Promises Made and Kept: an Interview with Dr. Marilyn Warburton

We are pleased to bring you the first in our new series of interviews with CGIAR Scientists, exploring the life and work of Dr. Marilyn Warburton, Molecular Geneticist at CIMMYT, and recipient of the CGIAR Promising Young Scientist Award in 2002. In this article, we explore the work Dr. Warburton has undertaken on her journey from Tucson to El Batan, and her hopes for the future.

Officially recognized 4 years ago as a "promising young scientist," Marilyn Warburton still works to help ensure that crop breeding makes good on its promise to alleviate poverty and hunger

Receiving the Promising Young Scientist Award for her work on crop genetic diversity had an effect on Marilyn Warburton that was … well, diverse.

"It was intimidating," confesses the American molecular geneticist at the International Maize and Wheat Improvement Center (CIMMYT), who was 34 when she received the award in 2002. "I felt that I had to live up to that promise. At the same time, it was hugely flattering - verification that people thought what I was doing was important. I guess you could say it was motivating."

Dr. Warburton's list of recent papers in peer-reviewed publications certainly indicates a motivated scientist. She had five published in 2004 and seven in 2005. Less than 2 months into 2006, she had three papers published and another two in press.

"I wasn't first author on all of them," she hastens to add. "But I was for two of them each year. I think that's a good target."

The CGIAR Promising Young Scientist Award recognized Dr. Warburton for developing a fast, inexpensive way to accurately analyze genetic diversity in maize and wheat using molecular characterization. This development helps plant breeders use that diversity to improve cultivars' pest and disease resistance, boosting the value and reliability of harvests in normal years and promising to help make catastrophic crop failure a thing of the past.

The danger of depending on crops with narrow genetic bases was dramatically demonstrated in the Great Irish Famine of 1845-47, when an epidemic of potato late blight wiped out the island's entire potato crop. Nearly 3 million people, or a third of the population, either starved or emigrated. Yet the lesson went largely unlearned, and the genetic bases of crops continued to narrow.

"What really focused crop scientists' attention on the problem was the southern corn leaf blight that hit the US in 1970," relates Dr. Warburton. "A large part of the US maize crop was susceptible to this one disease."

Landraces, or early forms of crop species, typically have less genetic diversity than their wild cousins. One reason is the genetic bottleneck caused by descent from only a few individual plants whose spontaneous hybridization or mutation made them attractive to farmers. Farmer selection for agronomic traits further reduces diversity, and this process accelerated in the early years of modern crop improvement.

The diversity of wheat improved by CIMMYT dropped well below that of wheat landraces in the middle of the 20th century, then held steady as CIMMYT began to use more diverse breeding materials from around the world. The last decade has seen a dramatic return of CIMMYT varieties' genetic diversity to a level comparable with that of landraces. This has come about through the contributions of so-called synthetic wheat. Molecular breeders create these new wheat types by crossing two wild relatives of wheat to create the tetraploid (doubled) genome of durum wheat, adding a third wild species to create the hexaploid (tripled) genome of bread wheat. Synthesized wheat lines cross easily with popular cultivars, bringing to them a wealth of newly harnessed genetic diversity.

"Basically breeders reenact in the lab the crosses that originally created wheat, which happened only once in nature," Dr. Warburton explains. "Each time they synthesize wheat in the lab, they greatly expand the gene pool."

Citing the stem rust fungus that emerged in Uganda in 1999 as the worst threat facing wheat farmers today, the molecular geneticist is hopeful that breeding programs now have materials diverse enough to create and deploy resistant wheat cultivars in time to stop the epidemic.

"Like other advances, restoring diversity without sacrificing agronomic traits owes everything to teams of scientists working together," she stresses. "Nothing happens in isolation. Progress depends on everyone contributing."

Cataloging wheat genetic diversity contributes by telling breeders where to find useful diversity, despite complications arising from the unwieldy size of the wheat genome. Maize poses a different problem, as it outcrosses to create heterogeneous populations. Determining the relatedness of two populations depends on first defining an average for each. Dr. Warburton and her colleagues have simplified the process.

"We randomly choose 15 individuals from a given population of maize and treat it as a single sample," she explains. "In theory, those 15 individuals can contain 30 alleles of each gene, two from each individual. The computer program we wrote at CIMMYT allows us determine the frequencies of the various alleles in the sample and deconstruct it to calculate how many individuals have each allele. This defines the population. Our method lets us look at hundreds of populations cost effectively."

Dr. Warburton and her colleagues nevertheless have their work cut out for them categorizing the huge wheat and maize germplasm collection at CIMMYT. Progress so far has polished the Center's reputation for cataloging germplasm, attracting eager collaborators. Dr. Warburton recently worked with the Seed and Plant Improvement Institute of Iran to determine the relationships among early maturing Iranian lines of inbred maize, for which pedigree information is usually lacking, despite the crop's relatively recent introduction into the country.

Another recent project explored the genetic diversity and relationships of wheat landraces in Oman, where the crop has been grown for more than 3,000 years. Results suggest that wheat populations that were once widespread in India, Iran and Pakistan have been conserved in the remote mountain oases of this isolated land on the eastern tip of Arabia.

Raised in the similarly arid but less exotic environs of Tucson, Arizona, Marilyn Louise Warburton kept lots of pets as a child and was active in 4-H, an agriculture- and outdoors-oriented youth organization. Science was her favorite school subject, so naturally she started out at the University of Arizona majoring in veterinary science.

"After my first undergraduate genetics class, I knew this was what I wanted to do," she recalls. "But I switched to plants when my advisor told me there were too many vets."

Having earned her BS and MS in Tucson, she went to the University of California at Davis for a PhD in plant genetics. She continued at Davis as a post-doc fine-mapping tomatoes, moved to Illinois to work on crop diversity at the National Soybean Germplasm Repository, and turned to maize and wheat on arrival at CIMMYT's Applied Biotechnology Center in 1998.

"It isn't difficult to switch crops," she notes, "but now I'm going into a different area of research."

With a fellowship commemorating CGIAR cofounder Frosty Hill, Dr. Warburton is currently on sabbatical at Cornell University, expanding her range of expertise to include association mapping. "Many of the tools are the same as in what I was doing, but the analysis is different," she observes. "Association mapping looks at diversity that causes specific traits and asks why some varieties are better at certain things than other varieties."

A separate challenge facing Dr. Warburton is how to balance a heavy workload with the demands of parenthood. Now separated from her husband, she brought her two sons, aged 2 and 6, to Cornell for her year-long sabbatical. However, during most of her travels away from CIMMYT's research campus near Mexico City, she depends on her in-laws, who live nearby, to keep the kids.

"You need strong family support in this line of work, because you travel so much," she says. "Without them, I don't know how I'd manage."