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Seed priming improves the germination performance of cumin (Cuminum syminum L.) under temperature and water stress
Industrial Crops and Products 42 (2013) 454–460
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Seed priming improves the germination performance of cumin (Cuminum syminum L.) under temperature and water stress A. Rahimi ∗ Department of Agronomy and Plant Breeding, Agriculture College, Vali-e-Asr University of Rafsanjan, Rafsanjan, Iran
a r t i c l e
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Article history: Received 31 March 2012 Received in revised form 7 June 2012 Accepted 17 June 2012 Keywords: Drought stress Germination rate Germination uniformity Temperature
a b s t r a c t Farmers typically practice ‘on-farm’ priming to improve germination performance under temperature or drought stress in semi-arid regions. The aim of this research was to evaluate the effects of osmopriming (−0.8 and −1.2 Mpa and control with no prime) on the vigor and germination performance of Cumin (Cuminum syminum L.) seeds at different temperature incubation under drought stress. Germination performance was evaluated by final germination percentage, germination rate and uniformity and radicle and plumule length. The results showed that osmopriming (−0.8 and −1.2 Mpa of PEG6000 solution) accelerate seed germination to the largest extent and improved the germination rate (T50 ) and the uniformity of germination (T10–90 ) under drought stress especially in 15 ◦ C incubation compared to 10 ◦ C and 25 ◦ C. This treatment also improved stress tolerant by improving germination performance at 10, 15 and 25 ◦ C and under water stress of −0.4 and −0.8 Mpa of PEG6000 solution. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Cumin (Cuminum cyminum L.) is a member of Umbelliferae and annual plant which originated in the Iran, Egypt, Turkistan and East Mediterranean which is valued for its aroma, medicinal and therapeutic properties. Iran is one of the most important cumin exporters in the world market and is grown mainly in the province of Khorasan. The seeds contain 3–4% volatile oil and about 15% fixed oil (Sowbhagya et al., 2008). Cumin is mostly cultivated in rain-fed system in North east of Iran which mostly encounters to low soil moisture in seedling growth stage. Rapid seed germination and stand establishment are critical factors for crop production under stress conditions. In many crop species, seed germination and early seedling growth are the most sensitive stages to stresses. Seed priming is known as the seed treatment which improves seed lot performance under environmental conditions (Ashraf and Foolad, 2005). Therefore seed germination performance (rate of germination, seed vigor and uniformity) is very important for successful productions of cumin in this area due to the seeds are occasionally sown in seedbeds having unfavorable moisture because of the lack of rainfall at sowing. Priming allows some of the metabolic processes necessary for germination to occur without germination take place. In priming, seeds are soaked in different solutions with high osmotic potential. This prevents the seeds from absorbing in
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enough water for radicle protrusion, thus suspending the seeds in the lag phase (Tiriki et al., 2009; Taylor et al., 1998). McDonald (1999), in a comprehensive review article summarized the knowledge accumulated to the end of the previous century about seed priming and seed vigor. It is suggested that priming treatments are successfully applied either to poor germinating seed lots or to seeds which are sown under different stress conditions. A common stress, under field conditions, is low temperatures, and many priming treatments were effective in improving germination under cold temperatures (Cheen et al., 2010; De Atrip et al., 2007). Among the effective priming treatments is seed osmoconditioning which is a pre-sowing hydration treatment, developed to improve seedling synchronization and establishment (Tzortzakis, 2009; Yu-jie et al., 2009). The osmotic solutions induce a water stress that prevents the completion of seed germination (radicle emergence) but does not prevent earlier stages of germination. Seed priming has been found a double technology to enhance rapid and uniform emergence, and to achieve high vigor and better yields in cumin (Nematollahi et al., 2009). Although, the previous studies indicate that some benefits are associated with pre-sowing treatments for seed vigor enhancement of some field crops (Farooq et al., 2007, 2006; Basra et al., 2006, 2005; Kaur et al., 2005; Giri and Schilinger, 2003; Chiu et al., 2002), there is a dearth of information about the germination performance of primed seeds of cumin at different temperatures under water stress. Average annual rainfall in Iran is about 251 mm. In dry years, when seed zone water is inadequate, farmers have to delay planting which will reduce grain yield potential compared with early planting (Nematollahi et al., 2009). Osmopriming and
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hydropriming of cumin seeds may improve germination and emergence and may promote vigorous root growth (Yuan-Yuan et al., 2010; Nematollahi et al., 2009). Therefore, the aims of the present study were to determine the suitable per-sowing treatments to enhancement of germination performance of cumin seeds under drought stress at different temperature incubations. Furthermore, the study examined the possibilities to overcome drought stress by seed pretreatments with PEG6000 at different temperature. 2. Materials and methods 2.1. Plant materials Native seed lots of cumin (C. syminum L.) were procured from the medicinal plant research, Firdausi University of Mashhad, Iran which collected the seed in the same year that the study was undertaken. This native seed lot was widely cultivated in North east of Iran as rain-fed system. 2.2. Seed priming treatment For osmotic pretreatment, cumin seeds were placed on a PEG6000 solution at −0.8 and −1.2 Mpa of polyethylene glycol (PEG6000 ) at 15 ◦ C for 48 h under dark conditions. The concentration of the PEG solution was calculated according to Michel (1983). After priming, the seeds were rinsed with distilled water three times and dried for 48 h at 25 ◦ C to the original moisture content (∼12–13%) as the unprimed seeds and immediately used for germination tests. 2.3. Experiments layout 2.3.1. Germination of primed and unprimed seeds under different temperatures A two-way factorial experiment based on a randomized complete design (RCD) with four replications was used to compare different priming conditions under different temperature incubations. Surface sterilized seed lots were osmoprimed at −0.8 and −1.2 Mpa with PEG6000 and unprimed seed (UPS) as a control and set at three constant temperature 10, 15 and 25 ◦ C incubation for 15 days in darkness. For the germination tests, four replicates of 50 seeds of each primed and unprimed seeds were imbibed on two layers of blotter paper in 9-cm-diameter Petri dishes at 10, 15 and 25 ◦ C incubation. Primed and unprimed Seeds were surface sterilized by soaking in 0.4% sodium hypochlorite (v/v) for 60 seconds (s), followed by three 60 s rinses in the sterile distilled, deionized (dd) water, and then dried at room temperature. Final germination percentage (FGP), germination rate, germination uniformity, radicle and plumule length and seed vigor were recorded to evaluate germination performance. Daily germination percentage was recorded and subjected to statistical analysis. Germination rate (T50 ) was defined as days needed to reach 50% of FGP. Germination uniformity (T10–90 ) was defined as days needed for 10% of FGP to 90% of FGP. Germination was defined as protrusion of a visible radicle to 1 mm. Radicle and plumule length were measured at the end of each experiment (15 days). The vigor index (VI) was calculated as the product of seedling dry weight by germination percentage (ISTA, 1996). 2.3.2. Germination of primed and unprimed seeds under water stress Germination test of primed and unprimed seeds were carried out in a temperature controlled incubator at 15 ◦ C in darkness under water stress. Treatments were arranged in a completely randomized design with four replications of 50 seeds. Polyethylene glycol (PEG6000 ) solutions for germination tests were prepared according
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to Michel (1983) to give approximately −0.4 and −0.8 Mpa osmotic potentials. Primed and unprimed seeds were surface sterilized as described above before evaluating germination performance. 2.3.3. Germination of cumin seed in water stressed condition under different temperatures This experiment was carried out in three levels of water stress (−0.4 and −0.8 Mpa osmotic potentials and distilled water as a control) under different temperature incubations (10, 15 and 25 ◦ C). For the germination tests, four replicates of 50 seeds of unprimed seeds were surface sterilized and imbibed on two layers of blotter paper in 9-cm-diameter Petri dishes at 10, 15 and 25 ◦ C incubation under different water stress. The germination performance was evaluated as described above. 2.4. Data analysis Data from all experiments were separately analyzed using the general linear models (GLM) procedure and the least significant difference option of Statistical Analysis System software version 9.1.3 (SAS Institute, Cary, NC). Data for germination percentage were subjected to arcsine transformation before the analysis of variance. Mean comparisons were performed by LSD test if F-test was significant at (p < 0.05) to determine whether differences among means were significant between treatments within each osmopriming, drought stress and temperature. 3. Results 3.1. Germination of primed and unprimed seeds under different temperatures Final germination percentage (FGP) in the primed (PS1 and PS2) and unprimed seeds (UPS) differed at three examined temperatures. When germinated at 25 ◦ C temperature, the FGP of primed seeds with −0.8 Mpa PEG (SP1) was significantly higher compared to SP2 and UPC seeds, but the germination rate and uniformity of primed seeds (SP2) at 15 ◦ C were greater than the SP1 and UPS (p < 0.05). It is observed an improper control of seed priming result in negative effects on germination percentage under 25 ◦ C incubate condition. Seed germinated at 10 ◦ C in primed seeds (PS2) had greater T50 (germination rate) of 4.91 d and T10–90 (uniformity of seeds) of 5.37 d compared to PS1 and UPC seeds. Similarly, the greatest germination rate and uniformity were observed at 15 ◦ C (T50 of 4.20 d and T10–90 of 4.78 d), which were not significantly different from that in PS1 (T50 of 4.53 d and T10–90 of 4.87 d) and UPS (T50 of 4.87 d and T10–90 of 5.66 d) (Table 1). However, no significant differences of T10–90 were observed between 15 and 25 ◦ C. Out of priming treatments, incubate seeds under 15 and 25 ◦ C, accelerated germination rate and T10–90 to the largest extent. Only at 25 ◦ C treatment observed an adverse effect on FGP (Table 1). Radicle and plumule length of cumin seeds were significantly affected by interaction between prime and temperatures. Radicle and plumule length of cumin seeds were significantly longer in PS compared to UPS under 10 and 15 ◦ C. Vigor index was not different (p > 0.05) under any of the three levels of temperature in prime and unprimed cumin seeds (Table 1). None of the applied methods of priming and incubation temperatures improved seed vigor. 3.2. Germination of primed and unprimed seeds under water stress The highest germination percentage was found in distilled water (Control) in prime and unprimed seeds, followed by −0.4 Mpa and −0.8 Mpa. Primed seeds of cumin performed significant higher germination percentage in drought stress compared to UPS (Table 2).
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Table 1 Comparison of final germination percentage (FGP), germination rate (T50 ), germination uniformity (T10–90 ), radicle and plumule length and vigor index of primed and unprimed seeds under different temperature incubations. Temperature (◦ C)
Priming type (PEG solution)
FGP (%)
T50 (days)
T10–90 (days)
Radicle length (mm)
Plumule length (mm)
Vigor index
10
Unprimed (UPS) −0.8 Mpa (SP1) −1.2 Mpa (SP2) Mean
64 b 73 a 63 b 66.7 A
6.16 a 5.91 a 4.91 b 5.7 A
7.53 a 7.33 a 5.37 b 6.7 A
32 b 36 a 40 a 36 A
26 b 33 a 29 b 29.4 A
4.1 a 5.3 a 4.9 a 4.8 A
15
Unprimed (UPS) −0.8 Mpa (SP1) −1.2 Mpa (SP2) Mean
63 a 69 a 59 b 63.9 A
4.87 a 4.53 a 4.20 a 4.5 B
5.66 a 5.16 a 4.78 a 5.2 B
28 b 35 a 34 a 32.3 AB
22 b 27 a 28 a 25.8 AB
3.6 a 4.3 a 4.6 a 4.2 A
25
Unprimed (UPS) −0.8 Mpa (SP1) −1.2 Mpa (SP2) Mean LSDa
52 b 67 a 46 c 54.3 B 7
5.16 a 5.12 a 4.37 b 4.9 A 0.8
6.08 a 6.02 a 4.87 b 5.7 A 1.26
24 b 28 b 31 a 27.6 B 5.1
24 a 24 a 23 a 23.7 B 4.7
3.6 a 3.5 a 4.2 a 3.7 A 0.72
Means within the same columns at the same temperature followed by the same letter are not different at p < 0.05 according to least significant different test. a This parameter is for mean comparison of interaction effect.
The germination rate and uniformity of seeds were not significantly affected by water stress (p < 0.05), while they were significantly affected by interaction between prime and water stress in UPS (T50 of 4.31 d and T10–90 of 4.41 d in primed seeds (PS2) compared to 5.16 d and 6.08 d, respectively, in UPC seeds) (Table 2). Radicle and plumule length of cumin seeds were significantly affected by interaction between prime and drought stress. Radicle and plumule length of cumin seedling were significantly decreased by increasing drought stress in PS and UPS however, primed seed had significantly greater radicle and plumule length. Vigor index was also significantly affected by drought stress, priming and interaction between prime and drought stress (p > 0.05) (Table 2). Drought stress (−0.4 and −0.8 Mpa) showed substantial reduction of vigor index in PS and UPS although, unprimed seed was more susceptible (Table 2). Results also indicated that vigor index were significantly higher in PS1 and PS2, however there was no significant difference between PS1 and UPS. No positive effect of seed priming in high drought stress (−0.8 Mpa) was observed on seed vigor of cumin compared to UPS. 3.3. Germination of cumin seed in water stressed condition under different temperatures Final germination percentage (FGP) in different temperature incubation differed at three examined drought stress. The lowest (30%) was at 25 ◦ C in drought stressed seed (−0.8 Mpa PEG solution). Seed germination was significantly lower under extreme
temperatures of 25 ◦ C compared with 10 and 15 ◦ C incubation. Germination capacity for control seeds was 88, 87 and 89%, respectively at 10, 15 and 25 ◦ C with no significant differences (Table 3). The rate of germination decreased with an increase in drought stress at all temperature regimes and increase with an increased temperature regime. The rate of germination was lowest (5.95 d) at 10 ◦ C followed by 15 ◦ C (5.45 d) in highest drought stress and the highest germination rate was recorded at 15 ◦ C, in all drought stress. Despite of 10 and 15 ◦ C no significant difference observed in low and high drought stress in 25 ◦ C (Table 3). Uniformity of seeds was only affected by water stress in 25 ◦ C (T10–90 of 5.70 d in −0.4 Mpa compared to 4.91 d and 5.08 d in control and −0.8 Mpa drought stress, respectively) (Table 3). The highest T10–90 (6.08 d) was found in 10 ◦ C, followed by 15 and 25 ◦ C (Table 3). Radicle and plumule length of cumin seeds were significantly decreased with increasing drought stress in all temperatures incubation. However, lower temperature had significantly greater radicle and plumule length (Table 3). Vigor index was also significantly affected by drought stress and interaction between temperatures and drought stress (p > 0.05) (Table 3). Higher temperature was related to higher reduction of vigor index (Table 3). 3.4. Seed germination trends Among the treatments, few of them significantly stimulated seed germination (Figs. 1–3). Germination in UPS commenced on
Table 2 Comparison of final germination percentage (FGP), germination rate (T50 ), germination uniformity (T10–90 ), radicle and plumule length and vigor index of primed and unprimed seeds under different water potential at 15 ◦ C in darkness. Priming types
Water potential (Mpa)
FGP (%)
T50 (days)
T10–90 (days)
Radicle length (mm)
Plumule length (mm)
Vigor index
Unprimed (UPS)
Control −0.4 −0.8 Mean
90 a 60 b 31 c 60.3 B
5.16 a 5.25 a 5.91 a 5.43 A
6.62 a 6.54 a 6.08 a 6.41 A
30 a 28 a 20 b 26 B
26 a 21 b 17 c 21.3 B
5.7 a 4.1 b 1.2 c 3.6 A
−0.8 Mpa (PS1)
Control −0.4 −0.8 Mean
86 a 70 b 49 c 68.3 A
5.05 b 4.91 b 5.70 a 5.2 A
5.95 a 6.25 a 6.20 a 6.13 A
37 a 34 a 27 b 32.6 A
36 a 29 b 18 c 27.6 A
4.7 a 4.5 a 1.9 c 4.3 A
−1.2 Mpa (PS2)
Control −0.4 −0.8 Mean LSDa
89 a 68 b 44 c 67 A 7.5
4.31 c 4.41 c 4.83 a 4.51 B 0.38
4.41 b 5.41 a 5.20 a 5.06 B 0.85
44 a 38 b 26 c 36 A 5.5
35 a 29 b 17 c 27 A 5.3
6.9 a 4.7 b 2.8 c 4.8 A 1.3
Means within the same columns at the same temperature followed by the same letter are not different at p < 0.05 according to least significant different test. a This parameter is for mean comparison of interaction effect.
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Table 3 Comparison of final germination percentage (FGP), germination rate (T50 ), germination uniformity (T10–90 ), radicle and plumule length and vigor index of unprimed cumin seeds under different water potential and temperatures. Temperature (◦ C)
Water potential (Mpa)
FGP (%)
T50 (days)
T10–90 (days)
Radicle length (mm)
Plumule length (mm)
Vigor index
10
Control −0.4 −0.8 Mean
88 a 71 b 61 b 73 A
5.05 b 5.45 b 5.95 a 5.48 A
6.57 a 6.95 a 6.72 a 6.08 A
44 a 37 b 26 b 35.6 A
38 a 29 b 21 c 29.3 A
7.4 a 4.9 b 2.1 c 4.8 A
15
0 −0.4 −0.8 Mean
87 a 67 b 56 b 66 AB
4.10 c 4.55 b 5.25 a 4.51 B
4.91 b 5.70 a 5.08 b 5.2 B
39 a 35 a 24 b 32.6 A
35 a 27 b 17 c 26.3 AB
6.4 a 4.5 b 1.6 c 4.1 AB
25
0 −0.4 −0.8 Mean LSDa
89 a 57 b 30 c 58 B 13.5
4.62 c 4.95 a 5.35 a 4.94 B 0.42
5.50 a 5.50 a 5.83 a 5.61 B 0.68
32 a 30 a 22 b 28 B 5.4
32 a 24 b 15 c 23.6 B 4.3
5.5 a 3.8 b 1.2 c 3.5 B 0.81
Means within the same columns at the same temperature followed by the same letter are not different at p < 0.05 according to least significant different test. a This parameter is for mean comparison of interaction effect.
day 4 under 25 ◦ C, and on day 6 in lowest temperature (10 ◦ C) while in primed seeds (PS) germination commenced on days 2, 3 and 4 in 25, 15 and 10 ◦ C, respectively. However, germination of unprimed seeds was significantly commenced later with lesser slopes (Fig. 1). Higher temperature caused rapid germination in UPS and PS. Germination started in primed seeds (PS1 and PS2) on day 2 and 3 under 15 and 25 ◦ C, respectively and on day 5 under 10 ◦ C (Fig. 1). Osmopriming with −0.8 and −1.2 Mpa PEG solution increased seed germination (20 and 30%) at the first four days compared to UPS, thus confirming its role as a stimulatory agent (Fig. 1). Results also indicated that Osmopriming with −0.8 and −1.2 Mpa PEG solution accelerated seed germination of cumin in drought stress as seed germination in UPS commenced on day 4 and 6 under −0.8 and −1.2 Mpa PEG solutions and on day 2 and 3 in PS1 and PS2, respectively (Fig. 2). However drought stress significantly decreased germination percentage and reduced germination trend (Figs. 2 and 3). Over 50% of seeds in the control treatment (unstressed seeds) had already germinated after 1 week in 25 ◦ C incubation while it was significantly reduced in drought stress condition especially in −0.8 Mpa PEG solutions (Fig. 3). This percentage increased to a maximum of 90, 60 and 40% in control, −0.4 Mpa and −0.8 Mpa, respectively during the second week. However, germination frequency was strongly affected by drought stress and temperature such that only 82, 58.4 and 30.7% of the seeds germinated in control, −0.4 Mpa and −0.8 Mpa treatments in 25 ◦ C during the second week incubation in 25 ◦ C, respectively (Fig. 3). The greatest inhibition of germination occurred at the higher temperature (25 ◦ C) in drought stress incubation (Fig. 3). No further germination was observed over the course of the experiment. Results also showed that germination trend significantly diminished in drought stress under higher temperature (Fig. 3). This percentage increased to a maximum of 90% during the second week.
4. Discussion 4.1. Germination of primed and unprimed seeds under different temperatures The main aim of the experiment was to determine the effects of different osmopriming, drought stress condition and temperature treatments on seed germination behavior of cumin. A wide variety of pre-sowing hydration treatments have been used to enhance seed germination response. Seed priming is a regular step before sowing in a few vegetables and flower crops in some countries. The mechanism of seed priming is to initiate the repairing
system for membrane and the metabolic preparation for germination through controlling water absorption rate of seed (Zhang et al., 2011; Cheen et al., 2010). Thus, primed seeds with a prolonged phase II are likely more prepared for germination than unprimed seeds. However, an improper control of seed priming may result in negative effects on germination. For example, 60% of pretreated seeds of Beta vulgaris failed to germinate when primed at −2.0 Mpa and 25 ◦ C for 14 d by PEG 8000 (Capron et al., 2000). We made a similar observation in our study of cumin seeds where seeds primed at −1.2 Mpa had a reduced FGP of 46% when germinated at 25 ◦ C compared to unprimed seeds with a FGP of 52% (Table 1). Capron et al. (2000) suggested that improper control of seed partial hydration may cause degradation of protective proteins (such as LEA), and render the primed seeds desiccation-intolerant. The beneficial effects of seed priming to improve germination and emergence at low temperature have been reported on some crop species, such as spinach (Cheen et al., 2010), cucumber (Shu et al., 2006), and sugar beet (Mostafa et al., 2007). The results of this study on cumin were very consistent with the above reports and indicated that the priming cumin seeds with incorporation −0.8 and −1.2 Mpa resulted in better germination and emergence at 15 ◦ C compared with the non-priming (Tables 1 and 2). It is noticeable from Fig. 1 that significant differences existed in germination percentage among incubation temperatures. Seeds of cumin germinated better in the intermediate incubation temperatures (15 ◦ C). Primed and unprimed seeds of cumin incubated under high temperatures seemed to be subjected to more environmental stress, which is indicated by delayed germination (Table 1 and Fig. 1). Under such conditions, changes in the incubation temperature particularly in unprimed seeds may result in malfunctioning of enzymatic systems (Cheen et al., 2010). The substantial reduction of seedling growth also observed in the present study at 25 ◦ C which is also reported by Tzortzakis (2009) in Cichorium intybus and De Atrip et al. (2007) in Alnus glutinosa. We also found that seed germinated at 15 ◦ C in primed seeds (especially in −1.2 Mpa) had greater T50 (germination rate), T10–90 (uniformity of seeds), radicle and plumule length compared to unprimed seeds. Although based on the combined results of FGP, T50 and T10–90 , 15 ◦ C appeared to be the optimal temperature for germination of cumin seed which the FGP at 25 ◦ C was significantly less (p < 0.05) than that at 10 and 15 ◦ C (54.3% vs 63.9% and 66.7%). Thus, 15 ◦ C was adjudged to be the optimal temperature for all germination tests in this study (Table 1). Researches explain that priming is a practical technique to increase germination rate and consistence, as well as vigor increase and a better performance in vegetables, flower plant and crops (Rouhi et al., 2011; Farooq et al., 2008; Chiu et al., 2002; Bruggink et al., 1999).
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Fig. 1. Cumulative seed germination of pre-sowing treated and control of cumin seeds germinated in vitro in different temperatures. Values represent mean (±SE) of measurements made on twelve independent Petri dishes per treatment.
4.2. Seed priming increases temperature-stress tolerance Osmopriming improved cumin seed germination performance at 15 ◦ C as indicated by higher FGP and lower T50 and T10–90 (Table 1), indicating an improved chilling tolerance. Reports from other crops, such as Spinacia oleracea (Cheen et al., 2010) and
Fig. 2. Cumulative seed germination of pre-sowing treated and control of cumin seeds germinated in vitro under different water stress at 15 ◦ C incubation. Values represent mean (±SE) of measurements made on twelve independent Petri dishes per treatment.
Momordica charantia (Lin and Sung, 2001), also suggested that priming improved seed germination at suboptimal temperatures. Our data indicated that osmopriming also resulted in a significant improvement of FGP, T50 and T10–90 at 25 ◦ C and lowering radicle and plumule length compared to that of unprimed seeds
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specifically this native cultivar. This study also provides a practical priming procedure to improve cumin germination performance in drought stress which is priming seeds at −0.8 Mpa at 15 ◦ C for 2 d (Table 2 and Fig. 2). A similar priming protocol was used by Pill et al. (1994) to test seed germination performance of Echinacea purpurea and Cheen et al. (2010) on S. oleracea. In their study, metrically and osmotically priming seeds for 10 d at −0.4 Mpa and 15 ◦ C resulted in highest germination percentage, rate, and uniformity among the total eight protocols examined. Water uptake is expected to be greatly reduced when seeds are primed at a low osmotic potential, relatively cooler temperature and for a short priming duration. Therefore, we suggest that primed seeds exhibiting an unimproved germination may not have experienced partial hydration period that was sufficiently long to allow germinationpromoting metabolism during the phase II. 4.3. Seed priming increases tolerance to water stress Orthodox seeds acquire desiccation tolerance in the late embryogenesis stage, and gradually lose this ability upon water inhibition. Our results indicate that priming cumin seeds with −0.8 Mpa PEG at 15 ◦ C for 2 d enhanced desiccation tolerance in germinating seeds: at −1.2 Mpa seed pretreatment, seeds exhibited improved germination rate and uniformity while improved FGP, radicle length, plumule length and seed vigor were not different between seed pretreatment between −0.8 and −1.2 Mpa treatment (Table 2 and Fig. 2). A similar finding was reported for Helianthus annuus seeds where hydropriming at 25 ◦ C for 48 h improved germination rate under osmotic stresses imposed by PEG and sodium chloride (Kaya et al., 2006). 5. Conclusions
Fig. 3. Cumulative seed germination of cumin seeds germinated in vitro in different temperatures under water stress. Values represent mean (±SE) of measurements made on twelve independent Petri dishes per treatment.
and at the other temperature (Table 1). However, the germination performance of primed seeds at 25 ◦ C was inferior to those germinated at 15 ◦ C (optimum temperature): the average FGP of seeds germinated at 15 ◦ C was 63.9% compared to 54.3.7% at 25 ◦ C (Table 1). This reduction in germination performance might be related to “thermo-inhibition” (Ashraf and Foolad, 2005; Leskovar and Esensse, 1999). These authors further suggested that ‘thermoinhibition’ might also be mediated by the pericarp acting as a physical barrier to oxygen uptake. Improved germination of primed cumin seeds at 15 ◦ C temperature may be associated with leaching of germination inhibitors during osmopriming in PEG6000 solution. Nematollahi et al. (2009) reported a significant increase in FGP of cumin seeds (to more than 80% at 25 ◦ C) that were both scarified and osmoprimed. We found a significantly improved germination at 15 ◦ C and 25 ◦ C by only priming cumin seeds at −0.8 Mpa for 2 d (Table 1). The present study is the first to provide an optimal seed pre-treatment to improve germination of cumin seeds,
During the osmopriming experiment upon this plant, seed pretreatment with −0.8 Mpa was the best pretreatment to accelerate germination performance under different temperature incubation and drought stress compared with UPS. It seems that the temperature of 15 ◦ C is near the optimum temperature of germination for this plant. Regarding the positive effects of seed priming on germination characteristic of cumin, it could be used as pre-sowing treatment in field conditions. In order to have the best performance of cumin germination in low temperature and drought stress condition, seed pretreatment of −0.8 and −1.2 Mpa recommended, respectively. Considering the positive effect of osmopriming to improve germination performance (Higher FGP, seed vigor and Radicle and plumule length and greater T50 and T10–90 ) of cumin at low temperature (15 ◦ C) in drought stress condition (Table 3), Proper priming treatment can stimulate seed germination, improve seedling quality, and enhance drought tolerance of seedlings. Finally it is recommended that the results of this study to be investigated in the farm condition in order to confirm the fulfilled experiments of this project. References Ashraf, M., Foolad, M.R., 2005. Pre-sowing seed treatment a shotgun approach to improve germination, plant growth, and crop yield under saline and non-saline conditions. Adv. Agron. 88, 223–271. Basra, A.S., Farooq, M., Afzal, I., Hussain, M., 2006. Influence of osmopriming on the germination and early seedling growth of coarse and fine rice. Int. J. Agric. Biol. 8, 19–21. Basra, S.M.A., Farooq, M., Tabassum, R., 2005. Physiological and biochemical aspects of seed vigor enhancement treatments in fine rice (Oryza sativa L.). Seed Sci. Technol. 33, 623–628. Bruggink, G.T., Ooms, J.J., Van der Toorn, P., 1999. Induction of longevity in primed seeds. Seed Sci. Res. 9, 49–53. Capron, I., Corbineau, F., Dacher, F., Job, C., Côme, D., Job, D., 2000. Sugar beet seed priming: effects of priming conditions on germination, solubilization of 11-S globulin and accumulation of LEA proteins. Seed Sci. Res. 10, 243–254.
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Cheen, K., Arora, R., Arora, R., 2010. Osmopriming of spinach (Spinacia oleracea L. cv. Bloomsdale) seeds and germination performance under temperature and water stress. Seed Sci. Technol. 38, 45–57. Chiu, K.Y., Chen, C.L., Sung, J.M., 2002. Effect of priming temperature on storability of primed sh-2 sweet corn seed. Crop Sci. 42, 1996–2003. De Atrip, N., O’Reilly, C., Bannon, F., 2007. Target seed moisture content, chilling and priming pretreatments influence germination temperature response in Alnus glutinosa and Betula pubescens. Scan. J. For. Res. 22, 273–279. Farooq, M., Basra, M.A., Wahid, A., Cheema, Z.A., Cheema, M.A., Khaliq, A., 2008. Physiological role of exogenously applied glycinebetaine to improve drought tolerance in fine grain aromatic rice (Oryza sativa L.). J. Agron. Crop Sci. 194, 325–333. Farooq, M., Basra, S.M.A., Khan, M.B., 2007. Seed priming improves growth of nursery seedling and yield of transplanted rice. Arch. Agron. Soil Sci. 53, 311–322. Farooq, M., Basra, S.M.A., Hafeez-u-Rehman, A., 2006. Seed priming enhances emergence, yield and quality of direct-seeded rice. Crop Manage. Physiol. 3, 42–44. Giri, G.S., Schilinger, W.F., 2003. Seed priming winter wheat for germination, emergence and yield. Crop Sci. 43, 2135–2141. ISTA, 1996. Rules for Seed Testing. International Seed Testing Association. Seed Science and Technology Zurich, Switzerland. Kaur, S., Gupta, A.K., Kaur, N., 2005. Seed priming increases crop yield possibly by modulating enzymes of sucrose metabolism in chickpea. J. Agron. Crop Sci. 191, 81–87. Kaya, M.D., Okcu, G., Atak, M., Cikili, Y., Kolsarici, O., 2006. Seed treatments to overcome salt and drought stress during germination in sunflower (Helianthus annuus L.). Eur. J. Agron. 24, 291–295. Leskovar, D.I., Esensse, V., 1999. Pericarp, leachate, and carbohydrate involvement in thermo-inhibition of germinating spinach seeds. J. Am. Soc. Hortic. Sci. 124, 301–306. Lin, J.M., Sung, J.M., 2001. Pre-sowing treatments for improving emergence of bitter gourd seedlings under optimal and sub-optimal temperatures. Seed Sci. Technol. 29, 39–50. McDonald, M.B., 1999. Seed deterioration: physiology, repair and assessment. Seed Sci. Technol. 27, 177–237. Michel, B.E., 1983. Evaluation of the water potentials of solutions of polyethylene glycol 8000 both in the absence and presence of other solutes. Plant Physiol. 72, 66–70.
Mostafa, G., Mohammad, J.A., Ghazaleh, S., 2007. Incorporation of plant growth regulators into the priming solution improves sugar beet germination, emergence and seedling growth at low-temperature. Pakistan J. Biol. Sci. 10 (19), 3390–3394. Nematollahi, E., Bannayan, M., Souhani Darban, A., Ghanbari, A., 2009. Hydropriming and osmopriming effects on cumin (Cuminum Cyminum L.) seeds germination. World Acad. Sci. Eng. Technol. 57, 526–529. Pill, W.G., Crossan, C.K., Frett, J.J., Smith, W.G., 1994. Matric and osmotic priming of Echinacea purpurea (L.) Moench seeds. Sci. Hortic. (Amest.) 59, 37–44. Rouhi, H.R., Abbasi Surki, A., Sharif-Zadeh, F., Tavakkol Afshari, R., Aboutalebian, M.A., Ahmadv, G., 2011. Study of different priming treatments on germination traits of soybean seed lots. Not. Sci. Biol. 3 (1), 101–108. SAS Institute, 2004. SAS/STAT User’s Guide [Computer Software and Manual]. SAS Institute, Cary, NC. Shu, Y.J., Zhou, Y.L., Zhang, Z.X., Sui, Y.H., 2006. Effect of salicylic acid on chilling resistance of germinating cucumber seeds. Chin. Agric. Sci. Bull. 22 (10), 285–287. Sowbhagya, H.B., Sathyendra Rao, B.V., Krishnamurthy, N., 2008. Evaluation of size reduction and expansion on yield and quality of cumin (Cuminum cyminum) seed oil. J. Food Eng. 84, 595–600. Taylor, A.G., Allen, P.S., Bennett, M.A., Bradford, K.J., Burrisand, J.S., Misra, M.K., 1998. Seed enhancements. Seed Sci. Res. 8, 245–256. Tiriki, I., Kizilsmsek, M., Kaplan, M., 2009. Rapid and enhanced germination at low temperature of alfalfa and white clover seeds following osmotic priming. Trop. Grasslands 43, 171–177. Tzortzakis, N.G., 2009. Effect of pre-sowing treatment on seed germnation and seedling vigour in endive & chicory. Hortic. Sci. (Prague) 36 (3), 117–125. Yuan-Yuan, S., Yong-Jian, S., Ming-Tian, W., Xu-Yi, L., Xiang, G., Rong, H., Jun, M., 2010. Effects of seed priming on germination and seedling growth under water stress in rice. Acta Agron. Sin. 36 (11), 1931–1940. Yu-jie, L., Dorna, H., Su-juan, G., Ming-pu, Z., 2009. Effects of osmopriming and hydropriming on vigour and germination of China aster (Callistephus hinensis (L.) Nees.) seeds. For. Stud. China 11 (2), 111–117. Zhang, Y., Liu, H., Shen, S., Zhang, X., 2011. Improvement of eggplant seed germination and seedling emergence at low temperature by seed priming with incorporation SA into KNO3 solution. Front. Agric. China 5 (4), 534–537.
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Seed priming improves the germination performance of cumin (Cuminum syminum L.) under temperature and water stress A. Rahimi ∗ Department of Agronomy and Plant Breeding, Agriculture College, Vali-e-Asr University of Rafsanjan, Rafsanjan, Iran
a r t i c l e
i n f o
Article history: Received 31 March 2012 Received in revised form 7 June 2012 Accepted 17 June 2012 Keywords: Drought stress Germination rate Germination uniformity Temperature
a b s t r a c t Farmers typically practice ‘on-farm’ priming to improve germination performance under temperature or drought stress in semi-arid regions. The aim of this research was to evaluate the effects of osmopriming (−0.8 and −1.2 Mpa and control with no prime) on the vigor and germination performance of Cumin (Cuminum syminum L.) seeds at different temperature incubation under drought stress. Germination performance was evaluated by final germination percentage, germination rate and uniformity and radicle and plumule length. The results showed that osmopriming (−0.8 and −1.2 Mpa of PEG6000 solution) accelerate seed germination to the largest extent and improved the germination rate (T50 ) and the uniformity of germination (T10–90 ) under drought stress especially in 15 ◦ C incubation compared to 10 ◦ C and 25 ◦ C. This treatment also improved stress tolerant by improving germination performance at 10, 15 and 25 ◦ C and under water stress of −0.4 and −0.8 Mpa of PEG6000 solution. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Cumin (Cuminum cyminum L.) is a member of Umbelliferae and annual plant which originated in the Iran, Egypt, Turkistan and East Mediterranean which is valued for its aroma, medicinal and therapeutic properties. Iran is one of the most important cumin exporters in the world market and is grown mainly in the province of Khorasan. The seeds contain 3–4% volatile oil and about 15% fixed oil (Sowbhagya et al., 2008). Cumin is mostly cultivated in rain-fed system in North east of Iran which mostly encounters to low soil moisture in seedling growth stage. Rapid seed germination and stand establishment are critical factors for crop production under stress conditions. In many crop species, seed germination and early seedling growth are the most sensitive stages to stresses. Seed priming is known as the seed treatment which improves seed lot performance under environmental conditions (Ashraf and Foolad, 2005). Therefore seed germination performance (rate of germination, seed vigor and uniformity) is very important for successful productions of cumin in this area due to the seeds are occasionally sown in seedbeds having unfavorable moisture because of the lack of rainfall at sowing. Priming allows some of the metabolic processes necessary for germination to occur without germination take place. In priming, seeds are soaked in different solutions with high osmotic potential. This prevents the seeds from absorbing in
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enough water for radicle protrusion, thus suspending the seeds in the lag phase (Tiriki et al., 2009; Taylor et al., 1998). McDonald (1999), in a comprehensive review article summarized the knowledge accumulated to the end of the previous century about seed priming and seed vigor. It is suggested that priming treatments are successfully applied either to poor germinating seed lots or to seeds which are sown under different stress conditions. A common stress, under field conditions, is low temperatures, and many priming treatments were effective in improving germination under cold temperatures (Cheen et al., 2010; De Atrip et al., 2007). Among the effective priming treatments is seed osmoconditioning which is a pre-sowing hydration treatment, developed to improve seedling synchronization and establishment (Tzortzakis, 2009; Yu-jie et al., 2009). The osmotic solutions induce a water stress that prevents the completion of seed germination (radicle emergence) but does not prevent earlier stages of germination. Seed priming has been found a double technology to enhance rapid and uniform emergence, and to achieve high vigor and better yields in cumin (Nematollahi et al., 2009). Although, the previous studies indicate that some benefits are associated with pre-sowing treatments for seed vigor enhancement of some field crops (Farooq et al., 2007, 2006; Basra et al., 2006, 2005; Kaur et al., 2005; Giri and Schilinger, 2003; Chiu et al., 2002), there is a dearth of information about the germination performance of primed seeds of cumin at different temperatures under water stress. Average annual rainfall in Iran is about 251 mm. In dry years, when seed zone water is inadequate, farmers have to delay planting which will reduce grain yield potential compared with early planting (Nematollahi et al., 2009). Osmopriming and
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hydropriming of cumin seeds may improve germination and emergence and may promote vigorous root growth (Yuan-Yuan et al., 2010; Nematollahi et al., 2009). Therefore, the aims of the present study were to determine the suitable per-sowing treatments to enhancement of germination performance of cumin seeds under drought stress at different temperature incubations. Furthermore, the study examined the possibilities to overcome drought stress by seed pretreatments with PEG6000 at different temperature. 2. Materials and methods 2.1. Plant materials Native seed lots of cumin (C. syminum L.) were procured from the medicinal plant research, Firdausi University of Mashhad, Iran which collected the seed in the same year that the study was undertaken. This native seed lot was widely cultivated in North east of Iran as rain-fed system. 2.2. Seed priming treatment For osmotic pretreatment, cumin seeds were placed on a PEG6000 solution at −0.8 and −1.2 Mpa of polyethylene glycol (PEG6000 ) at 15 ◦ C for 48 h under dark conditions. The concentration of the PEG solution was calculated according to Michel (1983). After priming, the seeds were rinsed with distilled water three times and dried for 48 h at 25 ◦ C to the original moisture content (∼12–13%) as the unprimed seeds and immediately used for germination tests. 2.3. Experiments layout 2.3.1. Germination of primed and unprimed seeds under different temperatures A two-way factorial experiment based on a randomized complete design (RCD) with four replications was used to compare different priming conditions under different temperature incubations. Surface sterilized seed lots were osmoprimed at −0.8 and −1.2 Mpa with PEG6000 and unprimed seed (UPS) as a control and set at three constant temperature 10, 15 and 25 ◦ C incubation for 15 days in darkness. For the germination tests, four replicates of 50 seeds of each primed and unprimed seeds were imbibed on two layers of blotter paper in 9-cm-diameter Petri dishes at 10, 15 and 25 ◦ C incubation. Primed and unprimed Seeds were surface sterilized by soaking in 0.4% sodium hypochlorite (v/v) for 60 seconds (s), followed by three 60 s rinses in the sterile distilled, deionized (dd) water, and then dried at room temperature. Final germination percentage (FGP), germination rate, germination uniformity, radicle and plumule length and seed vigor were recorded to evaluate germination performance. Daily germination percentage was recorded and subjected to statistical analysis. Germination rate (T50 ) was defined as days needed to reach 50% of FGP. Germination uniformity (T10–90 ) was defined as days needed for 10% of FGP to 90% of FGP. Germination was defined as protrusion of a visible radicle to 1 mm. Radicle and plumule length were measured at the end of each experiment (15 days). The vigor index (VI) was calculated as the product of seedling dry weight by germination percentage (ISTA, 1996). 2.3.2. Germination of primed and unprimed seeds under water stress Germination test of primed and unprimed seeds were carried out in a temperature controlled incubator at 15 ◦ C in darkness under water stress. Treatments were arranged in a completely randomized design with four replications of 50 seeds. Polyethylene glycol (PEG6000 ) solutions for germination tests were prepared according
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to Michel (1983) to give approximately −0.4 and −0.8 Mpa osmotic potentials. Primed and unprimed seeds were surface sterilized as described above before evaluating germination performance. 2.3.3. Germination of cumin seed in water stressed condition under different temperatures This experiment was carried out in three levels of water stress (−0.4 and −0.8 Mpa osmotic potentials and distilled water as a control) under different temperature incubations (10, 15 and 25 ◦ C). For the germination tests, four replicates of 50 seeds of unprimed seeds were surface sterilized and imbibed on two layers of blotter paper in 9-cm-diameter Petri dishes at 10, 15 and 25 ◦ C incubation under different water stress. The germination performance was evaluated as described above. 2.4. Data analysis Data from all experiments were separately analyzed using the general linear models (GLM) procedure and the least significant difference option of Statistical Analysis System software version 9.1.3 (SAS Institute, Cary, NC). Data for germination percentage were subjected to arcsine transformation before the analysis of variance. Mean comparisons were performed by LSD test if F-test was significant at (p < 0.05) to determine whether differences among means were significant between treatments within each osmopriming, drought stress and temperature. 3. Results 3.1. Germination of primed and unprimed seeds under different temperatures Final germination percentage (FGP) in the primed (PS1 and PS2) and unprimed seeds (UPS) differed at three examined temperatures. When germinated at 25 ◦ C temperature, the FGP of primed seeds with −0.8 Mpa PEG (SP1) was significantly higher compared to SP2 and UPC seeds, but the germination rate and uniformity of primed seeds (SP2) at 15 ◦ C were greater than the SP1 and UPS (p < 0.05). It is observed an improper control of seed priming result in negative effects on germination percentage under 25 ◦ C incubate condition. Seed germinated at 10 ◦ C in primed seeds (PS2) had greater T50 (germination rate) of 4.91 d and T10–90 (uniformity of seeds) of 5.37 d compared to PS1 and UPC seeds. Similarly, the greatest germination rate and uniformity were observed at 15 ◦ C (T50 of 4.20 d and T10–90 of 4.78 d), which were not significantly different from that in PS1 (T50 of 4.53 d and T10–90 of 4.87 d) and UPS (T50 of 4.87 d and T10–90 of 5.66 d) (Table 1). However, no significant differences of T10–90 were observed between 15 and 25 ◦ C. Out of priming treatments, incubate seeds under 15 and 25 ◦ C, accelerated germination rate and T10–90 to the largest extent. Only at 25 ◦ C treatment observed an adverse effect on FGP (Table 1). Radicle and plumule length of cumin seeds were significantly affected by interaction between prime and temperatures. Radicle and plumule length of cumin seeds were significantly longer in PS compared to UPS under 10 and 15 ◦ C. Vigor index was not different (p > 0.05) under any of the three levels of temperature in prime and unprimed cumin seeds (Table 1). None of the applied methods of priming and incubation temperatures improved seed vigor. 3.2. Germination of primed and unprimed seeds under water stress The highest germination percentage was found in distilled water (Control) in prime and unprimed seeds, followed by −0.4 Mpa and −0.8 Mpa. Primed seeds of cumin performed significant higher germination percentage in drought stress compared to UPS (Table 2).
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Table 1 Comparison of final germination percentage (FGP), germination rate (T50 ), germination uniformity (T10–90 ), radicle and plumule length and vigor index of primed and unprimed seeds under different temperature incubations. Temperature (◦ C)
Priming type (PEG solution)
FGP (%)
T50 (days)
T10–90 (days)
Radicle length (mm)
Plumule length (mm)
Vigor index
10
Unprimed (UPS) −0.8 Mpa (SP1) −1.2 Mpa (SP2) Mean
64 b 73 a 63 b 66.7 A
6.16 a 5.91 a 4.91 b 5.7 A
7.53 a 7.33 a 5.37 b 6.7 A
32 b 36 a 40 a 36 A
26 b 33 a 29 b 29.4 A
4.1 a 5.3 a 4.9 a 4.8 A
15
Unprimed (UPS) −0.8 Mpa (SP1) −1.2 Mpa (SP2) Mean
63 a 69 a 59 b 63.9 A
4.87 a 4.53 a 4.20 a 4.5 B
5.66 a 5.16 a 4.78 a 5.2 B
28 b 35 a 34 a 32.3 AB
22 b 27 a 28 a 25.8 AB
3.6 a 4.3 a 4.6 a 4.2 A
25
Unprimed (UPS) −0.8 Mpa (SP1) −1.2 Mpa (SP2) Mean LSDa
52 b 67 a 46 c 54.3 B 7
5.16 a 5.12 a 4.37 b 4.9 A 0.8
6.08 a 6.02 a 4.87 b 5.7 A 1.26
24 b 28 b 31 a 27.6 B 5.1
24 a 24 a 23 a 23.7 B 4.7
3.6 a 3.5 a 4.2 a 3.7 A 0.72
Means within the same columns at the same temperature followed by the same letter are not different at p < 0.05 according to least significant different test. a This parameter is for mean comparison of interaction effect.
The germination rate and uniformity of seeds were not significantly affected by water stress (p < 0.05), while they were significantly affected by interaction between prime and water stress in UPS (T50 of 4.31 d and T10–90 of 4.41 d in primed seeds (PS2) compared to 5.16 d and 6.08 d, respectively, in UPC seeds) (Table 2). Radicle and plumule length of cumin seeds were significantly affected by interaction between prime and drought stress. Radicle and plumule length of cumin seedling were significantly decreased by increasing drought stress in PS and UPS however, primed seed had significantly greater radicle and plumule length. Vigor index was also significantly affected by drought stress, priming and interaction between prime and drought stress (p > 0.05) (Table 2). Drought stress (−0.4 and −0.8 Mpa) showed substantial reduction of vigor index in PS and UPS although, unprimed seed was more susceptible (Table 2). Results also indicated that vigor index were significantly higher in PS1 and PS2, however there was no significant difference between PS1 and UPS. No positive effect of seed priming in high drought stress (−0.8 Mpa) was observed on seed vigor of cumin compared to UPS. 3.3. Germination of cumin seed in water stressed condition under different temperatures Final germination percentage (FGP) in different temperature incubation differed at three examined drought stress. The lowest (30%) was at 25 ◦ C in drought stressed seed (−0.8 Mpa PEG solution). Seed germination was significantly lower under extreme
temperatures of 25 ◦ C compared with 10 and 15 ◦ C incubation. Germination capacity for control seeds was 88, 87 and 89%, respectively at 10, 15 and 25 ◦ C with no significant differences (Table 3). The rate of germination decreased with an increase in drought stress at all temperature regimes and increase with an increased temperature regime. The rate of germination was lowest (5.95 d) at 10 ◦ C followed by 15 ◦ C (5.45 d) in highest drought stress and the highest germination rate was recorded at 15 ◦ C, in all drought stress. Despite of 10 and 15 ◦ C no significant difference observed in low and high drought stress in 25 ◦ C (Table 3). Uniformity of seeds was only affected by water stress in 25 ◦ C (T10–90 of 5.70 d in −0.4 Mpa compared to 4.91 d and 5.08 d in control and −0.8 Mpa drought stress, respectively) (Table 3). The highest T10–90 (6.08 d) was found in 10 ◦ C, followed by 15 and 25 ◦ C (Table 3). Radicle and plumule length of cumin seeds were significantly decreased with increasing drought stress in all temperatures incubation. However, lower temperature had significantly greater radicle and plumule length (Table 3). Vigor index was also significantly affected by drought stress and interaction between temperatures and drought stress (p > 0.05) (Table 3). Higher temperature was related to higher reduction of vigor index (Table 3). 3.4. Seed germination trends Among the treatments, few of them significantly stimulated seed germination (Figs. 1–3). Germination in UPS commenced on
Table 2 Comparison of final germination percentage (FGP), germination rate (T50 ), germination uniformity (T10–90 ), radicle and plumule length and vigor index of primed and unprimed seeds under different water potential at 15 ◦ C in darkness. Priming types
Water potential (Mpa)
FGP (%)
T50 (days)
T10–90 (days)
Radicle length (mm)
Plumule length (mm)
Vigor index
Unprimed (UPS)
Control −0.4 −0.8 Mean
90 a 60 b 31 c 60.3 B
5.16 a 5.25 a 5.91 a 5.43 A
6.62 a 6.54 a 6.08 a 6.41 A
30 a 28 a 20 b 26 B
26 a 21 b 17 c 21.3 B
5.7 a 4.1 b 1.2 c 3.6 A
−0.8 Mpa (PS1)
Control −0.4 −0.8 Mean
86 a 70 b 49 c 68.3 A
5.05 b 4.91 b 5.70 a 5.2 A
5.95 a 6.25 a 6.20 a 6.13 A
37 a 34 a 27 b 32.6 A
36 a 29 b 18 c 27.6 A
4.7 a 4.5 a 1.9 c 4.3 A
−1.2 Mpa (PS2)
Control −0.4 −0.8 Mean LSDa
89 a 68 b 44 c 67 A 7.5
4.31 c 4.41 c 4.83 a 4.51 B 0.38
4.41 b 5.41 a 5.20 a 5.06 B 0.85
44 a 38 b 26 c 36 A 5.5
35 a 29 b 17 c 27 A 5.3
6.9 a 4.7 b 2.8 c 4.8 A 1.3
Means within the same columns at the same temperature followed by the same letter are not different at p < 0.05 according to least significant different test. a This parameter is for mean comparison of interaction effect.
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Table 3 Comparison of final germination percentage (FGP), germination rate (T50 ), germination uniformity (T10–90 ), radicle and plumule length and vigor index of unprimed cumin seeds under different water potential and temperatures. Temperature (◦ C)
Water potential (Mpa)
FGP (%)
T50 (days)
T10–90 (days)
Radicle length (mm)
Plumule length (mm)
Vigor index
10
Control −0.4 −0.8 Mean
88 a 71 b 61 b 73 A
5.05 b 5.45 b 5.95 a 5.48 A
6.57 a 6.95 a 6.72 a 6.08 A
44 a 37 b 26 b 35.6 A
38 a 29 b 21 c 29.3 A
7.4 a 4.9 b 2.1 c 4.8 A
15
0 −0.4 −0.8 Mean
87 a 67 b 56 b 66 AB
4.10 c 4.55 b 5.25 a 4.51 B
4.91 b 5.70 a 5.08 b 5.2 B
39 a 35 a 24 b 32.6 A
35 a 27 b 17 c 26.3 AB
6.4 a 4.5 b 1.6 c 4.1 AB
25
0 −0.4 −0.8 Mean LSDa
89 a 57 b 30 c 58 B 13.5
4.62 c 4.95 a 5.35 a 4.94 B 0.42
5.50 a 5.50 a 5.83 a 5.61 B 0.68
32 a 30 a 22 b 28 B 5.4
32 a 24 b 15 c 23.6 B 4.3
5.5 a 3.8 b 1.2 c 3.5 B 0.81
Means within the same columns at the same temperature followed by the same letter are not different at p < 0.05 according to least significant different test. a This parameter is for mean comparison of interaction effect.
day 4 under 25 ◦ C, and on day 6 in lowest temperature (10 ◦ C) while in primed seeds (PS) germination commenced on days 2, 3 and 4 in 25, 15 and 10 ◦ C, respectively. However, germination of unprimed seeds was significantly commenced later with lesser slopes (Fig. 1). Higher temperature caused rapid germination in UPS and PS. Germination started in primed seeds (PS1 and PS2) on day 2 and 3 under 15 and 25 ◦ C, respectively and on day 5 under 10 ◦ C (Fig. 1). Osmopriming with −0.8 and −1.2 Mpa PEG solution increased seed germination (20 and 30%) at the first four days compared to UPS, thus confirming its role as a stimulatory agent (Fig. 1). Results also indicated that Osmopriming with −0.8 and −1.2 Mpa PEG solution accelerated seed germination of cumin in drought stress as seed germination in UPS commenced on day 4 and 6 under −0.8 and −1.2 Mpa PEG solutions and on day 2 and 3 in PS1 and PS2, respectively (Fig. 2). However drought stress significantly decreased germination percentage and reduced germination trend (Figs. 2 and 3). Over 50% of seeds in the control treatment (unstressed seeds) had already germinated after 1 week in 25 ◦ C incubation while it was significantly reduced in drought stress condition especially in −0.8 Mpa PEG solutions (Fig. 3). This percentage increased to a maximum of 90, 60 and 40% in control, −0.4 Mpa and −0.8 Mpa, respectively during the second week. However, germination frequency was strongly affected by drought stress and temperature such that only 82, 58.4 and 30.7% of the seeds germinated in control, −0.4 Mpa and −0.8 Mpa treatments in 25 ◦ C during the second week incubation in 25 ◦ C, respectively (Fig. 3). The greatest inhibition of germination occurred at the higher temperature (25 ◦ C) in drought stress incubation (Fig. 3). No further germination was observed over the course of the experiment. Results also showed that germination trend significantly diminished in drought stress under higher temperature (Fig. 3). This percentage increased to a maximum of 90% during the second week.
4. Discussion 4.1. Germination of primed and unprimed seeds under different temperatures The main aim of the experiment was to determine the effects of different osmopriming, drought stress condition and temperature treatments on seed germination behavior of cumin. A wide variety of pre-sowing hydration treatments have been used to enhance seed germination response. Seed priming is a regular step before sowing in a few vegetables and flower crops in some countries. The mechanism of seed priming is to initiate the repairing
system for membrane and the metabolic preparation for germination through controlling water absorption rate of seed (Zhang et al., 2011; Cheen et al., 2010). Thus, primed seeds with a prolonged phase II are likely more prepared for germination than unprimed seeds. However, an improper control of seed priming may result in negative effects on germination. For example, 60% of pretreated seeds of Beta vulgaris failed to germinate when primed at −2.0 Mpa and 25 ◦ C for 14 d by PEG 8000 (Capron et al., 2000). We made a similar observation in our study of cumin seeds where seeds primed at −1.2 Mpa had a reduced FGP of 46% when germinated at 25 ◦ C compared to unprimed seeds with a FGP of 52% (Table 1). Capron et al. (2000) suggested that improper control of seed partial hydration may cause degradation of protective proteins (such as LEA), and render the primed seeds desiccation-intolerant. The beneficial effects of seed priming to improve germination and emergence at low temperature have been reported on some crop species, such as spinach (Cheen et al., 2010), cucumber (Shu et al., 2006), and sugar beet (Mostafa et al., 2007). The results of this study on cumin were very consistent with the above reports and indicated that the priming cumin seeds with incorporation −0.8 and −1.2 Mpa resulted in better germination and emergence at 15 ◦ C compared with the non-priming (Tables 1 and 2). It is noticeable from Fig. 1 that significant differences existed in germination percentage among incubation temperatures. Seeds of cumin germinated better in the intermediate incubation temperatures (15 ◦ C). Primed and unprimed seeds of cumin incubated under high temperatures seemed to be subjected to more environmental stress, which is indicated by delayed germination (Table 1 and Fig. 1). Under such conditions, changes in the incubation temperature particularly in unprimed seeds may result in malfunctioning of enzymatic systems (Cheen et al., 2010). The substantial reduction of seedling growth also observed in the present study at 25 ◦ C which is also reported by Tzortzakis (2009) in Cichorium intybus and De Atrip et al. (2007) in Alnus glutinosa. We also found that seed germinated at 15 ◦ C in primed seeds (especially in −1.2 Mpa) had greater T50 (germination rate), T10–90 (uniformity of seeds), radicle and plumule length compared to unprimed seeds. Although based on the combined results of FGP, T50 and T10–90 , 15 ◦ C appeared to be the optimal temperature for germination of cumin seed which the FGP at 25 ◦ C was significantly less (p < 0.05) than that at 10 and 15 ◦ C (54.3% vs 63.9% and 66.7%). Thus, 15 ◦ C was adjudged to be the optimal temperature for all germination tests in this study (Table 1). Researches explain that priming is a practical technique to increase germination rate and consistence, as well as vigor increase and a better performance in vegetables, flower plant and crops (Rouhi et al., 2011; Farooq et al., 2008; Chiu et al., 2002; Bruggink et al., 1999).
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Fig. 1. Cumulative seed germination of pre-sowing treated and control of cumin seeds germinated in vitro in different temperatures. Values represent mean (±SE) of measurements made on twelve independent Petri dishes per treatment.
4.2. Seed priming increases temperature-stress tolerance Osmopriming improved cumin seed germination performance at 15 ◦ C as indicated by higher FGP and lower T50 and T10–90 (Table 1), indicating an improved chilling tolerance. Reports from other crops, such as Spinacia oleracea (Cheen et al., 2010) and
Fig. 2. Cumulative seed germination of pre-sowing treated and control of cumin seeds germinated in vitro under different water stress at 15 ◦ C incubation. Values represent mean (±SE) of measurements made on twelve independent Petri dishes per treatment.
Momordica charantia (Lin and Sung, 2001), also suggested that priming improved seed germination at suboptimal temperatures. Our data indicated that osmopriming also resulted in a significant improvement of FGP, T50 and T10–90 at 25 ◦ C and lowering radicle and plumule length compared to that of unprimed seeds
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specifically this native cultivar. This study also provides a practical priming procedure to improve cumin germination performance in drought stress which is priming seeds at −0.8 Mpa at 15 ◦ C for 2 d (Table 2 and Fig. 2). A similar priming protocol was used by Pill et al. (1994) to test seed germination performance of Echinacea purpurea and Cheen et al. (2010) on S. oleracea. In their study, metrically and osmotically priming seeds for 10 d at −0.4 Mpa and 15 ◦ C resulted in highest germination percentage, rate, and uniformity among the total eight protocols examined. Water uptake is expected to be greatly reduced when seeds are primed at a low osmotic potential, relatively cooler temperature and for a short priming duration. Therefore, we suggest that primed seeds exhibiting an unimproved germination may not have experienced partial hydration period that was sufficiently long to allow germinationpromoting metabolism during the phase II. 4.3. Seed priming increases tolerance to water stress Orthodox seeds acquire desiccation tolerance in the late embryogenesis stage, and gradually lose this ability upon water inhibition. Our results indicate that priming cumin seeds with −0.8 Mpa PEG at 15 ◦ C for 2 d enhanced desiccation tolerance in germinating seeds: at −1.2 Mpa seed pretreatment, seeds exhibited improved germination rate and uniformity while improved FGP, radicle length, plumule length and seed vigor were not different between seed pretreatment between −0.8 and −1.2 Mpa treatment (Table 2 and Fig. 2). A similar finding was reported for Helianthus annuus seeds where hydropriming at 25 ◦ C for 48 h improved germination rate under osmotic stresses imposed by PEG and sodium chloride (Kaya et al., 2006). 5. Conclusions
Fig. 3. Cumulative seed germination of cumin seeds germinated in vitro in different temperatures under water stress. Values represent mean (±SE) of measurements made on twelve independent Petri dishes per treatment.
and at the other temperature (Table 1). However, the germination performance of primed seeds at 25 ◦ C was inferior to those germinated at 15 ◦ C (optimum temperature): the average FGP of seeds germinated at 15 ◦ C was 63.9% compared to 54.3.7% at 25 ◦ C (Table 1). This reduction in germination performance might be related to “thermo-inhibition” (Ashraf and Foolad, 2005; Leskovar and Esensse, 1999). These authors further suggested that ‘thermoinhibition’ might also be mediated by the pericarp acting as a physical barrier to oxygen uptake. Improved germination of primed cumin seeds at 15 ◦ C temperature may be associated with leaching of germination inhibitors during osmopriming in PEG6000 solution. Nematollahi et al. (2009) reported a significant increase in FGP of cumin seeds (to more than 80% at 25 ◦ C) that were both scarified and osmoprimed. We found a significantly improved germination at 15 ◦ C and 25 ◦ C by only priming cumin seeds at −0.8 Mpa for 2 d (Table 1). The present study is the first to provide an optimal seed pre-treatment to improve germination of cumin seeds,
During the osmopriming experiment upon this plant, seed pretreatment with −0.8 Mpa was the best pretreatment to accelerate germination performance under different temperature incubation and drought stress compared with UPS. It seems that the temperature of 15 ◦ C is near the optimum temperature of germination for this plant. Regarding the positive effects of seed priming on germination characteristic of cumin, it could be used as pre-sowing treatment in field conditions. In order to have the best performance of cumin germination in low temperature and drought stress condition, seed pretreatment of −0.8 and −1.2 Mpa recommended, respectively. Considering the positive effect of osmopriming to improve germination performance (Higher FGP, seed vigor and Radicle and plumule length and greater T50 and T10–90 ) of cumin at low temperature (15 ◦ C) in drought stress condition (Table 3), Proper priming treatment can stimulate seed germination, improve seedling quality, and enhance drought tolerance of seedlings. Finally it is recommended that the results of this study to be investigated in the farm condition in order to confirm the fulfilled experiments of this project. References Ashraf, M., Foolad, M.R., 2005. Pre-sowing seed treatment a shotgun approach to improve germination, plant growth, and crop yield under saline and non-saline conditions. Adv. Agron. 88, 223–271. Basra, A.S., Farooq, M., Afzal, I., Hussain, M., 2006. Influence of osmopriming on the germination and early seedling growth of coarse and fine rice. Int. J. Agric. Biol. 8, 19–21. Basra, S.M.A., Farooq, M., Tabassum, R., 2005. Physiological and biochemical aspects of seed vigor enhancement treatments in fine rice (Oryza sativa L.). Seed Sci. Technol. 33, 623–628. Bruggink, G.T., Ooms, J.J., Van der Toorn, P., 1999. Induction of longevity in primed seeds. Seed Sci. Res. 9, 49–53. Capron, I., Corbineau, F., Dacher, F., Job, C., Côme, D., Job, D., 2000. Sugar beet seed priming: effects of priming conditions on germination, solubilization of 11-S globulin and accumulation of LEA proteins. Seed Sci. Res. 10, 243–254.
460
A. Rahimi / Industrial Crops and Products 42 (2013) 454–460
Cheen, K., Arora, R., Arora, R., 2010. Osmopriming of spinach (Spinacia oleracea L. cv. Bloomsdale) seeds and germination performance under temperature and water stress. Seed Sci. Technol. 38, 45–57. Chiu, K.Y., Chen, C.L., Sung, J.M., 2002. Effect of priming temperature on storability of primed sh-2 sweet corn seed. Crop Sci. 42, 1996–2003. De Atrip, N., O’Reilly, C., Bannon, F., 2007. Target seed moisture content, chilling and priming pretreatments influence germination temperature response in Alnus glutinosa and Betula pubescens. Scan. J. For. Res. 22, 273–279. Farooq, M., Basra, M.A., Wahid, A., Cheema, Z.A., Cheema, M.A., Khaliq, A., 2008. Physiological role of exogenously applied glycinebetaine to improve drought tolerance in fine grain aromatic rice (Oryza sativa L.). J. Agron. Crop Sci. 194, 325–333. Farooq, M., Basra, S.M.A., Khan, M.B., 2007. Seed priming improves growth of nursery seedling and yield of transplanted rice. Arch. Agron. Soil Sci. 53, 311–322. Farooq, M., Basra, S.M.A., Hafeez-u-Rehman, A., 2006. Seed priming enhances emergence, yield and quality of direct-seeded rice. Crop Manage. Physiol. 3, 42–44. Giri, G.S., Schilinger, W.F., 2003. Seed priming winter wheat for germination, emergence and yield. Crop Sci. 43, 2135–2141. ISTA, 1996. Rules for Seed Testing. International Seed Testing Association. Seed Science and Technology Zurich, Switzerland. Kaur, S., Gupta, A.K., Kaur, N., 2005. Seed priming increases crop yield possibly by modulating enzymes of sucrose metabolism in chickpea. J. Agron. Crop Sci. 191, 81–87. Kaya, M.D., Okcu, G., Atak, M., Cikili, Y., Kolsarici, O., 2006. Seed treatments to overcome salt and drought stress during germination in sunflower (Helianthus annuus L.). Eur. J. Agron. 24, 291–295. Leskovar, D.I., Esensse, V., 1999. Pericarp, leachate, and carbohydrate involvement in thermo-inhibition of germinating spinach seeds. J. Am. Soc. Hortic. Sci. 124, 301–306. Lin, J.M., Sung, J.M., 2001. Pre-sowing treatments for improving emergence of bitter gourd seedlings under optimal and sub-optimal temperatures. Seed Sci. Technol. 29, 39–50. McDonald, M.B., 1999. Seed deterioration: physiology, repair and assessment. Seed Sci. Technol. 27, 177–237. Michel, B.E., 1983. Evaluation of the water potentials of solutions of polyethylene glycol 8000 both in the absence and presence of other solutes. Plant Physiol. 72, 66–70.
Mostafa, G., Mohammad, J.A., Ghazaleh, S., 2007. Incorporation of plant growth regulators into the priming solution improves sugar beet germination, emergence and seedling growth at low-temperature. Pakistan J. Biol. Sci. 10 (19), 3390–3394. Nematollahi, E., Bannayan, M., Souhani Darban, A., Ghanbari, A., 2009. Hydropriming and osmopriming effects on cumin (Cuminum Cyminum L.) seeds germination. World Acad. Sci. Eng. Technol. 57, 526–529. Pill, W.G., Crossan, C.K., Frett, J.J., Smith, W.G., 1994. Matric and osmotic priming of Echinacea purpurea (L.) Moench seeds. Sci. Hortic. (Amest.) 59, 37–44. Rouhi, H.R., Abbasi Surki, A., Sharif-Zadeh, F., Tavakkol Afshari, R., Aboutalebian, M.A., Ahmadv, G., 2011. Study of different priming treatments on germination traits of soybean seed lots. Not. Sci. Biol. 3 (1), 101–108. SAS Institute, 2004. SAS/STAT User’s Guide [Computer Software and Manual]. SAS Institute, Cary, NC. Shu, Y.J., Zhou, Y.L., Zhang, Z.X., Sui, Y.H., 2006. Effect of salicylic acid on chilling resistance of germinating cucumber seeds. Chin. Agric. Sci. Bull. 22 (10), 285–287. Sowbhagya, H.B., Sathyendra Rao, B.V., Krishnamurthy, N., 2008. Evaluation of size reduction and expansion on yield and quality of cumin (Cuminum cyminum) seed oil. J. Food Eng. 84, 595–600. Taylor, A.G., Allen, P.S., Bennett, M.A., Bradford, K.J., Burrisand, J.S., Misra, M.K., 1998. Seed enhancements. Seed Sci. Res. 8, 245–256. Tiriki, I., Kizilsmsek, M., Kaplan, M., 2009. Rapid and enhanced germination at low temperature of alfalfa and white clover seeds following osmotic priming. Trop. Grasslands 43, 171–177. Tzortzakis, N.G., 2009. Effect of pre-sowing treatment on seed germnation and seedling vigour in endive & chicory. Hortic. Sci. (Prague) 36 (3), 117–125. Yuan-Yuan, S., Yong-Jian, S., Ming-Tian, W., Xu-Yi, L., Xiang, G., Rong, H., Jun, M., 2010. Effects of seed priming on germination and seedling growth under water stress in rice. Acta Agron. Sin. 36 (11), 1931–1940. Yu-jie, L., Dorna, H., Su-juan, G., Ming-pu, Z., 2009. Effects of osmopriming and hydropriming on vigour and germination of China aster (Callistephus hinensis (L.) Nees.) seeds. For. Stud. China 11 (2), 111–117. Zhang, Y., Liu, H., Shen, S., Zhang, X., 2011. Improvement of eggplant seed germination and seedling emergence at low temperature by seed priming with incorporation SA into KNO3 solution. Front. Agric. China 5 (4), 534–537.