Pathogenicity of Fungi Isolated fromDendroctonus valens, D. brevicomis,andD. ponderosaeto Ponderosa Pine Seedlings

Abstract

Two-year-old ponderosa pine [Pinus ponderosa] seedlings were wound-inoculated with fungi isolated from the bark beetles Dendroctonus valens, D. brevicomis, and D. ponderosae, Leptographium terebrantis from D. valens, Ceratocystis minor from D. brevicomis, and C. clavigera from D. ponderosae each killed a high proportion of seedlings, whereas other fungal and control treatments did not. L. terebrantis caused greater mortality than either C. minor or C. clavigera. Seedlings killed by these fungi were bluestained, although the amount of stain varied. Surviving seedlings had large deposits of resin on the wound surface and in the xylem beneath the wound. Seedlings inoculated with sterile control blocks had less phloem necrosis, less xylem resinosis, and healed faster than did seedlings inoculated with fungi. Inoculating with C. ips in combination with L. terebrantis caused significantly less seedling mortality than did inoculating with L. terebrantis alone, indicating an inhibitory effect by C. ips. Similar effects were observed with combined inoculations of C. ips and C. clavigera or of C. nigrocarpa and C. minor. The imperfect form (Sporothrix) of C. nigrocarpa isolated from mycangia of D. brevicomis females had the same inhibitory effect on C. minor-caused mortality as did C. nigrocarpa isolated from either the surface of beetles or the phloem surrounding beetle galleries. Seedlings with smaller stem diameters had a higher mortality rate than did larger ones, and seedlings that had set bud apparently were more resistant to infection than seedlings that had just begun to elongate.