Click on any
image for a more
detailed view

Symptoms and signs

Symptoms of brown root rot disease are similar to those caused by other root rot pathogens: slow plant growth, yellowing and wilting of leaves, defoliation, branch dieback, and plant death (Figure 2). These aboveground symptoms are caused by a root and butt rot that hinders uptake and transport of water and nutrients from the soil. Fallen trees with visible rot are another general indication of the disease (Figure 3). Although dead wood is initially discolored reddish brown, it later becomes white, dry, and crumbly (Figure 4).


Figure 2		Figure 3

Figure 4		Figure 5


Figure 6		Figure 7

Signs of the pathogen, unlike the symptoms, are distinctive for this disease. Phellinus noxius forms a thick, dark brown to black crust of mycelium around infected roots and lower stems (Figure 5), which gives the disease its name. The leading edge of the crust is creamy white, glistens with drops of clear, brownish exudate, and is usually noticeable even in the dark understory of the rainforest (Figure 6). Patches of white mycelium are present between the bark and sapwood (Figure 7). As colonization progresses, white, soft, crumbly wood becomes laced with reddish strands of fungus hyphae that turn black with age (Figure 8). Sporocarps, or fruiting bodies, are brown to black and rough on the sterile surface (Figure 9), gray to gray-brown on the spore-forming surface (Figure 10).


Figure 8		Figure 9

Figure 10

RETURN TO TOP