Glyphosate-resistant soybean cultivar yields compared with sister lines

Herbicide-resistant crops like glyphosate resistant (GR) soybean [Glycine m ar (L.) Merr.] are gaining acceptance in U.S. cropping systems. Comparisons from cultivar performance trials suggest a yield suppression may exist wit h GR soybean. Yield suppressions may result from either cultivar genetic di fferentials, the GR gene/gene insertion process, or glyphosate. Grain yield of GR is probably not affected by glyphosate. Yield suppression due to the GR gene or ifs insertion process (GR effect) has not been reported. We con ducted a field experiment at four Nebraska locations in 2 yr to evaluate th e GR effect on soybean yield, Five backcross-derived pairs of GR and non-GR soybean sister lines were compared along with three high-yield, nonherbici de-resistant cultivars and five other herbicide-resistant cultivars. Glypho sate resistant sister lines yielded 5% (200 kg ha(-1)) less than the non-GR sisters (GR effect). Seed weight of the non-GR sisters,vas greater than th at of the GR sisters (in 1999) and the non-GR sister lines were 20 mm short er than the GR sisters. Other variables monitored were similar between the two cultivar groups. The high-yield, nonherbicide-resistant cultivars inclu ded for comparison yielded 5% more than the non-GR sisters and 10% more tha n the GR sisters.