Durian (Durio zibethinus Murr.) is a popular fruit tree grown extensively in Southeast Asia for its highly valued fruits. A stem canker was found on many durian trees in an orchard in Sungai Liang, Brunei Darussalam. This disease, commonly known as patch canker, is widespread in other countries in this region. Although symptoms were found in the main trunk near the base and on lower branches, they were prominent at the point of branching between the main trunk and lateral branches. The symptoms were characterized by a reddish brown discoloration of the outer bark, areas of necrosis on the bark, and a reddish brown discoloration in the outer sapwood. Disease symptoms of the tree canopy ranged from gradual defoliation to dieback of twigs from the top of trees. Cultures of a single fungus derived from infected bark from canker margins were grown on potato dextrose agar and tap water agar. Abundant sporangial production by the fungus occurred on these media and the fungus was identified as Phytophthora palmivora (E. J. Butler) E. J. Butler. This is the first published report of patch canker of durian caused by P. palmivora in Brunei Darussalam. The disease could pose a threat to the durian industry in this country.
