Transfer of the P‐type of Heterobasidion annosum from old‐growth stumps of Picea abies to Picea abies and Larix×eurolepis

Abstract

SummaryThe infection of Picea abies and Larix x eurolepis by Heterobasidion annosum was studied in felled trees in Sweden. Thinnings were carried out in two stands of L. x eurolepis, 15 and 20 years old, and in a 25‐year‐old stand of P. abies, established on a site heavily infected by H. annosum. The 15‐ and 20‐year‐old L. x eurolepis stands exhibited the greatest incidence of butt rot with infections amounting to 38 and 57%, respectively, of removed trees. The incidence of butt rot in the P. abies stand was only 5%. Heterobasidion annosum was the main butt rot causing fungus. All isolates of H. annosum were of the P‐intersterility group. Transfer of H. annosum from old‐growth P. abies stumps to trees felled in the thinning of the next generation was demonstrated by somatic incompatibility tests. However, the majority of infections could not be connected with decay already established in the previous generation. In L. c eurolepis, rot columns were frequent, including also several genotypes in the same stem, and typically positioned in the inner sapwood. The few infections of P. abies were situated in the heartwood.