Effects of Salicylic Acid on Wheat Germination

American-Eurasian J. Agric. & Environ. Sci., 13 (12): 1603-1608, 2013 ISSN 1818-6769 © IDOSI Publications, 2013 DOI: 10.5829/idosi.aejaes.2013.13.12.12268

Effects of Salicylic Acid on Wheat Germination Parameters under Drought Stress 1

A. Movaghatian and 2F. Khorsandi

Department of Agroecology, Shahid Chamran University, Ahvaz, Iran Department of Soil Science, Darab Branch, Islamic Azad University, Darab, Iran 1

2

Abstract: A laboratory experiment was conducted to investigate the effects of seed priming with salicylic acid (SA) on germination characteristics of wheat (Chamran cv.) under drought stress. The experimental design was completely randomized design with five SA concentrations (0, 0.00001, 0.001, 0.1 and 1 mM), four levels of stress (0, -3, -6 and -9 bar) with three replications. The seeds were soaked in SA solution for 12 hrs and after drying, were placed in Petri dishes containing 7 ml of polyethylene glycol solution. For eight days the germination traits were monitored and germination percentage and rate, radicle and plumule lengths and seed vigor were measured. The results showed that drought stress inhibited all of the germination characteristics measured. Primed seeds with 0.00001 mM SA had the highest germination percentage and rate, and radicle and plumule lengths. The 0.00001 mM SA concentration had the highest germination percentage under high stress (-9 bar) and the highest germination rate under medium stress (-6 bar). Low concentrations of SA had more positive effects on wheat germination than high concentrations. Based on the results of this study, seed priming of wheat with low concentrations of SA (0.00001 mM) is recommended under low to high drought stress conditions. Key words: Plant hormone

Plant growth regulators

INTRODUCTION Plants in natural environments are subject to a variety of stresses which have negative effects on their growth. Water shortage or drought stress is the most limiting factor for agricultural production [1]. Plants respond to drought stress at the physiological, cellular and molecular levels, but the extent of damage depends on the age and stage of plant growth [2]. Seed germination is an important biological process in growth cycle of the plant species. Successful plant establishment in most cases ends up in acceptable and economical final yield [3]. Poor plant establishment is a common cause of reduction in plant yields in arid and semi-arid areas [4]. Drought stresses can reduce germination and, therefore, reduce seedling emergence and inhibit further growth in plants. Seed priming with various plant growth hormones, such as salicylic acid, is a common technique for increasing the speed and uniformity of germination and seedling emergence under stress [5]. During priming, the Corresponding Author:

Seed priming

Triticum aestivum

Water stress

seeds are usually exposed to an external water potential which is sufficient enough to prevent germination, but let biochemical and physiological processes occur before germination within the seed. Salicylic acid is a naturally occurring plant hormone of phenolic nature that has diverse effects on tolerance to abiotic stresses [6, 7]. Application of SA induced tolerance in plants to many biotic and abiotic stresses including fungi, bacteria and viruses, chilling, salinity, drought and heat [8]. It participates in regulation of physiological process in plants such as stomata closure, ion uptake and transport, inhibition of ethylene biosynthesis, transpiration, stress tolerance, membrane permeability and photosynthesis and growth [7, 9]. The effects of SA on physiological processes of plants depend on its concentration, type of plant, the stage of plant growth and environmental conditions; thus, it can have beneficial or inhibitory effects on plant physiological processes. Salicylic acid has improved salt tolerance of wheat seedlings [10] and drought tolerance

A. Movaghatian, Department of Agroecology, Shahid Chamran University, Ahvaz, Iran.

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Am-Euras. J. Agric. & Environ. Sci., 13 (12): 1603-1608, 2013

of Arabidopsis seedlings [11]. Effects of salicylic acid on After disinfection, wheat seeds (Chamran cv.) were seed germination are conflicting. While Shakirova et al. immersed for 12 hours in every solution of salicylic acid [12] and El-Tayeb [13] reported stimulating effects of and control in the dark at 25°C. At the end of this period, salicylic acid on germination of wheat and barley, the seeds were removed and dried. 15 seeds were placed Rajasekaran et al. [14] reported that salicylate had no on a filter paper in a clean and sterilized Petri dish, and 7 significant effects on seed germination. ml of polyethylene glycol solution was added to cover the Iran is located in arid and desert belt of the world. seeds. Petri dishes were transferred to a germinator set at Therefore, a large part of the country is faced with high 25°C and 60% relative humidity. They were inspected temperatures, fresh water shortage and high evaporative daily and the number of germinated seeds (>2 mm radicle) demand and thus the risk of erosion, salinization of soil were counted. On the eighth day the seeds were taken out and water resources and drought stress in farm fields and of the Petri dishes, and their radicle and plumule lengths orchards. It is anticipated that future global warming and were measured. Germination percentage (GP), germination climate change, will result in reduced rainfall, higher rate (GR) and seed vigor index (VI) were also calculated temperatures and greater incidence of drought according to the following equations [17]. phenomenon in many parts of the country [15]. Nf Ni SL × GP Wheat (Triticum aestivum L.) is produced as a strategic, GP = GR VI = = irrigated crop extensively in many parts of Iran. N i 100 Given the importance of wheat crop as irrigated crop and high potential of drought stress occurrence in the N, Nf and Ni are total number of seeds, number of country, studies on crop management and irrigation under seeds germinated and seeds germinate at the day i, drought stress conditions are needed. Therefore, the main respectively, and SL is radicle length plus plumule length. purpose of this study was to investigate the effect of The data were statistically analyzed by MSTATC different concentrations of salicylic acid on wheat statistical software. The comparison between treatments germination and seedling characteristics under drought was performed by Duncan's multiple range test (DMRT) stress. The results of this study can be helpful in wheat at 5% probability level. management and irrigation at planting and germination stage. RESULTS AND DISCUSSION

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MATERIALS AND METHODS This experiment was conducted at the Plant Physiology Laboratory of Shahid Chamran University. The experimental design was completely randomized in a factorial arrangement with three replications. Treatments consisted of four drought stress levels of 0 (control), -3, -6 and -9 bar, and five salicylic acid concentrations of 0 (control), 0.00001, 0.001, 0.1 and 1 mM. Drought stress treatments were prepared by using polyethylene glycol 6000 [16]. The pH of salicylic acid and control solutions were adjusted to 6.5.

Germination Percentage: Germination percent (GP) was significantly affected by salicylic acid (SA), droughts stress and their interaction (Table 1). SA increased GP at 0.00001 and 0.001 mM concentrations as compared to the control, but the increases were not significant (Table 2). The 1 mM SA concentration significantly reduced GP. The highest GP (97.2%) was observed at 0.00001 mM SA concentration, and the lowest GP (78.3%) was observed at 1 mM concentration. Shakirova et al. [12] stated that various concentrations of SA show different hormonal effects, having inhibitory or positive effects on seed germination and growth. While, high level of drought

Table 1: Analysis of Variance test results for the characteristics measured in the experiment Source of variation

df

Germination percentage

Germination rate†

Radicle length (mm)

Plumule length (mm)

Seed vigor

Replication Salicylic acid (A) Drought stress (B) A×B Error CV

2 4 3 12 38

76.29 ** 731.49 ** 5630.71 ** 639.59 63.82 8.9

0.53 ns ** 4.43 ** 340.34 ** 2.29 0.47 8.8

1.49 ns 1.36 ns ** 43.59 1.85 ns 1.16 23.8

0.042 ns ** 1.82 ** 69.54 ** 1.08 0.42 25.8

195.47 ns ns 28.14 ** 25200.1 ns 157.43 121.02 16.2

ns

NS: Not significant *, **: Significant at 0.05 and 0.01 probability levels, respectively. † Number of seeds germinated per day

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Am-Euras. J. Agric. & Environ. Sci., 13 (12): 1603-1608, 2013 Table 2: Interactive effects of drought stress and salicylic acid concentration on germination traits of wheat (Chamran cv.)

Drought stress (bar)

Salicylic Acid concentration (mM) --------------------------------------------------------------------------------------------------------------------------------------------------------------------0 0.00001 0.001 0.1 1 Mean†

Germination percentage* 0 100.0 a -3 100.0 a -6 93.3 a -9 66.7 b § Mean 90.0 AB

100.0 a 100.0 a 100.0 a 88.9 a 97.2 A

100.0 a 100.0 a 100.0 a 84.4 a 96.1 A

100.0 a 100.0 a 97.78 a 44.44 c 85.6 BC

100.0 a 100.0 a 95.6 a 17.8 d 78.3 C

100.0 A 100.0 A 97.3 A 60.4 B

Germination rate (number of seeds germinated/day) * 0 12.5 b 14.2 a -3 7.3 c 7.9 c e -6 5.8 7.4 c -9 2.8 f 4.1 f Mean 7.1 B 8.4 A

14.5 a 7.7 c 7.4 c 3.7 f 8.3 A

15.0 a 7.7 c 7.1 cd 1.3 g 7.8 AB

14.2 a 7.8 c 6.0 de 0.7 g 7.2 B

14.1 A 7.7 B 6.8 C 2.5 D

Radicle length (mm)* 0 -3 -6 -9 Mean

5.13 a-e 5.12 a-e 4.28 c-g 2.74 f-h 4.32 A

4.91 b-e 6.52 ab 6.04 a-d 2.35 gh 4.95 A

4.69 b-f 6.13 a-c 4.22 c-g 3.10 e-h 4.54 A

5.02 a-e 7.16 a 5.56 a-d 1.23 h 4.74 A

5.48 a-d 5.80 a-d 3.89 d-g 1.21 h 4.10 A

5.05 AB 6.15 A 4.80 B 2.13 C

Plumule length (mm)* 0 -3 -6 -9 Mean

7.68 a 4.44 bc 0.73 ef 0.13 f 2.84 A

3.73 b-d 3.67 cd 2.82 d 0.22 f 2.90 A

4.05 b-d 3.02 d 0.54 ef 0.17 f 1.94 B

4.53 bc 3.76 b-d 1.67 e 0.16 f 2.53 AB

4.94 b 3.37 cd 0.97 ef 0.11 f 2.35 AB

4.99 A 3.65 B 1.34 C 0.16 D

Seed vigor* 0 -3 -6 -9 Mean

112.0 a 95.7 a 48.5 b 18.9 c 68.8 A

98.6 a 99.00 a 65.8 b 4.8 c 67.0 A

92.3 a 98.9 a 57.6 b 14.5 c 65.9 A

90.9 a 101.9 a 61.0 b 12.5 c 66.6 A

104.0 a 94.8 a 67.2 b 12.0 c 69.5 A

99.6 A 98.1 A 60.0 B 12.5 C

* For each germination trait, numbers with the same letter are not statistically different than each other according to Duncan’s Multiple Range test at 5%probability level. † For each germination trait, the means within each column with the same letter are not statistically different than each other according to Duncan’s Multiple Range test at 5%probability level. § For each germination trait, the means within each row with the same letter are not statistically different than each other according to Duncan’s Multiple Range test at 5%probability level.

stress (-9 bar) significantly decreased GP, there was no statistical differences between other stress levels (Table 2). Under drought stress, water absorption by seed is impaired and á-amylase enzyme activity is inhibited due to high osmotic pressure [18]. None of the SA concentrations significantly affect GP at 0 to -6 bar stress levels (Table 2). But at high stress level (-9 bar), 0.00001 and 0.001 mM concentrations significantly increased GP while 0.1 and 1 mM levels significantly reduced GP of wheat seeds. In fact, 0.00001 and 1 mM SA concentrations had the highest and lowest GP, respectively, at -9 bar stress level (Table 2). Zare et al. [19] also reported significant increase in germination of fox berry (Sanguisorba minor L.) with the use of salicylic acid under drought and salinity stresses. The results of many

other studies with SA under stress conditions has shown that lower concentrations of SA is often more effective than higher concentrations [6, 8]. Application of high SA concentration (1 mM) negatively affected growth, photosynthesis and yield of mungbean under salinity stress [6]. Under both saline and non-saline conditions N, P, K and Ca concentrations were reduced, antioxidant enzyme activities declined and thus, photosynthesis and growth were retarded [6]. The same has been reported for wheat [20]. Sharafizad et al. [21] investigated the effects of 0, 0.7, 1.2 and 2.7 mM concentrations of SA on wheat (Chamran cv.) seed germination under drought stress (0, -5, -10 and -15 bar). They reported that the highest GP and the affecting traits on it were obtained by seed soaking at lowest SA concentration (0.7 mM).

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Germination Rate: Germination rate (GR) is one of the most important indicators to evaluate the tolerance in plant [22]. The effects of SA, drought stress and their interaction on GR of wheat were highly significant (Table 1). SA application increased mean GR in all concentration levels, but only at 0.00001 and 0.001 mM the increases were significant (Table 2). The highest mean GR was observed in 0.00001 mM SA concentration. In contrast, increasing drought stress levels significantly reduced GR of wheat seeds (Table 2). The same trend was observed at each SA concentration level. Under non-stress condition (0 bar), all SA concentrations significantly increased GR, but there was no significant difference among other SA concentrations (Table 2). At -3 bar, there was no significant differences among SA concentration levels. All SA concentrations increased GR at -6 bar significantly except in 1 mM level (Table 2). But at -9 bar the higher SA concentrations (0.1 and 1 mM) significantly decreased GR of wheat seeds. The highest GR at any drought stress level was observed with 0.00001 mM SA concentration, although it was significant only at 0 and -6 bar stress levels (Table 2). Radicle Length: Drought stress had significant effect on radicle length of wheat seedlings, but the effects of SA and its interaction with drought stress on this trait was not significant (Table 1). Although, the effect of SA on radicle length was not significant, the maximum mean radicle length of 4.95 mm was observed at 0.00001 mM concentration (Table 2). Drought stress significantly reduced mean radicle length at -6 and -9 bars (Table 2). These observations were consistent with findings of Kafi et al. [22] in lentil. Interaction of SA and drought stress was non-significant (Table 1). This means that the effect of SA concentrations on wheat radicle length followed the same trend at all drought stress levels. None of the SA concentrations improved radicle length significantly at each stress levels, however, 0.00001 mM had the highest radicle lengths at 0, -3 and -6 bars (Table 2). At -9 bar, highest radicle length was observed at 0.001 mM concentration. Although SA did not increase radicle length of wheat seedlings in this experiment, Zare et al. [19] reported increased radicle lengths of fox berry seedlings with the used of SA at high levels of salinity and drought stresses. Plumule Length: The effects of SA, drought stress and their interaction on plumule length of wheat seedlings were highly significant (Table 1). The 0.001 mM SA concentration significantly reduced mean plumule length

of wheat seedling as compared to 0 and 0.00001 mM concentrations, while mean plumule lengths at other concentrations were not significantly different than control (Table 2). Increasing drought stress levels significantly reduced mean plumule length of wheat seedlings (Table 2). Under drought stress conditions, water uptake, as well as hormone and enzyme activities are reduced and thus, transfer of food to fetus is disrupted, which results in reduced shoot growth and length [22]. The same trend was observed at each SA concentration level. At non stress treatment (0 bar) all SA concentrations significantly reduced plumule length, but there was no significant difference among concentration levels (Table 2). At -3 bar, 0.001 mM concentration significantly reduced plumule length as compared to control. However, at -6 bar, 0.00001 mM SA concentration significantly increased plumule length compared to all other treatments (Table 2). At -9 bar, there was no significant differences between SA concentrations. Zare et al. [19] reported no effect of SA on root and shoot lengths of fox berry, while other experiments have reported an increase in shoot lengths of wheat, barley and canola as a result of treatment with salicylic acid [23, 24]. Seed Vigor: Drought stress had significant effect on seed vigor index (SV) of wheat, but the effects of SA and its interaction with drought stress on this trait was not significant (Table 1). The mean SV values decreased significantly at -6 and -9 bar drought stress levels (Table 2). The same trend was also observed at each SA concentration levels. However, Basra et al. [25] reported that primed soybean seeds showed more vigor under salt stress. There were no significant effects of SA concentration on SV at any stress level (Table 2). Ghanbari et al. [26] reported that 1 and 2 mM SA concentrations increased seed vigor of radish significantly at 4 dS/m salinity stress level. CONCLUSIONS The overall results of this experiment showed the inhibitory effects of drought stress on germination indices of wheat (Chamran cv.). However, seed priming with SA improved and enhanced germination traits under various stress levels, thus, reducing some of the inhibitory effects of drought stress. Based on the results, it can be concluded that low concentrations of SA have more positive effects on wheat germination than medium and high concentration. The 0.00001 mM SA concentration significantly improved germination percentage and

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germination rate particularly at medium (-6 bar) and high (-9 bar) drought stress levels. This means that seed priming of wheat with this low concentration of SA will speed up the germination time and enhance the establishment of seedlings. Therefore, the planted seeds will be less susceptible to soil-borne pests and diseases, and produce more biomass and photosynthetic capacity, especially in areas with shortage of irrigation water resources at planting stage. This has positive consequences on management of this crop at planting and germination stage. Based on the results of this study, seed priming of wheat (Chamran cv.) with low concentrations of SA (0.00001 mM) is recommended under low to high drought stress conditions.

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