LASER IRRADIATION EFFECTS on SCORZONERA (Scorzonera Hispanica L.) SEED GERMINATION and SEEDLING EMERGENCE
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ISSN 1644-0692 www.acta.media.pl Acta Sci. Pol. Hortorum Cultus, 14(2) 2015, 145-158 LASER IRRADIATION EFFECTS ON SCORZONERA (Scorzonera hispanica L.) SEED GERMINATION AND SEEDLING EMERGENCE Marcela Krawiec, Agata Dziwulska-Hunek, Agnieszka Sujak, Salwina Palonka University of Life Sciences in Lublin Abstract. Laser stimulation is a non-expensive and environmentally safe way of the im- proving of seeds quality. The objective of the study was to determine the effect of He-Ne laser irradiation on the germination parameters of scorzonera seeds. Seeds were character- ized with different quality expressed by germination capacity. Experimental material con- sisted of 4 lots of scorzonera seeds having initial germination capacity between 50.8 and 93.0%. Seeds were treated with laser He-Ne light of surface power density of 3 mW·cm-2 and the time of exposition of 0 (control), 1, 5, 10 and 30 minutes. After pre-sowing stimu- lation of seeds the following parameters were estimated: germination energy, germination capacity, mean germination time, speed of germination, hypocotyl length, length of radi- cle, fresh and dry weight of seedling, field emergence, mean emergence time and speed of emergence. Pre-sowing laser treatment resulted in increasing of the several parameters such as germination energy, germination capacity, speed of germination, hypocotyl and radicle length, as well as fresh and dry weight of seedlings. Laser light stimulation was the most effective in the case of low quality seeds (initial germination capacity of 50.8%). Irradiation of the seeds belonging to this group also resulted in the increase of the seedling emergence and the speed of emergence. Key words: scorzonera, He-Ne laser light, seed quality, germination capacity, emergence INTRODUCTION Scorzonera hispanica L. is known like a root vegetable mostly in Europe. It is called a scorzonera, black salsify, black oyster plant or viper’s grass. Black salsify, which originates from Southern Europe, is a perennial frost-hardy meadow plant. In cultivation it is treated like a biennial. In first year it forms a leaf rosette and a taproot, up to 0.5 m Corresponding author: Marcela Krawiec, University of Life Sciences in Lublin, Poland, Leszczyńskiego 58 Street, 20-068 Lublin, e-mail: [email protected] © Copyright by Wydawnictwo Uniwersytetu Przyrodniczego w Lublinie, Lublin 2015 146 M. Krawiec, A. Dziwulska-Hunek, A. Sujak, S. Palonka long, that has a milky white interior with dark brown or blackish skin. It is the taproot which is most often eaten as a vegetable. Young leaves are used as a salad. In the sec- ond year, the inflorescence stems and seeds are formed [Nuez and Bermejo 1994, Kilian et al. 2009]. Roots of this vegetable may be consumed raw, cooked and as well as fro- zen or canned food [Nuez and Bermejo 1994]. Scorzonera is known for the high content of polysaccharide inulin in its root. This compound as a prebiotic stimulates growth of the useful intestinal bacteria (Bifidobacteria species and other bacteria), thanks to mak- ing the operation of the alimentary canal more efficient, thus preventing constipation [Kelly 2008]. Scorzonera is propagated from the seed. The achenes are 10 to 20 mm long, cylin- drical, whitish and rough [Nuez and Bermejo 1994]. Scorzonera belongs to vegetables which seed quite quickly loose its viability. Under good storage conditions seed main- tain a high germination capacity for only two years [Stephens 1994]. Therefore the challenge of the modern agriculture is to accomplish high crop yield of the cultivated plants with usage of environmentally friendly agricultural methods. The important factor increasing crop is usage of a high quality sowing material charac- terized with high germination capacity and delivery of the rapid and uniform seedling emergence. Laser light irradiation, magnetic or electric field treatment are the environ- mentally friendly physical methods of improving seed quality [Pietruszewski 2002, Soltani et al. 2006, Gładyszewska 2011]. Particularly beneficial effects were observed after application of laser light. Laser is the device producing monochromatic and coher- ent light with a parallel beams. Due to a very narrow emission line and a parallel beams it is possible to focus the laser radiation within the very defined area and to obtain a relatively high power density [Hoffmann 1996]. The laser stimulation method uses the physical phenomenon consisting of the ability to absorb and store light energy, trans- form into chemical energy, store it and use it in the growth, later [Gładyszewska 2011]. In most experiments He-Ne lasers are applied. Single cases of application of semicon- ducting, argon or CO2 lasers happen. Domination of the He-Ne lasers is strictly con- nected to its characteristic wavelength of 632.4 nm which corresponds to red light as- signed as having the positive effect on plants [Dziwulska 2006]. Experiments conducted in different laboratories indicate the positive effect of irra- diation of the seeds on the growth and development of the cultivating plants. Results obtained by different groups indicate that the pre-sowing laser treatment influences mostly the process of seed germination and the seedling growth at the very early stages [Dziwulska 2006, Muszyński and Gładyszewska 2008, Dziwulska-Hunek et al. 2009, Soliman and Harith 2010, Sujak et al. 2013]. Some authors showed that in some cases the effects of laser irradiation occur also in the later development stages which results in the increasing of the crop yield, improvement of crop quality, acceleration of the plant growth and ripening, increase of the plant mineral content or the increase of the plant resistance to stress [Vasilevski and Bosev 1997, Truchliński et al. 2002, Podleśny and Podleśna 2004, Sujak et al. 2009, Ćwintal and Dziwulska-Hunek 2013]. Many authors demonstrate that the success of stimulation caused by monochromatic and low intensity laser light is dependent on wavelength, irradiation time and irradiation dose [Rybiński 2000, Hernandez et al. 2006, 2010, Soliman and Harith 2010]. Lower doses of laser light activate plants, resulting in increasing bioenergetical potential of the _____________________________________________________________________________________________________________________________________________ Acta Sci. Pol. Laser irradiation effects on scorzonera (Scorzonera hispanica L.) seed germination... 147 cell and higher activation of their biochemical and physiological processes. Higher doses influence genetical material of the cell leading to genetic changes of plant traits [Rybiński 2000]. Usually the seeds of high quality were subjected to experiments on the effect of the pre-sowing laser irradiation. Often unexpected circumstances force to sow the seeds of the reduced quality such as old, defective or improperly stored. Such sowing material produces weak and thinned out field emergences what negatively affects the crop yield. The objective of the presented study was to determine the effect of laser irradiation on the germination of scorzonera seeds of different quality and on its emergence. MATERIAL AND METHODS Experiments were conducted in the year 2013 in the Department of Physics and in the Department of Horticultural Seed Production and Nursery of the Life Sciences Uni- versity in Lublin, Poland. The experimental material consisted of 4 lots of scorzonera seeds cv. ‘Maxima’. Seeds collected in the years 2009, 2010, 2011 and 2012 (marked as lots 1, 2, 3 and 4, respectively) were used. Seeds were characterized with different qual- ity expressed by an initial germination capacity (tab. 2). Seeds were stored in the fridge at the temperature of 5°C. The meteorological conditions in the years of seed harvest were very similar and did not differ the germination capacity. While measuring 3 months after harvest it oscillated between 85 and 90%. Seeds were stimulated with the He-Ne light of a surface power density of 3 mW·cm-2 and the exposition times of 0 (control), 1, 5, 10 and 30 min. The appliance using the method of variable energy doses was used [Koper 1996] with the vertical direction of interacting with seeds He-Ne laser beam. Laser beam falled from the top onto the seeds equally distributed underneath. The exposition time was measured with a timer. The following parameters were estimated after pre-sowing seed stimulation with la- ser light: germination energy, germination capacity, mean germination time, speed of germination, hypocotyl length, length of radicle, fresh and dry weight of seedling, field emergence, mean emergence time and speed of emergence. The assessment of the selected germination parameters was conducted under the standard germination test done in 4 repetitions on 100 of seeds from each experimental setting. Seeds were sown on moistened double blotting paper on the day following laser stimulation. Then they were rolled up and placed upright in containers. The containers were covered with plastic bags. The seeds germinated in a thermostat at temperature of 20°C (±1°C), in darkness. The conditions of the seeds germination followed all routine seed testing rules given by ISTA [2004]. The germination energy (expressed in terms of the rate of normally germinating seeds) was calculated after 4 days from sowing the seeds on blotting paper, while the germination capacity was estimated after 8 days [ISTA 2004]. Everyday counting of the normally germinating seeds allowed for estimation of the mean germination time based on Pieper’s coefficient [W] and of the speed of