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Re: [SANET-MG] Reproductive isolation in hybrid seed production



Hi Dale,
About the comment "* We excluded a dozen or so screwed up fields in which the two inbredparents were not flowering synchronously. In such cases, a high levelof contamination is likely, no matter what you do. This is anotherreason to not buy brand-X seed." comment:You seem to be confessing that you selected the data from fields likely to give you the results that were desired. Of course, that selection was not mentioned in the publication as many editors would not have allowed the results to be published.Certainly the editors of Crop Science should publish a note on the excluded fields for the sake of full and truthful reporting.

Turning to your comment:"Keep in mind that the sample that had 21% contamination was just one
sample out 1575 samples." Comment: From the paper the data were summarized as follows:"The distribution of out-crossing percentages for the nearly 1800 seed samples evaluated in this study. Across 3 yr of study, approximately 65% of the samples collected from the field margins and field midpoints had out-crossing levels of 1% or less. Out-crossing levels greater than 6% were rare, but levels as high as 21% out-crossing were reported. The extent of out-crossing varied by year and by location within the field. In 1998, for example, no out-crossing was detected in 60% of the field midpoint samples or in 56% of the field margin samples. None of the field midpoint samples collected in 1998 reported more than 4% out-crossing. The highest level of out-crossing observed at the field margin was 7%. In 1999 and 2000, fewer field midpoint and field margin samples had zero out-crossing, and the level of out-crossing was more variable along the field margins. Out-crossing values as high as 21% were observed at the field margin and up to 15% at the field midpoint. In general, out-crossing along the field margins was greater and more variable than that observed at the field midpoints" The point here is that there is lots of contamination. If 5% contamination is good enough for hybrids it certainly is not for GM contamination. The hybrid study suggests that organic and conventional corn may be far more polluted by GM  transgenes than has been allowed for export to most countries.It seems to be time to explore the GM contamination more fully and by independent investigators who do not avoid fields likely to caused increased % of GM contamination! sincerely,Joe


Dale Wilson wrote:
Hi Joe,

The report below is on hybrid seed production and seed
contamination by out crossing from nearby commercial corn fields shows that corn near the margins of fields
may have as much as 21% contamination from the commercial
crops.

Keep in mind that the sample that had 21% contamination was just one
sample out 1575 samples.  It probably arose from contamination of the
stock seed, not pollen introgression in the current generation.  The
average contamination of the samples was about 1.8%, which is itself a
considerable overstatement for two reasons: 1) the distribution is very
much skewed to the right, and 2) the samples at the margin represent
smaller pieces of the fields (progressively thinner shells of area as
you go outward on the transect).  A weighted average gives you
something like 1%.
Also, this sample of 315 fields was a susbsample of a much larger
population of seed production fields.  The 315 were chosen because they
appeared to have an incipient contamination problem (nearby corn grain
field flowering synchronously with the seed field).

This suggests that non-GM or organic corn may be more extensively
polluted by GM pollen than has previously been acknowledged.

No, that is not true.  Our study shows that normal corn seed fields*
with adjacent pollen sources will produce seed with around 1%
contamination on average.  The quality standard for labeling has been
5% for many years.  But seed growers can do better than 1% if they need
to for specific purposes.  Isolation distance was important (not too
surprising).  Isolation in time is even better (we didn't study that
though).  Border rows of pollen parent didn't help as much as people
tend to think.  If a company wants to make a particularly pure seed lot
they can use isolated fields and/or heart-cut fields to avoid the
margins.

I would suggest that organic growers who want to avoid GMO
contamination should:
1. Get your seed from a company with some control over how the seed was
produced, and the wherewithal to test it for GMO contamination.
2. Demand pure seed from your seed dealer, they should be able to find
a clean lot.
3. Talk to your neighbors and make sure they are not going to plant a
big GMO field near by, and if so, try to arrange different flowering
dates.
4. Walk your fields and rouge out off-type plants before they flower in
your grain field.
5. Consider growing white corn.  Most varieties are yellow, and
contamination from yellow corn will show up as yellow kernels in the
white.  You can remove the yellow kernels before you plant the seed,
and so remove most contamination.

Managing Reproductive Isolation in Hybrid Seed Corn Production
D. S. Ireland, D. O. Wilson, Jr., M. E. Westgate,*, J. S. Burris
and M. J. Lauer.

Dale

* We excluded a dozen or so screwed up fields in which the two inbred
parents were not flowering synchronously.  In such cases, a high level
of contamination is likely, no matter what you do.  This is another
reason to not buy brand-X seed.

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