RICE SEED INVIGORATION
Farooq, M., Basra, S.M.A., Cheema, M.A. and Afzal, I. (2006), Seed Sci. & Technol., 34, 521-528
Integration of pre-sowing soaking, chilling and heating treatments for vigour enhancement in rice (Oryza sativa L.) M. FAROOQ1, S.M.A. BASRA1, M.A. CHEEMA2 AND I. AFZAL1 1
2
Department of Crop Physiology, University of Agriculture, Faisalabad-38040, Pakistan (E-mail:
[email protected]) Department of Agronomy, University of Agriculture, Faisalabad-38040, Pakistan
(Accepted February 2005)
Summary A study was conducted to evaluate the possibility of integration of different pre-sowing seed treatments (viz. soaking, chilling and heating). Soaking was successfully integrated with heating in fine rice as indicated by lower values of time to start germination, time to 50% germination, mean germination time and mean emergence time and higher values of final germination percentage, germination index, energy of germination, root and shoot length and seedling fresh and dry weight compared with all other treatments including control. Soaking and chilling combination performed better than other treatments including control in coarse rice.
Introduction Rice is a versatile crop; it can grow at the elevation of more than 3000 m in the Himalayas and at sea level in the deltas of great rivers of Asia. It is one of the most important cereal crops and is the staple food of majority of the peoples of the world. In Pakistan it ranks 2nd in consumption after wheat. Farmers have adopted traditional seed soaking for rice nursery sowing for decades, but this results in poor germination and uneven nursery stand (Ahmad, 1998). Improved seed invigoration techniques are being used in many parts of the world to reduce the germination time, synchronize germination, improve germination rate and increase seedling stand (Khan, 1992; Lee and Kim, 2000). These include water soaking (Rudrapal and Nakamura, 1988), hardening (Nath et al., 1991; Basra et al., 2003, 2005) and seed priming (Khan, 1992; Jett et al., 1996; Basra et al., 2002). Soaking by submerging seeds in water can be performed with or without aeration. Since water is not limited, seeds eventually germinate, assuming that seeds are viable, not dormant, oxygen is available and a suitable temperature is employed. As no chemicals are used during this process, it is an environmentally safe technique. Gerber and Caplan (1989) reported that soaking sweet corn seeds in aerated deionized water at 20°C for 0, 15, 6, 12, 24 or 48 h and then surface drying reduced the percentage of ungerminated seeds. Emergence of seedlings under cold stress was increased by priming up to 24 h although soaking for 48 h proved detrimental (Gerber and Caplan, 1989). Pre-sowing seed soaking of wheat cv. PBW 138 for 24 h increased grain yield by 10.3, 16.3 and 21.2% compared with sowing untreated seeds (Kahlon et al., 1992). 521
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Dry heat treatment of seeds is used for two purposes, one is to control the external and internal seed borne pathogens (Fourestto et al., 1990), the other is to break the dormancy of seeds (Zhang, 1990). In general, high temperature in dry heat treatment reduces seed viability and seedling vigour, but use of an optimum temperature for breaking dormancy promotes seed germination and seedling emergence in cereal crops (Lee et al., 2002). The degree of promotion of seed germination by dry heat treatments showed a wide intraspecific variation (Jeffery et al., 1988; Herranz et al., 1998). Non-lethal dry treatment before radicle emergence effectively promoted the germination of barley and wheat seeds (Dell’ Aquilla and Di Turi, 1996; Dell’ Aquilla and Di Turi, 1998). Pre-sowing chilling treatments are also being used effectively, either alone or integrated with other invigoration techniques in order to shorten the emergence time and to protect seeds from abiotic and biotic stresses during critical phase of seedling establishment (Basra et al., 2002). In earlier studies, different pre-sowing seed treatments have successfully been integrated for vigour enhancement (Taylor et al., 1998). More recently Farooq et al. (2006) have synergistically integrated seed hardening and osmopriming techniques for rice seed invigoration naming the technique “osmohardening”. Moreover alternate cycles of high and low temperature pre-sowing treatments have also been found effective for vigour enhancement in both fine and coarse rice (Farooq et al., 2005). The present study investigated the possibility of utilizing the beneficial effects associated with each treatment by their integration on the germination and seedling vigour in both coarse and fine rice.
Material and methods Seed materials Seeds of coarse rice cultivar KS-282 and of fine rice cultivar Super-Basmati were used. These seeds were obtained from Rice Research Institute, Kala Shah Kakoo, District Sheikhupura, Pakistan. The initial seed moisture contents were 7.89% and 8.06% for coarse and fine rice respectively (on dry weight basis). Seed treatments Soaking: A weighed quantity (100 g) of seeds of both coarse and fine rice were soaked in continuously aerated 500 mL of tap water for 24 h. Aeration was provided with the help of aeration pump. It was followed by forced air-drying (with electric ceiling fan) under shade. Heating: For dry heat treatment, 250 g seeds of each cultivar were incubated at 40°C for 24 h in an oven (EYLA Forced Air oven, WFO-600 ND, Rikakikai Co. Ltd. Tokyo, Japan). The seeds were incubated in glass jars tightly covered with lids. Chilling: A weighed quantity (250 g) of both coarse and fine rice were sealed in polythene bags and placed in refrigerator (Model National NR 245 TES) at -19±2°C for 24 h. 522
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The study was consisted of following treatment combinations: S+C =Soaking followed by chilling S+H =Soaking followed by heating S+C+H =Soaking followed by chilling followed by heating S+H+C =Soaking followed by heating followed by chilling After treatment using the prescribed method and duration, seeds were sealed in polythene bags and stored in refrigerator for further use. Germination test Seeds were sown in petri dishes between layers of moist filter papers at 27°C in the incubator. Germination was observed daily according to the AOSA method (AOSA, 1990). The time to 50% germination (T50 ) was calculated according to the following formula of Coolbear et al. (1984) modified by Farooq et al., (2005): ´ ¥N ¦ ni µ (t j t i ) 2 ¶ T50 t i § n j ni
Where N is the final number of germination and ni , nj are cumulative number of seeds germinated by adjacent counts at times ti and tj when ni < N/2 < nj. Mean germination time (MGT) was calculated according to the equation of Ellis and Roberts (1981): ¤ Dn MGT ¤n Where n is the number of seeds, which were germinated on day D, and D is the number of days counted from the beginning of germination. Germination index (GI) was calculated as described in the Association of Official Seed Analysts (1983) as the following formula: GI
No. of germinated seeds Days of first count
No. of germinated seeds Days of final count
Energy of germination was recorded on the 4th day after planting. It is the percentage of germinating seeds 4 days after planting relative to the total number of seeds tested (Ruan et al., 2002). Seedling emergence Control and treated seeds were sown in plastic trays (25 in each) containing moist sand, replicated four times and were placed in growth chamber (Windon, England). Day and night lengths were kept 15 and 9 h with 30°C and 24°C temperatures respectively. The relative humidity was maintained at 70%. Emergence was recorded daily according to the seedling evaluation of the Handbook of Association of Official Seed Analysts (1990). Mean emergence time was calculated according to the method described earlier. 523
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Results Germination All treatments of fine rice reduced the time to the start of germination, which was most rapid after soaking plus heating. A similar pattern was observed in T50 and MGT where all the seed treatments resulted in lower values than that of control. However, the lowest T50 and MGT was recorded in seeds subjected to S+H (table 1). All treated seeds had higher germination percentage and higher germination index (GI) than the control. However, a statistically higher GI was noted in seeds subjected to soaking, chilling and heating compared with other treatments, followed by soaking, heating and chilling treatment. Seed treatments also resulted in higher energy of germination. Seed treatments did not affect radicle length significantly (table 1). A significant increase in plumule length was noted in seeds subjected to S+H+C, S+C and S+C+H. Table 1. Effect of seed treatments on the germination vigour of fine and coarse rice. Treatments
Time to start germination (h)
T50 (days)
MGTd (days)d
Control
80.00 a
4.40 a
4.85 a
S+C
48.00 b
3.06 b
S+H
40.00 b
2.13 c
FGP (%)
GI
GE (%)
Radicle length (mm)
Plumule length (mm)
73.00 c
43.02 c
21.66 b
65.6
51.7 b
3.20 b
86.33 a
65.83 b
82.00 a
64.3
73.0 a
3.10 b
82.00 ab
65.65 b
72.66 a
62.3
49.2 b
Fine rice
S+C+H
48.00 b
2.96 b
3.43 b
84.333 a
84.72 a
66.00 a
61.0
62.4 ab
S+H+C
48.00 b
2.76 b
3.23 b
79.66 b
69.44 b
77.33 a
62.1
73.7a
LSD at 0.05
15.25
0.5639
0.539
3.022
7.213
n.s.
14.54
24.45
Coarse rice Control
88.00 a
4.16 a
4.83 a
90.67 a
46.49 b
31.00 bc
25.3 d
45.7 c
S+C
64.00 b
3.22 b
3.83 b
88.67 a
67.63 a
73.00 a
76.9 a
94.0 a
S+H
72.00 b
4.00 a
4.46 ab
86.33 a
49.33 b
39.33 bc
51.6 bc
79.8 ab
S+C+H
88.00 a
4.10 a
4.86 a
59.67 b
31.33 c
26.33 c
64.9 ab
68.2 bc
S+H+C
56.00 c
3.26 b
3.83 b
82.00 a
61.66 a
55.33 ab
42.2 c
85.8 ab
LSD at 0.05
10.002
0.7301
0.756
18.57
11.12
26.09
16.36
23.94
Figures not sharing the same letters differ significantly at p<0.05 S+C =Soaking followed by chilling; S+H =Soaking followed by heating; S+C+H =Soaking followed by chilling followed by heating; S+H+C =Soaking followed by heating followed by chilling.
In coarse rice, seeds subjected to soaking, heating and chilling (S+H+C) had the earliest germination, followed by soaking and chilling (table 1). Seeds subjected to soaking and chilling also had the statistically lowest T50 and MGT, followed by S+H+C in both cases (table 1). The highest germination percentage was however recorded in the control seeds. The soaking, heating and chilling treatment resulted in lower FEP than that of control (table 1). A statistically significant increase in GI, GE, radicle and 524
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plumule length was observed in seeds subjected to S+C, while S+H and S+C+H increased radicle length and there was an increase in both GI and GE after S+H+C (table 1). All treatments increased plumule length, with the greatest increase in S+C, followed by S+C+H (table 1). Seedling vigour In fine rice, all the treatments resulted in lower MET compared with control, although, the lowest MET was observed in seeds subjected to soaking, heating and chilling followed by the soaking and heating treatment (table 2). All the treatments also resulted in improved emergence percentage than that of control, with highest final emergence percentage observed in seeds subjected to soaking, chilling and heating. The longest roots and shoots were observed in seeds subjected to soaking and heating that was statistically at par with that of soaking, heating and chilling (table 2). All the seed treatments resulted in higher seedling fresh and dry weight compared with that of control with, maximum fresh and dry weight noted in seeds subjected to S+H+C and soaking and heating (table 2). Table 2. Effect of seed treatments on seedling vigour of fine and coarse rice. Treatments
MET (days)
FEP (%)
Root length (cm)
Shoot length (cm)
Seedling fresh weight (mg)
Seedling dry weight (mg)
Fine rice Control
8.51 a
41.42 c
45.O5 b
30.88 b
131.25 b
S+C
5.695 bc
76.00 b
42.58 b
38.30 b
139.50 b
126.25 a
90.750 b
S+H
4.99 cd
85.19 ab
73.64 a
75.17 a
165.71 a
124.50 a
S+C+H
6.372 b
90.25 a
42.60 b
36.01 b
117.50 c
100.75 b
S+H+C
4.69 d
89.45 a
69.92 a
72.52 a
174.50 a
127.50 a
LSD at 0.05
0.8605
12.57
13.23
20.99
11.230
13.450
Coarse rice Control
6.26 a
92.47 a
88.64 a
61.98 a
182.50 b
101.25 d
S+C
6.10 b
78.10 b
39.81 c
40.63 b
153.75 bc
129.75 c
S+H
5.76 c
82.23 ab
64.82 b
57.82 a
187.75 b
167.50 b
S+C+H
6.34 a
59.24 c
55.15 b
58.27 a
222.75 a
181.25 a
S+H+C
5.83 c
78.11 ab
54.42 b
60.87 a
170.25 b
138.50 c
LSD at 0.05
0.07
12.50
14.32
13.64
22.234
11.235
Figures not sharing the same letters differ significantly at p<0.05 S+C =Soaking followed by chilling; S+H =Soaking followed by heating; S+C+H =Soaking followed by chilling followed by heating; S+H+C =Soaking followed by heating followed by chilling.
In coarse rice, statistically lower MET was noted in with soaking, heating and chilling treated seeds, with a statistically similar MET after soaking and heating, soaking, chilling and heating gave a similar MET to that of the control (table 2). Statistically similar maximum emergence percentages were noted in the control, after soaking and heating and after soaking, heating and chilling. Soaking, chilling and heating treatment gave the 525
M. FAROOQ, S.M.A. BASRA, M.A. CHEEMA AND I. AFZAL
lowest emergence percentage. Maximum root length was noted in control and all the treatments reduced root length. Maximum shoot length was also recorded in untreated seeds (table 2). Seedling fresh weight was significantly increased in seeds subjected to soaking, chilling and heating while seeds subjected to soaking and heating had similar seedling fresh weight to that of the control. Reduced seedling fresh weight was noted in soaking and chilling treated seeds. In contrast minimum seedling dry weight was noted in untreated seeds and all the seed treatments resulted in higher seedling fresh weight. Maximum seedling fresh weight was noted in seeds subjected to soaking, chilling and heating (table 2). Discussion Pre-sowing soaking, heating and chilling treatments were successfully integrated for vigour enhancement in both coarse and fine rice as shown by their significant effects on the germination and seedling vigour (tables 1, 2). Earlier and synchronized germination was observed in the treated fine rice seeds compared with that of control as depicted by lower MET, T50 and MGT, and higher FGP, GI, GE, FEP, root and shoot length, and seedling fresh and dry weight (tables 1, 2) that shows that the enhancement by individual soaking, chilling or heating has been integrated synergistically. However, the most effective integration was found after soaking and heating (S+H) followed by soaking, heating and chilling (S+H+C) (table 1). This suggests that the synergistic effects of S+H were affected antagonistically when chilling treatments were integrated with S+H treatments (table 1). In coarse rice, earlier and uniform germination was observed in seeds subjected to S+H+C as was shown by lower value of time to start germination, T50 and MGT, MET, and higher value of FEP, GI, GE and, shoot length and plumule length [except for radicle length and seedling fresh and dry weight] (tables 1, 2), this was followed by S+C in case of germination as indicated by higher values of GI, GE, and radicle and plumule length (table 1). Moreover, seeds subjected to S+C+H resulted in higher shoot length and, seedling fresh and dry weight (table 2). This all shows that the enhancement by individual soaking, chilling or heating has been integrated synergistically in both rice types. Pre-sowing chilling treatments have been used separated or in integration with other invigoration techniques in order to shorten the planting and emergence, and to protect seeds from abiotic and biotic stresses during critical phase of seedling establishment. Furthermore, different pre-sowing seed treatments have successfully been integrated for vigour enhancement. In both fine and coarse rice, vigour enhancements by dry heat treatment and chilling have also been reported earlier (Farooq et al., 2004). In other attempts seed hardening was synergistically integrated with osmoconditioning for rice seed invigoration (Basra et al., 2004; Farooq et al., 2005). The present study shows that soaking, heating and chilling treatments can effectively be integrated for vigour enhancement in both coarse and fine rice. However, soaking was most successfully integrated with heating in fine rice. While, in coarse rice, soaking and chilling combination performed better than other treatments.
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