Spore deposition of Heterobasidion annosum coll. in Picea abies stands of North Karelia, eastern Finland

Spore deposition of Heterobasidion annosum coll. was measured with the wood disc method in 20 Norway spruce stands in June, July and September 1999 in North Karelia, eastern Finland. The study area crossed the presently known northern boundary of the distribution area of H. annosum (62 degrees 45 'N ). The spore deposition rate decreased northwards and in the northernmost p arts of the study area, deposition was detected only in September. On avera ge 71% of the sport deposition consisted of intersterility group P and 29% oi intersterility group S. The proportion of S-type in the deposition incre ased northwards. Most of the isolated colonies were homokaryons, bur the pr oportion of heterokaryons increased with increasing deposition rate.