Comparative survival of conidia of eight species of Bipolaris, Curvularia, and Exserohilum in soil and influences of swine waste amendments on survival

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. Conidia produced on cellulose-containing substrates were added to soil between porous nylon mesh membranes, incubated for 0–12 weeks, retrieved, and plated on cornmeal agar to induce germination as an indicator of viability. In three experiments, significant variation in spore germination was attributed to fungal species, incubation time in soil, and species × time interactions. Few or no differences in viability of conidia of the eight species were evident prior to incubation in soil, 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 4–8 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. The most frequent and strong reductions in survival of conidia in waste-amended soils were observed with B. stenospila. 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 that previously received commercial applications of liquid swine waste.