| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
a Dep. of Entomology, Soils, and Plant Sciences, Clemson Univ., Clemson, SC 29634
b Dep. of Applied Economics and Statistics, Clemson Univ., Clemson, SC 29634. Technical Contribution no. 5328 of the Clemson University Experiment Station. This material is based on work supported by the CSREES/USDA, under project number SC-1700197 and by grants from the United Soybean Board and the South Carolina Soybean Board
* Corresponding author (cry{at}clemson.edu).
 |
ABSTRACT |
|---|
 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Abbreviations: MFAL, modified fatty acid breeding line • NCAUR, USDA National Center for Utilization Research.
|
NOTES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Received for publication May 23, 2007.
a Dep. of Entomology, Soils, and Plant Sciences, Clemson Univ., Clemson, SC 29634
b Dep. of Applied Economics and Statistics, Clemson Univ., Clemson, SC 29634. Technical Contribution no. 5328 of the Clemson University Experiment Station. This material is based on work supported by the CSREES/USDA, under project number SC-1700197 and by grants from the United Soybean Board and the South Carolina Soybean Board
* Corresponding author (cry{at}clemson.edu).
A primary focus for soybean [Glycine max (L.) Merr.] breeders recently has been the development of cultivars with improved oil qualities such as reduced palmitic acid (16:0) and linolenic acid (18:3). A backcross breeding program was used to develop five low 16:0, two low 16:0 + 18:3, and one low 18:3 modified fatty acid breeding lines (MFALs). Research objectives were (i) to determine planting date effects on fatty acid content in the eight MFALs and (ii) to compare the MFALs to parental cultivars for seed composition and agronomic traits. The eight MFALs and four control cultivars were evaluated at two planting dates at Clemson, SC, in 2001, 2003, and 2004. Planting dates were chosen to simulate full season and double crop planting dates for South Carolina soybean production. Agronomic traits including seed yield, plant height, lodging, maturity date, seed size, and seed quality were measured, and seeds were analyzed for protein, oil, and fatty acid levels. Planting date had a significant effect on all agronomic variables, as well as on protein, oil, and palmitic and linolenic acid. There was a decrease in palmitic acid at the late planting date, while the early planting date resulted in a decrease in linolenic acid levels. The effect of genotype was significant for all agronomic and seed composition variables measured when averaged across planting dates. It appears that planting date may be manipulated to reduce palmitic or linolenic acid of MFALs, although the extent of the reduction varies with genotype.
Abbreviations: MFAL, modified fatty acid breeding line • NCAUR, USDA National Center for Utilization Research.
|
INTRODUCTION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Soybean seed composition is known to be affected by environmental factors. Composition of soybean seeds has been shown to differ across environments and years (Cherry et al., 1985; McClure, 1999; Schnebly and Fehr, 1993). Differences in soybean seed composition are likely due to variable weather conditions that occur across locations and years (Primomo et al., 2002). It is hypothesized that temperature is the environmental factor with greatest influence on soybean seed composition. During the oil deposition phase (R5–R6 growth stage) of seed maturation, high temperatures result in increased oil content and decreased protein content (Piper and Boote, 1999). Temperature conditions during soybean seed development are considered to have the greatest effect on the unsaturated fatty acid composition of soybean seed (Howell and Collins, 1957; Slack and Roughan, 1978). Results from a study working with reduced palmitic acid germplasm in the southern United States and Puerto Rico indicated substantial variability in palmitic acid levels (Rebetzke et al., 2001). Much of this variability was associated with changes in minimum temperatures during the growing season. Results from Carver et al. (1986) suggested that oleic acid levels increased and linoleic and linolenic acid levels decreased when soybean was grown in warmer environments. Lines bred for reduced levels of linolenic acid tended to be less sensitive to environmental variability as compared to saturated and monounsaturated fatty acids (Carver et al., 1986).
In light of such research results, it is intuitive that planting date may affect the fatty acid profile of a given soybean genotype. Differences in planting date affect temperatures that a soybean crop will be subjected to during the oil deposition phase of seed maturation and length of the growing season. Results from Takagi et al. (1979) indicate that the fatty acid composition of soybean seeds is also affected by length of growth period. Photoperiodism is the principle physiological process that drives reproduction and maturation in soybean. Planting date influences length of the growing period since it dictates the number of days a crop will have for development before maturation.
Results from Wilcox and Cavins (1992) suggest that palmitic and linolenic acids may decrease with later planting dates while stearic acid levels are slightly increased. Results from that study also suggest that increasing temperature during the last 20 d of seed maturation results in a concomitant decrease in the level of linolenic acid. Results from Schnebly and Fehr (1993) indicate that planting date had a significant effect on fatty acid levels in some genotypes and years. When averaged across years, planting date did not produce significant differences in genotypes with modified palmitic acid profiles. Contrary to findings by Wilcox and Cavins (1992), results from Schnebly and Fehr (1993) also provide evidence that temperatures during the last 20 d of seed maturation could not definitively explain differences in soybean seed composition. Oliva et al. (2006) conducted a stability analysis of 13 genotypes having modified fatty acid profiles along with four commercial cultivars over 10 environments. They regressed fatty acid levels on average temperature during the final 30 d of the reproductive growth period. Over all genotypes, they found that oleic acid content increased with an increase in temperature while linolenic acid content decreased with an increase in temperature. There were stability differences among genotypes as mid-oleic acid genotypes were less stable than were genotypes with lower levels of oleic acid. They also reported that linolenic acid in the lowest linolenic acid lines was influenced less by changes in temperature when compared with lines and cultivars with normal linolenic acid contents.
Crude soybean oil from conventional genotypes typically contains 10% palmitic acid (16:0), 4% stearic acid (18:0), 22% oleic acid (18:1), 54% linoleic acid (18:2), and about 10% linolenic acid (18:3) (Wilson, 2004). At least two recessive alleles control expression of the low-16:0 trait in soybean (Erickson et al., 1988; Schnebly et al., 1994; Stojsin et al., 1998). When combined, these two alleles result in less than 4% 16:0, thus reducing the level of saturated fatty acid. At least two recessive alleles control expression of a low-18:3 trait in soybean (Fehr et al., 1992). Combination of these alleles results in less than 3% 18:3 in crude oil. When refined, naturally low-18:3 oils have oxidative stability and flavor characteristics that are superior to hydrogenated soybean oil.
Hybridizations were made with two low-16:0 lines and one low-18:3 line developed by the USDA Soybean Genetics program at Raleigh, NC, with the intent to backcross the desirable fatty acid traits into higher-yielding and improved agronomic genotypes. Adapted cultivars used as recurrent parents were Hagood (MG VII) (Shipe et al., 1992) and Maxcy (MG VIII) (Shipe et al., 1995). A cross of Dillon (MG VI) (Shipe et al., 1997) by a low 18:3 line was also made. A total of eight modified fatty acid lines were developed. Objectives of the study were (i) to determine the effect of planting date on fatty acid content in eight modified fatty acid lines (MFALs) and (ii) to compare them to parental cultivars Dillon, Maxcy, and Hagood for seed composition and agronomic traits. To date, planting date effects on soybean seed composition have not been investigated for germplasm adapted to the southeastern U.S. growing region.
|
MATERIALS AND METHODS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
The eight modified fatty acid lines were selected as single plants in the F4 generation and initially evaluated in preliminary breeder tests at Blackville and Florence, SC, in 2000 for seed composition, agronomic traits, and seed yield. Eight MFALs and four control cultivars were planted in 2001, 2003, and 2004 at the Simpson Agricultural Experiment Station located near Pendleton, SC, eight miles from the Clemson University campus. Pedigrees of all breeding lines tested are shown in Table 1. Two planting dates were used each year to simulate full season and double crop planting dates in the piedmont region of South Carolina as follows: 2001 (May 24 and June 28), 2003 (May 29 and June 27), 2004 (May 24 and June 22). Soil type of the site is classified as a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults) and represents the Southern Piedmont growing region of South Carolina.
Experimental design within each planting date and year was a randomized complete block with three replications. During all years, each experimental area was chisel plowed, fertilized, and disked before planting. Plots consisted of four rows spaced 0.96 m apart and 6 m in length. A preplant fertilizer was applied according to soil test results, and dolomitic limestone was applied to adjust soil pH to values that were conducive to soybean growth and development. Preplant herbicides were incorporated into the soil to prevent early weed competition. In season, soybeans were mechanically cultivated to reduce weed competition and increase root zone aeration as needed. Insecticides were applied as needed to control herbivory.
Plant variables measured in the field included flower color, pubescence color, plant height, lodging, and maturity date. Lodging ratings were taken on a whole-plot basis using a scale of 1 to 5 (1 = all plants erect, 5 = all plants lodged) as used in the uniform USDA soybean tests (Kenty and Mosely, 1995). Maturity dates were recorded when 95% of pods had reached mature pod color (R8 growth stage) (Fehr and Caviness, 1971). Before harvest, plots were end trimmed and 3.6 m of the two center rows were harvested for seed yield and composition determinations. Seed was air dried and then weighed. Individual plot weights were corrected to a 13% moisture, and yields were computed as kilograms per hectare.
Seed quality ratings were made on each plot using the system for the uniform USDA soybean tests (Kenty and Mosely, 1995), with a value of 1 indicating no visible signs of damage or discoloration and 5 indicating 
80% of seed were damaged or discolored. Seed size was measured for each plot as the average weight of 100 seeds.
A 25-g seed sample from each plot was analyzed for oil and protein content using near-infrared analysis at the USDA National Center for Utilization Research (NCAUR), in Peoria, IL. A 10-seed sample from each plot was analyzed for fatty acid composition at Raleigh, NC, Soybean and Nitrogen Fixation Unit, USDA-ARS (Rebetzke et al., 1998) in 2001 and 2004 and in Peoria, IL (NCAUR) in 2003.
Statistical analysis was based on a split-split-plot design with planting date as the main plot factor, genotype as the split-plot factor, and year as the split-split-plot factor. The model used was
 |
Analysis of variance was used to test the significance of model terms, and least significant differences were used for mean separation tests. A significance level (alpha) of 0.05 was used in all tests. Comparisons were made between planting dates for each genotype and between planting date means. Comparisons were also made among genotypes across planting dates. The general linear model of the Statistical Analysis System (SAS Institute, Carey, NC) was used for all calculations.
Data included in the statistical analysis and presented were from years 2001, 2003, and 2004. Data collected in 2002 were omitted from analysis due to severe drought and infestations of velvet bean caterpillar [Anticarsia gemmatalis (Hübner)] and soybean looper [Pseudoplusia includens (Walker)]. Insect damage and drought stressed plants such that data from 2002 experiments were not indicative of the true agronomic performance and seed composition of the genotypes being evaluated.
|
RESULTS AND DISCUSSION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
|
|
Later planting dates produced significantly lower (p = .0519) palmitic acid levels when means were computed across years and genotypes (Table 5 ). Lower palmitic acid levels at the late planting date are in agreement with a previous study showing that palmitic acid levels tend to decrease with successively later planting dates (Wilcox and Cavins, 1992). Significant differences for palmitic acid levels were also recorded between genotype means. The MFAL SC01-51, selected for both low palmitic and low linolenic acids, produced the lowest palmitic acid concentration (40.3 g kg–1). As expected, seven MFAL selected for low palmitic acid levels produced significantly lower levels of palmitic acid compared with the four control cultivars.
|
Early and late planting dates were not statistically different for oleic acid when averaged across years and genotypes (Table 4), but there were differences among genotypes. Oleic acid levels ranged from 258.0 to 198.8 g kg–1 among genotypes, which is in the normal range for most commercial cultivars (Wilson, 2004). Soyola produced the highest level of oleic acid, while the MFAL SC9634-1657 produced the lowest. Generally, MFALs tended to produce somewhat higher levels of oleic acid compared with parental cultivars.
No significant effect (p = 0.0687) of planting date on linoleic acid levels was observed when means were computed across years and genotypes (Table 4). Only one MFAL, SC9634-1657, and Hagood had higher levels of linoleic acid at the early planting date. Significant differences existed between genotypes for mean levels of linoleic acid when averaged across years and planting dates (Table 2). All MFALs produced significantly higher levels of linoleic acid than the four control cultivars. The eight MFALs exhibited a range of 588.2 to 657.6 g kg–1, while the four control cultivars ranged from 550.6 to 577.1 g kg–1 linoleic acid.
The effect of planting date, genotype, and planting date x genotype interactions were all highly significant on linolenic acid levels (Table 2). The late planting date produced the highest mean linolenic acid level (73 g kg–1) (Table 6 ). Significant differences among genotypes for mean linolenic acid levels were observed when averaged across years and planting dates. Mean linolenic acid levels for genotypes ranged from 93.1 to 40.4 g kg–1. The MFALs SC00-1741 and SC01-51 were bred for low linolenic acid levels and produced the lowest mean levels of linolenic acid. These two lines were equal to Soyola (42.1 g kg–1), a commercial low-linolenic cultivar (Burton et al., 2004).
|
|
|
Highest lodging ratings overall occurred at the early planting date, which is likely a result of taller plants (Table 4). Significant effects of genotype, planting date, and genotype x planting date were observed for lodging (Table 7). None of the MFALs had mean lodging scores greater than control cultivars, and two lines, SC99-1034 and SC9631-1505, had scores lower than the control cultivars Maxcy and Hagood, respectively. Lodging ratings for specific genotypes at the late planting date were generally lower than the early planting date but significant only for Soyola.
The late planting date produced a significantly later mean maturity date with a difference of 7 d (Table 4). Genotype and planting date x genotype interaction had highly significant effects on maturity (Table 7). All genotypes except Hagood had later maturity dates when planted in late June. Two MFALs derived from Maxcy crosses and the low 16:0 Hagood line, SC9631-1505, were later than the respective recurrent parents. With a mean maturity date of October 25, SC00-1741 was later than parental cultivar Dillon by 4 d. Soyola was earlier than all other genotypes, with a mean maturity date of October 17.
Seed size was greater at the late planting date across years and genotypes by 1.3 g 100 seed–1 (Table 4). Genotype also had significant effects on seed size (Table 7), while planting date x genotype interaction was not significant. All genotypes except SC9629-1327 and SC99-1034 had larger seed at the late planting date. Significant differences for seed size were recorded between genotypes, with a mean range of 13.1 to 15.6 g kg–1 (data not shown). Four MFALs had larger seed than the recurrent parents Maxcy and Hagood. Soyola had smaller seed (13.1 g kg–1) than all other control cultivars and MFALs.
Planting date (Table 4) and genotype effects were significant for seed quality (Table 7). Planting date x genotype interactions did not have a significant effect. The late planting date produced significantly better (lower) seed quality ratings (2.3) compared with the early planting date (2.7). The early planting date produced significantly poorer seed quality ratings for three MFALs and the control cultivar Maxcy. When compared for genotypes across planting dates and years, MFALs compared favorably with control cultivars for seed quality
|
CONCLUSIONS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
The early planting date produced significantly higher protein and oil content than the late planting date. These findings are consistent with a study by Piper and Boote (1999) with regard to seed oil increase at higher growth temperatures. However, the protein content data from this study are not consistent with Piper and Boote (1999), who found that protein content decreases with increasing temperature. Significantly higher palmitic acid levels were also observed at the early planting date, which is consistent with the findings of Wilcox and Cavins (1992). There were no significant differences for stearic, oleic, or linoleic acid when comparing planting dates averaged across all genotypes. The late planting date resulted in significantly higher levels of linolenic acid, which is also consistent with the findings of Wilcox and Cavins (1992). Oliva et al. (2006) also reported increases of linolenic acid at lower seed development temperatures over most genotypes evaluated but found that some low linolenic genotypes tended to be more stable than conventional-level linolenic genotypes.
The effect of genotype was significant for all agronomic and seed composition variables measured. Significant genotype x planting date interactions were recorded for seed yield, plant height, lodging, and maturity. Significant interactions were also observed for seed protein, palmitic, stearic, oleic, linoleic, and linolenic acids. Reduced levels of palmitic and linolenic acid have been achieved in the breeding program, but seed yields of the MFALs are generally lower than parental cultivars, with the exception of low-linolenic SC00-1741. Low-palmitic MFALs were generally shorter than parental cultivars, and the Maxcy-derived MFALs had lower seed oil contents than Maxcy.
In summary, planting date had a significant effect on all agronomic variables and four seed composition variables. Planting date did not significantly affect fatty acid composition, with the exception of palmitic and linolenic acid. Based on these data, soybean producers in the southeastern United States should be able to produce modified fatty acid genotypes with fatty acid profiles similar to those of the genotypes in this study at late planting dates with minimal impact on stearic, oleic, and linoleic fatty acids. If the objective is to produce genotypes with reduced levels of linolenic acid, a May planting date should be considered. A later planting date may result in slightly lower levels of palmitic acid, but the reduction appears to be genotype specific.
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.
Received for publication May 23, 2007.
|
REFERENCES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
dms/qatrans2.html (verified 24 Oct. 2007). U.S. Food and Drug Administration, Washington, DC.This article has been cited by other articles:
|
|
 |
|
  C. Carrera, M. J. Martinez, J. Dardanelli, and M. Balzarini Water Deficit Effect on the Relationship between Temperature during the Seed Fill Period and Soybean Seed Oil and Protein Concentrations Crop Sci., May 11, 2009; 49(3): 990 - 998. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Vadose Zone Journal | |||
| Journal of Natural Resources and Life Sciences Education |
Soil Science Society of America Journal | ||||
| Journal of Plant Registrations | Journal of Environmental Quality |
The Plant Genome | |||
