They Use Plant Genome Map To Increase Food Production In Crops
ITHACA, N.Y. -- With a burgeoning world population and fewer places to grow food, Cornell University scientists have begun to locate high-production genes from wild plants to put into domesticated, edible crop plants -- thus boosting food production worldwide, according to their report in the journal Science.
"We are fortunate to be living at a time when genetic modification holds much promise for improving crop performance," said Susan R. McCouch, Cornell assistant professor of plant breeding. "However, most of the advances in molecular genetics have been directed toward traits other than yield, largely because of the complexity of this trait." McCouch and Steven D. Tanksley, Cornell's Liberty Hyde Bailey Professor of Plant Breeding and Biometry, have co-authored the article on how they have learned to increase production of certain plants by using wild genes, "Seed Banks and Molecular Maps: Unlocking Genetic Potential from the Wild," in Science, (Aug. 22, 1997).
While examining wild rice and tomatoes, McCouch, Tanksley and their colleagues have systematically used molecular markers to map genes of rice and tomato plant varieties and looked for specific loci or genes -- known as the Quantitative Trait Locus, or QTL -- that would tend to boost production. Before the availability of molecular markers, breeders had no way of finding the genes from the wild species because there was no way to identify the functions of genes controlling complex (or quantitative) traits in any species.
The researchers have genetically mapped rice and made the information available through the rice genes database over the World Wide Web at http://probe.
The researchers started with domesticated rice, Oryza sativa. By combining genes from the wild variety with genes from domesticated rice, the researchers observed between a 15 percent and 17 percent improvement in grain yield. Using QTL analysis, they deduced that the yield improvement was the result of two production-boosting QTLs: simply named YLD1 and YLD2, coming from the wild rice, O. rufipogon.
Results from harvesting wild tomato QTLs were also dramatic. In extensive testing, tomato QTLs from the wild species Lycopersicon hirsutum outperformed the elite tomato variety by 48 percent for yield, 22 percent for soluble contents and 33 percent for fruit color. Tanksley said this research has been confirmed around the world under a variety of conditions, and fruit size has been increased in tomato lines by introduction of genes, identified through genetic mapping, from the tomato ancestor L. pimpinellifolium.
In tomato and rice plant varieties, the researchers sampled a variety of wild species available in seed repositories and found a high proportion -- almost a 50 percent increase -- of useful QTL alleles (mutated genes) that could boost plant production. "This underscores the point that exotic germplasm often contains genes that are capable of improving traits," Tanksley said.
Wild plant species of rice, considered one of the world's top staple crops, were domesticated about 10,000 years ago, during humanity's transition from nomadic hunter-gatherers to agrarians. "Considering that flowering plants [like rice and tomatoes] first evolved over 150 million years ago, crop plants as we know them have existed for the mere blink of an evolutionary eye," Tanksley said.
Modern plant breeding -- agricultural practices for the past 100 years -- might be a victim of its own success. While plant breeding techniques have been successful in developing high-yielding rice and tomato species, the process itself threatens the genetic base. New plant varieties are usually derived from crosses between close relatives, the researchers explained, and this results in a "genetic bottleneck" that can result in losing plant production and making plants more vulnerable to pests and disease.
Said McCouch: "Owing to the advent of molecular mapping and our ability to scan the genomes of wild species for new and useful genes, we may be now in a position to unlock the genetic potential of those germplasm resources."