Asian Scientist Magazine (Oct. 3, 2023) – Since 2020, the Covid-19 pandemic has caused almost 7 million deaths worldwide and long-term cardiorespiratory ailments for many others. But the human population is not the only one that suffers from fast-spreading diseases. Plants like cassava do too, and humans have good reason to take notice.
Used as both a food and industrial crop, cassava plantings are estimated to cover over 3.5 million hectares in Southeast Asia—supporting roughly 2 million households in the region. The crop plays a significant role in global food systems. Cassava’s hardy roots are processed into starch and flour, the fundamental ingredients to almost everything we see on our dining tables today. These range from noodles and dairy products to bubble tea and gluten-free biscuits. Cassava is also used to make pharmaceuticals, paper and textiles, and dry cassava chips are used in animal feed and ethanol production.
Despite its reputation as a hardy crop, cassava plantations are now plagued with a serious pandemic: the cassava witches’ broom disease (CWBD), and more recently, cassava mosaic disease (CMD).
The cost of contagion
CMD was introduced to Southeast Asia through just a single plantation in the Northeast of Cambodia. From there, it spread quickly throughout the country, a significant part of southern Vietnam and around half of Thailand, Dr Jonathan Newby, Cassava Program Leader at the Alliance of Bioversity International and CIAT told Asian Scientist.
“If you put all that together, around 30 to 40 percent of the [cassava plantations] in mainland Southeast Asia are affected,” said Newby. He explained that infection happens either through transmission from whiteflies, or by planting already infected stems.
Infected cassava plants have a big impact on yield. If a plant is infected within the first three months, the yield might be cut by up to half, making the crop very uneconomic for farmers to grow. If plants are infected later in the season, the yield that year might be economically viable, but farmers are left without clean planting material the following year.
Unmasking the silent threat
To protect the livelihoods of those along the cassava supply chain, Newby and his team at the Alliance as well as national partners in Laos, Cambodia, and Vietnam, are researching ways to quickly multiply and disseminate healthy cassava stems for farmers to plant in the short term and develop disease-resistant varieties of cassava in the long run. He added that building linkages among partners in mainland Southeast Asia is key to safeguarding the industry.
If CMD is not prevalent in the particular area, the Alliance cassava team recommends farmers plant healthy cassava stems that are of existing varieties. If the plantation has been infected, the Alliance provides farmers with access to healthy new varieties of disease-resistant seeds.
However, this remains a temporary solution as resistant varieties currently produce lower starch yields. In Vietnam, only six out of hundreds of newly introduced disease-resistant clones from other cassava-growing regions have been found to be potentially commercially viable as a stop gap measure while new varieties are developed within Asia.
“If you plant in an area with a lot of disease pressure, you might only get 2.4 tons per hectare of starch. If you planted the disease-resistant variety, you could get 13.5 tons. However, if you are in an area with not much disease, you would still get a better yield planting an elite variety that does not have resistance,” explained Newby.
Even if it costs money, maintaining clean planting material and learning how to recognize the disease ultimately pays for itself, he added. The team is currently working with farmers to understand their cropping patterns, develop management practices to reduce disease impacts on farms and are involving farmers in the evaluation process for new varieties.
Agricultural alchemy: The Resilience Factor
In the long term, developing high-yield varieties that are optimized for both disease resistance and yield high levels of starch remains the ultimate priority.
But genetically breeding disease resistance into a crop like cassava does not just happen overnight. In fact, one cycle of the entire process might take up to eight years, said Newby. This is why the current temporary solution has been a critical time-buying element.
“It also demonstrates why we need to be taking pre-emptive action and preparing for other diseases that could be between continents,” Newby added.
Education and engagement with farmer communities can manifest very differently across the region. In Cambodia, information is spread organically through large Facebook groups, which may be threatened by sellers who falsely market their products as resistant varieties just to make a quick buck.
By creating educational content and partnering with NGOs, Newby and team are working to realize their long-term vision of securing a resilient future for Southeast Asia’s cassava crops.
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Cover image: Alliance of Bioversity and CIAT/Ysabel Lee
This article does not necessarily reflect the views of AsianScientist or its staff.
