Soil Fungistasis Research Articles

Volatile Factor in Soil Fungistasis

SOIL fungistasis was originally described by Dobbs and Hinson1 as a widespread phenomenon in which viable fungal spores were unable to germinate in natural soil. Although no precise and universally accepted explanation for this phenomenon is available, fungistasis is usually considered to result from biological activity in soil2,3. Failure to extract an inhibitory factor5–7 has led to the nutritional theory2,3 that the phenomenon can be explained wholly by the lack of nutrients essential for germination in the soil micro-environments of fungal spores. On the other hand, some have suggested that there are inhibitors in soil, the effects of which are nullified by the addition of suitable nutrients4,6,8,9. We report here evidence of a volatile factor in soil which induces fungistasis.

Soil Fungistasis: Mechanism in Sterilized, Reinoculated Soil

Soil Fungistasis: Mechanism in Sterilized, Reinoculated Soil

Soil fungistasis with respect to pH and profile.

Soil fungistatic activity was determined in different soils using the sterile cellophane–agar diffusion method. Comparing 35 soil samples from eight profiles, the inhibitory effect on Trichoderma koningi was found to increase with increasing soil pH irrespective of the depth at which the soil samples were taken.The fungistatic principle of seven soils was compared using 24 test fungi. Nearly all fungi affected by soil fungistasis were more strongly inhibited with increasing soil alkalinity.Susceptibility of some fungi to the fungistatic principle varied considerably with the age of the cultures from which the spores were collected. Inhibition of germination was significantly dependent on the length of preactivation of the agar discs over the soil. In some instances the inhibitory effect was considerably reduced if the agar discs were removed onto glass for the germination test after preactivation on cellophane over soil.

Influence of Nitrogen Fertilizers on Washington Creeping Bentgrass, Agrostis palustris Huds. II. Incidence of Dollar Spot, Sclerotinia homoeocarpa, Infection1

AbstractA field experiment was established to evaluate influence of nitrogenous fertilizers on susceptibility of ‘Washington’ creeping bentgrass, Agrostis palustris Huds., to dollar spot disease, Sclerotinia homoeocarpa F. T. Bennett. The field study also supplied soil and plant tissue used in a series of laboratory experiments to investigate effects of activated sewage sludge and processed tankage on growth of S. homoeocarpa in pure culture. Influences of nitrogenous fertilizer on soil fungistasis and on plant tissue fungistasis were also investigated.High levels of available nitrogen reduced dollar spot injury in field tests. Activated sewage sludge, which was most effective in producting disease resistant turf, did not possess any measurable fungitoxic agents. Soil microbiological activity, fertility, fungistasis and pH were not altered significantly by fertilizer treatment.

Isolation and characterization of a fungistatic principle produced by bacteria.

A fungistatic principle produced by a bacterium Pseudomonas sp. was isolated, characterized, and its potential role in soil fungistasis considered. The principle was isolated from a concentrated cultural filtrate of the bacterium by the use of column chromatography, and characterized by its solubility and elemental analysis and by infrared, nuclear magnetic resonance, and mass spectra. The fungistatic principle was an unsaturated, aliphatic, hydroxyketone with a molecular weight of approximately 166. This compound could be recovered from soil only with organic solvents and, therefore, it was concluded that the principle probably does not contribute to soil fungistasis.

Fungistatic properties of soils exposed to different antecedent environments.

A Toledo silty clay soil with different cropping histories was tested for fungistatic activity by an agar-ring method using Bipolaris sorokiniana (Sacc.) Shoemaker as the assay organism. Although all soils exhibited considerable fungistatic activity, the magnitude varied only slightly with their cropping histories. Fungistatic activity of soil cropped to alfalfa was somewhat higher than that of soil obtained from rotation plots with oats or soybeans as the last crop. Attempts were made to extract fungistatic material from soil using water, ethanol, or ether. Although the fungistatic properties of the extracts were lost when sterilized by steam or filtration, nonsterilized extracts were inhibitory to the test fungus.Nutrient studies revealed that fungistasis was suppressed when sucrose, peptone, or yeast extract was added to the soil. Evidence was obtained that soil toxin penetrated Millipore filters and cellophane when they were used as substrates in bioassay of soil fungistasis. Fritted glass, clay filters, Saran wrap, and parchment paper were unsuitable for detecting fungistasis since they were inhibitory to the assay fungus. Evidence in support of the theory that food material added to or along with the test conidia increased soil fungistasis was not demonstrated. Conversely, our findings suggest that soil fungistasis is a natural phenomenon, which is characteristic of certain soils.

Indirect Assay Methods to investigate Soil Fungistasis with Special Consideration of Soil-pH

Indirect Assay Methods to investigate Soil Fungistasis with Special Consideration of Soil-pH

Sensitivity of Malayan isolates of Fusarium to soil fungistasis

Spore germination of various isolates of Fusarium (isolated from Malayan sources) was inhibited when placed on cellulose film in contact with soil moistened with distilled water. Intraspecific variations in sensitivity to mycostasis were recorded suggesting physiological differences between isolates of the same species. The addition of glucose frequently masked the mycostatic factor while autoclaving the soil completely removed it. The growth of fungal mycelium in contact with soil followed a similar pattern and when hyphae grew in contact with autoclaved soil sporulation was frequently observed. The similarities between the results outlined in this investigation and results from different countries is discussed and it is suggested that pathogenic fungi frequently have to overcome soil mycostasis before they can establish themselves in a new environment.

Activation of Soil Microflora by Fungus Spores in Relation to Soil Fungistasis

Summary: Bacterial numbers in natural soil supplemented with living fungus spores or cell-free aqueous washings of spores, then incubated for 8 hr or more, were several-fold higher than those in non-supplemented soil. Rates of oxygen uptake in natural soil supplemented with washed or unwashed fungus spores, cell-free aqueous washings of spores, killed spores, or diluted nutrients, were several-fold higher than those in non-supplemented soil. Increased respiration occurred rapidly on addition of these supplements to soil. A single brief water washing of urediospores of Puccinia rubigo-vera or of conidia of Neurospora sp. extracted about 10% of the spore dry weight. Washed bacteria or Streptomyces spp., when incubated with fungus spores in absence of added nutrients, inhibited fungus spore germination, whereas sterile filtrates of bacteria were not inhibitory. The results indicate that fungus spores, by virtue of nutrients in their exudates, stimulate rapid activity of microbes in soil, and that the enhanced microbial activity causes inhibition of fungal spore germination.

The nature of the widespread soil fungistasis.

SUMMARY: Fungistasis of Conover loam, muck, and hardwood forest soils to conidia of Glomerella cingulata, Fusarium oxysporum f. lycopersici, and Penicillium frequentans was demonstrated by indirect methods such as agar disks, double agar layer plates, and cellophan folds, as well as by direct placement of spores on or in soils. All attempts to extract toxic substances from soil with water or organic solvents failed. Fungistatic volatile substances could not be demonstrated in soil. Redox, pH, and osmotic conditions were not responsible for soil fungistasis. Various lines of evidence led to the conclusion that the so-called widespread soil fungistasis as observed by indirect methods is the result of production of antibiotics by soil microbes growing on the surface of the assay media, and is not due to a reserve of toxic substances in soils. The possibility is suggested that individual fungus spores serve as nutrient microsubstrates in soil and stimulate the rapid growth of soil microbes on their surface or in their immediate vicinity, and that this results in the production of sufficient fungistatic substances to prevent spore germination. Preliminary evidence in support of this suggestion are results with concentrated 50% ethanol washings from teliospores of Ustilago zeae which markedly stimulated growth of mixed soil microbes and of pure cultures of Streptomyces sp. and Pseudomonas sp., known antibiotic producers, in agar media.

Some aspects of soil fungistasis.

SUMMARY: A series of fungi with varying degrees of sensitivity to soil fungistasis was selected as the result of agar disk and buried-slide tests with 17 fungi and one soil. Six out of 7 different soils exhibited a spectrum of inhibition of the test series of fungi similar to that of the first soil tested. The exception was a very acid raw humus soil which only inhibited the acid-sensitive fungus Acrostalagmus cinna-barinus. Fertilizer treatments of two series of plots at Rothamsted were found to affect soil fungistasis only through their influence on soil pH. Inhibitory effect decreased with increasing soil acidity, being absent from the most acid plot tested. From the results of experiments in which three fungi were pre-incubated before exposure to the influence of soil, it is suggested that spores are most sensitive to soil fungistasis at an early stage in the process of germination.

An Investigation of Fungistasis in Nigerian Soils

SUMMARY: The presence of a fungistatic factor in Nigerian soils was demonstrated by the use of a technique in which disks of agar were placed on filter-paper in contact with moist unsterile soil and inoculated with fungal spores. After incubation the disks were examined and the percentage of germinated spores recorded. Inhibition of spore germination was not caused by autoclaved soil, nor when 0·5 % (w/v) glucose was present in the agar. The presence or absence and the type of vegetation had little effect on the fungistatic power of the soil. In two profiles examined, the property of fungistasis was confined, approximately, to the upper 40 cm. of the soil. Of nineteen species of fungi tested by the agar disk method, the germination of eleven was significantly inhibited, of seven unaffected and of one stimulated. The data obtained suggest that the phenomenon described in Nigerian soils is similar to that reported from other parts of the world.

Fungistasis in Soils

THE work recently described by Dobbs and Hinson1, suggesting the occurrence of a widespread fungistasis in soils, prompts us to describe certain observations we have made of a somewhat similar nature.

A widespread fungistasis in soils.

A widespread fungistasis in soils.