How sweet it can be

Agricultural Research, April, 2004 by Don Comis

J. Mitchell McGrath may not seem the man to be cast in the role of a revolutionary. But he is part of a new guard of younger geneticists at ARS who are leading a genetic revolution in the sugar beet breeding industry. It began 10 years ago, according to Thomas K. Schwartz, executive vice president of the Beet Sugar Development Foundation of Denver, Colorado.

Schwartz says that this new guard brings the tools of molecular biology to sugar beet breeding for the first time--without necessarily using genetic engineering--allowing a look at how a sugar beet grows, down to the level of gene molecules. He cites McGrath, in ARS's Sugar Beet and Bean Research Unit at East Lansing, Michigan; Leonard W. Panella at Fort Collins, Colorado; and John Weiland at Fargo, North Dakota, as examples of scientists ushering in an era of faster, gene-based sugar beet breeding.

Under a MOU (memorandum of understanding) with USDA, first signed in the 1940s, the foundation provides germplasm, research assistance, and funding for these and a handful of other ARS geneticists from Maryland to California who are mapping the sugar beet genome. The group is one of just a few in the world working on the sugar beet genome and the only public breeding group in the United States doing so. ARS shares all its data publicly.

Though half of America's sweet tooth Cravings--and a third of the world's--are satisfied by beet sugar, Schwartz says the industry is still considered a small one--a minor specialty crop. There are only five small sugar beet breeding companies in the world, all overseas, and the foundation represents all but one of them.

USDA's Long-Term Agreement With Industry

The foundation acts as a research arm and umbrella organization for its member companies. The MOU that's evolved over the years charges ARS with developing basic germplasm lines and releasing them to the foundation, which distributes them to members.

"Our companies are best suited for commercial development," Schwartz says. "They're not suited for the type of genetic program McGrath and his colleagues around the country are working on. That's very specific, and expensive, research." It recently yielded about 20,000 sugar beet gene indicator tags--ESTs(expressed sequence tags)--which represent some, but not all, of the 30,000 genes thought to make up the functional part of the genome.

The latest project funded under the MOU calls for screening the sugar beet genome with another new tool, a BAC (bacterial artificial chromosome) library. McGrath explains that a BAC library uses safe strains of Escherichia coli bacteria to store sugar beet DNA. These sequences are then either screened with genetic markers or compared with sequences of known genes to connect them with possible traits. The same thing is done with ESTs.

McGrath began with sugar beet DNA he prepared with Weiland and worked with a contract firm to prepare and package the library. Each clone in the library of 38,400 cloned bacteria stores a different DNA sequence from the beet's genome.

"We chop up sugar beet DNA and connect segments to bacterial plasmids that carry the DNA into E. coli bacteria," McGrath says. Schwartz explains that member seed companies can then either buy cloned copies of the living bacterial library or DNA samples on filters, as two have already done, or they can rely on McGrath or the contract firm to compare their germplasm's DNA sequences with those in the library to identify traits--or at least chromosome location--associated with each DNA sequence.

"This is an important first step to create order in these early days of sugar beet genome mapping," says McGrath. "We don't have a common language for any of the beet's nine chromosomes."

But Will It Sprout?

Schwartz says that seedling emergence is one of the most important traits to sugar beet growers everywhere. At an industry meeting in 1996, Schwartz saw McGrath bombarded with requests for help on emergence. As one grower put it, "If we don't get it out of the ground, it's no good to us."

"McGrath put his nose to the grindstone," Schwartz says, "and quickly came back with a simple test for the emergence trait, which he gave to the foundation, and two possible genetic markers for seedling emergence and vigor. His test for emergence has already led to commercial varieties with higher germination rates." He developed it by growing seeds in pure water--comparable to the multiple stresses seeds encounter in the field.

His possible genetic markers promise to help identify and locate the emergence genes on the chromosomes, one of the goals of the genome project.

Paul Pfenninger, vice president of agriculture for the Monitor Sugar Company in Bay City, Michigan, agrees that farmers' greatest concerns are that the seed sprout and that the seedling survive its first month--what's called "seedling vigor."

"One unique thing about sugar beets is that only about half of the seeds actually sprout," says Pfenninger. "Those tiny seedlings are exposed to everything from soil crusting to insects to disease to strong winds. A 40-mile-per-hour wind in that first month or so could wipe out a third of your seedlings. They're too delicate to withstand the sandblasting caused by strong winds carrying dirt particles."