The Mechanism of Pathogenicity of Sirex Noctilio on Pinus Radiata I. Effects of the Symbiotic Fungus Amylostereum Sp. (Thelophoraceae)

Effects on P. radiata of the fungus, Amylostereum sp., which is injected into the sapwood of the stem by S. noctilio, are described. The fungus causes the sapwood to dry out in advance of the mycelium, and tests were made to find whether it kills the tree by restricting sap flow to the crown, or by producing toxins. No systemic toxic effects could be attributed to the fungus, which appeared to act by restricting sap supply, but rapidly developing systemic effects were observed after experimental S. noctilio attack, implying that a secretion of the insect was involved in pathoge~icity.