Embrapa identifies first case of "Witch's broom" in cassava in Brazil

Based on biological and molecular analyses, Embrapa Amapá and Embrapa Cassava and Fruits confirmed to the Ministry of Agriculture and Livestock (MAPA) the first report of the presence in Brazil of the fungus Ceratobasidium theobromae, also known as Rhizoctonia theobromae, which causes the cassava ″witches' broom″ disease. 

The pathogen was confirmed by a report from MAPA, through species identification analysis performed by a team from the ministry.     

The disease was found in cassava plantations in the indigenous lands of Oiapoque, on the border with French Guiana.  Photo: Adilson Lima

The disease was detected in cassava plantations in the indigenous lands of Oiapoque, a municipality in the state of Amapá, located on the border between Brazil and French Guiana. The presence of Ceratobasidium theobromae represents a risk of a significant reduction in the productivity of affected cassava plants. To date, this fungus has not been detected in other hosts in Brazil.    

"Witch's broom" is so named because it leaves the branches of plants dry and deformed, including dwarfism and proliferation of weak and thin shoots on the stems, similar to an old broom. As the disease progresses, chlorosis, wilting and drying of the leaves, apical death and death of the shoots are common.

Ceratobasidium theobromae can spread through infected plant material, cutting tools, and possible soil and water movement. ″The movement of plants and agricultural products between regions can facilitate the spread of the pathogen, increasing the risk of infection in new areas,″ Embrapa’s Technical Note warned. (read the full file in Portuguese here).

Researchers from the French Center for Agricultural Research for International Development (CIRAD/France), in partnership with the International Center for Tropical Agriculture (CIAT/Colombia), collected and isolated Ceratobasidium theobromae in affected areas with similar signs in French Guiana, close to the borders with Brazil and Suriname.

Embrapa also emphasized that the detection of Ceratobasidium theobromae in Brazil requires immediate cooperation between technical assistance agents, state plant protection agencies, researchers, farmers and government authorities as a fundamental practice to implement effective containment, management, and control measures, in order to guarantee the safety and sustainability of agricultural production. Embrapa's discovery can contribute to the scientific advancement of research related to the genetic improvement of cassava and recommendation of measures to control the disease.

Collection history of infected material

In March 2023, a team from Embrapa Amapá participated in the 29th Assessment and Planning Assembly of the Indigenous Peoples and Organizations of the Municipality of Oiapoque (APIO), an event held by the Council of Chiefs of the Indigenous Peoples of Oiapoque (CCPIO). 

The research institution was asked to assess and carry out actions within its attributions to mitigate the occurrence of diseases affecting cassava plantations. The following week, a team verified in loco the signs compatible with the cassava 'witch's broom' disease in the indigenous villages of Ahumãm, Anawerá, Tuluhi and Tukay.

Subsequently, the same signs were detected in the villages of Kuahí, Ywawká, Karibuen, Kuai, Ariramba, Galibi, Lençol, Manga, Zacarias and Japiim. 

According to the Technical Note from Embrapa Amapá, when the first signs of the disease were detected, infected cassava stems were transported to the Plant Protection laboratory of Embrapa Amapá, to isolate the probable etiological agent of the disease under laboratory conditions.

Molecular analysis of the fungus

With the evolution of signs of disease in the fields of the Oiapoque indigenous people, new samples of infected plants were analyzed in the Phytopathology Laboratory of Embrapa Mandioca e Fruticultura (Bahia), to conduct the molecular diagnosis of the causal agent of this new epidemic outbreak in the state of Amapá. 

The samples were then lyophilized and preserved at -80 °C for deep sequencing analyses on high-performance sequencers (High-Throughput Sequencing) on Illumina and Nanopore platforms, in partnership with the German Collection of Microorganisms and Cell Cultures (Deutsche Sammlung von Mikroorganismen und Zellkulturen - DSMZ), in Germany.

Then, the sequencing of joint samples (pools) was conduct based on the different tissues collected (leaves, petioles and stems), and the comparison between the pathogens with the greatest agreement between them, the presence of endemic pathogens and those of importance to the crop, as well as potential pathogens not reported in Brazil.

A large set of pathogens and endophytic organisms were detected by the technique used and are associated with the culture, but never reported associated with the signs observed in loco, except for Ceratobasidium theobromae, a fungus never before reported in the American continent.

Recommendations to reduce the impact

To reduce the impacts of the new disease, Embrapa recommended strategies that ranged from the protocol for early detection of the pathogen, use of proven healthy cuttings, good agricultural practices, among others, involving the various agents that act in the respective recommendations:

1. Monitoring and Surveillance: Intensify the monitoring of cultivation areas for early identification of symptoms.

1.1. Establish a protocol for early detection of the pathogen via PCR and/or via HTS sequencing to support monitoring and surveillance actions

1.2. Accredit laboratories to perform diagnosis and indexing for pathogens of importance to the culture

2. Quarantine: Implement quarantine measures to restrict the movement of plant material from affected areas.

3. Healthy cuttings: Use of cuttings with proven health and produced in regions without the disease, or in conditions that do not allow the development of the pathogen (for example, thermal chambers, nurseries, and greenhouses)

4. Chemical Treatment: Use of specific fungicides to control the spread of the pathogen, under local regulations.

5. Cultural Practices: Remove and eliminate the burning of diseased plants to reduce inoculum in affected areas and decrease the incidence of new infected plants.

6. Asepsis/sanitization of tools used to destroy plants with signs of disease. Wash with water and detergent and then sanitize with a 1.25% sodium hypochlorite solution.

7. Bag and quickly wash clothes, shoes and hats and/or caps used when visiting areas affected by the disease, to prevent the spread of spores to other regions of the country.

8. Develop publications, videos and posters to inform the general public about the signs and modes of transmission of the disease.

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