Date released
16 June 2023

Spreading diseases cause a devastating toll

Cassava is a key commercial crop in mainland South-East Asia that provides the livelihood for around 2 million smallholder growers. It fuels an ever-growing global market for cassava roots, starch and chips which are used to produce a range of traditional and modern food, textiles, ethanol, animal feed and new products such as biodegradable plastics. 

But as the market is growing so are 2 serious emerging diseases. They are cassava witches' broom disease (CWBD) and cassava mosaic disease (CMD). Both diseases can cause severe yield losses or crop failure, rendering the crop unprofitable.

In South-East Asia, the cassava sector relies on strong trading across countries of feedstock (roots) for processing. Therefore, the 2 diseases have quickly crossed the national borders, spreading across an estimated 37% of Cambodia, Vietnam, Thailand and Laos' cassava areas. These infections have caused millions of dollars in revenue loss for smallholder farmers and threatened to stifle the booming cassava industry.

'CMD has infected almost 100% of cassava stems in our province. Our farmers have suffered serious income loss, and the industry is struggling to secure enough clean roots for their production,' said Mr Nguyen Dinh Xuan, the Director of Tay Ninh Department of Agriculture and Rural Development.

Tay Ninh province is Vietnam's central cassava production hub, responsible for half of the country's production. It is also a hub for the popular cassava trading routes between Vietnam and Cambodia.

Farmer harvesting cassava
Cassava is an important source of income for 20,000 smallholder families in Tay Ninh province of Vietnam. The new disease-resistant clones introduced by the project are already in farmers’ field. Some are strongly favoured by farmers such as HN1 breed for their high productivity. Photo: ACIAR

Cassava Disease Project Tay Ninh Vietnam

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Farmers displaying cassava
Ms Pham Thi Nhan (left) from the Hung Loc Agricultural Research Center and Ms Cu Le Thuy (right), the CIAT project coordinator, in the field in Tay Ninh province. Photo: ACIAR

Clean planting materials must be ready

Before the official reports of CMD in Vietnam, ACIAR had initiated scoping research to confirm the disease's presence in many provinces.

'Back in 2015, the region had no formal seed system to act as a clean stem resource. While addressing the threat of CMD, we had to keep cassava production viable in the short term by providing clean planting materials for cassava growers and processors. At the same time, we needed to start the long-term breeding actions immediately,' said ACIAR Research Program Manager, Crops, Dr Eric Huttner.

In 2019, ACIAR funded a project led by the International Center for Tropical Agriculture (CIAT) to improve the resilience of cassava production systems and value chains in Cambodia, Laos, Thailand and Vietnam.

'Our project involves several components, one of which is to identify which available varieties are least disease-susceptible in the short term and to provide them for farmers and processors quickly,' said ACIAR project leader, Dr Jonathan Newby.

The project also introduced CMD-resistant varieties from the International Institute of Tropical Agriculture (IITA) and CIAT in Colombia. From these 2 sources of germplasm, after only 3 years, the researchers have supported the Government of Vietnam in releasing the first generation of CMD-resistant varieties, which are now in farmers' fields.

Creating a new clone usually takes 7 to 8 years. But thanks to quick access to the tested germplasm, we have released 6 disease-resistant varieties for Vietnam


Ms Pham Thi Nhan,
Deputy Director of Hung Loc Agriculture Research Center in the south of Vietnam,
one of the key collaborating partners of the project.

These varieties have provided much-needed relief for smallholder farmers like Mr Bui Cong Ngoc, a cassava farmer and stem trader. He has engaged in breeding with the research team since the beginning of this project.

'To be honest, I used to doubt that researchers could create these disease-resistant varieties. Before the project, I tried all healthy breeds available in Vietnam from the provinces where CMD was absent. However, they were still infected when planted in Tay Ninh.

'But the new breeds have proven to be disease-resistant for 5 years now, which gives us lots of hope,' said Mr Ngoc.

Continuous improvement involves many players

Researchers still need to improve the disease-resistant breeds. It is just the beginning of a new journey.

'In provinces like Tay Ninh, the disease-free varieties alone are not enough. The industry relies heavily on high starch content for the competitive production of starch, which also determines the market price that farmers receive. Farmers and industry need high productivity to compete in a global market against alternatives,' said Dr Newby. 

Therefore, continued genetic improvement through breeding to increase the starch yield is critical. The CIAT researcher team will work with many local players to achieve this.

The local stem trader Mr Ngoc has been actively engaging in the multiplication of the least-susceptible varieties and the newly released disease-resistant breeds. He even tried growing these breeds in different cassava areas in Vietnam to test their capacity for massive growth.

'I am a local, and I grow cassava myself. I can tell which breed can adapt well and its strengths and weaknesses, and I learn how to improve them. I will plant the best-performing breeds in Tay Ninh and other areas to evaluate their performance in different climate zones in Vietnam. Then I can advise local farmers to grow them or not, so they can avoid losing their money,' said Mr Ngoc.

Researcher measuring starch content of cloned cassava
A researcher from Hung Loc Agricultural Research Center measuring the starch content of the new clones. Photo: ACIAR

The research team is also working to fix some flaws of the breeds. For example, they are susceptible to cassava witches' brooms (CWB) in South-East Asia. CWB is becoming a more serious disease whose causal pathway is much less known than CMD.

'One of our next major outcomes can be understanding the pathogen for cassava witches' broom. And in the next phase, we will continue to develop CWB management protocol,' said Dr Newby.

A strong partnership against new emerging disease

One of the strongest outcomes of the project is the comprehensive partnership on the ground.

‘When I think about the sustainability of this project, I think of the partnerships and the capacity building for local researchers. People and institutions involved will strengthen their capacity but those regional partnerships will also get much stronger. We will get solutions developed in Vietnam flowing through to Laos and Cambodia and back and forth,' said Dr Newby. 

'By participating in this project, we gain a good network of scientists from around the world and from the region to share experiences and exchange difficulties. Based on this sharing, we can develop the most optimal pest and disease management solutions,’ said Ms Nhan.

Ms Nhan's Hung Loc Agriculture Research Center also supports many young researchers participating in the project. They have greatly improved their thinking and working approach through online training, fieldwork and other collaborative opportunities.

'Accessing all the richness of the research network helps our young researchers better shape their future research projects,' Ms Nhan said.

The project has also seen partnerships strengthen in the industry.

'We have had traders and policymakers join us out in the field who are very interested in the results. We have a lot of support for the national programs to take over and scale the innovations coming out of the research project,’ said Dr Jonathan Newby.

The Tay Ninh Department of Agriculture and Rural Development plans to establish a cassava research centre in their province that aims to create new varieties for the future.

'CMD-resistant breeds are one goal but we want to enhance our capacity and resource to cope with new emerging diseases and the current climate changes. We need a wide range of breeds to prepare for the future,’ said Mr Nguyen Dinh Xuan, Director of Tay Ninh Department of Agriculture and Rural Development.

Learn more about the project via the ACIAR website.