The Taste of Summer

Minnesotans could have fresh, homegrown tomatoes . . . just in time for the holidays

Nothing evokes summer more than the taste of a fresh tomato still warm from the sun. Maybe we in the Upper Midwest enjoy tomatoes so much because the short growing season means that we have just a few weeks each year to enjoy the sweet vine-ripe fruit.

tomato varietiesThe novel tomato
varieties are bred to
grow fruit in a range of
colors and shapes. All
photos by Chanbin Chen

But what if that short season could be overcome by a fast-growing, high-yield, easily harvested breed that, by the way, tastes great? And what if that tomato not only could be grown all summer long but also as an edible decoration for your holiday table?

An enthusiastic backyard gardener rather than a professional plant breeder, Assistant Professor Changbin Chen set his sights on building a better tomato about five years ago. In addition to fast growth and high yield, Chen aimed for a dwarf plant that wouldn’t need to be staked so that the fruit could be machine harvested on large-scale farming operations, as well as hand-picked from small container gardens.

The long-term goal of Chen’s research in the Department of Horticultural Science is to make stable aneuploidy tomato seed stock through chromosome rearrangement. “Most plants cells are diploids, meaning that they have two sets of chromosomes, one set from the mother and one set from the father,” Chen explains. “We wanted to rearrange the chromosome patterns and to create plants with aneuploidy cells, that is cells with additional chromosomes added to the two sets of chromosomes. That’s how you can get a high level of diversity in a short time.”

In order to generate desired traits as starting tomato varieties for building stable aneuploidy tomato seeds stock, Chen and his students started with two very different tomato varieties, which offered a large number of chromosome combinations and possible recombination. They crossed a bush variety with a stable inbred line screened from a hybrid variety called Big Zack, a flavorful tomato that produces fruit along long vines. Using tweezers, students painstakingly removed anther cones—which hold the pollen—from the flowers of one plant to prevent self-pollination, and then pollinated those flowers over successive days with the pollen of the other tomato variety.

By screening these crosses, Chen’s research team developed seven varieties of dwarf tomatoes with fruit of different colors, sizes and shapes. “If you have a good phenotype—like disease resistance or high yield—you want to keep it,” says Chen. In this case, it took five generations to create the desired varieties to be used for future breeding of stable aneuploidy seed stock.

Chen is concentrating on three lines, one of which has heart-shaped fruit and the other two oblong, pointed fruit that resemble holiday lights. The plants, which grow from 8 to 14 inches tall, are easy to grow in Zone 2 and grow so quickly that two crops can be grown in a single season in Zones 4 and 5. The bushes produce 80 to 120 medium-sized tomatoes per plant, with a potential yield of 60,000 pounds of fruit per acre per crop. This compares with other high-yield varieties that average 46,000 pounds per acre. Because of the plants’ compact size, an acre of land can host up to 40,000 plants.

tomato rearrangementChen's process of chromosome rearrangement produces more
consistent results than traditional tomato breeding methods.

In addition to traditional markets, such as fresh food stores and tomato processing plants, Chen thinks that the dwarf tomato plants have great potential for the live potted plant market. “You could go to the farmers market and not only buy tomatoes but bring home the whole plant,” he says.

The Green Barn Garden Center and Farm in Isanti, Minn., has offered an acre of land for a large-scale farm test this spring. The growers also will try raising the novel varieties in the greenhouse, with the goal of producing fruit-filled potted plants in time for the 2014 holiday season.

Chen is working with the university’s Office of Technology Commercialization to license the new tomato varieties, where they will join the many cold-hardy varieties of apples, grapes, mums, azaleas and other plants that the university has patented over the years. The new tomatoes, which have not yet been named, should be available in 2015 or 2016.

In the meantime, Chen and his students will work on developing a strain with even sweeter fruit, increasing the sugar concentration in these tomatoes from an average of 3.5 percent to 6 percent or higher. “We will do this by prolonging leaf growth and life,” Chen explains. “The longer the leaves live, the more photosynthesis occurs and the more sugar that is produced. In rice, just two additional days of sunshine can increase the amount of sugar and starch by 15 percent. We want to do that with tomatoes.”

–Julie C. Lund