Abstract: Background and Objective: Magnesium is a mineral element that affects growth, crop yield as well as agricultural product quality. This work aimed to investigate the effect of magnesium on growth, fruit yield and some biochemical indices of hydroponic black tomato. Materials and Methods: The black tomatoes were grown in the modified Hoagland solutions by various concentrations of magnesium (0, 24, 48 and 96 ppm). Experiments have been conducted by using Randomized Complete Block Design (RCBD) with three replications. Duncan’s Multiple Range Test was being used at the 5% level of significance (p = 0.05). Results: The plant height of black tomato was higher in the magnesium-free plot than that in all magnesium treated plots. However, magnesium treatment improved the yield of black tomatoes, especially at a concentration of 48 ppm. The total soluble sugar and anthocyanin content were higher in magnesium-treated plots compared to the magnesium-free plot. Conclusion: The current study provides further insight into the effectiveness of magnesium on the growth, yield as well as the biochemical characteristics of black tomato. Especially, magnesium at 48 ppm had the maximum effect on plant growth, fruit yield and quality of black tomatoes grown in hydroponic solution.
INTRODUCTION
Generally, mineral elements influence on growth, yield and quality of plants. Therefore, each crop requires and responds differently to different elements1. To now, the response of black tomato to magnesium concentrations has not been well clear and might need to investigate since this mineral element is one of the essentialnutrients for a plant and as such is of crucial importance in the context of agriculture.
Tomatoes (Solanum lycopersicum) are an important fruit vegetable that is second to potatoes in Solanaceae. Currently, tomatoes are produced worldwide. The tomato crop area was about 4.85 million metric hectares and the total world production was 182.3 million metric tons2. Tomatoes are healthy food. Tomato fruits are rich in water, vitamins and minerals, especially potassium. These fruits are also abundant in carotenoids and lycopene3-5. Unfortunately, tomatoes only contain negligible amounts of anthocyanins, which are powerful antioxidants with high nutraceutical value due to their anti-inflammatory and anti-carcinogenic effects on human health6 in their fruits7-8. However, some tomato varieties rich in anthocyanins were made by genetic engineering or conventional breeding9.
Magnesium is a major mineral nutrition element that plays an important role in plants. This mineral element plays a central role in chlorophyll biosynthesis and CO2 fixation10. Magnesium activates enzymes involved in photosynthesis and ATP biosynthesis10, promotes the biosynthesis of nucleic acids and proteins11. Besides, Magnesium also involves the transport of metabolic substances (photoassimilates) in the phloem12. Besides, magnesium has been shown to affect plant diseases13. Therefore, magnesium is related to plant growth, yield and quality11,14.
Many studies reported that magnesium also had a major role in crop quality. When the mandarin “Murcott” has been treated by MgSO4 or Mg(NO3)2, the total soluble sugars and ascorbic acid content in fruits were increased however, the total acidity was decreased15. Anthocyanin content rose in many plants treated by magnesium, such as Anthurium andraeanum16. When ryegrass was planting in Hoagland solution supplementing magnesium, nitrate absorption and assimilation in roots decreased17.
Due to the unclear role of magnesium on growth, yield, quality of black tomato recently, studies of this factor will provide scientific and practical benefits for farmers in agricultural production, particularly the hydroponic cultivation of black tomato. The present study aimed to explore the effect of magnesium on growth, fruit yield and some biochemical indices of hydroponic black tomato.
MATERIALS AND METHODS
Study area: This study was conducted at the greenhouse at Faculty of Natural Sciences of Hung Vuong University, from November, 2018-April, 2019 cultivation period.
Black tomato seedlings were sown from seeds (made in the USA, imported and distributed by Duc Thang Investment and Services Co., Ltd.). Nutrition solution is Hoagland modified by altering the concentration of magnesium (0, 24, 48 and 96 ppm).
Research procedure: Seeds of black tomato were sown in plastic cups containing coco chips. Four-week-old seedlings with a height of 18±3 cm were transferred to polystyrene foam containers (with a size of 49 cm×36 cm×31 cm) containing 20 L nutrient solutions. Each plot consisted of 18 plants, grown in 6 containers (3 plants each container) The pH of the solution was maintained with the range of 6-6.5. The concentration of the nutrient solution was verified by a TDS meter every day. The nutrient solution was replaced every week.
Plant height, number of branches, number of fruits, fruit weight and fruit yield were collected from 18 plants per plot. One fruit was selected at random from the observed plants to determine the fruit weight (g) by using an analytical balance (Ohaus Pioneer PA413, USA) with an accuracy of 0.001g.
Three fruits randomly taken from each experimental plot were used to determine the biochemical indices involved in fruit quality. Total soluble sugar was extracted from 0.1 g dry fruit then were estimated by the Anthrone method using glucose as standard18. Anthocyanins were extracted from one g of tomato fruit by ethanol concentrated HCl (pH = 1) as previously described by another study19 before absorbance measurements at 530 and 657nm using UV-VIS GENESYS 10 uv (Thermo Electron Corporation, USA). The corrected value of absorbance was calculated (A530-0.25A657) to eliminate the absorbance of chlorophyll and degradation products20. The results were expressed as anthocyanin content per gram of fresh weight. Nitrate content was determined by the described colorimetric method21.
Statistical analysis: All data were statistically analyzed by using the analysis of variance and means separated by Duncan’s Multiple Range Test at the 5% level of significance (p = 0.05).
RESULTS AND DISCUSSION
Influence of magnesium on plant height and number of branches of black tomato: Plant height of black tomato under the influence of Mg was estimated at 4 and 8 weeks after transferring day (Fig. 1). The results showed that magnesium treated plants were shorter than non treated plants. At eight weeks after transferring day, the plant height was the highest at the magnesium-free plot (86.3 cm). The shortest plants were recorded in a 24 ppm magnesium treated plot (59.9 cm). When plants were grown in nutrient solution containing 48 ppm of magnesium, the plant height at four weeks after transferring day was 69.4 cm. Similarly, this value was 68.8 cm when plants treated with 96 ppm of magnesium. At eight weeks after transferring day, the plant height still reached the highest at the magnesium-free plot (163.6 cm) while the shortest plants were observed in the 24 ppm magnesium treated plot (133.1 cm). The plants treated by 48 and 96 ppm of magnesium achieved 148.8 and 146.4 cm in height, respectively.
Among three magnesium treatments (24, 48 and 96 ppm), only 48 ppm of concentration of magnesium affected the number of branches (p = 0.05) (Fig. 2). No significant differences were observed between the two other magnesium treatments (24 and 96 ppm) and the control. The number of branches (at eight weeks after transferring day) recorded was 1.94; 2.06; 2.67 and 2.00 at 0, 24, 48 and 96 ppm of magnesium treatments.
Influence of magnesium on the number of fruits, fruit weight and yield of black tomato: The data in Table 1 showed that the number of fruits, fruit weight and yield of Mg-treated tomato plants was higher in comparison with non-treated ones. Indeed, the number of fruits/plant treated with 0, 24, 48 and 96 ppm of magnesium was 10.44, 12.78, 17.78 and 14.94, respectively. Similarly, the entire magnesium treatments make an increase in fruit weight (42.36, 49.97 and 47.35 g, respectively) compared to the control (38.50 g/fruit). The average fruit yield of plants grown in the nutrient solution added magnesium was higher than that in the control treatments. Certainly, fruit productivity in 24, 48 and 96 ppm magnesium treatment plots were higher than the control.
| Fig. 1: | Effect of magnesium on plant height of black tomato Within a block, means followed by the same letter are not significantly different according to Duncan’s Multiple Range test (p = 0.05) |
| Fig. 2: | Effect of magnesium on branch numbers of black tomato Means followed by the same letter are not significantly different, according to Duncan’s Multiple Range test (p = 0.05) |
| Table 1: Effect of magnesium on the number of fruits, fruit weight and yield of black tomato | |||
| Magnesium concentration (ppm) | Number of fruits |
Fruit weight (g) |
Yield (g/plant) |
| 0 | 10.44±1.17d |
38.50±1.76d |
401.03±39.09d |
| 24 | 12.78±1.55c |
42.36±1.24c |
540.68±74.86c |
| 48 | 17.78±1.90a |
49.97±1.34a |
886.72±81.13a |
| 96 | 14.94±1.78b |
47.35±1.59b |
706.05±72.90b |
Within a column, means followed by the same letter are not significantly different according to Duncan’s Multiple Range test (p = 0.05) |
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The highest values in number of fruits/plant, fruit weight and fruit yield were observed in the plot supplemented with 48 ppm of magnesium.
Influence of magnesium on some biochemical indices involved in fruit quality of black tomato: The total soluble sugars content is affected by different levels of magnesium at level 0.05 (Fig. 3). In comparison to the magnesium-free treatment, 24, 48 and 96 ppm of magnesium treatments exhibited 1.88, 3.70 and 5.24-fold increase of total soluble sugars content.
| Fig. 3: | Effect of magnesium on total soluble sugars content of black tomato fruits Means followed by the same letter are not significantly different, according to Duncan’s Multiple Range test (p = 0.05) |
| Fig. 4: | Effect of magnesium on anthocyanin content of black tomato fruits Means followed by the same letter are not significantly different, according to Duncan’s Multiple Range test (p = 0.05) |
| Fig. 5: | Effect of magnesium on nitrate content of black tomato fruits |
The influence of magnesium on anthocyanin content of black tomato fruit was investigated (Fig. 4). The results exhibited no significant change of anthocyanin content in fruit between magnesium-free and 24 ppm magnesium treatments. The anthocyanin content in fruits of two theses plots was 2.74 and 2.80 mg g–1 based on the fresh weight. Values of anthocyanin content in the fruit of 48 and 96 ppm magnesium treated plants went up to 4.67 and 4.36 mg g–1 based on fresh weight, respectively, which were not significantly different.
However, the nitrate content in the fruit of black tomato kept the same range in all experimental plots (Fig. 5). Indeed, this value in magnesium-free and 24, 48 and 96 ppm magnesium treatment was 7.07, 7.32, 7.33 and 7.23 mg kg–1 fresh weight, respectively.
Black tomatoes are grown in a modified Hoagland nutrient solution by removing or changing magnesium levels to investigate the role of this mineral element in plant growth, yield and fruit quality. Many works reported the role of magnesium in plants. Some of them focus on a combination of magnesium and other mineral elements such as potassium22, calcium23,24. In this study, the tomato plants were higher in the magnesium-free plot than in all of magnesium treated plots. This result did not support the observation of Ye et al.25. They reported that magnesium deficiency inhibited the plant height of oranges (Citrus sinensis)25. Similarly, magnesium deficiency also decreases the plant height of tomato plants22. The plant height of black tomatoes grown in the 48 and 96 ppm magnesium supplemented solution was higher than that in the 24 ppm magnesium supplemented solution. This observation was possibly due to the balance between the concentration of magnesium and other mineral elements in the nutrient solution22.
A magnesium deficiency reduced the number of fruits, fruit weight and yield of black tomatoes. Magnesium supplementation has increased the number of fruits, fruit weight as well as yield. Magnesium at 48 ppm (concentration in normal Hoagland solution) gives the maximum values. Excess magnesium causes undesirable black tomato growth (number of branches) and yield. This result supports the works of Kasinath et al.26. They reported that the lowest number of fruits, fruit weight and yield of tomato were observed in the plot without magnesium supplementation. The highest values of the number of fruits, fruit weight and fruit yield were observed at the magnesium supplementation at 50 kg ha–1. Magnesium supplemented at higher than this level reduced these values26. Similarly, these results were in agreement with those reported15, that foliar applications of magnesium improved nutrients status, yield and fruit quality of Murcott mandarins. Correspondingly, Altarugio et al.27 presented that foliar spraying of magnesium enhanced the yield performance in soybean and corn crops. The increase in total sugar accumulation in black tomatoes treated with magnesium was different from that in grapes. Zlámalová et al.28 reported that the total sugar content of grapes (such as glucose and fructose) was lower (mostly insignificantly) by 0.5-4.3% in all fertilized treatments than that in the control. Magnesium at concentrations of 48 and 96 ppm increased anthocyanin accumulation in black tomato fruits. This result strongly supports the result reported by Wang et al.29, that foliar application of magnesium enhanced the accumulation of anthocyanin in the Feizixiao lychee (Lychee chinensis Sonn.) pericarp, compared to control fruit. On the other hand, the nitrate content in black tomato fruits was not significantly different between the magnesium treated plots and magnesium-free plot. The nitrate content in fruits in all experimental plots was below WHO standards (150 mg kg–1).
CONCLUSION
This work allows investigating the effectiveness of magnesium on the growth, yield as well as the biochemical characteristics of black tomato. Supplementation of magnesium caused a decrease in plant height but an increase of fruit yield. Besides, added magnesium enhanced the total soluble sugars and anthocyanin content in fruits. Magnesium at 48 ppm was maximum affected on plant growth, fruit yield and quality of black tomatoes grown in hydroponic solution.
SIGNIFICANCE STATEMENT
This study discovered the effect of magnesium on yield and quality of black tomato, especially at a concentration of 48 ppm that can be beneficial for the hydroponic production of this fruit vegetable. This study will help the researchers to uncover the critical areas of cultivation techniques that many researchers were not able to explore. Based on this research a new theory has been obtained that magnesium concentrations can affect the accumulation of anthocyanin in black tomato.
ACKNOWLEDGMENT
This work was funded by the fundamental research program of Hung Vuong University (Project grant No. 26/2018/HĐKH). The authors are grateful to Dr. Van HuyNguyenand MSc. Travis Stahlfor checking the English language in the manuscript.