From idea to supermarket: the process of berry breeding

Agricultural Research, Oct, 2003 by David Elstein

If you ask Chad Finn whether he has any nicknames, the first one he is likely to say is "plant geek" An even better name may be "fruit geek."

Ninety miles south of Portland, Oregon, the ARS geneticist and fruit breeder is surveying a field of new berry seedlings in Corvallis. "I enjoy getting paid to look at fruit in a field with the beautiful, mountains in the background," Finn explains. He only wishes it were for more than the 6 weeks a year that he spends full time in the field.

Finn works out of the Horticultural Crops Research Laboratory. He is responsible for genetics research and breeding of blackberries, strawberries, blueberries, and raspberries for one of USDA's oldest fruit-breeding programs, dating back to the 1920s. The program's early leaders developed a series of berry cultivars that became the foundation of the small fruits industry in the Pacific Northwest.

Finn's job is not for those who like instant results. He gives an example of a blackberry released in 1996 that took 9 years to create, which was "as quick as it could be." That blackberry was designed to be planted in backyard gardens and did not have to be tested to see how well it could be harvested and processed, which can add years to the process. Strawberries take less time to breed, since they grow and fruit more quickly than blackberries, while blueberries usually take a lot longer.

Why Does It Take So Long?

Plant breeding is a process that has been conducted for hundreds of years, though the science underpinning it was developed in the 20th century. The procedures are practically identical for all the fruits that Finn breeds.

A successful cultivar must be appealing to consumers' taste buds, economical to produce commercially, and, ideally, widely adapted to environmental stresses and tolerant of pests.

The first step is to make a cross between two parent plants. Finn listens to various groups including growers, processors, and other fruit breeders to decide what his objectives should be. He then chooses parents he thinks are most likely to produce offspring that meet those objectives.

For instance, he may want to create a new blackberry cultivar that produces large yields and is thornless--something very important to growers.

Finn makes a cross of the two parents with a female and male flower. For the female, he and his staff emasculate the flower (remove the male parts). He then places a bag over the emasculated flowers to keep unwanted pollen out. Finn lets the flowers develop for a few days. Meanwhile, the anthers containing the pollen are dried and then stored in a refrigerator to keep them fresh.

With a small paintbrush, Finn pollinates the emasculated flowers with the pollen. He does this every few days, and fruit eventually develops in the bag. Ripe fruit is mashed and treated with an enzyme, pectinase, to remove the flesh from the seeds.

Seeds of blackberries and raspberries, which have thick, protective outer layers, are soaked in concentrated acid to digest the layers. To mimic winter, all seeds are placed in moistened peat moss and refrigerated for 2 months. The seeds are placed in a greenhouse to germinate, and eventually the seedlings are planted in the field.

Each type of fruit takes a different amount of time after planting before Finn gets a representative crop to evaluate. Strawberries can be evaluated 1 year after planting, while blackberries and raspberries take 2 years, and blueberries take 3 to 4.

"It's the breeder's responsibility to be in the field to make the decision on which plants to select," Finn explains. He says he studies the plants and their fruit to see whether they exhibit the characteristics that are important to growers, processors, and consumers. And maybe most importantly, he tastes the fruit.

Only one half to one percent of the fruit Finn planted a few years ago will make it past this point. "I replicate only the ones I have a very good feeling about," Finn says. Since it costs a lot of money in labor and land to grow these selections in a replicated trial, he must be picky about which ones he decides to continue working on.

The few he does like are repeatedly evaluated to make sure they meet the criteria needed for commercial success. He pays careful attention to yield data; the fruit may taste delicious and look great, but growers need to be able to grow plentiful yields.

During the evaluation period, ARS virologist Robert Martin tests the selections for viruses. If any are detected, Martin uses heat therapy to eliminate them. "Having virus-free stock for the commercial nurseries is critical as it allows the growers to start with the healthiest planting stock," Finn says.

At this point, Finn identifies a few advanced selections--the best of the best. He may continue growing these on ARS-owned fields, or he may get some outside help. For additional field trials, Finn often turns to nurseries, such as Fall Creek Farm and Nursery of Lowell, Oregon. The nurseries grow advanced selections on their land to see how they grow in a different environment. This information helps Finn evaluate which prospective cultivars are best. Nurseries benefit too. "We get a firsthand idea of the varieties that show promise," says David Brazelton, president of Fall Creek.