Abstract
Soybean [Glycine max (L.) Merrill] seed has poor storability under high temperature and high humidity. It loses viability in a relatively short time. Seed aging of stored soybeans leads to poor germination and a decrease in yield. The accelerated aging vigor test, which provides useful information for determining seed storability as well as field emergence potential, is a rapid aging experiment and could be used to determine soybean seed quality. This study was conducted to determine the seed viability of Korean soybean cultivars and soybean lines with altered fatty acid compositions under accelerated aging conditions. Results demonstrated that Songhagkong, a Korean soybean cultivar, was the most stable at 3, 4, and 5 days of accelerated aging conditions. Furthermore, two soybean lines with high stearic acid content exhibited >70.0% reduction rate, whereas three soybean lines with high oleic acid content exhibited 7.4%-11.8% reduction rates. Soybean lines with mid-oleic acid and elevated linolenic acid contents exhibited various reduction rates depending on genotypes. Therefore, these soybean lines can be used as breeding material for developing a new soybean cultivar with strong seed vigor and better storability under unfavorable conditions. Therefore, a genetic study on this soybean cultivar is warranted.
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Key words: Soybean, Accelerated aging, Seed vigor, Germination, Fatty acids
INTRODUCTION
Soybean [
Glycine max (L.) Merrill] is a highly valued legume crop in the world. Soybean seeds contain 18%-20% fat, 40%-45% protein, and 24%-26% carbohydrate (
Gowda and Kaul 1982). However, soybeans have poor storability under high temperature and humidity conditions. They lose their viability in a very short time period, even in a good nonporous storage container (
Woodruff 1998). The factors that should be considered for seed storability include genetics, environmental conditions during seed production, pests, seed oil content, seed moisture content, mechanical damage of seeds during processing and packaging, air temperature, and relative air humidity during storage (
Guberac et al. 2003;
Heatherly and Elmore 2004;
Sun et al. 2007).
Seed vigor affects both the productivity and storability of seeds. Vigorous seeds can be stored and produce uniform seedling stands and productive plants. Several vigor tests have been developed to fulfill the demand for a rapid estimation of seed vigor in seed science. One of the most important vigor tests is the accelerated aging test, because it is rapid, simple, and inexpensive; requires no sophisticated equipment; and can be performed by anyone without training (
AOSA 1983;
TeKrony et al. 1989;
Ferguson 1990). The basic concept of the accelerated aging test is that before the germination test, the seeds are placed at 40℃-45℃ and approximately 100% relative humidity for specific time periods depending on crop species (AOSA 1983). The basis for this test is that higher vigor seeds tolerate the high-temperature and high-humidity treatment and thus retain their vigor to produce normal seedlings in the germination test. After the accelerated aging treatment, high-vigor seeds exhibit better germination and field emergence than low-vigor seeds. Similarly, seed perfor-mance has been associated with germination rates after accelerated aging in a wide range of environmental con-ditions (
Delouche and Baskin 1973). The seed vigor test can be used to not only predict field emergence but also evaluate the storage potential for crop seeds under favorable or unfavorable conditions.
Egli and TeKrony (1995) indicated that soybean seed lot with higher germination rates after accelerated aging testing manifested a high probability of adequate seedling emer-gence under severe environmental conditions.
Marwanto (2003) reported that germination after weather stress pos-itively correlated with soybean seed quality. Furthermore,
Phan et al. (2006) examined soybeans with higher percentages of seed germination after the accelerated aging test. The internationally accepted accelerated aging con-dition for soybean seed vigor tests is 41℃ for 72 hours, whereas pea seeds were tested under different accelerated aging conditions (
Hampton et al. 2004).
Currently, soybeans are grown throughout the world. In general, tropical regions have relatively higher temperatures with higher humidity during the soybean growing season, which cause poor germination in farm fields and poor storability, leading to reduced soybean production in the tropics and subtropics. In South Korea, the weather con-ditions during the soybean planting season comprise drought and heavy rain in a short time period, which result in unstable seedling emergence in the soybean field. Therefore, soybean seeds with higher vigor under unfavorable condi-tions such as drought, high temperature, and high humidity are required in the farmer’s field. Accordingly, this study was conducted to determine seed vigor under accelerated aging conditions for Korean soybean cultivars and soybean lines with altered fatty acid profiles.
MATERIALS AND METHODS
Temperature and relative humidity conditions for the accelerated aging test
Seeds of soybean accessions were placed in a micro tip box (5.5 cm in height × 7 cm in width × 11 cm in length) with a screen tray. Next, 90 mL of distilled water was added into the micro tip box at the bottom, and its lid was tightly wrapped using parafilm. Then, the box was placed in an incubator at ∼40℃ for 72 hours with >90% relative humidity. The processes of the accelerated aging test are illustrated in
Supplementary Fig. S1.
The sensor of the data logger (Model number DT.171) was placed in the micro tip box to determine the suitable temperature and relative humidity for the accelerated aging conditions in the micro tip box (
Supplementary Fig. S2). The temperature and relative humidity were measured every hour in a 40℃ drying oven.
After subjecting the seeds to accelerated aging conditions, 30 seeds from the accelerated aging and control conditions for soybean accessions were evaluated for seed germination. A paper towel was placed in the glass petri dish and mois-tened with distilled water. Germinated seeds were recorded daily from 1 to 5 days in the germination test. A sprout length of 2 cm was considered germinated seeds. The reduction rate of germination was calculated using the following formula:
Reduction rate (%)
= 100 ‒ [(germination rates under accelerated conditions / germination rates under control conditions) × 100]
Soybean cultivars and experimental lines
To evaluate the seed germination rates under the ac-celerated aging test, 134 Korean soybean cultivars were tested and compared between accelerated aging (42℃ and >90% relative humidity) and control conditions at 3 days. Initially, 30 seeds from each cultivar were evaluated for germination rates. A total of 52 soybean cultivars with >50% germination rates under accelerated aging conditions were evaluated again for further analysis. Finally, 24 Korean soybean cultivars were evaluated under accelerated aging conditions in three successive days from 3 to 5 days. Next, 30 seeds from each cultivar were evaluated and compared between accelerated aging and control conditions for the germination test in the glass petri dish with paper towel. The experimental design was completely randomized with two replications.
To evaluate the seed vigor of soybean experimental lines with altered fatty acid profiles, 11 soybean experimental lines were investigated under accelerated aging conditions for the germination test, which included 2 experimental lines with elevated stearic acid content, 2 experimental lines with mid-oleic acid content, 2 experimental lines with high oleic acid content, and 5 experimental lines with elevated linolenic acid content. Pungsanamul (
Lee et al. 2015), Daepung (
Park et al. 2005), Uram (
Ko et al. 2016), and Sunpung were used as check cultivars with normal fatty acid profiles. Moreover, the soybean cultivar Hosim (
Lee et al. 2018) with a high oleic acid content was investigated under accelerated aging conditions. The experimental design was completely randomized with two replications.
Fatty acid profiles of the soybean lines expressed as the percentage of each fatty acid were obtained using an Agilent series 7890A capillary GC equipped with an ionization detector (Agilent Technologies Inc., Wilmington, DE, USA). In order to extract the oil from seeds, ap-proximately 0.2 g crushed seeds were stored in l mL of extraction solution (chloroform: hexane: methanol [8:5:2 v/v]) for ∼12 hours. Approximately 100 mL of the extracted solution was transferred to vials with adding 75 mL of methylation reagent (0.25 M methanolic sodium methoxide: petroleum ether: ethyl ether [1:5:2, v/v/v]) and 1 mL of hexane was added. The five fatty acids obtained were separated on a DB-FFAP capillary Agilent column (30 m × 0.25 mm, 0.25 mm, Agilent Technologies Inc., Wilmington, DE, USA). Standard fatty acid mixtures (Fame #16, Restek) were used for reference calibration.
Statistical analysis
Data were analyzed in a completely randomized design. Statistical analyses were performed using SAS v9.4 (SAS Institute 2013). Mean differences among the genotypes with germination rates were analyzed by applying Fisher’s least significant difference (LSD) test at P ≤ 0.05 using PROC GLM.
RESULTS
Variation in seed vigor after accelerated aging treatment
To determine the suitable temperature and relative humidity for the accelerated aging conditions in the micro tip box, the temperature and relative humidity were measured every hour in a 40℃ drying oven. The tem-perature and relative humidity measured for 24 hours are presented in
Supplementary Table S1. The result showed that temperature and relative humidity were stabilized at approximately 42℃ and >90% after 3 hours of accelerated aging treatment, respectively, and hence this accelerated aging method was used in this study.
For the 134 Korean cultivars, the germination rates for control and accelerated aging conditions were 53.3%-100.0% and 0.0%-100.0%, with an average of 88.4% and 40.2%, respectively (
Supplementary Table S2). The reduction rate of germination was 0.0%-100.0%, with an average of 42.6%. The phenotypic distribution of reduction rates for the 134 Korean soybean cultivars after the accelerated aging test at 3 days is presented in
Table 1, which shows that 52 soybean cultivars exhibited >50% germination rates.
Among the 52 cultivars, 24 had sufficient seeds for 3 successive days of the accelerated aging test from 3 to 5 days (
Table 2). The germination rates under the control and accelerated aging conditions of 3 different days were 76.7%-100.0% for control conditions, 40.0%-85.0% at 3 days, 0.0%-68.3% at 4 days, and 0.0%-51.7% at 5 days, with an average of 86.9%, 64.7%, 19.2%, and 8.7%, respectively. The reduction rates of germination under the accelerated aging conditions of 3 different days were 7.4%-57.1%, 2.7%-100.0%, and 26.1%-100.0%, with an average of 24.7%, 76.8%, and 89.6%, respectively.
The germination rates under the control conditions for the three soybean cultivars Wonheug, Jangmikon, and Igsannamulkong were the highest (100%), whereas that for Saealkong was the lowest (56.7%). At 3 days after the accelerated aging treatment, Namhaekong showed the highest germination rate of 81.7%, and Sogang showed a germination rate of 40.0%; the reduction rate between the accelerated aging and control conditions was 57.1%. The germination rate of the cultivar Songhagkol under accel-erated aging conditions at 4 days was with the highest (68.3%), whereas the germination rate for the two cultivars Dajangkong and Jangmikong was the lowest (0.0%). The reduction rates of germination for Jangmikong and Song-hagkong were 100% and 2.4%, respectively. At 5 days of accelerated aging treatment, the germination rate for the cultivar Songhagkol was the highest (68.3%), whereas nine cultivars, including Saebyeolkong, Dajangkong, Soyeon, Seonam, Jinpumkong2ho, Daewonkong, Jangmikong, Saealkong, and Daepung, showed the lowest germination rate (0.0%). Songhagkong exhibited the lowest reduction rate (26.1%).
Soybean breeding lines with altered fatty acid profiles under accelerated aging conditions
The germination and reduction rates varied among 16 soybean accessions, including lines with altered fatty acid profiles (
Table 3). The germination rates under control and accelerated aging conditions were 35.0%-100.0% and 15.0%-88.3%, with an average of 82.9% and 47.6%, res-pectively, and the reduction rates were 3.3%-80.0%, with an average of 42.8%. The germination rates under control conditions were 100% for RIL49, 1190-2, 85-3-3-1, and Daepung cultivars. However, two soybean genotypes, viz., 22-3 (50.0%) and 276-5-1 (60.0%), exhibited relatively lower germination rates under control conditions than other genotypes. Among the check soybean cultivars with nor-mal fatty acid profiles, Pungsannamul showed 14.7% reduction rate, whereas other soybean cultivars with nor-mal fatty acid profiles showed >35.0% reduction rate. Interestingly, two soybean lines with high stearic acid content exhibited >70.0% reduction rate, whereas three soybean lines with high oleic acid content exhibited 7.4%-11.8% reduction rates. Soybean lines with mid-oleic acid and elevated linolenic acid contents exhibited varied reduction rates according to genotypes.
DISCUSSION
For the accelerated aging test, the suitable temperature, relative humidity, and the duration of accelerated aging treatment are different according to the plant or crop species.
Komba et al. (2006) suggested accelerated aging conditions of 41℃ for 72 hours for seed vigor test in brassica species but 41℃ for 48 hours in kale (
Brassica oleracea L var acephala DC).
Santipracha et al. (1997) reported accelerated aging conditions of 44℃ for 96 hours for seed vigor test for hybrid corn (
Zea mays L.) in humid tropics, whereas AOSA (1983) and
ISTA (1995) recom-mended accelerated aging conditions of 42℃ for 96 hours and 45℃ for 72 hours for corn seeds, respectively. For soybean, the internationally accepted accelerated aging condition for seed vigor tests is 41℃ for 72 hours (
Hampton et al. 2004). In the present study using the micro tip box, the accelerated aging treatment conditions reached ∼42℃ and >90% relative humidity for 3 hours (
Supplementary Table S1); thus, the period of accelerated aging was after 72 hours in this study.
A higher temperature and a higher relative humidity would accelerate deterioration and reduce the vigor of seeds during storage, whereas a lower temperature and a lower relative humidity would retard deterioration.
Ghassemi-Golezani et al. (2010) reported that a decrease in germina-tion rate can be related to physiological and biochemical changes during seed aging. The processes during aging decrease plasma membrane sustainability, change the molecular structure of nucleic acid, and decrease enzyme activities during seed senescence (
Justice and Bass 1978).
Kapoor et al. (2010) demonstrated that accelerated aging conditions affected all physiological parameters in cowpea seeds, resulting in a decrease in seed viability, germination rate, and vigor correlated with biochemical changes (decreased the content of soluble proteins and sugar) as-sociated with seed aging. In the present study, to determine seed viability during prolonged storage under unfavorable conditions, high-yield Korean soybean cultivars were investigated under accelerated aging conditions. The suggested period of accelerated aging for soybeans is 3 days. A total of 24 Korean cultivars were evaluated for 3 successive days of the accelerated aging test from 3 to 5 days to identify the soybean cultivar exhibiting strong seed vigor under prolonged accelerated aging conditions (
Table 2). Cultivar Songhagkong was the most stable with high germination rates among the Korean soybean cultivars under the accelerated aging conditions at 3, 4, and 5 days. This cultivar can be used as breeding material to develop a new soybean cultivar with strong seed vigor and better storability under unfavorable conditions. Moreover, a genetic study on this soybean cultivar will also be required.
Lipid oxidation, lipid peroxidation, and autooxidation of unsaturated fatty acids under seed aging conditions such as natural and accelerated aging conditions damage the DNA and cellular system of plants (Al-maskri
et al. 2002;
Alexeyev 2009). Saturated fatty acids with no double bond and monounsaturated fatty acids with one double bond are less vulnerable to lipid peroxidation, whereas polyunsa-turated fatty acids with double bonds in cellular membrane phospholipids are susceptible to lipid peroxidation (
Porter 1984;
Gutteridge 1995;
Catalá 2006;
Anjum et al. 2015;
Demidchik 2017). Lipid peroxidation causes loss of mem-brane integrity, oxidation, and impairment of DNA, RNA, and proteins, resulting in the loss of seed vigor (
Farmer and Mueller 2013;
Nowicka et al. 2013). Unsaturated fatty acids exert a significant effect on seed degradation (
Priestley 1986). The deterioration of seeds during storage causes a decrease in the fatty acid content and an increase in the malondialdehyde level, which is associated with lipid peroxidation (
Tian et al. 2008). According to the results of the present study, two soybean lines with high stearic acid content exhibited a reduction rate of >70.0%, whereas three soybean lines with high oleic acid content exhibited reduction rates of 7.4%-11.8% (
Table 3). Soybean lines with mid-oleic acid and elevated linolenic acid contents exhibited variations in reduction rates according to geno-types.
CONCLUSION
The accelerated aging vigor test is an excellent method for determining changes in seed vigor during storage. Germination rates, seed viability, and seed vigor are affected by storage temperature and relative humidity in soybean genotypes. The Songhagkong cultivar was the most stable and showed the highest germination rate among the Korean cultivars under accelerated aging con-ditions of 3 different days in this study. Furthermore, three soybean lines with high oleic acid content exhibited reduction rates of 7.4%-11.8%. These soybean lines can be used as breeding material to develop a new soybean cultivar with strong seed vigor and better storability under unfavorable conditions. Moreover, a genetic study on this soybean cultivar will also be required.
ACKNOWLEDGEMENTS
This work was carried out with the support of the Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ01416803), Rural Development Administration, Jeonju, Republic of Korea.
Table 1Frequency distribution of germination reduction rates after accelerated aging in Korean soybean cultivars.
Table 1
|
Class intervals for reduction rate (%) |
|
|
0-10 |
11-20 |
21-30 |
31-40 |
41-50 |
51-60 |
61-70 |
71-80 |
81-90 |
91-100 |
|
Number of cultivars |
15 |
10 |
8 |
14 |
13 |
11 |
16 |
17 |
19 |
11 |
Table 2Variation of germination rates under accelerated aging conditions at three different days for 24 Korean soybean cultivars.
Table 2
|
Name |
Control (%) |
Germinationz) (%) |
|
|
3 daysy)
|
Reduction ratex) (%) |
4 days |
Reduction rate (%) |
5 days |
Reduction rate (%) |
|
Saebyeolkong |
80.0 |
61.7 |
22.9 |
20.0 |
75.0 |
0.0 |
100.0 |
|
Wonheug |
100.0 |
46.7 |
53.3 |
6.7 |
93.3 |
10.0 |
90.0 |
|
Dajangkong |
70.0 |
53.3 |
23.9 |
0.0 |
100.0 |
0.0 |
100.0 |
|
Soyeon |
90.0 |
55.0 |
38.9 |
15.0 |
83.3 |
0.0 |
100.0 |
|
Sojeong |
93.3 |
65.0 |
30.3 |
66.7 |
28.5 |
33.3 |
64.3 |
|
Sogang |
93.3 |
40.0 |
57.1 |
18.3 |
80.4 |
11.7 |
87.5 |
|
Haman |
96.7 |
70.0 |
27.6 |
21.7 |
77.6 |
10.0 |
89.7 |
|
Dawonkong |
76.7 |
51.7 |
32.6 |
20.0 |
73.9 |
5.0 |
93.5 |
|
Singang |
93.3 |
48.3 |
48.2 |
8.3 |
91.1 |
6.7 |
92.8 |
|
Seonam |
90.0 |
68.3 |
24.1 |
15.0 |
83.3 |
0.0 |
100.0 |
|
Jinpumkong 2ho |
93.3 |
68.3 |
26.8 |
1.7 |
98.2 |
0.0 |
100.0 |
|
Saedanbaeg |
66.7 |
55.0 |
17.5 |
20.0 |
70.0 |
10.0 |
85.0 |
|
Pung-won |
90.0 |
70.0 |
22.2 |
23.3 |
74.1 |
13.3 |
85.2 |
|
Dachae |
90.0 |
85.0 |
5.6 |
48.3 |
46.3 |
10.0 |
88.9 |
|
Daewonkong |
93.3 |
68.3 |
26.8 |
6.7 |
92.8 |
0.0 |
100.0 |
|
Jangmikong |
100.0 |
76.7 |
23.3 |
0.0 |
100.0 |
0.0 |
100.0 |
|
Igsannamulkong |
100.0 |
83.3 |
16.7 |
26.7 |
73.3 |
15.0 |
85.0 |
|
Jinpumkong |
83.3 |
71.7 |
13.9 |
25.0 |
69.9 |
20.0 |
75.9 |
|
Namhaekong |
90.0 |
81.7 |
9.2 |
11.7 |
87.0 |
3.3 |
96.3 |
|
Songhagkong |
70.0 |
75.0 |
‒7.4 |
68.3 |
2.4 |
51.7 |
26.1 |
|
Saealkong |
56.7 |
53.3 |
5.9 |
1.7 |
97.0 |
0.0 |
100.0 |
|
Haepum |
83.3 |
63.3 |
24.0 |
20.0 |
75.9 |
5.0 |
93.9 |
|
Daepung |
90.0 |
71.7 |
20.3 |
5.0 |
94.4 |
0.0 |
100.0 |
|
Hosim |
95.0 |
68.3 |
28.1 |
11.7 |
75.0 |
3.3 |
96.5 |
|
LSD 5% |
17.4 |
27.2 |
25.6 |
27.7 |
31.7 |
14.3 |
16.0 |
Table 3Variation of germination rates under accelerated aging conditions at three different days for soybeans genotypes with altered fatty acid profiles.
Table 3
|
Name |
Germination ratez) (%) |
Reduction ratex) (%) |
Fatty acid traits |
|
|
Control |
Accelerated agingy)
|
|
348-1-4 |
75.0 |
15.0 |
80.0 |
High stearic acid (15.8%) |
|
363-1-2 |
80.0 |
23.0 |
71.3 |
High stearic acid (11.5%) |
|
RIL68 |
90.0 |
78.0 |
13.3 |
Mid oleic acid (30.2%) |
|
RIL49 |
100.0 |
30.0 |
70.0 |
Mid oleic acid (33.9%) |
|
CR10-248 |
85.0 |
75.0 |
11.8 |
High oleic acid (81.6%) |
|
CR10-251 |
85.0 |
76.0 |
10.6 |
High oleic acid (77.3%) |
|
1190-2 |
100.0 |
25.0 |
75.0 |
Elevated linolenic acid (11.3%) |
|
124-3-4 |
75.0 |
15.0 |
80.0 |
Elevated linolenic acid (11.5%) |
|
22-3 |
50.0 |
25.0 |
50.0 |
Elevated linolenic acid (17.5%) |
|
276-5-1 |
60.0 |
58.0 |
3.3 |
Elevated linolenic acid (15.4%) |
|
85-3-3-1 |
100.0 |
41.0 |
59.0 |
Elevated linolenic acid (15.2%) |
|
Hosim |
95.0 |
88.0 |
7.4 |
High oleic acid (78.9%) |
|
Pungsannamul |
95.0 |
81.0 |
14.7 |
Normal |
|
Daepung |
100.0 |
58.0 |
42.0 |
Normal |
|
Uram |
95.0 |
48.0 |
49.5 |
Normal |
|
Sungpung |
90.0 |
58.0 |
35.6 |
Normal |
|
Mean |
82.9 |
47.6 |
42.8 |
|
|
LSD 5% |
16.1 |
20.9 |
23.9 |
|
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