Variation in spread ofHeterobasidion annosumin clones ofPicea abiesgrown at different vegetation phases under greenhouse conditions

Abstract

Forty‐nine Picea abies (L.) Karst clones were inoculated under greenhouse conditions with a Heterobasidion annosum (Fr.) Bref. isolate of the S intersterility group. The cuttings were inoculated at the following vetetation stages; bud‐flushing stage, vegetative stage and after bud‐set. Fungal growth in sapwood and lesion length in the inner bark were measured after 34 days. The susceptibility of the various clones to H. annosum was strongly correlated among the three vegetation stages, both in terms of mean growth and mean growth ranking. Partitioning of variance components showed that variation in growth was explained by physiological stages and clone to 4% and 24%, respectively, and for interaction between clone and physiological stage to 9%. Corresponding values for lesion length in the inner bark were 3%. 14% and 5%, respectively. Fungal growth in wood and lesion length in the inner bark were strongly correlated (r 2 ranging between 0.23 and 0.36). When cuttings were inoculated during bud‐flushing, le...