Effect of different priming treatments on seed germination of sago palm (Cycas revoluta L.)
Authors: Ullah Zia , Hassan Imran , Hafiz Ishfaq Ahmed , Abbasi Nadeem Akhtar 
Published: January 2021

King sago palm or sago cycas are the other name of Kangi palm (Cycas revoluta) sago palm has been used as an indoor and outdoor landscape plant for centuries. The present study was conducted to estimate the effect of different priming treatments on seed germination of sago palm (Cycas revoluta L.) in the research area of Department of Horticulture PMAS, University of Arid Agriculture Rawalpindi, Pakistan. The Experiment consisted of ten treatments; the seeds without pulp were soaked in solution of 500, 750 and 1000 ppm GA3 and 2%, 3% and 4% solution of KNO3 for 24 hr at room temperature. In case of hot water treatment, seeds were primed at 80oC, 90oC and 100oC for 30, 20 and 10 minutes respectively.  The effect of different concentrations of gibberellic acid (GA3), potassium nitrate (KNO3) and hot water on various parameters like germination rate, germination percentage, germination value, decayed seed percentage, time of germination, number of leaves and seedling height were studied. Significant results of germination rate (55.56 days), germination value (192.19) were achieved from 500 ppm GA3. Maximum germination percentage (73.33%) and number of leaves (2) were observed in KNO3 at 2% followed by 500 ppm GA3. Similarly lowest decayed seed percentage (26.66%) and time of germination (59.41 days) were noted in 2% KNO3. The seedling height was optimum (19.33 cm) in 3% KNO3 followed by 2% KNO3. Best germination results were obtained due to permeability of hard seed coat made by low concentrations of priming treatments (KNO3 @ 3%).Key wordCycas revoluta, gibberellic acid, potassium nitrate, germination parametersINTRODUCTIONThe sago palm (Cycas revoluta L.) is one of the important cycad commonly known as Kanghi palm or Japanese sago or simply sago palm. The cold hardy sago palm has been used as an indoor and outdoor landscape plant for centuries. It is used as a significant or focal point in any landscape design. Despite its importance in ornamental industry, it is facing certain problems regarding its germination due to its hard seed coat. It has been estimated that over 25% of all palm species require over 100 days for germination and they have less than 20% total germination (Tomlinson, 1990). So, there is a serious need of consideration to sort out this major issue. The reasons for this remain obscure, as little research work has been accomplished on seed dormancy in palms. Certain mechanical and chemical scarification, pretreatments were proved to be effective in germination of the hard-seeded species of Cycas and some other species (Frett, 1987; Chauhan et al., 2009; Rouhi et al., 2010). Cycad seeds respond to various pretreatment, including scarification, depulping and exposure to some chemical materials like gibberellic acid (GA3), potassium nitrate (KNO3) and soaking in hot water for specific period of time.The overall development of plant is regulated by the growth hormones, nutrient and environmental factors. They also vary in their germination requirement (Chauhan et al., 2009). KNO3 is most widely used chemical for promoting germination. Solutions of 0.1 to 0.2% KNO3 are common in routine germination testing and are recommended by the Association of Official Seed Analysts and the International Seed Testing Association for germination tests of many species (Copeland and McDonald, 1995).OBJECTIVESThe objectives of the present research was to minimize the time period of seed germination and to enhance percentage of germination by breaking the external dormancy through different levels of chemicals including GA3, KNO3 and hot water.MATERIALS AND METHODSThis study was conducted in the research field of Department of Horticulture PMAS, Arid Agriculture University Rawalpindi. An experiment was conducted by using Completely Randomized Design (CRD).The seeds of sago palm were collected from 10-15 years old female stocks growing at a commercial garden located in suburb of Islamabad city. Uniform, equal and the same weight and healthy seeds were selected. The seeds had diameter 2.54 to 5.08 cm. Seeds were soaked in fresh water for two weeks to remove pulp from the upper surface of hard seed coat. Seeds without pulp were soaked in solution of 500, 750 and 1000 ppm GA3 and 2%, 3% and 4% solution of KNO3 for 24 hr at room temperature. In case of hot water treatment, seeds were primed at 80oC, 90oC and 100oC for 30, 20 and 10 minutes respectively (Table 1). Then seeds were washed with few drops of tween twenty in order to remove surface tension. Seeds were dried at 24oC room temperature. After sterilization, 10 seeds of sago palm were planted in each pot of 14 inch diameter containing sterilized soil media ( Sand, soil, FYM 1:1:1) at 4-8 cm depth and incubated in a greenhouse at daytime temperature of 25±2°C and relative humidity of 60-80% and watered weekly depending on weather conditions. Germination was evaluated at the end of 10 months. Seed emergence was recorded as germination index. The data for germination rate (days), germination percentage (%), germination value, seed decayed percentage (%) and time of germination (days) were recorded during the course of study. After seed germination, observations were recorded for number of leaves an d seedling height. The data collected was compiled and analysed statistically by using computer software germination; observations were recorded for number of leaves  (Steel and Torrie, 1980).RESULTS AND DISCUSSIONAnalysis of data showed that parameters related to germination significantly affected by hydro and chemical priming treatments (Table 2). Seeds treated with 500 ppm GA3 showed maximum germination rate (55.56 days) which was statistically significant with control.  Hot water treatments observed average germination rate. Minimum germination rate (159.88 days) was recorded in unprimed seeds. Gibberellin encourage germination by inducing hydrolytic enzymes that weaken the hurdle tissues such as the endosperm or seed coat, inducing mobilization of food reserves in seed and stimulating expansion of the embryo (Bewley and Black, 1994; Dhoran and Gudadhe, 2012).Germination rate (days) and germination percentage (%): The data regarding germination percentage indicated that difference between primed and non-primed seeds was statistically significant. Lower concentrations of potassium nitrate (KNO3) @ 2% and gibberellic acid (GA3) @ 500 ppm treatments significantly affected the germination percentage 73.33% and 70% respectively as compared to control (33.33%). Significant improvement in seed germination might be due to enhanced breakdown of reserve metabolites present in seed. The lower concentration of KNO3 has promoting effect on seed germination as compared to its higher concentration. This leads to supposition that higher concentrations exercise decreasing effects on seed germination by causing death of cells and ultimately result in loss of seed viability (Nascimento, 2003; Ramzan et al., 2010).Germination value: Analysis of variance revealed that germination value was affected by various priming treatments (Table 2). Result regarding germination value (192.19) was highest in T1 (500 ppm GA3) followed by 186.42 in T4 (3% KNO3) and 184.12 in T2 (750 ppm GA3). Minimum germination (74.43) was noted in control. The gibberellic acid has positive effect on germination value due to its hormonal regulation capability and retarding effect against abscisic acid present in dormant seeds (Var et al., 2010; Zarchini et al., 2013; Pipinis et al., 2015).Decayed seed percentage (%): Data regarding decayed seed percentage have displayed in Table 2. The difference between primed and non-primed seed was significant and primed seed have minimum decayed seed percentage as compared to non-primed seeds. Lowest decayed seed percentage (26.66%) was recorded when 2% KNO3 was applied followed by 30% when 500 ppm GA3) was applied. Whereas maximum decayed (66.66%) of seeds was occurred in untreated seeds. It is reported that scarified treatments have improved germination as compared to non-scarified seeds. Decayed seed percentage might be highest in control due to impermeability of hard seed coat (Fallahabadi et al., 2012).Time of germination (days): Potassium nitrate showed a statistically significant effect on reducing the germination time (Table 2). Minimum time of germination (59.41 days) was recorded in seeds treated with 2% KNO3 followed by 3% and 4% KNO 3 levelswhich took 63.81 days and 72.15 days respectively while maximum time duration was taken by control (204.58 days). Reduction in seed germination time was occurred when seeds of Descurainia sophia and Plantago ovate were primed with 0.3% KNO3 (Ali et al., 2010; Gashi et al., 2012). Stimulating effect of nitrate for seed germination might be due to dormancy breakage (Hilhorst, 1990). It stimulates oxygen uptake (Hilton and Thomas, 1986) and KNO3 act as co-factor for phytochrome (Mavi et al., 2006).Number of leaves: Analysis of data showed that number of leaves influenced by different treatments. Hormonal priming with 2% KNO3 gave maximum number of leaves per seedling followed by priming with 3% KNO3, 4% KNO3 and in 500 ppm GA3, 750 ppm GA3 and  1000 ppm GA3 in improving number of leaves per seedling as compared to other physical priming treatments, while results of minimum number of leaves were achieved in non-primed seeds. It was suggested that potassium is an important macronutrient that plays a key role in carbohydrate metabolism and photosynthesis (Marschner, 2011; Kazemi, 2013).Seedling height (cm): Analysis of variance exposed that there was a significant difference between primed and non-primed seed for seedling height (Table. 2). It was found that maximum seedling height was 19.33 cm influenced by 3% KNO3 while minimum 11.33 cm observed in 90oC hot water. It is reported that foliar application of K, improved the chlorophyll and fruits-NK content (Sarrwy et al., 2010; Marschner, 2011; Kazemi, 2013).CONCLUSIONThe present study was undertaken to assess the effect of different priming treatments on seed germination of Cycas revoluta L. The results of the study clearly indicated that germination rate and germination value were maximum at lower concentration of gibberellic acid (500 ppm GA3). 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