June 15, 1995

Revolutionary Method Using Genetic "Maps and Markers" Promises to Increase Rice Yields by 15-20 Percent in Hungry South Asia

Method Would Deploy Untapped Potential of World's Plant Genetic Diversity; Cornell Scientist Says Method Is Akin to Providing Plant Breeders with X-Ray Vision

WASHINGTON, D.C., A team of scientists with Cornell University and China's Hunan Hybrid Rice Research Center are systematically harvesting high-yielding plant genes using molecular maps and markers to boost the yields of the world's most important food crop. The method promises to increase rice yields by 15-20 percent over a four- to five-year period, announced the scientists today at an international conference on agriculture and the environment. The method could sustain incremental yield increases in rice of 3-5 percent per year over the next 15-25 years, the scientists said. The scientists also hope to apply the same method to other major food staples, including wheat, maize, and beans.

How South Asia home to half of the world's poor will feed itself to the year 2020 and beyond remains a serious question. Rice yield growth rates have been stagnating in this region, and the population is expected to increase from about 1 billion in 1990 to almost 2 billion in 2020. Food deficits are likely to triple by the year 2020.

"It is essential that farmers boost crop yields in South Asia in the coming years," said Susan McCouch, assistant professor at Cornell University's College of Agriculture and Life Sciences, in a presentation to the international conference, A 2020 Vision for Food, Agriculture, and the Environment. The conference was cosponsored by the International Food Policy Research Institute (IFPRI), a Washington, D.C.-based nonprofit research organization, and the National Geographic Society. "In South Asia, including Bangladesh, India, Nepal, Pakistan, and Sri Lanka, there will be about 75 million malnourished children in the year 2020. Our approach for increasing rice yields, combined with the International Rice Research Institute's `super' rice plant, hold the key to feeding South Asia."

The use of molecular maps and markers to identify and deploy high-yielding genes in rice and other crops is a dramatic departure from traditional plant breeding methods. In traditional plant breeding, breeders first identify parents that express desirable traits and then cross them in order to combine the best features of each parent in the offspring. The Cornell/Hunan team, however, uses molecular maps and markers to identify important yield-enhancing genes that are not apparent in low-yielding plants.

"What we are doing turns past plant breeding logic on its head," said McCouch. "Just as two brown-eyed parents can have a blue-eyed baby, two average-yielding crops can create a high-yielding plant. In both cases, the offspring express genes that were hidden in the parents. With molecular maps and markers, we now have a kind of X-ray vision that can detect high-yielding genes and bring them together in varieties that will outperform any that exist today. We can `see' inside the rice genome itself, and we are finding genes that were completely hidden to plant breeders in the past."

The Cornell/Hunan team is seeking to make nonhybrid, or "inbred," rice plants that give the same high yields as China's powerful hybrid rice varieties. China's hybrid rice, which was created in the 1970s, increased rice yields significantly throughout the country and now accounts for nearly half of the production in China's rice-growing area.

"When you cross two genetically different, unrelated lines of plants, you often see vigor and performance that are better than in either of the two parents," said McCouch. "This is known as `heterosis' or `hybrid vigor.' This is the basis for the success of hybrid rice and hybrid maize. Chinese hybrid rice is created with two good-, but not excellent-yielding varieties that together create plants with huge yields."

However, an inbred rice plant would be a far more efficient method of boosting crop yields across South Asia because farmers could save seeds from year to year. Hybrid seeds must be recreated each year. In China, the government issues new hybrid rice seeds to farmers annually. "Hybrid rice is not financially feasible in most of South Asia today," said McCouch. "But the yield potential of hybrid rice is urgently needed. That's why we are trying to duplicate the yield potential of China's hybrid rice in an inbred rice plant. We are seeking to identify the yield-enhancing genes from hybrid rice, in addition to harvesting high-yielding genes from wild relatives of rice that have never before been cultivated."

A team of researchers led by Steven Tanksley, professor at Cornell University's College of Agriculture and Life Sciences, pioneered the use of molecular maps and markers to identify high-yielding genes in tomatoes. The team is nearing success in achieving super, high-yielding tomato plants whose yield surpasses that of all other tomatoes currently on the market. "One of the most exciting aspects of Tanksley's groundbreaking work in tomato is that the method used can be applied to rice and other major food crops of the world," said McCouch.

The technology will enable breeders and scientists to unlock the untapped potential of thousands of plant varieties that have been preserved for safekeeping in gene banks around the world. "We estimate that 75 percent of the genetic variation in rice has not been captured in currently cultivated rice plants," said McCouch. "Plant breeding has already mined most of the yield potential in `elite' rice varieties domesticated rice has reached a yield plateau. But there is an enormous opportunity for more high-yielding potential that, until now, we have not been able to exploit. The genes we seek have not been obvious in the behavior of plants."

With the molecular markers and statistical tools, the research team is systematically returning to populations of wild species and identifying novel, yield-enhancing genes that lie buried in this unexploited germplasm. The molecular maps provide a way for the team to rapidly determine the location of the genes along the chromosomes and their effects on plant performance. The team then augments the performance of domesticated varieties with genes from wild species. "The positive genes we harvest from wild and unadapted germplasm will be completely new genes with which breeders have never worked before," said McCouch. "These new genes will also increase the genetic diversity of cultivated rice and enhance the rice gene pool."

According to McCouch, new genes tend to invigorate germplasm populations. "Genetics is an interaction of all kinds of genes. There is an infinite potential for doing better as long as the genetic pool remains extremely varied. Our program seeks to unlock this potential."

And this research has great potential to do more than help create a single plant, says McCouch. "There is so much genetic variation out there that we believe we can harvest one or two yield-enhancing genes from almost any wild plant, thereby creating numerous varieties of new, high-yielding cultivars."

The work by the Cornell/Hunan team also has wide implications for other crops because the use of molecular maps and markers to harvest high-yielding genes can be applied to other food staples. "We will be able to exploit the potential of our global gene banks for numerous crops around the world," said McCouch.

Cornell University's College of Agriculture and Life Sciences seeks to discover and disseminate knowledge for the purpose of advancing agriculture, food systems and nutrition, biological sciences, environmental quality, and community and rural development throughout New York State, the nation, and the world.

The Hunan Hybrid Rice Research Center was founded by the Chinese government in 1984, the tenth anniversary of the commercial success of hybrid rice in China. Currently, the center has more than 80 research scientists and more than 200 lab and field technicians. It is the only public institution in the world whose efforts are focused on all aspects of research on hybrid rice.