Induction of disease resistance in Norway spruce (Picea abies) by necrotizing fungi

Abstract

Norway spruce trees (Picea abies) preinoculated with the root rot fungus Heterobasidion annosum, Nectria fuckeliana or a pathogenic strain of the blue‐stain fungus Ceratocystis polonica were more efficiently protected against a subsequent massive inoculation with pathogenic C. polonica than trees pretreated with nonpathogenic C. polonica or sterile malt agar. Control trees that received no pretreatment were extensively colonized by the mass inoculation. There was a strong negative correlation between the length of the phloem necroses induced by the pretreatment inoculations and the extent of host symptoms caused by mass inoculation with pathogenic C. polonica. The degree of induced resistance in Norway spruce thus depended on the amount of host tissue destroyed by the pretreatment.