Micromorphology of abnormal and decayed xylem in rubberwood canker

Abstract

Typical symptoms of rubberwood canker found in East Kalimantan, Indonesia, differ from those of conventional rubberwood peach canker. Rubberwood canker showed a conspicuous longitudinal canker with exposed xylem that was discolored and decayed. Bark wounds, resulting from regular tapping, were enclosed within the xylem, and the tissues had become integrated. The characteristics of abnormal and decayed xylem in this rubberwood canker were analyzed by light microscopy and scanning electron microscopy. Xylem in the vicinity of the enclosed bark contained fewer vessels of smaller diameter and shorter length, and significantly wider rays compared with normal xylem. Around the wide growth zones of the canker, axial cells were disoriented and warped toward the canker zones. In view of the separation among cells, and the concentric degradation of the cell walls starting from the lumen surfaces, decayed xylem appeared to be caused mainly by white-rot fungal attack.