Radial and concentric clefts in the secondary wall (S-2) of Norway spruce tracheids during incipient stages of decay by Stereum sanguinolentum (Alb. & Schw., Fr.)

Delignification of tracheids within Norway spruce wood by Stereum sanguino- lentum was associated with the presence of radial and concentric clefts con taining minute cell wall entities in the secondary wall (S-2). Light and tr ansmission electron microscopy (TEM) revealed that hyphae growing on the in ner secondary wall (S-3) within the lumen of tracheids induced selective de lignification and the formation of radial and concentric clefts in the adjo ining secondary cell wall (S-2). Enzymatic action and the resulting shrinka ge stresses may cause the wall to separate along inherent radial and concen tric planes of weakness. The present study supports former observations of a radial and concentric arrangement of cell wall constituents within the se condary wall (S-2).