DEVELOPMENT OF MYCORRHIZAE, EXTRAMATRICAL MYCELIUM AND SCLEROTIA ON PINUS STROBUS SEEDLINGS

SUMMARY On Pinus strobus seedlings cultured in growth pouches successful ectomycorrhiza formation took place upon inoculation with Pisolithus tinctorius, Cenococcum geophilum, Suillus granulatus, Suillus tomentosus, Paxillus involutus, Hebeloma cylindrosporum and Thelephora terrestris. Under the conditions used ectomycorrhizae formed within 2 weeks and some of them, P. tinctorius, P. involutus and T. terrestris, developed mantles and Hartig nets in less than 5 days. Mycelial strand formation took place around the root system of P. strobus 2 weeks after inoculation with P. tinctorius. Sampling on the 93rd day revealed no difference in ectomycorrhizal formation or the development of mycelial strands and sclerotia between root systems that were or were not illuminated. However, low light intensities on the aerial parts of the seedlings reduced the mycelial strands and sclerotia formation. Variation of nitrogen and phosphorus concentration added to the pouches were also studied. Increased concentrations of nitrogen, keeping phosphorus constant, led to greener seedlings and increased amount of ectomycorrhizal, mycelial strands and sclerotia. No sclerotia were formed in the complete absence of added nitrogen. Both the percentage of ectomycorrhizal short roots and the phosphorus contents of the seedlings increased in proportion to the amounts of nitrogen added. Increased concentrations of phosphorus, keeping nitrogen constant, led to a reduction in the percentage of ectomycorrhizal short roots without affecting the nitrogen content of the seedlings, the hyphal strands and sclerotia formation. The observations on the ontogeny of the sclerotia of P. tinctorius reported here for the first time fully support their identity as sclerotia.