Urgent Action Needed to Combat Cassava Witches’ Broom Disease in South America

Alliance researchers and partners, including Embrapa, Brazil’s largest agricultural research organization, have launched a rapid response plan aimed at slowing the spread of a potentially devastating disease affecting cassava crops, crucial for food security and the livelihoods of millions.

The Emergence of a New Threat

In 2023, cassava farmers in remote French Guiana faced a devastating surprise: their crops began to wither away, leaving them with little more than stunted roots. Instead of harvesting healthy root clusters, they pulled up stems that were battered and small, reminiscent of carrots. Upon investigation, researchers uncovered the alarming reality: cassava witches’ broom disease (CWBD), driven by a poorly understood fungus, marked its first appearance in the Americas. This discovery was confirmed following an expedition in 2024 that highlighted the gravity of the situation.

Spreading Contagion

Simultaneously, Brazil, the largest cassava producer in Latin America, reported early instances of the disease in 2025, with confirmed cases documented in two distant locations within the country—each more than 1,000 km apart. The disease has a staggering plant infection rate of up to 90% in regions of Southeast Asia where it was previously identified, raising alarms for the health of cassava crops in South America.

A Call to Action

In response, researchers from the Alliance of Bioversity International and CIAT, along with Embrapa, mobilized a rapid-response plan in June 2025. “We are facing an emergency,” stated Paulo Melo, a researcher at Embrapa, during a strategizing meeting in Colombia. He emphasized the essential role cassava plays for Brazilian producers, especially for women and Indigenous communities.

The Importance of Cassava

Cassava serves as a staple food for approximately 800 million people worldwide, providing vital calories, carbohydrates, vitamins, and micronutrients. Its ability to thrive under harsh conditions makes it a critical crop for food security. Given that many African countries consume more cassava per capita than Brazil, the threats posed by CWBD’s emergence in South America also have potential global repercussions.

Risk Assessment and Research

The rapid spread of CWBD in Brazil is especially concerning because the plant’s center of origin lies in the Amazon. This region is home to the most natural biodiversity of cassava, hosting many wild relatives. The concern is heightened by the possibility that the fungal pathogen might also affect cacao crops, another vital agricultural industry in South America.

Scientific Strategies for Prevention

To counteract CWBD, the Alliance-Embrapa collaboration is focused on mapping both the distribution and severity of the disease in northeastern Brazil. The immediate goal involves deploying molecular detection tools initially developed for Southeast Asia to enable on-site identification of the fungus.

Collecting Genetic Diversity

As part of this emergency response, researchers plan to collect wild cassava relatives and local landraces—varieties cultivated by farmers over generations—before they become infected by CWBD. Brazil boasts extensive collections of cassava varieties, and Embrapa aims to expedite collection expeditions to gather resistant varieties and potentially introduce them to the Alliance’s Future Seeds gene bank in Colombia.

Building a Collaborative Framework

With a commitment to disrupting the spread of the disease, Embrapa’s Jane Simoni remarked, “Our main focus now is stopping witches’ broom to protect the lives and livelihoods of millions.” This effort ties directly into promoting food security, mitigating hunger, and aiding impoverished communities throughout Latin America.

Understanding the Fungal Pathogen

Alliance scientists have been crucial in revealing the nature of the fungus responsible for CWBD, identified as Ceratobasidium theobromae. Researchers overcame significant challenges to isolate and cultivate the fungus, allowing them to study its effects on cassava under controlled conditions.

Looking Ahead

As researchers continue to investigate, they are wary of the unique environmental conditions in the Amazon which may promote the rapid spread of CWBD. They predict the fungus could extend its reach further into South America, escalating the urgency of their research efforts.

Conclusion

Collaboration between various organizations offers hope in the fight against cassava witches’ broom disease. As we work together to confront this emerging threat, it is imperative to mobilize resources and expertise quickly. The situation remains a critical challenge, and immediate action is essential to safeguard food security in the region.