Fungistasis in Soils

Abstract

SUMMARY 1. Fungistasis in soil is a widespread phenomenon affecting most fungal propagules, though some are insensitive. In most instances, it is coexistent with the presence of living microorganisms, and is annulled by energy‐yielding nutrients. Fungistasis with characteristics similar to that in soil may also occur on leaves of plants. 2. Germination and growth of bacteria and actinomycetes is also restricted in soils. The characteristics of their inhibition appear to be the same as those for fungi. Therefore, the concept of a widespread microbial inhibition in soil can be applied to all three groups of microorganisms. 3. Fungistasis can be detected by various direct methods, or indirectly by methods involving the use of porous or permeable carriers. It may be expressed as a restriction on the final amount of germination (the usual parameter), germination rate (with time), and rate of germ‐tube or hyphal growth. Since the expression of fungistasis is often complete in soil, titration with nutrients may be required to distinguish between the sensitivities of different fungi. 4. Fungistasis generally is expressed most strongly at soil moisture contents somewhat less than saturation. Its expression usually is maximal in neutral or slightly alkaline soils. In acidic conditions fungistasis may be lessened because of suppression of bacterial and actinomycete activity. Increased sensitivity of some fungi in soils of pH > 7.0 may be caused by a directly unfavourable effect of pH on the fungus. 5. Fungal species with small spores tend to be highly sensitive to fungistasis. These spores tend to germinate slowly and to require exogenous nutrients for germination. By contrast, species with larger spores and sclerotia often do not require exogenous nutrients for germination. The larger spores tend to germinate rapidly and to exhibit low sensitivity, as compared with small spores. A few nutrient‐independent spores are insensitive to fungistasis. At least a part of the difference in sensitivity is related to germination time; spores which germinate slowly compete poorly with the soil micro‐flora for their nutrients. 6. Fungistasis is often temporarily annulled by enriching the soil with energy‐yielding nutrients. Usually, complex materials such as plant residues are most effective. A few weeks after such treatment, the level of fungistasis may, however, be increased. Annulment of fungistasis by compounds not utilized as energy sources has not yet been demonstrated. 7. Several soils naturally suppressive to Fusarium wilt diseases were more fungistatic to Fusarium than soils conducive to wilt. Potential means by which fungistasis may be manipulated to control root‐infecting fungi are (a) through stimulation of germination with nutrients, thus exposing the germ tube to lysis, and (b) by increasing the fungistatic level of soil through appropriate amendments. 8. Volatile substances identified in soils, some of which are potentially inhibitory to fungi include (a) ammonia, which apparently is evolved from ammonium salts in some ar...

Microbial Community Composition Affects Soil Fungistasis

“…The vast majority of natural soils suppress the germination and growth of fungi to a certain extent (29). This phenomenon, referred to as widespread soil fungistasis, was first described by Dobbs and Hinson (11).…”

“…This phenomenon, referred to as widespread soil fungistasis, was first described by Dobbs and Hinson (11). The intensity of fungistasis is dependent on the physical and chemical soil properties as well as soil microbial activity (1,12,29,33,37). The importance of the last factor was demonstrated by the relief of fungistasis by (partial) sterilization treatments and addition of antibiotics (12,41,43).…”

“…In general, plant pathogenic fungi appear to be more sensitive than saprophytic fungi (8,17). The sensitivity of plant pathogenic fungi to fungistasis is thought to protect them from germinating and initiating growth under unfavorable conditions (17,29). However, this protection comes at a cost, since the viability of resting structures decreases during prolonged incubation in soils (30).…”

“…However, this protection comes at a cost, since the viability of resting structures decreases during prolonged incubation in soils (30). The negative effects of fungistasis on the inoculum density of plant pathogenic fungi has been suggested as a mechanism to explain the commonly found correlation between fungistasis and disease suppressiveness (21,24,25,29). Therefore, manipulation of fungistasis has often been mentioned as a potential measure to control plant pathogenic fungi (20,29).…”

Resistance to Pythium Seedling Disease in Soybean

“…A QTL for partial resistance to P. sojae was reported on MLG F between marker Satt252 and Satt423 (Burnham et al, 2003b) and QTL's conferring resistance to Meloidogyne javanica, M. arenaria, Heterodera glycines, and soybean sudden death syndrome (SDS) have been mapped on the MLG F (Concibido et al, 1994;Hnetkovsky et al, 1996;Tamulonis, et al, 1997a;Tamulonis et al, 1997b;Webb et al, 1995). Nutrient availability is a limiting factor for microbial growth and activity in agricultural soils, as a result plant pathogenic fungi and oomycetes propagules survive in soils in a state of exogenous dormancy or fungistasis (Lockwood, 1977). In order for a successful hostpathogen interaction to be initiated, fungistasis must be overcome by external stimulants (Curl and Truelove, 1986;Mitchell, 1976).…”