Response of Tomato and Pepper Transplants to Light Spectra Provided by Light Emitting Diodes

Transcription

1 International Journal of Vegetable Science, 19: , 2013 Copyright Taylor & Francis Group, LLC ISSN: print / online DOI: / Response of Tomato and Pepper Transplants to Light Spectra Provided by Light Emitting Diodes Jamal Javanmardi and Shandiz Emami Department of Horticultural Sciences, Faculty of Agriculture, Shiraz University, Shiraz, Iran Growing conditions during transplant production influence seedling quality and performance, transplant establishment, and subsequent yield. The effects of spectra combinations of blue, red, and white light, generated by monochromic light-emitting diodes (LEDs), on physiological and morphological characteristics of tomato (Solanum lycopersicum L.), cv. Kingston, and pepper (Capsicum annuum L.), cv. California Wonder, seedlings were investigated. Tomato and pepper transplants treated with monochromic red, or combinations of red with blue light, produced greater stem diameter, whereas blue light alone, or in combination with red, reduced transplant height. In tomato the most lateral branches were produced on seedlings under blue light, but pepper transplants were not affected. The most leaf area in tomato and pepper transplants was obtained under monochromatic blue or red light, respectively. Proline, an important compound related to plant stress tolerance, was produced at the highest level under blue light in both plants. For tomato, red light alone or in combination with blue or white light reduced the number of leaves required before the first cluster. This occurred in pepper transplants when higher ratios of red light (up to 100%) were applied. For both plants rates of first cluster formation and first yield were higher when combinations of blue and red lights (regardless of their ratio) were used. The most vitamin C was in fruit produced on plants developed from transplants grown under blue light. Fruit total soluble solids were also higher in tomato plants developed from blue light treated tomato seedlings. There appear to be beneficial effects due to exposure of plants during seedling development to light spectra that extends beyond transplanting. The effects of light spectra appear to be genus or species specific. The LED technology did not differ from other technologies and has merit for production of some vegetable seedlings. Keywords Light conditioning, Photomorphogenesis, Proline, Transplant height control, Vitamin C. Address correspondence to Jamal Javanmardi, Department of Horticultural Sciences, Faculty of Agriculture, Shiraz University, Shiraz, Iran. javanm@shirazu.ac.ir

2 Tomato and Pepper Transplants 139 The use of healthy transplants is important for vegetable production. For vegetables there are advantages to transplanting over direct seeding. It is necessary to improve transplant quality so that transplants establish more quickly in the field. Due to high moisture levels, low light levels, and dense plantings in transplant production greenhouses, the potential for producing etiolated seedlings is high. Etiolated transplants establish later in the field or greenhouse with reduced and delayed early yield (Javanmardi, 2009). Control of transplant height is a practical approach for dealing with those issues. Plant physiological responses can be utilized instead of chemical growth retardants, which may pose concerns about health issues and environmental pollution, to control plant height. The U.S. Food and Drug Administration and U.S. Environmental Protection Agency restricted chemical growth regulators for vegetables (Patil et al., 2001). Currently, vegetable transplant height can be controlled by biological methods, physical methods, and changes in environmental conditions (Javanmardi, 2009). A quality transplant has a thick stem, short internodes, and large and dark green leaves. These features improve root development after transplanting and affect early yield quality and quantity (Brazaitytė et al., 2009). Light quality and quantity are important factors for producing quality vegetable transplants. Changes in light quality can be employed by monochrome diodes (Brown et al., 1995) or optical filters (Masson et al., 1991) or covering tunnels or greenhouses with photoselective filters (Kozai et al., 1999). It has been reported that pepper seedling height was reduced by 30% during a 4- week period when photoselective filters when a ratio of 2.2 transmission (red : far-red) was used (Kozai et al., 1999). Advances in light-emitting diode (LED) technology have made them an excellent light source for research purposes. Their small size, durability, long life, cool emitting temperature, and the option to select specific wavelengths for targeted plant response make LEDs more suitable for plant-based uses than many other light sources (Massa et al., 2008). The LED can make photon fluxes well in excess of 2000 µmol m 2 s 1 (Tennessen et al., 1995). This study was undertaken to determine the best combination of light spectra using monochrome diodes to improve tomato (Solanum lycopersicum L.) and pepper (Capsicum annuum L.) seedlings (two economically important vegetable crops that are practically produced through transplanting) and to determine how the lights affected posttransplant performance. MATERIALS AND METHODS Plant Material Seed of tomato, cv. Kingston, and sweet pepper, cv. California Wonder, were sown in plastic pots (450 ml volume) containing peat and perlite (60:40 v:v).

3 140 J. Javanmardi and S. Emami Pots with plants were maintained at 25/21 C (light/dark) and 60% 70% relative humidity in a growth chamber. Pots were subirrigated at 3-day intervals and fertilized according to the method recommended for production of tomato and pepper seedlings (Javanmardi, 2009) for 6 weeks. The sandy-loam soil was plowed and disked to turn under existing plant material. Preplant fertilization was applied according to soil test results and was composed of ammonium phosphate (150 kg ha 1 ), potassium sulfate (15 kg ha 1 ), urea (75 kg ha 1 ), zinc sulfate (40 kg ha 1 ), copper sulfate (10 kg ha 1 ), ferric sulfate (25 kg ha 1 ), and manganese sulfate (25 kg ha 1 ). Fertilizers where applied in two bands at a depth of 5 cm located 15 to 20 cm to either side of plant rows. A drip tube system was used for consequent irrigation/fertilization (fertigation). The fertilizers applied during the growing period were through fertigation using a Venturi apparatus. Drip irrigation was based on crop evapotranspiration estimates from tensiometers placed in production beds. Black polyethylene mulch was used to cover 15-cm-tall raised beds to conserve soil moisture and suppress weeds. Six-week-old seedlings were transplanted into mulches 50 cm apart on 75-cm row spacing. Cultural practices consisted of standard recommendations for growing tomatoes and peppers for fresh market production according to Thamburaj and Singh (2001). No side branch pruning was applied for plants. Light Treatments In a growth chamber, plants were subjected to monochromic lighting using LED sticks. Each light treatment was assembled in four rows of LEDs spaced 15 mm apart on a cm board (total of 320 LED chips). Nine different light combinations with white (W), red (R), and blue (B) LED sticks were used. The DC power was adjusted (using rotary potentiometers) for every treatment to provide an average instantaneous photosynthetic photon flux inside chambers of 300 µmol/m 2 s 1. Multiple light scans within chambers indicated that the inside chamber spectral distribution was uniform. The daily photosynthetic photon flux integral was recorded with an LI-1000 data logger (LI-COR Inc., Lincoln, Neb.) fitted with an LI-190SB quantum sensor. The photoperiod was 16 h day 1 for all treatments. Light treatments were started immediately after seed emerged and lasted for 6 weeks. Treatments (compartments where the pots were located) were separated using aluminum foil sheets to prevent light contamination. Pretransplanting Assays Data of transplant characteristics were recorded in the sixth week after plant emergence, before transplanting to the field. Shoot and root fresh and

4 Tomato and Pepper Transplants 141 dry weights, stem diameter, transplant height, leaf number, and number of lateral branches were determined. Chlorophyll Content Determination Chlorophyll content was determined as described by Saini et al. (2001). Samples of fully expanded leaves (0.5 g) of randomly selected plants per replicate were used. Samples were homogenized with 5 ml of acetone (80% v/v) using a pestle and mortar and passed through filter paper (Whatman No. 2, Maidstone, Kent, UK). The process was conducted in the dark to avoid photobleaching. Absorbance was measured with an ultraviolet-visible spectrophotometer (Camspec M108, Spectronic Instruments, Leeds, U.K.) at 652 nm and total chlorophyll content was calculated using the following equation: Total chlorophyll (mg g 1 FW) = [D 652 V] V/W where V is the total volume of acetone extract (ml) and W is the fresh sample weight (g). Proline Content Determination Proline content was determined according to the method of Bates et al. (1973) with slight modifications. Briefly, leaf samples (0.3 g) were ground in 10 ml of 3% sulfosalicylic acid and centrifuged at 10,000 g for 10 min. The supernatants (2 ml) were mixed with 2 ml of freshly prepared acid ninhydrin solution (1.25 g of ninhydrin, 30 ml of glacial acetic acid, 20 ml of 6 M orthophosphoric acid) and incubated in boiling water for 30 min. The reaction was terminated by transferring the samples onto ice; the mixtures were extracted with 5 ml of toluene and vortexed for 15 s and the tubes left undisturbed for at least 20 min at room temperature to allow separation of toluene and aqueous phases. The toluene phase was collected and absorbance values were measured at 520 nm with the spectrophotometer. The concentration of proline was calculated using a standard curve. Posttransplanting Assays To evaluate the effects of light combinations during seedling production on posttransplanting crop vegetative and regenerative characteristics, the remaining seedlings of each treatment were transplanted into the field as described above. Established transplant percentage, number of days to first flower and fruit formation, number of leaves before the first flower, first and second fruit yield per plant, average fresh and dry fruit weight, fruit vitamin C content (Association of Official Analytical Chemists, 1984), and total soluble solids (using refractometer) were assayed.

5 142 J. Javanmardi and S. Emami Statistical Analysis The first part of this study (before transplanting) was arranged in a completely randomized design with nine treatments and five replicates, each of which consisted of three pots. The second part of the experiment (after transplanting to the field) was arranged in a randomized complete block design with five replicates, each of which consisted of seven plants. Two plants on each end of the rows were not used for assays. Statistical analysis of all data was performed using MSTAT-C (Michigan State University, East Lansing, Mich.) statistical software and means were compared using Duncan s multiple range test. RESULTS AND DISCUSSION Analysis of variance (ANOVA) indicated that most traits exhibited differences with exceptions of the number of seedling lateral branches in pepper (Tables 1 and 2). Pretransplant Characteristics Stem Diameter Red light alone, or combinations of red and blue light, produced among the highest stem diameter in tomato and pepper seedlings. The red with white light treatment had the same effect on pepper seedlings (Table 1). In contrast, Głowacka (2004) stated that for tomato blue light induced shorter stems and internodes with thicker stems and higher dry weight. Transplant stem diameter is considered an important character of a quality transplant (Javanmardi, 2009). Plant Height Increasing transplant height is a common problem in transplant production. This happens due to optimum environmental conditions provided for transplant production (suitable relative humidity, sufficient nutrition, mild temperatures with no fluctuations, less wind, and lower ultraviolet light because of greenhouse coverings), which lead to suitable growth, but due to high planting densities and competition for light, seedlings become etiolated and exhibit a spindly habit (Javanmardi, 2009). Tomato and pepper seedlings grown under full white light were tallest (Table 1); blue light alone, or in combination with red, reduced tomato and pepper transplant height. These results using LED technology agree with studies on tomato plant height, which was reduced by exposure to blue light compared to natural light (Mortensen and Strømme, 1987) and the considerable inhibiting effect of blue light on

6 Table 1: Quantitative characteristics of tomato and pepper seedlings treated with ratios of light spectra before transplanting. Ratio light type a Stem diameter (mm) Plant height (cm) Number of lateral branches Leaf area (cm 2 ) Chlorophyll (mg g 1 fw) Proline (mg g 1 dw) W R B Tomato Pepper Tomato Pepper Tomato Pepper Tomato Pepper Tomato Pepper Tomato Pepper e b 3.56e 18.40a 15.20a 4e 0a 260f 163abc 10.50a 11.60a 12.68e 10.88e cd 4.22d 17.20b 11.52b 4e 0a 290e 160abc 9.90b 10.80b 13.24e 12.56e cd 5.22ab 14.00c 9.80cd 6c 0a 305d 160abc 9.60b 10.50bc 17.54d 16.23d a 5.78a 12.40de 8.92cd 7b 0a 320b 168a 9.70b 10.10cd 19.57c 18.74c d 4.22d 16.40b 10.20c 4e 0a 295e 159abc 9.90b 10.70b 16.02d 15.20d cd 4.64cd 12.80d 9.28cd 5d 0a 310cd 159abc 9.80b 9.80de 21.20bc 20.20bc bc 5.16bc 10.80f 7.48ef 8a 0a 334a 165ab 8.90c 8.70g 26.54a 25.47a ab 5.60ab 12.00df 8.72de 6c 0a 320b 155c 9.20c 9.40ef 19.84bc 19.51bc ab 5.72ab 11.60ef 7.00f 7b 0a 318bc 158bc 9.13c 9.20f 21.57b 21.08b F (ANOVA) NS a Combinations of LED sticks: white (W), red (R), and blue (B). b Values in each column followed by the same letter are not significantly different at P 0.05, Duncan s multiple range test. NS,, Nonsignificant and significant at 5% and 1%, respectively. 143

7 144 Table 2: Characteristics of tomato and pepper plants grown under different light spectra during transplant production. Ratio light type a Established transplants (%) Number of leaves before first flower Days to first flower after transplantation Days to first fruit set after transplantation First yield per plant (g) Fruit vitamin C (mg/100 g FW) Fruit total soluble solids (%) W R B Tomato Pepper Tomato Pepper Tomato Pepper Tomato Pepper Tomato Pepper Tomato Pepper Tomato Pepper cb b 78e 11.67a 14.00b 7.67ab 9.67b 15.33ab 35.67bc 1177f bc 20.03e b 3.73d 6.80abc b 84d 10.33a 12.33cd 7.33b 9.33b 14.00bcd 35.33c 1507e bc 20.53e b 4.43c 7.03abc ab 93bc 8.33b 12.33cd 7.33b 9.00b 14.33bc 34.67c 1753d bc 22.20cd b 4.50c 6.23c a 98ab 7.33b 9.67f 6.33c 7.33c 13.00cde 33.33d 2440bc ab 23.43bc b 5.50b 6.83abc ab 91c 11.00a 13.67bc 8.00ab 9.00b 15.00b 35.00c 1603de bc 21.37de b 4.17cd 6.67bc ab 95abc 10.67a 14.33ab 7.33b 11.00a 15.00b 37.00a 1720d c 24.10b b 4.63c 7.17abc a 100a 10.67a 15.67a 8.00a 10.00ab 16.67a 36.67ab 2307c d 25.77a a 6.43a 7.87a a 100a 7.33b 10.67ef 5.00d 6.67c 12.67de 32.33d 2693a a 24.07b b 5.27b 7.37ab a 100a 8.00b 11.33de 5.33d 7.33c 12.33e 33.00d 2530ab ab 23.80b b 5.70b 6.77bc F (ANOVA) a Combinations of LED sticks: white (W), red (R), and blue (B). b Values in each column followed by the same letter are not significantly different at P 0.05, Duncan s multiple range test. NS,, Nonsignificant and significant at 5% and 1%, respectively.

8 Tomato and Pepper Transplants 145 tomato transplant growth (Głowacka, 2004). It has been reported that height reduction under different light spectra (using photoselective films) is species dependent (Cerny et al., 2000). Genera and species responses may be due to different synergistic interactions of the blue light receptor and phytochrome on promotion or inhibition of stem elongation (Heo et al., 2002). Red and far-red irradiation enhance cell extension (Rajapakse and Kelly, 1994), but blue irradiation inhibits cell extension (Oyaert et al., 1999). To determine how light has stimulated tomato and pepper seedling stem elongation and describe whether it was through cell division or cell expansion, other work has shown that phytochromes regulate stem elongation by both cell division and expansion (Neff et al., 2000). It is believed that phytochrome activity during cell elongation is controlled via gibberellin biosynthesis (Damayanthi-Ranwala and Decoteau, 1998). The use of selected light could be a nonchemical alternative for regulating transplant height as well as reducing potential environmental pollution and health impacts from using chemical plant growth retardants. These results emphasize that the use of LED technology as a source of light for transplant production is suitable, recommendable, and economical. Number of Lateral Branches Tomato seedlings were influenced by light quality treatments, with the highest number of lateral branches occurring under blue light, but pepper transplants were not affected (Table 1). The formation of lateral breaks has been reported to be stimulated by blue light compared to natural light and inhibited by green and yellow light in tomato (Mortensen and Strłmme, 1987). According to these results, it appears that blue light has a stronger effect on side branching than red light and that the effect is plant species specific. Leaf Area and Chlorophyll Content The most leaf area in tomato transplants was obtained under blue light (Table 1). Leaf area of pepper plants treated with monochromatic red light was similar to all other treatments except the 2R:1B and 1R:2B treatments, which resulted in less leaf area. Leaves are especially affected by spectral quality (Schuerger et al., 1997). The responses were genera specific even though both species are in the same family. In tomato, the lowest chlorophyll values were observed in blue light alone or combinations of blue with red light; in pepper the lowest chlorophyll value was observed under only blue light. Blue light is considered an important factor in the formation of chlorophyll and chloroplast development (Akoyunoglou and Anni, 1984). It has also been reported that chlorophyll concentrations were lower in broccoli (Brassica oleracea L. Botrytis group; Green Duke ) plantlets maintained under blue light than under red light (Kubota et al., 1996).

9 146 J. Javanmardi and S. Emami Proline Content Changes in light quality influence plant hormones. Phytochromes are the most important pigments that control plant physiological responses to light spectra (Patil et al., 2001). Blue-biased conditions enhance concentrations of amino acids (particularly aspartic and glutamic acids) and proteins; in contrast, red-biased sources increase concentrations of soluble sugars and starch in leaves (Warrington and Mitchell, 1976). Proline is an important compound related to plant stress tolerance and was highest under only blue light in tomato and pepper (Table 1). Posttransplanting Characteristics Transplant Establishment In tomato there was little difference in percentage of plant establishment (Table 2). In pepper, with the exception of the 3W and 2W:1R treatments, plant establishment was higher than 90% (Table 2). Leaf Number Preceding the First Flower The number of leaves produced before the first flower has a strong impact on earliness. The fewer the number of leaves needed before first flower, the earlier the crop. Formation of 7 11 and 8 12 leaves before the first flower is required for tomato and pepper plants, respectively (Wien, 1997). For tomato, monochromatic red light treatment alone, or in combination with blue or white, reduced the number of leaves required before the first cluster (Table 2). The red spectrum likely overrides the effects of blue or multispectrum light. This contradicts the findings of Rajapakse and Kelly (1992), who stated that blue light would not affect the number of leaves set. This is an instance where the technology is not as important as the effect. However, the technology could have contributed to the effect. In pepper transplants, the higher ratio of red light (up to 100%) reduced the required number of leaves before the first flower formation (Table 2). First Cluster, Fruit Formation, and Yield In tomato transplants, time to first cluster formation was higher when white light, blue light, and the 2W:1B combinations of light were used. Shorter time to flowering was obtained in plants developed from transplants grown under 2R:1B and 1R:2B (Table 2). In pepper, among the longest times to flowering was when monochromatic blue light and the 1W:2B combination was used. Monochromatic red and 2R:1B and 1R:2B combinations of light resulted

10 Tomato and Pepper Transplants 147 in fewer days to first flower formation (Table 2). Application of blue light during transplant production was reported to accelerate formation of flower buds in tomato (Głowacka, 2004). Fewer days to first fruit formation was observed with red light and combinations of red with blue light in both species. For tomato and pepper plants yields were among the highest when treatment was with 2R:1B and 1R:2B light combinations (Table 2). Fruit Vitamin C and Total Soluble Solids Content The highest vitamin C content was in tomato and pepper fruit in plants subjected to only blue light during transplant production. Total soluble solids were higher in similarly treated tomato seedlings. In pepper there was not a clear response due to manipulation of light (Table 2). The higher vitamin C and total soluble solids content of tomato fruit could be due to the greater number of side branches and leaf area produced under blue light. A recent study has revealed the strong effects of light on ascorbate content and ascorbate-related gene expression in tomato plant (Massot et al., 2012). Although some results obtained differed from previous light manipulation research, those could be due to the source of light supplied, especially if heat from the bulbs is not an issue, or because the quality of the light from LEDs are different than other types of light. Monochromatic LEDs can be used as an environmentally friendly and economical method to achieve the desired plant growth and development. The effects of light spectra manipulation during transplant production can extend beyond transplanting and are related to plant genus or species. Earlier crop and higher early yield can be obtained when light combinations of 2R:1B or 1R:2B are used during tomato and pepper transplant production periods. REFERENCES Akoyunoglou, G. and H. Anni Blue light effect on chloroplast development in higher plants. Blue light effects in biological systems. Springer-Verlag, Berlin. Association of Official Analytical Chemists Official methods of analysis. 14th ed. Association of Official Analytical Chemists, Washington, D.C. Bates, L.S., R.P. Waldren, and I.D. Teare Rapid determination of free proline for water stress studies. Plant Soil 39: Brazaitytė, A., P. Duchovskis, A. Urbonavičiūtė, G. Samuolienė, J. Jankauskienė, A. Kasiulevičiūtė-Bonakėrė, Z. Bliznikas, A. Novičkovas, K. Breivė, and A. Žukauskas The effect of light-emitting diodes lighting on cucumber transplants and after-effect on yield. Zemdirbyste Agriculture 96: Brown, C.S., A.C. Schuerger, and J.C. Sager Growth and photomorphogenesis of pepper plants under red light emitting diodes with supplemental blue or far-red lighting. J. Amer. Soc. Hort. Sci. 120:

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