Scientists investigating ways of getting varieties resistant to Cassava Mosaic Virus (CMV) and Cassava Brown Streak Virus (CBVS) still have a way to go because the team is aiming at eradicating all the four types of viruses at a go.
The National Agricultural Crop Resources Research Institute Namulonge (NaCRRI) is currently conducting research using both the conventional and biotechnology methods on cassava.
Genetic improvementThe research which has been going on since 2005 is an initiative of the US-based
VIRCA is about developing transgenic virus resistant cassava in
The chief investigator, Dr Titus Alicai, says in 2005 the National Biosafety Committee gave his team permission to proceed with the research where they undertook to study the general behaviour of the virus before embarking into real research work.
Earlier, in the 1990s, efforts were undertaken to eradicate CMV, which was a major problem that time. However, in 2000, scientists discovered CBSV, which is a devastating disease resulting into poor yields since it causes rotting of the roots.
Control virusesThe two have since been identified having variants: Cassava Brown Streak Uganda Virus (CBSUV) which was first spotted in
Scientists at NaCRRI have come up with varieties that are tolerant to CMV as well as CBSV. These were bred using conventional means and are already released to farmers. One such variety is Nase14, which is farmer preferred.
However, the VIRCA project is aimed at developing cassava varieties that are resistant to the four viruses. But the scientists can only achieve this by first developing resistance to each virus independently.
Dr Alicai says they are currently breeding varieties which are resistant to CBSUV with plantlets at the field trial site in Namulonge. Once the team generates data from this trial, they will be able to stack resistance for the four viruses in the same plant.
ACMV and EACMS cause very devastating symptoms on the leaves thereby inducing dramatic loss in the yields but CBSV and CBSUV cause extremely damaging symptoms on the tubers rendering them inappropriate for consumption.
"The experiment we are conducting is important because for the first time it will demonstrate that it is possible to control one of the two viruses involved in CBSV and if successful we will generate data to help us know how to control both viruses and thereby control the disease altogether," he explains.Though the cassava viruses have been spreading rapidly in farmers' fields, this has been mainly caused by the white flies which feed and suck the sugar in the leaves thereby contracting the virus and transferring it to another plant.At the laboratory, the scientists identify a resistant gene from a cassava variety and transfer it to the preferred variety through gene silicing approach.
"What we do is transfer a piece of genetic information from the virus and copy it to the plant in the laboratory and allow it to grow on a DNA. This process makes the plant to produce molecules that will fight the virus," Dr Alicai says.
Food for millionsThe virus-resistant varieties the team is working on are TME204 and Ebwanatereka varieties, which are farmer preferred. It is estimated that these viruses are causing
Further estimates show that farmers especially in Mukono and Luweero districts are experiencing 100 per cent loss as a result of cassava brown streak epidemic.Cassava is food for over 600 million people globally, it has been grown by farmers in
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