Isolation, Selection, and Identification of Phytophthora spp. Causing Pod Rot of Cocoa

Cocoa pod rot caused by Phytophthora spp. is a major constraint to cocoa production. This study aimed to isolate, characterize, and identify Phytophthora isolates associated with cocoa pod rot in Vinh Long province, Vietnam, to support disease-management strategies.

Twenty diseased cocoa pod samples were collected from 20 orchards in Phu Tuc and Tan Phu communes. Seven Phytophthora isolates were recovered and evaluated for colony growth, morphology, and pathogenicity. Four representative isolates were identified using ITS-rDNA sequencing and phylogenetic analysis.

The isolates grew fastest on PCA medium, followed by V8 and PDA, with colony radii of 3.51–4.43, 2.93–3.99, and 2.03–3.42 cm, respectively, at 96 h after inoculation. All isolates produced papillate sporangia and terminal or intercalary chlamydospores and caused dark brown to black lesions on cocoa pods. Re-isolation fulfilled Koch’s postulates. PT10T was the most aggressive isolate, producing an 8.30-cm lesion diameter at 5 days after inoculation. The four sequenced isolates showed 100% ITS-rDNA similarity to P. palmivora and clustered with reference sequences of this species.

Morphological, pathogenicity, and ITS-rDNA evidence supported identification of the sequenced isolates as P. palmivora. However, single-locus identification may not fully resolve closely related Phytophthora species.

P. palmivora was associated with cocoa pod rot in the surveyed orchards, with PT10T showing the greatest aggressiveness. These findings provide isolates for further studies on biological control and integrated disease management.