Effect of season and different fungi on phenolics in response to xylem wounding and inoculation in Eucalyptus nitens BY K. M. BARRY 1,2 , N. W. DAVIES 3 and C. L. MOHAMMED 1,2,4 1 CRC for Sustainable Production Forestry, GPO Box 252–12, Hobart, Tasmania, Australia 7001. E-mail: Karen.Barry@ffp.csiro.au; 2 School of Agricultural Science, University of Tasmania, GPO Box 252–54, Hobart, Tasmania, Australia 7001; 3 Central Science Laboratory, University of Tasmania, GPO Box 252–74, Hobart, Tasmania, Australia 7001; 4 CSIRO Forestry and Forest Products, GPO Box 252–12, Hobart, Tasmania, Australia, 7001 Summary Pot-grown and plantation-grown Eucalyptus nitens trees (approximately 2 and 3 years old, respect- ively) were experimentally wounded and inoculated with different fungi and in different seasons. Decay lesion development and defence zones were assessed. Two zones were described, a narrow brown decay interface (interface reaction zone, IRZ) and a diffuse zone beyond this being either pale brown or purple (reaction zone, RZ). The total phenol levels in the reaction zone were determined. Selected phenolics (pedunculagin, tellimagrandin 1, tetragalloylglucose, pentagalloylglucose and catechin) were quantified by liquid chromatography–mass spectrometry (LC–MS). A range of fungi (mainly decay-causing) were used to inoculate wounds and the results indicated that more extensive decay lesions were generally associated with greater production of soluble phenols in response. Sterile inoculations and weakly aggressive fungi were associated with no or little xylem discoloration, whereas aggressive fungi elicited more discoloration and phenolic accumulation in advance of infection. This indicates that phenol accumulation is not a generalized response to wounding, but a variable response due to the interaction between microorganisms and sapwood. In plantation-grown trees examined 6 months after wounding, purple reaction zones were commonly associated with large decay lesions. Seasonal differences in decay column area caused by Ganoderma applanatum were not significant 1 month after wounding and inoculation. 1 Introduction Eucalyptus nitens (Maiden) is an important plantation-tree species being grown for solid wood products in Tasmania. As pruning is required, this is done early (beginning at age 3–4 years) to decrease the proportion of the knotty core. It is hoped that decay arising from the wounds will be restricted to the knotty core. Mechanisms of plant defence in woody xylem involve both a reaction zone, which forms in the tissue present at the time of wounding and a barrier zone which is formed by the cambium subsequently (SHIGO and MARX 1977; PEARCE 1996). Barrier zones are considered more resistant to fungal spread than reaction zones (SHIGO and MARX 1977; BAUCH et al. 1980) but are usually limited in extent above and below a wound. For decay columns spreading well beyond a wound, the reaction zone is likely to be more important long-term. The ability of different fungi to penetrate these defence zones (SCHWARZE and BAUM 2000) will determine the development of decay. Wounds offer a wide array of microorganisms the opportunity to colonize compromised plant tissue, in a process which has been termed ‘unspecialized opportunism’ (RAYNER and BODDY 1988). The ability of a fungus to invade beyond this compromised tissue may depend For. Path. 32 (2002) 163–178 Ó 2002 Blackwell Verlag, Berlin ISSN 1437–4781 Received: 16.10.2001; accepted: 17.1.2002; editor: J. N. Gibbs U. S. Copyright Clearance Center Code Statement: 1437–4781/2002/3203–0163 $15.00/0 www.blackwell.de/synergy