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CROP BREEDING, GENETICS & CYTOLOGY

Seed Source Effect on Field Emergence of Soybean Lines with Reduced Phytate and Raffinose Saccharides

^a Dep. of Agronomy, Iowa State Univ., Ames, IA 50011-1010
^b Pioneer Hi-Bred International, Inc., P.O. Box 177, Johnston, IA 50131-0177

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

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Soybean [Glycine max (L.) Merr.] lines homozygous for the mips allele (mips lines) have reduced phytate P and raffinose saccharides in the protein meal. Less phytate is desirable for reducing the P content of manure from nonruminant animals and less raffinose saccharides increases the amount of metabolizable energy available to them. Field trials indicated that seedling emergence percentage of mips lines was less for seed produced in a subtropical environment than a temperate environment. The objective of this study was to determine if field emergence of mips lines is influenced by the environment used for seed production. Seed of six mips lines and four commercial cultivars (Mips lines) produced in four temperate and 12 subtropical environments during 2 yr was evaluated for field emergence percentage, seed viability percentage, and germination percentage in warm germination, cold vigor, and accelerated aging tests. The field emergence percentage of mips lines was significantly less than Mips lines for all seed sources. The mips lines had a mean field emergence of 63% for temperate sources and 8% for subtropical sources while Mips lines had a mean field emergence of 77% for temperate sources and 83% for subtropical sources. The mean seed viability percentage for the mips lines based on the tetrazolium test of 88% for temperate sources and 70% for subtropical sources accounted for only part of the differences in field emergence. Differences in field emergence between the mips and Mips lines were not consistently predicted by the warm germination and cold vigor tests for temperate sources. The accelerated aging test effectively differentiated the field emergence potential of the mips and Mips lines for all seed sources. Seed source should be a consideration when evaluating the field emergence of mips lines in a breeding program or for obtaining acceptable plant populations in commercial fields.

Abbreviations: AOSA, Association of Official Seed Analysts • MG, maturity group

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
A COMMON SOURCE of protein in livestock feed is soybean meal. The carbohydrate fraction of soybean meal contains raffinose saccharides. Nonruminant animals cannot readily digest raffinose saccharides because they lack the necessary -galactosidase enzyme in their intestinal mucosa (Sebastian et al., 2000). The poor digestion of raffinose saccharides reduces the amount of metabolizable energy obtained from soybean meal. Microflora in the lower intestine are able to metabolize the raffinose saccharides, which results in the production of flatulents (Hawton et al., 1996).

More than 60% of the total P in soybean meal is in the form of phytate (myo-inositol 1,2,3,4,5,6-hexaphosphate) (Nelson et al., 1968; Erdman, 1979). Phytate P is unavailable to nonruminant animals because they lack the phytase enzyme (Pointillart, 1994). To meet the P needs of nonruminant animals, producers add inorganic P and phytase supplements to their feed rations. The addition of inorganic P increases feed costs and the undigested phytate P in the livestock excrement contributes to P pollution in areas with intense nonruminant livestock production (Pointillart, 1994).

A recessive allele, mips, was developed by chemical mutagenesis that significantly reduced the content of raffinose saccharides and phytate P in soybean seed (Sebastian et al., 2000). For soybean lines with the mips mips genotype (mips lines), stachyose is reduced to 5 µmol g^-1 of seed dry weight and raffinose is reduced to 10 µmol g^-1 compared with 75 µmol g^-1 of stachyose and 20 µmol g^-1 of raffinose in conventional Mips lines (Sebastian et al., 2000). The reduction in raffinose and stachyose increases the sucrose to 244 µmol g^-1 in mips lines compared with 165 µmol g^-1 of sucrose in conventional lines (Hitz et al., 2002). For the mips lines, phytate P is reduced to 56 to 73 µmol g^-1 of seed dry weight and inorganic P is increased to 32 to 76 µmol g^-1 compared with 125 to 155 µmol g^-1 of phytate P and 1.5 to 2.7 µmol g^-1 inorganic P in conventional lines (Hitz et al., 2002). When compared with conventional lines, mips lines produce a soybean meal that has nutritional advantages for nonruminant animals (Cromwell et al., 2000; Spencer et al., 2000).

Field trials conducted by Pioneer Hi-Bred International (Pioneer) in 1999 indicated that field emergence of mips lines was less for seed produced in Puerto Rico than the midwestern USA. The same mips lines had not been grown in both environments, and it was impossible to determine whether the differences in field emergence were due to seed source or genetic variation among lines. The objective of this study was to determine if field emergence of mips lines is influenced by the environment used for seed production.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Six mips lines and four commercial cultivars (Mips lines) developed by Pioneer were grown in 16 environments for seed production. The mips lines and their Maturity Groups (MGs) were LPR1001 (MG III), LPR1002 (MG II), LPR1003 (MG III), LPR1004 (MG III), LPR1005 (MG III), and LPR1006 (MG III). The Mips lines and their MGs were ‘93B45’ (MG III), ‘93B65’ (MG III), ‘93B82’ (MG III), and ‘9306’ (MG III).

All the seed for the study was produced in Pioneer nurseries. There were 200 seeds of each line planted at 26 seeds m^-1 in two-row plots spaced 0.76 m apart during May 1999 at Bethany, MO; 150 seeds planted at 20 seeds m^-1 in two-row plots spaced 0.76 m apart during May 2000 at Atlantic, IA; 132 seeds planted at 20 seeds m^-1 in rows spaced 0.76 m apart during October 1999 and 2000 at Semillas, Chile; and 400 seeds planted at 33 seeds m^-1 in rows spaced 0.76 m apart under natural daylength conditions during October 1999 and 2000 and January 2000 and 2001 at Waimea, HI; Puerto Vallarta, Mexico; and Salinas, PR. Each line was harvested separately at maturity with a stationary thresher or self-propelled plot combine. The soil type at Bethany is a Grundy silt loam (fine, smectitic, mesic Aquertic Argiudolls), at Atlantic is a Marshall silt loam (fine-silty, mixed, superactive, mesic Typic Hapludolls), at Waimea is a Nonopahu clay (fine, mixed, active, isohyperthermic Chromic Haplotorrerts), at Salinas is a San Anton clay loam (fine-loamy, mixed, superactive, isohyperthermic Cumulic Haplustolls). The soils at Semillas and Puerto Vallarta have not been classified.

The 10 lines from each of the eight sources grown during the summer of 1999 through the spring of 2000 were evaluated for field emergence percentage and for germination percentage in warm germination, cold vigor, and accelerated aging tests during the summer of 2000. The same tests were conducted during the summer of 2001 for the eight sources grown during the summer of 2000 through the spring of 2001. A tetrazolium test was conducted on all sources during the fall of 2001.

The field emergence tests for both years were at Johnston, Durant, and Atlantic, IA. The lines and sources were evaluated in a randomized complete-block design with two replications at each location. The soil type at Johnston is a Waukegan loam (fine-silty over sandy or sandy-skeletal, mixed, superactive, mesic Typic Hapludolls), at Durant is an Atterberry silt loam (fine-silty, mixed, superactive, mesic Udollic Endoaqualfs), and at Atlantic is a Marshall silt loam (fine-silty, mixed, superactive, mesic Typic Hapludolls). At each location, 150 seeds were planted at a seeding rate of 20 seeds m^-1 in two-row plots 3.7 m long with 0.76-m spacing between rows. Field emergence percentage was determined for each plot by counting the number of plants present between the V2 and V4 stages and dividing by the number of seeds planted (Fehr and Caviness, 1977).

The warm germination, cold vigor, and accelerated aging tests were conducted as a randomized complete-block with four replications of 50 seeds each. A replication was a germination cart containing all the lines and sources. A cart was 0.5 m wide by 0.7 m deep by 1.6 m tall and consisted of one end made of Plexiglas for light penetration, two solid aluminum walls, and an aluminum door that was sealed with rubber gaskets to minimize moisture escape. The fiberglass trays holding the test samples were 0.4 m x 0.6 m. Each tray accommodated eight 50-seed samples.

For the warm germination and cold vigor tests, the 50 seeds of each line and source of a replication were planted on two layers of 22-ply Versapak (National Packing Services Corp., Green Bay, WI) measuring 0.4 m x 0.6 m that had been moistened with 815 mL of tap water (AOSA, 2000a). The seeds were planted in 10 rows with the seeds spaced 19 mm apart within and 25 mm between rows. The seeds were covered with 13 mm of moist sand, and the tray was placed on a shelf in the germination cart. For the warm germination test, each cart was placed in a 25°C germination chamber for 7 d, after which germination percentages were determined according to the Association of Official Seed Analysts (AOSA) guidelines (AOSA, 1992). For the cold vigor test, each germination cart was placed in a 10°C germination chamber for 7 d, followed by 7 d in a 25°C germination chamber (AOSA, 1983). Germination percentages were determined after the 14-d period (AOSA, 1992).

For the accelerated aging test, each 50-seed sample of a line and source was placed in a wire basket over 40 mL of distilled water in a sealed box (AOSA, 1983). The boxes were placed in a chamber at 41°C for 72 h. The samples were removed from the chamber and planted in the same manner as the warm germination and cold vigor tests. Each cart was placed in a 25°C germination chamber for 7 d, after which germination percentages were determined (AOSA, 1992).

A tetrazolium test was conducted to assess seed viability. The 10 lines from each of the eight seed sources in a year were evaluated in a randomized complete-block with four replications of 50 seeds each. Each replication of each line and source was imbibed for 12 h at 25°C by placing the seed between brown paper towels moistened with tap water (AOSA, 2000b). The seeds were removed from the towels and placed in a 1.0% 2,3,5-triphenyl tetrazolium chloride solution for 2 h, after which each seed was classified as viable or dead according to AOSA guidelines to determine the viability percentage (AOSA, 2000b).

The data for all experiments were analyzed as a randomized complete-block design with a factorial arrangement of lines and sources. Lines and sources were considered fixed effects, and locations for the field emergence tests were considered random effects. Data from each experiment were analyzed with the general linear models (GLM) procedure of the SAS software package (release 8.2) (SAS Institute, 2001). The sums of squares for genotype were partitioned into among mips lines, among Mips lines, and the orthogonal comparison between the two groups.

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
There were significant differences (P < 0.01) among lines and sources for field emergence, tetrazolium, warm germination, cold vigor, and accelerated aging tests in both years. The means of the mips lines were significantly different than the means of the Mips lines and the line x source interactions were significant for the five tests each year. Significant differences were observed among the mips lines for all the tests in both years. No significant differences were observed among the Mips lines, except for accelerated aging in 2000 and 2001.

Seed of the mips lines produced in the temperate environments of Semillas, Atlantic, and Bethany had more than a three-fold greater field emergence than any of the subtropical sources (Table 1). The seed source effect altered the relative performance of the mips and Mips lines for field emergence. The difference between the mips and Mips lines was less from the temperate sources of Atlantic, Bethany, and Semillas than for the subtropical sources of Waimea, Salinas, and Puerto Vallarta. The mips lines had 12 percentage units less field emergence for the Atlantic source, 8 less for Bethany, 14 less for Semillas 2000, and 24 less for Semillas 2001. There were five mips lines that were not significantly different than a Mips line for the Atlantic source, five for Bethany, three for Semillas 2000, and one for Semillas 2001. In contrast, the differences in mean field emergence between the mips and Mips lines for the 12 subtropical sources ranged from 58 percentage units for Puerto Vallarta January 2000 to 85 for Puerto Vallarta October 2001. None of the mips lines were equal to any of the Mips lines for the subtropical sources.

The tetrazolium test indicated that reduced seed viability of the mips lines accounted for only part of the reduction in field emergence. The test was not considered effective for predicting the poor field emergence of mips lines from the subtropical sources. Three germination tests were evaluated for their effectiveness in predicting field emergence of mips lines. The warm germination and cold vigor tests did not consistently predict the differences in field emergence between the mips and Mips lines for the four temperate sources (Table 1). No significant difference between the mips and Mips lines was observed in the warm germination test for Semillas 2001 or in the cold vigor test for Semillas 2000 (Table 1). The two methods were effective in predicting the differences in field emergence between the mips and Mips lines for all the subtropical sources. The maximum difference between the two groups of lines in both the warm germination and cold vigor tests was 91 percentage units for Waimea January 2001, which had a difference of 83 percentage units in the field emergence test. Although the warm germination and cold vigor tests differentiated mips and Mips lines, they overestimated the field emergence percentages that would be achieved from all sources. This overestimation would be a consideration if the tests were used to determine the seeding rate necessary to achieve a desired plant population.

The accelerated aging test was the most effective at differentiating the field emergence of the mips and Mips lines regardless of the seed source (Table 1). The differences between the groups based on accelerated aging were similar to differences in field emergence for subtropical sources. For the temperate sources, accelerated aging produced greater differences between the two groups than observed for field emergence. The ability of the accelerated aging test to identify the emergence potential of mips lines regardless of the seed source would be useful in a breeding program. Lines from one source that performed well in the accelerated aging test would be expected to perform well when the seed was produced in other environments. If mips lines were developed that germinated as well as Mips lines in the accelerated aging test, they would be expected to emerge as well as Mips lines in field tests. The accelerated aging test may be useful for evaluating the potential field emergence problems of soybean lines with other unique agronomic and seed traits developed by mutagenesis and genetic engineering in the future.

Additional research will be needed to understand the reason for the seed source effect on field emergence of mips lines. In preliminary tests, the P contents of the soils from the 16 sources were evaluated and no consistent differences were observed that could explain the major reduction in field emergence for the subtropical sources. Differences in temperature and humidity between temperate and subtropical environments during seed development and maturation may have contributed to the seed source effect. Another difference between the temperate and subtropical environments to consider is the daylength during the growing season. The daylength of <12 h in the subtropical environments shortens the time from planting to harvest by more than one month compared with plantings in temperate environments. The compressed reproductive period in the subtropical environments may alter seed components in a way that is detrimental to field emergence.

	ACKNOWLEDGMENTS

 
The authors thank the soybean breeding staff of Pioneer Hi-Bred International, Inc. for assisting with the development and evaluation of the lines used in this study.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Project No. 3732 and supported by the Hatch Act, State of Iowa, Raymond F. Baker Center for Plant Breeding, and Pioneer Hi-Bred International, Inc.

Received for publication October 25, 2002.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 

• AOSA. 1983. Seed vigor testing handbook. Publ. no. 32. Association of Official Seed Analysts, Lincoln, NE.
• AOSA. 1992. Seedling evaluation handbook. Publ. no. 35. Association of Official Seed Analysts, Lincoln, NE.
• AOSA. 2000a. Rules for testing seeds. Association of Official Seed Analysts, Lincoln, NE.
• AOSA. 2000b. Tetrazolium testing handbook. Publ. no. 35. Association of Official Seed Analysts, Lincoln, NE.
• Cromwell, G.L., S. Traylor, M.D. Lindemann, H.L. Stilborn, and T.E. Sauber. 2000. Bioavailability of phosphorus in low oligosaccharide, low-phytate soybean meal for chicks. Poult. Sci. 79(Suppl.):127.
• Erdman, J.W., Jr. 1979. Oilseed phytates: Nutritional implications. J. Am. Oil Chem. Soc. 56:736–741.
• Fehr, W.R., and C.E. Caviness. 1977. Stages of soybean development. Spec. Rep. 80. Iowa Agric. Home Econ. Exp. Stn., Ames, IA.
• Hawton, J.D., L.J. Johnston, T.M. Salzer, and G.C. Shurson. 1996. Applications of nutritionally improved corn and soybeans for swine. p. 263–304. In Proc. 57th Minnesota Nutrition Conf., Univ. of Minnesota, St. Paul, MN.
• Hitz, W.D., T.J. Carlson, P.S. Kerr, and S.A. Sebastian. 2002. Biochemical and molecular characterization of a mutation that confers a decreased raffinosaccharide and phytic acid phenotype on soybean seeds. Plant Physiol. 128:650–660.[Abstract/Free Full Text]
• Nelson, T.S., L.W. Ferrara, and N.L. Storer. 1968. Phytate P content of feed ingredients derived from plants. Poult. Sci. 47:1372–1374.[ISI][Medline]
• Pointillart, A. 1994. The importance of cereal phytases. Feed Mix 2:12–15.
• SAS Institute. 2001. The SAS system for Windows. Release 8.2. SAS Inst., Cary, NC.
• Sebastian, S.A., P.S. Kerr, R.W. Pearlstein, and W.D. Hitz. 2000. Soybean germplasm with novel genes for improved digestibility. p. 56–74. In J.K. Drackely (ed.) Soy in animal nutrition. Federation of Animal Sci. Soc., Savoy, IL.
• Spencer, J.D., G.L. Allee, J.W. Frank, and T.E. Sauber. 2000. Nutrient retention and growth performance of pigs fed diets formulated with low-phytate corn and/or low-phytate/low oligosaccharides soybean meal. J. Anim. Sci. 78(Suppl. 2):73.

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