Cassava, banana and plantain, staple foods for millions of the world's poorest people, are notoriously difficult to breed. But an international team of scientists aims to change that, using a revolutionary new approach to plant breeding developed at the University of California, Davis.

The project is supported by a grant of $1.2 million from the NSF-BREAD (Basic Research to Enable Agricultural Development) program, a joint initiative of the Bill & Melinda Gates Foundation and the National Science Foundation.

"These are very important food security crops, but they take a long time to reproduce and it's difficult to create new varieties," said Simon Chan, assistant professor of plant biology at UC Davis.

Recently Chan and the other team members -- Hernan Ceballos, of the International Center for Tropical Agriculture in Cali,  Colombia; Jim Lorenzen, from the International Institute of Tropical Agriculture in Tanzania; and Leena Tripathi of the International Institute for Tropical Agriculture in Nairobi, Kenya -- were invited, with other recipients of NSF-BREAD grants, to present their work to Bill Gates at the foundation's headquarters in Seattle.

"He was very interested in the science and had good questions for everyone," Chan said.

Most successful crop varieties are hybrids created by crossing two inbred varieties. While this is relatively easy to do in well-established annual crops like maize or wheat, it is much harder with slower-growing crops like cassava, banana and plantain. As a result, cassava, banana and plantain growers are currently forced to create new varieties by crossing two hybrid parents -- a highly unpredictable process.

New crop varieties allow farmers to cope with pests, disease, drought and other problems.

Working with the small laboratory plant Arabidopsis thaliana, Chan's lab recently discovered a method to create plant seeds that carry the DNA from only one of their parents, allowing breeders to immediately create a hybrid that "breeds true," dramatically cutting the time required to create new crops with traits such as disease- or drought-resistance.

"What's exciting is that what started with Arabidopsis is already jumping from a little plant to big crops," Ceballos said.

With the NSF-BREAD grant, the research team will develop Chan's technology for use with these major crop plants.

Skirting sterility

Cassava is a perennial plant grown as an annual crop. Farmers harvest the edible roots just before the rainy season, then take the stems and replant them for the next year. Cassava is drought resistant and particularly adapted to harsh, poor environments.

Because farmers replant the stems from year to year, the crop basically reproduces as a clone. To produce an improved hybrid through conventional methods could take hundreds of thousands of crosses over many decades, Ceballos said.

"We find good hybrids by chance, but we want to find them by design," he said.

Cultivated bananas and plantains (a starchy cousin of the banana that has to be cooked before eating) are practically sterile. Breeding new hybrids requires either using the occasional fertile seeds from domestic crops or seeds from wild bananas, which are a threatened resource, Lorenzen said.

Chan's technology could be used to make homozygous plants -- with identical sets of chromosomes -- that could be tested for new and useful traits, then used to breed new hybrids, Lorenzen said.

Propagating crop plants like cassava, banana and plantain as vegetative clones is a big disadvantage when it comes to storing and distributing the plants, Chan said. Seeds are much hardier and easier to store and ship than roots or stem cuttings. Seeds are also less susceptible to viruses, and not subject to the same quarantine rules as vegetable materials.

The ability to propagate these crops as seeds would be a "huge, huge advantage," Chan said.

The objective of the NSF-BREAD program, part of the NSF's Plant Genome Research Program, is to support innovative basic scientific research designed to address key constraints to agriculture in the developing world. The program is jointly funded by the Bill & Melinda Gates Foundation and the NSF, and grants are reviewed and awarded through the same processes as other NSF grants.