FEMS Microbiology Ecology 12 (1993) 169-176 © 1993 Federatmn of European Microbiological Societies 0168-6496/93/$06.00 Published by Elsevier 169 FEMSEC 00465 The importance of inoculum size for the competitive ability of wood decomposing fungi Lillian Holmer and Jan Stenlid Department of Forest Mycology and Pathology, Swedtsh Unwersity of Agricultural Sctences, Uppsala, Sweden (Received 7 December 1993; revision received 15 March 1993; accepted 24 March 1993) Abstract" Competitmn among wood decay fungi was studied wtth a technique using sectors of various sizes of 8 cm diameter wood discs. The sectors representing 8-92% of the discs were precolonized by Heterobasidmn annosum (Fr.) Bref., Resmtcmm btcolor (Alb. & Sehw. ex Fr.) Parm, Phanerochaete sangumea (Fr.) Hjortstam and Comophora sp. DC. ex Me'rat before they were combined pairwise in close contact on top of water agar m 9 cm Petri dishes. Discs were regularly inspected for mycelial overgrowth and after 10 weeks mycelia were reisolated. Competitive success, measured as the replacement of the opposing fungus, was generally greatest for mycelia with sectors representing 92% of a disc and smallest for 8% sectors. R. btcolor was the most, and H. annosum the least, competitive of the species investigated. The results indicate that mycelial size could be one major factor influencing the competitive success in nature. However, when paired on nutrient agar, the results of the interactions between the four spectes did not correspond to those in wood discs. Key words" Inoculum size; Secondary resource capture; Heterobasidion annosum; Resmicium bicolor; Phanerochaete sangumea; Contophora sp. Introduction In wood decaying fungi primary resource cap- ture occurs when the fungus establishes in the absence of competitors [1]. In contrast, secondary resource capture involves the replacement of or- ganisms already present. Saprotrophic decay fungi may arrive and establish themselves at the re- Correspondence to. Dr. L. Holmer, Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, Box 7026, S-750 07 Uppsala, Sweden. Fax +46-18-30 92 45. source unit as asexual or sexual spores or they may grow in soil as hyphal aggregates or cords. The latter mode of spread facilitates secondary resource capture since it allows water and nutri- ents to be imported from an old substrate (i.e., a food base) [2]. Competition or combat [1], involving hyphal interactions, occurs to some extent in connection with primary resource capture and is almost al- ways involved in secondary resource capture. The outcome is a summation over time and space of many individual interactions. Under such circum- stances it is likely that size will sometimes play a role in determining the balance between two competing mycelia. Although inoculum potential, Downloaded from https://academic.oup.com/femsec/article/12/3/169/613881 by guest on 25 January 2023