Coinoculation of containerized Douglas-fir (Pseudotsuga menziesii) and maritime pine (Pinus pinaster) seedlings with the ectomycorrhizal fungi Laccaria bicolor and Rhizopogon spp.

 Coinoculations with mycelium of Laccaria bicolor and spores of Rhizopogon spp. included in alginate gel have been carried out to determine: (1) the ability of the mixed inoculum to produce dual-colonized containerized Douglas-fir and maritime pine planting stocks and (2) the colonization pattern of the two fungi in individual root systems. For both tree species, the maximal proportion of dual-colonized seedlings obtained almost never exceeded 50%. The rest of the seedlings remained colonized by a single fungus or were non-colonized. In Douglas-fir inoculations, the relationship between the dual-colonized seedlings obtained and the initial dose of the two fungi was highly significant. The highest proportion of dual-colonized seedlings was obtained when the highest dose of R. subareolatus was used (10⁶ spores/seedling), regardless of the dose of L. bicolor. Among the treatments producing 25% or more dual-colonized seedlings, differences in the proportion of Laccaria/Rhizopogon mycorrhizas and total root colonization percentages were not clearly related to the initial combination of doses. The proportion of dual-colonized maritime pine seedlings was not significantly related to the initial inoculation doses of the two fungi. The proportion of Laccaria/Rhizopogon mycorrhizas was not significantly different among treatments with 25% or more dual-colonized seedlings, whereas total colonization percentages ranged from 37% with the combination 0.08/10⁴ (g L. bicolor / spores R. roseolus per seedling) to 74% with the combination 0.08/10⁶, this difference being statistically significant. Accepted: 15 September 1998