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IPPC Pest Alert – Rhizoctonia theobromae (Cantharellales: Ceratobasidiaceae)

Other scientific names: Ceratobasidium theobromae, Oncobasidium theobromae, Thanatephorus theobromae
Date of Issue: 27 November 2025.

Rhizoctonia theobromae, (Cantharellales: Ceratobasidiaceae)

Figure 1: Vascular streak dieback (VSD) symptoms on cacao caused by Rhizoctonia theobromae. Credits: Ali, S.S., Asman, A., Shao, J., et al. (2019). Draft genome sequence of fastidious pathogen Ceratobasidium theobromae, which causes vascular-streak dieback in Theobroma cacao. Fungal Biology and Biotechnology 6:14. Licensed under CC BY 4.0.

Figure 2: Cassava Witches' Broom Disease (CWBD) symptoms in French Guiana caused by Rhizoctonia theobromae (a, b) Broom-like growths; (c) Vascular necrosis in an infected stem cross-section. Credit: Pardo, J.M., Gil-Ordóñez, A., Leiva, A.M., et al. (2024). First report of cassava witches' broom disease and Ceratobasidium theobromae in the Americas. New Disease Reports 50(1): e70002. Licensed under CC BY 4.0.

Reason for this alert

Rhizoctonia theobromae is a fungal pathogen of significant economic concern that has demonstrated recent intercontinental spread. Rhizoctonia theobromae is native to Southeast Asia and Melanesia, where it has long been established on cacao 5, 10. It has also been consistently detected and localized in cassava plants affected by Cassava Witches’ Broom Disease (CWBD) and it is strongly suggested by recent scientific evidence as the causal agent of the disease 1, 4. It has recently jumped from its native range in Asia to South America, where it was first detected in 2023 on Cassava 2, 3, 13. Considering its potential to spread through asymptomatic planting material 4 and the substantial economic damage it causes, the Pest Outbreak and Alert Response Systems (POARS) Steering Group assessed and qualified R. theobromae as an emerging pest of global concern.

Based on the assessment conducted the pest meets the criteria for (i) recent geographical spread, with outbreaks across multiple, non-contiguous regions; (ii) limited but expanding distribution in endangered areas; (iii) substantial economic impact, with yield losses up to 50% in cassava and 30–40% in cacao; (iv) high likelihood of further introduction, primarily through asymptomatic infected planting material; (v) significant risk management challenges, due to latent infections, diagnostic difficulties, and limited field-level control options.

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Distribution

  • Asia (native region): Rhizoctonia theobromae is the confirmed causal agent of Vascular Streak Dieback (VSD) on cacao in Indonesia, Malaysia, and Vietnam 10, and strongly supported as the causal agent of Cassava Witches’ Broom Disease (CWBD) on cassava in Lao PDR4 and the Philippines 12.
  • Latin America and the Caribbean (Recent introduction): First detected in 2023 on cassava (CWBD) in French Guiana2 and Brazil 3.
  • Pacific (native region): Papua New Guinea 5.

Hosts

  • Cacao (Theobroma cacao).
  • Cassava (Manihot esculenta) consistently detected in plants affected by Cassava Witches’ Broom Disease (CWBD) and considered a strongly associated host.

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Impact

In cacao, Rhizoctonia theobromae is the causal agent of Vascular Streak Dieback (VSD), characterized by leaf chlorosis, vascular discoloration (streaking), branch dieback, and potential tree mortality. It is a major limiting factor for cacao production in Southeast Asia and Melanesia 5.

In cassava, recent scientific evidence strongly supports R. theobromae as the causal agent of Cassava Witches’ Broom Disease (CWBD) in key production areas such as Lao PDR 4 and the Philippines 2. In other parts of Southeast Asia, the fungus has been consistently detected and localized in diseased plants and is regarded as a strongly associated or putative causal agent 1, 4. Although the etiology of CWBD was historically attributed to other causes, the latest primary research consistently points to R. theobromae as the dominant pathogen associated with the disease 1, 4, 12.

The economic impacts reported for CWBD are substantial, with yield losses of up to 50% due to reductions in root volume and starch content 1, 8. These losses pose a direct threat not only to the commercial viability of the starch industry but also to food security, particularly for indigenous communities in newly affected areas of South America, where cassava is a primary food source 3.

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Pathways

The primary pathway for the international spread and entry of R. theobromae into new areas is the trade and movement of infected plants for planting, particularly cacao seedlings and cassava stem cuttings 2, 3. In cassava, the fungus has been detected and localized within vascular tissues of plants affected by Cassava Witches’ Broom Disease (CWBD) 4. Although its causal role remains under investigation, these findings indicate that asymptomatic planting material could serve as a potential carrier. Because the fungus occurs at very low titers and is often undetectable even in symptomatic tissues 9, it may escape standard phytosanitary inspection procedures. Detection is further hindered by its fastidious growth, which complicates isolation and culturing in routine diagnostics 9.

Once introduced into a new area, spread occurs primarily through human-assisted movement of infected or contaminated planting material between farms and regions, a common practice in both cassava and cacao production systems. Natural spread is believed to occur through wind-dispersed basidiospores released from infected leaf scars or petiole surfaces under humid conditions 5. However, current evidence indicates this mechanism is limited to short distances (less than ~100 m) and contributes mainly to localized, within-plantation spread rather than long-distance or regional dissemination.

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Expert Working Group (EWG) Activation

Given the global significance of Rhizoctonia theobromae and the need for coordinated technical guidance, the IPPC will establish a dedicated Expert Working Group (EWG) to develop global materials to support contracting parties in prevention, preparedness, and response. The IPPC Secretariat will issue a public call for experts to ensure broad, multidisciplinary participation in this process.

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Disclaimer

IPPC Pest Alerts are an early warning tool for emerging pests identified through routine POARS horizon scanning, which includes scientific and technical sources and specialized databases. The information contained herein is considered current as of the date of issue.

While produced by the IPPC Secretariat, these alerts are intended for informational purposes only and do not constitute an official declaration of pest status by the IPPC or FAO. In some cases, the sources of information might not have been confirmed with the corresponding National Plant Protection Organization (NPPO) at the time of publication. The IPPC Secretariat and the FAO assume no liability for the accuracy or completeness of this information, nor for any actions taken in reliance thereon. This alert should be used with these limitations in mind.

If you have any questions or comments about this alert, please e-mail us at IPPC@fao.org

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References

  1. Leiva, A.M., Pardo, J.M., Arinaitwe, W., et al. 2023. Ceratobasidium sp. is associated with cassava witches’ broom disease, a re-emerging threat to cassava cultivation in Southeast Asia. Scientific Reports, 13: 22500.
  2. Pardo, J.M., Gil-Ordóñez, A., Leiva, A.M., et al. 2024. First report of cassava witches’ broom disease and Ceratobasidium theobromae in the Americas. New Disease Reports, 50(1): e70002.
  3. Oliveira, S.A.S., Sheat, S., Margaria, P., et al. 2025. Rhizoctonia theobromae associated with a severe witches’ broom outbreak in cassava of the Brazilian rainforest and evidence of its Southeast Asian origin. bioRxiv (preprint).
  4. Gil-Ordóñez, A., Pardo, J.M., Sheat, S., et al. 2024. Isolation, genome analysis and tissue localization of Ceratobasidium theobromae, a new encounter pathogen of cassava in Southeast Asia. Scientific Reports, 14: 18139.
  5. Guest, D. & Keane, P. 2007. Vascular-streak dieback: a new encounter disease of cacao in Papua new guinea and Southeast Asia caused by the obligate Basidiomycete Oncobasidium theobromae. Phytopathology, 97(12): 1654–1657.
  6. Pardo, J.M., Chittarath, K., Vongphachanh, P., et al. 2023. Cassava witches’ broom disease in Southeast Asia: A review of its distribution and associated symptoms. Plants, 12(11): 2217.
  7. Harni, R., Amaria, W., Mahsunah, a. & Lakani, I. 2019. Effects of Trichoderma metabolites and botanical fungicides against VSD in cacao. Jurnal Tanaman Industri dan Penyegar, 6(3): 109–118.
  8. Landicho, D. 2024. Addressing cassava witches’ broom disease impacts (media brief). DOST-PCAARD.
  9. Ali, S.S., Asman, A., Shao, J.Y., et al. 2019. Draft genome sequence of fastidious pathogen Ceratobasidium theobromae, which causes vascular-streak dieback in Theobroma cacao. Fungal Biology and Biotechnology, 6: 14.
  10. Samuels, G.J., Ismaiel, A., Rosmana, A., et al. 2012. Vascular Streak Dieback of cacao in Southeast Asia and Melanesia: in planta detection of the pathogen and a new taxonomy. Fungal Biology, 116(1): 11-23.
  11. McMahon, P. & Purwantara, A. 2016. Vascular streak dieback (Ceratobasidium theobromae): History and biology. In B. A. Bailey & L. W. Meinhardt (Eds.), Cacao diseases: A history of old enemies and new encounters (pp. 307–335). Springer.
  12. Landicho, D.M., Montañez, R.J.M., Manayon, V.S., et al. 2025. Detection, isolation, and identification of Rhizoctonia theobromae associated with cassava witches’ broom disease in the Philippines. Physiological and Molecular Plant Pathology, 140: 102872.
  13. Embrapa. 2024. Embrapa identifies the first case of witches' broom in cassava in Brazil. Official Communication. Available at: https://www.embrapa.br/en/busca-de-noticias/-/noticia/91690274/embrapa-identifies-first-case-of-witches-broom-in-cassava-in-brazil.

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Notes

Additional notes, if any.

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