Scientists are hoping the seed of three new sunflower
germplasm lines will sow greater success in fighting the fungus that
causes head rot. Agricultural Research
Service (ARS) and North Dakota State University (NDSU) scientists
at Fargo and Carrington cooperatively developed, tested, and released
the sunflower lines for their resistance to Sclerotinia sclerotiorum,
the culprit behind head rot.
Sclerotinia can cause both head and stalk rots
in sunflower, making it double trouble. Recently, between 5 and 8 percent
of the U.S. sunflower crop, especially in the Northern Great Plains,
was affected by these two diseases, with losses reaching $100 million
in peak years like 1999.
Sclerotinia head rot happens less often, but it's
just as destructive, since infected flower heads can disintegrate before
harvest. "Even slight head-rot infections, while not substantially
reducing yields, will cause discolored seeds, which for the confection
sunflower, may mean rejection by processors," explains Tom Gulya,
a plant pathologist at ARS's Red River Valley Agricultural Research
Center, in Fargo. The fungus "also produces sclerotia that can
be the same size and shape as the seed." Though nontoxic to consumers,
the hard sclerotia sometimes end up in confection seed and can chip
a tooth if bitten.
Gulya, ARS plant geneticist Jerry Miller, and NDSU colleague
Bob Henson used conventional breeding techniques to develop the three
germplasm lines' improved resistance to head rot using French, Russian,
and other sunflower sources. Gulya cautions that the lines aren't immune
to head rot, but are significantly more resistant than existing germplasm,
a feature that's sure to aid sunflower growers. "Breeders working
on other Sclerotinia-prone crops are also making progress,"
Gulya adds, "but they can't yet claim total immunity to this pathogen."
In field trials from 2000 to 2002, experimental hybrids
with germplasm line RHA 440 yielded 2,086 pounds of seed per acre; hybrids
with RHA 439 yielded an average of 1,914 pounds per acre; and hybrids
with HA 441 yielded 1,745 pounds per acre. Three commercial checks yielded
1,969 pounds per acre. Since head rot outbreaks in the field are too
sporadic, the researchers relied on NDSU's Sclerotinia Mist Nursery
at Carringtoncoupled with artificial inoculation techniques devised
by Gulya and NDSU associates.
Head rot resistance is tested by spraying sunflower heads
with lab-produced ascospores, an infectious stage of Sclerotinia.
Immediately afterwards, the mist system is turned on, and it runs intermittently
around the clock for the next 3 weeks. By then, heads are showing varying
amounts of rot, and the researchers start taking notes. Over 3 years
of such testing, the average disease incidence in line RHA 440 was 33
percent; in RHA 439, 16 percent; in HA 441, 8 percent; and in the commercial
checks, 58 percent.
Gulya and Miller estimate it could take seed companies
3 to 5 years to incorporate head-rot resistance from the lines into
commercial hybrids. Breeders will also have to incorporate high oleic
acid content, resistance to imidazolinone herbicides, and other mandatory
agronomic traits to satisfy today's growers' needs, they add.By
Agricultural Research Service Information Staff.
This research is part of Plant Diseases, an ARS National
Program (#303) described on the World Wide Web at www.nps.ars.usda.gov.
Gulya, Jr., and Jerry
F. Miller are in the USDA-ARS Sunflower
Research Unit, P.O. Box 5677, Fargo, ND 58105; phone (701) 239-1316,
fax (701) 239-1346.
"New Sunflower Germplasm Holds Its Own Against Head Rot"
was published in the May
2004 issue of Agricultural Research magazine.