Use of mycelial slurries of mycorrhizal fungi as inoculum for commercial tree seedling nurseries

Blended mycelial slurries of a variety of ectomycorrhizal fungi were assessed for their suitability as inoculum for containerized tree seedlings. Mycelium of most fungi tested, with the exceptions of Pisolithustinctorius (Pers.) Coker & Couch and Paxillusinvolutus (Batsch.: Fr.) Fr., withstood blending well. Viability remained high after storage in modified Melin-Norkrans agar medium, water, or dilute saline at either 4 °C or room temperature, indicating that slurries are robust enough to tolerate conditions that would be encountered in a commercial setting. Experiments investigating methods for applying slurries to containerized seedlings were conducted using Hebelomalongicaudum (Pers.: Fr.) Kummer. Slurry infectivity dropped after it was mixed into a peat-vermiculite growing medium, particularly in the presence of high levels of fertilizer. This indicated that incoculum should not be added to multipots until short roots capable of becoming mycorrhizal are present and that contact of the inoculum with fertilizer should be avoided. Injection of slurry into the root zone resulted in the most consistently high colonization, but application of the slurry to the surface of the growing medium was also effective, the latter being more feasible in a commercial setting. Mycorrhizae developed with as little as 1 mg mycelium per seedling, although 100 mg gave more consistent results. In inoculation trials in which slurries of nine representative fungi were injected into the root zones of 8-week-old black spruce or jack pine seedlings, five of the fungi consistently formed mycorrhizae. For these fungi, slurries could be an effective inoculum.