Emergence of Ceratobasidium theobromae as a pest of cassava, and first report in the Americas
Ceratobasidium theobromae (syn. Rhizoctonia theobromae) is a known pathogen causing vascular-streak dieback of cocoa (Theobroma cacao) in South-East Asia and Melanesia.
Since 2020, an emerging disease (cassava witches’ broom disease) was observed in cassava (Manihot esculenta) in South-East Asia. Symptoms include dwarfism, weak sprouts with short petioles and vascular necrosis. Whereas cassava witches’ broom disease has been associated with phytoplasmas (e.g. ‘Candidatus Phytoplasma asteris’ and ‘Candidatus Phytoplasma luffae’) in some South-East Asian countries, in others (Cambodia, Laos, the Philippines, Vietnam), it was shown to be associated to the fungus C. theobromae, although Koch’s postulates have not yet been fully verified on cassava. In 2023 similar symptoms were observed in cassava-growing communes in French Guiana and in the neighbouring Brazilian state of Amapa. It is suspected that infected plants for planting of cassava (stem cuttings) are the pathway of spread for the pathogen. These first findings in the Americas underlines the need to take quarantine measures to prevent further spread of this disease in cassava (and cocoa) growing regions.
Finally, it may be noted that the causal agent of vascular streak dieback of ornamental plants (EPPO Alert List), is closely related to Ceratobasidium theobromae but is now considered a separate species of Ceratobasidium (EPPO RS 2024/110).
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