INOCULUM CONCENTRATION AND THE COLONIZATION OF PICEA-SITCHENSIS STUMPS BY BASIDIOSPORES OF HETEROBASIDION-ANNOSUM

The colonization of Sitka spruce stumps by Heterobasidion annosum, and the population structure of colonies, was determined 2-3 yrs after in oculation with a 10-fold dilution series of basidiospore suspensions. Artificially inoculated stumps were infected more frequently than the controls, which received only natural inoculum. The extent of coloniza tion tended to increase with increasing dilution and reached a maximum at the penultimate dilution, but differences were not significant bec ause of large within-treatment variation. At the higher dilutions stum ps fell into poorly-colonized and heavily-colonized groups suggesting that some stumps are inhibitory to infection whereas others are extrem ely susceptible. Colonized areas resulting from the higher dilution tr eatments tended to comprise fewer larger genets than those from more h ighly concentrated spore treatments. The results suggest that the succ ess of establishment by H. annosum in basidiospore-colonized stumps re presents the outcome principally of intraspecific competition and the constraints on colonization operating within stumps.