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

Xylem defence responses occurring in pot-grown Eucalyptus nitens (Maiden) s aplings were analysed within the first few weeks following stem wounding an d inoculation with the non-aggressive decay fungus Ganoderma adspersum (Sch ulz). 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 w as detectable within 12 h and vessel tyloses were present after 3 days. Con centration 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 2 1 days. Suberin was not detected. Early accumulation of water content has b een proposed as a defence component of host pathogen interactions in woody angiosperm xylem but this was not obvious for E. nitens. Nuclear magnetic r esonance imaging NMR imaging or MRI was used to measure small-scale distrib utions in moisture content around the inoculated stem wounds in intact E. n itens saplings. Some moisture accumulation was detectable at lesion margins of wounds analysed after 3 weeks. However. this was not detectable by grav imetric measurements. This increase in moisture content may be a consequenc e of wound physiology rather than an active defence response. (C) 2001 Acad emic Press.