Physiological and morphological effects of glyphosate applications on glyphosate-resistant cotton

Decreased boll retention and pollination problems in glyphosate-resistant (GR) cotton treated with glyphosate have been reported by growers in the Southeastern USA. Greenhouse and field studies support these reports, demonstrating a glyphosate-induced decrease in boll retention, seeds per boll, and pollen viability. C-14-glyphosate absorption and translocation studies showed that glyphosate accumulated in reproductive tissues as well as other sink tissues such as roots. Reproductive square tissue (floral bud) of both GR and conventional cotton was more sensitive to glyphosate than leaf tissue, as measured by accumulation of shikimic acid per muM translocated glyphosate. In phytotron experiments, 45 to 55% of pollen grains from glyphosate-treated GR cotton were deformed when stained with fluorescein diacetate. Anther filaments of glyphosate-treated GR cotton flowers failed to elongate normally, resulting in a greater distance between the receptive stigma tip and the pollen containing anthers. GR cotton reproductive sensitivity to glyphosate resulting in decreased pollen viability, and poor pollen deposition may explain grower observed boll retention and pollination problems.