Fast- and slow-growing subalpine fir produce lesions of different sizes in response to inoculation with a blue-stain fungus associated with Dryocoetes confusus (Coleoptera: Scolytidae)

Abstract

Trees with low vigor and reduced radial growth may be more susceptible to attack by bark beetles because of reduced host defenses. Fungi associated with bark beetles may be used to elicit an induced defense response from the host. A blue-stain fungus isolated from Dryocoetes confusus Swaine was used to examine the morphology of the hypersensitive response of fast- and slow-growing subalpine fir trees in British Columbia. Twenty fast-growing and 20 slow-growing trees were inoculated with the blue-stain isolate, and the dimensions of the resultant lesions were compared between fast- and slow-growing trees and between fungus and control treatments at 3, 7, 10, 17, and 41 d after inoculation. The length and width of the lesions was greater in response to fungus versus control treatments at 7, 10, 17, and 41 d after inoculation. The length of the lesions was significantly greater in fast- than in slow-growing trees at 7, 10, and 17 d after inoculation. There was no significant difference in the size of the lesions between fast- and slow-growing trees 41 d after inoculation. The temporary difference in the size of the lesions between fast- and slow-growing trees suggests that host vigor affects the induced defense response within a certain time frame.Key words: Abies lasiocarpa, Dryocoetes confusus, host vigor, defense, blue-stain fungi, Ophiostoma.