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CROP BREEDING, GENETICS & CYTOLOGY

Relationship of Elevated Palmitate to Soybean Seed Traits

^a Dep. of Agronomy, Iowa State Univ., Ames, IA 50011 USA

wfehr{at}iastate.edu

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
Soybean [Glycine max (L.) Merr.] oil with elevated palmitate content may be useful for producing solid fat at room temperature without hydrogenation. This study was conducted to determine the relationship between elevated palmitate and soybean seed traits. A total of 92 soybean cultivars and lines with palmitate contents ranging from 103 to 427 g kg^-1 were evaluated in a randomized complete-block design with two replications at each of three Iowa locations in 1997. Seed from each plot was analyzed for protein, oil, palmitate, stearate, oleate, linoleate, and linolenate contents. The phenotypic correlations were significant (P < 0.05 or 0.01) and positive between palmitate and protein (0.25), stearate (0.58), and linolenate (0.86) contents. There were significant (P < 0.01) negative phenotypic correlations of palmitate content with oil (-0.84), oleate (-0.94), and linoleate (-0.96) contents. Lines with >400 g kg^-1 palmitate had protein contents equal to conventional cultivars, but their oil contents were reduced by more than 30 g kg^-1. None of the lines with >400 g ka^-1 had oleate, linoleate, or linolenate contents equal to conventional cultivars. These relationships will influence the feasibility of developing soybean cultivars with elevated palmitate content that are acceptable for other seed components.

Abbreviations: GLM, general linear model

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
SOYBEAN GENOTYPES have been reported with a range of palmitate contents from <40 to 380 g kg^-1 (Fehr et al., 1991; J.M. Narvel, 1999, unpublished data). Soybean oil with <40 g kg^-1 palmitate is more desirable than conventional soybean oil, with 110 g kg^-1 palmitate, for reducing the risk of coronary heart disease (Hu et al., 1997). The development of cultivars with elevated palmitate may be desirable for producing an oil with improved oxidative stability that can be interesterified to make solid fat at room temperature that does not contain trans-fatty esters (Kok et al., 1999; Shen et al., 1997).

Elevated palmitate content up to 240 g kg^-1 has been associated with changes in agronomic and seed traits. Hartmann et al. (1996) compared soybean lines with the fap2-bfap2-bfap4fap4 genotype containing 240 g kg^-1 palmitate and lines with the Fap2-bFap2-bFap4Fap4 genotype containing normal palmitate of 110 g kg^-1. In two populations, they observed significant negative phenotypic correlations of palmitate content with protein, oil, stearate, oleate, and linoleate contents, and a significant positive phenotypic correlation with linolenate content.

Recently, soybean genotypes with a range of palmitate contents have been developed by combining alleles developed by chemical mutagenesis. The purpose of this study was to evaluate the relationship of palmitate contents ranging from 100 to > 400 g kg^-1 in these genotypes with their seed traits.

	Materials and methods

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The experiment consisted of 92 soybean cultivars and lines with different combinations of major genes that control palmitate content (Table 1) . Some of the lines had major genes that have not been fully characterized. Modifying genes also are responsible for differences in palmitate content among the genotypes (Hartmann et al., 1996).

A five-seed bulk sample from each of five random plants in each plot was analyzed for fatty ester content with a gas chromatograph, as described by Hammond (1991). The mean of the five plants was used for data analysis. A bulk of seed from the five plants used for fatty ester analysis was evaluated for protein and oil content with a near-infrared reflectance whole grain analyzer. Protein and oil contents were adjusted to 13% moisture.

Analyses of variance were conducted with the general linear model (GLM) procedure of the SAS software (SAS Institute, 1992). Location and replication were considered random effects, and genotype was considered a fixed effect. Genotype means across locations were used for the regression of the seed traits on palmitate content with the GLM procedure and to compute the phenotypic correlation coefficients between palmitate content and the seed traits with the correlation (CORR) procedure of SAS.

	Results and discussion

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
Significant differences (P < 0.01) were observed among genotypes for the seven traits. Averaged across the three locations, palmitate content ranged from 103 to 427 g kg^-1, protein from 341 to 388 g kg^-1, oil from 98 to 190 g kg^-1, stearate from 35 to 80 g kg^-1, oleate from 76 to 242 g kg^-1, linoleate from 261 to 569 g kg^-1, and linolenate from 78 to 155 g kg^-1.

The mean palmitate contents of 259 g kg^-1 at the Agronomy Farm, 260 g kg^-1 at the Burkey Farm, and 257 g kg^-1 at Cedar Falls were not significantly different. The genotype x location interaction for palmitate content was not significant. The absence of a significant location effect and genotype x location interaction indicated that a limited number of environments are needed to assess the palmitate content of soybean genotypes.

Palmitate content was significantly associated with all the seed traits (Fig. 1) . The association between palmitate and protein was relatively weak, based on the small regression and phenotypic correlation coefficients for the two traits (Fig. 1a). There were genotypes with normal and elevated palmitate that had similar protein contents. It should be possible to develop cultivars with a range of elevated palmitate contents that have protein contents similar to conventional cultivars.

View larger version (18K): [in this window] [in a new window]   Fig. 1 Regression of soybean seed traits on palmitate content, phenotypic correlation coefficients between palmitate content and seed traits, and significance of the regression and correlation coefficients at the 0.05 (*) and 0.01 (**) probability levels

The association between palmitate and stearate was influenced by 14 genotypes that had stearate contents >60 g kg^-1 and palmitate contents >350 g kg^-1 (Fig. 1c). When the genotypes were included in the regression and correlation determinations, there was a relatively strong association between palmitate and stearate (Fig. 1c). When the genotypes were excluded, the regression coefficient was reduced from 0.07 (P = 0.01) to 0.02 (P = 0.05) and the correlation coefficient was reduced from 0.58 (P = 0.01) to 0.27 (P = 0.05). Excluding those genotypes, there were lines with elevated palmitate that had normal stearate contents. It should be possible to develop soybean cultivars with elevated palmitate that have normal or elevated stearate content.

There was a strong negative association of palmitate content with oleate and linoleate contents (Fig. 1d and 1e). None of the genotypes with elevated palmitate had oleate or linoleate contents similar to those of genotypes with normal palmitate. Hartmann et al. (1996) observed similar strong negative associations of elevated palmitate with reduced oleate and linoleate. Cultivars with elevated palmitate would be expected to have reduced contents of the two fatty esters.

Palmitate and linolenate contents were positively associated (Fig. 1f). The same positive association was reported by Hartmann et al. (1996) and Bravo et al. (1999) for genotypes with 250 g kg^-1 palmitate. The increase in linolenate was not expected because of the reduction in oleate and linoleate that was observed with increased palmitate. Our study supports the conclusion of Hartmann et al. (1996) that the development of cultivars with elevated palmitate and normal linolenate would be difficult, unless genes for reduced linolenate were included in the breeding program. Bravo et al. (1999) combined the fan1(A5) and fan2 alleles for reduced linolenate with the fap2-b and fap4 alleles for elevated palmitate and obtained lines with >250 g kg^-1 palmitate and <50 g kg^-1 linolenate. They did not recover any lines that had linolenate content <30 g kg^-1, as has been obtained when the alleles for reduced linolenate were in a genotype with the Fap2 and Fap4 alleles for normal palmitate. The unexpected result emphasized that it is not always possible to predict the way in which soybean oil composition will be changed by combining major genes for altered fatty esters.

With the available genotypes, it was not possible to evaluate the relationship of elevated palmitate with agronomic traits. Research is in progress to determine the agronomic performance of genotypes with >400 g kg^-1 palmitate. It also would be appropriate to evaluate oil with >400 g kg^-1 palmitate for oxidative stability in frying applications and for producing plastic fats without hydrogenation (Shen et al., 1997; Kok et al., 1999).

	NOTES

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Journal Paper no. J-18379 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA, Project no. 3107.

Received for publication May 17, 1999.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 

• Bravo J.J., Fehr W.R., Welke G.A., Hammond E.G., Cianzio S.R. Family and line selection for elevated palmitate of soybean. Crop Sci. 1999;39:679-682.[Abstract/Free Full Text]
• Burton J.W. Breeding soybeans for improved protein quantity and quality. In: Shibles R., ed. Proc. of the World Soybean Res. Conf. III. Ames, IA. 12–17 Aug. 1984. Boulder, CO: Westview Press, 1985:361-367.
• Fehr W.R., Welke G.A., Hammond E.G., Duvick D.N., Cianzio S.R. Inheritance of reduced palmitic acid content in seed oil of soybean. Crop Sci. 1991;31:88-89.
• Hammond E.G. Organization of rapid analysis of lipids in many individual plants. In: Linskens H.F., Jackson J.F., eds. Modern methods of plant analysis. Vol. 12. Berlin: Springer-Verlag, 1991:321-330.
• Hartmann R.B., Fehr W.R., Welke G.A., Hammond E.G., Duvick D.N., Cianzio S.R. Association of elevated palmitate content with agronomic and seed traits of soybean. Crop Sci. 1996;36:1466-1470.[Abstract/Free Full Text]
• Hu F.B., Stampfer M.J., Manson J.E., Rimm E., Colditz G.A., Rosner B.A., Hennekens C.H., Willett W.C. Dietary fat intake and the risk of coronary heart disease in women. N. Eng. J. Med. 1997;337:1491-1499.[Abstract/Free Full Text]
• Kok L.L., Fehr W.R., Hammond E.G., White P.J. Trans-free margarine from highly saturated soybean oil. J. Am. Oil Chem. Soc. 1999;In press.
• SAS Institute. SAS guide for personal computers, 6th ed Cary, NC: SAS Inst, 1992.
• Shen N., Fehr W., Johnson L., White P. Oxidative stabilities of soybean oils with elevated palmitate and reduced linolenate contents. J. Am. Oil Chem. Soc. 1997;74:299-302.[ISI]

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