Estimating the Individual Effects of the Reduced ... - PubAg - USDA

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RESEARCH

Estimating the Individual Effects of the Reduced Palmitic Acid fapnc and fap1 Alleles on Agronomic Traits in Two Soybean Populations Andrea J. Cardinal,* Ralph E. Dewey, and Joseph W. Burton

ABSTRACT Major fap alleles that reduce palmitate content in soybean [Glycine max (L.) Merr.] seed oil also can reduce seed yield. One of these alleles, fapnc, has been shown to be a deletion in the GmFATB1a gene. Allele-specific primers that amplify GmFATB1a can be used to test precisely if the fapnc allele has an effect on agronomic traits. The objectives of this study were to determine if the segregation of the fapnc allele explained a significant amount of genetic variation in several agronomic traits; to determine if the fap1 allele or minor palmitate genes have an effect on agronomic traits; and to confirm if GmFATB1a maps to the distal region on linkage group A1. GmFATB1a-specific primers were used to genotype lines from two populations segregating for fapnc, fap1, and fan alleles and modifier genes. The fapnc allele explained a significant portion of the genetic variation in seed yield, plant height, protein content, and stearic acid content in both populations. After removing the effect of fapnc from the model, the genetic correlation between palmitate and yield was significant in one population but not significant between palmitate and height, indicating that fap1 has a small but significant effect on seed yield but no effect on plant height. The fap1 and/ or modifier genes significantly affected stearic acid content. GmFATB1a mapped 20 cM distal to Satt684 on linkage group A1. Breeding efforts did not totally eliminate the negative influence of the fapnc allele on seed yield and plant height.

A.J. Cardinal and R.E. Dewey, Department of Crop Science, North Carolina State University, Box 7620, Raleigh. NC 27695; J.W. Burton, USDAARS, 3127 Ligon St, Plant Sci. Res., Raleigh, NC 27607. Received 27 June 2007. *Corresponding author ([email protected]). Abbreviations: BLUP, best linear unbiased predictor; FATB, 16:0-ACP thioesterase gene; 16:0, palmitic acid; 18:0, stearic acid; 18:1, oleic acid; 18:2, linoleic acid; 18:3, linolenic acid; PCR, polymerase chain reactions; QTL, quantitative trait locus; SSR, single sequence repeat.

S

oybean [Glycine max (L.) Merr.] oil quality can be improved through genetic alteration of the seed oil. Reducing the palmitic acid (16:0) content in soybean oil would be desirable to decrease the health risks of coronary diseases and breast, colon, and prostate cancers associated with the consumption of this fatty acid (Hu et al., 1997; Henderson, 1991). Several lines with reduced palmitic acid content have been developed by mutagenesis, including C1726 ( fap1fap1 genotype), ELLP2 ( fapxfapx genotype), A22 ( fap3fap3 genotype), and J3 (sop1sop1 genotype) (Fehr et al., 1991; Stojšin et al., 1998; Rahman et al., 1996; Wilcox and Cavins, 1990). Other lines, including N79-2077 ( fapnc fapnc genotype) and its derived line N79-2077-12, were developed by selection of a natural mutation (Burton et al., 1983; Burton et al., 1994b). Five genes have been identified to affect reduced palmitic acid content, yet their allelic relationships are not completely known. Three genes, fap1, fap3, and fapx, are at independent loci (Schnebly et al., 1994; Stojšin et al., 1998; Wilcox et al., 1994; Kinoshita et al., 1998; Primomo, 2000; Primomo et al., 2002). In addition, the genes sop1 and fapnc are independent of the fap1 locus, but the allelic relationship of sop1 to the other loci is unknown (Kinoshita et al., 1998; Wilcox et al., 1994). Molecular data suggest that fapnc and fap3 are at the same Published in Crop Sci. 48:633–639 (2008). doi: 10.2135/cropsci2007.05.0251 © Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.

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locus (Dewey, personal communication, 2006). A major palmitate quantitative trait locus (QTL), believed to be the Fapnc locus, was mapped to 14 cM distal of Satt684 on linkage group A1 (Li et al., 2002). In addition to these major genes, minor effect or modifier genes also influence the low palmitic acid content in soybean oil (Horejsi et al., 1994; Rebetzke et al., 1998b, 2001; Stojšin et al., 1998; Li et al., 2002). One minor palmitate QTL was mapped near Satt175 and Satt306 on Linkage group M (Li et al., 2002). The mode of action of the fapnc mutation is the best understood of the major palmitate acid genes at the molecular level. Biochemical studies have demonstrated that the triacylglycerol composition of lines homozygous for the fapnc mutation was related to the amount of 16:0 produced in the plastids (Wilson et al., (2001a,b). Furthermore, molecular genetic studies demonstrated that fapncfapnc genotypes have reduced accumulation of transcripts corresponding to a 16:0-ACP thioesterase (FATB) gene (Wilson et al., 2001b) and possess a deletion mutation that eliminates one of the FATB genes normally present within the soybean genome (Wilson et al., 2001a). More recently, analysis of the soybean FATB gene family revealed that the isoform designated as GmFATB1a represents the specific gene deleted in lines possessing the fapnc allele (Cardinal et al., 2007). Allele-specific primers corresponding to GmFATB1a were developed, and the segregation at that locus accounted for 62 to 70% of the genotypic variation in palmitic acid content in two populations (Cardinal et al., 2007). Although reducing the palmitate content of soybean seeds is a desirable goal, several studies have shown that the presence of major fap alleles is also associated with reductions in yield (Ndzana et al., 1994; Rebetzke et al., 1998a; Cardinal and Burton, 2007). Similarly, Cardinal and Burton (2007) reported that fapnc, fap1, or both had a significant positive genetic correlation with yield and plant height in the populations studied, indicating that lines with reduced palmitate content also tended to have reduced seed yield and plant height. These effects were attributed to either pleiotropy or linkage to unfavorable yield or plant height genes. The implications to plant breeding of these two possibilities are very different since unfavorable linkages can be broken by recombination but negative associations attributed to pleitropy cannot be changed. In addition, a positive genetic correlation between palmitic and stearic acids was observed in three populations (Cardinal and Burton, 2007), and fapncfapnc genotypes had significantly reduced stearic acid content in the oil (Cardinal et al., 2007). These findings suggest that the development of low palmitic, high stearic acid germplasm, useful for the baking industry, could be difficult. Although we have recently confirmed that unfavorable genetic correlations are observed between the reduced palmitate fapnc and fap1 alleles and plant height and yield (Cardinal and Burton, 2007; Cardinal et al., 2007), no 634

attempt was made to discriminate which specific low palmitic allele was responsible for the undesirable associations. The objectives of this study were (i) to estimate the amount of genetic variation in seed yield, plant height, flowering date, maturity date, protein and oil content, and fatty acid composition that is explained by the segregation of the fapnc allele; (ii) to determine if the fap1 allele or minor palmitate genes have an effect on these agronomic traits by estimating the genotypic and phenotypic correlations between palmitic acid content with other fatty acids and agronomic traits after the effect of the fapnc allele has been accounted for in the statistical model; and (iii) to confirm that the fapnc gene maps to the same genomic region of a major palmitate QTL reported by Li et al. (2002).

MATERIALS AND METHODS Development of Populations Two F4 -derived populations were developed by single seed descent (Brim, 1966). One population (FAHH00) was derived from the cross of a high-yielding line, ‘Corsica’ (Kenworthy, 1996), and a low linolenic, low palmitic acid line, N97-368111. A second population (FADD00) was derived from the cross of high yielding line, ‘Brim’ (Burton et al., 1994a) and a low linolenic, low palmitic line, N97-3708-13. N97-368111, N97-3708-13, and the cultivar Satelite are sister lines that were derived from different F3 plant selections from the cross ‘Soyola’ ×{‘Brim’(2) × [N88-431(2) × (N90-2013 × C1726)]} (Burton et al., 2004). The pedigree of these lines has been described by Cardinal et al. (2007) and Cardinal and Burton (2007). Briefly, N97-3681-11 and N97-3708-13 are F4 -derived lines homozygous for the low palmitic fapnc mutant allele from N79-2077-12, the low palmitic fap1 mutant allele from C1726, and the low linolenic fan (PI123440) allele. In addition, N973681-11 and N97-3708-13 are closely related to Brim, and the coefficient of parentage between these lines and Brim is 0.777. Therefore, genetic segregation in the Brim × N97-3706-13 (FADD00) population is expected to be limited to only 22% of the soybean genome.

Phenotypic Evaluation of Populations Each population was evaluated in separate field experiments. Ninety-eight F4 -derived lines and the parents of the FADD00 population and 99 F4 -derived lines and one parent (N97-368111) of the FAHH00 population were grown in Plymouth (NC) in 2002 and Caswell and Plymouth (NC) in 2003. Corsica was not included in the evaluation of the FAHH00 population because it is a very early variety and it is not adapted to North Carolina growing conditions. Within each environment, the experimental design for each population was a 10 × 10 lattice with two replications. Experimental units for the FADD00 and FAHH00 populations were four 4.88-m rows spaced at 1.27 m apart, where only the middle two rows end-trimmed to 3.96 m were harvested. Flowering date was recorded in each plot in both populations at the R2 stage as number of days after planting (Fehr and Caviness, 1977). Maturity date was recorded in each plot

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in both populations as number of days after planting to the R8 stage (Fehr and Caviness, 1977). Plots were mechanically harvested, and yield and moisture content were measured on every plot in FADD00 and FAHH00. Yields were adjusted to 13% moisture content. Ratings for lodging were taken whenever variation for this trait was observed in the populations. A five-point lodging scale was used, where a rating of 1 was given to perfectly erect plants and a lodging rating of 5 was given to plants lying on the ground. Height from the soil to the tip of a plant in cm was measured on an average plant in each plot. A 30-g sample of seed from each plot was analyzed for fatty acid content using gas-liquid chromatography of the methyl esters at the USDA-ARS Soybean and Nitrogen Fixation Research Unit, Raleigh, NC. Fatty acid content is reported in g kg–1 of total lipids. Protein and oil contents (dry weight basis) in all the populations were analyzed by near infrared reflectance spectroscopy at the USDA North Regional Research Center, Peoria, IL, in 2003.

Genotypic Evaluation of Populations DNA was extracted with a cetyltrimethylammonium bromide protocol by Li et al. (2002) from a bulk of leaf tissue from several plants of each line of populations FADD00 and FAHH00. Allelespecific primers for the fapnc allele (FATB1a) were used to perform polymerase chain reactions (PCR) with genomic DNA from each line in the two populations of this study (Cardinal et al., 2007). The PCR, amplification conditions, and band visualization methodology were described by Cardinal et al. (2007). The genotype for the fapnc allele was scored as presence or absence of a 312-bp band or 411-bp band, depending on the primer pair combination used for genotyping the fapnc allele (Cardinal et al., 2007). In addition, single sequence repeat (SSR) loci that have been mapped to linkage group A1 and M (Song et al., 2004) near the palmitate QTL reported by Li et al. (2002) were screened in the parents of the two populations to detect polymorphisms. Satt684, Satt276, and Satt042 from linkage group A1 were genotyped only in population FAHH00 since they were not polymorphic in FADD00. Only Sat_148 on linkage group M was genotyped in FAHH00, since all other SSRs in the nearby genomic region were monomorphic in both populations.

Statistical Analysis of Populations All the traits in each population were analyzed as a lattice design across environments with Proc Mixed, SAS 8.2 (Littell et al., 1996). Environments, replications, incomplete blocks, lines, and lines x environment interactions were considered random effects. To determine if the fapnc marker allele explained a significant amount of genetic variation of each trait in the FADD00 and FAHH00 populations, a best linear unbiased predictor (BLUP) was obtained for each line (Littell et al., 1996). Then, the BLUPs for each fatty acid and agronomic trait of each line were used to perform a t test to compare the mean effect of inheriting one or two copies of the fapnc marker allele (heterozygous or homozygous wild-type) versus zero copies (homozygous mutant). The fapnc marker class was the independent variable, and the BLUPs of each line for each fatty acid and agronomic traits were the dependent variable in the analysis. The mean of lines homozygous or heterozygous for the fapnc marker allele (presence of wild-type allele), the mean of CROP SCIENCE, VOL. 48, MARCH– APRIL 2008

lines homozygous for the absence of fapnc marker allele (mutant allele), the standard deviation of those means, the difference between means, and the R-square for the model were obtained using SAS Proc GLM, SAS 8.2. (SAS Institute, 1999). To determine if other low palmitate genes ( fap1 and minor genes) segregating in these populations are correlated with agronomic traits and other fatty acids in the soybean oil, genetic and phenotypic correlations between these traits were estimated after the effect of the fapnc gene had been accounted for in the model. This analysis was performed only for those traits that had significant overall genetic correlations in these populations (Cardinal and Burton, 2007) or that have been shown to be affected by the fapnc marker allele in previous studies (Cardinal et al., 2007). Genetic and phenotypic correlations with their standard errors were obtained by estimating genetic, genetic by environment, and error covariances by treating pair of traits as repeated measurements in a combined lattice design analysis across environments with the SAS Proc Mixed procedure (Holland, 2006). The fapnc marker allele was used as a class variable in the model. Genetic and phenotypic correlations were considered significant if their absolute value exceeded 1.96 times their standard error (Holland, 2006).

RESULTS AND DISCUSSION The Effect of the fapnc Allele on Agronomic Traits The mean yield of lines homozygous for the fapnc allele was significantly lower than the mean of lines heterozygous or homozygous for the Fapnc allele in both populations (Table 1). The grouping of lines heterozygous or homozygous for the Fapnc allele caused a bias and underestimation of the true differences between the fapncfapnc and the FapncFapnc genotypic classes. However, our significant differences would have remained significant if this bias had been removed. The number of observed homozygous lines for the fapnc allele was significantly less than expected for F4-derived populations. A possible explanation is that only F4:6 lines that produced enough seed to plant replicated yield trials were selected for this study, and unintended selection against fapnc fapnc lines due to their insufficient seed production might have occurred, as discussed by Cardinal et al. (2007). The differences between the two fapnc groups is almost three times greater in FAHH00 than in FADD00; however, the fapnc explained roughly the same amount of the genetic variation in seed yield in these populations, 22 to 27%. These results are in agreement with those observed by Rebetzke et al. (1998a), in which seed yield reduction was observed in fapncfapnc lines from the cross of the original unimproved low palmitic acid line to two high-yielding MG II cultivars. Therefore, several rounds of backcrossing to a high-yielding background have apparently reduced the yield drag but have not eliminated it. After the effect of the fapnc allele was removed, by including the fapnc marker as a class variable in the statistical model, a significant genetic correlation between palmitic acid content and seed yield was observed in

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Table 1. Means and standard deviations of palmitic acid content in total seed lipids in the seed, yield, date of flowering (R2), maturity date (R8), protein and oil contents, lodging rating, and height of lines homozygous (fapncfapnc) and of lines heterozygous or homozygous (Fapnc-) for the GmFATB1a allele for two F4-derived populations. Significance of differences between means were determined with a t test, and the R2 for the difference of those means was obtained from the model using SAS Proc GLM. Fapnc genotype

N†

Palmitate (g kg –1)

Yield (kg ha –1)

R2 (DAP)†

fapncfapnc

21

48.6 (8.7)

2455 (226)

59.6 (4.3)

145.2 (8.5)

438.18 (6.15)

190.41 (8.70)

2.57 (0.24)

94.3 (13.1)

Fapnc-

78

89.2 (11.7)

2727 (212)

57.6 (6.2)

142.4 (8.9)

429.69 (10.43)

195.87 (6.44)

2.61 (0.27)

107.3 (14.1)

–40.6***

−272***

NS§

NS

8.49***

−5.46***

NS

−13.0***

69.4

21.5

2.0

1.8

11.5

9.5

0.5

13.1

R8 (DAP)

Protein (g kg –1)

Oil (g kg –1)

Lodging

Height (cm)


Population Corsica × N97-3681-11 (FAHH00)

Difference 2

R (%)

Population Brim × N97-3708-13 (FADD00) fapncfapnc

24

53.8 (8.6)

2650 (79)

66.1 (2.1)

150.1 (2.8)

439.8 (4.20)

190.0 (4.08)

2.5 (0.2)

105.3 (5.1)

Fapnc-

74

89.2 (12.9)

2741 (61)

67.2 (2.6)

150.0 (2.8)

437.6 (4.43)

188.9 (3.67)

2.5 (0.2)

114.0 (5.7)

–35.4***

−91***

NS

NS

2.15*

NS

NS

−8.7***

62.2

26.5

3.8

0

4.4

1.8

2.1

31.5

Difference R2 (%) *Significant p < 0.05. ***Significant p < 0.001. †

N, number of lines with a specific Fapnc genotype.

‡

DAP, days after planting.

§

NS, not significant.

population FADD00 only (Table 2). In this case, the genetic and phenotypic correlations observed between palmitic acid and seed yield are probably caused by the effect of the fap1 allele since Rebetzke et al. (1998a) showed that minor palmitate genes did not affect yield. These results demonstrate that by reducing the “background variability” of yield genes segregating at loci not linked to the low palmitic acid trait (population FADD00), we increase the power to detect differences in seed yield caused by the other fap allele and/or minor genes segregating in the population. The differences between the two populations could be attributed to the close genetic relationship of the parents of FADD00 population. In the FADD00 population, many genomic regions that could affect seed yield independent of palmitic acid content are not segregating. This should reduce the variability arising from non-fap-associated sources and provide a better estimate of the actual mean seed yield difference between the two fapnc groups. When we compare the genetic correlation coefficients between palmitic acid and seed yield before (0.840 in FADD00 and 0.466 in FAHH00, Table 3 in Cardinal and Burton, 2007) and after adjusting for the effect of the fapnc allele (Table 2) in the model, we observe a substantial reduction in the coefficient magnitude due to the effect of the fapnc allele, and this correlation becomes nonsignificant in FAHH00. Collectively, the results presented here, together with those published previously, clearly demonstrate that the fapnc allele (or closely linked loci) has a significant effect on seed yield and that fap1 (or minor palmitate alleles) has a smaller but significant effect on seed yield in at least some populations. 636

Lines homozygous for the fapnc allele on average were significantly shorter than lines heterozygous or homozygous the Fapnc allele (Table 1). Similar differences in average plant height were observed between reduced ( fapncfapnc) and normal palmitate (Fapnc–) lines in another population reported previously (Rebetzke et al., 1998a). Thirteen and 32% of the genetic variation in height is explained by the Fapnc locus in FAHH00 and FADD00, respectively (Table 1). Palmitic acid was not significantly correlated with plant height after the effect of the fapnc allele was taken into account in the model in both populations (Table 2). All these results, in conjunction with the significant genetic correlations between these two traits in these populations when the genotype of the fapnc is not included in the model (0.453 in FADD00 and 0.253 in FAHH00, in Cardinal and Burton, 2007), demonstrate that the fapnc allele reduces plant height but that the fap1 allele and the minor palmitate alleles segregating in these populations do not affect this trait.

The Effect of the fapnc Allele on Seed Composition There were significant differences in protein content between lines homozygous for the fapnc allele and lines heterozygous or homozygous for the Fapnc allele (Table 1). Lines homozygous for the fapnc allele had a significant increase in protein content. However, the differences in protein content between the two fapnc groups and the amount of the genetic variation in protein explained by these differences are almost three times larger in FAHH00 than in FADD00. The differences between the two populations could again be attributed to the same causes as

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Table 2. Genetic (above diagonal) and phenotypic correlation coefficients (below diagonal) and standard error of the correlation coefficients (parenthesis) between palmitic and linolenic acids and agronomic traits after adjusting for the effect of the fapnc marker allele in two F4-derived populations.† Population FAHH00


Corsica × N97-3681-11

Traits Palmitate (g kg –1) Yield (kg ha –1) R2 (DAP) R8 (DAP) Protein (g kg –1) Oil (g kg –1) Height (cm)

FADD00 Brim × N97-3708-13

†

0.055 (0.065) –0.135 (0.086) –0.247 (0.078) 0.015 (0.079) 0.274 (0.075) –0.105 (0.081)

Yield (kg ha –1)

R2 (DAP)††

R8 (DAP)††

Protein (g kg –1)

Oil (g kg –1)

Height (cm)

0.020 (0.126)

–0.173 (0.103)

–0.294§ (0.101)

0.062 (0.114) –0.414 (0.118)

0.421 (0.094) 0.153 (0.128)

–0.123 (0.106)

–0.772 (0.049) –0.174 (0.063) 0.032 (0.066)

–0.668 (0.053)

0.572§ (0.233)

0.160 (0.137) –0.222 (0.306)

0.186 (0.050)

Protein (g kg –1)

0.115 (0.066)

0.040 (0.058)

Oil (g kg –1) Height (cm)

0.163 (0.074 –0.054 (0.062)

0.132 (0.054)

0.223 (0.113) 0.458 (0.248)

–0.096 (0.113)

Only those pairs of traits with significant overall genetic correlations (Cardinal et al., 2007) were tested.

†† §

Palmitate (g kg –1) Yield (kg ha –1) R2 (DAP) R8 (DAP)


DAP, days after planting.

Significant correlations in bold.

explained for seed yield. Rebetzke et al. (1998a) did not observe significant differences in the mean protein content between groups that inherited the fapnc allele or the Fapnc allele, albeit the same trend was observed. Palmitic acid was not significantly correlated with protein content after the effect of the fapnc allele was taken into account in the model in both populations (Table 2). These results and the significant genetic correlation between these two traits in population FAHH00 reported by Cardinal and Burton (2007) demonstrate that the fapnc allele slightly increases protein content but the fap1 allele and the minor palmitate alleles segregating in these populations do not. These observations could be an indirect consequence of the yield reduction caused by fapnc. In soybean, the negative genetic correlation between yield and protein is well documented (Burton, 1987). There was a significant difference in oil content between the two fapnc genotypic groups in FAHH00 only, and this difference explained 12% of the genotypic variation of oil (Table 1). Rebetzke et al. (1998a) observed significant differences in oil content between fapnc genotypic groups; however, the effect was in the opposite direction to CROP SCIENCE, VOL. 48, MARCH– APRIL 2008

those estimated in our study. Palmitic acid and oil content were significantly correlated in both populations when the effect of the fapnc allele is removed (Table 2). A significant overall genetic correlation was observed between palmitic acid and oil content in FAHH00 (0.503 in FAHH00 in Cardinal and Burton, 2007). Together these results demonstrate that the fapnc allele slightly increases oil content in one genetic background and that the fap1 allele and the minor palmitate alleles segregating in these populations can also affect this trait in some genetic backgrounds.

The Effect of the fapnc Allele on Fatty Acids of the Seed Oil There was a significant positive genetic correlation between palmitic and stearic acids in both populations after adjusting for the effect of the fapnc allele (Table 3). These estimates are between 45 and 60% of estimates from the statistical model that does not account for the effect of this locus (0.768 in FADD00 and 0.516 in FAHH00 in Cardinal and Burton, 2007). Also, Cardinal et al. (2007) reported that the fapnc allele explained between 23 and 50% of the genetic variation of stearic acid in these populations. All these observations

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confirm that in addition to fapnc, the fap1 and/or minor palmitic acid genes have a significant effect on stearic acid content similar to those reported in three populations by Ndzana et al. (1994) and one population by Primomo et al. (2002). There was no significant genetic correlation between palmitic and oleic acids in FADD00 after adjusting for the effect of the fapnc allele (Table 3). Cardinal et al. (2007) reported a significant difference in oleic acid content between fapnc allele groups in this population and Cardinal and Burton (2007) reported a significant overall genetic correlation between palmitic and oleic acids in this population; therefore, the results taken together imply that the fap1 and/or the minor genes do not significantly affect oleic acid as reported by Primomo et al. (2002). Ndzana et al. (1994) reported a significant correlation between palmitic and oleic acid content using materials containing both fap1 and fap3, but the individual effects of each fap allele were not discerned in that study. Palmitic acid was negatively correlated with linoleic acid after adjusting for the effect of the fapnc allele (Table 3) in FADD00. The segregation at the Fapnc locus explained 8 and 25% of the genotypic variation in linoleic acid in FADD00 and FAHH00, respectively (Cardinal et al., 2007), and palmitic acid was overall negatively correlated with linoleic acid in both populations (−0.469 in FAD00 and −0.522 in FAHH00 in Cardinal and Burton, 2007). Thus, a large proportion of the genetic variation in linoleic acid was accounted for by the fapnc allele in FAHH00, making the genetic correlation not significant. It is probable that some genetic variation in linoleic acid content can still be explained by segregation of the fap1 allele or

minor genes in FADD00, in agreement with observations in several populations by Primomo et al. (2002).

Genetic Mapping of the GmFATB1a Gene Markers Satt684, Satt276, and Satt042 mapped in one linkage group A1 in that order in population FAHH00 (data not shown). The genetic distance between Satt684 and Satt276 was 14 cM, and between Satt684 and Satt042, 28 cM. The Fapnc locus (GmFATB1a gene) mapped 20 cM distal to Satt684 but could not be linked to the other two markers in the same group (data not shown). Our results are in agreement with the genomic location of the major palmitate QTL reported previously (Li et al., 2002). Only one SSR marker on linkage group M (Sat_148) was polymorphic in FAHH00. Sat_148 is near Satt175, where a minor palmitate QTL was previously reported (Li et al., 2002). There was no association between palmitate content and the segregation at the Sat_148 locus in FAHH00 (data not shown). Therefore we could not validate the presence of a minor palmitate QTL in this genomic region. In conclusion, lines homozygous for the fapnc allele have consistently reduced seed yield and plant height with a very small increase in protein content. Genotypes homozygous for the fap1 allele have reduced seed yield in some genetic backgrounds. In addition, genotypes homozygous for fapnc or fap1 have reduced stearic acid content. Breeding efforts have reduced the linkage drag in lines homozygous for the fapnc allele but have not totally eliminated the negative effects on seed yield and height. Because it is desirable for human consumption to reduce the total

Table 3. Genetic (above diagonal) and phenotypic correlation coefficients (below diagonal) and standard error of the correlation coefficients (parenthesis) between fatty acids after adjusting for the effect of the fapnc marker allele in two F4-derived populations.† Population FAHH00 Corsica × N97-3681-11

Traits


Stearate (g kg –1) 0.206†† (0.105)

Palmitate (g kg –1) Stearate (g kg –1) Oleate (g kg –1)

0.195 (0.078)

Linoleate (g kg –1)

–0.021 (0.074)

Brim × N97-3708-13

Palmitate (g kg –1) Stearate (g kg –1) Oleate (g kg –1) Linoleate (g kg –1)

–0.128 (0.082) 0.406†† (0.104) 0.292 (0.062) –0.083 (0.072) –0.262 (0.073)

–0.150 (0.062)

Linoleate (g kg –1) †



–0.134 (0.117)

–0.868 (0.030)

Linoleate (g kg –1) FADD00

Oleate (g kg –1)

–0.925 (0.011) –0.432 (0.062) 0.035 (0.118)

–0.877 (0.017) –0.113 (0.073)

0.186 (0.074) –0.409 (0.094) –0.302 (0.119) –0.833 (0.036)

–0.211 (0.105) –0.413 (0.098) 0.075 (0.117)

0.039 (0.118) –0.382 (0.097)

–0.204 (0.076)

Only those pairs of traits with significant overall genetic correlations (Cardinal et al., 2007) were tested.

††

Significant correlations in bold.

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content of saturated fatty acids (especially palmitic acid) in the soybean oil, future breeding efforts should take into account that there is a yield penalty when these low palmitate alleles are introgressed into high-yielding cultivars. Acknowledgments This project was funded by the United Soybean Board.


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