EFFECTS OF GLYPHOSATE ON ROUNDUP READYCOTTON REPRODUCTIVE GROWTH

摘要

Roundup Ready technology is an additional tool that can be used against weed problems. However, previous studies haveindicated that lint yield can be negatively impacted when plants are treated with over-the-top Roundup applications.Consequently, damage to reproductive organs by glyphosate has been proposed to be one cause of lint yield reduction. In thisstudy Deltapine 5690 RR was cultivated under field conditions. Roundup Ultra was applied using 3 different rates at threedifferent stages of plant growth; 4, 8, and 12-leaf. The rates used bracketed the single over-the-top recommended rate ofRoundup Ultra of 1qt/A until the 4-leaf stage. Twelve hours after natural pollination, the degree of anther opening, and thenumber of pollen grains attached to the stigma were determined for first position flowers. As the rate of glyphosate increasedand the stage of application was delayed, a greater number of anthers remained closed and fewer pollen grains were attached tothe stigma. This effect was accentuated in nodes 9-11. Pollen tube rate of growth, and travel distance were measured at differenttimes after artificial pollination. No significant differences were found across all treatments. This data suggested that glyphosatehas no inhibitory effects on pollen tube growth within the style. Box-mapping data indicated that, as the rate of glyphosateincreased and the stage of application was delayed, less retention of first position fruit was observed within node range 6-10.We believe that this reduction in first position fruit retention was due to low pollen availability during pollination. Plants thatproduced fewer or no first position fruit within nodes 6-10, following glyphosate treatment, attempted to compensate yield lossesby shifting fruiting patterns toward more distal positions. The closer the glyphosate application was to floral development, thegreater the effect upon pollen availability. We concluded that Roundup Ready cotton yield was negatively affected only at the 12-leaf stage of application due to low pollen availability in first position flowers within nodes 6-10. Over the top applications ofRoundup showed no detrimental effects on lint yield when applied within the labeled rate.