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Effects of different light types on root formation of Ocimum basilicum L. cuttings
Scientia Horticulturae 164 (2013) 552–555
Contents lists available at ScienceDirect
Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti
Effects of different light types on root formation of Ocimum basilicum L. cuttings You Jin Lim, Seok Hyun Eom ∗ Department of Horticultural Biotechnology, College of Life Sciences, Kyung Hee University, Yongin, Gyeonggi 446-701, Republic of Korea
a r t i c l e
i n f o
Article history: Received 28 January 2013 Received in revised form 10 September 2013 Accepted 29 September 2013 Keywords: Cuttings Propagation Light emitting diodes Sweet basil
a b s t r a c t Sweet basil is usually propagated by cuttings due to the ease of this method and the ability to establish mature plants quickly. However, slow root formation in this method limits early stage plant growth. To improve the efficiency of root formation, we evaluated the effects of different types of light on sweet basil cuttings. Basil cuttings were initially separated into NAA or non-NAA treatment groups to evaluate hormonal effects on rooting. Then, basil cuttings were irradiated with red, blue, fluorescent light, or natural sunlight for 16 h per day. Adventitious root and shoot fresh weights as well as chlorophyll content were measured at 2, 4, and 6 weeks. Blue light was the most effective at improving root formation. Root establishment was about three times faster upon treatment with blue light than natural sunlight; root growth under blue light for 2 weeks was similar to that under natural sunlight for 6 weeks. NAA treatment of the cutting surface significantly improved root growth under blue light as compared with non-NAA treatment. The effects of NAA treatment on growth under other light types were not significantly different. However, longer exposure to blue light resulted in leaf etiolation of older leaves. Our results indicate that use of blue LEDs to irradiate basil cuttings significantly reduced the time required for both root formation and the development of conventional cuttings compared to other light types. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Ocimum basilicum L. (sweet basil), a member of the family Lamiaceae, is native to India and other Southeast Asian countries. It is popularly cultivated worldwide as a food additive and herb. Although seed propagation is widely used to propagate O. basilicum (Heywood, 1978), poor germination rates spurred the development of alternative propagation methods (Purcino et al., 2012). Furthermore, seed propagation requires relatively long periods of seedling growth. Cutting is an alternate basil propagation method that results in rapid growth. Conventional cuttings are usually propagated in greenhouses under either artificial light or natural sunlight (Preece and Huetteman, 1991; Purcino et al., 2012). Successful propagation of cuttings in many plants requires about 6 weeks (Ofori et al., 1996; Tchoundjeu and Leakey, 1996). This relatively long growth period limits the efficient use of facilities and energy, thereby decreasing cost efficiency. A reduction in the cutting production period would therefore be of economic benefit to the nursery industry. Light control is one of the main factors required for efficient root formation along with other environmental factors such as temperature and humidity (Mortensen and Strømme, 1987; Rein et al.,
∗ Corresponding author. Tel.: +82 312013860. E-mail address: [email protected] (S.H. Eom). 0304-4238/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scienta.2013.09.057
1991). The need to control temperature and humidity to propagate cuttings has already been well established. In contrast, light quality strongly affects photosynthesis, chlorophyll formation, shoot and root elongation, flower bud formation, and seed germination and rooting. Light-emitting diodes (LEDs) have recently been introduced as an irradiation source for plants to facilitate vegetative growth. Advantages of LEDs versus other electric light sources include longevity, safety, wavelength specificity, small mass and volume, and being a solid-state device (Barta et al., 1992; Bula et al., 1991). Among the visible light spectrum, red and blue light not only affect photosynthesis, but also plant development and morphology. Blue light is necessary for the morphologically healthy growth of plants (Okamoto et al., 1996). The important roles of blue light include stomatal control that affects transpiration (Schwartz and Zeiger, 1984), CO2 exchange, stem elongation (Cosgrove, 1981), phototropism (Blaauw and Blaauw-Jansen, 1970), and inhibition of seedling growth in growth medium (Thomas and Dickinson, 1979). In contrast, red light plays a major role in plant photosynthesis. Under red light, plantlet leaves undergo elongation and show reduced chlorophyll content (Lacona and Muleo, 2010; Nhut et al., 2003). Further, red light leads to randomization of hypocotyl orientation (Hangarter, 1997; Robson and Smith, 1996). Although the high cost of LEDs has limited their application in commercial-scale farming, LED systems could benefit both vegetative propagated production and sprout production, because these systems do not require long growth periods or large plant
Y.J. Lim, S.H. Eom / Scientia Horticulturae 164 (2013) 552–555
sizes (Bula et al., 1991). In this study, we evaluated the efficacy of different light sources in establishing sweet basil cuttings. 2. Materials and methods 2.1. Plant materials Sweet basil seed was purchased from Chung-ang Flower Seed Company (An-yang, Korea) who imported it from the Netherlands in 2010. Fresh shoots were cut from mature sweet basil plants grown in a greenhouse for 3 months. Cuttings were about 8 cm in length. Four leaves from the bottom part of each cutting were removed. Individual cuttings were initially weighed and then planted in 24-well plug trays (7 cm × 7 cm × 8 cm) containing vermiculite. Two treatments were applied to the cut surface: the cut surface was coated with NAA powder (0.4% 1-naphthylacetamide powder, ISK Co., Japan) or the cut surface was not treated with NAA. 2.2. Light irradiation and growth conditions Light sources used in this experiment were red (625 nm) and blue (460 nm) LEDs (P5II model supplying 3.3 V and 1 W per module, Seoul Semiconductor, Seoul, Korea), fluorescent light (FL), and natural sunlight (GH). FL was used as a positive control for artificial light because it contains the entire visible light spectrum range and is commonly used for in vitro plant culture. Plug trays containing planting basil cuttings were placed under red LEDs (RL), blue LEDs (BL), FL, or GH. GH was maintained at 23 ± 3 ◦ C for 16 h a day and above 21 ± 2 ◦ C at night. A culture room with LED and FL chambers was maintained at 24 ± 2 ◦ C by air- and temperature-controlling ventilation. Irradiation intensity of artificial light was set to 30 mol m−2 s−1 . Photoperiod was set to 16 h per day. Humidity in the culture room was maintained between 60 and 70%. Plants were irrigated with distilled water daily as required during the experimental period. 2.3. Plant growth and chlorophyll measurement Cuttings were weighed initially before planting and again after 2, 4, and 6 weeks of culture under different light treatments. Four cuttings per 24 plant-potted plate were collected every 2 weeks to measure root and shoot fresh weights and chlorophyll content. Plant growth was determined based on the difference between the collected sample fresh weight and initial fresh weight. For chlorophyll analysis, leaves of another four cuttings in the 24 plant-potted plate of each light treatment were selected and collected every 2 weeks for 6 weeks after initiation of the experiment. Chlorophyll analysis of young leaves positioned on the third part from the growing tip was performed. Fresh leaf tissue (0.013–0.015 g) was extracted in 2 ml of 99.9% methanol for 48 h at 4 ◦ C in a dark chamber. Extracts were filtered using 0.45 m cellulose acetate syringe filters (DISMIC® -13cp, Toyo Roshi Kaisha Ltd., Japan). Absorbance was measured at both 645 nm and 663 nm using a spectrophotometer (S-4100, Scinco, Seoul, Korea). Total chlorophyll content was calculated using the following formula (Arnon, 1949; Mackinney, 1941): total chlorophyll (mg g−1 fresh wt.) = (8.02 × A663 + 20.20 × A645 ). 2.4. Statistical analysis Biomass and length of basil plants are presented as means with standard errors for each treatment. Means of all data were subjected to standard ANOVA procedures using SAS software (SAS version 9.2, SAS Institute Inc., Cary, NC, USA). Significant
553
differences among treatment means were determined at the 5% level using Duncan’s multiple range test.
3. Results and discussion Sweet basil cuttings grown under different light treatments (GH, FL, BL, and RL) were harvested every 2 weeks, and their root and shoot fresh weights as well as chlorophyll content were measured. Cuttings were initially divided into two groups: NAA treatment or non-NAA treatment. BL induced faster root formation than the other light treatments. As shown in Fig. 1, root fresh weight in the BL treatment group was about 4.3 times higher than that in the FL treatment group. Root growth in response to BL treatment increased significantly until 6 weeks. Other light treatments induced slow increases in root growth until 6 weeks as compared to BL treatment. Root growth under FL was the poorest among the light treatments. Auxin effect was observed under BL in the 2nd and 4th weeks of treatment and RL in the 4th week of treatment as root growth increased. The cutting surface subjected to NAA treatment displayed better root growth under BL than the non-NAA treatment. Cuttings treated with or without NAA were not significantly different from one another at two weeks of GH, FL, or RL treatment; the exception was cuttings grown under BL. Adequate light quality for root growth appears to be plant species specific. In the case of tomato seedling cuttings, effective rooting has been observed under continuous white light irradiation, whereas root formation is reduced under darkness, red, or blue light (Tyburski and Tretyn, 2004). Blue light significantly retarded root formation of Prunus serotina axillary shoot cuttings, whereas yellow light induced the highest rooting percentage and root growth (Fuernkranz et al., 1990). In the sweet basil cuttings, shoot growth was stimulated continuously by RL treatment for 6 weeks, whereas other light treatments only slightly increased shoot growth (Fig. 2). BL treatment induced vigorous shoot growth only during the initial period of light treatment. RL and BL treatment induced similar increases in shoot growth until 2 weeks. However, after 2 weeks, shoot growth induced by RL treatment maintained a faster growth pattern, whereas that induced by BL treatment increased only slightly (Fig. 2). Shoot growth under GH was the slowest. No hormonal effect on shoot growth was observed for any of the light treatments. Mortensen and Strømme (1987) reported that plant height in tomato and chrysanthemum was strongly reduced by blue light treatment and increased by yellow and green light treatments. In our basil cutting study, regardless of NAA treatment, we found that shoot height under BL was not strongly inhibited (Fig. 3), whereas non-cuttings of tomato and chrysanthemum showed reduced height under BL. Efficient nutritional uptake was verified by strong and early root establishment under BL treatment. Total chlorophyll content of leaves subjected to GH or BL treatment decreased at 6 weeks as compared with chlorophyll content at 2 weeks, while chlorophyll content under FL and RL was similar for these two time periods. Chlorophyll content did not differ significantly according to light quality, culture period, or hormone treatment except for the second week of FL treatment. In cuttings not treated with NAA, total chlorophyll content under BL treatment decreased gradually from a fresh weight of 5.52 mg g−1 at 2 weeks to a fresh weight of 3.84 mg g−1 at 6 weeks. Under BL treatment, leaf etiolation progressed from the bottom of leaves. Hormonal effect on chlorophyll contents was not observed for any of the treatments (Table 1). It was previously reported that chlorophyll content in pea seedlings increased rapidly upon initial treatment with blue light compared to other light treatments (Wu et al., 2007). However, the increase was delayed when blue light treatment was continuous. We found that a long BL irradiation period resulted in chlorophyll
554
Y.J. Lim, S.H. Eom / Scientia Horticulturae 164 (2013) 552–555
Fig. 1. Effects of light type on the root growth of basil cuttings: (A) GH, (B) FL, (C) RL and (D) BL. Data represent the mean ± SE. Significant differences (p < 0.05) between non-NAA and NAA treatments according to Duncan’s multiple range are indicated by an asterisk.
Fig. 2. Effects of different light types on shoot growth of basil cuttings: (A) GH, (B) FL, (C) RL and (D) BL.
Y.J. Lim, S.H. Eom / Scientia Horticulturae 164 (2013) 552–555
555
Table 1 Total chlorophyll contents of basil young leaves grown under different light sources subjected to non-NAA or NAA treatment. Cultivation (weeks)
Hormonal treatment
GH
FL
RL
BL
Total chlorophyll content (mg g−1 fresh wt.) 2
Non-NAA NAA
4.90aa 4.57a
5.08a 6.01a*
6.04a 5.99a
5.52a 5.19a
4
Non-NAA NAA
5.18ab 5.04a
4.78bc 5.35a
5.86a 5.97a
4.11c 5.24a
6
Non-NAA NAA
4.13b 4.01b
6.01a 5.53a
5.93a 5.98a
3.84b 4.13b
a Different letters (a–c) in each row indicate significant difference at the level of p < 0.05 by Duncan’s test; mark (*) in the same light quality and cultivation periods comparison between hormonal treatment indicates significant difference at p < 0.05.
References
Fig. 3. Periodical root formation and shoot growth of basil cuttings under different light sources.
degradation. Therefore, BL should only be used to induce plant growth. BL treatment induced a darker green leaf color than natural sunlight (Mortensen and Strømme, 1987). 4. Conclusions In this study, we observed that root formation of basil cuttings was stimulated under BL treatment. BL is necessary for the healthy growth of plants (Okamoto et al., 1996). However, continuous plant exposure to BL for longer than 2 weeks could negatively affect the shoot growth of cuttings from crops with a similar leaf morphology to that of sweet basil. Nursery plant industry currently utilizes natural sunlight, fluorescent light, or shade partial light to stimulate the growth of sweet basil cuttings. Under these conditions, cutting production can be time-consuming and careful management is required for disease control and plant survival. Thus, we suggest using blue LED irradiation as an alternative method for efficient cutting production. Acknowledgements This study was supported by a grant from the Korea Healthcare Technology R&D Project, Ministry of Health & Welfare, Republic of Korea (Grant No. HI10C2162).
Arnon, D.I., 1949. Copper enzymes in isolated chloroplasts. Polyphenoloxidase in Betavulgaris. Plant Physiol. 24, 1–15. Barta, D.J., Tibbitts, T.W., Bula, R.J., Morrow, R.C., 1992. Evaluation of light emitting diode characteristics for a space-based plant irradiation source. Adv. Space Res. 12, 141–149. Blaauw, O.H., Blaauw-Jansen, G., 1970. The phototropic responses of Avena coleoptiles. Acta Botan. Neer. 19, 755–763. Bula, R.J., Morrow, R.C., Tibbitts, T.W., Barta, D.J., Ignatius, R.W., Martin, T.S., 1991. Light-emitting diodes as a radiation source for plants. HortScience 26, 203–205. Cosgrove, D.J., 1981. Rapid suppression of growth by blue light. Plant Physiol. 67, 584–590. Fuernkranz, H.A., Nowak, C.A., Maynard, C.A., 1990. Light effects on in vitro adventitious root formation in axillary shoots of mature Prunus serotina. Physiol. Plant. 80, 337–341. Hangarter, R.P., 1997. Gravity, light and plant form. Plant Cell Environ. 20, 796–800. Heywood, V.H., 1978. Flowering Plants of the World. Oxford University Press, UK, pp. 239–240. Lacona, C., Muleo, R., 2010. Light quality affects in vitro adventitious rooting and ex vitro performance of cherry rootstock Colt. Sci. Hortic. 125, 630–636. Mackinney, G., 1941. Absorption of light by chlorophyll solutions. Biol. Chem. 140, 315–322. Mortensen, L.M., Strømme, E., 1987. Effects of light quality on some greenhouse crops. Sci. Hortic. 33, 27–36. Nhut, D.T., Takamura, T., Watanabe, H., Okamoto, K., Tanaka, M., 2003. Responses of strawberry plantlets cultured in vitro under superbright red and blue lightemitting diodes (LEDs). Plant Cell Tissue Organ Cult. 73, 43–52. Ofori, D.A., Newton, A.C., Leakey, R.R.B., Grace, J., 1996. Vegetative propagation of Milicia excelsa by leafy stem cuttings: effects of auxin concentration, leaf area and rooting medium. Forest Ecol. Manage. 84, 39–48. Okamoto, K., Yanagi, T., Takita, S., Tanaka, M., Higuchi, T., Ushida, Y., Watanabe, T., 1996. Development of growth apparatus using blue and red LED as artificial light source. Acta Hort. 440, 111–116. Preece, J.E., Huetteman, C.A., 1991. Micro- and cutting propagation of silver maple. I. Results with adult and juvenile propagules. J. Am. Soc. Hortic. Sci. 116, 142–148. Purcino, M., Machado, M.P., Biasi, L.A., 2012. Effect of leaves on the rooting of cuttings of clove basil (Ocimum gratissimum L.) and anis (Ocimum selloi Benth.). Revista de Ciências Agroveterinârias 11, 93–98. Rein, W.H., Wright, R.D., Seiler, J.R., 1991. Propagation medium moisture level influences adventitious rooting of woody stem cuttings. J. Am. Soc. Hortic. Sci. 116, 632–636. Robson, P.R.H., Smith, H., 1996. Genetic and transgenic evidence that phytochromes A and B act to modulate the gravitropic orientation of Arabidopsis thaliana hypocotyls. Plant Physiol. 110, 211–216. Schwartz, A., Zeiger, E., 1984. Metabolic energy for stomatal opening: roles of photophosphorylation and oxidative phosphorylation. Planta 161, 129–136. Tchoundjeu, Z., Leakey, R.R.B., 1996. Vegetative propagation of African Mahogany: effects of auxin, node position, leaf area and cutting length. New Forests 11, 125–136. Thomas, B., Dickinson, H.G., 1979. Evidence for two photoreceptors controlling growth in de-etiolated seedlings. Planta 146, 545–550. Tyburski, J., Tretyn, A., 2004. The role of light and polar auxin transport in root regeneration from hypocotyls of tomato seedling cuttings. Plant Growth Regul. 42, 39–48. Wu, M.C., Hou, C.Y., Jiang, C.M., Wang, Y.T., Wang, C.Y., Chen, H.H., Chang, H.M., 2007. A novel approach of LED light radiation improves the antioxidant activity of pea seedlings. Food Chem. 101, 1753–1758.
Contents lists available at ScienceDirect
Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti
Effects of different light types on root formation of Ocimum basilicum L. cuttings You Jin Lim, Seok Hyun Eom ∗ Department of Horticultural Biotechnology, College of Life Sciences, Kyung Hee University, Yongin, Gyeonggi 446-701, Republic of Korea
a r t i c l e
i n f o
Article history: Received 28 January 2013 Received in revised form 10 September 2013 Accepted 29 September 2013 Keywords: Cuttings Propagation Light emitting diodes Sweet basil
a b s t r a c t Sweet basil is usually propagated by cuttings due to the ease of this method and the ability to establish mature plants quickly. However, slow root formation in this method limits early stage plant growth. To improve the efficiency of root formation, we evaluated the effects of different types of light on sweet basil cuttings. Basil cuttings were initially separated into NAA or non-NAA treatment groups to evaluate hormonal effects on rooting. Then, basil cuttings were irradiated with red, blue, fluorescent light, or natural sunlight for 16 h per day. Adventitious root and shoot fresh weights as well as chlorophyll content were measured at 2, 4, and 6 weeks. Blue light was the most effective at improving root formation. Root establishment was about three times faster upon treatment with blue light than natural sunlight; root growth under blue light for 2 weeks was similar to that under natural sunlight for 6 weeks. NAA treatment of the cutting surface significantly improved root growth under blue light as compared with non-NAA treatment. The effects of NAA treatment on growth under other light types were not significantly different. However, longer exposure to blue light resulted in leaf etiolation of older leaves. Our results indicate that use of blue LEDs to irradiate basil cuttings significantly reduced the time required for both root formation and the development of conventional cuttings compared to other light types. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Ocimum basilicum L. (sweet basil), a member of the family Lamiaceae, is native to India and other Southeast Asian countries. It is popularly cultivated worldwide as a food additive and herb. Although seed propagation is widely used to propagate O. basilicum (Heywood, 1978), poor germination rates spurred the development of alternative propagation methods (Purcino et al., 2012). Furthermore, seed propagation requires relatively long periods of seedling growth. Cutting is an alternate basil propagation method that results in rapid growth. Conventional cuttings are usually propagated in greenhouses under either artificial light or natural sunlight (Preece and Huetteman, 1991; Purcino et al., 2012). Successful propagation of cuttings in many plants requires about 6 weeks (Ofori et al., 1996; Tchoundjeu and Leakey, 1996). This relatively long growth period limits the efficient use of facilities and energy, thereby decreasing cost efficiency. A reduction in the cutting production period would therefore be of economic benefit to the nursery industry. Light control is one of the main factors required for efficient root formation along with other environmental factors such as temperature and humidity (Mortensen and Strømme, 1987; Rein et al.,
∗ Corresponding author. Tel.: +82 312013860. E-mail address: [email protected] (S.H. Eom). 0304-4238/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scienta.2013.09.057
1991). The need to control temperature and humidity to propagate cuttings has already been well established. In contrast, light quality strongly affects photosynthesis, chlorophyll formation, shoot and root elongation, flower bud formation, and seed germination and rooting. Light-emitting diodes (LEDs) have recently been introduced as an irradiation source for plants to facilitate vegetative growth. Advantages of LEDs versus other electric light sources include longevity, safety, wavelength specificity, small mass and volume, and being a solid-state device (Barta et al., 1992; Bula et al., 1991). Among the visible light spectrum, red and blue light not only affect photosynthesis, but also plant development and morphology. Blue light is necessary for the morphologically healthy growth of plants (Okamoto et al., 1996). The important roles of blue light include stomatal control that affects transpiration (Schwartz and Zeiger, 1984), CO2 exchange, stem elongation (Cosgrove, 1981), phototropism (Blaauw and Blaauw-Jansen, 1970), and inhibition of seedling growth in growth medium (Thomas and Dickinson, 1979). In contrast, red light plays a major role in plant photosynthesis. Under red light, plantlet leaves undergo elongation and show reduced chlorophyll content (Lacona and Muleo, 2010; Nhut et al., 2003). Further, red light leads to randomization of hypocotyl orientation (Hangarter, 1997; Robson and Smith, 1996). Although the high cost of LEDs has limited their application in commercial-scale farming, LED systems could benefit both vegetative propagated production and sprout production, because these systems do not require long growth periods or large plant
Y.J. Lim, S.H. Eom / Scientia Horticulturae 164 (2013) 552–555
sizes (Bula et al., 1991). In this study, we evaluated the efficacy of different light sources in establishing sweet basil cuttings. 2. Materials and methods 2.1. Plant materials Sweet basil seed was purchased from Chung-ang Flower Seed Company (An-yang, Korea) who imported it from the Netherlands in 2010. Fresh shoots were cut from mature sweet basil plants grown in a greenhouse for 3 months. Cuttings were about 8 cm in length. Four leaves from the bottom part of each cutting were removed. Individual cuttings were initially weighed and then planted in 24-well plug trays (7 cm × 7 cm × 8 cm) containing vermiculite. Two treatments were applied to the cut surface: the cut surface was coated with NAA powder (0.4% 1-naphthylacetamide powder, ISK Co., Japan) or the cut surface was not treated with NAA. 2.2. Light irradiation and growth conditions Light sources used in this experiment were red (625 nm) and blue (460 nm) LEDs (P5II model supplying 3.3 V and 1 W per module, Seoul Semiconductor, Seoul, Korea), fluorescent light (FL), and natural sunlight (GH). FL was used as a positive control for artificial light because it contains the entire visible light spectrum range and is commonly used for in vitro plant culture. Plug trays containing planting basil cuttings were placed under red LEDs (RL), blue LEDs (BL), FL, or GH. GH was maintained at 23 ± 3 ◦ C for 16 h a day and above 21 ± 2 ◦ C at night. A culture room with LED and FL chambers was maintained at 24 ± 2 ◦ C by air- and temperature-controlling ventilation. Irradiation intensity of artificial light was set to 30 mol m−2 s−1 . Photoperiod was set to 16 h per day. Humidity in the culture room was maintained between 60 and 70%. Plants were irrigated with distilled water daily as required during the experimental period. 2.3. Plant growth and chlorophyll measurement Cuttings were weighed initially before planting and again after 2, 4, and 6 weeks of culture under different light treatments. Four cuttings per 24 plant-potted plate were collected every 2 weeks to measure root and shoot fresh weights and chlorophyll content. Plant growth was determined based on the difference between the collected sample fresh weight and initial fresh weight. For chlorophyll analysis, leaves of another four cuttings in the 24 plant-potted plate of each light treatment were selected and collected every 2 weeks for 6 weeks after initiation of the experiment. Chlorophyll analysis of young leaves positioned on the third part from the growing tip was performed. Fresh leaf tissue (0.013–0.015 g) was extracted in 2 ml of 99.9% methanol for 48 h at 4 ◦ C in a dark chamber. Extracts were filtered using 0.45 m cellulose acetate syringe filters (DISMIC® -13cp, Toyo Roshi Kaisha Ltd., Japan). Absorbance was measured at both 645 nm and 663 nm using a spectrophotometer (S-4100, Scinco, Seoul, Korea). Total chlorophyll content was calculated using the following formula (Arnon, 1949; Mackinney, 1941): total chlorophyll (mg g−1 fresh wt.) = (8.02 × A663 + 20.20 × A645 ). 2.4. Statistical analysis Biomass and length of basil plants are presented as means with standard errors for each treatment. Means of all data were subjected to standard ANOVA procedures using SAS software (SAS version 9.2, SAS Institute Inc., Cary, NC, USA). Significant
553
differences among treatment means were determined at the 5% level using Duncan’s multiple range test.
3. Results and discussion Sweet basil cuttings grown under different light treatments (GH, FL, BL, and RL) were harvested every 2 weeks, and their root and shoot fresh weights as well as chlorophyll content were measured. Cuttings were initially divided into two groups: NAA treatment or non-NAA treatment. BL induced faster root formation than the other light treatments. As shown in Fig. 1, root fresh weight in the BL treatment group was about 4.3 times higher than that in the FL treatment group. Root growth in response to BL treatment increased significantly until 6 weeks. Other light treatments induced slow increases in root growth until 6 weeks as compared to BL treatment. Root growth under FL was the poorest among the light treatments. Auxin effect was observed under BL in the 2nd and 4th weeks of treatment and RL in the 4th week of treatment as root growth increased. The cutting surface subjected to NAA treatment displayed better root growth under BL than the non-NAA treatment. Cuttings treated with or without NAA were not significantly different from one another at two weeks of GH, FL, or RL treatment; the exception was cuttings grown under BL. Adequate light quality for root growth appears to be plant species specific. In the case of tomato seedling cuttings, effective rooting has been observed under continuous white light irradiation, whereas root formation is reduced under darkness, red, or blue light (Tyburski and Tretyn, 2004). Blue light significantly retarded root formation of Prunus serotina axillary shoot cuttings, whereas yellow light induced the highest rooting percentage and root growth (Fuernkranz et al., 1990). In the sweet basil cuttings, shoot growth was stimulated continuously by RL treatment for 6 weeks, whereas other light treatments only slightly increased shoot growth (Fig. 2). BL treatment induced vigorous shoot growth only during the initial period of light treatment. RL and BL treatment induced similar increases in shoot growth until 2 weeks. However, after 2 weeks, shoot growth induced by RL treatment maintained a faster growth pattern, whereas that induced by BL treatment increased only slightly (Fig. 2). Shoot growth under GH was the slowest. No hormonal effect on shoot growth was observed for any of the light treatments. Mortensen and Strømme (1987) reported that plant height in tomato and chrysanthemum was strongly reduced by blue light treatment and increased by yellow and green light treatments. In our basil cutting study, regardless of NAA treatment, we found that shoot height under BL was not strongly inhibited (Fig. 3), whereas non-cuttings of tomato and chrysanthemum showed reduced height under BL. Efficient nutritional uptake was verified by strong and early root establishment under BL treatment. Total chlorophyll content of leaves subjected to GH or BL treatment decreased at 6 weeks as compared with chlorophyll content at 2 weeks, while chlorophyll content under FL and RL was similar for these two time periods. Chlorophyll content did not differ significantly according to light quality, culture period, or hormone treatment except for the second week of FL treatment. In cuttings not treated with NAA, total chlorophyll content under BL treatment decreased gradually from a fresh weight of 5.52 mg g−1 at 2 weeks to a fresh weight of 3.84 mg g−1 at 6 weeks. Under BL treatment, leaf etiolation progressed from the bottom of leaves. Hormonal effect on chlorophyll contents was not observed for any of the treatments (Table 1). It was previously reported that chlorophyll content in pea seedlings increased rapidly upon initial treatment with blue light compared to other light treatments (Wu et al., 2007). However, the increase was delayed when blue light treatment was continuous. We found that a long BL irradiation period resulted in chlorophyll
554
Y.J. Lim, S.H. Eom / Scientia Horticulturae 164 (2013) 552–555
Fig. 1. Effects of light type on the root growth of basil cuttings: (A) GH, (B) FL, (C) RL and (D) BL. Data represent the mean ± SE. Significant differences (p < 0.05) between non-NAA and NAA treatments according to Duncan’s multiple range are indicated by an asterisk.
Fig. 2. Effects of different light types on shoot growth of basil cuttings: (A) GH, (B) FL, (C) RL and (D) BL.
Y.J. Lim, S.H. Eom / Scientia Horticulturae 164 (2013) 552–555
555
Table 1 Total chlorophyll contents of basil young leaves grown under different light sources subjected to non-NAA or NAA treatment. Cultivation (weeks)
Hormonal treatment
GH
FL
RL
BL
Total chlorophyll content (mg g−1 fresh wt.) 2
Non-NAA NAA
4.90aa 4.57a
5.08a 6.01a*
6.04a 5.99a
5.52a 5.19a
4
Non-NAA NAA
5.18ab 5.04a
4.78bc 5.35a
5.86a 5.97a
4.11c 5.24a
6
Non-NAA NAA
4.13b 4.01b
6.01a 5.53a
5.93a 5.98a
3.84b 4.13b
a Different letters (a–c) in each row indicate significant difference at the level of p < 0.05 by Duncan’s test; mark (*) in the same light quality and cultivation periods comparison between hormonal treatment indicates significant difference at p < 0.05.
References
Fig. 3. Periodical root formation and shoot growth of basil cuttings under different light sources.
degradation. Therefore, BL should only be used to induce plant growth. BL treatment induced a darker green leaf color than natural sunlight (Mortensen and Strømme, 1987). 4. Conclusions In this study, we observed that root formation of basil cuttings was stimulated under BL treatment. BL is necessary for the healthy growth of plants (Okamoto et al., 1996). However, continuous plant exposure to BL for longer than 2 weeks could negatively affect the shoot growth of cuttings from crops with a similar leaf morphology to that of sweet basil. Nursery plant industry currently utilizes natural sunlight, fluorescent light, or shade partial light to stimulate the growth of sweet basil cuttings. Under these conditions, cutting production can be time-consuming and careful management is required for disease control and plant survival. Thus, we suggest using blue LED irradiation as an alternative method for efficient cutting production. Acknowledgements This study was supported by a grant from the Korea Healthcare Technology R&D Project, Ministry of Health & Welfare, Republic of Korea (Grant No. HI10C2162).
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