Biological species of Armillaria and their mycoparasitic associations with Rhodophyllus abortivus in Hokkaido

Specimens of basidiomes and/or rhizomorphs of Armillaria mellea complex and basidiomes of Rhodophyllus abortivus, developing on the same decaying stumps or stems of forest trees, were collected in three forests in Hokkaido. Normal basidiomes of R. abortivus were found near to, but free from, the rhizomorphs and/or basidiomes of Armillaria. while abnormal basidiomes, as carpophoroid forms, were developed on the rhizomorphs of Armillaria. Of three mycoparasitic Armillaria isolates found with R. abortivus, one was identified as A. gallica and two as A. jezoensis. The isolates of R. abortivus showed excellent mycelial growth and rhizomorph formation on PDA. However, on MDA, RMDA and BMDA, they showed poor aerial mycelia growth and no rhizomorphs. In the contrapositional cultures, the growth of A. gallica was completely inhibited by R. abortivus on PDA but only slightly inhibited on MDA and RMDA. On the other hand, mutual inhibition at a distance was observed on BMDA. The mycelial growth and rhizomorph formation in A.jezoensis were severely inhibited by the colony of R. abortivus on PDA, but only slightly inhibited on MDA. On RMDA and BMDA, the colonies of two Armillaria species and R. abortivus showed mutual inhibition at a distance and apparent rhizomorph formation by both Armillaria species