Dr. Wayne W. Hanna has been searching for it for nearly 20 years. Every year or two, he breeds new millet plants and combs the fields for one with the required characteristics. "We've searched thousands of plants to find the one we want," said Dr. Hanna, a research geneticist for the United States Department of Agriculture in Tifton, Ga.
So far, he has not found it. Nor has anyone else found what a small but growing number of pursuers describe as the holy grail of agriculture. But when they do find it, Dr. Hanna says, it will promise a "revolution" in world food production.
The goal is a plant that will reproduce asexually, so that its seeds will grow into exact genetic copies, or clones, of the parent. This process, called apomixis, occurs naturally in hundreds of plants, including dandelions, crab apples, citrus, blackberries and the grass used on many lawns.
In other cases, farmers can achieve asexual reproduction by grafting, as is done with grape vines, or by vegetative propagation, as when a piece of potato is planted and grows into a new plant. But the world's major food grains do not reproduce asexually. If they could, some scientists say, it would greatly simplify crop breeding. A high-yielding corn, wheat or rice plant could reproduce itself unchanged for generations.
"Once this occurs, the ramifications could well dwarf the green revolution in terms of its impact," said Dr. David M. Stelly, a professor of soil and crop sciences at Texas A&M University, who has dubbed this the "asexual revolution."
But apomixis could also represent a threat to the seed companies, changing the balance of power between the companies and farmers. It is thus being swept up in the worldwide controversy over agricultural biotechnology. Right now high yields are obtained using hybrids, which are crosses between two different varieties. But hybrids, which display a somewhat mysterious "hybrid vigor," take years of painstaking, costly breeding to develop. Moreover, because crops reproduce sexually, the children of hybrids vary in their characteristics and generally do not retain the high yield of the parent. So farmers cannot save the seed from one year's crop to plant the next, but must buy new seeds every year, providing seed companies with recurring income.
Apomixis would greatly simplify development of hybrids, putting them within reach of developing countries, which most need the higher food output but which now generally cannot afford it.
With apomictic hybrids, seed could be saved and planted the next year without loss of yield. And a farmer obtaining a few such seeds could reproduce and multiply them, just as it is possible to make numerous perfect copies of a software program.
"This is a way for local farmers to take control of their seeds," said Dr. Michael Freeling, a professor of genetics at the University of California at Berkeley. "It puts the seed companies out of business."
'Asexual revolution' would be a boon to the world's farmers.
Indeed, apomixis is being championed by some in the developing world as the antidote to the controversial "terminator" technology, an experimental method of making plants infertile so that farmers have to buy new seeds every year. "It's the challenger to the terminator technology," said Dr. Stephen L. Goldman, a professor of biology at the University of Toledo, who is working to create apomictic corn. "It has enormous political implications."
In fact, worried that a big seed company could patent apomixis technology and deny access to the rest of the world, apomixis researchers meeting in Bellagio, Italy, in 1998 issued a declaration calling for "broad and equitable access to plant biotechnologies, especially apomixis technology." Dr. Tony Cavalieri, director of research for Pioneer Hi-Bred International, the nation's largest seed company, played down the threat to seed companies. "Most of the people who buy our seeds are interested in the newest hybrids," he said. "They're not interested in planting the same hybrids for 20 years." Indeed, he and others said, apomixis could help seed companies by speeding up plant breeding.
Some experts worry that apomixis technology could lead to more uniformity in crops, which would make them more susceptible to being wiped out by a disease or pest. But others counter that because of the ease of creating hybrids with apomixis, crop variability could actually be increased. Until recently seed companies viewed apomixis as a distant and uncertain prospect, but now they are starting to take notice, in part because sophisticated gene-hunting technologies might finally allow scientists to understand how the process works.
"Now it looks more approachable," said Dr. Cavalieri of Pioneer. While not doing apomixis research on its own, his company is providing money and technology for Dr. Hanna's work in Georgia and for a project in Mexico to try to develop apomictic corn.
Novartis, the Swiss drug and seed company, the French government, and Groupe Limagrain, a French seed company, are also sponsors of the program in Mexico, which is based at the International Maize and Wheat Improvement Center.
There are different forms of apomixis and the same plant can exhibit both sexual and asexual reproduction. In sexual reproduction, the female egg and male sperm cell each contain half a set of chromosomes, so that when they combine, the embryo has a full set, half from the father and half from the mother.
With apomictic plants, the embryo, which is inside the seed, contains a full set of chromosomes from the mother. So far, scientists have tried to make apomictic crops mainly through conventional breeding. Dr. Hanna crossed pearl millet, a crop used mostly for cattle in the United States but grown for human food in Africa and India, with a wild relative that is naturally apomictic. (Although the wild relative does not need a partner to reproduce, its pollen can be used to fertilize a sexually reproducing plant.)
The plants formed by such a cross were half millet, half wild relative and some of them were apomictic. Dr. Hanna chose the apomictic ones and crossed them again with pearl millet, and again selected the apomictic ones. With each repeat of this process, the offspring become more like the crop and less like the wild relative -- except that they remain apomictic. That, at least, was the theory. But after eight generations, Dr. Hanna has found that the offspring so far do not produce enough seeds to make them suitable as a commercial crop.
Similar slow progress has occurred at the project in Mexico, where scientists started by crossing corn with tripsacum, a wild relative that was naturally apomictic. But after several generations, the offspring still had too many of the characteristics of the wild relative to make a viable crop.
The cross-breeding approach is based on the assumption that apomixis is controlled by a single gene or a group of genes that are inherited together. Dr. Yves Savidan, the director of the international maize and wheat center project, and Dr. Peggy Ozias-Akins, the gene scientist working with Dr. Hanna, say that inheritance patterns and gene mapping show this to be the case. But some other scientists believe apomixis is controlled by many genes on different chromosomes, which could explain why the cross breeding approach has not worked yet.
Dr. John G. Carman, a professor of plant genetics at Utah State University, is trying to achieve apomixis by crossing two plant varieties, neither of which is apomictic by itself. One of the plants develops its egg earlier in the process of flower bud development than the other. Dr. Carman hopes that the offspring of such a mating will get confusing signals about when to develop the egg, with the result that the plant will skip egg formation and produce an embryo with a full set of maternal chromosomes. He said he believed this was how apomicts evolved during the ice age, when great movements of ice and earth brought together plants from different latitudes with different development times.
Dr. Carman, who has had some limited success with this approach, has formed a company, F1 Technologies.
But some scientists say the best chance for success now lies in using modern gene-sequencing and gene-mapping techniques to find the gene or genes responsible for apomixis, and then transferring them to crops. Scientists in Australia, Switzerland and at Berkeley are using chemicals or radiation to induce mutations in arabidopsis, a model plant used in research. If a mutation causes the sexually producing plant to turn apomictic, the gene can be fished out since arabidopsis is having its genome sequenced. Dr. Robert L. Fischer, a professor of plant and microbial biology at Berkeley, has already found one gene that imparts a trait associated with apomixis.
Most scientists interviewed said it would take at least five years to produce apomictic crops and some said it could be more than 10. Still, hope springs eternal like the millet in Dr. Hanna's field. "It's been a lifelong quest," said Dr. Hanna, who next year will plant 10,000 to 15,000 new plants, the ninth generation of his back crosses. He will search again for specimens that are apomictic but otherwise enough like millet to become a commercial crop.
"It could be next year," he said. "It could be a plant in there."
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Last Updated on 4/25/00
By Karen Lutz Benbrook