Forest Nursery Soils Research Articles

Assessment of Macro and Micro Mineral Compositions at Different Depths of Forest Nursery Soils in Federal University of Agriculture Abeokuta, Nigeria

Forest soil is characteristically fundamental in the establishment of healthy seedlings for eventual planting out on the field. It is composed of mineral particles, organic matter, water, air, and numerous microorganisms. Two forest nursery soils at different depths were investigated at the Federal University of Agriculture Abeokuta (FUNAAB) for their mineral compositions. With the aid of a soil auger, twenty soil samples were randomly collected from different points in two sites at different depths (0-15 cm and 15-30 cm, air dried and taken to the laboratory for further analysis. Site 1 and site 2 (frequently cultivated portion for agroforestry bare-root seedlings and intermittently used portion). The obtained data were subjected to descriptive statistics. The composition of mineral elements varied with sites and depths. The level of Potassium was higher at depths 0 – 15 cm and 15 – 30 cm in site 2 than other macro-minerals (Sodium, Calcium and Magnesium) when compared between sites. The order of concentration includes K>Mg>Na>Ca. Micro-minerals were significantly higher at soil depth 0 – 15 cm in site 2 than site 1 (Fe>Zn>Mn>Cu). At soil depth 15 – 30 cm, levels of copper, zinc and manganese were significantly higher (p < 0.05) in site 1 with the following trend Cu>Fe>Zn>Mn. The study showed that forest nursery soils varied in their mineral composition along with depth in the studied sites. Site 2 had better physicochemical properties and higher level of some essential minerals needed for good performance of seedling growth at nursery stage.

Влияние высокоактивных соединений на механические свойства древесины двухлетних сеянцев сосны обыкновенной в лесных питомниках

Scots pine (Pinus sylvestris L.) has the leading environment-forming function. Also, the pine is an economically valuable tree species in the Ural region. The long-term use of the pesticide complex in forest nurseries has led to the pesticide pollution of the arable soil, which causes disruption in the pine seedlings growth, weakening their ability to overcome the difficult period of transportation into the forest environment. The use of biostimulants created from extracts of fir and spruce needles, as well as organic ameliorant (forest litter from pinebirch plantations), is considered as a way to reduce the negative impact of pesticides on pine seedlings. At the same time, biologically active preparations and substrates can lead to shifts in the metabolic processes of young plants, which affect the formation of physical characteristics of the stems. The research aims at assessing how wood density changes under the influence of highly active substances of different nature in two-year-old Scots pine seedlings grown in forest nurseries of the Middle Urals. The study objects were two-years-old pine seedlings dug out in autumn from sylvicultural fields and experimental sites in different forest nurseries. Morphometric parameters of seedlings were determined in the laboratory conditions. The basic wood density of stems in the 1st and 2nd years of growth was determined by the method of maximum humidity. It was found that the metabolic activity of pesticides and biostimulants leads to changes in the formation of physical properties of stems at the initial stages of pine growth: when growing seedlings in pesticide-polluted soil, the height of seedlings is lower, and the basic density of stem wood is higher, compared to control group. Forest litter from mixed plantations (birch-pine), when introduced to the forest nursery soil, produces seedlings of greater height and has no significant effect on the formation of physical and mechanical properties of wood. The seed treatment by biostimulants leads to a rapid increase in the stems size, but the wood density decreases, relative to the control option. Corrective measures and the development of balanced agronomic machinery for production of pine with the required physical qualities of wood are needed in the future. The study of the qualitative characteristics formation features of trees, when using intensive technologies in nurseries, is necessary for the development of target models for the subsequent use of such seedlings in forest management.

Monitoring of biological activity indicators of forest nursery soils in Siberia

The universality, comprehensiveness and adequacy of biological soil diagnostics methods make them widely used in monitoring studies of anthropogenic effects on the soil. Soil samples of forest nurseries have been studied, directly under seedlings and in the steam field. Anthropogenic loading changes the biological parameters of the soil, leading to a decrease in soil fertility. The results of the assessment of the biological state of forest nursery soils used for the planting material of coniferous seedlings in Siberia by the level of enzymatic activity are presented. Analysis of soil quality by methods of research of oxidative and hydrolytic enzymes was carried out. Monitoring of enzymatic activity indicators of soils of forest nurseries of Krasnoyarsk region showed that by activity of catalase, invertase of urease they belong to medium-enriched. It has been established that in the soil of Uyarsky, Kansky and Kuraginsky forest nurseryscientists there is the highest rate of proteolytic activity. Low level of catalase enzyme activity revealed in Kazatinsky nursery against the background of high soil contamination with phytopathogenic microorganisms.

Biological Control of Pythium Damping –off in Seedlings with Streptomyces Sp.

Damping-off is one of the severe diseases caused by soil-borne pathogens notably Pythium sp. the causative agent of this infection in raising tree saplings in forest nurseries. Biological control is an eco-friendly approach in disease management compared to chemical fungicides which in turn affects the soil environment. Biocontrol of Pythium sp. has been emphasized in vegetable nurseries than forest nurseries. The present research work is focused on identification of effective antagonistic organism from forest nursery soils against Pythium aphanidermatum. Bacteria were isolated from various forest soils collected from Boluvampati, Sirumugai and Mettupalayam forest nurseries in Coimbatore district and soil samples were screened for antifungal activity against Pythium aphanidermatum by dual culture technique. Among 245 bacterial isolates, one isolate KUMB1.1 exhibited clear zone of inhibition of 1cm and it was identified by 16S rDNA sequencing as Streptomyces sp. Solvent extraction was performed to isolate an active compound using ethyl acetate, dichloromethane, n-butanol, hexane and chloroform in the ratio 1:1. The antifungal activity of compound was performed by well plate method against Pythium sp. and n-butanol extract exhibited zone of inhibition. The antifungal activity of Streptomyces sp. was tested in a model plant Solanum lycopersicum (Tomato) seeds raised in Pythium aphanidermatum infested soils in seed trays under in vitro conditions. Pre-emergence and post-emergence disease incidences were observed, and the results exhibited promising efficacy of Streptomyces sp. against the fungal pathogen Pythium aphanidermatum. Seedbed study was carried out in Gmelina arborea seeds, where the seeds are treated with Streptomyces culture broth. In which seed treatment shows 43% increase in germination compared with control.

Evaluation of Biocontrol Efficacy of Herbal and Bioformulations against Root Rot Pathogen Fusarium Solani in Tomato

Background/Objectives: Fusarium solani cause various plant diseases that usually weaken or destroy plant tissues and reduce crop yields varying from 30-40% and root diseases are estimated to cause 10-15% yield losses annually in the world Soil borne pathogen Fusarium solani which causes root rot at the seedling stage itself leading to wide loss of the crop. Solanum lycopersicum (tomato) is one of the most versatile vegetable with wide usage in Indian culinary tradition. Since the use of chemical fungicides cause environmental pollution and adverse effect on human health, there is need to shift to biological control. Methods: Bacterial isolates were obtained from forest nursery soil samples and screened against F. solani. Of which one isolate showed promising efficacy against the pathogen. Preparation of oil based liquid bioformulation using glycerol, coconut oil and culture filtrate of biocontrol agent and herbal formulation using neem, garlic, ginger and clove blended together with water in the ratio 1:2 showed inhibitory effect on F.solani. Findings: Biocontrol agent was identified by 16S rDNA sequencing as Bacillus velezensis FZB42. Tomato seeds were coated with Gum Arabic as adhesive along with liquid bioformulation and herbal formulation showed great inhibitory effect against the F. solani in invitro conditions, increased the germination percentage of seeds and also the germination was faster when compared with the control. Applications: Technology transfer of application of this formulation to the farmers will be initiated which will help them to raise the seedlings in an ecofriendly method.

Study on the effect of organic fertilizers on soil organic matter and enzyme activities of soil in forest nursery

Abstract The aim of the study was to assess the effects of organic fertilization on selected chemical properties of the soil and the activity of dehydrogenase and β-glucosidase in the soil of forest nursery. The main goal was to evaluate the role of organic fertilizers in carbon storage in the forest nursery soil. Sample plots were located in northern Poland in the Polanów Forest District on a forest nursery. Soil samples were collected from horizon 0–20 cm for laboratory analyzes. In soil samples pH, soil texture, and organic carbon, nitrogen, base cation contents, dehydrogenase activity and β-glucosidase activity were determined. The obtained results were used to evaluate the carbon storage. The results confirm the beneficial effect of the applied organic fertilizer on chemical properties of the soils under study and their biological activity. The applied organic fertilizers had an impact on increased accumulation of soil organic matter. In the soils investigated, there was an increase in the activity of such enzymes as dehydrogenases and β-glucosidase.

Mycoflora of forest nursery soils, and parasitic damping off of seedling roots

Mycoflora of forest nursery soils, and parasitic damping off of seedling roots

Effect of soil fungi communities on the growth of damping-off pathogens in relation to incubation temperature and medium pH

Four communities of saprotrophic fungi from a forest nursery soil were tested for their effect on the <i>in vitro</i> growth of damping-off pathogens: <i>Rhizoctonia solani, Fusarium avenaceum, F. culmorum, F. oxysporum</i> and <i>F. solani</i> in relation to incubation temperature (5, 10, 15, 20 or 25°C) and medium pH (4.3; 5.6 or 7.5). The soil fungi communities weakly suppressed the growth of pathogens studied only at the lower temperatures (5 or 10°C). At the higher temperatures the communities tested supported the growth of all pathogens. The supporting effct was increasing with the increase of temperature, independently of pH. The effect was highly dependent on incubation temperature and not dependent on medium pH (P<0.05, analysis of variance). Duncan's multiple range tests indicate no significant differences (in the majority of combinations) in the effect of soil fungi communities on the <i>in vitro</i> growth of tested pathogens between temperatures 15, 20 and 25°C, independently of medium pH. The growth of the pathogens studied was suppressed mainly by: <i>Gliocladium catenulatum, Trichoderma atroviride, T. koningii, T. viride, Truncalella truncata<i> and <i>Zygorrhynchus moelleri</i>

Pathogenicity and Virulence of Pythium Species Obtained from Forest Nursery Soils on Douglas-Fir Seedlings.

Pythium species are common soilborne oomycetes that occur in forest nursery soils throughout the United States. Numerous species have been described from nursery soils. However, with the exception of P. aphanidermatum, P. irregulare, P. sylvaticum, and P. ultimum, little is known about the potential for other Pythium species found in nursery soils to cause damping-off of tree seedlings. A greenhouse study was conducted to evaluate the pathogenicity and virulence of 44 Pythium isolates representing 16 species that were originally recovered from soil at three forest nurseries in Washington and Oregon. Seeds of Douglas-fir (Pseudotsuga menziesii) were planted into soil infested with each of the isolates. Seedling survival, the number of surviving seedlings with necrotic root lesions, and taproot length were evaluated 4 weeks later. Responses of Douglas-fir to inoculation varied significantly depending on Pythium species and isolate. Eight species (P. dissotocum, P. irregulare, P. aff. macrosporum, P. mamillatum, P. aff. oopapillum, P. rostratifingens, P. sylvaticum, and P. ultimum var. ultimum) significantly reduced the number of surviving seedlings compared to the noninoculated treatment. However, all Pythium species caused a greater percentage of seedlings to develop root lesions (total mean 40%) than was observed from noninoculated seedlings (17%). Taproot length varied little among Pythium treatments and was not a useful character for evaluating pathogenicity. Results confirm the ability of P. irregulare, P. mamillatum, and P. ultimum var. ultimum to cause damping-off of Douglas-fir seedlings, and are indicative that other species such as P. dissotocum, P. aff. macrosporum, P. aff. oopapillum, P. rostratifingens, and P. sylvaticum may also be responsible for seedling loss.

Influence of Isolation Method on Recovery of Pythium Species from Forest Nursery Soils in Oregon and Washington.

Pythium species are common damping-off pathogens that can cause stunting, chlorosis, and death of conifer seedlings in the Pacific Northwest (PNW) region of the United States. Despite the prevalence and importance of these pathogens in forest nurseries, relatively little is known about the identity of Pythium species associated with forest nursery soils in Washington and Oregon. A limited number of studies have reported P. aphanidermatum, P. irregulare, P. mamillatum, and P. ultimum as the predominant species in the PNW, but most studies of this genus in forest nurseries have not reported Pythium species identity. In an attempt to identify Pythium species associated with forest nursery soils, field surveys were conducted at three forest nurseries (two in Oregon and one in Washington) in 2008 using three isolation methods. Pythium species were isolated by plating soil onto a semiselective medium or by baiting soil with rhododendron leaf disks and Douglas-fir needle segments. One hundred isolates were randomly selected from each isolation method at each nursery (900 isolates total) and identified on the basis of the internal transcribed spacer (ITS) sequence. Nineteen Pythium species were identified during the survey. Species richness and abundance were strongly influenced by both nursery and isolation method. Of the 300 isolates obtained from each nursery, P. irregulare was the most commonly isolated species from nursery A in Washington (65% incidence). P. 'vipa' and P. dissotocum were the most commonly isolated species from nurseries B and C in Oregon, respectively (53 and 47% incidence, respectively).

Distribution and genetic diversity of the root‐rot pathogen Neonectria macrodidyma in a forest nursery

SummaryThe aim of this study was to assess genetic diversity and spatial distribution of 123 strains of the root‐rot pathogen Neonectria macrodidyma isolated from fine living roots of bare‐root nursery cultivated Pinus sylvestris. We found that ITS rDNA sequences were 100% identical for all strains. Arbitrary primed PCR fragment analysis showed the presence of two distinct N. macrodidyma types (Type 1 and Type 2), which included respectively 11 and 14 genotypes composed of 1–29 strains. Results of this study indicate that N. macrodidyma is commonly associated with fine living roots of pine seedlings, is largely disseminated by asexual means of local genotypes and has even distribution in the forest nursery soils. In living roots, N. macrodidyma is likely present as dormant propagules but under favourable conditions, it may develop rapidly and have a significant negative effect on plant health and productivity.

Fungi in Roots of Nursery Grown Pinus sylvestris: Ectomycorrhizal Colonisation, Genetic Diversity and Spatial Distribution

The aims of this study were to investigate patterns of ectomycorrhizal (ECM) colonisation and community structure on nursery grown seedlings of Pinus sylvestris, spatial distribution of ECMs in the nursery plot and genetic diversity of commonly isolated ECM basidiomycete Hebeloma cavipes. One hundred seedlings were sampled in 225 m(2) area using a systematic grid design. For each seedling, 20 individual root tips were randomly collected, morphotyped, and surface sterilised for fungal isolation in pure culture. Results showed that ECM community was comprised of nine distinct morphotypes among which Thelephora terrestris (39.7%), Hebeloma sp. (17.8%) and Suillus luteus (6.1%) were the most abundant. Spatial distribution of ECMs in the nursery plot was determined by their relative abundance: even in common ECMs and random in rare ones. Fungal isolation yielded 606 pure cultures, representing 71 distinct taxa. The most commonly isolated fungi were the ascomycetes Neonectria macrodidyma (20.3%), Phialocephala fortinii (13.5%), Neonectria radicicola (6.3%) and the ECM basidiomycete H. cavipes (4.5%). Intraspecific genetic diversity within 27 H. cavipes isolates was studied using two methods: restriction digestion of the amplified intergenic spacer of nuclear ribosomal DNA and genealogical concordance of five genetic markers. Five and eight genotypes were revealed by each respective method, but both of those were largely consistent, in particular, in determining the largest genotype (A) composed of 18 isolates. Mapping positions for each H. cavipes isolate and genotype in the field showed that isolates of the A genotype covered a large part of the nursery plot. This suggests that H. cavipes is largely disseminated by vegetative means of local genotypes and that nursery cultivation practices are likely to contribute to the dissemination of this species in the forest nursery soils.

Effect of pyroligneous acid (wood vinegar) on the microbial succession in a forest nursery soil.

Effect of pyroligneous acid (wood vinegar) on the microbial succession in a forest nursery soil.

Impact of Ectomycorrhizosphere on the Functional Diversity of Soil Bacterial and Fungal Communities from a Forest Stand in Relation to Nutrient Mobilization Processes

The ectomycorrhizal symbiosis alters the physicochemical and biological conditions in the surrounding soil, thus creating a particular environment called ectomycorrhizosphere, which selects microbial communities suspected to play a role in gross production and nutrient cycling. To assess the ectomycorrhizosphere effect on the structure of microbial communities potentially involved in the mobilization of nutrients from the soil minerals in a poor-nutrient environment, we compared the functional diversity of soil and ectomycorrhizosphere bacterial communities in a forest stand. Two hundred and sixty-four bacterial strains and 107 fungal strains were isolated from the bulk soil of an oak (Quercus petraea) stand and from oak-Scleroderma citrinum ectomycorrhizosphere and ectomycorrhizae, in two soil organo-mineral horizons (0 to 3 cm and 5 to 10 cm). They were characterized using two in vitro tests related to their capacities to mobilize iron and phosphorus. We demonstrated that the oak-S. citrinum ectomycorrhizosphere significantly structures the culturable bacterial communities in the two soil horizons by selecting very efficient strains for phosphorus and iron mobilization. This effect was also observed on the diversity of the phosphate-solubilizing fungal communities in the lower soil horizon. A previous study already demonstrated that Laccaria bicolor-Douglas fir ectomycorrhizosphere structures the functional diversity of Pseudomonas fluorescens population in a forest nursery soil. Comparing to it, our work highlights the consistency of the mycorrhizosphere effect on the functional diversity of bacterial and fungal communities in relation to the mineral weathering process, no matter the fungal symbiont, the age and species of the host tree, or the environment (nursery vs forest). We also demonstrated that the intensity of phosphorus and iron mobilization by the ectomycorrhizosphere bacteria isolated from the lower soil horizon was significantly higher compared to that which was isolated from the upper horizon. This reveals for the first time a stratification of the functional diversity of the culturable soil bacterial communities as related to phosphorus and iron mobilization.

Fumigant distribution in forest nursery soils under water seal and plastic film after application of dazomet, metam‐sodium and chloropicrin

Adequate concentration, exposure time and distribution uniformity of activated fumigant gases are prerequisites for successful soil fumigation. Field experiments were conducted to evaluate gas phase distributions of methyl isothiocyanate (MITC) and chloropicrin (CP) in two forest-tree nurseries. Concentrations of MITC and CP in soil air were measured from replicated microplots that received dazomet, metam-sodium and CP. Half of the plots were covered with high-density polyethylene tarp immediately after fumigation; the other half were not covered but received daily sprinkler irrigation for 1 week to create and maintain a water seal. The magnitude of MITC concentrations was similar between nurseries for metam-sodium in both tarp and water seal treatments and for dazomet in the tarp treatment. Consistently greater MITC and CP concentrations were found in the upper 30 cm of soil in the tarped plots compared with the water-sealed plots. Despite potential environmental and economic benefits with the water seal method, tarp covers were more reliable for achieving and maintaining higher MITC and CP concentrations and less prone to variations due to irrigation/rain, soil bulk density and other environmental conditions.

Degradation of Methyl Isothiocyanate and Chloropicrin in Forest Nursery Soils

Recent studies have observed enhanced degradation of methyl isothiocyanate (MITC) from repeated fumigation in agricultural soils. Little is known about fumigant degradation in forest and nursery soils. This study was conducted to determine degradation rates of MITC and chloropicrin (CP) in two forest soils and the impacts of nursery management on degradation of MITC and CP. The half-life values of MITC and CP were evaluated in the laboratory under isothermal conditions (22 +/- 2 degrees C). Three rates representing 0.5x, 1x, and 2x field application rates for each fumigant were used in laboratory incubations. Effect of microbial degradation was determined by conducting incubations with both fresh and sterilized soils. Soil moisture effects were also studied. There was no difference in MITC or CP degradation between fumigated and nonfumigated forest nursery soils. Soil sterilization and high soil moisture content (15% by wt.) reduced MITC and CP degradation. The degradation rates of MITC and CP varied with factors such as nursery history, fumigant application rates, and freshness of tested soils.

Mechanisms of N 2O production following chloropicrin fumigation

Soil fumigation has recently been shown to affect the greenhouse gas balance by increasing emissions of nitrous oxide (N 2O) following chloropicrin (CP) application. However, the exact mechanisms of this increase were not investigated. The purpose of this study was to elucidate potential mechanisms of CP-induced N 2O production through laboratory incubations using chemical inhibitors (acetylene, antibacterial, antifungal, and oxygen), isotopically labeled 15N-CP, and pH modifications of a forest nursery soil. Results showed that N 2O production increased by 12.6 times following CP fumigation. Microbial activity contributed 82% to the CP-induced N 2O production, with the remaining 18% from abiotic processes as determined by incubation with sterilized soil. Inhibitor studies suggested that 20% of the N 2O production was from bacteria and 70% from fungi. There were no significant differences in N 2O production following CP fumigation under various levels of acetylene (0, 10, and 10 kPa), suggesting that traditional nitrification and denitification reactions did not significantly contribute to N 2O production following CP fumigation. 15N labeled studies indicated that 12% of fumigant source N was incorporated into the produced N 2O. No enrichment in N 2 was observed, indicating that N 2O was one of the terminal biotic mineralization products of CP. Production of N 2O is aerobic and production rates increased with increasing oxygen concentrations. Our data strongly suggested that fungal mediated denitrification reactions under aerobic conditions were the primary mechanism for CP-induced N 2O production.

Greenhouse gas production and emission from a forest nursery soil following fumigation with chloropicrin and methyl isothiocyanate

Soil fumigation is commonly used to control soil-borne pathogens and weeds. Our aim was to examine the effects of soil fumigation with chloropicrin (CP) and methyl isothiocyanate (MITC) on CH 4, N 2O and CO 2 production and emission. These effects on a SE USA forest nursery soil were examined in field and laboratory experiments. Following field fumigation, CH 4 surface emissions and concentrations in the soil atmosphere were unaffected. Both fumigants increased N 2O emissions rates significantly compared to non-fumigated controls, and the effects were still evident after 48 d. These findings are in contrast to fertilizer-induced N 2O emissions, which generally return to background within 2 wk after application. Depths of N 2O production were different for the two fumigants as determined by soil gas sampling, suggesting fumigant-specific stimulation mechanisms. CO 2 emissions (0–15 d) were not altered significantly, although sub-surface CO 2 concentrations did increase following fumigation with CP or MITC and remained elevated for CP treatment on d 48. CP-induced N 2O production was also stimulated in aerobic laboratory incubation studies, with surface soils exhibiting 10 to 100-fold greater production rates. MITC and a combination of CP/MITC also stimulated N 2O production, but the effect was significantly less than for CP alone. MITC suppressed and CP did not effect CO 2 production in the laboratory incubation. By comparing sterilized to non-sterile soils, >95% of these effects appear to be of biotic origin.

Survival in the soil of the ectomycorrhizal fungus Laccaria bicolor and the effects of a mycorrhiza helper Pseudomonas fluorescens

In disinfected forest nursery soils, inoculating Douglas fir ( Pseudotsuga menziesii) seedlings with the ectomycorrhizal fungal strain Laccaria bicolor S238N significantly increases tree growth after outplantating. However, the success of the inoculation depends on survival of the fungal inoculum in the soil during the pre-symbiotic life of the fungus. We followed the survival of L. bicolor S238N in autoclaved nursery soil in the glasshouse, and under gnotobiotic conditions in autoclaved or γ-irradiated nursery soil. We also studied the effect of the mycorrhiza helper bacterium Pseudomonas fluorescens BBc6R8, which promotes the Douglas fir- L. bicolor S238N symbiosis, on fungal viability. In the glasshouse, fungal viability was assessed by trapping with Douglas fir seedlings. We showed that the fungus retained its viability in a pre-symbiotic state in the soil at least for 23 weeks, which is much longer than that reported in the literature for other ectomycorrhizal fungi. The bacterium did not significantly modify the survival of the fungus. In the gnotobiotic experiments, ergosterol, a specific fungal membrane component, was used to quantify fungal biomass. Fungal behaviour differed with the disinfection technique used, which modified the chemical characteristics of the initial soil. There was no fungal growth in the autoclaved soil but there was a rapid increase of fungal biomass in the irradiated soil. The effect of the bacterium on fungal biomass also varied with a significant stimulation in the autoclaved soil vs. a significant inhibition in the irradiated soil. Our results show that the beneficial effect of the bacterium on the fungus depends on the condition of the fungus, i.e. the greatest benefit occurs when the fungus is growing under unfavourable conditions.

Effects on growth and comparison of root tissue colonization patterns of Eucalyptus viminalis by pathogenic and nonpathogenic strains of Fusarium oxysporum.

Soilborne pathogens, especially Fusarium oxysporum, are responsible for damping-off and root necrosis in Eucalyptus nurseries. New technologies are increasingly considering strategies for plant disease control other than chemical fungicides. Among these, natural fungal antagonists, which are colonizers of the root cortex, are potential biocontrol agents. An in vitro system was used: (1) to test the pathogenic effects of F. oxysporum strain Foeu1 which was recovered from a forest nursery soil; (2) to explore the potential of the nonpathogenic F. oxysporum strain Fo47, which is known for its efficiency in biological control, to suppress damping-off of Eucalyptus seedlings; (3) to compare the patterns of root colonization and host response to invasion by the two Fusarium strains inoculated separately in a time-course study. Root inoculation of E. viminalis with F. oxysporum strain Foeu1 caused damping-off in young seedlings in vitro, whilst disease symptoms were not visible in plants inoculated with F. oxysporum strain Fo47 or when both strains (Foeu1 + Fo47) were inoculated simultaneously. Each strain showed similarities in patterns of root tissue colonization, and in the processes of root penetration and initial colonization. Differential effects on root tissue were observed with fungal development within the cortex: ingress of strain Foeu1 was accompanied by severe host-cell alterations whilst no tissue damage occurred with development of strain Fo47.