Morphological, molecular and pathogenic characterization of Phytophthora palmivora isolates causing black pod rot of cacao in Colombia

Abstract

Aim of study: To characterize isolates of Phytophthora sp. causing black pod rot (BPR) of cacao (Theobroma cacao L.). Area of study: Eight cocoa-growing regions in Colombia. Material and methods: Sixty isolates of Phytophthora sp. were obtained from tissues of cacao pods showing symptoms of BPR. Isolates were characterized using the morphology of sporangia and chlamydospores, molecular sequencing of regions of nuclear DNA (rDNA-ITS) and mitochondrial (COX) and virulence in different genotypes of cocoa pods. Main results: A high phenotypic variability between the isolates was determined, being the pedicel length and the length/width ratio (L/W) the most stable characters for species identification. Short pedicels with an average of 3.13 μm ± 0.28 and a length/width ratio of sporangia (L/W) with an average of 1.55 μm ± 0.11 were established as the most consistent morphological characteristics within palmivora species. Research highlights: Phytophthora pamivora was the only species associated to BPR, identified using morphology together with sequence analyses.

Keywords

• theobroma cacao l.
• phytophthora sp.
• sporangia
• pedicel
• chlamydospores