INSTYTUT DENDROLOGII

Abstract: Two field inoculation experiments were conducted to study intraspecific variation in vertical spread of the P-, S- andF-IS-group isolates of Heterobasidion annosum in stems of Pinus sylvestris, Picea abies and Abies alba. Host-plants were inoculated with four isolates of each IS group after 10 mm long wounds made with a sterile knife (experiment 1) or 3 mm diameter radial holes made with a drill (experiment 2). On pine, the P-group isolates were more virulent than S andF isolates in terms of infection frequency, mortality rate andvertical spread in sapwood. The S isolates had higher incidence of infection and extensive growth on spruce than on pine. The F isolates were significantly less virulent on pine andspruce than on fir. Vertical spreadof all IS groups on fir was similar. In spite of between-strain-within-IS group variation in vertical spreadon each host, the study provided strong evidence for the occurrence of intraspecific differences in the host preference. In the interspecific analysis with three hosts, the isolates, IS groups andhost × strain andhost × IS group interactions accountedfor most of the explainedvariation, while host-plants accountedfor the smallest portion of the variance.

Additional key words: between-strain-within-hosts variation, host preference, intersterility groups, vertical spread in sapwood, wounding methods