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CROP BREEDING, GENETICS & CYTOLOGY

Association of Elevated Palmitate with Agronomic and Seed Traits of Soybean

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011

* Corresponding author (wfehr{at}iastate.edu)

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
A soybean [Glycine max (L.) Merr.] oil containing an elevated content of saturated fatty esters can be used to produce a plastic fat at room temperature without hydrogenation. Soybean genotypes with 400 g kg^-1 palmitate in their seed oil have been developed by combining mutant alleles for elevated palmitate. The purpose of this study was to determine the feasibility of developing cultivars with 400 g kg^-1 palmitate that would have agronomic and seed traits comparable to cultivars with less palmitate. Comparisons were made in replicated tests at three locations in Iowa during 2000 between 27 random BC₁F_2:4 lines with 400 g kg^-1 palmitate (400P lines) and 27 lines with 260 g kg^-1 (260P lines) from each of three populations. Seedling emergence averaged 23% less in the 400P lines than the 260P lines across the three populations. Mean seed yields adjusted for plant density by covariate analysis averaged 814 g kg^-1 less for the 400P lines than the 260P lines. None of the 400P lines yielded as much as any of the 260P lines in the three populations. The 400P lines had significantly less plant height by 9 cm, smaller seed size by 15 mg seed^-1, greater protein by 9 g kg^-1, and lower oil by 16 g kg^-1, oleate by 39 g kg^-1, and linoleate by 80 g kg^-1 than the 260P lines averaged across the three populations. Mean differences between the 400P and 260P lines were not consistently significant across the three populations for lodging score, stearate, or linolenate. With the mutant alleles involved in this study, it is not likely that soybean cultivars with 400 g kg^-1 palmitate could be developed that had comparable seed yield and oil content to cultivars with less palmitate.

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
SOYBEAN GENOTYPES that have palmitate contents from <40 to >400 g kg^-1 in their seed oil have been developed by combining mutant alleles obtained through chemical mutagenesis (Fehr et al., 1991; Stoltzfus et al., 2000). An oil with elevated palmitate has higher oxidative stability than conventional soybean oil containing 110 g kg^-1 palmitate, which may be desirable for food and industrial applications (Shen et al., 1997). A soybean oil with a total palmitate and stearate content of 433 g kg^-1 was used to produce by interesterification a plastic fat at room temperature as a substitute for hydrogenation of conventional oil (Kok et al., 1999). The interesterified product did not have the trans-fatty esters formed by hydrogenation that are considered undesirable for human health (Hu et al., 1997).

The commercial use of soybean oil with 400 g kg^-1 palmitate would depend on the price of the oil compared with that obtained from conventional cultivars. The price of the oil would depend on the seed yield, oil content, and other important agronomic and seed traits of cultivars with 400 g kg^-1 palmitate compared with those of conventional cultivars. Hartmann et al. (1996) compared the agronomic and seed traits of soybean lines containing 240 g kg^-1 palmitate with conventional lines from the same populations. Three of the most important mean differences they observed across two populations were 5.6% lower seed yield, 14 g kg^-1 lower protein, and 35 g kg^-1 lower oil for lines with elevated palmitate compared with conventional lines. They considered it feasible to develop cultivars with elevated palmitate that had acceptable seed yield and protein, but that it would be difficult to obtain an oil content comparable to that of conventional cultivars. Bravo et al. (1999) and Stoltzfus et al. (2000) also reported significant negative correlations between palmitate and oil content in soybean. The objective of our study was to determine the feasibility of developing acceptable cultivars for agronomic and seed traits that have 400 g kg^-1 palmitate.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
The lines evaluated in this study were obtained from three backcross populations. The donor plants with >440 g kg^-1 palmitate were obtained from a series of crosses that involved new mutant lines with >150 g kg^-1 palmitate selected at Iowa State University in 1994. Each mutant line was crossed to a line with the fap2-b and fap4 alleles that together produce 260 g kg^-1 palmitate. Progeny from the crosses that had >310 g kg^-1 palmitate were intercrossed to determine if they had different alleles for elevated palmitate, and progeny with >440 g kg^-1 palmitate were obtained. The genotype of the F₂ plants for the major genes controlling >440 g kg^-1 palmitate could not be determined because the alleles in the new mutant lines were not known. It was assumed that each plant had fap2, fap4, and at least two other alleles (Stoltzfus et al., 2000).

At Ames, IA, in 1997, the donor F₂ plants were mated to the lines A97-877006, A97-877027, and A96-496018 that had the genotype fap2-b fap4, 260 g kg^-1 palmitate, and good agronomic traits. The F₁ seeds of the three populations were planted in October 1997 at the Iowa State University–University of Puerto Rico soybean breeding nursery at Isabela, Puerto Rico. Each of 300 F₂ seeds from the three populations were split with a razor blade. The one-third of the seed that did not contain the embryonic axis was analyzed for fatty ester content by gas chromatography as described by Hammond (1991). The remaining part of the seed with the embryonic axis was saved for planting. The seeds with >410 g kg^-1 were planted at Isabela during February 1998, and the F₂ plants were backcrossed to their respective recurrent parent. The BC₁F₁ seeds were planted at Isabela during May 1998 to obtain BC₁F₂ seeds.

Each of 1000 F₂ seeds from each of the three backcross populations were split and analyzed for fatty ester content to identify seeds with the appropriate palmitate content. The backcross population derived from A97-877006 designated Population 1 had 88 seeds with 260 g kg^-1 and 95 with >400 g kg^-1 palmitate, Population 2 derived from A97-877027 had 108 seeds with 260 g kg^-1 and 92 with >400 g kg^-1 palmitate, and Population 3 derived from A96-496018 had 78 seeds with 260 g kg^-1 and 102 with >400 g kg^-1 palmitate. The selected seeds were planted at Puerto Rico during October 1998, and each BC₁F₂ plant was harvested individually. A bulk of five BC₁F₃ seeds from each plant was analyzed for fatty ester content, and the 50 BC₁F₂ plants with the lowest and the 50 with the highest palmitate were selected. The plants with the lowest palmitate had from 184 to 299 g kg^-1 and were designated 260P lines. The plants with the highest palmitate had from 411 to 482 g kg^-1 and were designated 400P lines.

In 1999, a separate experiment was grown for each population at Ames that included 50 260P lines, 50 400P lines, and 10 check lines and cultivars. Each experiment was grown as a randomized complete-block design with one replication at the Agronomy Farm and one at the Burkey Farm of the Agricultural Engineering and Agronomy Research Center. The soil type at both locations is a Nicollet loam (fine-loamy, mixed, superactive, mesic Aquic Hapludolls). The single-row plots were 0.76 m long with 1.02 m between rows and a 1.07-m alley between the ends of the plots. The seeding rate was 20 seeds per plot. Each plot was evaluated for maturity and harvested with a self-propelled plot combine. A bulk of seven seeds from each plot was analyzed for fatty ester content. Selection of lines for the replicated test in 2000 was based on palmitate content and maturity. There were 27 lines with 260 g kg^-1 and 27 lines with >400 g kg^-1 palmitate chosen for each population. For each line selected with >400 g kg^-1 palmitate, a line with 260 g kg^-1 palmitate and similar maturity was chosen to minimize the impact of maturity on comparisons between the two groups.

For each population, the 27 BC₁F_2:4 260P lines, 27 400P lines, and six check lines and cultivars were grown as a separate experiment. Each experiment was grown at Ames, Grand Junction, and Hubbard, IA, in a randomized complete-block design with two replications at each location. The soil type at the three locations is a Nicollet loam. The two-row plots were 3.1 m long with a spacing of 0.69 m between the two rows of each plot, and 1.02 m between adjacent plots. A 0.91-m alley separated the ends of the plots. The seeding rate was 17.4 seeds m^-1 of row.

Each plot was evaluated for plant density, maturity, lodging, height, seed yield, seed size, and protein, oil, and fatty ester content. The plant density in each plot was determined at V2 when there was a fully developed trifoliolate leaf at the node above the unifoliolate node (Fehr and Caviness, 1977). The number of plants in each plot was converted to plants m^-2. Maturity was recorded as days after 31 August when 95% of the pods on the main stem had reached their mature color. Lodging was scored after maturity from 1, all plants erect, to 5, all plants prostrate. Plant height was measured after maturity from the soil surface to the terminal node of the main stem. Each plot was harvested in bulk with a two-row self-propelled combine. Plot weight and moisture were used to determine seed yield in kg ha^-1 on a 13%-moisture basis. Seed size was determined by weighing 200 random seeds and converting the weight to mg seed^-1. Protein, oil, and moisture content were measured on a seed sample of 300 g with an Infratech 1221 near-infrared whole grain analyzer (Tecator AB, Hooganas, Sweden). Protein and oil were expressed on a 13%-moisture basis. The fatty ester content of a bulk sample of seven seeds from each plot was analyzed by gas chromatography by Pioneer Hi-Bred International, Inc., Johnson, IA. The data were expressed as the normalized percentage of all identified fatty esters and converted to g kg^-1 by multiplying the percentage by 10.

Seed yields of the lines were adjusted for plant density. An analysis of covariance was performed using the general linear models procedure (GLM) of the SAS software package (release 8.1) (SAS Institute, 2000). The data for each experiment in 2000 were analyzed with the GLM procedure of the SAS software package (SAS Institute, 2000). The check lines and cultivars were not included in the analyses of variance. Environments and replications were considered random effects and lines were considered fixed effects. The sums of squares for genotypes were partitioned into among 260P lines, among 400P lines, and the orthogonal comparison between the two groups. The significance of the mean squares for genotypes was evaluated with an F-test using the genotype x environment interaction mean squares.

Estimated processed value on a kilogram and hectare basis was determined as described by Brumm and Hurburgh (1990). The price of soybean oil used in the calculation was $0.339 kg^-1 and of soybean meal was $0.1728 kg^-1, based on the closing prices of the July futures on the Chicago Board of Trade on 13 June 2001. The price of hulls was $0.02 kg^-1.

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
There were significant (P < 0.05) differences for mean palmitate content between the 260P and 400P lines in the three populations (Table 1). The 260P lines had at least 93 g kg^-1 less palmitate than any of the 400P lines in the same population. The differences between the two groups made it possible to effectively assess the impact of elevating palmitate to 400 g kg^-1.

Soybean plants can adapt readily to differences in plant population by branching. No differences in seed yield have been observed with up to threefold differences in plant density (Johnson and Harris, 1967; Swearington, 1981). Despite this observation, the potential impact of plant density on yield in this study was minimized by adjusting yields of the lines for plant density by covariate analysis. Only adjusted yields are presented.

Mean seed yields were significantly (P < 0.05) lower for the 400P lines than the 260P lines in Populations 1 and 2 (Table 1). The difference was not significant (P < 0.07) in Population 3. The 400P lines yielded 718 kg ha^-1 (36.5%) less in Population 1, 844 kg ha^-1 (39.9%) less in Population 2, and 881 kg ha^-1 (41.8%) less in Population 3 than the 260P lines. None of the 400P lines yielded as well as any of the 260P lines in the same population. The phenotypic correlation coefficients between palmitate and yield were significant and negative in the three populations ranging from -0.91 to -0.97 (Table 2). It is unlikely that cultivars with 400 g kg^-1 palmitate could be developed with yields comparable with cultivars of conventional palmitate content, at least with the mutant alleles for elevated palmitate used in this study.

The mean seed size of 400P lines was significantly smaller than that of the 260P lines in Populations 2 and 3, but not in Population 1 (Table 1). The 400P lines weighed 15 mg seed^-1 less than the 260P lines in Population 1, 13 mg seed^-1 less in Population 2, and 17 mg seed^-1 less in Population 3. The smaller seed size should not be a negative factor in a cultivar development program. The smaller size would result in more seeds kg^-1, which could reduce the cost of seed for planting.

There was a significantly greater mean protein content and lower oil content in the 400P lines than the 260P lines (Table 1). The increase in protein of 9 g kg^-1 was less than the decrease in oil of 16 g kg^-1 averaged across the three populations. Stoltzfus et al. (2000) also observed that the increase in protein associated with elevation of palmitate was considerably less than the decrease in oil. Hartmann et al. (1996) reported a decrease in both mean protein and oil for lines with 240 g kg^-1 palmitate compared with conventional lines. At current prices for soybean oil and meal, the mean estimated processed value for soybean grain would be $0.008 kg^-1 less for 400P lines in Population 1, $0.004 kg^-1 less in Population 2, and $0.007 kg^-1 less in Population 3 than for the 260P lines. When the 400P lines were compared with the mean of the three conventional cultivars in the study, ‘9204’, ‘9281’, and ‘93B82’ from Pioneer Hi-Bred International, the 400P lines had $0.033 kg^-1 less estimated processed value for each of the three populations. The lower estimated processed value for a kilogram of the 400P lines than the conventional cultivars reflected their lower content of both protein and oil.

The combination of lower seed yield and estimated processed value for a kilogram of grain resulted in major differences in the estimated processed value for a hectare. The mean value for the 400P lines was $160 ha^-1 less in Population 1, $179 ha^-1 less in Population 2, and $191 ha^-1 less in Population 3 than for the 260P lines. In comparison with the mean of the three check cultivars, the 400P lines had $292 ha^-1 less estimated processed value in Population 1, $304 ha^-1 less in Population 2, and $340 ha^-1 less in Population 3. To recover the same gross income from a hectare, a producer would have to be paid an appreciable premium for growing a cultivar with 400 g kg^-1 instead of a cultivar with conventional palmitate.

The increase in palmitate for the 400P lines was associated with significant decreases in oleate and linoleate in the three populations (Table 1). Similar results were reported by Hartmann et al. (1996) and Stoltzfus et al. (2000). The 400P lines had 39 g kg^-1 less oleate and 80 g kg^-1 less linoleate than the 260P lines averaged across the three populations. Some of the 400P lines in Populations 1 and 2 had oleate contents greater than some of the 260P lines, but none of the 400P lines in Population 3 equaled any of the 260P lines. None of the 400P lines had linoleate contents equal to that of the 260P lines in any of the populations. The variation in oleate and linoleate within the 400P lines indicated that it would be possible to select for the two traits when developing cultivars with 400 g kg^-1 palmitate.

No significant differences were found between 260P and 400P lines for mean stearate and linolenate in the three populations (Table 1). The ranges for the two traits were comparable for the two groups of lines. There was significant variation among the 400P lines for both traits in Populations 2 and 3, but not Population 1. It should be possible to use the variation to select for stearate and linolenate in breeding for 400 g kg^-1 cultivars.

The development and commercial use of cultivars with 400 g kg^-1 palmitate would be primarily impacted by the negative associations of elevated palmitate with seed yield and oil content. The oil would have to be valuable enough for food and industrial applications to offset the extra cost associated with the lower seed yield and oil content compared with a conventional soybean cultivar.

	ACKNOWLEDGMENTS

 
The authors thank Silvia Cianzio for assisting with the development of the lines used in the study, Susan L. Johnson and Kevin O. Scholbrock for their assistance in collecting the field data, and Pioneer Hi-Bred International, Inc. for conducting the fatty ester analyses.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Journal Paper No. J-19528 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA. Project No. 3732 and supported by the Hatch Act, State of Iowa, and Iowa Soybean Promotion Board.

Received for publication August 31, 2001.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 

• Bravo, J.J., W.R. Fehr, G.A. Welke, E.G. Hammond, and S.R. Cianzio. 1999. Family and line selection for elevated palmitate of soybean. Crop Sci. 39:679–682.[Abstract/Free Full Text]
• Brumm, T.J., and C.R. Hurburgh. 1990. Estimating the processed value of soybeans. J. Am. Oil Chem. Soc. 67:302–307.
• Fehr, W.R., and C.E. Caviness. 1977. Stages of soybean development. Rep. 80. Iowa State Univ. Agric. Exp. Stn., Ames, IA.
• Fehr, W.R., G.A. Welke, E.G. Hammond, D.N. Duvick, and S.R. Cianzio. 1991. Inheritance of reduced palmitic acid content in seed oil of soybean. Crop Sci. 31:88–89.
• Hammond, E.G. 1991. Organization of rapid analysis of lipids in many individual plants. p. 321–330. In H.F. Linskens and J.F. Jackson (ed.) Modern methods of plant analysis. Vol. 12. Springer-Verlag, Berlin.
• Hartmann, R.B., W.R. Fehr, G.A. Welke, E.G. Hammond, D.N. Duvick, and S.R. Cianzio. 1996. Association of elevated palmitate content with agronomic and seed traits of soybean. Crop Sci. 36:1466–1470.[Abstract/Free Full Text]
• Hu, F.B., M.J. Stampfer, J.E. Manson, E. Rimm, G.A. Colditz, B.A. Rosner, C.H. Hennekens, and W.C. Willett. 1997. Dietary fat intake and the risk of coronary heart disease in women. New Engl. J. Med. 337:1491–1499.[Abstract/Free Full Text]
• Johnson, B.J., and H.B. Harris. 1967. Influence of plant population on yield and other characteristics of soybeans. Agron. J. 59:447–453.[Abstract/Free Full Text]
• Kok, L.L., W.R. Fehr, E.G. Hammond, and P.J. White. 1999. Trans-free margarine from highly saturated soybean oil. J. Am. Oil Chem. Soc. 76:1175–1181.[ISI]
• SAS Institute. 2000. SAS guide for personal computers. 8th ed. SAS Inst., Cary, NC.
• Shen, N., W. Fehr, L. Johnson, and P. White. 1997. Oxidative stabilities of soybean oils with elevated palmitate and reduced linolenate contents. J. Am. Oil Chem. Soc. 74:299–302.[ISI]
• Stoltzfus, D.L., W.R. Fehr, and G.A. Welke. 2000. Relationship of elevated palmitate to soybean seed traits. Crop Sci. 40:52–54.[Abstract/Free Full Text]
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