By Mary Hearty
The Kenya Agricultural and Livestock Research Organization (KALRO) has developed a new cassava variety that is resistant to viral diseases. The genetically modified cassava variety will now help boost production for smallholder farmers in East Africa, and improve their livelihood through increased income.
“The improved cassava variety was developed through the VIRCA Plus Project, which was started to develop cassava that is resistant to cassava mosaic disease (CMD) and cassava brown streak disease (CBSD), with an aim of enhancing the livelihoods of smallholder farmers by delivering cassava varieties that are enhanced for resistance to virus diseases,” Dr Catherine Taracha, the Lead Gene Editing Expert and Director of KALRO Biotechnology Centre said during a media briefing with Africa Science Media Centre (AfriSMC).
The VIRCA Plus project team is a multidisciplinary team in seven institutions from four countries consisting of virologists, plant physiologists, breeders, biotechnologists, molecular biologists, agronomists, regulatory scientists, communication and management.
According to Dr. Taracha, there are two major diseases which are a challenge to cassava production. These are Cassava Mosaic Disease (CMD), where you get crinkling of the leaves and Cassava Brown Streak Disease (CBSD), where you get streaks of brown on the cassava and malformation of the roots.
These diseases are transmitted by whiteflies and by farmers sharing the cuttings when these cuttings have diseases. For CMD, this disease has been managed through conventional breeding. But for CBSD, there is no known source of the resistance, genetic engineering was used to introduce a gene with resistance to the virus was introduced in to the cassava.
With regards to the cost of CBSD, she emphasized that it has serious implications for smallholder cassava farmers in rural communities and growing industries that are dependent on cassava as raw material.
“You can get the yield losses on susceptible cultivars of up-to 70 percent valued at over 7.5 billion Kenya shillings in 8 Eastern and Central African countries,” she said.
“The virus resistant cassava will have the farmer preferred qualities; resistant to diseases; there will be no special farming practices needed; and it will be distributed through existing national seed delivery systems; and can be further developed by breeders.”
Besides, she noted: “Gene editing technology has been commonly used to produce virus resistant crops since 1990s. At the moment, there are virus resistant crops that have been approved for commercialization using this technology in other parts of the world like papaya, plum, beans, and squash.”
“And what normally happens is, a bunch of the DNA from part of the virus is integrated into plant genome. Then the plant’s defenses are activated to recognize, target and degrade the virus pathogen,’ Dr Taracha explained.
The VIRCA Plus journey started in 2008 with trait discovery, and that was where there was product concept, gene discovery and proof of concept. Then it moved to product development, where there was various field evaluations, and variety development.
The Director of the KALRO Biotech Centre further elaborated that the improved cassava went through a multi-step laboratory process from leaf extract to formation of a transgenic plant.
Thereafter, it went through molecular screening tests in the laboratory, where various selected lines were advanced for virus and performance testing in the greenhouse.
From the laboratory, CBSD resistance was then evaluated for performance in the greenhouse, where a resistant plant is taken and binded using an infected CBSD bud.
From the result, she said, “there were 25 improved cassava lines tested in confined field trials (CFTs). And these trials were done in areas where there were high whitefly populations. They were planted in both Kenya and Uganda.”
Results showed that disease resistant cassava variety increased usable storage root yield 20 times, meaning, more than 95 percent of roots lost to BSD that did not have the resistance, but more than 98 percent of the root cassava were disease-free.
The CBSD resistant variety was then planted over multiple locations and the same resistance was observed.
From the research, they found out that the CBSD-resistant cassava is very safe based on International Food, Feed and Environmental Safety guidelines.
“We were able to take the seeds and the roots of our improved cassava to a laboratory in the US for safety evaluation and we found that the cassava just remains the same as the convention cassava that has not been improved,” she said.
“Also, we looked at the cassava plant characteristics of the improved cassava as well as the conventional cassava, and characteristics remained the same. The nutrition composition was also not altered. Again, there was no negative effect on the environment.”
Dr. Taracha observed that evidence from planting the CBSD resistant variety event 4046 in Uganda and Kenya demonstrated that there was sustained resistance across multiple generations and different locations.
The improved cassava will be beneficial to breeders, farmers, processors and consumers because it is a source of CBSD resistance for breeders; there will be availability of good quality planting materials both for the breeders and the farmers.
Additionally, there was need to combine CMD and CBSD to develop dual disease resistant cassava varieties through conventional cross breeding. So, they took the improved cassava and crossed it with one that has latent CMD resistance. This was done several times and they managed to get seeds which were then germinated and they got seedlings.
Later, they took them through various evaluations to ascertain that both CMD resistant and CBSD resistant were in the plant. The progeny were evaluated at KALRO in Mtwapa and Alupe in Kenya and Serere in Uganda. And the result was still sustained.
KALRO applied to NBA for environmental release and placing on the market of CBSD resistant cassava on 9th March 2020 to the Kenya National Biosafety Authority (NBA). Thereafter, the NBA engaged the public for their opinion on the product, which was carried out on 10th June 2020 via Zoom and Facebook live due to the pandemic. “We actually got 1192 participants and the total comments from the public were 3342,” she distinguished.
The NBA recently approved the variety for environmental release .This means that the variety will now be put under the national performance trials (NPTs). The NPTs involves testing the Distinctness, Uniformity and Stability (DUS) of the new cassava variety. This will be done for a period of two seasons or two years since each season will take between 9-12 months.
Some of the areas that KALRO has mapped for the NPTs include Alupe, Kakamega, Kibos, Homabay and Oyani in the western part of the country while in the coastal region which also grows a significant amount of cassava, Mpeketoni, Mtwapa, Matuga, Kikoneni and Msabaha have also been listed. However, only three locations will be selected from per region.
After the NPTs have been carried out within the two years (two seasons), the report will be sent to the National Variety Release Committee (NVRC) of the ministry of Agriculture. The Committee, which will determine whether or not the variety should be commercialized, is comprised of the Kenya Plant Health Inspectorate Services (KEPHIS) and cassava breeders, among other value chain players.
Dr. Taracha said, if approved, the new cassava variety, will be distributed to smallholder farmers by KALRO free of charge because there will be no technology fee applied it since the variety is be wholly owned KALRO.
“There are those who sell cutting as a business, those will sell but from KALRO (seed units) it will be absolutely free because there is no intellectual property issue involved,” she reiterated.
With the average production annually of cassava in Kenya resting at 970,000 tonnes, she notes that cassava has a lot of potential making the new varieties very marketable not just because of food security but also for production of other items such as making biodegradable bags, sanitizers, animal feeds, industrial starch among others.
Additional reporting by Sharon Atieno
