Interactions of soil fungi on cellulose film

Abstract

A simple cultural method whereby pieces of cellulose film are laid on sand saturated with mineral salt solution was used to study interactions of soil fungi. These were inoculated on to the film in pairs about o·8 cm. apart, or singly at one end. Pythium oligandrum was non-cellulolytic. It was grown opposite six isolates of soil fungi of differing cellulolytic capacities. It grew well in association with Botryotrichum piluliferum, Fusarium culmorum and F. oxysporum, very poorly with Stachybotrys atra and Trichoderma viride, and not at all with Rhizoctonia solani. The interactions of the six cellulolytic species were studied in pairs; R. solani was the most powerfully cellulolytic but S. atra the most competitive. Individual competitive characteristics led to dominance of one fungus over another in any given pair; cellulolytic activity was secondary to this. Pythium ultimum and P. debaryanum, also non-cellulolytic species, were grown opposite F. culmorum and R. solani, and were stimulated to develop by both these fungi. Numerical estimates were made of the reproductive bodies of the Pythium species grown alone and in association with these fungi. The advantages of using discrete pieces of cellulose over conventional agar media in studying interactions of soil fungi are discussed. The ecological status of Pythium species is considered. The spiny-spored forms include pathogens and sugar fungi; the sugar fungi may be understood in the original sense of Burges, or parasitic on cellulose-decomposing fungi. The smooth-spored P. ultimum and P. debaryanum also may be parasitic sugar fungi in the latter sense. Emphasis is laid upon the specificity of fungus interactions.