Glyphosate-Resistant
Soybean Cultivar Yields Compared with Sister Lines
Agronomy Journal
93:408-412 Mar/Apr01
R. W. Elmore, F.
W. Roeth, Lenis A. Nelson,
Charles A. Shapiro, Robert
N. Klein, Stevan Z.
Knezevic, and Alex Martin.1University of Nebraska South Central Research and Extension Center, Clay Center, NE 68933
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
Herbicide-resistant crops like glyphosate resistant (GR) soybean (Glycine max (L.) Merr.) are gaining acceptance in U.S. cropping systems. Comparisons from cultivar performance trials suggest a yield suppression may exist with GR soybean. Yield suppressions may result from either cultivar genetic differentials, 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 its insertion process (GR effect) has not been reported. We conducted a field experiment at four Nebraska locations in 2 years to evaluate the GR effect on soybean yield. Five backcross-derived pairs of GR and non-GR soybean sister lines were compared along with 3 high-yield, non-herbicide-resistant cultivars and 5 other herbicide-resistant cultivars. GR sister lines yielded 5% (200 kg ha-1) less than the non-GR sisters (GR effect). 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. Other variables monitored were similar between the two cultivar groups. The high-yield, non-herbicide-resistant cultivars included for comparison yielded 5% more than the non-GR sisters and 10% more than the GR sisters.INTRODUCTION
Soybean improvement through the incorporation of genetic resistance or tolerance is an accepted practice in soybean cultivar development for yield-limiting factors such as diseases (Athow, 1987) and nematodes (Riggs and Schmitt, 1987). A goal of plant breeders is to maintain the productivity of the parent line in the absence of the yield-limiting factor. Comparisons of near-isogenic lines with and without the tolerance or resistance genes are important to ascertain if grain yields are suppressed.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:
Field experiments were planted at four Nebraska locations in 1998 and 1999 (Tables 1 and 2). Corn was grown prior to the experimental year in both years at all locations. Subplots were 4 - 0.76 m rows by 9.1 m in length. Seeding rate was 370 000 seed ha-1. Field preparation activities varied by location and year: Lincoln Agronomy farm 1998 and 1999 - disk and field cultivate in spring; North East Research and Extension Center-Haskell Ag Lab 1998 - disk and field cultivate in spring, 1999 - fall disk, spring disk and field cultivate; South Central Research and Extension Center 1998 - 2 passes of mulch master (John Deere, Moline IL) in spring; 1999 - rototilled in spring; West Central Research and Extension Center (WCREC): 1998 and 1999 - ridge till. Plots were sprayed with the pre-emergence herbicide combination of metolachlor and metribuzin to help control weeds. Glyphosate was also applied at the WCREC location to control emerged weeds (Table 3). The experiments were maintained weed-free by hand weeding. We used a randomized complete block experimental design with 4 replications at all locations except only 3 replicates were used at WCREC in 1999.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 Nebraskas 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:
On average, non-GR sister lines yielded 5% (200 kg ha-1) more than the GR sisters when averaged over all locations and both years (Table 5). Non-GR sister grain yields were greater than those of their associated GR sisters in two of the five pairs (Table 4). Results were similar in the single-year analyses (data not shown). Grain yields of sister-line pairs are shown in Figure 1. The greater number of data points to the right of the 1:1 ratio line indicates that the non-GR sisters yielded more on the average than their GR sister counterparts. This reinforces the previous statement on the average soybean yields of the non-GR sisters relative to the GR sisters in the individual years and in the 2-year analysis (Table 5).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:
Yields were suppressed with GR soybean cultivars. Our other work showed that there was no effect of glyphosate on GR cultivars (Elmore et al., 2001). The work reported here demonstrates that a 5% yield suppression was related to the gene or its insertion process and another 5% suppression was due to cultivar genetic differential. Producers should consider the potential for 5-10% yield differentials between GR and non-GR cultivars as they evaluate the overall profitability of producing soybean. Cultivar choices are best based on i) previous weed pressure and success of control measures in specific fields, ii) the availability and cost of herbicides, iii) availability and cost of herbicide-resistant cultivars, and iv) yield, and not solely on whether cultivars are herbicide resistant. Based on our results from this study and those of Elmore et al., 2001, the yield suppression appears associated with the GR gene or its insertion process rather than glyphosate itself.REFERENCES:
Athow, K.L. 1987. Fungal diseases. p. 687-727. In J.R.Wilcox et al. (ed.) Soybeans: improvement, production, and uses, 2nd edition. Agron. Monogr. 16. ASA, CSSA, and SSSA, Madison WI.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 GMOs 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:
We thank the Nebraska Soybean Board who partially supported the research. Technical support personnel at the various locations were: Clay Center - Sharon Hachtel, George Hoffmeister Jr., Ralph Klein, Perry Ridgeway, Irv Schleufer, and Sandy Sterkel; Lincoln - Greg Dorn and John Eis; North Platte - Jeff Goulis; Concord - Lisa Lunz and Ray Brentlinger. We appreciate their efforts!Table 1. Location, important activity dates, and water received, Nebraska, 1998-1999.
| Location | City | date |
date |
applied |
date |
||
| AgronomyFarm | Lincoln | ||||||
| NEREC-HAL | Concord | ||||||
| SCREC | ClayCenter | ||||||
| WCREC | |||||||
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.
| Location | |||
| AgronomyFarm | |||
| NEREC-HAL | |||
| SCREC | |||
| WCREC |
Table 3. Preplant and preemergence herbicide application information by location and year, Nebraska, 1998-1999.
| Location | Date |
(kg ha-1) |
||
| AgronomyFarm | ||||
| AgronomyFarm | ||||
| NEREC | ||||
| NEREC | ||||
| SCREC | ||||
| SCREC | ||||
| WCREC | ||||
| WCREC |
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.
| No. | Company | Mg ha-1 |
||
| 1 | Asgrow | |||
| 2 | Pioneer | |||
| 3 | Golden Harvest | |||
| 4 | Hoegemeyer | |||
| 5 | Desoy | |||
| 6 | M/W Genetics | |||
| 7 | Pioneer | |||
| 8 | Asgrow | |||
| 9 | NC+ | |||
| 10 | NC+ | |||
| 11 | NC+ | |||
| 12 | NC+ | |||
| 13 | Stine (1998 only) | |||
| 14 | Stine (1998 only) | |||
| 15 | Stine | |||
| 16 | Stine | |||
| 17 | Stine | |||
| 18 | Stine |
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
Ά 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.
| Variety group (entries in each group) |
31 May |
@ mat. (R7) |
fr 31 May |
fr 31 May |
|||||
| Non-GR Sisters (9,11,15,17) |
|||||||||
| GR Sisters (10,12,16,18) |
|||||||||
| S.E. | |||||||||
| # locations reporting data: 1998/1999 |
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.
| Cultivar group (entries in each group) |
31 May |
@ mat. (R7) |
fr 31 May |
fr 31 May |
|||||
| Liberty Link (LL)/STS (1) |
|||||||||
| STS (2, 3) |
|||||||||
| All glyphosate-resistant cultivars (7,8,10,12,16,18) | |||||||||
| Non-herbicide-resistant controls (4, 5, 6) | |||||||||
| S.E. | |||||||||
| # locations reporting data: 1998/1999 |
* 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.
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