Cassava industry overcoming challenges: Developing varieties resistant to mosaic disease

Farmers await disease-resistant cassava varieties

In the cassava fields of Tan Hoi Commune (Tay Ninh Province), wilted and yellowing plants have become a familiar sight to local residents. Mr. Bui Cong Ngoc, a farmer who has long been attached to cassava cultivation, shared that the occurrence of what he calls a “combined disease” has become increasingly common, causing serious losses for local growers.

According to Mr. Ngoc, cassava mosaic disease is the main culprit that weakens the plant’s resistance, making it more susceptible to secondary infections such as gummosis, witches’ broom, and root collar rot. “Mosaic disease has wiped out around five to seven major local cassava varieties, and almost all non-resistant ones have now degenerated,” he said.

The disease has not only spread widely across Tay Ninh but has also expanded rapidly nationwide. Since it first appeared in 2017, cassava mosaic disease has affected large cultivation areas across the Southeastern region and beyond.

Mr. Ngoc further explained that efforts to control the disease have been largely unsuccessful because most cassava diseases are caused by viruses. “From witches’ broom to mosaic disease - they’re all viral. Farmers can only focus on intensive care, organic fertilization, and keeping the plants healthy while waiting for new resistant varieties. For cassava growers, this disease can wipe out entire crops or, at best, reduce yields and starch content by 50-60%. At this point, only the development of resistant varieties can ensure the survival of the cassava industry,” he shared.

What cassava farmers hope for most now is the early introduction of new varieties that are disease-resistant, high-yielding, and able to maintain stable starch content. Mr. Ngoc expressed his confidence in research institutes and supporting organizations such as the Agricultural Genetics Institute, CIAT, and the Hung Loc Center, which are actively conducting experiments and screening new varieties.

“At present, several cassava varieties resistant to mosaic disease have shown promising initial results, but full replacement will still require time for testing and evaluation. Only then can cassava production truly regain its stability,” Mr. Ngoc said with optimism.

Scientists step in

Confronted with this harsh reality, the scientific community has embarked on an ambitious race to develop disease-resistant cassava varieties through biotechnology. Prof. Dr. Le Huy Ham, Principal Investigator of the project “Research and application of molecular markers in breeding cassava varieties resistant to mosaic disease” - funded by the Thien Tam Foundation under Vingroup - shared that the five-year project is now more than halfway through its implementation.

According to Prof. Dr. Le Huy Ham, the project consists of three main components. The first focuses on developing molecular markers associated with starch content, branching level, and disease resistance, in collaboration with scientists from the International Center for Tropical Agriculture (CIAT). Initial results have successfully identified several markers distributed across the cassava genome.

The second component involves breeding cassava varieties resistant to mosaic virus by transferring resistance genes from international varieties into local Vietnamese ones. However, this process is far from simple, as cassava rarely flowers in lowland regions. To overcome this challenge, the research team established a hybridization site in Lam Dong Province, where the cooler climate is more favorable for flowering. They also employed red-light illumination systems to induce synchronized flowering between parent plants, enabling controlled crossbreeding.

The third component focuses on field trials, evaluation, and selection of promising hybrid cassava lines. During 2023 - 2024, the research team successfully obtained a large number of hybrid seeds, which are now being tested at experimental sites in Tay Ninh, Yen Bai, and Phu Tho. Initial results have been highly encouraging, with several lines showing theoretical yields of around 50 tons per hectare, starch content of 26-27%, and strong resistance to the cassava mosaic virus. “Given our current progress, we are confident that the project’s goals will be achieved - and possibly even exceeded,” affirmed Prof. Dr. Le Huy Ham.

Beyond breeding new varieties, the project also contributes to building a scientific foundation for the sustainable development of Vietnam’s cassava industry. “If we learn to return to the soil what the plant takes from it, cassava can absolutely develop sustainably, as demonstrated in Tay Ninh and the Central Highlands,” Prof. Ham emphasized.

According to him, the newly developed sets of molecular markers will help shorten the breeding cycle and increase selection accuracy, thereby accelerating cassava varietal improvement in the years ahead. After more than three years of implementation, the project “Research and application of molecular markers in breeding cassava varieties resistant to mosaic disease” has identified several promising cassava lines with high yield potential, stable starch content, and outstanding disease resistance.

In parallel, the research team has successfully developed a genetic map identifying key traits such as disease resistance, starch content, and branching characteristics. This serves as a foundational database for building a molecular marker system that will support the breeding of next-generation cassava varieties in the coming phase.

These initial achievements have opened a new pathway for Vietnam’s cassava industry - one that enables the country to take the initiative in developing its own disease-resistant varieties. This progress is expected to play a crucial role in strengthening agricultural exports and safeguarding the livelihoods of millions of farming households nationwide.