Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 5, 2005
Publication Date: January 1, 2006
Citation: Pratt, R.G. 2006. Comparative survival of conidia of eight species of Bipolaris, Curvularia, and Exserohilum in soil and influences of swine waste amendments on survival. Applied Soil Ecology. 31:159-168. Interpretive Summary: Plant pathogenic fungi are the principal causes of infectious diseases in plants. All plant parts can be penetrated, infected, and rotted or killed by certain pathogenic fungi. Strongly pathogenic fungi may weaken, stunt, or cause death of individual plants of any size or age. Soilborne diseases, caused by fungi that survive in soil and attack roots of plants below ground, are often the most difficult to control. Some past research has indicated that adding swine and poultry wastes to soil can reduce survival of certain soilborne fungi and severity of diseases that they cause. This study was conducted to compare the suitability of eight plant-pathogenic fungi for use as test organisms to reveal negative effects of animal wastes on their survival in soil. The eight fungi are closely related pathogens that cause foliar and soilborne diseases of many turf and forage grasses and small grains. Microscopic spores (survival structures similar to seeds) of these fungi were incubated in soils in porous membranes, retrieved, and assayed for survival. Spores that survived during incubation in soil germinated when applied to agar; those that had died did not germinate. Three of the eight fungi tested were considered most suitable for use in studies on survival of spores in soil, and on effects of animal wastes on survival, because moderate to high survival occurred after 4 to 8 weeks when tests would be run. When spores of these fungi were added to soils from farms where swine wastes had and had not been applied, survival of spores was often reduced in soils to which wastes had been applied previously. These results indicate that the three fungi may be used as test organisms to evaluate antifungal effects of animal wastes added to soil, and that antifungal effects are observed with these fungi in soils from commercial farms where swine wastes have been applied.
Technical Abstract: Survival of conidia of eight species of Bipolaris, Curvularia, and Exserohilum in soil was compared to identify the species most suitable for use in experiments to assay fungitoxicity of soils amended with animal wastes and agricultural byproducts. Spores produced on cellulose substrates were added to soil between porous nylon mesh membranes, incubated for 0-12 weeks, retrieved, and plated on agar to induce germination as an indicator of viability. Few or no differences in viability of conidia of the eight species were evident initially, but numerous significant differences (P=0.05) were observed between species after incubation for 2-12 weeks in soil. Survival of conidia usually was greatest for C. lunata, B. sorokiniana, and B. stenospila; least for B. cynodontis, B. hawaiiensis, and E. rostratum; and intermediate or inconsistent for B. spicifera and C. geniculata. C. lunata, B. sorokiniana, and B. stenospila appear most capable of survival in soil as conidia and most suitable for use as test organisms to evaluate fungitoxicity of amended soils. When conidia of these species were incubated for 4 or 8 weeks in three soils with and without previous commercial swine waste applications, survival was often significantly (P=0.05) reduced across soils or in individual soils that had received swine waste. Results indicate that the eight species of fungi studied differ significantly in ability of conidia to survive in soil, that three species exhibit the greatest potential for survival, that these species may be used to bioassay soils for fungitoxicity, and that conidia of these species exhibit slight to strong reductions in survival in soils to which liquid swine waste had been applied.