Scientists use new tech to develop disease-free cassava seeds

Scientists are applying the Semi-Autotrophic Hydroponics (SAH) technology to rapidly multiply improved virus-free cassava seedlings. This is aimed at addressing the problem of disease contamination in planting materials, improving yields and inspiring agricultural industrialisation in the country.

The project is the brainchild of the International Institute of Tropical Agriculture (IITA) in collaboration with the Kenya Agriculture and Livestock Research Organisation (KALRO).

“In Kenya, cassava has always been considered a poor man’s crop, whose calories only come in handy when all other crops have failed,” said Dr Morag Ferguson, a molecular geneticist at IITA and the project lead.

However, the scientists say the crop, now threatened by emerging pests and diseases, has 75 per cent starch, “and this is massive for industrial use and therefore has a massive international demand.”

Unlike the traditional method, where farmers use cassava stem cuttings as planting materials in the field, the SAH technique is done in a laboratory setting and in screen houses. Small pieces of mature and disease-free cassava stems, at least with a node and a terminal bud, are introduced into modified soil in trays in a controlled environment suitable for cassava propagation.

Small cuttings are sometimes treated with rooting hormones to boost root development and after the roots appear, the seedlings are transplanted into much bigger containers to strengthen. “Using the technology, one plant can produce hundreds of seedlings, and indeed, this is making a massive difference to the rate at which clean planting materials can be multiplied and distributed to farmers in need,” said Dr Ferguson.

So far, the SAH lab and a screen house have been established at KALRO Muguga Centre and hundreds of thousands of cassava seedlings are steadily growing at different stages.

One important thing, said Dr Ferguson, is to start with virus-free planting materials. “If a cassava plant is infected by a virus and it is chopped into more planting materials, the virus will permanently remain in those materials. This means that the new shootings will automatically be infected,” she said.

Farmers in different parts of the country have witnessed the technology. According to Justus Puka, a smallholder farmer from Essong’olo Village in Vihiga County, many important cassava species are almost extinct due to the cassava mosaic disease, which keeps spreading due to repeated propagation of infected planting materials.

“We previously had different varieties and one in particular, locally known as nylon due to its fast growth, is nowhere to be found,” said Mr Puka.

Mr Puka and fellow farmers have always relied on cassava stem cuttings as planting material, which are normally shared among farmers. “Little did we know that sharing infected cuttings was equivalent to sharing the virus,” said the farmer.

So far, IITA is building capacities for entrepreneurs in Western Kenya and within the Coastal region to multiply seeds at the community level before they are distributed to smallholder farmers nationwide. “The team is operating under the country’s seed regulations, where varieties to be multiplied must first be released through legal processes,” said Dr Ferguson.

Apart from being used as human food, cassava is an industrial raw material for medicine, cosmetics, textiles, paper, confectionery, beverages, animal feed, biodegradable food containers, adhesives and glues, chemicals and ethanol-based fuel, among other products.

Once established in the field, the crop needs moisture for the first two months, but after that, it can withstand prolonged periods of drought. In severe conditions, cassava sheds its leaves as a coping mechanism. Once it rains, it uses the stored carbohydrates in the stem to produce leaves again.

One study in the ScienceDirect scientific journal found that cassava leaves are a rich source of protein, minerals and vitamins. Still, they have to be processed to rid them of hydrogen cyanide. The processing involves repeatedly pounding the leaves followed by boiling them in water to release the toxicity.

Low cassava production in Kenya has been blamed on a lack of regular supply of improved varieties. In the late 1980s and early 90s, there was an outbreak of the cassava mosaic disease. However, some new disease-tolerant varieties were brought from Uganda and introduced to Western Kenya.

Currently, IITA has a breeding programme in Tanzania and Uganda, through which it has bred a new variety resistant to cassava mosaic disease and brown streak disease. The breed was naturally bred over a period of about 20 years.

The brown streak disease has been present for many years in the coastal regions of Mozambique, Malawi and the Kenyan Coast. In 2004, it started spreading inland to Western Kenya and Uganda and slowly moved to the Eastern Democratic Republic of Congo.

Today, IITA has developed high-yielding varieties resistant to the two diseases. The varieties are sweet and high-yielding and adapted to both coastal and Western Kenya. Typically, cassava yields 10 tonnes per hectare, but the new varieties can produce up to 40 tonnes per hectare with proper agronomy practices.

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