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Unintended Effects of Genetic Manipulation
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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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