Building a better tomato

Tomatoes in December? There was a time when that would have sounded absurd. But these days, you don’t have to give up having tomatoes in your salads or on your sandwiches just because the season has changed. Food scientists have developed tomatoes that are available year-round — and cost less than $2 per pound.

The problem, of course, is that the hard, tasteless red spheres in markets this time of year bear little resemblance to fruit harvested at the peak of the season.

Since plants were first grown for food, farmers, and more recently plant breeders, have selected their best plants, saved the seeds and planted what they hoped would be improved varieties. Through much of the last half of the 20th century, scientists and plant breeders largely devoted their efforts to practical matters, creating tomatoes that were fast-growing, firm, robust and easy to harvest. They developed new and exciting molecular techniques to select for the traits they wanted, but there were some unintended consequences of their selections, such as inferior flavor.

Lately, my colleagues and I have been working on ways to reintroduce some of the memorable tastes and smells that have been lost, without sacrificing the benefits. The goal is to have hardy, economical fruit year-round that tastes like what’s harvested at the peak of the season.

But it’s complicated. Tomatoes are among the most genetically diverse crops we have, in large part due to human intervention. When tomatoes arrived in Europe from the New World, farmers worked to adapt them to a range of European climates. Then, as they became more popular and integrated into a wide variety of foods, consumers wanted specific types of fruit for specific uses. For slicing and eating in sandwiches, the ideal tomato was large, round, not too juicy and red. Small, sweet cherry tomatoes were perfect for eating raw as snacks. For sauces, small, dense, meaty tomatoes were desirable.

To get tomatoes for these uses that could be stored for long periods, breeders have crossed conventional tomatoes with wild or mutant varieties. Other genetic selection has been in pursuit of varieties in which all the fruits on a plant tended to ripen at the same time to facilitate an efficient harvest. At the same time, there has been a companion movement: A community of heirloom tomato growers has focused on ensuring that lesser-known breeds are preserved — hence an array of tomatoes that are small and large, round and oval, and come in shades of yellow, orange, white, purple and green.

In general, food in the United States has become more plentiful and cheaper. The USDA reports that American consumers spend just 6% of their budgets on food — less than any other country in the world. Europeans spend about 15% of their budgets on food, while underdeveloped countries can spend nearly 50%. But fresh produce is often more expensive than other kinds of food because it is perishable, and some kinds of fruits, like those delicious heirloom tomatoes that haven’t been selected for hardiness, are especially delicate and therefore pricey.

In the last 20 years, scientists have started to identify which tomato genes produce which traits, and they have put that knowledge to good use. For example, tomato seeds with the “VFNT� designation, valued by home gardeners and large-scale producers alike, contain genes that make plants resistant to certain kinds of nematodes, bacteria and viruses.

Today, we are finally beginning to understand why fruit with some of the traits we’ve selected for also seem to be missing some of the traits we prize. For instance, about 70 years ago, tomato growers began selecting varieties in which the unripe fruit is uniformly light green in color. They found these fruits to be easier to harvest as they matured, and therefore more economical. My colleagues and I recently discovered, however, that the gene that produces this uniform light green color in young fruit ultimately diminishes the sweetness and redness of the fruit as it ripens. The result? Tomatoes that are easy to harvest and ship but not as tasty as we might like.

Now the challenge is to find the genes that control the juiciness and taste we all love, and find a way to produce tomatoes that have those genes as well as the hardiness and longevity of modern supermarket tomatoes. Then we might have tomatoes that taste like summer at winter holiday dinners.

Ann Powell is a biochemist in the Department of Plant Sciences at UC Davis.