Building a Better Berry
Small-fruit geneticist Stan Hokanson displays several elite wild strawberries
collected by collaborators. The small, highly aromatic berries (left) are from
plants collected in Alberta, Canada. The larger berries are from a type
collected in Alaska that may prove to be cold hardy.
Early in the next century, a whole new strawberry may grace our tables and
our taste buds with its beauty and unique new flavors and textures. This year
and next, six researchers across the country are selecting the best parents for
reconstituting the commercial strawberry.
With clipboards in hand, the scientists roam plots of 20 to 40 elite
genotypes of two species from North and South America, scoring each for about
18 characteristics growers and consumers prize. Their mission: Broaden the
genetic base of today's strawberry and build a bigger, better one in the
The six researchers are evaluating the original two parent species of
today's commercial strawberry, Fragaria x ananassa. It got its start
accidentally some 250 years ago in a European botanical gardenthe result
of a chance hybridization between two New World species.
One parent, F. virginianagood at tolerating heat and
droughtarrived in Europe from North America by the late 1500s, possibly
brought back by the legendary navigator and explorer Jacques Cartier. In the
early 1700s, a French spy carried F. chiloensis, the other parent, from
Chile. Acclaimed in Chile for its large fruit, it was a big disappointment in
Europe. The spy had unwittingly collected only female plants that failed to
produce fruit . . . until they were planted among F. virginiana clones
"Now we can pick the most outstanding genotypes of those two parent
species for breeding," says ARS
geneticist Stan C. Hokanson, who is at Beltsville, Maryland.
Some of the elite genotypes come from the ARS National Clonal Germplasm
Repository at Corvallis, Oregon. Others were recently collected in native
habitats from Chile to the U.S. Rockies to Ontario, Canada, and evaluated by
enthusiasts like James F. Hancock.
Professor of horticulture at Michigan State University in East Lansing,
Hancock oversees the evaluation project. He says about 10 serious evaluations
have been done with New World genotypes.
"We tried to pick the best from these and select a representative
sample. It's like doing the final cut."
Besides Hokanson, Hancock's other cooperators are ARS geneticist Chad E.
Finn at Corvallis; James J. Luby, professor of horticulture at the University
of Minnesota in St. Paul; Barbara L. Goulart, retired associate professor of
horticulture at Pennsylvania State University in University Park; and Thomas M.
Sjulin, research department manager with Driscoll Strawberry Associates, Inc.,
of Watsonville, California.
"The beauty of testing in multiple sites is that each site has a
different stress regime," says Hokanson at Beltsville's Fruit Laboratory.
"The sites provide extreme cold, high heat, dampness, widely varying soil
quality, and different insects and diseases for us to evaluate genotype
Each genotype usually has something to offer, says Hokanson. For example,
"one with small fruit may have fruit quality traits or disease resistance
we can use." Researchers may also find genotypes to extend the fruiting
season. The first strawberries to market command the highest prices. In
Hokanson's plots last April, most of the species collection was in flower when
commercially available cultivars were just waking from their winter naps.
One Peruvian genotype flowered nearly 2 weeks before the earliest cultivars.
"It's exciting to find these kinds of outliers. They provide much more
potential for improvement," Hokanson says. He adds that one genotype from
Alabama and another from Mississippi were disease free last fall, "when
all the cultivars were covered with leaf spot, scorch, and powdery
The researchers will also be looking for new sources of the day-neutral
habit that keeps today's cultivars bearing fruit in cycles throughout the
growing season. Until the late 1970s, commercial plants fruited for only a few
weeks each season. Then Royce Bringhurst of the University of California at
Davis collected a subspecies of F. virginiana that blooms out of
season in Utah's Wasatch Range. Genes from that mountain clone revolutionized
Strawberries are grown around the world, mostly in the Northern Hemisphere.
The United States, the leading producer, accounts for about 20 percent of the
total, followed by Spain, Japan, Poland, Italy, Korea, and China. The lion's
share of U.S. fresh-market production comes from California and Florida.
Driscoll's Tom Sjulin hopes to find genes for pest and disease resistance.
He says some of the wild material promises good resistance to two diseases that
plague growers in other parts of the country: verticillium wilt and red stele.
"There will be fewer and fewer chemicals in the future," says
Sjulin, noting the impending loss of methyl bromide and possibly other
important soil fumigants.
For California growers who plant a new crop each year, Sjulin wants to find
genes that direct more energy into flowers and less into runners, as well as
genes that trigger flowering under a wider range of temperatures. And he would
like to capture the succulent taste of some eastern-grown strawberries for new
West Coast cultivars.
ARS' Finn wants "to get a species core we know quite a lot about.
Hopefully, other researchers will build on this information," he says.
Finn planted extra F. chiloensis genotypes in his plots at Corvallis
because this species is indigenous to mild West Coast climates from northern
California up to British Columbia, as well as down to Chile. "We have a
better chance of growing them here," he says.
Most strawberries grown in the Pacific Northwest are for processing. So Finn
will be watchful for fruit having rich color, high acidity, and high sugars to
fulfill processors' wish lists. And he hopes to find some novel
characteristics. "Maybe there's something out there that doesn't rot for 2
weeks after harvest."
Sjulin says it will take at least 12 yearsmore likely 15 to 20to
get desirable traits from F. virginiana and F. chiloensis into a
commercial variety. Fortunately, he adds, "Driscoll takes the long view on
variety development and is committed to maintaining a broad genetic base."
The evaluation project is supported by a USDA small-fruit germplasm
evaluation grant. Hancock's group at East Lansing multiplied the genotypes and
distributed plants to cooperators. Everybody got a core group of about 20
genotypes. Some got more because of geographic location.
"It's amazing how many people have been willing to cooperate on
this," says Hancock, who began the project 6 years ago with Luby and Adam
Dale, professor of horticulture at the University of Guelph, Ontario.
"We're all friendswe share a common interest."
Adds Hokanson, "What really makes this interesting is that we know how
the cultivated strawberry originated accidentally, and now we can go back and
do it better."By Judy
McBride, Agricultural Research Service Information Staff.
This research is part of Plant, Microbial, and Insect Genetic Resources,
Genomics, and Genetic Improvement, an ARS National Program described on the
World Wide Web at http://www.nps.ars.usda.gov/programs/cppvs.htm.
Stan C. Hokanson is at the
Laboratory, Bldg. 010A, Room 210, 10300 Baltimore Ave., Beltsville, MD
20705-2350; phone (301) 504-6768, fax (301) 504-5062.
Chad E. Finn is in the
Horticultural Crops Research Unit, 3420 N.W. Orchard Ave., Corvallis, OR
97330-5098; phone (541) 750-8759, fax (541) 750-8764.
"Building a Better Berry " was published in the
September 1999 issue of
Agricultural Research magazine.