Morpho-molecular identification of Phytophthora palmivora and Lasiodiplodia theobromae associated with cacao pod rot in South Sulawesi, Indonesia

Abstract

Cacao pod rot is one of the most destructive diseases limiting cacao production worldwide, predominantly caused by Phytophthora palmivora. However, field observations in South Sulawesi, Indonesia, suggested the involvement of other fungi in association with pod rot symptoms. This study aimed to identify and characterize the pathogen species associated with pod rot disease on cacao and to assess their pathogenicity through detached pod assays. Isolation and morphological characterization of isolates from symptomatic pods revealed three genera: Phytophthora, Lasiodiplodia, and Fusarium. Pathogenicity tests showed that only P. palmivora and L. theobromae induced pod rot symptoms, whereas Fusarium sp. was non-pathogenic under the test conditions. Symptom development assays demonstrated that infection by P. palmivora occurred rapidly, producing brown necrotic lesions and white mycelial growth, while L. theobromae infection developed more slowly and was accompanied by gray mycelium and black conidiophore masses. Phylogenetic analyses based on the ITS and tef1-α regions confirmed the isolates as P. palmivora and L. theobromae. These findings demonstrate that P. palmivora remains the primary causal agent of cacao pod rot in South Sulawesi, while L. theobromae can act as an opportunistic pathogen associated with secondary colonization and tissue deterioration.