Initial defence responses in sapwood of Eucalyptus nitens (Maiden) following wounding and fungal inoculation

Xylem defence responses occurring in pot-grown Eucalyptus nitens (Maiden) saplings were analysed within the first few weeks following stem wounding and inoculation with the non-aggressive decay fungus Ganoderma adspersum (Schulz). The fungus colonized the dead xylem cells up to 5 mm above and below the wound after 30 days. Evidence of xylem cell death and discolouration was detectable within 12 h and vessel tyloses were present after 3 days. Concentration of tetra-galloylglucose increased by 3.5-fold within 24 h, while the trend for total phenols was a slow increase reaching a maximum after 21 days. Suberin was not detected. Early accumulation of water content has been proposed as a defence component of host-pathogen interactions in woody angiosperm xylem, but this was not obvious for E. nitens. Nuclear magnetic resonance imaging (NMR imaging or MRI) was used to measure small-scale distributions in moisture content around the inoculated stem wounds in intact E. nitens saplings. Some moisture accumulation was detectable at lesion margins of wounds analysed after 3 weeks. However, this was not detectable by gravimetric measurements. This increase in moisture content may be a consequence of wound physiology rather than an active defence response. © 2001 Academic Press.