Scientists have determined how to fortify the cassava plant, a staple root crop in many developing countries, with enough vitamins, minerals and protein to provide the poor and malnourished with a day's worth of nutrition in a single meal.
The researchers have further engineered the cassava plant so it can resist the crop's most damaging viral threats and are refining methods to reduce cyanogens, substances that yield poisonous cyanide if they are not properly removed from the food before consumption. The reduction of cyanogens also can shorten the time it takes to process the plant into food, which typically requires three to six days to complete.
Studies also are under way to extend the plant's shelf life so it can be stored or shipped.
The international team of scientists hopes to translate the greenhouse research into a product that can be field tested in at least two African nations by 2010. Funded by more than $12.1 million in grants from the Bill & Melinda Gates Foundation, the group of researchers is led by Richard Sayre, a professor of plant cellular and molecular biology at Ohio State University.
Sayre presented an update on the BioCassava Plus project June 30 at the American Society of Plant Biologists meeting in Mérida, Mexico.
"This is the most ambitious plant genetic engineering project ever attempted," Sayre said. "Some biofortification strategies have the objective of providing only a third of the daily adult nutrition requirements since consumers typically get the rest of their nutritional requirements from other foods in their diet. But global food prices have recently gone sky high, meaning that many of the poorest people are now eating just one meal a day, primarily their staple food.
"So what we're working on has become even more important in the last year than it was when we started, not just in regions where people are malnourished, but across developing countries where food has gotten so expensive that people can't afford the diverse diet that they're used to."
Cassava (Manihot esculenta) is the primary source of calories for an estimated 800 million people worldwide, including 250 million people in sub-Saharan Africa, the current focus of the Gates-funded project. But the plentiful crop has several drawbacks. It is composed almost entirely of carbohydrates so it does not provide complete nutrition.
"So what we're working on has become even more important in the last year than it was when we started, not just in regions where people are malnourished, but across developing countries where food has gotten so expensive that people can't afford the diverse diet that they're used to."
The roots can be banked in the ground for up to three years, providing food security, but the plant must undergo time-consuming processing immediately after harvest to remove compounds that generate cyanide. Unprocessed roots also deteriorate within 48 hours after harvest, limiting the food's shelf life. And a plant disease caused by the geminivirus reduces yields by 30 percent to 50 percent in many areas in sub-Saharan Africa, a major blow to farm productivity.
Sayre and colleagues from multiple institutions set out to tackle virtually all of cassava's problems to make the plant more nutritious and to increase the crop's revenue-producing potential for farmers.
Sayre reported that the research team has been able to address each of the plant's deficiencies in individual transgenic plants. The next step will be to combine some or all of the bioengineered traits into a single, farmer-preferred cultivar, with the goal of eventually developing cassava varieties that carry all of the improvements developed by the researchers.
"We've begun field trials in Puerto Rico to make sure the plants perform as well outside as they do in greenhouses, and we hope to start field trials in the target countries of Nigeria and Kenya by 2009," Sayre said.
The labs in the project have used a variety of techniques to improve on the model cassava plant used for the research. They used genes that facilitate mineral transport to produce a cassava root that accumulates more iron and zinc from the soil. To fortify the plants with a form of vitamin E and beta-carotene (also called pro-vitamin A because it converts to vitamin A in the body), the scientists introduced genes into the plant that increase terpenoid and carotenoid production, the precursors for pro-vitamin A and vitamin E. They achieved a 30-fold increase in pro-vitamin A, which is critical for human vision, bone and skin health, metabolism and immune function.