View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Universiti Putra Malaysia Institutional Repository ISSN: 1511-3701 Pertanika J. Trop. Agric. Sci. 33 (2): 243 - 250 (2010) © Universiti Putra Malaysia Press Dormancy and Cardinal Temperatures during Seed Germination of Five Weedy Rice (Oryza spp.) Strains Adam B. Puteh*, Roziah Rosli and Rosli B. Mohamad Department of Crop Science, Faculty of Agriculture, Universiti Putra Malaysia, 43400 UPM, Serdang, Selangor, Malaysia *E-mail: [email protected] ABSTRACT Temperature during seed imbibition has been found to influencegermination rate and final percentgermination. Seeds of one cultivated variety and five weedy rice strains, collected from different localities in Peninsular Malaysia, were used to determine their degree of dormancy and cardinal temperatures. Meanwhile, standard germination and tetrazolium chloride (TTC) tests were used to evaluate the percentage of seed viability and degree of dormancy. Seed germination test at six different constant temperatures (between 10 and 35oC) was applied to determine the cardinal temperatures estimated by linear regression models, base temperature, Tb, optimum temperature, To, and maximum temperature, Tc. The TTC test was found to be a simple and quick test to determine the degree of seed dormancy among different weedy rice strains, when used together with a standard germination test. Germination rate was found to be related to the degree of dormancy but it had no influence on the range ofcardinal temperatures. The Tb among the fiveweedy rice strains was in the range of o o o 2-7.3 C. The To varied between 28.1 and 37.5 C, with an average of 32.5 C. This temperature (To) was higher o o than that of the cultivated MR73 variety (24.3 C), whereas the range of Tc was 42.2-43.3 C. The study indicated that the non-dormant cultivated rice seed had lower Tb and To values than the dormant seed of weedy rice. Keywords: Weedy rice, germination, seed dormancy, cardinal temperatures INTRODUCTION the temperature range at which weedy rice Weedy rice (Oryza spp.) infestation occurs in seed germinates will help to predict seedling most major rice-growing areas of the world. emergence. The invasive nature of weedy rice has become Temperature is an important single factor a major concern, especially in direct seeded rice affecting the capacity for germination by cultivation. In Malaysia, the presence of weedy regulating dormancy, and it also critically rice in a direct-seeded field can reduce yield up determines the rate of progress toward to 74% (Bakar et al., 2000). Early shattering completion of germination once a seed is has enabled them to escape harvest, while seed stimulated (Alvarado and Bradford, 2002; dormancy ensures their survival in the soil seed Bradford, 2002). The degree of seed dormancy bank. The degree of infestation through soil seed influences the temperature range, at which seed bank germination varies between production will germinate, with the range increasing as years. Nonetheless, the reasons behind these seeds loose dormancy (Benech-Arnold et al., observations are not known. Thus, determining 2000; Vegis, 1964). These critical temperatures, Received: 3 April 2009 Accepted: 8 December 2009 *Corresponding Author Adam B. Puteh, Roziah Rosli and Rosli B. Mohamad which are commonly referred to as cardinal temperature during imbibition, and there has temperatures, consist of the base and maximum been no record of its cardinal temperatures temperatures, below or above which germination to date. Thus, understanding the variation will not occur, while the optimum temperature is in temperature during seed imbibition may where germination is the most rapid (Bradford, establish germination responses of weedy rice 2002). This concept was initially proposed on strains seedling emergence in the field. The the whole plant basis, but it is also applicable aims of this study were to (1) determine the to seed during germination. Bewley and Black cardinal temperatures, base (Tb), optimum (To) (1994) described cardinal temperatures as and maximum (Tc) of the different weedy rice the range of temperatures over which seeds strains, and (2) determine the germination rate of a particular genotype could germinate. In within these cardinal temperatures. cultivated rice varieties, a high percentage of germination is attained in two days at 27-37oC, MATERIALS AND METHODS while no germination is found to occur at 8oC and 45oC (Yoshida, 1981). However, the cardinal Plant Material temperatures for seed germination have never For the purpose of this study, five weedy rice been reported in weedy rice strains, which strains and one cultivated variety were used. are helpful for predicting the degree of seed Seeds of the cultivated variety MR 73 were dormancy and infestation in the field. obtained from the Malaysian Agriculture Models which describe seed germination Research and Development Institute (MARDI). behaviour, in response to a range of temperatures The seeds of five weedy rice strains were during imbibition, have been proposed and randomly collected from several locations developed (Covell et al., 1986; Ellis and in Malaysia, namely Seberang Perak, Kuala Butcher, 1988; Alvarado and Bradford, 2002; Pilah, Besut, Perlis, and Kemubu Agricultural Hardegree, 2006). The model commonly Development Authority in Peninsular Malaysia. known as the thermal time model has been Hereafter, these five strains are termed as SP, KP, extensively used and successfully applied Besut, Perlis and KADA strains, respectively. to describe germination timing and seedling The seeds were collected in January and emergence in crops (Finch-Savage and Phelps, February 2008 and stored at 0oC in double sealed 1993) and weed species (Roman et al., 2000). plastic bags for two months before conducting This particular thermal time model predicts the study. Seed moisture was kept in the range germination rate at sub-optimal temperatures of 9-11% prior to storage and at the start of the (from the minimum temperature to the optimum experiments. temperature) and supra-optimal temperature (i.e. from the optimum temperature to the maximum temperature) in a linear function (Hardegree, Seed Viability Tests 2006). The thermal time model has also been For standard germination test, the imbibing seeds successfully used to predict weeds seedling were left at ambient temperature in the laboratory emergence in the field under temperate growing at 25±3oC. The seeds were germinated on double conditions (Forcella et al., 2000; Vleeshouwers layered moistened (±10mL distilled water) filter and Kropff, 2000). papers (Whatman, no. 1, in 80 mm diameter by Natural selection on germination responses 10 mm deep disposable plastic Petri dishes. The to seasonal environmental cues in some seeds were soaked in 10% Clorox for surface species has been proposed as a significant sterilization for 3 min. prior to the testing. determinant for the genotype to establish in a Seedling evaluation on the number of given seasonal environment (Donohue, 2005). germinated seeds was done daily, starting on day However, little information is available on the 2 after imbibition for 14 days. Seeds which did germination responses of weedy rice strains to not germinate after 14 days were considered as 244 Pertanika J. Trop. Agric. Sci. Vol. 33 (2) 2010 Dormancy and Cardinal Temperatures during Seed Germination of Five Weedy Rice (Oryza spp.) Strains dead seeds. In contrast, seeds were considered The reciprocals of the time to germination were as germinated when the radical emergence was plotted to estimate the optimum temperature, at >5 mm. The test was replicated twice with 50 which the rate of germination was maximum seeds per replication. (To). The rates of germination were also For the tetrazolium chloride test, two subjected to the linear regression analysis to replicates of 50 seeds per replicate were imbibed describe cumulative germination response in distilled water at room temperature for 24 h. of temperature (SAS Institute, 2005). The The middle portion of the seeds was pierced cumulative percentage germination (CGP), with a needle before soaking them in 0.1% of obtained from the germination tests at different 2, 3, 5-triphenyl tetrazolium chloride (TTC) temperatures, were used to calculate the cardinal salt solution. The seeds imbibing in the TTC temperatures. Intersected-line models were solution were exposed to 35oC in the oven for used as proposed by Garcia-Huidobro et al. 2 h. Viable seed was evaluated based on the (1982). The equation used to describe the rates topographical staining pattern on the embryo, as of germination between base and up to optimum described in the ISTA procedure (ISTA, 1993). temperatures is as follows: 1/t = (T – Tb)/θ1 (1) Seed Germination Test at Different Temperature In order to describe the germination responses A germination test at different temperatures for above To, but below the maximum temperature all the seeds was conducted in the germination (Tc), equation (2) was used: chamber in darkness. Nonetheless, the 1/t = (Tc – T)/θ2 (2) preliminary works did not show any seed sensitivity to light during germination (Rosli, where t is the time taken in days for the CGP 2008). Meanwhile, the preparation of seeds and to reach a given percentage, T is the temperature, imbibition media are similar to the procedures while Tb, To and Tc are the base, optimum and used for the standard germination test, as maximum temperatures, respectively. These described above. The imbibing seeds were models predict the germination rate for a given exposed to the constant temperatures of 10, seed fraction (sub-optimal and supra-optimal 15, 20, 25, 30, or 35oC. This experiment was range) in a linear function of temperature. The performed in two replications consisting of 50 intercepts of the fitted linear regression lines on seeds per replicate. Seeds were considered as the temperature axes were used to estimate Tb germinated when the radicle was >5 mm. The and To. To, was calculated as the intercept of sub- evaluation was done daily for 20 days, beginning optimal and supra-optimal temperature function on Day 2 after sowing.