Scientists develop new Nigerian cassava

By Abdallah el-Kurebe with Agency reports
Plant scientists at ETH Zurich have developed a new Nigerian cassava preferred by consumers and farmers that is resistant to the two major virus diseases in Africa and now billed to test the cassavas resistant on the African soil.

According to a release, researchers at ETH Zurich led by a Professor of Plant Biotechnology, Wilhelm Gruissem and his senior scientist, Dr. Hervé Vanderschuren, “Gene technology has been used to develop a new cassava variety that is resistant to the feared cassava brown streak virus. The virus infects the edible starchy roots and turns them brown, which makes the roots unpalatable for consumers,” they stated.

The researchers used the Nigerian TME 7 cassava variety, also known as “Oko-iyawo,” that is naturally resistant to cassava mosaic disease, which is caused by another virus that is severely impacting cassava production all of Africa.

The virus said to have originated from East Africa, is threatening to spread to Central and West Africa thereby becoming threat to cassava, which is one of the most important crops in tropical countries of Sub-Saharan Africa.

Explaining that it is difficult to control the whitefly, even if African farmers could afford to buy insecticides, Prof. Gruissem said: “This resistance is not changed by the new resistance to the brown streak virus. The brown streak virus is most likely transmitted by the same silverleaf whitefly (Bemisia tabaci) that also spreads cassava mosaic disease. This tiny insect sucks on plant juices, and in doing so transmits the viruses into the cassava plant. The silverleaf whitefly population has hugely increased in recent decades.”

“This is posing a greater threat than ever to the growth of cassava. This is why it is much more efficient and more environmentally friendly to protect cassava against viruses using genetic modification,” he emphasized.

According to Gruissem, in order to make cassava resistant to the brown streak virus, “the researchers modified the genetic make-up of one variety of cassava to produce small interfering RNA molecules (siRNA).

The plant produces the siRNA naturally after virus infection, but the researchers have now tricked cassava to produce the siRNA in all of its parts before the virus can infect it.

As soon as the virus attacks the plant, the short siRNA stops the virus by attaching to the genome of the virus that is also made of RNA,” the statement read adding, “This prevents the virus from multiplying and spreading throughout the plant.”

Glasshouse trials, the statement furthered, have shown that the new gene producing the siRNA protects cassava effectively from the virus.

“Even several months after infection of the transgenic cassava plants with the brown streak virus, the scientists did not find any evidence that the virus could multiply. The production of the siRNA does not affect cassava itself. It grows normally and produces healthy roots.”

The researchers targeted a part of the virus RNA genome that has been highly conserved during evolution with very rare changes, “making it more difficult for the virus to adapt to the siRNA-mediated immunity.”

The ETH Zurich scientists chose the Nigerian TME 7 from dozens of potential varieties because it is popular among consumers and farmers and has the best prerequisites for successful cultivation.

As the next step, Prof. Gruissem and Dr. Vanderschuren with some colleagues in Africa, plan to test if the improved cassava variety in the field remains resistant to both viruses under natural conditions.

The German-based Fiat Panis Foundation, which has supported cassava research at ETH, has already reserved funds for field experiments and ETH Zurich scientists are also actively engaged in transferring the technology to interested research institutes in Africa to develop virus resistance in local varieties preferred by consumers in their countries.