Study: Gene change that ripens tomatoes uniformly also makes them less flavorful

Posted: June 29, 2012 at 7:11 am

There's a reason people crowd the tomato stands at the farmers market. Its diverse and vibrant tomatoes seem to taste better than the perfectly red ones at the supermarket, even if parts of the fruit aren't as ripe as others.

A study in today's issue of Science lends credence to what your taste buds have been telling you.

Researchers from UC Davis, Cornell University and other institutions have pinpointed the genetic change that makes many commercial tomatoes ripen uniformly. But they also discovered that the same genetic change makes a tomato produce less sugar so it is less sweet and flavorful.

"What this paper shows is that a pretty tomato comes at a cost in flavor," said Harry Klee, a University of Florida horticulturalist not involved in the study.

Some tomato varieties, when unripe, have dark green "shoulders" topping an otherwise light green tomato. This makes the top of the tomato redden more slowly than the rest as it ripens.

For some consumers, a partially red tomato is less appealing. Salsa companies, for example, don't want green chunks of tomato in their glass jars. And uneven ripening makes commercial and mechanical harvesting of tomatoes more difficult.

So for 70 years, since breeders discovered a naturally occurring variety of tomato that ripened uniformly, lots of tomatoes have been bred that way. These tomatoes are some of the most flawlessly red supermarket ones, and are in nearly all pizza sauces, tomato soups and ketchups.

Breeders knew they were selecting tomatoes to have a particular version of some gene. But they didn't know which one, or what it did. James Giovannoni, an author of the study at the Boyce Thompson Institute for Plant Research at Cornell, likened it to having a Google map zoomed in only as far as California. Now, he said, "we're at your house in Sacramento."

The researchers discovered the gene, GLK2, and the version of it with a DNA difference that makes a tomato ripen uniformly.

By turning other genes on and off, it controls a tomato's chloroplasts, the factories that convert the sun's energy into sugar and make plants green.

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Study: Gene change that ripens tomatoes uniformly also makes them less flavorful

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