Glyphosate-resistant cotton showed abnormal reproductive development when
sprayed with glyphosate.
Manipulated Organism:
Cotton (Gossypium hirsutum).
Inserted Transgenes:
CP4 EPSPS gene cloned from Agrobacterium, which produces an
herbicide-resistant version of the enzyme targeted by the herbicide
glyphosate (Roundup).
Goal of This Study:
Although glyphosate is not lethal to glyphosate-resistant (GR) cotton
(as intended), there have been "[n]umerous reports of increased
boll abscission and pollination problems in response to glyphosate
applications...occasionally leading to yield loss and a modified
fruiting pattern" (p. 438). To investigate this phenomenon further,
the authors characterized the effects of glyphosate on floral anatomy,
pollen deposition, and pollen morphology.
Results of This Study:
-
In the flowers of GR cotton sprayed with glyphosate, there was 40% less
loose pollen per stigma compared with unsprayed GR cotton. (Reduced
pollen coverage can reduce the cotton yield from that boll.)
-
One reason for the reduced pollen coverage appeared to be a significant
increase in the distance between the pollen-producing anthers and the
stigma, which is the organ through which pollen reaches the ovary.
(Cotton is primarily self-pollinated, although if insect pollinators
were present, this increased distance might not be as deleterious.)
-
Spraying with glyphosate also reduced pollen viability by 50% in the first
four weeks of flowering. Microscopic examination of the pollen showed a
variety of cellular abnormalities at various stages of pollen
development.
Additional Comments:
The two GR cotton varieties in this study clearly did not have complete
resistance to the herbicide.
Source:
Pline, W. A., R. Viator, J. W. Wilcut, K. L. Edmisten et al. (2002).
"Reproductive Abnormalities in Glyphosate-resistant Cotton Caused by Lower
CP4-EPSPS Levels in the Male Reproductive Tissue," Weed Science
vol. 50, pp. 438-47.
Author Affiliations:
North Carolina State University.
Funding:
Not mentioned.
Product Status:
GR cotton is grown worldwide, including since 1997 in the US.
Copyright 2009 The Nature
Institute.
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