Pinus contorta susceptibility to Heterobasidion spp. : a study of stumps, roots and artificial spore infections of stumps

Abstract: The Lodgepole pines susceptibility to Heterobasidion spp. was investigated in three parts ofthis study. In the first part, discs from freshly cut stumps were collected and analyzed to seeif the fungi can spread and grow naturally in Lodgepole pine stands. In the second part, rootsamples were collected from Lodgepole pines planted in former infected Norway sprucestands to see if the fungi can spread through root contacts. For the third part, new stumpswas created and artificially infected with spores of both the S‐type (H. parviporum) and theP‐type (H. annosum) of the fungi to find out if the Lodgepole pine is susceptible to them.None of the stumps from recently thinned stumps were infected and it was later discoveredthat these stands in fact were thinned one and two years ago which probably has had influenceon the result. Infected roots were found on four out of 15 trees that were expected tobe infected and totally 17 % of all sampled trees, with and without symptoms, were infected.On all stumps that were artificially infected with the P‐type and all but one stump that wereartificially infected with the S‐type, infections were found 51 days after the time of infection.These results indicates that the Lodgepole pine is susceptible to both types of the fungi andthat it can be infected through root contacts which means that Heterobasidion spp. may be athreat to the Lodgepole pines. Because of this, new management methods such as stumptreatment during thinning, stump removal and a better habitat adaptation when re‐plantingstands with Lodgepole pine might be necessary.