First Report of Neofusicoccum parvum Causing Pod Rot on Cacao in Hawaii

Abstract

HomePlant DiseaseVol. 103, No. 6First Report of Neofusicoccum parvum Causing Pod Rot on Cacao in Hawaii PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Neofusicoccum parvum Causing Pod Rot on Cacao in HawaiiA. S. Puig, J. P. Marelli, T. K. Matsumoto, L. M. Keith, and O. A. GutierrezA. S. Puig†Corresponding author: A. S. Puig; E-mail Address: alina.puig@ars.usda.govhttp://orcid.org/0000-0002-4662-4658Subtropical Horticultural Research Station, USDA-ARS, Miami, FL; Search for more papers by this author, J. P. MarelliMars/USDA Cocoa Laboratory, Miami, FL 33158; and Search for more papers by this author, T. K. MatsumotoDaniel K. Inouye U.S. Pacific Basin Agriculture Research Center, USDA-ARS, Hilo, HISearch for more papers by this author, L. M. Keithhttp://orcid.org/0000-0001-9974-1818Daniel K. Inouye U.S. Pacific Basin Agriculture Research Center, USDA-ARS, Hilo, HISearch for more papers by this author, and O. A. GutierrezSubtropical Horticultural Research Station, USDA-ARS, Miami, FL; Search for more papers by this authorAffiliationsAuthors and Affiliations A. S. Puig1 † J. P. Marelli2 T. K. Matsumoto3 L. M. Keith3 O. A. Gutierrez1 1Subtropical Horticultural Research Station, USDA-ARS, Miami, FL; 2Mars/USDA Cocoa Laboratory, Miami, FL 33158; and 3Daniel K. Inouye U.S. Pacific Basin Agriculture Research Center, USDA-ARS, Hilo, HI Published Online:2 Apr 2019https://doi.org/10.1094/PDIS-10-18-1719-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Cacao (Theobroma 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. Symptomatic tissue was sampled from lesion margins and inserted into a healthy, green cacao pod to maximize recovery of primary pathogens (Chee and Foong 1968). After 3 days, tissue was excised from the margins of emerging lesions, surface disinfested in 70% ethanol for 20 s, and plated on half-strength potato dextrose agar (1/2 PDA). Samples from two of the three farms yielded Phytophthora palmivora, the causal organism of black pod rot, one of the most economically important diseases of T. cacao. However, all samples from the third farm yielded a fast-growing fungus with white, aerial mycelia that turned dark gray within 4 days. Disease incidence at this farm was less than 1% (four affected trees), with all infections emanating from the peduncle. A single organism was recovered from three of the five pods sampled, with no organisms being recovered from the other two. A single representative isolate (H23) was used for molecular analysis and pathogenicity tests. DNA was extracted from 10-day-old mycelium, using the Qiagen DNeasy Plant Mini Kit, and the organism was identified by amplifying and sequencing, and by depositing in GenBank sequences of the internal transcribed spacer region (ITS; primers ITS1F/ITS4; MH449672), the translation elongation factor 1-α gene (TEF1; primers EF1-728F/EF1-986R; MH93602), and a partial sequence of the β-tubulin gene (BT; primers Bt2a/Bt2b; MH936021). BLASTN analysis identified the organism as Neofusicoccum parvum based on the ITS (99% match to MF631021), TEF1 (100% match to FJ150710), and BT (100% match to KX464975) sequences. All matching sequences were generated from organisms isolated in Hawaii from a range of host plants such as Metrosideros polymorpha, Pipturus albidus, T. cacao, and Leucadendron cultivar Safari Sunset. Owing to recent additions and reorganization of the Neofusicoccum genus, searches were limited to entries published or modified between 2012 to 2018 to ensure accuracy. To confirm pathogenicity, artificial inoculations were done using 4- × 15-cm2 pieces of immature cacao pods (clones SCA 6, EQX 3348-52, and GNV 164). Plugs of 1/2 PDA with actively growing mycelia were inoculated into wounds made with a 6-mm-diameter cork borer. A P. palmivora isolate from cacao served as a positive control and 1/2 PDA as a negative control. Four replications were inoculated with N. parvum, four with P. palmivora, and three with 1/2 PDA, and they were then kept at 25°C in the dark for 5 days. Necrotic lesions identical to those originally seen on the field-collected samples developed on all pathogen-inoculated pieces. A Welch’s ANOVA with posthoc t tests for mean separation determined that lesion radii were significantly higher for N. parvum (33.9 ± 5.8 mm) and P. palmivora (29.4 ± 1.6 mm) versus the negative control (1.3 ± 0.6 mm) (P = 0.0006). The pathogens were reisolated and identified based on colony morphology. Although N. parvum has been reported to cause dieback on ‘ōhi‘a trees in Hawaii (Hughes et al. 2018) and blueberry in Chile (Espinoza et al. 2009), 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.The author(s) declare no conflict of interest.