gm-cotton/report-4
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.
This document: http://natureinstitute.org/nontarget/gm-cotton/report-4