Seed priming has proved to be an effective pre-germination seed invigoration technique for different crops to improve seed and seedling performance under different abiotic stresses. In Bangladesh, winter rice is very often exposed to cold waves just after sowing in the nursery bed resulting in poor seed germination and seedling emergence, yellowish and thin seedlings production, and a very low survival rate. Seed priming may mitigate the cold stress during seed germination and seedling emergence and helps in the quality seedling production of winter rice. To evaluate the efficacy of different seed priming techniques in increasing seedling emergence, growth, vigor and survivability of winter rice cultivars under cold stress, a pot experiment was conducted at the Department of Agronomy, Bangladesh Agricultural University during December 2018 to January 2019. The experiment comprised two factors, (A) Winter rice variety namely, i) BRRI dhan29 and ii) BRRI dhan36; (B) Seed priming agent namely i) Control (no priming), ii) 20000 ppm NaCl, iii) 30000 ppm NaCl, iv) 20000 ppm KCl, v) 30000 ppm KCl, vi) 20000 ppm CaCl2, vii) 30000 ppm CaCl2, viii) 50 ppm CuSO4, ix) 75 ppm CuSO4, x) 10000 ppm ZnSO4, xi) 15000 ppm ZnSO4, xii) 2 ppm Na2MoO4, xiii) 3 ppm Na2MoO4, xiv) 100 ppm PEG (Polyethylene glycol 4000) and xv) 150 ppm PEG. Seeds were sown on two different dates viz., 1st December and 1st January so that seedlings are exposed to cold stress at different stages. The experiment was laid out in a completely randomized design (CRD) with three replications. Results indicated that (in most of the cases) seed priming has a positive impact on seedling emergence rate (%), root length, shoot length, root shoot ratio, root dry weight, shoot dry weight, seedling dry weight and survival rate (%). Among the priming agents, KCl and CaCl2 performed best; while priming with NaCl and PEG showed no advantages over no priming for both the sowing dates. In general, BRRI dhan36 performed better than BRRI dhan29 in terms of seedling growth because of its higher tolerance to cold stress. But, both the varieties performed similarly in terms of emergence rate and survival rate. Thus, priming is an effective tool to increase seed germination, better seedling growth, and higher seedling survivability of winter rice under cold stress, and KCl (20000 ppm) or CaCl2 (20000 ppm) can be considered as a viable priming agent.
Seed invigorationseedling emergenceseedling mortalityseedling growthlow temperature stressIntroduction
Rice is grown in tropical and sub-tropical areas of the world, and is often threatened by low temperature stress. Rice plant is sensitive to chilling stress especially at the seedling and reproductive stages. Low temperature at an early stage may result in reduced germination, poor seedling establishment, stunted seedlings, yellowing or withering, and reduced tillering [1]. Unforeseeable cold stress (<10°C) at the reproductive stage delays heading and causes pollen sterility resulting in grain yield reduction [2]. This stress arrests the expression of full genetic potential of a rice variety through direct inhibition of metabolic reactions and, indirectly through cold-induced osmotic, oxidative and other stresses [3]. Under the sub-tropical condition of Bangladesh, winter rice is greatly affected by low temperature stress during crop establishment and reproductive stages [1]. Due to extreme low temperatures in December and January, the seedling mortality in nursery beds, as well as main field, often goes up to 90%, especially in the northern part of the country [4]. Therefore, farmers often cover the nursery beds with plastic sheet on cold nights to protect the young seedlings from low temperature and cold injury. Because of low temperature, seedling growth is often slow and farmers usually transplant relatively old seedlings (>45 days) to protect from cold injury [1]. Recently, more than 2.0 million hectares of rice crop in northern and north-eastern parts of Bangladesh have been affected by acute cold spell causing partial to total crop damage [4]. In the haor (wet-land ecosystem) areas of Bangladesh, farmers need to early transplanting of rice to protect the crop from the flash floods during the maturity stage and early-planted winter rice has often face low temperature at the reproductive stages (panicle initiation to flowering) [5]. As stated by Smillie et al. [6], photosynthesis is damaged by low temperature which limits growth and yield as there is less carbohydrate available for seed production.
Seed priming has proved to be an effective seed invigoration technique that might be resulted in increase seed performance by increasing the rate, percentage, and uniformity of seed germination and seedling emergence under stress conditions (e.g., salinity, temperature and drought stress). Usually, seed priming is used to curtail the duration between seed sowing and seedling emergence and to synchronize emergence [7,8]. Priming allows some of the metabolic processes essential for germination to occur. In this process seeds are soaked in different solutions with high osmotic potential that inhibits the seeds from absorbing sufficient moisture for radicle protrusion, thus suspending the seeds in the lag phase [9]. Beneficial effects of seed priming include enhanced, rapid and uniform emergence of seedlings [10–14], which leads to crops growing faster, flowering earlier and yielding higher [15,16]. Besides, seed priming enhances the uptake of nutrients and controls seed-borne pathogens [8]. A number of researches on vegetables, floriculture and some field crops demonstrated that seed priming has effectively improved germination and early seedling growth especially at suboptimal conditions [13,17]. Generally, various seed priming techniques, which include hydropriming, osmopriming, chemical priming, hormonal priming, biological priming, redox priming, and solid-matrix priming, are used to induce pre-germination changes [13,18,19]. Hydro priming increased the yield as a result of better germination and vigorous growth in mung bean [20], lentils [21] and in rice [22] under flooding stress, whereas, improved germination was also observed in polyethylene glycol-6000 (PEG-6000) primed rapeseeds [14].
Although, seed priming has been extensively studied as a tool for boosting up seed germination and seedling growth of different crop species including rice, but this issue has not been properly addressed so far especially with winter rice in sub-tropical conditions. Therefore, research is needed on this particular issue to increase the yield of rice in a sustainable way. The present study was therefore undertaken to evaluate the efficacy of different seed priming agents in increasing seed emergence, seedling growth, vigor and survivability of winter rice under cold stress and to assess the rice varietal responses to different seed priming agents under cold stress.
Materials and MethodsExperimental Site and Soil
The pot experiment was conducted at the Net House and Agro Innovation Laboratory, Department of Agronomy, Bangladesh Agricultural University during December 2018 to January 2019. The experimental site was situated at 23°77’ N latitude and 90°33’ E longitude at an altitude of 18.6 meter above sea level. The experimental soil was slightly acidic in nature (pH 6.8) with silty loam texture and low organic matter content (1.59%). The general fertility level of the soil was moderate (0.13% N, 13.9 ppm available phosphorus, 16.3 ppm available potassium and 0.28 ppm exchangeable potassium). The climate of the experimental site is characterized by scanty rainfall associated with moderately low temperatures during the experimental period. Average relative humidity in December 2018 and January 2019 were recorded 80.2 and 75.3%, respectively. Monthly total rainfall and cumulative sunshine hours during December and January were recorded as 17.7 and 2.13 mm and 201.7 and 228.4 hrs, respectively. The weekly mean temperature during the experimental period has been presented in Fig. 1.
Weekly average maximum, minimum and mean temperature in December 2018 and January 2019
Experimental Treatments and Design
The experiment comprised two factors. Factor A includes two high yielding winter rice varieties, namely i) BRRI dhan29 and ii) BRRI dhan36; factor B includes 15 seed priming agents such as i) Control (no priming), ii) 20000 ppm NaCl, iii) 30000 ppm NaCl, iv) 20000 ppm KCl, v) 30000 ppm KCl, vi) 20000 ppm CaCl2, vii) 30000 ppm CaCl2, viii) 50 ppm CuSO4, ix) 75 ppm CuSO4, x) 10000 ppm ZnSO4, xi) 15000 ppm ZnSO4, xii) 2 ppm Na2MoO4, xiii) 3 ppm Na2MoO4, xiv) 100 ppm PEG (Polyethylene glycol) and xv) 150 ppm PEG. The experiment was laid out in a completely randomized design (CRD) with three replications. Altogether there were 90 pots in the experiment. Plastic pot of size of 25 cm height and 22 cm diameter was used as the experimental unit.
Description of the Rice Varieties
BRRI dhan29: This variety was developed by the Bangladesh Rice Research Institute (BRRI) in 1980 from crossing between BG 90-2 and BR15-46-5 lines. It is a long duration and late harvest rice variety. It is characterized with weakly photoperiod sensitivity suitable for late transplanting among modern varieties in Bangladesh. It is a non-lodging type of rice variety and it takes about 160–165 days to complete its life cycle after transplanting with the average yield range of 7–8 t ha−1 [23].
BRRI dhan36: BRRI dhan36 was also developed by BRRI from the line IR 54791-19-2-3 (IRRI) and was released in 1998. Generally, the plant height is about 90 cm, clean rice, long slender. Planting time is mid to late November. Harvesting time is early to mid-April. General yield is 5–6 t ha−1. It is moderately resistant to tungro, tolerant to cold at the seedling stage [23].
Priming Agents Used
All the priming agents used in the experiment were of laboratory grade. Details of the priming agents are presented in Tab. 1
Description of the priming agents
Sl. No.
Priming agent
Chemical formula
Manufacturer
1.
Sodium chloride
NaCl
MERCK, India
2.
Potassium chloride
KCl
MERCK, India
3.
Calcium chloride
CaCl2
MERCK, India
4.
Copper sulphate
CuSO4.5H2O
MERCK, India
5.
Zinc sulphate
ZnSO4.7H2O
MERCK, India
6.
Sodium molybdate
Na2MoO4. 2H2O
MERCK, India
7.
Polyethylene glycol 4000
PEG 4000
LOBAL Chemie, India
Conduction of the ExperimentSeed Priming
Seeds of both the rice varieties were soaked in different priming agents solution (previously prepared using distilled water) as per treatments for 24 h at room temperature, (25 ± 2°C). The ratio of seed weight to solution volume was 1:5 (g mL−1). Then, seeds were removed from the priming agent solution followed by washing several times with distilled water to remove the traces of chemicals. Then, seeds were dried back to the original moisture content by forced air. Dried seeds were put in polythene bags and stored in a refrigerator at 5 ± 1°C until used. While control treatment received no prior seed priming.
Seed Sprouting
Both the primed (stored in refrigerator) and non-primed seeds were soaked in water for 24 h and then taken out of water and kept thickly in cloth bags. The seeds started sprouting after 48 h and were sown in the pot after 72 h.
Pot Preparation, Seed Sowing and Management
Each pot was filled up to 3/4th with 4.6 kg soil. Cowdung @ 100 g pot−1 was added and thoroughly mixed with the soil. Water was added and puddled manually to make a favorable condition for sowing seed. No chemical fertilizer was added to the pot soil. Sprouted seeds were sown in the pot @ 300 seeds pot−1. Seeds were sown on two different dates viz., 1 December and 1 January so that seedlings are exposed to cold stress at different stages. The seeds were protected from the birds after sowing. Weeds were manually uprooted when observed. Watering was done by a watering can as and when necessary to ensure the normal growth of the seedlings. Every pot was regularly monitored to record any insect pest or disease infestation. But no occurrence of insects or diseases was recorded.
Observations
Data were collected on emergence rate (%), survival rate (%), root and shoot length, root and shoot dry weight and seedling dry weight. For recording data on seedling growth, 20 seedlings were randomly uprooted from each pot at 10, 20 and 30 days after sowing (DAS). The emergence percentage was calculated at 15 DAS using the following formula [22]:Emergence (%)=No.ofgerminatedseedlingsNo.ofseedssown×100
Root length was measured from the base of the plant up to the end of the longest root and expressed in mm. Shoot length was measured from the base of the plant up to the tip of the longest leaf and expressed in mm. For root and shoot dry weight, 20 randomly selected seedlings were measured after separately drying the root and shoot in an oven at 60°C for 72 h. Finally root and shoot dry weight of each seedling was calculated and expressed in mg. The dry weight of the seedling was calculated as the sum of root and shoot dry weight and expressed in mg. The survival percentage is the ratio of the number of survived seedlings (at 30 DAS) to the number of seedlings that emerged (at 15 DAS) and expressed as a percent. It was calculated by the following formula:Survival (%)=No.ofsurvivedseedlingsNo.ofemergedseedlings×100
Statistical Analysis
The recorded data were undergone to homogeneity and normality checked prior to analysis of variance (ANOVA). The results of the homogeneity and normality test revealed that the data were normally distributed. ANOVA was done to test for statistical significance among treatments with the help of the computer package MSTAT-C. The mean differences among the treatments were adjudged using Duncan’s Multiple Range Test (DMRT) at a 5% level of significance.
ResultsSeedling Emergence
Variety had no significant effect on the emergence percentage of winter rice at both the sowing dates (Tab. 2). But numerically, BRRI dhan36 showed a higher emergence percentage compared to BRRI dhan29. Tab. 2 also shows that for both the varieties, the emergence percentage was higher in December sowing compared to January sowing. The priming agent exerted a significant effect on the emergence percentage of winter rice at both sowing dates (Tab. 3). In general, at both the sowing dates seed priming showed a positive effect on the emergence percentage. Priming with NaCl at any concentration reduced the emergence percentage. On the other hand, priming with 3 ppm Na2MoO4 resulted in a similar emergence percentage as shown in control. While all other priming agents increased the emergence percentage of winter rice compared to control (no priming). Irrespective of priming agents, December sowing showed a higher emergence percentage than January sowing.
Effect of variety on seedling emergence (%) and survival (%) of winter rice at different sowing dates
Variety
Emergence (%)
Survival (%)
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
BRRI dhan29
93.56
92.62
95.38
92.76
BRRI dhan36
94.24
93.78
95.51
93.31
p < 0.05
NS
NS
NS
NS
CV (%)
2.77
3.03
2.31
2.61
Note: NS = Not significant.
Effect of seed priming agent on emergence (%) and survival (%) of winter rice at different sowing dates
Priming agent
Emergence (%)
Survival (%)
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
Control (no priming)
92.17bc
90.33cde
93.17d
89.67e
20000 ppm NaCl
90.67cd
89.67de
93.17d
89.67e
30000 ppm NaCl
88.50d
89.50e
93.83cd
89.17e
20000 ppm KCl
93.83abc
93.17a−e
96.33abc
94.67abc
30000 ppm KCl
94.67ab
93.33a−d
96.33abc
95.33ab
20000 ppm CaCl2
95.67ab
94.67ab
96.67abc
96.00a
30000 ppm CaCl2
94.50ab
94.83ab
96.00a-d
95.83a
50 ppm CuSO4
95.67ab
95.33a
97.83a
95.67a
75 ppm CuSO4
95.83a
94.83ab
97.50ab
95.83a
10000 ppm ZnSO4
96.50a
95.50a
94.83a-d
93.83a-d
15000 ppm ZnSO4
96.17a
96.33a
95.00a-d
93.67a-d
2 ppm Na2MoO4
93.33abc
92.83a-e
94.50bcd
90.67de
3 ppm Na2MoO4
92.17bc
91.17b-e
95.33a-d
91.17de
100 ppm PEG
94.00abc
93.00a-e
95.50a-d
92.00cde
150 ppm PEG
94.83ab
93.50abc
95.67a-d
92.33b-e
p < 0.05
*
*
*
*
CV (%)
2.77
3.03
2.31
2.61
Note: * = Significant at 5% level of probability.
Seedling Survival Percentage
Variety showed no significant effect on the survival percentage of winter rice seedlings at both the sowing dates (Tab. 2). Numerically, BRRI dhan36 showed a higher survival percentage compared to BRRI dhan29. Like the emergence percentage, the survival percentage also was higher in December sowing than January sowing. A significant effect of priming agent was found for the survival percentage of winter rice seedlings at both the sowing dates (Tab. 3). A clear advantage of seed priming in terms of seedling survival percentage over no priming was evident only for priming with KCl, CaCl2, and CuSO4 at December sowing and KCl, CaCl2, CuSO4 and ZnSO4 at January sowing. It may be noted that December sowing showed a higher survival percentage than January sowing.
Seedling Root Length
Varietal effect on seedling root length was found significant in December sowing but non-significant in January sowing at all the 3 observations (Tab. 4). In December sowing, seedling root length of BRRI dhan36 was respectively 5, 6 and 10 mm higher than those of BRRI dhan29 at 10, 20 and 30 days after sowing (Tab. 4).
Effect of variety on root length and shoot length of winter rice seedlings at different sowing dates
Root length (mm)
Variety
10 DAS
20 DAS
30 DAS
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
BRRI dhan29
39.00b
34.18
89.27b
97.89
114.44b
136.11
BRRI dhan36
44.67a
34.71
95.76a
96.79
124.49a
134.33
p < 0.05
**
NS
**
NS
**
NS
CV (%)
12.72
12.28
7.44
6.69
5.95
5.79
Shoot length (mm)
BRRI dhan29
91.64b
77.82b
155.80b
136.56a
233.64
243.38
BRRI dhan36
103.44a
81.82a
169.84a
132.12b
235.82
245.62
p < 0.05
*
*
*
*
NS
NS
CV (%)
7.26
7.84
4.99
5.47
6.82
4.14
Notes: * = Significant at 5% level of probability, NS = Not significant, DAS = Days after sowing.
The priming agent exerted a significant effect on the root length of winter rice seedlings at all the observations for both the sowing dates except at 10 DAS for January sowing (Tab. 5). Seed priming with KCl or CaCl2 at either concentration resulted in the longest root at all the growth stages for both the sowing dates. In general, seed priming with NaCl or PEG produced no advantages in terms of root length, over no priming treatment. On the other hand, seed priming with CuSO4 or ZnSO4 produced a higher root length compared to no priming (Tab. 5).
Effect of seed priming agent on root length of winter rice seedlings at different sowing dates
Root length (mm)
Priming agent
10 DAS
20 DAS
30 DAS
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
Control (no priming)
39.00def
30.62
85.00cde
85.90g
115.2cde
126.3fg
20000 ppm NaCl
35.17ef
31.43
83.83de
86.07g
111.7de
123.5g
30000 ppm NaCl
34.00f
31.48
81.33e
87.75fg
108.5e
124.8fg
20000 ppm KCl
47.17ab
36.53
99.67a
107.8abc
128.2a
147.8a
30000 ppm KCl
44.67a-d
37.25
97.50ab
105.8a-d
125.0ab
147.7a
20000 ppm CaCl2
47.00abc
36.98
100.3a
108.9a
125.7ab
145.0ab
30000 ppm CaCl2
47.33a
36.75
99.67a
108.5ab
122.8abc
142.3abc
50 ppm CuSO4
43.50a-d
35.70
96.00ab
100.5b-e
123.3abc
140.8a-d
75 ppm CuSO4
44.00a-d
35.32
95.00ab
98.95de
119.3a-d
138.3a-d
10000 ppm ZnSO4
43.17a-d
35.15
93.67abc
99.73cde
121.0a-d
137.9a-e
15000 ppm ZnSO4
41.50a-e
35.23
92.00a-d
99.42de
117.5b-e
135.0b-f
2 ppm Na2MoO4
39.83c-f
34.83
93.50abc
95.38ef
119.2a-d
133.3c-g
3 ppm Na2MoO4
40.00b-f
34.75
92.50a-d
93.48efg
121.0a-d
131.6d-g
100 ppm PEG
41.17a-e
32.38
89.33b-e
91.88efg
118.8a-d
128.0efg
150 ppm PEG
40.00b-f
32.25
88.33b-e
89.93fg
114.8cde
126.0fg
p < 0.05
*
NS
*
*
*
*
CV (%)
12.72
12.28
7.44
6.69
5.95
5.79
Notes: * = Significant at 5% level of probability, NS = Not significant, DAS = Days after sowing.
Seedling Shoot Length
A significant effect of variety on seedling shoot length of winter rice was observed only at early stages (10 and 20 DAS), but not at later growth stage i.e., 30 DAS (Tab. 4). In case of December sowing, BRRI dhan36 performed better than BRRI dhan29 at 10 and 20 DAS. But for January sowing, BRRI dhan36 produced a longer shoot than BRRI dhan29 at 10 DAS; while at 20 DAS, BRRI dhan29 produced a longer shoot than BRRI dhan36 (Tab. 4). Seedling shoot length of winter rice was significantly affected by different seed priming agents at both the sowing dates (Tab. 6). In general, seed priming with KCl or CaCl2 performed the best in terms of seedling shoot length at all the growth stages for both the sowing dates. Seed priming with CuSO4 or ZnSO4, on the other hand, produced the longest shoot only at 20 and 30 DAS compared to control. No advantages of seed priming with NaCl, Na2MoO4 and PEG were evident as all those priming agents performed similarly to control in terms of seedling shoot length of winter rice (Tab. 6).
Effect of seed priming agent on shoot length of winter rice seedlings at different sowing dates
Shoot length (mm)
Priming agent
10 DAS
20 DAS
30 DAS
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
Control (no priming)
87.50f
71.87e
152.8def
126.3d
224.5cde
230.6fg
20000 ppm NaCl
88.50f
72.03e
147.2f
125.2d
216.7de
224.6g
30000 ppm NaCl
88.00f
71.80e
147.8ef
125.1d
210.3e
221.9g
20000 ppm KCl
109.0a
89.85a
174.0a
144.3a
247.5ab
259.4a
30000 ppm KCl
107.5ab
88.13ab
170.7ab
143.4ab
243.2abc
256.1ab
20000 ppm CaCl2
107.5ab
87.85ab
178.3a
144.2a
254.5a
260.1a
30000 ppm CaCl2
106.2abc
86.63ab
177.2a
143.3ab
250.7ab
257.4ab
50 ppm CuSO4
103.5a-d
84.08abc
161.3bcd
140.9ab
240.7abc
253.4abc
75 ppm CuSO4
99.33b-e
81.63bcd
162.8bcd
139.0abc
240.5abc
251.6a-d
10000 ppm ZnSO4
95.50def
78.02cde
163.8bc
136.3abc
240.7abc
248.4a-e
15000 ppm ZnSO4
96.50def
78.37cde
163.5bcd
134.3bcd
238.7abc
245.4b-e
2 ppm Na2MoO4
98.00cde
80.20b-e
163.5bcd
131.1cd
231.8bcd
239.0def
3 ppm Na2MoO4
94.00ef
77.67cde
163.0bcd
130.9cd
232.2bcd
237.6ef
100 ppm PEG
91.83ef
74.72de
158.8cd
125.5d
224.5cde
240.9c-f
150 ppm PEG
90.33ef
74.40de
157.5cde
125.3d
224.7cde
240.8c-f
p < 0.05
*
*
*
*
*
*
CV (%)
7.26
7.84
4.99
5.47
6.82
4.14
Notes: * = Significant at 5% level of probability, DAS = Days after sowing.
Seedling Root Dry Weight
Variety significantly affected seedling root dry weight of winter rice at 20 and 30 DAS for December sowing and 10, 20 and 30 DAS for January sowing (Tab. 7). For both the sowing dates, higher seedling root dry weight was recorded with BRRI dhan36 at all the growth stages compared to BRRI dhan29. Seed priming agent significantly affected seedling root dry weight of winter rice at all the observations for January sowing; while for December sowing, a significant effect was found at 10 and 20 DAS only (Tab. 8). Seed priming with KCl, CaCl2, CuSO4 and ZnSO4 produced the highest and statistically similar seedling root dry weight at all the observations. While, no advantage of NaCl, Na2MoO4 and PEG priming were evident since they produced statistically similar seedling root dry weight as observed in case of no priming (Tab. 8).
Effect of variety on root dry weight, shoot dry weight and seedlings dry weight of winter rice at different sowing dates
Root dry weight (g)
Variety
10 DAS
20 DAS
30 DAS
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
BRRI dhan29
9.18
10.71b
13.30b
16.85b
16.65b
21.51b
BRRI dhan36
9.33
12.96a
15.48a
17.81a
19.02a
24.62a
p < 0.05
NS
*
*
*
*
*
CV (%)
14.49
11.94
11.77
8.90
10.10
14.24
Shoot dry weight (g)
BRRI dhan29
10.42
14.16
15.51b
21.15b
20.86b
24.89b
BRRI dhan36
10.87
14.06
18.12a
22.99a
22.40a
26.70a
p < 0.05
NS
NS
*
*
*
*
CV (%)
12.55
16.93
10.60
12.26
8.59
10.14
Seedling dry weight (g)
BRRI dhan29
19.60
23.71b
28.81b
38.00b
37.51b
46.40b
BRRI dhan36
20.20
25.92a
33.60a
40.80a
41.42a
51.32a
p < 0.05
NS
*
*
*
*
*
CV (%)
10.34
15.13
7.45
6.86
5.52
8.32
Notes: * = Significant at 5% level of probability, NS = Not significant, DAS = Days after sowing.
Effect of seed priming agent on root dry weight of winter rice seedlings at different sowing dates
Root dry weight (g)
Priming agent
10 DAS
20 DAS
30 DAS
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
Control (no priming)
7.717de
9.667d
13.08cde
15.15f
16.87
20.13d
20000 ppm NaCl
7.450e
9.667d
12.55de
15.37f
16.85
19.68d
30000 ppm NaCl
7.300e
9.700d
12.32e
15.22f
16.37
19.85d
20000 ppm KCl
11.03a
13.43a
16.02a
19.32a
18.98
25.77ab
30000 ppm KCl
10.87a
13.52a
15.72ab
18.97abc
18.73
25.57ab
20000 ppm CaCl2
11.15a
13.60a
15.98a
19.08ab
19.37
26.65a
30000 ppm CaCl2
10.85a
13.45a
15.95a
18.55abc
19.25
26.62a
50 ppm CuSO4
10.30ab
12.48abc
15.27abc
17.77a-e
18.23
25.15ab
75 ppm CuSO4
10.02abc
12.57abc
15.28abc
17.53a-e
18.03
24.67abc
10000 ppm ZnSO4
9.467a-d
12.82ab
14.77a-d
16.92c-f
18.05
23.82a-d
15000 ppm ZnSO4
9.667abc
12.35abc
14.23a-e
17.02b-f
18.02
23.35a-d
2 ppm Na2MoO4
8.767b-e
11.22bcd
13.77a-e
18.38abc
17.52
21.83bcd
3 ppm Na2MoO4
8.500cde
11.13bcd
13.78a-e
18.23a-d
17.20
21.85bcd
100 ppm PEG
7.900de
11.20bcd
13.65b-e
16.27def
17.08
20.37cd
150 ppm PEG
7.883de
10.73cd
13.47b-e
16.18ef
16.97
20.65cd
p < 0.05
*
*
*
*
NS
*
CV (%)
14.49
11.94
11.77
8.90
10.10
14.24
Notes: * = Significant at 5% level of probability, NS = Not significant, DAS = Days after sowing.
Seedling Shoot Dry Weight
Seedling shoot dry weight of winter rice was significantly affected by variety at 20 and 30 DAS for both the December and January sowing, but not at 10 DAS at either sowing (Tab. 7). For, both the sowing dates, BRRI dhan36 produced a higher seedling shoot dry weight than BRRI dhan29 at both 20 and 30 DAS. Priming agent produced a significant effect on seedling shoot dry weight of winter rice at 10 DAS for January sowing and only for 30 DAS at December sowing (Tab. 9). Like the other parameters studied, seed priming with KCl and CaCl2 resulted in the highest seedling shoot dry weight at all the sampling dates for both December and January sowing. Although, seed priming with CuSO4, ZnSO4 and Na2MoO4 also performed the best in terms of seedling shoot dry weight in some cases (Tab. 9).
Effect of seed priming agent on shoot dry weight of winter rice seedlings at different sowing dates
Priming agent
Shoot dry weight (g)
10 DAS
20 DAS
30 DAS
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
Control(no priming)
9.617e
11.23efg
16.08
18.72def
20.72a-d
24.08
20000 ppm NaCl
9.783de
10.75fg
14.95
18.38ef
19.80d
24.07
30000 ppm NaCl
9.633de
10.12g
14.73
17.82f
20.03cd
24.23
20000 ppm KCl
12.22a
17.33a
17.97
24.88ab
23.05a
27.67
30000 ppm KCl
12.15ab
17.02ab
17.68
24.52ab
22.78ab
27.38
20000 ppm CaCl2
11.65abc
16.88ab
17.82
25.68a
23.15a
27.65
30000 ppm CaCl2
11.47a-d
16.50abc
17.90
25.77a
23.17a
27.73
50 ppm CuSO4
11.28a-e
14.93a-d
17.20
23.57abc
22.48abc
25.90
75 ppm CuSO4
11.08a-e
15.15a-d
17.22
23.22abc
22.03a-d
25.47
10000 ppm ZnSO4
10.80a-e
14.50a-d
17.13
22.05bcd
21.97a-d
26.43
15000 ppm ZnSO4
10.42b-e
14.55a-d
16.98
22.02bcd
21.75a-d
26.12
2 ppm Na2MoO4
10.18cde
13.95b-e
16.73
20.38c-f
21.27a-d
25.35
3 ppm Na2MoO4
9.950cde
13.60c-f
16.50
20.43c-f
21.03a-d
25.30
100 ppm PEG
9.750de
12.60d-g
16.63
21.97bcd
20.78a-d
24.68
150 ppm PEG
9.683de
12.55d-g
16.72
21.68b-e
20.43bcd
24.87
p < 0.05
*
*
NS
*
*
NS
CV (%)
12.55
16.93
10.60
12.26
8.59
10.14
Notes: * = Significant at 5% level of probability, NS = Not significant, DAS = Days after sowing.
Seedling Dry Weight
The seedling dry weight of winter rice was significantly affected by variety at all the observations for both December and January sowing, except at 10 DAS for December sowing (Tab. 7). Like other parameters, higher seedling dry weight was recorded with BRRI dhan36 compared to BRRI dhan29. A significant effect of seed priming agent on the seedling dry weight of winter rice was observed at all the growth stages for both December and January sowing (Tab. 10). In general, seed priming with KCl, CaCl2, CuSO4 and ZnSO4 resulted in the highest and statistically similar seedling dry weight. While other priming agents showed no advantages in terms of seedling dry weight production compared to no priming.
Effect of priming agent on seedling dry weight of winter rice seedlings at different sowing dates
Seedling dry weight (g)
Priming agent
10 DAS
20 DAS
30 DAS
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
1 Dec. sowing
1 Jan. sowing
Control (no priming)
17.33g
20.72d
29.17def
33.87d
37.58de
44.22de
20000 ppm NaCl
17.23g
20.38d
27.50ef
33.75d
36.65e
43.75e
30000 ppm NaCl
16.93g
20.05d
27.05f
33.03d
36.40e
44.08e
20000 ppm KCl
23.25a
28.55a
33.98a
44.20a
42.03a
53.43a
30000 ppm KCl
23.02a
28.45a
33.40ab
43.48ab
41.52ab
52.95a
20000 ppm CaCl2
22.80ab
28.47a
33.80a
44.77a
42.52a
54.30a
30000 ppm CaCl2
22.32abc
28.02ab
33.85a
44.32a
42.42a
54.35a
50 ppm CuSO4
21.58a-d
25.98abc
32.47abc
41.33abc
40.72abc
51.05ab
75 ppm CuSO4
21.10a-d
26.23abc
32.50abc
40.75bc
40.07a-d
50.13abc
10000 ppm ZnSO4
20.27b-e
26.03abc
31.90a-d
38.97c
40.02a-d
50.25abc
15000 ppm ZnSO4
20.08c-f
25.63abc
31.22a-d
39.03c
39.77a-d
49.47a-d
2 ppm Na2MoO4
18.95d-g
24.10a-d
30.50b-e
38.77c
38.78b-e
47.18b-e
3 ppm Na2MoO4
18.45efg
23.75a-d
30.28cde
38.67c
38.23cde
47.15b-e
100 ppm PEG
17.65efg
23.17bcd
30.28cde
38.23c
37.87cde
45.05cde
150 ppm PEG
17.57fg
22.68cd
30.18cde
37.87c
37.40de
45.52cde
p < 0.05
*
*
*
*
*
*
CV (%)
10.34
15.13
7.45
6.86
5.52
8.32
Notes: * = Significant at 5% level of probability, DAS = Days after sowing.
Discussion
Seedling emergence, survival and establishment are very crucial for plant growth and productivity under suboptimal/adverse conditions like moisture stress, salinity stress, temperature stress etc. As evident by earlier reports [24,25], seed priming, a prior encounter with a particular stress, is known to bestow plants with greater tolerance when exposed to subsequent stress of same or other type. It was therefore hypothesized that pre-sowing seed treatment could be helpful for faster and higher seed emergence, better survival, increased growth and more vigor of winter rice seedlings which is very often exposed to cold stress at nursery bed.
Seed priming enhanced seed germination and seedling performance compared with the non-primed seed in the current study confirms the potentiality of seed priming to mitigate cold stress during seed germination and seedling establishment in rice. Except NaCl and PEG, other priming agents in this study had a positive impact on seed germination, seedling emergence and survival percentage, and seedling growth in cold stress, and seed priming with KCl or CaCl2 performed the best. It was reported from the many previous studies that the delayed and non-uniform germination of rice under cold stress was mainly due to reducing water uptake, cell membrane injury, less cellular respiration, and elevated reactive oxygen species (ROS) levels [26–29]. In low temperatures, hindered the water uptake and root growth, resulting in a decreased seed germination was reported by Li et al. [27]. Oliver et al. [30] reported cold stress may create a metabolic imbalance in plant tissues and reduce the growth of the seedlings by suppressing cell elongation and division. Rahman et al. [31] reported the respiration is one of the most important metabolic events during seed germination which provides the energy for coleoptile elongation, and the respiration rate during seed germination is closely related to temperature. Low temperature reduces the respiration of seeds, and the longer the duration of low temperature, the greater the reduction of respiration rate [32].
Higher seedling growth under cold stress in the current study from the primed seed treatments was might be the consequence of rapid emergence due to earlier production of emergence metabolites. Khan et al. [33] opined that rapid imbibitions during priming disrupt the cell membrane, cause localized cells in cotyledons resulting in more vigorous seedlings. Starch metabolism, total soluble sugar contents and α-amylase activity are strongly linked to the seed germination and seedling growth of rice [32,34]. Du et al. [34] reported seed priming increase the antioxidants superoxide dismutase (SOD), peroxidase, catalase, and glutathione peroxidase contents in seedlings and decreases the stress-related malondialdehyde (MDA) content compared to non-primed seed and in this way, these enzymes protect the plants by alleviating low-temperature chilling effects. These findings are in line with those who also confirmed increased germination rate along with faster and synchronized emergence as a consequence of pre-sowing seed priming in different crop species including rice [35–37]. Arif et al. [38] reported genetic and structural repair along with rapid development of the immature embryo during seed priming are plausible justifications for increased germination rate.
Although NaCl mediated seed priming did not enhance seed emergence percentage in this study, conflicting findings have also been reported by Mamun et al. [35] in rice and Yadav et al. [39] in capsicum, where Osmo-hardening with NaCl enhanced germination rate. This was might be due to the variation in crop species used and NaCl concentration tested in different studies.
In this study, rice varietal effect was not significant for seed emergence and seedling survival percentage at either sowing date. But, most of the seedling growth parameters at different growth stages were significantly influenced by rice variety for both the sowing dates. It was evident that BRRI dhan36 performed better in terms of seedling growth than BRRI dhan29. This was might be due to the fact that BRRI dhan36 is considered as a moderately cold-tolerant rice variety especially at the seedling stage [3,26]. Varietal differences in seed germination and seedling growth of rice has also been reported by many researchers [35,36] which is mostly due to the genetic make-up of the variety.
Both seedling emergence percentage and seedling survival percentage were found higher in 1st December sowing compared to 1st January sowing. This might be the consequence of lower minimum and the average temperature in the 1st week of January (10.1°C and 18.2°C, respectively) than those of 1st week of December (15.0°C and 21.4°C, respectively). Xu et al. [37] reported that both the speed and rate of germination of rice seeds are reduced at the temperature below 18°C. Cruz et al. [40] also confirmed the reduction in germination percentage of rice seeds at low temperatures. Cruz and Milach [41] revealed that poor germination rate under chilling stress is due to damage to the plasma membrane resulting in the leakage of solutes especially amino acids and carbohydrates from the germinating rice seeds.
Root and shoot length and dry matter accumulation of rice seedlings at different stages were found significantly higher with BRRI dhan36 than with BRRI dahn29 at both the sowing dates. This was due to higher cold tolerance of BRRI dhan36 than BRRI dhan29 as reported by Rashid and Yasmeen [3]. Similar to the emergence percentage and seedling survival percentage, seedling growth and dry matter accumulation were recorded higher when sown on 1st December than 1st January sowing. This was due to comparatively low temperatures in January than in December. As recorded during the experimental period, the average temperature in December and January were respectively 20.3 and 18.1°C, respectively. Reduction in seedling growth due to cold stress has also been reported by many others [42–44]. Rice seedling growth, evaluated in terms of root and shoot length and dry weight, was positively influenced by seed priming for both the sowing. In most of the cases, all the priming agents performed better than unprimed control, but in some cases, performances of NaCl or PEG was not satisfactory, which may be due to their phytotoxic effects on rice seedlings.
Conclusions
The present study confirms the potentiality of seed priming as a tool for increasing seedling emergence and survival percentage, and enhancing seedling growth of rice even under cold stress. Seed priming with KCl and CaCl2 emerged as the best priming agents. Conclusively, these findings will provide new avenues for advancing seed priming to mitigate cold stress in winter rice particularly at the seedling stage; however, needs further validation this results in larger field trials in the natural environment. However, the present study did not examine the physiological and biochemical changes in rice seedlings under the influence of seed priming and cold stress to obtain a better understanding of priming-induced mechanisms and to provide a basis for further analyses.
The authors thankfully acknowledge the laboratory facilities provided by the Department of Agronomy, Bangladesh Agricultural University to conduct this research activity. The authors extend their appreciation to Taif University for funding current work by Taif University Researchers Supporting Project number (TURSP-2020/120), Taif University, Taif, Saudi Arabia.
Funding Statement: The current work was funded by Bangladesh Agricultural University Research System (BAURES, Bangladesh Agricultural University, Mymensingh through the research project number: 2018/597/BAU. Taif University Researchers Supporting Project number (TURSP-2020/120), Taif University, Taif, Saudi Arabia provided the APC of this publication.
Conflicts of Interest: The authors declare that they have no conflicts of interest to report regarding the present study.
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