Printer Friendly

Genetic fingerprinting helps sort out look-alikes.

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.

"Basically they're patterns of DNA that repeat themselves over and over again," she says. "We will use these markers to relate different plants within Brassica. Eventually we'll be able to tie these markers to certain traits, such as disease resistance, that curators want in their collections."

Researcher Sharon Bliek has begun similar preliminary work using Golden Delicious apple, in search of microsatellites that will provide genetic information about apples in general.

Apples are one of the biggest collections at Geneva, with about 3,500 accessions, including about 2,000 of the domestic apple, Malus x domestica. But curator Philip Forsline says genetic studies have shown that the apple collection needs greater genetic diversity--underscoring the need for exploration for wild varieties.

Forsline and several colleagues took such an exploration trip in September to the mountainous regions of Soviet Central Asia, thought to be the center of origin for the domestic apple. They went to Kazakhstan and Kyrgyzstan, now independent republics of the former Soviet Union located along the trade routes that ancient travelers followed to bring silk from China. On the way, they also brought apples that were growing on wild trees in the mountains. Apple trees still growing on those hillsides may contain genes for cold and drought tolerance, disease and insect resistance, and other traits that would bolster the Geneva collection.

"Genetic fingerprinting technology has helped us by giving us a more complete picture of the diversity in our collection and will assist with diversity studies of the wild apples we collected on the trip," Forsline says. "Because the trees and fruit look so similar, the only way you can determine their diversity is by examining their genetic makeup."

Once genetic diversity is identified, it becomes a matter of analyzing it to see what differences matter, says Warren Lamboy, who stores and analyzes the genetic data on a computer system. "For example, an apple that has bright red color, or resistance to apple scab disease--those genetic indicators are important."

Lamboy notes that much of the key genetic diversity is found in old varieties that have been farmed but haven't been bred into commercial cultivars. In a study of 14 types of Brassica--including cabbage, broccoli, cauliflower, and kale--the researchers found that there is very little genetic diversity in commercial cultivars.

"It's important to know that, because we want to maximize the diversity in what we keep in our collections," Lamboy says.

There's also the matter of economics, says Jim McFerson, the Brassicas curator who now heads the Plant Genetic Resources Unit. He points to the example of Golden Acre, an early-- maturing cabbage introduced into the United States around 1920. McFerson collected about 20 Golden Acre accessions from around the world and gave 14 of them to Kresovich and Win Phippen, a Cornell graduate student working for ARS at Geneva.

Their task: to establish and compare genetic markers in the Golden Acre plants--which all look virtually identical. "We've found that there is very little genetic diversity among them, based on DNA markers we've compared so far," Phippen says.

For a curator, that's important to know because it may affect which plants are are permanently maintained in a collection.

"It costs about $1,000 or more to regenerate seed for a given accession," McFerson estimates, "because of the carefully controlled pollination techniques that we must use. But if we've got 14 accessions that are essentially the same, it may not be necessary to regenerate all of them."

The resources and time taken to regenerate those plants could be used to do the same thing with other plants that have different, perhaps valuable genes. "The real issue for curators is how can we assemble the most genetic diversity with the least cost? Now the genetic identification technology will allow us to be more precise about each of the accessions that we keep."

Other cases where genetic identification has helped:

* Vetiver grass. This perennial, native to India, has been recommended for planting around the world to prevent soil erosion. The World Bank and U.S. Agency for International Development have been trying to determine the best varieties to recommend for planting, based on climate and other conditions. The scientists found that some varieties thought to be different were genetically identical, while others thought to be identical were actually different.

* Helicobacterpylori. Even bacterial look-alikes are being sorted out. While on a 1991-92 research fellowship at Washington University in St. Louis, Kresovich worked with university scientist Douglas Berg and others on a project to study genetic diversity among 64 isolates of this bacterium, now thought to be a cause of cancer, ulcers, and other gastric ailments.

The H, pylori strains were taken from veterans at Huntington, West Virginia, hospitals. Most of the patients had been diagnosed with chronic gastfitis. "It looks like the strains that are the biggest problem are of Asian origin--and the veterans who have them could have acquired them in Vietuam," Kresovich said. "Knowing the genetic diversity of the organism will be helpful in efforts to develop a vaccine against it."

Kresovich notes that all living organisms are defined largely by their DNA, whether they're bacteria, plants, or people. Along those lines, he's working with researchers at the Federal Bureau of Investigation's Forensic Research Laboratory at Quantico, Virginia, and with the Centers for Disease Control in Atlanta, Georgia. The FBI uses genetic fingerprinting to identify criminal suspects, while the CDC uses it to identify organisms that cause disease.

"Primarily, we're exchanging information to improve our fingerprinting methods," he says. "The techniques and goals are the same--whether it's a plant, a person, or a bacterium--to determine differences and similarities using DNA."

"The more you know about the germplasm, the better off you're going to be," Kresovich adds. "There is potentially a lot of redundancy in these collections. Each accession takes up space. Each one that's like another fills a spot on the ark that could have been used by a more valuable accession. "By Sean Adams, ARS.

Steve Kresovich is in the USDAARS Plant Genetic Resources Conservation Unit, Regional Plant Introduction Station, 1109 Experiment St., Griffin, Georgia 30223-1797; phone (404) 228-7207, fax (404) 229-3323.

Sharon Bliek, Phil Forsline, Warren Lamboy, Jim McFerson, and Arny Szewc-McFadden are in the USDAARS Plant Genetic Resources Unit, New York State Agricultural Experiment Station, Geneva, New York 14456; phone (315) 787-2244, fax (315) 787-2397.
COPYRIGHT 1993 U.S. Government Printing Office
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1993 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:plant genetics
Author:Adams, Sean
Publication:Agricultural Research
Date:Dec 1, 1993
Previous Article:Fighting the insect enemy in Somalia.
Next Article:Great-tasting peanuts? Try hairy!

Terms of use | Copyright © 2017 Farlex, Inc. | Feedback | For webmasters