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bioRxiv · 10.1101/2025.02.14.638269

Rhizoctonia theobromae associated with a severe witches' broom outbreak in cassava of the Brazilian rainforest and evidence of its Southeast Asian origin

Alves Santos de Oliveira, S.·Sheat, S.·Margaria, P.·Lopes Lima, A.·de Araujo dos Santos, J.·Souza Rocha, H.·Fleck da Silveira, H.·Ramos de Jesus, C.·Winter, S.
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Abstract

Cassava witches broom disease (CWBD) has emerged as a significant threat to cassava production in the Oiapoque region of Amapa, Brazil. Diseased plants exhibit stunted growth, vascular necrosis, abnormal shoot proliferation, and distinctive broom-like appearance. This study aimed to characterize the disease and identify its causal agent(s). The assessment by high-throughput sequencing of total nucleic acids (DNA and RNA) from affected cassava tissues revealed Rhizoctonia theobromae (syn. Ceratobasidium theobromae) associated with CWBD. PCR-based detection using species-specific primers confirmed the presence of R. theobromae in 74% of symptomatic samples. Genetic diversity analysis based on the Ca2+/calmodulin-dependent protein kinase gene showed low variability among Brazilian isolates compared with Asian populations, suggesting their recent introduction. This first report of R. theobromae causing CWBD in Brazil follows a recent report of the disease from French Guiana and highlights the urgent need for effective measures to prevent the further spread of this emerging pathogen, which poses a deadly threat to cassava cultivation in the rainforest, a significant risk to cassava production in Brazil, and regions with similar eco-climatic conditions.

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Alves Santos de Oliveira, S., Sheat, S., Margaria, P., Lopes Lima, A., de Araujo dos Santos, J., Souza Rocha, H., Fleck da Silveira, H., Ramos de Jesus, C., Winter, S.. 2025-02-18. Rhizoctonia theobromae associated with a severe witches' broom outbreak in cassava of the Brazilian rainforest and evidence of its Southeast Asian origin. https://doi.org/10.1101/2025.02.14.638269

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