Location: Subtropical Horticulture ResearchTitle: First report of Neofusicoccum parvum causing pod rot on cacao in Hawaii Author
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2019
Publication Date: N/A
Interpretive Summary: A trip was conducted to Hawaii to assess disease problems on the newly emerging cacao industry there. Three of the four farms visited had diseased pods, showing dark brown/black lesions. As expected, most symptomatic pods were infected with Phytophthora palmivora, which causes black pod rot, the most economically important disease of Theobroma cacao, however, a subset were instead infected with Neofusicoccum parvum. This is the first report of Neofusicoccum parvum causing pod rot on T. cacao. Hawaii has a rapidly growing cacao industry, and thus detailed knowledge of pathogens targeting the crop is critical.
Technical Abstract: Cacao production is a rapidly expanding industry in Hawaii, but little information exists regarding diseases present in the area. A trip was conducted in January 2018 to assess disease problems on Hawaii Island, and pods with firm, dark brown/black lesions were observed on three of the four farms visited. Samples from two of the three farms yielded P. palmivora, the causal organism of black pod rot, however, all samples from the third farm yielded a fast-growing fungus with white, aerial mycelia that turned dark gray within four days. The internal transcribed spacer (ITS) region, translation elongation factor 1-a (TEF1) gene, and a partial sequence of the ß-tubulin (BT) gene were amplified, sequenced, and deposited in GenBank. Blastn analysis identified the organism as N. parvum based on the ITS (MH449672, 99%), TEF1 (MH93602, 100%), and BT (MH936021, 100%) sequences. Artificial inoculations were carried out to confirm pathogenicity, and necrotic lesions identical to those originally seen on the field collected samples developed on all pathogen-inoculated pieces. Lesion radii were significantly higher for N. parvum (33.9mm ±5.8) versus the negative control (1.3mm ±0.6), (p=0.0006). The pathogens were re-isolated and identified based on colony morphology. To our knowledge, this is the first report of N. parvum causing pod rot on cacao. Hawaii has a burgeoning cacao industry, and thus detailed knowledge of pathogens targeting the crop is critical.