Spread of Heterobasidion annosum s.s. and Heterobasidion parviporum in Picea abies 15 years after stump inoculation

The tree pathogenic fungiHeterobasidion annosums.s. and Heterobasidion parviporumcause root and butt rot in Norway spruce (Picea abies) and produce serious economic losses to the forest sector in Europe. We experimentally studied inter- and intraspecific differences betweenH. parviporumandH. annosums.s. in the way they infect stumps and spread into neighbouring trees. ElevenH. parviporumand nineH. annosums.s. isolates were artificially inoculated on stumps of two spruce stands after first thinning. After 15 years, the same isolates were reisolated from neighbouring trees.Heterobasidion parviporumspread more frequently from the inoculated stumps to the neighbouring trees thanH. annosums.s. The surroundings ofH. annosums.s. stumps that did not spread were often colonized byH. parviporum.Heterobasidion annosums.s. spread was restricted mainly to the areas of the plot where no otherHeterobasidiongenotypes had been inoculated. In such cases,H. annosums.s. tended to develop into bigger genets thanH. parviporum. The probability of stump-to-tree spread ofH. parviporumdepended on the diameter of the stumps, suggesting thatH. parviporumspread may relate to the presence of heartwood. BothH. parviporumandH. annosums.s. proved to be strong pathogens on Norway spruce; however, when competing for the same trees,H. parviporumseemed capable of excludingH. annosums.s. from the stand.