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Canola seed index predicts field performance

Here is an easy calculation that seed growers and farmers can conduct to help assess canola vigour.


November 29, 2007
By Ralph Pearce


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As often happens in research, Dr. Bob Elliott made an unexpected discovery
while searching for something else. A Canola Seed Index, used to predict seedling
vigour and field growth, was developed out of earlier research on seed vigour
tests.

In 1998, Elliott, an ecological pest management researcher with Agriculture
and Agri-Food Canada's Saskatoon Research Centre, was attempting to streamline
and standardize vigour tests for canola. At that time in the industry, he says,
there were as many as a dozen different tests, which created confusion among
seed companies, seed laboratories and growers.

From 1998 to 2000, Elliott evaluated different seed lots of open-pollinated
and hybrid Argentine canola in six laboratories. He used eight different tests
(standard germination test, three pre-chill tests and four cold stress tests)
to assess emergence and establishment, and a seedling assay test to assess seedling
growth. To validate the tests, seed lots were grown at multiple locations with
plantings in early May when soil temperatures were 10 to 15 degrees C, and in
late May when temperatures were generally warmer.

Canola Seed Index calculation.

Thousand-seed weight (g) X germination
percentage = Canola Seed Vigour Index 100

Rating: Open-pollinated: 3.0 and above = Vigorous
Hybrid: 3.5 to 4.0 and above = Vigorous

"In the field tests, we focussed on seedling emergence, seedling establishment,
plant weight and total plant weight or biomass, calculated from plant densities
and individual plant weights," explains Elliott. "To identify which
tests were giving us the best indication of performance, we simply ran statistical
correlations between the germination of the seed lots in the different tests,
and the performance of those seed lots in the field in both early and late May
plantings."

From there, Elliott took his findings to the Canola Vigour Steering Committee,
which recommended the adoption of three of the tests, including the standard
germination test and two pre-chill tests. A seedling assay test was also recommended
but was not adopted by seed laboratories because of costs.

"Rejection of the seedling assay put us in a real predicament because
we knew that seed yields in canola were more highly correlated with plant weights
than with plant densities," says Elliott.

Research led to Canola Seed Index
Going back to the drawing board, Elliott wanted a test that provided an indication
of not just emergence and establishment but also plant growth and yield. "We
knew there was a direct correlation between seed size, or more appropriately
seed weight, and initial seedling weights in the field, so we thought maybe
a corresponding relationship existed with the seed lots we'd been evaluating
in the fields over those three years."

That train of thought led them to check thousand-seed weights and fresh weights.
"Perhaps to no one's surprise, there was a good fit, a very high correlation
between thousand-seed weight and initial plant weights and plant growth in the
field," says Elliott, adding that the initial rejection of the vigour assay
by the seed laboratories actually turned into a plus. "It forced us to
go back and re-think what vigour is all about and what are the fundamental aspects
affecting it."

Once Elliott established thousand-seed weight as a variable, he had a rough
method of assessing plant growth in the field. That led to the equation for
the Canola Seed Vigour Index, a product of the thousand-seed weight, multiplied
by the final germination of the seed lot, divided by 100. "With a seed
lot that has a thousand-seed weight of 4.0g and germination of 90 percent (either
in standard germination test or pre-chill test), the vigour index would be 4.0g
x 0.9 (90 percent) or 3.6," explains Elliott.

Open-pollinated canola varieties with a vigour index of 3.0 and above are classed
as a vigorous lot, according to Elliott. With hybrids, a solid rating is an
index above 3.5 to 4.0.

 18a
A Canola Seed Index scoring system will help growers select more
vigorous seed lots, says Bob Elliott.

Improved field performance
The bottom line is two-fold from Elliott's perspective. First is improving the
industry by raising the bar through standardization. If the seed quality improves,
then the state of the crop tends to follow suit. "We're finding a one unit
increase in the vigour index of a seed lot can translate to anywhere from 20
to 50 percent improvement in plant growth in the field and often times, an increase
in seed yield," he says.

The second goal is trying to narrow the gap on the range of thousand-seed weights
in the canola sector. Weights can vary from 2.6g to 3.8g for open- pollinated
varieties to 3.2g to 5.5g in hybrids. "We're finding that with better seed
lots, we can cut seeding rates down to three or four pounds an acre without
losing yield," outlines Elliott. "If we can reduce that seeding rate
by one pound per acre, this would translate to $50 to $60 million in savings
for canola producers."

Elliott is also interested from an entomological standpoint. Since most of
the canola seed is treated for control of flea beetles, an effective reduction
of seed without compromising establishment or yield, would reduce pesticide
inputs, correspondingly.

Eric Johnson is involved in this research as well. A weed biologist with Agriculture
and Agri-Food Canada's Sustainable Cropping Research Centre at Scott, Saskatchewan,
Johnson is interested in pushing the limits on the Seed Vigour Index, not only
to canola hybrids, but the impact of agronomic practices such as planting dates
and swathing times on producing high vigour canola seed. "We'd done work
with this before with our fall seeding and early spring seeding, and found that
early seeding tended to produce larger seed with higher vigour," says Johnson.

Although Johnson had not looked into swathing time, Cecil Vera at AAFC Melfort
did, and found early swathing at 60 percent moisture reduced the vigour substantially.
"If it was hot and dry in July and August, and the canola was swathed early,
the vigour of that seed dropped dramatically, yet in a cooler year, early swathing
wasn't quite as detrimental." Swathing at less than 20 percent seed moisture
content generally resulted in the highest seed vigour.

Like Elliott, Johnson sees the rapid adoption of canola hybrids as the next
challenge for the Seed Vigour Index, but only as a short-term hurdle, especially
as research is expanded to look further at hybrid vigour, tillage practices,
drought stress and additional research into planting dates and swathing.

"It raises the bar on the standards and it gives another dimension to
the standards, rather than a straight germination test," says Johnson,
adding that the index calculation is a very simple one. "It's not difficult
or onerous and for the seed laboratories, it's another service they can offer."

A big plus to growers
Despite the notion that some seed lots will not meet the minimum standards of
the vigour index, Johnson believes this to be a big plus for seed growers, especially
as its applications continue to expand. "The majority of growers can meet
that standard, so it's going to be good for the seed growers," he says,
noting there are times when canola germination and emergence are poor due to
a multitude of reasons, yet the seed is blamed unfairly. "With these standards,
the seed growers can say, 'I've met a pretty good standard here, in both germination
and in seed weight, so is it really the seed that's suspect?'"