Early stages of decay in Eucalyptus grandis trees inoculated with brown-rot fungi

Abstract

In natural ecosystems, brown-rot fungi are major biodegrading agents of standing trees and dead wood. Decay caused by basidiomycetes results in structural instability and therefore negatively affects the quality and quantity of the produced wood. Fungal attack can also trigger defense mechanisms within the tree aimed at delaying or halting the progress of infection. As these defense mechanisms can decrease the value of the wood, their identification and study are of foremost importance. In this work, healthy trees of Eucalyptus grandis W.Hill — a widely commercialized species in Uruguay — were inoculated with Laetiporus sulphureus and Gloeophyllum trabeum. The decay process was characterized in terms of chemical and anatomical changes, and the defense mechanisms elicited by the tree were identified. Three months after inoculation, no symptoms of infection could be detected with the naked eye; however, microscopic analysis revealed anatomical and chemical changes (weakening, delamination, and rupture of vascular and parenchymal cells) and decreased holocellulose and lignin contents. Compartmentalization and the production of kino were used by the tree as defense mechanisms.