Geneticists find reason for store tomatoes’ flavor loss

Scientists have caught the culprit behind those tasteless tomatoes that sink your salsa, toughen your tart and rattle your ratatouille.

Turns out, tomato growers’ best intentions over decades are to blame.

By breeding tomatoes to ripen evenly and harvest easier, growers unwittingly robbed those sumptuous ruby reds of their taste.

Now, University of California, Davis biochemist Ann Powell and her team have pinpointed the genetic mutation responsible for that loss of sweetness.

What makes tomatoes look so nice in a supermarket display is a disabled GLK2 gene. And it created this unintended consequence: fruit that tastes like soggy cardboard, with juice unfit for even the worst bloody mary.

“It wasn’t malicious,” said Powell, whose team’s findings are reported in today’s issue of the journal Science. “It’s the one trait that helps make tomato production an economic and efficient process, making fresh fruit available to all of us.”

In a comparison of genetically modified plants, developed by Mendel Biotechnology in Hayward, Calif., tomatoes with the normal version of the gene had 20 percent higher sugar levels than plants with the mutation. They were also 30 percent higher in lycopene, a red pigment and phytochemical thought to be useful in human nutrition.

This intact gene can be found in sweet cherry tomatoes or eccentric heirloom varieties, costing $6 a pound, with characteristic dark green shoulders.

Working with researchers at Cornell University and in Spain, who were mapping regions of the tomato genome, the scientists discovered that the GLK gene controls the development of chloroplasts. Chloroplasts are the structures in the plant cells that enable plants to photosynthesize, using the energy of sunlight to create sugars.

Breeding for the uniform ripening trait has the unintended effect of causing poor chloroplast development, which in turn decreases the production of key ingredients that give tomatoes their sweetness.

For 70 years, breeders have selected varieties with this easy-harvesting and uniform-ripening trait – unaware that there would be a trade-off in taste. Before modern genetics, noted Powell, there was no reason to think the traits would be linked.

The discovery of the genetic differences has significant implications for the U.S. tomato industry, which annually harvests more than 15 million tons of the fruit for processing and fresh-market sales.

For instance, the sweeter tomatoes don’t need as much time to cook – which saves energy for processing companies that make sauce.

Perhaps easy-to-harvest modern tomatoes could be genetically designed to taste more like their ancestors, Powell said.

While the old-fashioned gene may be largely gone, it’s not forgotten. It could be re-introduced, she said.