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Building a better strawberry.

Building a Better Strawberry

Since history began, the strawberry has been a favorite fruit.

The Roman stateman Cato personally supervised strawberry growing on his estate. And as early as the 1400's, Western European monks were using the wild strawberry to illustrate their hand-written manuscripts.

"Today, strawberries mean good, healthy eating," says Gene J. Galletta, ARS plant geneticist. He and plant pathologist John L. Maas play a key role in ensuring that the supply in the Northeastern United States is plentiful and the quality good.

At the ARS Fruit Laboratory in Beltsville, Maryland, these scientists are breeding disease-resistant plants that produce bigger, better tasting strawberries that are easier for farmers and home gardeners to grow.

Sweet, juicy strawberries not only taste good, but they're also full of nutrition. Low in calories and carbohydrates, the raw fruit is a good source of fiber, potassium, iron, and vitamin C.

And they're a major flavor and/or fruit component of many food items.

Strawberries also contain ellagic acid. According to Maas, "Medical researchers have found, in experimental studies, that this naturally occurring organic compound inhibits the start of cancer caused by certain chemicals."

According to Dr. Gary D. Stoner, of the Medical College of Ohio, the acid "prevents procarcinogens from breaking down and may act as a trapping agent for carcinogenic metabolites."

However, scientists don't yet know how much ellagic acid you would need to eat to reap benefits.

"We know that ellagic acid is found in strawberry roots, leaves, and fruit. In fact, it's also present in several other small fruits and nuts. But we had no idea about the genetics of the acid," explains Maas.

He, Galletta, and Shiow Y. Wang, ARS chemist, have just finished testing about 50 strawberry varieties and breeding selections to see just how much ellagic acid each has. They found that ellagic acid ranges 4.4 to 9.5 times higher in leaves than in fruit pulp and twice as high as in the seeds. Importantly, this shows that "breeding for high ellagic acid in the fruit should be highly successful."

He estimates that there is about an ounce of ellagic acid in 25 pounds of strawberries.

Maas and Galletta work closely with the North American Strawberry Growers Association in their efforts to improve the fruit. Scientists from universities in 13 States are also cooperators.

"We're proud of our research program. If all pesticides were banned tomorrow, we'd lose only about 20 percent of the crop to pests and diseases we couldn't control," Galletta says. "Many other crops could be completely wiped out."

Galletta can well be proud; he picked up the strawberry research challenge from George Darrow, who began USDA's strawberry improvement effort over 70 years ago at Glenn Dale, Maryland. Darrow bred for resistance against red stele root rot, a disease that was devastating to the crop in the 1930's.

Today, Galletta continues to strive for a disease-free plant. Working with plant pathologist Barbara J. Smith and plant geneticist Creighton L. Gupton has brought Galletta a step closer to that goal.

At the ARS Small Fruit Research Station in Poplarville, Mississippi, these scientists have been screening thousands of strawberry plants a year, hoping to find plants not affected by anthracnose, a fungal disease that reached epidemic levels in the 1970's.

"The ARS station here at Poplarville was selected for anthracnose screening because there are no commercial strawberry plantings in the area," Smith says.

"Used alone, none of the fungicides registered for use on strawberries control anthracnose. We've been using a combination of cultural practices and fungicide sprays," Smith says. "But the future lies in resistant varieties." If proper breeding methods are used, anthracnose resistance, according to Gupton, will be easily transmitted from parent plants to offspring.

And now, after about 15 years of work, they will soon be ready to release

several strawberry varieties that stand up against this disease. These varieties have been field-tested in Alabama, Louisiana, Florida, North Carolina, and Mississippi.

During field tests, Smith rates the strawberries for yield, fruit size, shape, color, and flavor as well as for resistance to other diseases and insects. "Besides being anthracnose resistant, the selections we're releasing rate high in all these categories," she says.

Strawberries have also been improved in terms of their fruiting timetable. Building on research done by Donald H. Scott and Arlen D. Draper (retired ARS horticulturist and geneticist), Galletta developed two everbearing strawberries, Tribute and Tristar.

These berries, well suited for the Northeast and the Midwest, bear fruit 4 months longer than conventional spring-fruiting types.

A light-insensitive gene from a Rocky Mountain strawberry species was transferred into the new varieties, making them day-neutral.

"Conventional strawberry plants initiate flowers as day length changes in the fall, then bear fruit the following spring. We picked names with "tri" in them, such as Tribute and Tristar, because they bear fruit in the spring, summer, and fall," he says.

Galletta says that most of the strawberries grown on the East Coast are for local markets and pick-your-own operations. The exception is Florida, the third largest strawberry producer in the United States. California is number one, followed by Oregon. These three states account for 90 percent of U.S. strawberry production.

Galletta, who has spent his entire career trying to build a better strawberry, bites into his work with gusto. "Strawberries appeal to almost everyone," he says. "They're popular in Europe, Asia, Central and South America, and Oceania and are becoming well liked in Africa and other tropical countries. We must work harder to extend the shelf life of the berries and to develop new berry products that can be shipped without refrigeration. Most importantly, we need to reduce grower costs."

Fumiomi Takeda, plant physiologist at the ARS Kearneysville, West Virginia, research station, believes growers can determine plants' water needs simply by looking for drops of moisture on plant leaves.

"Strawberry plants growing in soil with adequate moisture produce water droplets on leaf margins during the night. But droplets don't form on leaves of water-stressed plants," Takeda says.

"Growers would look for these drops of moisture at dawn and be able to schedule irrigation without having to use expensive moisture-sensing equipment."

PHOTO : Plant geneticist Gene Galletta and plant physiologist John Maas evaluate the yield and quality of a berries from day-neutral plants.

PHOTO : John Maas and Gene Galletta examine the growth of micropropagated strawberries.
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Author:Stanley, Doris
Publication:Agricultural Research
Date:Sep 1, 1991
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