Phytophthora palmivora Causing Disease on Theobroma cacao in Hawaii

Commercial production of cacao in Hawaii has doubled in the past 10 years, and farmers are receiving premium prices for their beans from the expanding local confectionery industry. Black pod, caused by Phytophthora spp., is the only major cacao disease that has been reported in Hawaii but distribution and molecular identification are lacking. To determine the species of Phytophthora affecting Theobroma cacao, a sampling trip was conducted on Hawaii Island and Oahu. Ten isolates of Phytophthora palmivora were obtained from diseased cacao on Hawaii Island, but none from Oahu, despite the presence of symptomatic pods. No other Phytophthora species were found. Laboratory studies showed that all isolates produced lesions on unwounded cacao pods, but they differed in terms of their temperature–growth responses. Fungicide sensitives for a subset of isolates (n = 4) were determined using media amended with a range of fungicide concentrations. The Hawaiian isolates of P. palmivora were more sensitive to mefenoxam, chlorothalonil, and fosetyl-Al, than isolates from Ghana (n = 2) and Mexico (n = 1). This study identifies P. palmivora as a causal agent of black pod in Hawaii based on molecular data and provides valuable preliminary information on fungicide resistance and temperature response that can be used to improve disease management.