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Effect of GA3 and Other Plant Growth Regulators on Hybrid Rice Seed Production

D.K. Tiwari, P. Pandey, S.P. Giri and J.L. Dwivedi
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The aim of the present investigation is to identify a suitable and cost efficient substitute of Gibberellic acid to enhance hybrid rice seed production. The experimental material comprising both the parental lines of hybrid NDHR2 i.e., IR58025A and NDR3026-3-1R were treated with 34 treatment combination of different growth regulators and one untreated check were grown in randomized block design with three replications. The results indicated that the analysis of variance was significant for all the characters except plant height and effective tillers per plant. The exogenous application of various plant growth hormones significantly increases seed yield with a range of 14.85 g to 23.54 g. Treatment T26 (GA3 45g + C.C.) had highest significant increase in grain yield followed by T2 (GA3 45 g), T1 (GA3 30 g), T5 (NAA 200 g), T3 (NAA 100 g), T27 (Urea 2 g + C.C.) and T24 (GA3 45 g + K2PO4 2 g). The other yield components were also significantly increases with the foliar application of growth regulators. It is concluded that treatment combination T26 (GA3 45 g+ Urea 10g + Boric acid 2 g + ZnSO4 + K2 PO4 2 g) gave best results and could be used to enhance hybrid rice seed production and substitute of GA3 in India as well as other hybrid rice growing countries.

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D.K. Tiwari, P. Pandey, S.P. Giri and J.L. Dwivedi, 2011. Effect of GA3 and Other Plant Growth Regulators on Hybrid Rice Seed Production. Asian Journal of Plant Sciences, 10: 133-139.

DOI: 10.3923/ajps.2011.133.139

Received: December 14, 2010; Accepted: January 29, 2011; Published: June 10, 2011


Rice is one of the most important crops in the global food system providing energy, protein and vitamins for about half of the world population. At the current growth of population rice requirement increases dramatically and many nations are facing second-generation challenge of producing more rice at less cost in a deteriorating environment; hence, it is challenging task to ensuring food and nutritional security. Thus, improved technologies are required to bridge the gap to feed the increasing population. Therefore, enhancing productivity of rice through novel genetic approaches like hybrid rice was felt necessary. Future global rice production could be increased by efforts to increase rice production area or increase yield or a combination of both. Although future expansion of rice area may require large and costly investments, a substantial yield increase could be obtained with the wide adoption of hybrid rice (Nguyen, 2010).

The presence of sufficient hybrid vigour is an important pre-requisite for successful production of hybrid varieties. In 1976, Chinese scientists had made a crucial breakthrough, successfully commercializing what is known as three line hybrid rice, raising yields to more than 5 t ha-1 by 1983. As the technology advanced, nationwide rice yields averaged more than 6 t ha-1 by 1995. And by 2004, yields of super hybrid rice cultivated in selected regions had achieved yields of more than 10 t ha-1. Based on these achievements, super hybrid rice breeding program was proposed, in which the yield target is 13.5 t ha-1 and can be fulfilled by 2010 (Yuan, 2007, 2010; Li et al., 2009). Following the success of China, 18 other countries have intensified their research efforts to exploit the phenomenon of heterosis in rice (Lopez et al., 2003). Since rice is a self-pollinated crop, hybrid seed production must be based on male sterility systems. Currently, the most popular male sterility system for commercial exploitation of hybrid rice technology is the CMS, popularly known as the three-line system. Seed production technology is a key to the success of hybrid rice. To enhance the efficiency of hybrid seed production, it is necessary to increase the yield of hybrid seed by improving the out crossing capacity of CMS lines (Shi-Hua et al., 2006).

Plant hormones play a vital role in coordination of many growth and behavioral processes in the plant life. They regulate the amount, type and direction of plant growth. Remarkable accomplishments of Plant Growth Regulators (PGR) such as manipulating plant developments, enhancing yield and quality have been actualized in recent years using new emerging and efficient plant growth regulators. It has long been ascertained that plant hormones including auxins, gibberellins, cytokinin and ethylene etc., are involved in controlling developmental events such as cell division, cell elongation and protein synthesis. Plants have the ability to store excessive amounts of exogenously supplied hormones in the form of reversible conjugates which release active hormone when and where plant needs them during the growth period. Auxins (i.e., NAA) and gibberellins (i.e., GA3) being well known plant growth promoting hormones has shown to be involved in a variety of plant growth and development processes (Frankenberger and Arshad, 1995). Auxins may regulate cell elongation, tissue swelling, cell division, formation of adventitious roots, callus initiation and growth, induction of embryogenesis and promote cell wall loosening at very low concentration (Vanderhoff and Dute, 1981; Azad et al., 2004; Woodward and Bartel, 2005; Muthukumar et al., 2007; Abel and Theologis, 2010). Similarly, Gibberellins are plant hormones that participate in regulation of many growth and developmental processes in various plants (Hedden and Phillips, 2000; Olszewski et al., 2002; Naeem et al., 2001; Shah et al., 2006; Shibairo et al., 2006; Emongor, 2007). And these are especially important in regulating stem elongation (Dunand, 1998; Peng et al., 1999; Richards et al., 2001; Itoh et al., 2001; Spielmeyer et al., 2002; Schomburg et al., 2003; Sakamoto et al., 2004; Sun, 2004). Gibberellic acid is responsible for stimulating the production of mRNA molecules in the cells and mRNA produced in this form, codes for the hydrolytic enzymes, which in turn improves the chances of fast growth (Richards et al., 2001; Sun, 2004). Growth regulators are proved to improve effective partitioning and translocation of accumulates from source to sink in the field crops (Solaimalai et al., 2001; Senthil et al., 2003).

Hybrid rice seed production is quite complex. Many factors affect the yield and quality of hybrid seed. To increase the seed production a series of integrated technologies was also advanced, including the three factors for secure heading and flowering (temperature, sunlight and relative humidity), applying fertilizer and chemicals and spraying a low dosage of Gibberellic acid (GA3) to improve out-crossing posture. Application of GA3 is an important component of hybrid rice seed production technology. Its cost is very high in many countries. High seed yields in China have been achieved with a very high dosage of 150-300 g ha-1. Outside China, it is essential to reduce the cost of GA3, either by reducing the dosage or by producing cheap GA3 locally (Virmani et al., 2007). The advantage of hybrid rice cannot be fully utilized unless a cost effective seed production system successfully developed. Presently, use of a high cost chemical i.e., Gibberellic acid (GA3) is almost the prerequisite for rice hybrid seed production which increases the cost of hybrid seeds. Hybrid rice seed production is highly dependent on use of gibberellic acid (GA3). Outside China this is quite expensive (more than US$1.00 per gram), because it is imported. In China it is quite cheap (US$0.30 per gram) because it is produced locally, so it does not cost much to apply a high dosage of this growth regulator (Virmani et al., 2007). To overcome this problem, it is necessary to identify cheaper chemicals to substitute GA3. Keeping in view of these needs the present investigation was undertaken to study the effect of GA3 and other growth regulators on hybrid seed production.


The experimental material comprising both the parental lines of hybrid NDHR2 i.e., IR58025A and NDR3026-3-1R were treated with 34 treatment combination of different growth regulators and one untreated check were grown in randomized block design with three replications at Crop Research Station, Narendra Deva University of Agriculture and Technology, Kumarganj, Faizabad during wet season of 2001-02 and 2002-03. The experimental site is located at 26.47°N latitude, 82.12°E longitudes and an altitude of 113 m above mean sea level. This site is in the eastern Gangetic plains of India and has sandy loam soil texture. The detail of treatment combinations is presented in (Table 1). Single row of CMS line (A line) was sown followed by three rows of Restorer line (R line) at three-day interval, CMS line was also sown at seven days interval from last sowing of restorer line. Subsequently, the seedlings were mixed in equal proportion to the three dates of sowing before transplanting. R line was transplanted in paired rows with three seedling per hill keeping 30x15 cm spacing while, A line with single seedling with spacing of 15x15 cm. A line and R line were transplanted in the ratio of 2:6 in a plot of 3x5. GA3 and other chemical combinations were sprayed in two spraying i.e., at the time of heading and at 50% panicle emergence by Using Ultra-low Volume (ULV) sprayer. One, which remained untreated, was used as the control. The recommended agronomic practices followed to raise good crop stand. The data were recorded on 10 randomly selected plants from each replication for ten quantitative characters. The characters studied were; plant height (cm), effective tillers per plant, panicle length (cm), number of spikelets per panicle, number of fertile spikelets, spikelet fertility%, 100 grain weight (g), biological yield (g), grain yield per plant (g) and harvest index (%).

Table 1: Treatment combinations of various growth regulators
Image for - Effect of GA3 and Other Plant Growth Regulators on Hybrid Rice Seed Production
GA3: Gibberellic acid, NAA: Naphthalene acid, ZnSO4: Zinc sulphate, K2PO4: Potassium sulphate and chemical composition (i.e., C.C.) = (Urea 10 g+ Boric acid 2g+ZnSO4 2g+K2PO4 2g)

The general reference for data collection was standard evaluation system for rice (Anonymous, 2002; Virmani et al., 1997). Mean values were subjected to analysis of variance to test the significance for each character as per methodology advocated by Panse and Sukhatme (1967).


The analysis of variance was significant for all the characters except plant height and effective tillers per plant under various treatments of growth regulators (Table 2). The mean performance based on the pooled data of both two years indicated that all the traits were significantly influenced by the application of growth regulators compared to control i.e., untreated check (Table 3). Remarkable increase in growth and yield characteristics with the exogenous application of Gibberellic acid, NAA and other growth hormones were also reported by earlier workers such as Kalavathi et al. (2000), Yogesha et al. (2000) and Thangaraj et al. (2000) in rice, Naeem et al. (2001) in tomato, Sarkar et al. (2002) in soybean, Muthukumar et al. (2007) in baby corn (Zea mays L.), Shibairo et al. (2006) in potato, Shah et al. (2006) in black cumin (Nigella sativa L.), Emongor (2007) in cowpea and Mobin et al. (2007) in mustard. Better vegetative growth of a crop is largely responsible for higher seed yield because number of photosynthesizing sites i.e., number of vegetative branches is affected by initial growth stages. The significant increase in plant height was observed by all treatment combinations of the exogenous application of various growth regulators.

Table 2: The analysis of variance for different traits under various treatments of growth regulators in rice
Image for - Effect of GA3 and Other Plant Growth Regulators on Hybrid Rice Seed Production
**1% probability level of significance. The above table obtained by ANOVA and t test

Amongst them treatment T3 (71.52 cm) had highest estimate followed by T26 (71.47 cm), T6 (70.81 cm), T30 (70.12 cm), T12 (70.01 cm), T28 (69.65 cm) and T29 (69.65 cm). The increase in plant height is due to plant hormones promoted vegetative growth by active cell division, cell enlargement and cell elongation and thus helped in improving growth characteristics and also facilitated reproductive growth (Pareek et al., 2000). These findings were in closely agreement with the results of Subbaih and Mittra (1997) and Dunand (1998) who also reported significant increase in plant height, stem elongation and yield in response to Gibberellic acid application. Virmani et al. (2007) reported that differential application of GA3 also increases the relative height of the pollen parent over the seed parent.

More effective tillers per plant are believed to be closely associated with high seed yield per plant resulting high productivity. Hybrid rice relies mainly on tillers to obtain the desirable population; conventional rice relies on number of seedlings planted.

Table 3: Mean performance of various quantitative traits of rice under different levels of treatments with GA3 and other growth regulators (Pooled data of two years)
Image for - Effect of GA3 and Other Plant Growth Regulators on Hybrid Rice Seed Production
**Significant at 1% probability level of significance. In this table test of significance calculated by applying t test

About 85-90% of productive panicles of hybrid rice come from tillers. A perusal of data (Table 3) revealed that significant increase in effective tillers was ranged from 22.17 to 26.35 and highest estimate was recorded by the treatment combination T26 (26.35) followed by T2 (26.10), T3 (25.97), T1 (25.70), T9 (25.67), T7 (25.59) T5 (25.50), T22 (25.31) T21 (25.19), T4 (25.16) and T23 (25.09). Generally, larger panicle is associated with high number of grains panicle resulting into higher productivity; therefore significant increase for panicle length is desirable. The highest significant increase in panicle length were showed by the treatment T26 (18.12 cm) followed by T1 (18.10 cm), T5 (17.91 cm) and T3 (17.82 cm). The data also revealed that some treatment combinations give the decrease in panicle length as compare to control i.e., treatment combination T8 and T15. These results were in conformity with the results of Elankavi et al. (2009) who also observed that the exogenous application of GA3 significantly increases various growth characters viz., plant height, number of tillers and yield attributes in rice.

Regulating total spikelets is necessary to gain high hybrid rice yields. The number of spikelet per panicle ranged from 165 to 229. All treatment combination showed significant increase in spikelet number except T28, T21, T15 and T17. The number of fertile spikelets was highest with the application of GA3+ C.C (T26). Spikelet fertility % is very important in hybrid breeding programme because this trait has a direct effect on the seed yield. The successful utilization of CMS in development of hybrids is not possible unless the effective restorer lines are identified. More number of fertile spikelets is closely associated with high yield per plant resulting in high productivity. The range of spikelet fertility varied from 27.64 to 59.49%. Twelve treatment combinations showed above 45% spikelet fertility among them T26 (59.49 %) had highest estimate followed by T2 (58.88%) and T3 (54.74 %). Similar findings in rice were also reported by Bui et al. (1992), Kalavathi et al. (2000); Yogesha et al. (2000). Poor development of spikelets on the basal branches resulted in a high percentage (50-60%) of degeneration and sterility and, consequently, grain yield was poor. Application of gibberellic acid (GA3) and kinetin (6-furfuryl amino purine) improved development and grain yield on all branches (Patel and Mohapatra, 1992).

Biological yield significantly increased with the application of different combinations of growth regulators and it varied from 32.42 g to 41.31 g. The highest biological yield were recorded with the application of GA3 (45 g) followed by NAA (100 g), GA3 (30 g)+NAA (200 g), NAA (150 g) and GA3 (45 g)+c.c. against control (29.22 g). Similarly the highest harvest index was recorded by the T26 i.e., GA3 (45 g)+C.C. The 100 grain weight is one of the important common traits which influence the yield. All treatment combination gave the significant increase in 100 grain weight except T17. The highest significant increase in 100 grain weight were showed by the treatment T26 (8.75 g) followed by T2 (6.14 g), T28 (5.34 g) and (5.33 g). The grain yield is very complex trait. It is multiplicative end product of several basic components of yield i.e., panicle length, spikelet fertility, test weight, number of effective tillers and number of spikelets per panicle. In hybrid rice seed production seed yield mainly depends on floral traits of CMS line i.e., stigma exertion, opening angle of spikelets, panicle exertion percent, outcrossing rate and also agro-morphological traits of pollen parents. Therefore, to achieve higher yield improvements in these traits is a necessary requirement. The application of GA3 influences panicle exertion, spikelet opening angle and other floral traits which increases outcrossing rate of CMS lines leading higher yield. Xu and Li (1988) reported 13% higher seed yield with application of GA3 in rice. Similarly, Elankavi et al. (2009) observed up to 50.52% increase in grain yields over control. In present study the effect of growth regulators on grain yield showed that it was significantly increases with a range of 14.85 to 23.54 g. The treatment T26 i.e., GA3 (45 g)+C.C gave highest significant increase in seed yield followed by T2 (GA3 45 g), T1 (GA3 30 g), T5 (NAA 200 g), T3 (NAA 100 g), T27 (Urea 2 g+C.C.) and T24 (GA3 45 g+K2PO4 2 g). The increase in yield with the application of various plant growth regulators might be due to increased yield attributes, which in turn resulted from effective translocation of photosynthates. The plant growth hormones also increases mobilization of reserve food materials to the developing sink through increase in hydrolyzing and oxidizing enzyme activities and leads to yield increases (Jayachandran et al., 2000). While, Zahir et al. (2007) observed that exogenously supplied PGRs may undergo several metabolic processes in the soil resulting in loss of their activity and reduced availability to plants and such type of behavior was only seen with IAA and Gibberellic acid. These results were in conformity with a number of workers such as Know et al. (1990), Risheng et al. (1990), Aswathanarayana and Mahadevappa (1992), Bui et al. (1992), Yuan and Fu (1995), Pandey et al. (1996), Jayaraj and Chandrasekharan (1997), Subbaih and Mittra (1997), Mao et al. (1998), Singh and Sahoo (1998), Liang and Zaman (1999), Kalavathi et al. (2000), Yogesha et al. (2000), Thangaraj et al. (2000), Shi-Hua et al. (2006) and Elankavi et al. (2009).


Plant Growth Regulators (PGRs) and various chemical combinations significantly influence agronomical, morphological and physiological traits in rice and it was observed that at limited concentrations they stimulate rapid cell division resulting faster vegetation and reproductive growth. The treatment combination T26 i.e., (GA3 45 g+Urea 10 g+Boric acid 2 g+ZnSO4 2 g+K2PO4 2 g) gave the best effects as compared to all other treatment combinations for most of the characters and may be used as substitute of GA3 with low cost hybrid seed production in India as well as other hybrid rice growing countries and also to achieve higher seed yield with maximum economic return.


The authors are thankful to Directorate of Research, Narendra Deva University of Agriculture and Technology, Faizabad (U.P.) India, for providing the necessary funds and facilities to undertake the present study.


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