Norsazwan, Sinniah, Puteh, Namasivayam, Mohaimi and Aminuddin (2020). Seed Science and Technology, 48, 1, 49-55. https://doi.org/10.15258/sst.2020.48.1.07
Research Note
Temperature fluctuation improves oil palm (Elaeis guineensis) dura × pisifera seed germination
M.G. Norsazwan1, U.R. Sinniah1*, A.B. Puteh1, P. Namasivayam2, M. Mohaimi3 and I.A. Aminuddin3
1 Department of Crop Science, Faculty of Agriculture, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia (E-mail: [email protected]) 2 Department of Cell and Molecular Biology, Faculty of Biotechnology and Biomolecular Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia 3 Sime Darby Research Sdn Bhd, Jalan Klang Banting, Kelanang, 42700 Banting, Selangor, Malaysia *Author for correspondence
(Submitted June 2019; Accepted January 2020; Published online February 2020)
Abstract
Oil palm is mainly propagated using dura × pisifera (D × P) hybrid seeds. Among the issues in D × P seed production are relatively poor seed germination and uniformity, despite heat treatment at 40°C to break dormancy. The conditions for germination post-heat-treatment may be a contributing factor. This study aimed to evaluate and compare the effect of constant 30°C or ambient temperature fluctuation at two different locations, Sime Darby Oil Palm Breeding Seed Processing Renggam, Johor and the Seed Production Unit (SPU) Banting,
Selangor on oil palm D × P seed germination. At both locations, final mean germination percentage and speed were higher at fluctuating temperatures compared with constant 30°C. Under fluctuating conditions, the Oil Palm Breeding Seed Processing Renggam environment resulted in higher germination (85.8%) compared with SPU Banting (69.8%). Thus, the higher temperature amplitude (difference between daily maximum and minimum temperatures) was an important factor, resulting in higher germination. Therefore, oil palm can be germinated under ambient temperature conditions to obtain higher germination than under constant temperature, avoiding the need for maintaining expensive constant temperature germination rooms. In addition, a sufficiently high temperature amplitude can be beneficial in improving the ability to germinate and the speed of germination.
Keywords: D × P seeds, dormancy, germination, oil palm, temperature amplitude, temperature fluctuations
Experimental and discussion
The oil palm, Elaeis guineensis Jacq., is regarded as the highest yielding oilseed grown commercially in the world. On average, only 0.26 hectares of land is needed to produce one tonne of oil in comparison with other oilseeds such as soybean, sunflower and rapeseed, which require 2.22, 2.0 and 1.52 hectares, respectively (Corley and Tinker, 2003).
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49 M.G. NORSAZWAN, U.R. SINNIAH, A.B. PUTEH, P. NAMASIVAYAM, M. MOHAIMI AND I.A. AMINUDDIN
The majority of the commercial oil palm trees planted in the world are propagated from dura × pisifera (D × P) hybrid seeds. The D × P hybrid seedlings will then grow to produce fruitlets, that exhibit a thin endocarp with high mesocarp content and reasonable kernel size (Corley and Tinker, 2003; Fondom et al., 2010). In Malaysia, the production and distribution of D × P seeds (in the form of pre-germinated seeds) to major plantations or smallholders are conducted by licensed seed producers approved by the Malaysian Palm Oil Board (MPOB). All these producers are required to adhere to a standardised production system (Department of Standards Malaysia, 2005). D × P seeds are produced through the process of controlled pollination to prevent contamination from surrounding pollen source. The selected dura female inflorescence will be hand-pollinated with pisifera pollen. Malaysian Standards (2005) indicated that the selected dura palms must be covered with a polyethylene bag for at least seven days before, and four weeks after the controlled pollination commences. The fruit ripening generally happens between 20 to 24 weeks after pollination and is highly dependent on genotypic as well as environmental conditions (Corley and Tinker, 2003). However, for D × P seed production purposes, harvesting is done at approximately 20 weeks after pollination or less, to minimise loss due to natural detachment of oil palm fruitlets from the bunches. The harvested oil palm fruit bunch will then be processed to remove the mesocarp prior to germination. Oil palm seeds have been known to have exceptionally low germination in natural environments as they are highly dormant. It was reported that untreated D × P seeds recorded less than 25% germination after eight months (Norsazwan et al., 2016). Most of the studies conducted previously suggested that heat treatment was necessary to break the dormancy in oil palm seeds in order to enable germination to commence (Hussey, 1958; Rees, 1962; Corley and Tinker, 2003). To date, heat treatment of 40 ± 2°C for a period of 40 to 60 days prior to germination at 30 ± 2°C is practised by most commercial seed producers which results in, on average, 65% germination (Hussey, 1958; Corley and Tinker, 2003; Rao and Choong, 2014). In an attempt to increase the germination, most studies introduced various forms of treatments and assessed the direct effect on seed germination, with varying responses giving no concrete improvement in germination. It is known that seed dormancy and germination are two separate processes (Baskin and Baskin, 2004; Finch-Savage and Luebner-Metzger, 2006; Penfield, 2017). However, since it is a continuous progression it is hard to distinguish the mechanisms and factors specifically affecting each process. Norsazwan et al. (2016) showed that heat treatment prior to germination was able to accelerate embryo development as well as seed germination for D × P seeds. Theoretically, if dormancy has been successfully alleviated due to heat treatment, more seeds should germinate. However, despite the constant regime provided for germination of oil palm seeds after heat treatment, the variation in time to germinate as well as the percentage prompts questions regarding the effect of placing the seeds at constant temperature. Fluctuating temperature has been shown to play a vital role in seed germination of various species (Ellery, 2002; Brandel and Jensen, 2005; Liu et al., 2013). For instance, it was reported that many grassland species show improved germination when subjected to fluctuating temperature (Liu et al., 2013). This was attributed to fluctuating temperatures being a mechanism for seeds to detect gaps in vegetation canopies to induce germination.
50 OIL PALM SEED GERMINATION TEMPERATURE
Oil palm seedlings generally thrive well in a tropical environment with high daily temperature fluctuations along with rainfall throughout the year (Corley and Tinker, 2003). According to Laing and Evans (2011), the average diurnal changes in temperature in the tropics ranges between 6 and 10°C with minimum temperature at sunrise and maximum in the afternoon. This could possibly explain why current adoption of constant 30°C for germination by the majority of seed producers shows poor germination and low uniformity, despite the prior 40-60 days of heat treatment to break the seed dormancy (Norsazwan et al., 2016). Therefore, this study was designed to evaluate the effect of fluctuating temperature on oil palm D × P seed germination in comparison with the commercial practice of constant 30°C.
Freshly harvested D × P seeds from controlled pollination of CALIX600 dura mother palm sources were collected from Field PT100, Sime Darby Research, Banting, Malaysia at 20 weeks after pollination. Seed samples were subjected to the standard Sime Darby Research processing method. After being de-pericarped, seeds were treated with 0.05% benomyl 50% WP (95% a.i) solution for five minutes to prevent fungal infection. Seed samples were then air-dried at ambient temperature inside plastic containers while checking for damage or mesocarp remnants. The seeds were then subjected to heat treatment of 40 ± 2°C for 60 days. After that, the treated seeds were imbibed in water for seven days before commencing the germination test. The germination test was conducted as a two-factor nested design (location and temperature). This study was carried out at two different locations; Sime Darby Seed Production Unit (SPU) Banting (2°48'08.5 N 101°27'26.9 E), Selangor and Oil Palm Breeding (OPB) Seed Processing Renggam, Johor (1°52'37.1 N 103°22’56.1 E). At each location, imbibed oil palm D × P seeds were separated into plastic bags containing three replicates of 200 seeds. Each of the plastic bags with seeds was then placed in two different rooms; one with controlled 30 ± 2°C and another under ambient temperature fluctuations for 60 days. A datalogger was placed to monitor and record both daily temperature and relative humidity changes. Normal germinated seeds were monitored daily by recording number of seeds showing emergence of radicle protrusion from the fibre plug according to Sime Darby Research standard evaluation procedures. Mean germination time ( MGT) was evaluated as given below, modified from Ellis and Roberts (1980): ∑(nT) MGT = ∑n Where, n = number of germinated seeds T = germination day ∑n = final germination count
Analysis of variance was performed using SAS 9.4 (SAS Institute, Cary, NC).
Significant levels of P ≤ 0.05 were used for LSD test in evaluating the effect of temperature that was nested in each study location.
Oil palm D × P seeds germinated significantly higher at fluctuating temperatures in comparison with constant 30°C (figure 1). On average, OPB Seed Processing Renggam and SPU Banting recorded 85.8 and 69.8% final germination, respectively when
51 M.G. NORSAZWAN, U.R. SINNIAH, A.B. PUTEH, P. NAMASIVAYAM, M. MOHAIMI AND I.A. AMINUDDIN
30°C Fluctuating temperature 100 a
80 a b 60 b
40
20 Final germination (%) 0 Renggam Banting Location
Figure 1. Final germination percentage of oil palm D × P seeds after 60 days at two different locations and germination temperatures. The letters a and b shows that there is signifi cant difference between germination at 30°C compared with germination at fl uctuating temperature at each location. germinated under ambient fluctuating temperatures. Germination was 15-21% lower for seeds germinated at constant 30°C. Similarly, ambient fluctuating temperature in both OPB Seed Processing Renggam and SPU Banting recorded significantly faster germination with mean germination time of approximately 17 to 19 days as compared with more than 24 days at 30°C. Temperature has been shown to be one of the most important variables influencing germination (Milbau et al., 2009). Most tropical agricultural seeds germinate well at temperatures ranging between 20 and 30°C. However, other studies have indicated that seeds of some species require diurnal temperature fluctuations for favourable seedling establishment (Thompson et al., 1997). Oil palm seeds could be such a species, where germination is significantly influenced by temperature fluctuation, as shown based on the studies conducted in two geographically distinct locations. Higher germination in OPB Seed Processing Renggam could be attributed to higher differences between maximum and minimum daily temperature changes in comparison to SPU Banting (figure 2). In this study, OPB Seed Processing Renggam consistently recorded significantly higher temperature amplitude as compared with SPU Banting with averages of 6.9 and 3.5°C, respectively. The resulting cumulative germination also showed positive correlation with increasing amplitude. In the field, these daily temperatures can be different under a plant canopy or in an open field. Generally higher temperature amplitudes were found near a soil surface in open habitat, but lower under a plant canopy (Benech Arnold, 1988). Roberts (1988) mentioned that the most important aspect for fluctuating temperature environment was amplitude, which is the period of exposure above and below the median temperature as well as the number of fluctuation cycles. Mean temperatures recorded during the germination test period: 28.9°C at OPB Seed Processing Renggam and 28.7°C at SPU Banting were similar, however the final germination percentage differed markedly. Based on these findings, it is evident that oil palm seeds germinate better at fluctuating temperature, provided that the daily temperature amplitude is high enough to promote germination.
52
OIL PALM SEED GERMINATION TEMPERATURE Cumulative germination (%) germination Cumulative ) 100 80 60 40 20 0 ) and SPU Banting ( ) for 60 days after imbibition. Germination time (day after imbibition) , Banting 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
8 6 4 2 0
18 16 14 12 10 Temperature amplitude (ºC) amplitude Temperature with respective cumulative germination percentage (Renggam Figure 2. Daily temperature amplitude (differences between maximum and minimum temperatures) of OPB Seed Processing Renggam ( Figure 2. Daily temperature amplitude (differences
53 M.G. NORSAZWAN, U.R. SINNIAH, A.B. PUTEH, P. NAMASIVAYAM, M. MOHAIMI AND I.A. AMINUDDIN
Untreated D × P seeds recorded less than 25% germination after 32 weeks of evaluation (Norsazwan et al., 2016). The use of heat treatment followed by current adoption of 30°C for germination by most oil palm seed producers allows germination to commence albeit lower germination by 15-21%, with longer mean germination time. The requirement of higher temperature amplitude for germination can be linked to oil palm ecology. In the field, oil palm seeds are naturally dispersed underneath the plant canopy upon maturation. It is believed that the heat from the soil and mesocarp degradation breaks the seed dormancy and allows germination to commence (Corley and Tinker, 2003). For that reason, it is very common to see voluntary oil palm seedlings (VOPS) establish, particularly in a more mature field environment. However, natural germination of oil palm seeds is generally very slow due to its complex dormancy characteristics (Norsazwan et al., 2016). In other species, such as Eupatorium cannabinum L., an increase in seasonal temperature amplitude from 10°C (mid-April) to 17°C (mid- May) resulted in a 40% increase in germination (Brandel and Jensen, 2005). Similarly, in Arctotheca calendula, exposure to a temperature regime which simulates the daily summer soil surface temperature cycle was needed for efficient dormancy release and germination (Ellery, 2002). In conclusion, oil palm seeds had higher germination percentages and speed at fluctuating temperatures in comparison with the commercial practice of constant 30°C, based on studies conducted at two different seed production stations. Therefore, current adoption of constant 30°C during germination by the majority of oil palm producers is not optimal. Significant cost reduction can be achieved by germinating seeds in a room with ambient temperature fluctuations instead of maintaining 30°C throughout the year. Further studies are needed, to determine the optimum temperature amplitude range and cycles to enable higher germination with better uniformity.
Acknowledgements
We are extremely grateful to Sime Darby Research Sdn Bhd. for providing us with the materials, facilities and technical assistance throughout this study. Highest appreciation goes to Dr. David Ross Appleton (Head of Department, Biotechnology and Breeding, Sime Darby Research) for his valuable insights and comments on this manuscript. We also thank the Ministry of Higher Education Malaysia and Universiti Putra Malaysia for the financial support through SLAB scholarship and Junior Academic Scheme during this study period.
References
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54 OIL PALM SEED GERMINATION TEMPERATURE
Copeland, L.O. and McDonald, M.B. (2001). Seed germination. In Principles of Seed Science and Technology, 4th Edition, pp. 72-123, Springer Science and Business Media, New York. Corley, R.H.V. and Tinker, P.B. (2003). Seed germination and nurseries. The Oil Palm, 4th Edition, pp. 225-239, Blackwell Science, Oxford. Department of Standards Malaysia (2005). Oil Palm Seeds for Commercial Planting- Specification (Third Revision), Malaysian Standard MS 157: 2005, Standards and Industrial Research Institute of Malaysia Berhad, Selangor. Ellery, A.J (2002). Embryo dormancy responses to temperature in capeweed (Arctotheca calendula) seeds. Seed Science Research, 12, 181-191. Ellis, R.H. and Roberts, E.H. (1980). Towards a rational basis for testing seed quality. In Seed Production, (Ed. P.D. Hebblethwaite), pp. 605-635, Butterworths, London. Finch-Savage, W.E. and Leubner-Metzger, G. (2006). Seed dormancy and the control of germination. New Phytologist, 171, 501-523. Fondom, N.Y., Etta, C.E. and Mih, A.M. (2010). Breaking seed dormancy: revisiting heat-treatment duration on germination and subsequent seedling growth of oil palm (Elaeis guineensis Jacq.) progenies. Journal of Agricultural Science, 2, 101-110. Griffin, C. (2017). Temperature signals in seed germination. Science, 356, 1347-1348.
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