Genetic fingerprinting helps sort out look-alikes - plant genetics

Agricultural Research, Dec, 1993 by Sean Adams

If Steve Kresovich were judging an Elvis look-alike contest, he probably wouldn't pay much attention to the contestants' clothes, hair, or jewelry--or even to their voices. He'd ask for a genetic fingerprint. No need to guess anymore. Not with biotechnology techniques that scientists can use to establish "fingerprints" from genetic material called DNA, the stuff of which living things are made.

Kresovich and his Agricultural Research Service colleagues are using these techniques to fingerprint plant genetic material called germplasm to determine how one plant is genetically different from another.

"Because so many plants look the same, you really can't be certain about their genetic diversity unless you have a way to identify their genes," says Kresovich. "As with the Elvis lookalike contestants, it's hard to tell them apart visuallly. But if you could compare their genes, there wouldn't be any doubt that they were different."

DNA fingerprints, scientists say, will one day be as common as the ink thumbprint. Criminal suspects are now being convicted based on a genetic fingerprint from their semen or blood---even from a piece of hair or a tinge nail--that matches one found on a victim. On the other hand, wrongly convicted criminals are being released from prison, freed by a genetic fingerprint that didn't match their own.

Researchers today are also mapping the human genome--discovering genes linked to certain key diseases such as cystic fibrosis, so that they can be detected and treated sooner. And they're identifying valuable plant genes that could mean enhanced resistance to diseases, insects, and other threats to the food supply.

For the last several years, Kresovich and colleagues have been assessing the genetic diversity of germplasm collections held by the Plant Genetic Resources Unit at Geneva, New York, by identifying molecular markers.

At the New York State Agricultural Experiment Station at Cornell University's Geneva campus, he oversaw the unit that maintains germplasm collections of apples, grapes, broccoli, cauliflower, clover, tomatoes, celery, onions, and other crop plants. In July, he became head of the ARS Plant Genetic Resources Conservation Unit at Griffin, Georgia, where researchers are conducting similar work on other germplasm. The Griffin collections include forage grasses and legumes, peanuts, peppers, sorghum, sweetpotatoes, and watermelons, among others.

The genetic information of plants and other living organisms is stored in DNA. Except for clones, no two plants are likely to have the same DNA sequences. The differences in genetic composition are what Kresovich and other geneticists call genetic diversity. This diversity is contained in germplasm, the living tissue from which new plants can be grown. Germplasm can be cuttings, seeds, or even cells for culturing into a new plant.

For a genetic resources collection to be valuable, it should have genetic diversity. Let's say a new disease threatened the winter tomato crop in California or Florida, prompting plant breeders to look for germplasm with genetic resistance to the disease.

If a tomato germplasm collection contained 100 samples--what curators call accessions--but 75 of them had virtually the same genetic makeup, chances are slim it would have the right genes. But if 75 of those 100 accessions had widely divergent genetic compositions, a breeder would be more likely to find one with a gene to thwart the disease threat.

One of the main purposes of genetic resources collections is to preserve genetic diversity, as an insurance policy against future threats. "It relates to the story of Noah and the ark," Kresovich says. "If you've got 100 varieties of tomatoes and you can only save a few from the flood, which do you pick? How do you know you're saving the most useful ones?"

To make that decision, it would help to know something about each plant's DNA and the genes that are part of that genetic material. Today, it's not a flood of water threatening plants, but waves of development that threaten wild plants that contain the genetic diversity breeders seek.

Traditionally, curators have gained insight into a plant's genetic makeup by examining its overall form--leaves and fruit, for example--and other factors, such as how it responds to drought, disease, or insects. But looks can be deceiving.

"Curators need to know as much as possible about the genetic makeup and structure of their collections, especially where the strengths and weaknesses are," he says. 'That's the data we're beginning to provide to them."

Geneva houses the national germplasm collection for vegetables in the genus Brassica, which includes cabbage, kale, broccoli, cauliflower, and other vegetables that are valuable dietary sources of beta carotene, vitamin C, calcium, phosphorus, and other nutrients. There are 33 species and 2,000 accessions of Brassica at Geneva.

Amy Szewc-McFadden has begun to find markers in an oilseed rape cultivar called Jet Neuf, which was chosen to represent the Brassica genus. The markers she's using are called microsatellites.