Modes of Infection and Spread of Fomes Annosus

Abstract

The root and butt rot caused by Fomes annosus is one of the most eco­ nomically important diseases of conifers in the north temperate zone of the world. Sinclair (112) lists almost 150 species of trees, including some an­ giosperms, on which F. annosus has been reported. Species of Abies, Juni­ perus, Larix, Picea, Pinus, Pseudotsuga, and Tsuga are the major hosts. On most species of Pinus and Juniperus, F. annosus causes primarily a root rot and kills trees within several months to years after infection. The major exception is Pinus strobus, which is subject to typical butt rot as well as root rot, and trees usually remain alive for several years after infection un­ less windthrown. Spruces, true firs, larches, hemlocks, and Douglas fir may be killed by F. annosus when young, but later are primarily damaged by butt rot which may extend for several meters up the stem. Koenigs' (59) bibliography lists 438 references on F. annosus. Since then, more than 300 additional papers have been published. This review will not attempt to evaluate all aspects of the F. annosus problem. Instead, at­ tention will be focused only on the aspects of spread and infection which are important in devising controls for this disease. Regardless of host and type of disease produced, spread of F. a nnosus is accomplished in two major ways: (a) by spores, and (b) by growth of my­ celium across contacts between healthy and infected roots. Spores are re­ sponsible for initiation of new infection centers in previously uninfected stands whereas growth of mycelium at points of root contacts or grafts re­ sults in the enlargement of established infection centers. Factors relating to these two types of spread will be discussed separately.