of roots, although large differences existed in colonization among fungal species. Plants colonized by G. clarum and S. heterogama exhibited the least reduction in growth when exposed to Al, produced the highest concentrations of Al-chelating organic acids, and had the lowest concentrations of free Al in their root zones. This pattern provides evidence that variation among AM fungi in Al resistance conferred to their plant hosts is associated with the exudation of Al-binding organic acids from roots and highlights the role that AM fungal diversity may play in plant performance in acidic soil environments.     

Collembolan grazing affects the growth strategy of the cord-forming fungus Hypholoma fasciculare

Mycelia of cord-forming fungi show remarkable patterns of reallocation of biomass and nutrients indicating an important role of these, often extensive, organisms in the spatial translocation of energy and nutrients in forest soils. Despite the rich tradition of interaction studies between soil microarthropods and fungi, the spatial implications of these interactions, due to the potential growth responses of the fungi and to the translocation of energy and nutrients within the mycelial network, have been largely ignored. In this paper we analyse fungal growth responses in two-dimensional model systems composed of compressed soil, the cord-forming fungus Hypholoma fasciculare and three fungivorous Collembolan species. We hypothesised that (i) the highly co-ordinated nature of cord-forming fungi would lead to growth responses following collembolan grazing, and that, (ii) such changes are dependent on grazing intensity, and (iii) changes are dependent on the species grazing. Mycelial extent and hyphal cover decreased with increasing grazing density; at highest grazing density also the fractal dimension of the mycelial border decreased, indicating a less branched foraging front due to the regression of fine hyphae and the development of mycelial cords. Effects differed greatly between collembolan species although they exerted comparable grazing pressure (the smaller species were added in larger numbers according to their allometric size-metabolic rate relationships): while grazing by Folsomia candida resulted in less mycelial extension and hyphal cover, these variables were not affected when Proisotoma minuta and Hypogastrura cf. tullbergi grazed. The effects of a species mix suggested an additive effect of the component species. This shows that fungal mycelia may suffer from damage caused by few but large collembolans, affecting extension as well as coverage of the mycelium, but that fungi may compensate for the biomass loss caused by more but slightly smaller collembolans. In about 20% of the model systems H. fasciculare switched from a growth pattern with a broad contiguous foraging front and uniform growth in all directions to a pattern with fast growing sectors while other sectors stopped growth completely. The switch occurred in grazed systems exclusively; thus we interpret this observation as a fugitive response and as a strategy for quickly escaping from places where grazing pressure is experienced.     

Preference tests with collembolas on isogenic and Bt-maize

Collembolas are important members of belowground food webs. There is little information available on the effects of the plant residues of transgenic maize expressing Bacillus thuringiensis (Bt) toxin on soil animals, including collembola. This is why two questions were addressed in laboratory feeding experiments with three collembolan species: (i) Are collembola equally distributed on residues of isogenic and Bt-maize? and (ii) Do collembola show feeding preference to either of the maize types? Bt-maize (producing Cry1Ab toxin) proved to be a less preferred food source for Folsomia candida than the isogenic one. No similar phenomenon was found in the case of Heteromurus nitidus and Sinella coeca. F. candida reacted to as low as 3.45 (± 0.8 mg g⁻¹) Bt-toxin content of the maize. Our results show that the effect of the Bt-toxin producing maize on the collembolan is species specific.     

Soil biota effects on soil structure: Interactions between arbuscular mycorrhizal fungal mycelium and collembola

Soil aggregation is an important ecosystem process mediated by soil organisms. Collembola and arbuscular mycorrhizal (AM) fungi are major soil biota representing different functional groups, and are known as two key promoters of soil aggregation. Although several studies have experimentally demonstrated that AM fungi and, more recently, collembola affect soil structure, there is no study investigating how both soil organisms affect soil aggregation excluding the influence of plant roots, another important driver of soil aggregation. Considering the importance of AM fungi and collembola in terrestrial ecosystems, here we asked if both organisms have any influence on soil aggregation when roots are not present.In order to examine this question we conducted a completely factorial greenhouse study manipulating the presence of both collembola and AM fungi and excluded the roots of Plantago lanceolata using a 38 μm nylon screen compartment. We quantified soil aggregation as water stable soil aggregates in four size classes in the hyphal compartment and monitored a number of other explanatory variables, including AM (and non-AM) fungal soil hyphal length.The soil in the hyphal compartment showed greater soil aggregation with larger mean weight diameter when collembola were present, and a similar result was found in the presence of AM fungi, compared to control treatments. Moreover, combined presence of both AM fungi and collembola resulted in a non-additive increase of soil aggregation.Our study clearly indicated that collembola can enhance soil aggregation, that they can partially complement effects of AM fungi, and that these effects are independent of roots.     

Effects of soil application of olive mill wastewaters on the structure and function of the community of arbuscular mycorrhizal fungi

Recycling of olive mill wastewaters (OMW) into agricultural soils is a controversial issue since benefits to soil fertility should counterbalance potential short-term toxicity effects. We investigated the short-term effects of OMW on the soil-plant system, regarding the diversity, structure and root colonization capacity of arbuscular mycorrhizal (AM) fungi and the respective growth response of Vicia faba L, commonly used as green manure in olive-tree plantations. A compartmentalized pot system was used that allowed the establishment of an AM fungal community in one compartment (feeder) and the application of three OMW dose levels in an adjacent second compartment (receiver). At 0, 10, and 30 days after OMW treatment (DAT), V. faba pre-germinated seeds were seeded in the receiver compartment. At harvest, shoot and root dry weights, AM fungal root colonization, soil hyphal length and P availability were recorded in the receiver compartment. In addition, OMW effects on AM fungal diversity in plant roots were studied by DGGE. A transient effect of OMW application was observed; plant growth and AM fungal colonization were initially inhibited, whereas soil hyphal length was stimulated, but in most cases differences were absent when seeding was performed 30 DAT. Similarly, changes induced in the structure of the root AM fungal community were of transient nature. Cloning and sequencing of all the major DGGE bands showed that roots were colonized by Glomus spp. The transient effects of OMW on the structure and function of AM fungi could be attributed to OMW-derived phytoxicity to V. faba plants or to an indirect effect via alteration of soil nutritional status. The high OMW dose significantly increased soil P availability in the presence of AM fungi, suggesting efficient involvement of AM fungi in organic-P minerilization. Overall our results indicate that soil application of OMW would cause transient changes in the AM fungal colonization of V. faba plants, which, would not impair their long-term plant growth promoting ability.     

Food choice and reproductive success of Folsomia candida feeding on copper-contaminated mycelium of the soil fungus Alternaria alternata

We examined collembolan food preference for fungal mycelium grown on copper-contaminated medium, and the relationship between copper content, food selectivity and collembolan fitness when fed contaminated mycelium.To clarify whether collembolan food selectivity is related to fitness parameters, Folsomia candida were fed mycelium of the dark-pigmented fungus Alternaria alternata grown on medium with different copper concentrations. Copper-contaminated food (fungus grown on 50, 125, 250 and 500 μg Cu g^?1 medium, fresh wt.) was offered together with untreated food for 4 weeks. F. candida fed selectively on the provided mycelium and discriminated clearly between mycelium grown on high and low levels of contamination, distinctly preferring fungus grown on medium with a total copper concentration of 50 and 125 μg g^?1. In contrast, fungus grown on highly contaminated medium (250 and 500 μg g^?1) was avoided. Collembolan food preference generally matched fitness parameters. Reproduction was significantly affected by the total copper concentration of the fungal growth medium. When fed their preferred mycelium, collembolan reproduction was enhanced, whereas a diet of highly contaminated mycelium (250 or 500 μg g^?1) resulted in a strong decrease in reproduction. Adult survival was affected only marginally. Even though heavy metal contamination is a potential stress factor for many soil microarthropods, F. candida is able to discriminate between high and low quality food sources, and even benefits from moderately elevated copper concentrations.     

Fluorescence microscopy to study colonization of conidia and hyphae of Cochliobolus Sativus by soil microorganisms

Epi-fluorescence microscopy facilitated observations of the colonization of hyphae and conidia of C. sativus and other plant pathogenic fungi in soil. Of six fluorochromes examined, acridine orange and europium chelate effectively differentiated cells of bacteria and actinomycetes from the melanized fungal structures. Under u.v. radiation, the colonizing organisms fluoresced intensively while the pigmented conidia appeared dark. Periodic observations of hyphal fragments and conidia of C. sativus incubated in nonsterile soil revealed rapid colonization of their surface primarily by bacteria. Whereas up to 80% of the hyphal fragments of C. sativus were lysed after 32 days' incubation in soil, the conidia remained intact. However, disorganization of protoplasts and disappearance of conidial septa were evident after the fourth week. After 2, 3 and 5 weeks incubation of the plant pathogens in soil, no significant difference was noticed between microbial colonization of conidia on 8.0 μm pore size “Nucle-pore” membranes and those placed directly on the soil surface.