The mycelial interactions of strains of six cord-forming wood-inhabiting basidiomycetes were studied both against each other and against other fungi including Armillaria species on 2% malt extract agar, in wood lengths, and in non-sterile soil. Generally, cord-formers could be ranked in a combative order Phanerochaete velutina (DC ex Pers.) Parmasto =Phanerochaete laevis (Fr.) Erikss. & Ryv. > Steccherinum fimbriatum (Pers. ex Fr.) Erikss. =Hypholoma fasciculare (Huds. ex Fr.) Kummer =Phallus impudicus (L.) Pers. > Tricholomopsis platyphylla (Pers. ex Fr.) Sing. However, the outcome of interactions varied considerably according to circumstances. For example, in soil systems it depended on the extent to which encounters occurred between mycelia growing out from the wood inoculum blocks or within the inocula themselves. This depended in turn on the relative size of the inoculum blocks used for each strain.
Encounters between like mycelia growing out into soil led to the formation of persistent mycelial connectives between the inoculum blocks. However, those between unlike mycelia elicited discolouration and lytic reactions following either contact ('mycelial interference') between different species, or fusion and somatic incompatibility between different strains of the same species. Such reactions were followed either by replacement of one system by the other, or the development of mycelium-free zones of soil between deadlocked colonies.
After 3 months all pairings of cord formers against systems of Armillaria bulbosa (Barla) Kile and Watling, A. cepestipes Vel. f. pseudobulbosa Romagn. & Marxmuller and A. mellea (Vahl ex Fr.) Kummer in soil resulted in the colonisation of the Armillaria inocula to varying degrees and the death of virtually all associated rhizomorphs.