Fayetteville, Arkansas
May 19, 2009
Soybean producers rely on standard
germination test results when selecting quality seed to plant
their crops. But germination rates may not provide all the
information farmers need to choose the seed that will best meet
their management systems.
Seed vigor, or a seed's ability to make a stand and grow to
maturity, is at least as important as germination rate, said
Rick Cartwright, plant pathologist for the
University of Arkansas
System's Division of Agriculture. Germination rates, based on
standard tests conducted under optimum germination conditions,
don't tell a producer anything about the seeds' vigor.
 |
|
Program associate Sandy Goeke places 50 age-accelerated
soybean seed samples in a wrapper of germination paper.
They will then be incubated at 68 degrees Fahrenheit for
7 days. Afterward, vigor will be determined by the
number of seeds that have successfully germinated. |
"It became apparent that two seed
samples with the same germination rating didn't necessarily
start with equal vigor," Cartwright said. In addition, some seed
that remains in storage for June or July planting may not emerge
as well as it would if it was planted earlier.
The Arkansas Soybean Promotion Board asked the Division of
Agriculture to investigate a vigor test called accelerated aging
to see if it could give Arkansas producers additional reliable
information about their seed options.
Accelerated aging was standardized and approved by the American
Association of Official Seed Analysts and the International Seed
Testing Association in the 1990s, Cartwright said. Unlike
germination tests, however, vigor tests are not required by the
USDA or enforced by state regulatory agencies like the Arkansas
State Plant Board.
"Seed companies are likely to use seed vigor tests voluntarily,"
Cartwright said. "Because their reputation depends on the
quality of their seed, they want to know all they can about
their product."
Producers don't always have easy access to that information,
Cartwright said. "But, if they know what to ask for, some
companies are willing to provide it to them," he said.
The research began with a planting seed quality survey.
Extension soybean agronomist Jeremy Ross said researchers
collected some 440 seed samples from growers' planting stocks.
The division set up a lab at the Arkansas Agricultural Research
and Extension Center in Fayetteville to conduct accelerated
aging and other seed quality tests. Program associate Sandy
Goeke was trained to conduct the tests.
The point of accelerated aging is to put stress on the seed
before conducting a germination test, Cartwright said.
Samples are first subjected to an incubation chamber where they
are maintained at 41 degrees Celsius (105.8 degrees Fahrenheit)
for 72 hours. Then Goeke wraps the seeds in a special paper
designed to promote germination and places them in a second
incubator where they are maintained at optimum germination
conditions for seven days.
Afterward, the samples are evaluated to see how many seeds
germinated successfully. Samples stressed by accelerated aging
are also planted in test plots to see how they perform under
field conditions.
Cartwright said that germination rates for the seed collected
during the survey did not decline much from April through July,
even when stored before planting, but there was a definite
decline in vigor as measured by the accelerated aging test.
"It's pretty important to understand seed vigor in Arkansas,
where we commonly double crop soybeans behind wheat, because
germination conditions may be harsh," Cartwright said.
Plant pathologist John Rupe is conducting several field tests to
look at interactions of seed quality and vigor with pathogens
that cause seed and seedling diseases.
Using late maturity group 4 and early maturity group 5
varieties, planted in plots in Poinsett County and at the
Northeast Research and Extension Center at Keiser, Rupe is
evaluating the effects of three planting densities and two
planting dates on seeds with varying germination rates and vigor
results from the accelerated aging test. "We did stand counts
and are looking at yield results," he said.
In another test at the Vegetable Research Station at Kibler,
Rupe is evaluating practices that may improve seed production.
"If you have high germination rates and optimum planting
conditions, you may get a good stand no matter what the seed
vigor may be," Rupe said. "But under stressful conditions,
including the presence of pathogens, stands and yields can
suffer."
"What we're trying to determine," Rupe continues, "is, if you
have seed with vigor problems, is there anything you can do to
improve stands?"
Among the crop management practices that can be employed to
help, Rupe said, are selecting seeding rates, planting dates and
the use of seed treatments to ward off pathogens.
Rupe adds that division scientists are also looking at practices
that can help preserve vigor during seed storage.
Ross said an important part of the seed quality program is to
help farmers understand what the accelerated aging test is and
how it can help them. Debby Monfort, professional assistant in
plant pathology, is coordinating an education program with Ross
and Cartwright.
"Germination rates are pretty stable, but vigor is sort of a
moving number," Ross said. "Because the seed is a living
organism, it has metabolic processes that continue even during
storage. These processes may reduce vigor, especially if storage
temperatures and humidity stress the seed."
Especially for late planting dates in a double cropping system,
Ross said, it's important to get the stand up and the leaf
canopy closed to help shade out weeds.
"If you know you have poor quality seed, especially if you
expect poor growing conditions, you may want to increase the
seeding rate, wait until planting conditions are closer to ideal
or select a higher quality seed with good vigor," Ross said. |
|
