Glyphosate-Resistant Soybean Cultivar Yields Compared with Sister Lines

PRR-susceptible lines in the absence of PRR (Caviness and Walters, 1971; Singh and Lambert, 1985; Wilcox Herbicide-resistant crops like glyphosate resistant (GR) soybean and St. Martin, 1998). Singh and Lambert (1985) also [Glycine max (L.) Merr.] are gaining acceptance in U.S. cropping systems. Comparisons from cultivar performance trials suggest a yield reported no deleterious pleiotropic effects of the insersuppression may exist with GR soybean. Yield suppressions may result tion of the gene for PRR resistance. Thus, no yield supfrom either cultivar genetic differentials, the GR gene/gene insertion pression was associated with the incorporation of the process, or glyphosate. Grain yield of GR is probably not affected PPR genes into soybean cultivars. by glyphosate. Yield suppression due to the GR gene or its insertion Herbicide-resistant crops like glyphosate resistant (GR) process (GR effect) has not been reported. We conducted a field soybean are gaining widespread acceptance in U.S. experiment at four Nebraska locations in 2 yr to evaluate the GR cropping systems. This technology has promise in areas effect on soybean yield. Five backcross-derived pairs of GR and nonwhere other herbicides cannot effectively control weeds. GR soybean sister lines were compared along with three high-yield, However, potential yield suppression associated with nonherbicide-resistant cultivars and five other herbicide-resistant cultivars. Glyphosate resistant sister lines yielded 5% (200 kg ha21) less GR cultivars is a concern of producers and seed compathan the non-GR sisters (GR effect). Seed weight of the non-GR nies. Data from university soybean cultivar performance sisters was greater than that of the GR sisters (in 1999) and the trials in several states suggest a yield suppression may non-GR sister lines were 20 mm shorter than the GR sisters. Other exist with GR soybean (Minor, 1998; Nielsen, 2000; variables monitored were similar between the two cultivar groups. The Nelson et al., 1997, 1998, 1999; Oplinger et al., 1998; high-yield, nonherbicide-resistant cultivars included for comparison H.C. Minor, Univ. of Missouri, personal communicayielded 5% more than the non-GR sisters and 10% more than the tion, 1999). However, Delannay et al. (1995) stated that GR sisters. no yield suppresion was associated with the GR gene. This statement was based on unpublished research where six pairs of isopopulations with and without the S improvement through the incorporation of GR gene were compared (X. Delannay, personal comgenetic resistance or tolerance is an accepted pracmunication, Dec. 1999). He concluded that GR cultivars tice in soybean cultivar development for yield-limiting should perform as well as conventional cultivars of factors such as diseases (Athow, 1987) and nematodes (Riggs and Schmitt, 1987). A goal of plant breeders is equivalent maturities. The GR gene, CP4 EPSPS, from to maintain the productivity of the parent line in the breeding line 40-3-2 tested in the Delannay et al. study absence of the yield-limiting factor. Comparisons of remains as the source for resistance in current GR cultinear-isogenic lines with and without the tolerance or vars (X. Delannay, personal communication, Dec. 1999). resistance genes are important to ascertain if grain yields Yield suppression may result from either the GR are suppressed. gene/gene insertion, glyphosate (both individually or Phytophthora root rot (PRR, caused by Phytophthora collectively are termed yield drag), or cultivar genetic megasperma f. sp. glycinea Kuan and Erwin) was one differentiation (yield lag). Yield lag represents yield of the most destructive diseases of soybean (Athow, suppression due to the genetics of the cultivar or line 1987). It provides a good case study for this discussion. in which the GR gene is inserted. Thus, yield of GR In the early 1960s genetic resistance to PRR was incorcultivars may lag behind that of other cultivars simply porated into several cultivars through backcrossing probecause the GR gene was inserted in lower yielding or grams resulting in near-isogenic lines (Athow, 1987). older cultivars. Yield drag can result from either the Several researchers using near-isogenic lines have reGR gene or its insertion (GR effect) or the application ported that PRR-resistant lines perform the same as of glyphosate (herbicide effect). We reported that glyphosate did not suppress grain yield of GR soybean cultivars R.W. Elmore, and F.W. Roeth, Univ. of Nebraska, South Central and hence did not contribute to a yield drag (Elmore Res. and Ext. Center, Clay Center, NE 68933; L.A. Nelson and A. et al., 2001). Yield drag could also result from the GR Martin, Dep. of Agronomy, Univ. of Nebraska, Lincoln, NE 68583; R.N. Klein, Univ. of Nebraska-Lincoln, West Central Res. and Ext. Center, North Platte, NE 69101; and C.A. Shapiro and S.Z. Knezevic, Abbreviations: a.e., acid equivalent; GR, glyphosate resistant; LL, Univ. of Nebraska, Northeast Res. and Ext. Center–Haskell Ag Lab, liberty link; NEREC-HAL, Northeast Research and Extension CenConcord, NE 68728. Univ. of Nebraska, Lincoln, Agric. Res. Div. ter–Haskell Agric. Lab.; PRR, phytophthora root rot; R1, flowering; J. Ser. no. 13050. Received 12 June 2000. *Corresponding author R7, physiological maturity; R8, harvest maturity; SCREC, South Cen([email protected]). tral Research and Extension Center; STS, sulfonylurea-resistant soybean; WCREC, West Central Research and Extension Center. Published in Agron. J. 93:408–412 (2001).