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.

Oomycete species associated with Theobroma cacao crops in Colombia

“…The genus Phytophthora was not only the most abundant among the isolates, but also at least three species were associated with Colombian cacao crops, contrary to the results obtained by Rodríguez‐Polanco et al (2020). Neither P .…”

“…Hyphae were slightly septate and swellings were not observed overall. All these characteristics mostly agreed with morphological descriptions of the species, but curiously, the sporangia on V8 were smaller than previously reported in common guides (Erwin & Ribeiro, 1996), although inside the range reported for Colombian cacao crops (Rodríguez‐Polanco et al, 2020).…”

“…Since then, only two other studies in Colombia have been made, both identifying P . palmivora with black pod disease (Rodríguez‐Polanco et al, 2020; Villamizar‐Gallardo et al, 2019).…”

Resistance estimation to Phytophthora palmivora in cacao genotypes using artificial inoculation and natural infection in the field

“…Phytophthora palmivora (Pp) is the sole exception, colonizing every region where cacao is cultivated (Brasier and Griffin 1979;Marelli et al 2019). In addition to this, Pp is the most prevalent species in the producing areas in Colombia (Rodríguez-Polanco et al 2020b;Palacios Bejarano et al 2021).…”

“…Furthermore, the causal agent can also affect other cacao plant tissues (Surujdeo-Maharaj et al 2016), producing resistant and long-term survival structures (Ko 2003), accelerating plant tissue decomposition (Guest 2007) and increasing the negative impacts on cacao production. Technical progress is struggling against BPD dissemination, including early detection (Franco et al 2019;Yanac Montesino et al 2021), crop management strategies (Rodríguez-Polanco et al 2020c;Merga 2022;Misman et al 2022), and plant genetic programs (Pokou et al 2019;Fister et al 2020;Tijani et al 2020;Mucherino Muñoz et al 2021;Rêgo et al 2023).…”