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[SANET-MG] Reproductive isolation in hybrid seed production
It is difficult to find good reports on the pollution of organic corn
fields near GM corn production. 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. This suggests that
non-GM or organic corn may be more extensively polluted by GM pollen
than has previously been acknowledged. Off course, if 21% of the corn
on field margins was polluted by GM pollen this would immediately lead
to visits from roving bands of Monsanto lawyers (a major pest in corn
country).
Published in Crop Sci 46:1445-1455 (2006)
DOI: 10.2135/cropsci2004.0007
Managing Reproductive Isolation in Hybrid Seed Corn Production
D. S. Irelanda, D. O. Wilson, Jr.b, M. E. Westgatec,*, J. S. Burrisd and
M. J. Lauere
a Doebler's Pennsylvania Hybrids, Inc., daleireland@doeblers.com
b Landec Ag, Inc. 201 N. Michigan, Oxford, IN 47971, dwilson@landecag.com
c Department of Agronomy, Iowa State University, Ames, IA 50011
d Burris Consulting 1707 Burnett Ave, Ames, IA 50010,
burrisconsulting@msn.com
e Pioneer Hi-Bred International, Inc., 6900 NW 62nd Avenue, Johnston, IA
50131, Michael.Lauer@Pioneer.com
Abstract:Production of hybrid corn (Zea mays L) depends on
cross-pollination between male and female inbred parents. As such,
reproductive isolation of seed fields is required to ensure genetic
purity of the hybrid progeny. Customer demand for improved genetic
purity prompted the seed industry to examine the level of genetic purity
resulting from current isolation practices. A 3-yr study was conducted
to monitor purity of hybrid seed produced in 315 fields from 24 seed
companies in North America. Each field was near a commercial corn field
shedding pollen synchronously with the seed parent: a worse case
scenario. Seed samples were collected at five locations along a 200-m
transect established perpendicular to the nearest potential adventitious
pollen source, and 100 seed from each location were subjected to isozyme
analysis to determine percent out-crossing. Isolation distance, seed
field size, field block size, number of border rows, adventitious field
size, male:female row ratio, male population, and male pollen class were
analyzed as continuous predictors and as variable class predictors of
out-crossing at the field margins and field midpoints. Year had a
significant (p 0.05) impact on observed out-crossing. Isolation
distance, border rows, and male pollen class were significant predictors
of out-crossing at the field margin but not at the field midpoint. A
significant interaction between isolation distance and border rows was
observed at both the field margin and midpoint. There also was an
interaction between male:female ratio and male pollen class on
out-crossing at the field margin. These results indicate that current
practices used to isolate hybrid seed fields often achieve the goal of
producing 99% genetically pure seed, but much higher levels of
out-crossing can and do occur. Because out-crossing generally was
greater and more variable at the field margins than at the field
midpoint, adjustments to field management that focus on minimizing
out-crossing at the field margins should lead to consistently high
levels of genetic purity from hybrid seed fields.
From the report: "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."
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