GAINESVILLE, Fla. — Science is trying to build a better supermarket tomato.
Tomato plants grow from genetically modified tomato leaves.
David Manning for The New York Times
Harry J. Klee and his team are identifying genes
crucial to tomato flavor. Once crucial genes are identified, Dr. Klee’s
team uses traditional techniques of cross-pollination to produce a plant
with those genes.
At a laboratory here at the University of Florida’s Institute for Plant Innovation,
researchers chop tomatoes from nearby greenhouses and plop them into
glass tubes to extract flavor compounds — the essence of tomato, so to
speak. These flavor compounds are identified and quantified by machine.
People taste and rate the hybrid tomatoes grown in the university’s
fields.
“I’m 98 percent confident we can make a tomato that tastes substantially
better,” said Harry J. Klee, a professor of horticultural sciences. He
hopes that the fruits of his labor will be available to commercial
growers within four or five years and in supermarkets a couple of years
after that. He thinks he can make seeds for better tomatoes available to
home gardeners even sooner, within a year or two.
The insipid-tomato problem is well known both to salad lovers and scientists. For example, a gene mutation
that tomato breeders love because it turns the fruit a luscious red
also happens to make it blander. Refrigeration, transportation and other
factors also take their toll. Over the decades, the average tomato has
become not only less tasty but less nutritious.
Enter Dr. Klee, who helped found the Institute for Plant Innovation a
decade ago and has been in a quest for a more flavorful and nutritious
mass-market tomato ever since.
It is easy to find a better tasting and more nutritious tomato.
Go to a
farmer’s market or grow one in the backyard. It is also easy to breed a
plant that produces something tastier than a supermarket tomato — cross a
sweet heirloom with the supermarket variety. In the greenhouse, Dr.
Klee pulls one such hybrid tomato off a vine, and it does taste sweeter.
But a hybrid also loses some of the qualities highly valued by
commercial growers — it is not as fecund, not as resistant to disease,
not as easily grown, not as pretty.
As growers are paid by the pound, a better-tasting but less productive
tomato holds little economic appeal, and thus was the supermarket tomato
doomed to blandness.
Dr. Klee’s goal is to tweak the tomato DNA — through traditional
breeding, not genetic engineering — to add desired flavors while not
compromising the traits needed for it to thrive commercially. “I figure
that with approximately five key genes we could very significantly
improve flavor,” he said. He said three genes that control the
production of key flavor compounds have already been located. The next
step is to identify versions of the genes that lead the tomato plant to
produce more of them.
The chemistry of tomato flavor has three primary components: sugars,
acids and what are known as volatile chemicals — the flavor compounds
that waft into the air carrying the fruit’s aroma. There are more than
400 volatiles in a tomato, and Dr. Klee and his collaborators set out to
first determine which ones are the most important in making a tasty
tomato.
This involved grinding up a lot of tomatoes, looking at what was in
them, and asking a lot of people to taste them (unpulverized), gathering
comments like “a bland firm watermelon,” “soft and sloppy,” and “Sweet!
Finally a sample with some sweetness.”
From there, Dr. Klee and his collaborators, who include Linda Bartoshuk, director of human research at the university’s Center for Smell and Taste,
used statistics to correlate people’s preferences with the presence, or
absence, of particular flavor compounds, to devise a chemical recipe
for the ideal tomato.
The supermarket tomato — even when grown with care and picked ripe — did
not excel. “The best it will do is middle-of-the-pack,” Dr. Klee said.
Cherry Roma tomatoes were at the top of the charts, followed by heirloom
varieties like Matina, Ailsa Craig and Bloody Butcher. Other heirlooms
like Marmande and Oaxacan Pink ranked at the bottom, below the
supermarket tomatoes, though perhaps these particular types just do not
grow well in Florida.
The taste analysis produced several surprises. Some compounds, abundant
in many tomato varieties and thus thought to be major contributors to
flavor, turned out to be irrelevant, while others, in scant quantities,
had major influences. With the new knowledge, “you can’t help but get a
better tomato,” Dr. Bartoshuk said.
The most important attribute was sweetness. The sweeter the tomato, the
higher the rating. The biggest surprise, though, was that it was not
just sugar that made a tomato sweet. Some of the flavor compounds
enhanced the perception of sweetness.
That is the key to Dr. Klee’s plans. Tomato breeders have already tried
to maximize sugar, but the plants are bred to produce a lot of big
tomatoes all at once, and then do not have energy and sunlight through
photosynthesis to make enough sugar to go around.
The sweetness-enhancing compounds, however, are present in much smaller
quantities, so getting a plant to produce more of those is a much more
achievable goal, Dr. Klee said. (The compounds also offer promise for
sweetening other foods without adding the calories of sugar.)
“His work is really groundbreaking,” said James Giovannoni, a professor of plant biology at Cornell who studies the ripening of fruit and was one of the leaders in the sequencing of the tomato genome published last year.
He said Dr. Klee has been deciphering the molecular machineries in
tomatoes that produce the flavor compounds, and that is not an easy
task. “One, there is a lot of them,” Dr. Giovannoni said, “and two, a
lot of them are really not understood, how some of these produce these
compounds hasn’t been known.”
Modern genetic engineering has provided tools to study that, and
tomatoes are one of the most common plants that plant geneticists study,
much in the same way that animal geneticists focus on mice, and now
researchers can knock out particular compounds and see if they played a
key role in flavor or not.
There has been one genetically engineered tomato in the supermarket. In
the 1980s, plant geneticists at the University of California, Davis,
just as frustrated by bland tasting tomatoes, also tried to make a
better tomato. That led to a biotechnology company, Calgene, in 1994,
developing the Flavr Savr
tomato, the first genetically engineered food of any kind in the
supermarket, its DNA tweaked to inhibit a protein that turns a tomato
mushy over time. While it sold well, Calgene foundered in the logistics
of industrial agriculture and was bought by Monsanto, which discontinued
selling the seeds.
The Florida team is not repeating the Flavr Savr game plan.
Although Dr. Klee experiments with genetically engineered tomatoes to
test and confirm findings, he said that none of the ones eventually
destined for supermarkets will be — partly to avoid potential consumer
backlash and partly because his university cannot afford the estimated
$15 million that would be needed to obtain regulatory approval to sell a
genetically engineered tomato.
Instead, the tomato would be created through traditional breeding
techniques, but using genetic tests to determine which of the plants
possess the desired genes.
The quest for year-round produce at the supermarket has also led to
tomatoes being grown in less-than-ideal places — like Florida, where the
soil is too sandy and there are plenty of pests — when the traditional
tomato-growing areas farther north are too chilly.
Dr. Klee does not expect the improved tomato to taste as good as the
best heirlooms. Supermarket tomatoes would still be grown in large
quantities, picked green and shipped long distances before being gassed
with ethylene to ripen. In addition, the tomatoes are often mishandled
en route. Refrigeration, Dr. Klee notes, destroys the flavor compounds
in even the best tomato. “I might be able to get 75 percent” of the best
tomato in one that can be grown in greater quantities, he said.
Some traditional breeders are skeptical that Dr. Klee can do what he
thinks he can as quickly as he predicts. “I don’t think the taste of
tomatoes is going to be fixed by molecular biologists,” said David Francis,
a professor at The Ohio State University who has bred and released
several tomato varieties, “because flavor is a lot more complicated than
manipulating one or two genes.”
After working with tomatoes for so long, Dr. Klee admits he does not eat
many of them, but he does want the public to be able to buy appetizing
ones. Part of his quest is to get people to eat less junk food. If he
can improve the taste of tomatoes, he said, it could be an important way
to coax Americans to eat healthier foods.
Tomatoes aren’t the only focus of the Institute for Plant Innovation.
Researchers are working on a more fragrant rose, a project that involves
the genetic engineering feat of inserting — yes — a tomato gene in a
rose plant. They are also trying to grow tastier strawberries and
blueberries. One new blueberry variety could be described as positively
crispy, almost apple-like in its texture.
Consumers who tasted these blueberries liked their firmness, and the
quality is also a boon to growers, because the fruit lasts longer.
“It’s a blueprint,” Dr. Klee said of his tomato quest, “for a much bigger program of bringing back flavor.”
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