COMPARISON OF GREMMENIELLA-ABIETINA ISOLATES FROM PINUS-SYLVESTRIS AND PINUS-CONTORTA IN TERMS OF CONIDIAL MORPHOLOGY AND HOST COLONIZATION

Gremmeniella abietina isolates from Pinus contorta in northern Sweden produced, in vitro, shorter conidia with fewer septa compared with iso lates from Pinus sylvestris in the southern part of the country. After mycelial inoculation of shoots with G. abietina isolates from both ho st species, the resulting necroses were longer in P. sylvestris than i n P. contorta. Keeping seedlings in artificial mild winter climate or detaching shoots from the seedling before inoculation caused longer ne croses. No host specificity in colonization was found. Isolates from P . sylvestris caused longer necroses than did isolates from P. contorta , and both types of isolates caused longer necroses in P. sylvestris t han in P. contorta. The differences found between the two G. abietina populations probably reflect regional variation in the fungus.