The effect of seed moisture content of hybrid maize at harvest time on seed germination traits and antioxidant enzymes activity under simulated conditions of some environmental stresses

doi:10.21203/rs.3.rs-3749942/v1

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The effect of seed moisture content of hybrid maize at harvest time on seed germination traits and antioxidant enzymes activity under simulated conditions of some environmental stresses

https://doi.org/10.21203/rs.3.rs-3749942/v1

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published 19 Mar, 2024

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Seed quality of hybrid maize is affected by many factors, including maturity time and environmental conditions. In this study, the effect of four maturity times of hybridized maize from male and female plants was investigated in terms of grain moisture content (30, 35, 40 and 45%) in 2021 & 2022 in Kermanshah, Iran. The experiments were on maize seed vigor using the standard germination and simulated tests of cold, Hiltner brick gravel and germination test under drought stress conditions. The results showed that highest percentage and rate of germination were obtained from the treatment with 30% moisture content at maturity (99% and 0.037 germination per hour). Brick gravel and drought stress tests reduced germination percentage compared to the standard test. Based on Guasnr model, the nonlinear model of germination response curve was fitting to the percentage of moisture contents at maturity time for various tests. In general, due to the reduction in the slope of germination response curve at high moisture content at maturity time for different tests, 30 and 35% moisture content at maturity time were found to be appropriate to produce high quality maize seeds. The early harvest, or in other terms 45% moisture content of the seed at the time of harvest, resulted in enhanced activities of Catalase, Ascorbate peroxidase and Malone Dialdehyde enzymes in different tests. On the other hand, the maximum activities of the Antioxidant enzymes were found in the germination test under drought stress conditions in the amount of 36.6 µmolmin^− 1mgprotein Catalase and 2829 nmolmin^− 1mg Ascorbate peroxidase.

Catalase

Corn

Kernel

Maturity time

Test

Vigor

Zea mays L. is one of the most important crops grown in many countries around the world. This plant with a global annual production of 826 million tons, is the third largest produced cereal crop in the world. Considering the prediction that the world's food production will be limited to 9 billion people by 2050, maize has the potential to help meet the food demand of developing countries. Therefore, it is important to recognize factors that affect crop quality and production of maize (Riccetto et al., 2020).

Crop quality and production depend on several factors including seed quality (Rifna et al., 2019). The three most important criteria for evaluating seed quality are germination ability, vigor, and health. According to the International Seed Testing Association (ISTA, 2012), seed vigor is a set of properties of a seed that determine the potential level of seed activity and efficiency during germination. Seed quality is influenced by the moisture content of the seed during harvest as well as environmental factors. Indeed, these factors are interrelated. In the interest of high crop yields, it is important to investigate these factors (ISTA, 2017).

Seed maturity has a significant effect on seed quality as drying during seed maturity is an integral part of seed germination. The reduction in seed moisture content after physiological maturity stage (i.e., maturity for harvest) increases seed vigor. Therefore, optimal moisture content will improve germination percentage and seed quality. Seed quality is also improved by timely harvesting. Harvesting too early can have a negative effect on germination and can reduce seed vigor. On the other hand, harvesting too late can also significantly reduce seed quality due to seed aging, undesired environmental factors, or seed damage to the embryo during harvest. Therefore, determining an appropriate harvest time could successfully effect on plant seed quality (Benaseer et al., 2019).

The simplest evaluations to determine seed quality can be performed using a standard germination test. However, this test does not account for environmental stressors in the field resulting in unreliable estimates. Therefore, different tests along with standard germination test can provide a more complete estimate of quality (Kermode, 2017).

Seed vigor can be evaluated by tests that artificially create field environmental conditions. They determine seed germination as well as seedling emergence under field conditions. Among these tests, only a limited number are acceptable by seed experts and seed testing institutes. These tests include the standard germination, low temperature germination, brick gravel and germination under drought stress tests (Rezvani et al., 2017).

Studying the environmental effects, especially its interactions with seed moisture content, makes it possible to produce seeds with the desired quantity and quality. Current literature stresses the importance of timely harvests on seed moisture content to improve plant seed quality. However, there is a lack of scientific knowledge about the combined effect of moisture content and stress factors on plant seed vigor. This investigation aims to provide maize seed producers with insights for better harvest time management under various stress conditions.

Experimental treatments

An experiment on hybrid maize was conducted in three replications during years of 2021 to 2022 in Kermanshah, Iran (34°-18′ N, 47°- 4′ E and altitude of 1420 m above sea level). In this study, the treatments included four harvest times of hybrid maize in terms of grain moisture content (30, 35, 40 and 45%). Besides, the effect of these treatments on maize seed vigor was investigated using the tests, such as standard germination, cold, brick gravel and germination under drought stress tests.

Performing the experiment

In this study, the hybrid maize seeds of male and female from cultivar of AS71 (each on the appropriate planting date) were planted on Four planting rows 5 meters long with row spacing of 75 cm and density of 9 plants per square meter. The first and fourth rows of male corn and the second and third rows of female corn were planted. The required Nitrogen for the plants was provided from the source of urea fertilizer (500 kg.ha^− 1) in three equal parts before flowering. In order to supply phosphorus, 150 kg of diamonium phosphate per hectare was used before planting. Regarding potash, before planting, 100 kg.ha^− 1 of potassium sulfate was uniformly applied below the planting lines as strips. During the growing season of maize, weeding in the plots was done by hand. The plots were then irrigated in the form of ridge furrow. The level of used water was measured by a meter installed in the field, which was 9000 cubic meters per hectare. The maternal base ears were covered with envelopes immediately after emergence to protect external pollen. Since acceptance of male gametophyte of the mentioned ears, coincided with the beginning of pollination of the male flowers in the paternal rows, envelopes were placed on the male flowers overnight to collect the pollen. The envelope containing the pollen was then placed on the ear in the middle rows for fertilization. Next, pollen collection was repeated for three nights to ensure complete grain closure in rows (to prevent bareness). Finally, in order to conserve the ears, the envelope remained until the end of pollination period. The seeds were harvested when the ears reached the desired moisture content. Moreover, in order to measure seed moisture content, moisture content was frequently determined by a digital hygrometer (ISTA, 2012). The seeds were then separated from the ears to determine both their germination characteristics in different seed tests.

Measuring traits

After physiological maturity stage and removing two rows of the margins in each plot, an area equivalent to three square meters was harvested to determine grain yield. Finally, grain yield was reported with initial moisture content at harvest time and 14% moisture content during 2021 ˗ 2022.

The Germine software was used to calculate the maximum germination, germination rate, and germination uniformity (Soltani et al., 2002). Using this software, the time to onset of 50% germination (H₅₀) was calculated through linear interpolation method in cumulative germination curve.

Germination rate (R₅₀) was also evaluated inversely to the time of reaching 50% of the maximum germination percentage by Eq. 1.

Germination rate R₅₀ = 1.H₅₀ ^− 1 (1)

In this study, germination uniformity (GU) is refered to the time during which germination incresaes from 10% maximum (H10) to 90% maximum (H₉₀), which was calculated by Eq. 2 (Soltani et al., 2002).

Germination uniformity GU = D₉₀ ˗ D₁₀ (2)

Germination index (GI), or in other words, the mean germination time was further determined by Eq. 3.

GI= Ʃdi ni. Ʃni^− 1 (3)

Also, germination properties H₅ (time to 5% germination), H₁₀ (time to 10% germination), H₅₀ (time to 50% germination time), H₉₀ (time to 90% germination), and H₉₅ (time to 95% germination) were determined according to Guasnr model (Soltani et al., 2002). In addition, germination description process was performed based on this model.

The simulated tests of some stresses

The experiments were conducted on seed vigor and germination of hybrid maize under simulated tests of some stresses. These simulated tests were in the form of cold, Hiltner brick gravel tests and the standard germination (control) on seed vigor and drought stress test (with polyethylene glycol) on seed germination of hybrid maize.

Standard germination test

First, after disinfection with 5% sodium hypochlorite solution for 30 seconds, the seeds were washed with distilled water. They were then placed in a 12cm sterile disposable petri dish. Whatman No. 1 filter papers were placed in each petri dish and 5 ml of distilled water was poured into each petri dish. Next, the petri dishes were placed inside an incubator at the controlled temperature of 25 ± 1°C. Five days after the start of the experiment; 5 ml of distilled water was added to the petri dishes again. The germinated seeds were counted every 24 hours. In the end, the duration of standard germination test was estimated to be 6 days according to ISTA rules (ISTA, 2017).

Cold test

In order to perform cold test, the seeds were incubated for 5 days at 5°C and another 7 days at 25°C. At the end of the test, germination indices and seed vigor were evaluated according to standard germination test (AOSA, 1983).

Hiltner brick gravel test

To perform this test, 250 ml of distilled water was added to 1100 g of sterilized brick gravel and the resulting mixture was allowed to stand for one hour. Then, a 3cm thick layer of wet crushed brick was put at the bottom of the plastic box and 100 seeds of maize were planted into crushed brick layer without any contacts with each other to avoid infection. A 3–4 cm thick layer of wet brick gravel was also laid on them and the box was kept in the dark at 25°C for 14 days in an incubator. Finally, evaluation of germination indices and seed vigor was made according to standard germination test (AOSA, 1983).

Drought stress test

In order to perform this test, the seeds were subjected to the standard germination test, with the difference that instead of distilled water, solution of 6000 polyethylene glycol in concentrations of -1MPa was used (According to Eq. 4) (Michel and Kaufmann, 1973). Finally, evaluation of germination indices and seed vigor was made according to standard germination test.

Ψ_S = ˗(1.18 × 10^− 2) C ˗ (1.18 × 10^− 4) C² + (2.67 × 10^− 4) CT+(8.39 × 10^− 7) C²T (4)

where Ψ_S is Osmotic potential of PEG-6000, C is the concentration of PEG-6000 in g/kg H,O and T is the temperature in °C.

The comparison of means

The comparison for different tests was conducted using excel 2016 software. Means of different treatment were compared using standard error.

Cumulative Germination

The process of cumulative germination of maize in response to moisture content treatments at maturity time showed different patterns in standard germination test. The similarities and differences between germination responses of different moisture contents at maturity time are evident (Fig. 1). The nonlinear model of germination response curve showed a relatively similar trend to moisture content treatments at maturity time So that it followed Guasnr model. According to the results reported in Fig. 2, 30% moisture content at maturity time shows better germination parameters.

Moreover, in 2021, the shortest time until the beginning of 5, 10, and 95% of germination was observed in 30% moisture content treatment at maturity time, although it showed no difference with 35 and 40% moisture content at maturity time. Also, in 2022, the time it took until the beginning of 5 and 10% of germination showed no difference between moisture content treatments at maturity time. However, 30% moisture content treatment at maturity time was able to improve germination rate to some extent compared to other treatments. Therefore, in standard germination test, moisture contents at maturity time had different effects on germination indicators.

Based on Guasnr model, fitness of the nonlinear model of the germination response curve for the percentage of moisture content at maturity time for drought stress test of 1 MPa was similar to other tests (Fig. 2). According to Fig. 2, 30% moisture content treatment at maturity time showed the highest germination percentage and rate. However, a reduction in the slope of germination response curve relative to moisture content treatments at maturity time was observed for drought stress test, especially at 1 MPa. However, treatments with 40 and 45% moisture content at maturity time reduced germination process.

The shortest time until the onset of 5, 10, 50 and 95% germination was obtained from drought stress tests of 1 MPa in 30% moisture content treatment at maturity time (Fig. 2). Also, similar to other tests in this study, early harvest of seeds with high moisture content at maturity time delayed germination. However, the treatment with 30% moisture content at maturity time was able to improve germination rate to some extent compared to other treatments. Therefore, we can claim that moisture content treatments at maturity time have different effects on germination indicators in drought stress test.

According to Guasnr model, the nonlinear model of the germination response curve was also fitting to moisture content treatments at maturity time for the brick test (Fig. 3). Tables 8 and 9 show that 30% moisture content treatment at maturity time has led to an acceptable germination percentage and rate. Also, the reduction in the slope of germination response curve to moisture content treatments at maturity time was significant for brick gravel test, especially in 2021 (Fig. 3).

Moreover, in this work, the shortest time until the onset of different germination percentages during 2021 ˗ 2022 was observed with 30% moisture content treatment at maturity time. Also, the time it took until germination in 30% moisture content treatment at maturity time showed no difference with 35% moisture content treatment at maturity time. On the other hand, 45% moisture content treatment at maturity time caused a delay in germination time for different percentages.

Similar to standard germination test, the process of cumulative germination in response to different moisture content treatments at maturity time showed different patterns in cold test (Fig. 4). However, following Guasnr model, the nonlinear model of germination response curve displayed relatively similar trends for different moisture content treatments at maturity time for the cold test. Furthermore, according to the reported results in Fig. 4, 30% moisture content treatment at maturity time showed higher germination percentage and rate.

Additionally, in 2021, the shortest time until the beginning of maize germination at different times was observed in 30% moisture content treatment at maturity time. However, 40% moisture content treatment at maturity time delayed germination of maize seeds in the cold test. Also, the time until the onset of maize germination in 30 and 35% moisture content treatments at maturity time showed no difference.

Germination Max

The results showed that the increase in moisture content at the time of maturity resulted in the decrease of germination percentage in the standard, drought stress, brick gravel, and cold germination tests (Table 1). Therefore, the highest percentage of germination were obtained from the treatment with 30% moisture content at maturity time in the amount of 99%. But, the treatment with 45% moisture content caused the decline in the germination of maize in different germination tests during 2021 and 2022 (Table 1). Moreover, the treatment with 45% moisture content at maturity time compared to the treatment with 30% moisture content, reduced the germination percentage at maturity time for standard germination test (5%), drought stress test (48%), brick gravel test (20%), and cold test (8%) for 2021. For 2022, a similar germination tendency was discovered in comparison to 2021. So, the decline in the germination of the early seed harvest was obtained by drought stress and brick gravel tests. However, the germination response to moisture content at maturity time for the cold test was more in line with the standard germination test.

Table 1

Comparison of Germination Max (%) of maize seeds at harvest times on based of seed moisture content under simulated tests of some soil stresses (2021 and 2022)
Seed Moisture Content (%)	Standard germination		Drought stress		Brick gravel		Cold
	2021	2022	2021	2022	2021	2022	2021	2022
30	98.33±1.53	99.33±0.58	42.00±14.00	48.67±9.02	78.67±5.77	76.67±2.31	96.67±2.89	96.67±2.89
35	97.33±1.15	96.00±0.00	39.33±14.74	39.33±2.31	76.00±5.29	74.00±5.29	93.33±2.89	95.00±0.00
40	93.33±3.05	94.00±3.46	24.00±6.93	32.00±1.15	67.33±5.03	64.00±5.29	90.00±0.00	91.67±2.89
45	93.33±6.11	93.33±2.89	22.00±7.21	27.33±1.15	62.67±5.29	59.33±7.02	88.33±2.89	91.67±7.64
Data were expressed as mean ±SE (Standard Error).

Germination Rate

The increase in moisture content at the time of maturity reduced germination rate for drought stress, brick gravel and cold tests. So that the maximum germination rate was obtained in the treatment with 30% moisture content at maturity time in the amount of 0.037 germination per hour. However, the treatment with 45% moisture content at maturity time decreased the germination rate of maize for various tests in 2021 and 2022 (Table 2). Likewise, the germination rate of maize seeds in the treatment with 30% moisture content at maturity time displayed more similarity to the treatment with 35% moisture content for different tests in 2021 and 2022. Thus, the decrease of germination process in early seed harvest was obtained with different tests compared to the standard germination test.

Table 2

Comparison of Germination Rate (per hour) of maize seeds at harvest times on based of seed moisture content under simulated tests of some soil stresses (2021 and 2022)
Seed Moisture Content (%)	Standard germination		Drought stress		Brick gravel		Cold
	2021	2022	2021	2022	2021	2022	2021	2022
30	0.007±0.001	0.007±0.001	0.037±0.046	0.011±0.002	0.009±0.002	0.001±0.009	0.009±0.001	0.009±0.000
35	0.007±0.001	0.008±0.000	0.01±0.0007	0.011±0.001	0.009±0.002	0.001±0.009	0.008±0.001	0.008±0.001
40	0.006±0.001	0.007±0.000	0.01±0.0006	0.013±0.002	0.007±0.000	0.0006±0.008	0.007±0.000	0.007±0.000
45	0.006±0.000	0.008±0.001	0.009±0.002	0.011±0.004	0.007±0.000	0.0006±0.008	0.006±0.000	0.007±0.000
Data were expressed as mean ±SE (Standard Error).

Germination Uniformity

The decrease in germination uniformity was observed in standard, drought stress, brick gravel, and cold germination tests with increasing moisture content at maturity time (Table 3). So that the maximum germination uniformity was detected in the treatment with 30% moisture content at maturity time. However, early harvest treatment with 45% moisture content resulted in the decrease of maize germination uniformity for different tests in 2021 and 2022 (Table 3). The treatment with 45% moisture content at maturity time compared to the treatment with 30% moisture content resulted in the decrease of germination uniformity in 2021 and 2022 for standard test (26% and 31%) and drought stress test (3% and 21%). Also, the decrease of germination uniformity was detected in 2021 and 2022 for brick gravel test (17% and 24%) and cold test (17% and 15%). Nevertheless, the early harvest treatment with 45% moisture content has different effects on germination uniformity in different tests.

Table 3

Comparison of Germination Uniformity (hour) of maize seeds at harvest times on based of seed moisture content under simulated tests of some environmental stresses (2021 and 2022)
Seed Moisture Content (%)	Standard germination		Drought stress		Brick gravel		Cold
	2021	2022	2021	2022	2021	2022	2021	2022
30	96.36±16.03	114.29±29.81	81.02±12.72	89.69±9.32	89.90±25.16	84.21±15.93	87.41±7.61	93.60±21.40
35	92.59±25.36	87.97±30.50	82.72±5.32	77.49±10.49	86.45±6.22	79.45±10.20	91.17±19.11	102.11±5.87
40	78.01±13.58	81.31±17.43	72.24±20.99	49.92±11.12	79.59±2.97	71.88±25.98	89.58±18.84	98.29±5.10
45	70.75±9.87	78.22±8.41	78.20±7.01	70.40±20.46	74.8±25.98	64.19±15.40	72.65±12.23	79.87±35.43
Data were expressed as mean ±SE (Standard Error).

Germination Index

Different moisture content treatments at maturity time led to changes in Germination Index (GI), or in other words, the mean germination time in 2021 and 2022 (Table 4). So that the increase in germination index for the standard, drought stress, brick gravel, and cold tests was observed with an increase in moisture content at maturity time (Table 4). The minimum average germination time was detected in the treatment with 30% moisture content at maturity time. However, early harvest treatment with 45% moisture content increased average germination time of maize for various tests in 2021 and 2022 (Table 4). Nevertheless, different tests compared to the standard germination test displayed approximately identical effects on the germination index or in other words, the average germination time.

Table 4

Comparison of Germination Index of maize seeds at harvest times on based of seed moisture content under simulated tests of some environmental stresses (2021 and 2022).
Seed Moisture Content (%)	Standard germination		Drought stress		Brick gravel		Cold
	2021	2022	2021	2022	2021	2022	2021	2022
30	6.29±0.98	6.39±0.66	4.50±0.23	4.51±0.73	5.25±0.74	4.99±0.51	5.36±0.61	5.16±0.59
35	6.46±0.62	5.82±0.04	4.79±0.13	4.19±0.20	5.35±0.86	5.33±0.47	5.87±0.47	5.49±0.72
40	6.62±0.20	6.36±0.22	4.53±0.13	3.69±0.73	6.30±0.08	5.75±0.32	6.24±0.27	6.19±0.39
45	7.37±0.09	6.02±0.60	5.28±0.86	4.71±1.14	6.88±0.32	5.55±0.19	6.88±0.28	6.12±0.59
Data were expressed as mean ±SE (Standard Error).

Catalase

The results indicated that the early harvest coinciding with higher moisture content at maturity time, resulted in an increase in the activity of the Catalase antioxidant enzyme in standard, drought stress, brick gravel, and cold tests (Table 5). So that the maximum activity of the Catalase antioxidant enzyme was obtained in the treatment with 45% moisture content at maturity time for various tests in 2021 and 2022 (Table 5). The treatment with 45% moisture content at maturity time compared to the treatment with 30% moisture content resulted in an increase in the activity of the Catalase antioxidant enzyme for standard test (7% and 8%) and drought stress test (23% and 20%) in 2021 and 2022. Also, the increase in the activity of the Catalase antioxidant enzyme was detected for brick gravel test (13% and 12%) and cold test (15% and 16%) in 2021 and 2022. As a result, the maximum activity of the Catalase antioxidant enzyme in early seed harvest was obtained in the treatment with 45% moisture content using brick gravel test. Also, at a lower level, the activity of the Catalase antioxidant enzyme was detected in the brick gravel and the cold tests.

Table 5

Comparison of Catalase (molmin− 1mg protein) of maize seeds at harvest times on based of seed moisture content under simulated tests of some environmental stresses (2021 and 2022).
µ
Seed Moisture Content (%)	Standard germination		Drought stress		Brick gravel		Cold
	2021	2022	2021	2022	2021	2022	2021	2022
30	28.20±0.52	28.70±0.40	29.45±0.90	30.18±0.45	28.64±0.40	29.17±0.47	29.24±0.49	29.63±0.48
35	28.69±0.41	29.26±0.63	32.15±0.47	32.62±0.58	29.56±0.27	29.58±0.48	29.68±0.37	30.00±0.56
40	29.73±0.45	30.14±0.48	34.77±1.09	35.13±0.49	30.30±0.50	30.68±0.53	31.80±0.50	32.31±0.74
45	30.69±0.58	31.18±0.69	36.25±0.66	36.60±0.41	32.31±0.58	32.80±0.35	33.71±0.40	34.31±0.52
Data were expressed as mean ±SE (Standard Error).

Ascorbat Peroxidase

The early harvest of the maize seeds resulted in an increase in the activity of Ascorbate Peroxidase antioxidant enzyme similar to the activity of the Catalase enzyme antioxidant in standard, drought stress, brick gravel, and cold tests (Table 6). So that the maximum activity of the Ascorbate Peroxidase antioxidant enzyme was detected in the treatment with 45% moisture content for various tests in 2021 and 2022 (Table 6). The treatment with 45% moisture content at maturity compared to the treatment with 30% moisture content resulted in an increase in the activity of the Ascorbate Peroxidase antioxidant enzyme for standard test (1% and 1%) and drought stress test (6% and 6%) in 2021 and 2022. Also, the increase in the activity of the Ascorbate Peroxidase antioxidant enzyme was detected for brick gravel test (5% and 5%) and cold test (5% and 5%) in 2021 and 2022. As a result, the maximum activity of the Ascorbate Peroxidase antioxidant enzyme in early seed harvest was obtained in the treatment with 45% moisture content using brick gravel test.

Table 6

Comparison of Ascorbat Peroxidase (nmolmin− 1mg) of maize seeds at harvest times on based of seed moisture content under simulated tests of some soil stresses (2021 and 2022).
Seed Moisture Content (%)	Standard germination		Drought stress		Brick gravel		Cold
	2021	2022	2021	2022	2021	2022	2021	2022
30	2643±12	2645±11	2663±15	2671±16	2654±16	2659±13	2656±11	2667±16
35	2647±10	2655±15	2721±12	2724±6	2680±11	2694±9	2701±18	2713±12
40	2654±4	2654±4	2763±16	2769±14	2730±13	2748±17	2750±15	2762±18
45	2673±16	2681±15	2816±15	2829±18	2780±18	2784±15	2798±15	2806±13
Data were expressed as mean ±SE (Standard Error).

Malone Dialdehide

The delayed harvest of the maize seeds, or in other terms, 45% moisture content of the seed at the time of harvest, illustrated lower amount of Malone Dialdehyde (Table 7). On the other hand, early harvest at 45% moisture content of the seed resulted in an increase in the amount of Malone Dialdehyde for various tests in 2021 and 2022 (Table 7). So that the treatment with 45% moisture content at maturity time compared to the treatment with 30% moisture content resulted in an increase in the amount of Malone Dialdehyde for standard test (2% and 2%) and drought stress test (24% and 25%) in 2021 and 2022. Also, the increase in the amount of Malone Dialdehyde was obtained for brick gravel test (20% and 20%) and cold test (22% and 22%) in 2021 and 2022. As a result, the maximum amount of Malone Dialdehyde in early harvest of maize seeds was detected in the treatment with 45% moisture content using brick gravel test. Also, at a lower level, the increase in the amount of Malone Dialdehyde was detected in the brick gravel and the cold tests compared to the standard test.

Table 7

Comparison of Malone Dialdehide (nmol.mgFW− 1) of maize seeds at harvest times on based of seed moisture content under simulated tests of some environmental stresses (2021 and 2022).
Seed Moisture Content (%)	Standard germination		Drought stress		Brick gravel		Cold
	2021	2022	2021	2022	2021	2022	2021	2022
30	1855±12	1861±12	1912±10	1904±21	1871±25	1871±19	1891±21	1893±22
35	1861±12	1863±7	2108±19	2115±24	1930±9	1941±9	2019±20	2022±17
40	1879±17	1870±13	2231±18	2244±15	2161±20	2171±21	2240±13	2241±18
45	1902±14	1892±12	2367±28	2376±24	2242±20	2250±18	2302±21	2312±18
Data were expressed as mean ±SE (Standard Error).

In this study, the effect of moisture content on maize grain germination indicators, and seed quality were evaluated. Moisture content ranged from 30 ˗ 45% and was based on harvest times with early harvest times resulting in the highest moisture content (40 ˗ 45%). Lower moisture content (30%) occurred with harvesting after physiological maturity stage. The stress factors were introduced using low temperature germination, brick gravel and drought stress test. These findings are explained and compared in context of current research.

The germination rate and percentage of maize was strongly influenced by moisture content. The harvested seeds with 30% moisture content seemed to have the least pre-harvest aging and therefore had the highest germination. In general, germination does not occur until the seed has completed the minimum morphogenic stages required for embryonic development (Kermode, 2017). The larger and more mature the seed is the more the greater the seed vigor. Therefore, increasing germination percentage can be expected with reduced seed moisture content at harvest time (Duquette and Kimball, 2019). The germination percentage in the low temperature germination test showed a slight change compared with the standard test, and the seed germination rate was somewhat higher. This correlates with other reports that have found that cold pretreatments change indicators related to seed germination and vigor by activating the seed’s physiological mechanisms (Porto et al., 2019). Therefore, cold pretreatment could accelerate germination process by stimulating the germination process (Urbanova and Leubner-Metzger, 2018).

Germination indicators were expected to decline during this test as aging affects the activity of hydrolyzing enzymes and other cellular systems that transfer seed stock material (Bailly, 2004). In addition, reports attribute reduced seed vigor from seed tests to the complete degradation of the cytoplasmic membrane structure of seed cells (Rao et al., 2017). Our finding revealed that seed tests reduce vigor of maize seeds particularly with high moisture content from improper harvest time.

There have been many reports on reduced germination and related indicators in seeds affected by drought stress test with polyethylene glycol solution and mechanical stress with the brick test (Khodarahmpour, 2011; Tang et al., 2019). Both treatments resulted in the reduction in the slope of germination response curve to moisture content treatments at harvest time. Some researchers have attributed the germination response to drought stress due to the movement and transfer of seed stock as polyethylene glycol reduces hydrolysis of seed stock material (Zhenyi et al., 2019). Our findings indicated that the highest germination percentage and rate occurred with drought stress conditions of 1 MPa and 30% moisture content at harvest time. Results of the brick test clearly confirmed the reduction in germination indicators with inappropriate maturity moisture content. The high correlation of the brick test results has also been reported with field results for seed germination (Tekrony, 2003; Marcos Filho, 2015).

In summary, the findings from this study correlate well with current literature and adds to it by investigating how environmental factors combined with seed moisture content affect seed quality. It was found seed quality was best with 30% moisture content. On the other hand, treatments with 40 and 45% moisture content at harvest time significantly reduced germination process.

The seed deterioration process may be due to the denaturation of biomolecules, production and cumulation of toxic substances, and destruction of cell membrane structure (Ebone et al., 2019).

The reports show that the increase in the amount of Malone Dialdehyde during the deterioration process is due to the hydrolysis of storage materials during the germination process (Fotouo, M. et al., 2020). Thus, it can be assumed that this confirms the findings of this study in terms of the increase in the negative effects of early harvest of maize seeds at a moisture content of 45%. On the other hand, the increase in the activity of the Catalase and Ascorbate Peroxidase antioxidant enzymes during environmental stresses; including drought stress, brick gravel, and cold tests is a kind of defense mechanism for plants. This mechanism mainly happens due to the disruption of cytoplasmic membrane structure of the seed cells. Catalase is an enzyme that detoxifies hydrogen peroxide by converting it into water and eventually to oxygen (Kibinza et al., 2011). Moreover, the Ascorbate Peroxidase enzyme decreases the amount of hydrogen peroxide (Pandey et al., 2017). The increase in the capacity of the antioxidant enzymes is a general response to cell membrane destruction due to the seed deterioration (Ali & Elozeiri, 2017). Thus, it appears that the increase in the activity of antioxidant enzymes has been in response to the detrimental impacts of the oxygen produced by the deterioration of the maize seeds.

Results of this study showed that seed quality and its various aspects were influenced by the combined effect of environmental factors and moisture content. In particular, the slope of the germination response curve to moisture content at harvest time was observed for the brick gravel, and drought stress tests. Therefore, the maximum seed dry weight or weight harvest occurs after physiological maturity. The obtained results also indicated that environmental conditions during seed harvest time may have a role in seed vigor reduction by affecting seed aging process. Maize seed quality was best with 30% moisture content. On the other hand, treatments with 40 and 45% moisture content at harvest time significantly reduced germination process. As a result, 30% moisture content at harvest time under the influence of various environmental conditions is produced the highest quality seeds of maize.

The moisture content of 45% at maturity time, which resulted in an increase in the activity of Catalase and Ascorbate peroxidase antioxidant enzymes, was obtained in drought stress test. At a lower level, the activity of Catalase and Ascorbate peroxidase antioxidant enzymes was detected in the brick gravel and the cold tests. The increase in the amount of Malone Dialdehyde of the maize at 45% moisture content compared to 30% moisture content affirms this claim. Nevertheless, early seed harvest resulted in the increased negative effects of drought stress, brick gravel, and cold tests on the seeds compared to the standard germination test.

Acknowledgements

Hereby, we would like to express our appreciation of maize Cultivation Development Institute as well as the Islamic Azad University, Fasa Branch, Iran sincere assistance in fulfilling this study.

Statements & Declarations

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Competing Interests

The authors have no relevant financial or non-financial interests to disclose.

Data availability

All data generated or analysed during this study are included in this published article [and its supplementary information files].

Informed consent

No Human Participants and/or Animals were involved in this research.

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No competing interests reported.

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The effect of seed moisture content of hybrid maize at harvest time on seed germination traits and antioxidant enzymes activity under simulated conditions of some environmental stresses

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Abstract

Figures

Introduction

Materials and Methods

Experimental treatments

Performing the experiment

Measuring traits

The simulated tests of some stresses

Standard germination test

Cold test

Hiltner brick gravel test

Drought stress test

The comparison of means

Results

Cumulative Germination

Germination Max

Germination Rate

Germination Uniformity

Germination Index

Catalase

Ascorbat Peroxidase

Malone Dialdehide

Discussion

Conclusion

Declarations

References

Additional Declarations

Status:

Journal Publication

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