Glyphosate-Resistant Soybean Cultivar Yields Compared with Sister Lines 

Agronomy Journal 93:408-412 Mar/Apr01

¹Roger W. Elmore and Fred W. Roeth, University of Nebraska, South Central Research and
Extension Center, Clay Center,  NE 68933; Lenis A. Nelson and Alex Martin, Dept. of  Agronomy,
University of Nebraska, Lincoln, NE 68583;  Robert N. Klein, University of Nebraska, West Central Research and Extension
Center, North Platte, NE  69101; Charles A. Shapiro and Stevan Z. Knezevic, University of
Nebraska, Northeast Research and Extension Center-Haskell Ag Lab, Concord, NE 68728.

ABSTRACT

INTRODUCTION

Phytophthora root rot (PRR, caused by Phytophthora megasperma f. sp. glycinea Kuan and Erwin) was one of the most destructive diseases of soybean (Athow, 1987). It provides a good case study for this discussion. In the early 1960s genetic resistance to PRR was incorporated into several cultivars through backcrossing programs resulting in near-isogenic lines (Athow, 1987). Several researchers using near-isogenic lines have reported that PRR resistant lines perform the same as PRR susceptible lines in the absence of PRR (Caviness and Walters, 1971; Singh and Lambert, 1985; Wilcox and St. Martin, 1998). Singh and Lambert (1985) also reported  no deleterious pleiotropic effects of the insertion of the gene for PRR resistance. Thus, no yield suppression was associated with the incorporation of the PPR genes into soybean cultivars.

Herbicide-resistant crops like glyphosate resistant (GR) soybean  are gaining widespread acceptance in U.S. cropping systems. This technology has  promise in areas where other herbicides cannot effectively control weeds. However, potential yield suppression  associated with GR cultivars is a concern of producers and seed companies. Data from university soybean cultivar performance trials in several states suggest a yield suppression may exist with GR soybean (Minor, 1998;  H. C.  Minor, Univ. of Missouri, personal communication 1999; R.L. Nielsen, 2000; L. A. Nelson et al., 1997, 1998, 1999; Oplinger et al., 1998).  However, Delannay et al. (1995) stated that no yield suppression  was associated with the GR gene. This statement was based on unpublished research where six pairs of isopopulations with and without the GR gene were compared (X. Delannay, personal communication,  Dec. 1999). He concluded that GR cultivars should perform as well as conventional cultivars of equivalent maturities. The GR gene, CP4 EPSPS,  from breeding line 40-3-2 tested  in the Delannay et al. study remains as the source for resistance in  current GR cultivars (X. Delannay, personal communication,  Dec.1999).

Yield suppression  may result from either the GR gene/gene insertion, glyphosate (both individually or collectively are termed yield drag), or cultivar genetic differentiation (yield lag). Yield lag represents yield suppression due to the genetics of the cultivar or line in which the GR gene is inserted. Thus, yield of GR cultivars may ‘lag’ behind that of other cultivars simply because the GR gene was  inserted in lower yielding or older cultivars. Yield drag can result from either the GR gene or its insertion (GR effect) or the application of  glyphosate (herbicide effect). We reported  that glyphosate did not suppress grain yield of GR soybean cultivars and  hence did not contribute to a yield drag (Elmore et al., 2001). Yield drag could also result from the GR gene or its insertion process (GR effect); evidence of this has not been reported.

We designed two experiments to test for  yield drag: the effect of GR  gene insertion on GR (reported in this paper) and the effect of glyphosate (Elmore et al., 2001). To evaluate  the GR effect on yield and agronomic traits, field experiments were conducted at four Nebraska locations on five pairs of GR, non-GR sister lines in 1998 and on four pairs of GR, non-GR, sister lines in 1999. Eight other cultivars were included for comparison. We could not discern between yield drag associated  with the GR gene itself or effects of its insertion in this study. Thus reference to the GR effect could mean either or both of these possibilities.

MATERIALS AND METHODS:

Cultivars grown are shown in Table 4. Entries 1 to 3 were included based on their tolerance to glufosinate (Liberty Link, LL) and chlorimuron/thifensulfuron (sulfonylurea -resistant soybean, STS). Entries 4-6 were included because of  their high yield in the Univ. of Nebraska’s 1997 cultivar tests (Nelson, et al., 1997). Entries 7-8 were included since they were also in the companion study (Elmore et al., 2001); these cultivars were  provided by two of the major seed companies in Nebraska based on their maturities and yield . Entries 1-8 were included as checks. Backcross-derived BC3 and BC4  sister line pairs were provided by  two seed companies. The lines were chosen based on appropriate maturities for our locations. Unfortunately, isogenic lines of non-GR and GR cultivars or lines were not available.

Flowering date (R1), physiological maturity (R7) and harvest maturity (R8) (Ritchie et al., 1996) were recorded at several of the locations.  In addition, stand counts were taken during the vegetative stages, plant height at R7,  and lodging scores were recorded at R8. Seed weights were recorded at 3 locations in 1999. The center two rows of each plot were harvested with a small plot harvester for yield and seed weight determination.

Data were processed with SAS mixed models procedures (Littell et al., 1996). Cultivar was considered a fixed effect. Locations and  replicates and their interactions with the fixed effect were treated as random effects. Single-degree-of-freedom comparisons were used to isolate cultivar grouping differences: LL/STS vs. STS; STS vs. High yield ; LL/STS vs. High yield; LL/STS vs. all GR; STS vs. all GR; High yield vs. non-GR sisters; non-GR sisters vs. GR sisters; GR cultivars (7 and 8) vs. GR sisters; High yield vs. all GR; High yield vs. GR (7 and 8); 9 vs 10; 11 vs. 12; 13 vs. 14; 15 vs. 16; and 17 vs. 18. We also used correlation to compare grain yields of GR and non-GR sister lines.

Three sets of analyses were used for each variable. The first compared  all entries except 13 and 14 over both years. The second and third analyses included all entries in 1998 and 1999, respectively, since entries 13 and 14 were not available in 1999. Data presented are least squares adjusted means. Differences mentioned are significant at P < 0.05.
 

RESULTS AND DISCUSSION:

Seed weight of the non-GR sisters was greater than that of the GR sisters (in 1999) and the non-GR sister lines were 20 mm shorter than the GR sisters (Table 5). Other variables monitored were similar between the two cultivar groups. The GR sisters  yielded the same as the average of entries 7 and 8, two GR cultivars included in the study for comparison (data not shown). Entries 7 and 8 yielded the same as other GR cultivars in another study with other GR cultivars (Elmore et al., 2001). Yield of the GR check cultivar entry 8 was similar to those of the high-yield, non-herbicide-resistant cultivars (entries 4, 5, and 6). In addition, although no statistical comparisons were possible, yields of the highest yielding GR cultivars in the other study (Elmore et al. 2001) were similar to those of the high-yield, non-herbicide-resistant cultivars in this study (data not shown). The high-yield, non-herbicide-resistant cultivars (entries 4, 5, and 6) yielded 5% more than the non-GR sisters (Tables 5 and 6). This 5% difference is a yield lag. The GR gene in the GR sisters therefore reduced soybean yield 5% compared to the non-GR sisters and 10% when compared to high-yield, non-herbicide-resistant cultivars.

The high-yield, non-herbicide-resistant checks in the study, entries  4, 5, and 6, also yielded the same or more than the other herbicide-resistant cultivars included in the experiment (Tables 4 and 6).  The average yield of all 7 GR cultivars was similar to that of the LL/STS cultivar (entry 1), and greater than that of the average of the two STS cultivars (entries 2 and 3). A comparison of the means of the  STS cultivars shows that entry 3 yielded  less  than the other STS cultivar, entry 2, as well as the other herbicide-resistant cultivars (Table 4). Herbicide-resistant cultivars yielded from the same  to 15% less than the non-herbicide-resistant cultivars included in these studies (Table 4 and 6).

CONCLUSIONS AND IMPLICATIONS:

REFERENCES:

Caviness, C.E., and H.J. Walters. 1971. Effect of phytophthora rot on yield and chemical composition of soybean seed. Crop Sci. 71:83-84.

Delannay, X., T.T. Bauman, D.H.Beighley, M.J. Buettner, H.D.Coble, M.S. DeFelice, C.W. Derting, T.J. Diedrick, J.L. Griffin, E.S. Hagood, F.G. Hancock, S.E. Hart, B.J. LaVallee, M.M. Loux, W.E. Lueschen, K.W. Matson, C.K. Moots, E.Murdock, A.D. Nickell, M.D.K. Owen, E.H. Paschall II, L.M. Prochaska, P.J. Raymond, D.B. Reynolds, W.K. Rhodes, F.W. Roeth, P.L. Sprankle, L. J. Tarochione, C.N. Tinius, R.H. Walker, L.M. Wax, H.D. Weigelt, and S.R. Padgette. 1995. Yield evaluation of a glyphosate-tolerant soybean line after treatment with glyphosate. Crop Sci. 35:1462-1467.

Elmore, Roger W., Fred W. Roeth,  Robert N. Klein,  Stevan Z. Knezevic,  Alex Martin,  Lenis A. Nelson, and Charles A. Shapiro. 2001. Glyphosate-resistant soybean cultivar response to glyphosate. Agron. J. 93:404-407 (2001).

Littell, R.C., G.A.  Milliken, W.W. Stroup, and R. Wolfinger. 1996. SAS system for mixed models. SAS Institute Inc. Cary NC.

Minor, H. 1998. Performance of GMO’s vs. traditional varieties: a southern perspective p. 1-9. In Proceedings of the 28th Soybean Seed Research Conference, Chicago, IL, Dec. 1998.  American Seed Trade Assoc., Washington D.C.

Nielsen, R.L. 2000. Transgenic crops in Indiana: short term issues for farmers

Nelson, L.A.,  R.W. Elmore,  R.N. Klein, and C. Shapiro. 1997. Nebraska Soybean Variety Tests-1997. Nebraska Coop. Ext. E. C. 97-104-A.

Nelson, L.A.,  R.W. Elmore,  R.N. Klein, and C. Shapiro. 1998. Nebraska Soybean Variety Tests-1998. Nebraska Coop. Ext. E. C. 98-104-A.

Nelson, L.A.,  R. W. Elmore,  R.N. Klein, and C. Shapiro. 1999. Nebraska Soybean Variety Tests-1999. Nebraska Coop. Ext. E. C. 99-104-A.

Oplinger, E.S., M.J. Martinka and K.A. Schmitz. 1998. Performance of transgenic soybeans - Northern U.S.  P. 10-14. In  Proceedings of the 28th Soybean Seed Research Conference. Chicago, IL, Dec. 1998. American Seed Trade Assoc., Washington D.C..

Riggs, R.D., and D.P. Schmitt. 1987. Nematodes. P. 757-778. In J.R.Wilcox et al. (ed.) Soybeans: improvement, production, and uses, 2nd edition. Agron. Monogr. 16. ASA, CSSA, and SSSA,  Madison WI.

Ritchie, S.W., J.J. Hanway, and H.E. Thompson. 1996. How a soybean plant develops. Special Report No. 53. Iowa State Univ. Coop. Ext. Service. Ames IA.

Singh, N.B., and J.W. Lambert. 1985. Effect of gene Rps1 for resistance to phytophthora rot on yield and other characteristics of soybean. Crop Sci. 25: 494-496.

Wilcox, J.R., and S.K. St. Martin. 1998. Soybean genotypes resistant to Phytophthora sojae and compensation for yield losses of susceptible isolines. Plant dis. 82:303-306.

ACKNOWLEDGMENT:

Table 1. Location, important activity dates, and water received, Nebraska, 1998-1999.

^†   Growing season precipitation
^‡    Applications began on 20 July and 19 July and ended on 20 and 18 August for 1998 and 1999, respectively. A gated-pipe, gravity irrigation system was used. Irrigation amounts are not available

Table 2. Soils at each location, Nebraska, 1998-1999.

Table 3. Preplant and preemergence herbicide application information by location and year, Nebraska, 1998-1999.

^†   Clethodim and crop oil concentrate were applied at 0.11 kg ha^-1 + 1.10 1 ha^-1 on 25 June 1998
and 6 July 1999 for volunteer corn control

Table 4. Cultivars used in this study, Nebraska, 1998-1999.

^†   Two-year, four-location means except for one year means for entries 13 and 14
^‡   Resistant to Liberty, glufosinate
^§   STS, soybean resistant to chlorimuron/thifensulfuron
^¶   Glyphosate resistant soybean. Entries 7 and 8 were grown in the experiments discussed in Elmore et al.,
     2001
^*   Sister pairs followed by the same letter are not different (P < 0.05) based on single-degree-of-freedom
    comparisons

Table 5. Non-glyphosate-resistant sister lines (non-GR sisters) yielded more than their GR sisters averaged over all locations and two years. Growth and development of these two variety groups differed.

^†  1 to 5 scale with 1 = erect, and 5 = prostrate.
*  Means followed by the same letter within a column are similar (P < 0.05). Means were separated using single-degree-of-freedom comparisons.

Table 6. Herbicide-resistant varieties yielded less than the non-herbicide-resistant check varieties averaged over all locations and two years.

*  Means followed by the same letter within a column are similar (P < 0.05). Means were separated using single-degree-of-freedom comparisons.
^†  1 to 5 scale with 1 = erect, and 5 = prostrate.
^‡  Standard errors of the mean (S.E.) are the greatest encountered for the individual single-degree-of-greedom comparisons among means in each column. In all cases this was the S.E. associated with the LL/STS versus STS single-degree-of-freedom comparison.