Phytophthora palmivora as a Causal Pathogen of Stem Canker and Fruit Rot of Durio zibethinus in China

Durian (Durio zibethinus L.) is a high-value tropical seasonal fruit and an important cash crop in Southeast Asia. Durian introduction trials have been conducted in Hainan Province, China, and the first durian plantations have been established in recent years. However, the high temperature and humidity in Hainan Province favour plant diseases, severely affecting durian yield and quality. From July 2023 to June 2024, a disease survey was conducted in 21 durian orchards across six regions on southern Hainan Island, revealing that the primary diseases affecting durian were stem canker (black-head), fruit rot, and root rot. The main symptoms are stem necrotic blotch, brown root rot, and water-soaked fruit rot, which in severe cases can cause poor growth or extensive dieback of the durian tree. The causal pathogens were identified through morphological, molecular, and pathogenicity analyses. A total of 40 isolates were isolated from diseased durian fruits (30 isolates) and stems (10 isolates), exhibiting morphological characteristics similar to Phytophthora species. Further identification of the isolates was conducted using a combined dataset of ITS, tef-1α and CoxI, revealing that all the isolates belonged to Phytophthora palmivora. Pathogenicity tests confirmed P. palmivora as the pathogenic agent causing durian stem canker and fruit rot in Hainan Province. This study demonstrates that P. palmivora is the major causal agent of durian stem canker and fruit rot in China, providing a basis for improved durian disease identification and management.