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Danforth Center's disease-resistant cassava tuber, key to feeding Africa, cleared for final trial

Danforth Center's disease-resistant cassava tuber, key to feeding Africa, cleared for final trial


CREVE COEUR — A new disease-resistant crop variety, developed by the Donald Danforth Plant Science Center and a potential key to feeding large swaths of Africa, has been cleared for its final test, the center announced Wednesday.

Cassava, the starchy root of a tropical shrub, is a key food in sub-Saharan Africa but is threatened by cassava brown streak disease, which rots the tubers and can destroy entire fields.

“Often you can’t see it — the symptoms on the leaves can be very mild,” said Nigel Taylor, a Danforth Center scientist leading the project. “But when you dig up the storage roots there are big, brown lesions. It makes the roots inedible. You can’t feed them to animals. You can’t sell them — they’re ruined.”

Taylor’s team genetically engineered a disease-resistant variety of cassava as part of a project called Virus Resistant Cassava for Africa Plus and has been testing the variety in Kenya and Uganda.

The tests have been wildly successful: In experimental trials in more than 20 fields over multiple years, about 90% of the roots of standard plants rotted from the disease, he estimated. But only about 1% or less rotted among genetically modified plants.

“It is very, very dramatic,” Taylor said.

Until the mid-2000’s, the disease was not a major concern, and was “just kind of rumbling along in the background,” according to Taylor.

But in the past 15 years, he said, it rapidly spread across east and central Africa, and now threatens West African countries like Nigeria, where cassava is also a key crop. This impacts both subsistence farmers and farmers who sell cassava to industrial markets like the beer industry, Taylor said.

To develop a resistant variety, Taylor and his team used genetic modification technology called RNA-interference. They took little pieces of genetic information from the viruses and joined them with the cassava plant genome, a process that triggers naturally occurring defenses already present in the plant.

“It enables the plant to activate its defense mechanism before the pathogen is there,” Taylor said.

The Kenyan National Biosafety Authority cleared the disease-resistant cassava for release for national performance trials in Kenya. These trials will look at traits important to farmers, including performance against diseases, pest resistance, and yield.

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