Abstract:
Eucalyptus species are cultivated for forestry and are of economic importance. The fungal stem canker
pathogen Chrysoporthe austroafricana causes disease of varying severity on E. grandis. The Eucalyptus
grandis-Chrysoporthe austroafricana interaction has been established as a model system for studying
Eucalyptus antifungal defence. Previous studies revealed that the phytohormone salicylic acid (SA)
affects the levels of resistance in highly susceptible (ZG14) and moderately resistant (TAG5) clones. The
aims of this study were to examine histochemical changes in response to wounding and inoculation
as well as host responses at the protein level. The anatomy and histochemical changes induced by
wounding and inoculation were similar between the clones, suggesting that anatomical differences
do not underlie their different levels of resistance. Tyloses and gum-like substances were present after
inoculation and wounding, but cell death occurred only after inoculation. Hyphae of C. austroafricana
were observed inside dead and living cells, suggesting that the possibility of a hemibiotrophic
interaction requires further investigation. Proteomics analysis revealed the possible involvement of
proteins associated with cell death, SA signalling and systemic resistance. In combination with previous
information, this study forms a basis for future functional characterisation of candidate genes involved
in resistance of E. grandis to C. austroafricana.
