Wood Science and Technology Vol. 2 (1968) p. i15/127 Changes in Wood Properties at the Boundary of Polyporus amarus Decay Pockets 1 B y W. WAYNE WILCOX and BAXTE~ J . GARCIA Summary Incense cedar heartwood infected by the pocket rot fungus Polyporus amarus was subjected to microtensile testing and miscroscopical examination to determine effects of this fungus upon wood substance adjacent to advanced decay pockets. Although springwood of the annual ring nearest the decay pocket in some samples had a slightly lower tensile strength than springwood from the same ring but a distance from the pocket, the difference was not statistically significant. Microscopical examination revealed the presence of small, sparse bore holes and hyphae in approximately the same number inside and outside the advanced decay pockets, and in discolored regions of incipient decay. A few bore holes and hyphae were found in specimens from what was maeroscopically considered to be sound wood. Polarized illumination revealed no evidence of diffusion of cellulolytic enzymes from the hyphae in regions other than within advanced decay pockets, but the small numbers of hyphae and bore holes observed in decay pockets indicated that considerable enzyme diffusion might be necessary for decay to precede. The data suggest that possible alteration of physical, mechanical, and chemical properties in wood substance surrounding decay pockets need not be a significant factor for consideration in utilization of pecky incense cedar. Zusammenfassung Kernholz yon Zeder (Libocedru8 decurrens), das yon Polyporus amaru8 befallen worden war, wurde Mikro-Zugfestigkeitspriffungen und einer mikroskopischen Durchmusterung un~erwoffen. Es sollten die Answirkungen dieses Pilzbefalles auf jene Teile der Holzsubstanz gepriift werden , die unmittelbar an die Befallsstellen angrenzen. ]:)as Frfihholz eines Jahrringes, das einer Befallsste]le am n~chsten lag, zeigte zwar bei einigen Proben eine geringfiigig niedrigere Zugfestigkeit als das Friihholz desselben Jahrringes, das aber yon der Befallsstelle welter entfernt lag. Die Unterschiede waren jedoch statistisch nicht signifikant. Die mikroskopische Durchmusterung deckte das Vorhandensein yon kleinen, etwas zerstreut liegenden Bohr15chern und Hyphen auf, in etwa gleichgrol~er Anzahl innerhalb und aul~erhalb der Stellen fortgeschrittenen Befalls und in den verfi~rbten Bereichen des beginnenden Befalls. Einige wenige BohrlScher und Hyphen wurden ferner in Proben festgetsellt, die bei makroskopischer Betrachtung gesund erschienen. Im polarisierten Licht liel~ sich keine Diffusion yon ~us Hyphen stammenden celluloitischen Enzymen au~erhalb der Befallsbereiche beobachten. Die wenigen Hyphen und BohrlScher, die in den Befallsstellen beobachtet werden konnten, gaben aber einen Hinweis darauf, dal~ bei der Ausbreitung eine betr~chtliche Enzymdiffusion stattfinden mull Die ermitte]ten Werte weisen daranf hin, dal~ die mSglieherweise eintretende ~mderung der physikalischen, mechanischen und chemischen Eigenschaften des Holzes in unmittelbarer Umgebung der Befallsstellen als wichtige ]~aktoren bei der Verarbeitung dieses Holzes beachtet werden miissen. 1 Presented at the 1968 l%rest Products Research Society Annual lVIeeting. The cooperation and assistance of D. S. DEAL]~Y and the Kimberly-Clark Corporation, Anderson, California, for providing wood sample material is gratefully acknowledged. Appreciation also is extended to G. F. A~NESE, G.A. SYM]~S, D. B. HA~CSEN, D. C. DOOL~r, L. A. B]~AN, and R. G. MAY for technical assistance during portions of this work. 10" 116 W. WAYNE WILCOXand BAXT]~RJ. GARCIA Introduction Incense cedar ( L i b r o c e d r u s decurrens Torrey), although a minor species in terms of total volume, is destined to become more important as management of California forest land intensifies. This prediction is based upon the species' rapid growth rate, ease of establishment and abundance of regeneration, high decay resistance of the heartwood, and favorable physical and mechanical properties which are similar in m a n y respects to those of redwood. Before intensive managem e n t of incense cedar is feasible, the standing volume of mature and overmature trees must be utilized. Much of the volume of such trees is cull : as high a proportion as ~ to ~ of the total volume has been estimated as such [WAGE~E~ and BEGA 1958 ; K I ~ E Y 1950]. Almost all of this loss is due to pecky rot caused by P o l y p o r u s a m a r u s Hedgcock [BoYcE 1930; WAGENE~ and BEGA 1958]; it has been estimated t h a t 7 5 . . . 100 per cent of mature incense cedar trees are affected [MEI~]~CKE 1914]. To facilitate efficient utilization of the timber extensively affected b y this fungus, knowledge of the changes it produces in wood is necessary. The tissue adjacent to decay pockets presently is being utilized in the manufacture of pencil slats and as a fiber source, but it is not known whether the properties of this tissue differ from those of wood some distance from the visible degradation. Microscope technology has advanced considerably since the last detailed studies of the effects of P . a m a r u s infection on structure and composition of incense cedar cell walls. Furthermore, techniques have been devised for testing certain mechanical properties of small quantities of wood tissue. The present study was undertaken to apply some of these techniques to incense cedar heartwood infected with P . a m a r u s to increase knowledge necessary for efficient utilization of this material. Literature Review P . a m a r u s is one of a small group of decay fungi which produce deterioration in discrete pockets. Little is known about the mechanism b y which such pockets are delineated. I t has been hypothesized t h a t the limitation of decay to pockets by P . a m a r u s might be due to the sparse distribution of hyphae between pockets [HIY]~ElCT 1931], or to variation in chemical or physical properties of the wood or the fungus [BOYCE 1920; VO~ SCHRE~K 1900]. Workers appear to have considered each decay pocket as a separate entity, rather t h a n as a portion of a typical heartrot column. The boundary between decay and sound wood appeared very sharp and without gradation [WAGESIER and BEGA 1958; BOYCE 1920; V0~ SCHRE~K 1900; HA~K~ESS 1879]. t t y p h a e were common within the pockets but were rare outside the pockets [HUBERT 1931 ; BOYCE 1920; ~IARKI~ESS 1879]. Sometimes hyphae were rare both in advanced pockets and in the wood surrounding the pockets [BoYcE 1920; VO~ SGttRE1NK 1900], or abundant only in slightly decayed wood and its surrounding tissue [BoYcE 1920]. The incipient stage of decay has been described as a faint yellowish-brown discoloration occurring in patches but with the wood remaining firm [WAGE:NEILand BEGA 1958; BOYCE 1930]. The color gradually deepened and the wood became soft as decay progressed [WAGERER and BEGA 1958; BOYCE 1930; BOYCE 1920]. Microscopical investigations revealed t h a t in advanced stages of decay cellulose had been decomposed while lignin remained in the wall structure [BoYCE 1920;