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ARS Home » Northeast Area » Frederick, Maryland » Foreign Disease-Weed Science Research » Research » Publications at this Location » Publication #408657
Research Project: Diagnostics and Biological Approaches for Management of Emerging Oomycete Plant Pathogens

Location: Foreign Disease-Weed Science Research

Title: Fungal Pathogens of Cacao in Puerto Rico

Author
item Puig, Alina

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2023
Publication Date: 11/15/2023
Citation: Puig, A.S. 2023. Fungal Pathogens of Cacao in Puerto Rico. Plants. https://doi.org/10.3390/plants12223855.
DOI: https://doi.org/10.3390/plants12223855

Interpretive Summary: Cacao production is a rapidly expanding industry in Puerto Rico and producers have received international recognition for the quality of their beans. However, little is known about the diseases affecting the crop on the island. To determine which pathogens are present, a study was conducted at eight sites including commercial farms. The most frequently detected pathogens were part of the fungal groups Diplodia and Lasiodiplodia. Lab tests showed that both fungi caused disease on pods and stems, although the Lasiodiplodia fungi caused significantly more damage. These findings are important because they dispute the belief that Puerto Rico’s cacao disease issues are primarily caused by a water mold, Phythophthora palmivora. Instead, this study identifies Lasidioplodia and Diplodia fungi as the most common cacao pathogens on the island. This improved understanding will help scientists and farmers control disease by selecting fungicides effective against the organisms present.

Technical Abstract: Cacao production is a rapidly expanding industry in Puerto Rico, with new farmers having planted ~20,000 trees in the past few years. To determine the etiology and extent of diseases affecting cacao in Puerto Rico, a survey was done at eight sites around the island. Pod rot and branch dieback were observed all sites. Most organisms isolated from pod and stem samples were identified as Diaporthe spp. (48%) and Lasiodiplodia spp. (25%) based on sequences of the internal transcribed spacer and large subunit regions. Laboratory inoculations were done to determine the relative virulence of Lasiodiplodia and Diaporthe, on pods and stems. Phytophthora palmivora served as a positive control due to its well-established pathogenicity on all tissues. On pods, Lasiodiplodia sp. and P. palmivora caused significantly larger lesions (6.1 and 5.9cm, respectively) than Diaporthe sp. (2.7cm) four days post inoculation. All three species caused disease on stems, with no differences found among species. Although P. palmivora was thought to be the primary pathogen affecting cacao in Puerto Rico, this study identifies Lasidioplodia and Diplodia spp. as the common pathogens on the island. This improved understanding will help scientists and farmers control disease by selecting fungicides effective against both oomycetes and fungi.