Decline of Nine Tree Species Associated with Brown Root Rot Caused byPhellinus noxiusin Taiwan

Abstract

A decline disease characterized by brown root rot, wilting of foliage, leaf discoloration, a brown mycelial mat growing on roots and stem bases of affected trees, and ultimate death of some trees was found on several tree species growing in the eastern and western coastal regions of central and southern Taiwan. These tree species were mainly growing in landscape plantings rather than in the forest. Species affected by the disease included Acacia confusa, Bauhinia variegata, Calophyllum inophyllum, Casuarina equisetifolia, Ficus microcarpa, Koelreuteria henryi, Podocarpus macrophyllus var. macrophyllus, Salix babylonica, and Swietenia mahagoni. A fungus isolated from diseased tissue produced resupinate, brownish polyporus fruiting bodies on sawdust medium, and was identified as Phellinus noxius. Seedlings of the various host plants found naturally infected in the field were inoculated with P. noxius grown on camphor twig medium. Seedings of all inoculated species were infected, and the fungus was reisolated from diseased tissues. This is the first report of P. noxius on these hosts. In cross pathogenicity tests, isolates of P. noxius from twelve tree species were used to inoculate each of the host species except for the original source of the inoculum. All isolates caused infection on all eleven hosts, indicating that the pathogen does not exhibit host specificity. However, A. confusa and S. babylonica showed lower mortality than other hosts.