Conifer Seedling Root Fungi and Root Dieback in Finnish Nurseries

Fungi were isolated from the roots and growth substrate of bare-rooted and containerized Pinus sylvestris and Picea abies nursery seedlings displaying a root dieback. Isolations were also made from visually healthy seedlings. The potential pathogenicity of all isolated species was determined in laboratory trials. Cylindrocarpon spp., Fusarium spp. and Trichoderma viride were frequently isolated. The isolation frequency of a uninucleate Rhizoctonia-like fungus, Pythium spp. and Phytophthora undulatum from diseased containerized seedlings and their pathogenicity in tests suggest that these fungi are likely involved in the root dieback disease in containers. The pathogenic Rhizoctonia-like fungus in addition to Pythium spp. was also isolated from bare-rooted seedlings. In greenhouse tests Pythium spp. were more pathogenic to 4-week-old Scots pine seedlings grown before transplantation in unsterile substrate than to those seedlings grown axenically in agar. External factors are considered to have some role in the expression of disease.