Click on any
image for a more
detailed view

Disease Cycle and Epidemiology

Click on image for a more detailed view.

Epidemiology

Phellinus noxius is present in native tropical forests and plantations on infected roots and stumps and in woody debris. It does not form survival structures, such as sclerotia or resting spores, but may persist in dead roots and colonized wood for many years. Centers of disease radiate outward as roots of healthy trees come in contact with roots of diseased trees. Trees of all ages are susceptible. A mycelial crust forms around infected roots, secreting wood-rotting enzymes as it moves up the roots to the stem. Crusts 0.5-1.0 cm thick usually extend 1-2 m (3-6 ft) up the stem, though crusts almost 5 m (15 ft) high have been measured (Figure 18). If the tree does not die from severe root rot, it is killed when the crust surrounds the stem and the underlying mycelium destroys the sapwood. Sporocarps occasionally develop on standing dead trees, stumps, or trees blown down following severe root decay. Infection of freshly cut stumps or wounds by windborne basidiospores has been demonstrated experimentally but is not as important to disease spread as root-to-root contact. Basidiospores may, however, be responsible for some long distance dispersal of the fungus.

Figure 18