Commercial Vegetative Inoculum of Pisolithus tinctorius and Inoculation Techniques for Development of Ectomycorrhizae on Container-grown Tree Seedlings

Vegetative inoculum of Pisolithus tinctorius produced by research procedures at the Institute for Mycorrhizal Research and Development (IMRD) was compared with that produced in large commercial solid substrate fermentors by Abbott Laboratories. Effectiveness of P. tinctorius in forming ectomycorrhizae on container-grown seedlings from this inocula was observed on 10 pine species, Douglas-fir, western hemlock, and bur oak in tests at six locations in the United States and one in Canada. Inoculum was mixed into rooting media before sowing of seed. The Abbott inoculum (MycoRhiz®) was ineffective on pine seedlings in tests of 1977, but changes in fermentation procedures significantly improved inoculum effectiveness in 1978 and 1980 to such a degree that certain batches of MycoRhiz® were as effective as IMRD inoculum. A medium of vermiculite and 5 to 10 percent by volume peat moss with nutrient was best for growing mycelial inoculum. Peat moss, which contains humic acids, was used for keeping pH of inoculum below 6.0 at which range it was the most effective. Inoculum was most effective after leaching with water to remove nutrients. No one inoculum characteristic, such as number of P. tinctorius propagules in large and small particles, microbial contamination, residual glucose, bulk density, and moisture content, as well as results of a fast assay for ectomycorrhizal development on loblolly pine seedlings, was consistently correlated with effectiveness of inoculum in forming P. tinctorius ectomycorrhizae on seedlings in containers. A captan drench after seeding significantly improved effectiveness of inoculum that was initially low in effectiveness. Seedling growth was correlated with P. tinctorius ectomycorrhizal development in only a few tests. The probable cause for lack of growth stimulation of seedlings by P. tinctorius ectomycorrhizae is a photosynthate drain on the juvenile seedlings by P. tinctorius. Jack pine seedlings grown in a medium containing high levels of N, P, and K formed about half as many P. tinctorius ectomycorrhizae as similarly treated seedlings grown at about half of this fertility. The seedlings grown at high fertility were, however, larger regardless of ectomycorrhizal treatment. Results of the tests in 1978 and 1980 showed that viable vegetative inoculum of P. tinctorius in a substrate of vermiculite, peat moss, and nutrient can be produced by industrial fermentation procedures and used to form abundant P. tinctorius ectomycorrhizae on container-grown seedlings for practical use in forest regeneration. Forest Sci. 28:373-400.