Patterns of decay caused by Inonotus dryophilus (Aphyllophorales: Hymenochaetaceae), a white-pocket rot fungus of oaks

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Abstract
Decay of living white oaks (Quercus alba L. and Quercus macrocarpa Michx.) caused by the white-pocket rot fungus Inonotus (Polyporus) dryophilus (Berk.) Murr. was characterized using scanning electron and light microscopy. Delignified tissues lacked middle lamellae and degradation of the cell wall was characterized by the presence of cellulosic macrofibrils. Chemical analyses showed delignified tissues to be composed of 93.47% total sugars and 2.59% lignin, whereas sound heartwood had 64.48% total sugars and 24.99% lignin. Selective delignification occurred in axial parenchyma cells surrounding vessels of earlywood and latewood. Flame-shaped tracts of vessels with accompanying axial parenchyma, present throughout the latewood, provided avenues for radial movement of I. dryophilus. Dense groups of latewood fibers were not degraded. Inonotus dryophilus did not delignify ray parenchyma or adjacent axial parenchyma; instead, a typical white rot, differentiated microscopically by a shot-hole appearance, occurred. Tyloses did not restrict I. dryophilus movement in heartwood vessels of living oaks. Occluded latewood fibers and medullary rays were often left intact forming borders between white pockets.