Competition between ectomycorrhizal fungi colonizing Pinus densiflora

Interactive competition of Pisolithus tinctorius (Pers.) Coker et Couch with an unidentified species Tanashi 01 and Suillus luteus (L,: Fr.) S. F. Gray was investigated using a rhizobox. Pinus densiflora Sieb. et Zucc, was used as the host plant and mycelia were distinguished by hyphal color. The speed of mycelial spread differed between the fungi; P. tinctorius and Tanashi 01 grew faster than S. luteus. A P, tinctorius mycorrhizal seedling and a Tanashi 01 mycorrhizal seedling were transplanted on opposite sides of the rhizobox. The mycelia and mycorrhizae of P. tinctorius were overgrown by Tanashi 01 hyphae and development of P. tinctorius was gradually inhibited. The areas occupied by mycelia and mycorrhiza of P. tinctorius decreased by 52% and 37%, respectively, 154 days after transplantation relative to that at 91 days. In the overlap area of P. tinctorius and Tanashi 01, the latter fungus infected new root tips emerging from P. tinctorius mycorrhiza, which lacked a mantle of P, tinctorius hyphae, and formed a composite mycorrhizal structure. P. tinctorius mycorrhizae were progressively replaced by Tanashi 01 mycorrhizae. Mycelial spread of P. tinctorius and S. luteus were naturally inhibited but there was no interaction in mycorrhizal formation.