The search for better tomatoes.
Gene Research Finds New Use in Agricultural Breeding
By ANDREW POLLACK
NY Times March 7, 2001
nytimes.com
As the controversy surrounding
genetically modified foods intensifies,
scientists are trying to use the rapidly
growing knowledge about genes to enhance
conventional breeding of crops and
livestock rather than implant genes from one
species into another.
Many say such an approach is less likely to
arouse the public objections that have been
raised by the development of genetically
altered plants and animals.
The enhanced breeding approach involves testing which genes are in a plant or
animal, allowing researchers to select more easily which ones to cross. That can
shave years off the breeding of a new variety.
* * *
Compared with genetic engineering, this enhanced breeding has technical
advantages and disadvantages. But its biggest advantage is political. Many
opponents of bioengineered foods do not object to the technique because it avoids
artificially transferring genes between organisms. It is that transfer that opponents
say is unnatural and poses risks to human health and the environment.
Indeed, some opponents of genetically altered plants and animals even champion
the approach as a way for society and companies to reap some of the benefits of
genetic science and avoid the risks.
"I think that's where the future is, to upgrade classical breeding," said Jeremy
Rifkin, a prominent critic of the biotechnology industry. "Classical breeders and
geneticists can use the genome but not do gene splicing." Mr. Rifkin calls this
approach the soft path, and says better understanding of genes could even be used
to improve organic farming.
* * *
[Etc. etc. Companies mentioned include: Monsanto .... Pioneer Hi-Bred International (a unit of DuPont).... Mendel Biotechnology, a plant genetics company in Hayward, Calif ...... Syngenta (formed by the merger of the agricultural businesses of Novartis and AstraZeneca) .... AniGenics (a start- up in Concord, Mass.)....
* * *
Usually, scientists do not test for the genes themselves, since many of the genes are
still not known. Instead, they look for markers along the chromosome that are near
the gene and therefore tend to travel with the gene from one generation to the next.
The advantage of this technique is that the markers can be used even if the
breeders have not identified the gene. Genetic engineering can be done only if the
gene is known and isolated.
It is also possible to use markers to follow numerous traits through the breeding
process. Genetic engineering is at present limited to transferring only one or a few
genes. Yet many traits, like the yield of a crop, are governed by multiple genes.
But marker-assisted selection can be extremely difficult and has not lived up to the
expectations scientists had when the technique was first developed in the late
1980's, said Nevin D. Young, professor of plant pathology and biology at the
University of Minnesota. "Traditional breeding is like a dice-rolling experiment," he
said. "Markers are like loaded dice, but they're hardly precise surgical
instruments."
It can take years to find the associations between markers and traits, and
sometimes links cannot be found at all, he said. It also now costs about $1 to test
one marker in one plant, which makes it very expensive to test numerous genes in
thousands of plants. Still the costs of such genetic analysis are expected to drop
rapidly with the advancement of new DNA testing methods that are also being
developed for medical diagnosis.
One of the biggest opportunities presented by marker-assisted selection is to
improve the harnessing of wild relatives of crops. Human beings domesticated
plants by selecting for obvious traits, like bigger fruit. But over time, the genetic
variation in commercial crops has become limited, so when breeders cross these
crops, the possible outcomes are also limited.
"We've left behind in this process a huge reservoir of natural variation," said Steven
D. Tanksley, professor of plant breeding and plant biology at Cornell. All the
commercially grown tomatoes in the world, from the tiniest cherry tomato to the
beefiest beefsteak, have less genetic variation than the wild tomatoes in a single
valley in Peru, he said.
Breeders have tried to cross wild relatives with commercial crops but with limited
success. One problem, Dr. Tanksley said, is knowing which wild plants to pick.
Wild tomatoes often are small and green and taste bad. Someone just looking at
them would not think of using them in breeding.
But even small, green tomatoes can contain some genes for redness and large fruit.
The marker studies allow these genes to be found. "The markers allow you to scan
through the whole genome," he said. "You can pick out the flavor genes away from
the yucky gene."
Indeed, Dr. Tanksley has crossed wild green tomatoes with commercial red ones
and produced even redder ones. And he crossed small wild tomatoes with big
commercial ones and got even bigger ones.
Robert Goodman, a professor of plant pathology at the University of Wisconsin,
said there was still a risk that marker-assisted breeding could run into the same
opposition as transgenic crops because people might fail to make any distinction.
But if that does not happen, he said, the breeding approach could provide a way
out of the contentious debate.
"Maybe in five to eight years we'll look back on this argument over transgenics and
say, `How arcane,' " said Dr. Goodman, who once headed research at Calgene,
the company that marketed the first genetically modified crop, a tomato. "Not
because it became unpopular but simply because it got bypassed by the advances
made by breeding powered by genomics." |
