Ectomycorrhizal fungi as biological control agents against Rhizoctonia root infection of container-grown Scots pine seedlings

摘要

The ability of the ectomycorrhizal fungi (ECM), Laccaria bicolor, Laccaria proximo and Paxillus involutes, to prevent Rhizoctonia sp. root infection in Scots pine (Pinus sylvestris L.) was investigated. First the 5-week-old, containergrown seedlingswere inoculated with ECM fungi, and then six weeks later with two isolates of uninucleate Rhizoctonia (isolates 248 and 264). The seedlings were grown in a nursery field where they were irrigated, but not fertilized. One year after mycorrhizal inoculation, half of the seedlings were outplanted on a clear cut reforestation site, while shoot and root growth, mycorrhiza formation and Rhizoctonia infection was determined from the remaining seedlings. Rhizoctonia infection was recovered from 42 and 50 percent of the seedlings inoculated with only the isolates 264 and 248, respectively. L. proximo completely prevented the infection of both Rhizoctonia isolates, and also L. bicolor and P. involutus protected roots effectively. Both Rhizoctonia isolates changed the ECM community composition in the container media, that is they decreased the proportion of dark brown monopoid and dichotomous rnycorrhizae and they increased the abundance of light-brown, dichotomous mycorrhizae. L. proxima was the only fungus which clearly mitigated the changes in ECM composition caused by Rhizoctonia.