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Sunflower Scientists Keep
Looking Ahead
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Sunflowers.
(K9116-1)
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Agricultural Research Service sunflower
scientists, ever vigilant for new pathogen strains (causes of disease) that can
threaten commercial sunflower crops, have a successful track record in
countering them through plant breeding. In their continuing endeavor, these
researchers and their international colleagues currently focus mainly on three
major diseases: Sclerotinia stalk rot and head rot and downy mildew.
"To develop new sunflower breeding lines with disease resistance, we rely
heavily on genetic resources from wild sunflowers that evolved in their native
North America," says ARS plant pathologist Thomas J. Gulya, of the Red
River Valley Agricultural Research Center in Fargo, North Dakota.
The North Central Regional Plant Introduction Station—a joint venture
among ARS, 12 agricultural experiment stations, and Iowa State University, in
Ames—now provides a reservoir of 1,600 cultivated sunflower accessions
(specimens) and more than 2,200 accessions of the 49 wild sunflower species
from which scientists may draw for breeding experiments or research purposes.
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Plant pathologist Thomas Gulya compares a sunflower
seedling showing typical symptoms of downy mildew (left) with
a healthy seedling protected by a new fungicide.
(K9119-1)
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Scientists like Gulya are typically
unsung heroes. As diseases are controlled, the low incidence of epidemics tends
to go unnoticed. For example, some 15 years ago, a single registered fungicide
was so effective in controlling downy mildew that commercial plant breeders did
not include mildew resistance among their top breeding priorities. During the
past 2 years, however, ARS scientists at Fargo have found new
fungicide-resistant strains of downy mildew. Anticipating resistance and
continued evolution of other mildew races, Gulya and coworkers located new
sources of mildew resistance and transferred the genes into agronomically
acceptable germplasm. Now, new sunflower hybrids with USDA-bred resistance,
combined with fungicides, may avert calamities.
The fungus Sclerotinia causes sunflower diseases that account for half
of the disease-related yield losses in the Northern Great Plains. In some years
these losses total $15 million. Sclerotinia stalk rot, the most significant
sunflower disease in the United States, appears year in, year out, regardless
of weather.
With neither chemical-control nor genetic-resistance weapons, the U.S. grower
is nearly defenseless. ARS scientists have been searching for tolerance to the
disease, both in cultivated breeding lines and in wild sunflowers, for the past
two decades. Recent germplasm releases by the ARS team have given the sunflower
industry its first sources of tolerance to Sclerotinia stalk rot.
Sclerotinia head rot occurs during wetter-than-normal growing seasons—like
September 1999. More than 75 percent of the sunflower acreage in North Dakota
had head rot, which not only caused substantial yield losses, but also
contaminated the soil for many years. Whenever soil is highly contaminated with
sclerotia, growers must rotate to a crop like wheat, which is prone to scab,
instead of to other Sclerotinia-susceptible broadleaf crops, such as
soybeans, dry beans, or canola. ARS scientists had already been working with
researchers in Argentina and France to find sources of resistance to head rot,
but after the 1999 epidemic, head rot research became a much higher
priority.—By Ben Hardin,
Agricultural Research Service Information Staff.
This research is part of Plant Diseases, an ARS National Program (#303)
described on the World Wide Web at http://www.nps.ars.usda.gov.
Thomas J. Gulya is with the
USDA-ARS Northern Crop
Science Laboratory, Red River Valley Agricultural Research Center, P.O. Box
5677, University Station, Fargo, ND 58105; phone (701) 239-1316, fax (701)
239-1346. |
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"Sunflower Scientists Keep Looking Ahead"
was published in the November 2000
issue of Agricultural Research magazine.
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