Phylogenetic analysis and morphological characterization of Phytophthora palmivora causing stem canker disease of durian in Malaysia

Abstract Stem canker, caused by Phytophthora palmivora , poses a significant challenge for durian farmers in Malaysia. However, limited research has explored the genetic diversity of this pathogen using multiple genes. In this study, we aimed to characterize Phytophthora isolates associated with symptomatic durian tissues from four Malaysian states (Selangor, Perak, Pahang, and Melaka). We employed both morphological and molecular methods, including sequence analysis of the internal transcribed spacer (ITS) rDNA and the cytochrome oxidase c (COX) multi-locus combination of subunit I and subunit II gene regions. A total of 21 Phytophthora palmivora isolates were obtained from diseased durian stem tissues and identified based on phylogeny and morphological characteristics. Molecular identification using BLASTn analysis of the ITS and COX sequences confirmed their identity as P. palmivora showing sequence similarity ranging from 99 to 100% with the ex-type culture of P. palmivora (GenBank accession no. ON834450 for the ITS region and JF771543 for the COX region). Phylogenetic analyses of the ITS rDNA and COX further confirmed that all Phytophthora isolates belonged to P. palmivora , forming a distinct clade with reference P. palmivora isolates, with strong bootstrap values for the ITS (99%) and COX (76%) regions. Pathogenicity tests demonstrated that all isolates were pathogenic to durian leaves, with PMM02 displaying significantly lower virulence compared to other tested isolates. Detached leaf assays conducted with durian leaves from D10, D24 and Mousang King varieties revealed significance differences among durian varieties, with D10 exhibiting higher susceptibility to P. palmivora.