ARIZONA DAILY STAR Otto Ross February 3, 2010

A UA research team has taken the first step toward saving a food source that hundreds of millions of people rely upon.

By unlocking the cassava plant genome, the team hopes to combat a disease that infects the edible roots of the plant.

Cassava typically grows 5 to 6 feet tall and has a canopy of green, star-shaped leaves. The plant's root, when boiled or dried, can be eaten and prepared in a variety of ways. Cassava's resistance to drought and its rapid growth make it an ideal crop for people who live in harsh conditions and can't afford other sources of food.

About 700 million people in parts of central and eastern Africa rely upon the plant's root as their major source of calories every day, said Steve Rounsley, principal investigator for the project and associate UA professor of plant sciences.

But a sudden outbreak of the brown streak virus, transmitted by whiteflies, is infecting crops, making the plant's roots inedible and threatening the lives of millions. Some leaders in East Africa have called this virus the biggest food-security threat to their countries, Rounsley said.

"The poorest of the poor rely on cassava as their major source of calories," Rounsley said. "People who eat cassava can pretty much only afford to eat cassava. It would be catastrophic if they lost their crop."

In early November, Rounsley and his team released what they're calling the first draft of the cassava genome. The team hopes the DNA blueprint will help African cassava growers stop the spread of brown streak.

Having a complete genome allows researchers - and potentially African growers - to more easily compare varieties of cassava, find differences and isolate specific traits.

Once a trait, such as virus resistance, is located in the genome, growers can quickly identify virus-resistant plants and cross-breed them with their local variety of cassava.

By cross-breeding, growers eventually can produce a cassava plant almost identical to their regional variety but enhanced with a specific trait, such as virus resistance.

Without a genome to reference, cassava farmers are forced to grow hundreds of plants, then infect their crop with the virus to identify the resistant plants.

But since resistance can't be detected until the plants are about 2 years old and it takes many generations of cross-breeding to make a considerable change, the process is extremely expensive and time-consuming.

"It's an enormous benchmark to have this genome sequence of the cassava plant," said Judith Brown, a UA professor of plant science. "It's absolutely fantastic. It's really going to open some doors for new information about managing these debilitating diseases and pests."

Claude Fauquet, whom Rounsley calls the father of cassava genomics, is a plant biologist at the Danforth Plant Science Center in Missouri and has dedicated 35 years to studying cassava. He said that unlocking the cassava genome is especially important because it isn't a theoretical discovery but a practical one.

"Organizations are putting money towards training cassava breeders to use these tools so that maybe in two or three years they can benefit from it. None of this would have happened if the sequence had not been done."

On the same day that the UA team released the full genome, it was offered a grant from the Bill and Melinda Gates Foundation for $1.3 million over the next three years.

The team will use the money to further refine the genome and identify "markers," or differences in varieties of cassava, which it will add to an online database, Rounsley said.

This database of genetic markers will not only help isolate virus resistance but aid other cassava projects, such as increasing the plant's nutritional content.

While Rounsley said it will take years before growers are producing virus-resistant plants, he's hopeful that the database will be the first step toward helping people who need it most.