DECAY AND CANKER FORMATION BY PHELLINUS-PINI IN WHITE AND BALSAM FIR

P. pini (Thore ex Fr.) A. Ames var. cancriformans Larsen, Lombard, Aho and P. pini (Thore ex Fr.) A. Ames var. pini on white fir (A. concolor (Gord. and Glend.) Lind.) and balsam fir (A. balsamea Mill.), respectively, initiated a nonspecific host response in phloem and xylem. Light and scanning electron microscopy were used to elucidate canker formation and morphological characteristics of decayed wood. In phloem, cells occluded around infected areas but the fungus was not confined. Barrier zones in xylem consisted of numerous tangential series of resin ducts, parenchyma cells and twisted tracheids. Although many barrier zones are formed, often several within 1 annual ring, the fungus was not effectively compartmentalized. The successful penetration or evasion of barrier zones resulted in canker enlargement by both fungi. P. pini var. cancriformans caused a typical white rot decay of heartwood in white fir whereas P. pini var. pini in balsam fir caused a selective delignification of wood.