Susceptibility of conifer and broadleaf seedlings to Swedish S and P strains of Heterobasidion annosum

Seeldings of conifer and broadleaf species, 2‐4 years old, were inoculated with 10 Swedish S and P intersterility group strains of Heterobasidion annosum under greenhouse conditions. There were significant differences in infection incidence, growth in sapwood and mortality rates. Conifers were generally more susceptible to infection than broadleaf trees. Both intersterility groups developed poorly on Alnus glutinosa, Abies grandis, Poputus tremuta × tremutoides and Quercus robur , but the S‐interstedlity group also grew poorly on Pinus sp. and Betula pendula. Results were compared with field observations reported in the literature.