Effect of LED Light and Stem Training Methods on Morphological and Biochemical Characteristic of Greenhouse Grafted Tomato

Document Type : Full Paper

Authors

• Hamideh Nikkhah Amirabad ¹
• Seyyed Abdullah Eftekhari ²
• Reza Salehi ³
• Mokhtar Heidari ⁴

¹ Department of Horticultural Science, College of Agriculture, Shahid Chamran University of Ahvaz, Khuzestan, Iran.

² Department of Horticultural Science, College of Agriculture, Shahid Chamran University of Ahvaz, Khuzestan, Iran

³ Department of Horticultural Science, College of Agriculture, University of Tehran, Karaj, Iran

⁴ 4. Department of Horticultural Science, Agricultural Sciences and Natural Resources University of Khuzestan, Mollasani, Iran

Abstract

Keywords

• Blue light
• Pruning
• Red light
• Stock
• Tomato
• Vegetable Grafting

Main Subjects

• vegetable plant science

Extended Abstract

Introduction

     Tomato (Solanum lycopersicum L.) is a crucial horticultural crop worldwide. To boost yields, farmers use methods such as hybrid varieties, controlled environments, and soilless culture. Extending the production period in greenhouses can increase yield but also subjects plants to biotic and abiotic stresses. The repeated use of chemicals to manage these stresses poses environmental risks, leading to a shift towards sustainable methods like grafting. Grafting combines the characteristics of two plants, with a strong rootstock supporting the shoot of a valuable but stress-sensitive plant. This technique enhances stress tolerance, water and nutrient efficiency, yield, and fruit quality. Grafting improves resistance to salinity, water stress, soil-borne diseases and environmental stresses. Successful grafting depends on the effective healing of the wound at the graft junction. Another important practice is stem training, which optimizes plant management to increase yield and quality. Various training methods affect plant physiology and performance, with double-stemmed grafted plants showing better results. Light, crucial for photosynthesis, affects grafting success and plant growth. Studies show that a combination of red and blue light leads to better grafting results and overall growth. More research is needed on training methods and light effects on grafted tomatoes to fully realize their potential in soilless cultivation systems.

Materials and Methods

From autumn 2022 through spring 2023, a study was conducted at the research greenhouse, Department of Horticultural Sciences, College of Agriculture & Natural Resources, University of Tehran, Karaj, Iran. The research focused on tomato plants, specifically utilizing the SV4129TH variety as the scion and the Emperador variety as the rootstock. Employing a factorial design within completely randomized blocks, the experiment investigated the effects of different light spectra (red, blue, white, and a combination of red and blue light) on seedlings, alongside various plant training methods. Seeds were initially sown in trays filled with cocopeat and perlite (3:1 ratio). After three weeks, once the stem diameter reached 2 mm, the seedlings underwent splice grafting and were subsequently transferred to a controlled grafting chamber with a humidity level of 95% and a temperature maintained between 28-30°C. Over time, the humidity in the chamber was gradually reduced, while light intensity was incrementally increased to facilitate the acclimatization of the grafted seedlings. Once the seedlings developed three true leaves, they were trained either as two-stemmed or three-stemmed plants and then moved into growth cubes. During a one-month period, the seedlings were exposed to different light spectra using 18-watt LED wall washers, providing an intensity of 75 ± 5 µmol/m²/Sec. Upon the appearance of the first flower cluster, the plants were transplanted into cocopeat grow bags. The greenhouse maintained a diurnal temperature range of 23-24°C and a nocturnal range of 17-18°C, alongside a relative humidity of 65-70% and natural lighting. The plants were irrigated using a drip system with a modified Hoagland nutrient solution. Throughout the four-month growth period in the greenhouse, data on plant performance were collected during the final three months. Harvesting occurred at the ripened (red) stage of the fruits, which were promptly transported to the laboratory for comprehensive measurements. Parameters assessed included fruit dimensions (length, diameter), weight, yield, average weight, firmness, total soluble solids (TSS), ascorbic acid content, total titratable acidity, and lycopene levels. Additionally, measurements were taken for plant height, root volume, and the fresh and dry weights of stems, leaves, and roots.

Results and Discussion

    It was found that stem training had a significant influence on yield, fruit weight, fruit dry matter, and fruit firmness. Fruit shape index was unaffected by the stem training methods. Conversely, light treatments and their interaction with stem training methods did not show significant effects on these measured indices. Concerning yield, grafted tomato plants trained with three stems produced higher yields (9.11 kg) compared to plants trained with two stems (8.18 kg) and non-grafted single-stem plants (3.2 kg). This represents yield increases of 27% and 17%, respectively, over non-grafted single-stem plants. Regarding fruit characteristics, the stem training method influenced average fruit weight, with plants grafted with two stems exhibiting higher weights (185.83 g) than those with three stems (162.97 g) and non-grafted single-stem plants (131.51 g). Similarly, grafted plants having two stems showed higher fruit dry matter percentages (16.13%) compared to plants with three stems (11.78%) and non-grafted plants (11.36%). The study also emphasized significant variations in vegetative growth indices such as stem weight, leaf weight, root weight, root volume, plant height, and stem diameter across different stem training methods. These findings underscore the crucial role of stem training methods in influencing both the quality of fruit and the vegetative growth of tomato plants, particularly under varying light conditions.

The research investigated how different light spectra affected grafted tomato plants with either two or three stems. Despite exposing the plants to red, blue, white light, and combinations thereof, there was no significant impact observed on root growth, above-ground parts, or fruit quality metrics. This could be attributed to the completion of graft healing processes before the light treatments were administered. Earlier studies have emphasized the role of light in graft uptake and plant physiological processes. The study proposes that future research should delve into light spectra and other environmental factors such as temperature to gain deeper insights into their effects on grafted tomato plants. Overall, the study reaffirmed that grafted plants, particularly those trained with two or three stems, exhibit enhanced fruit quality and yield compared to non-grafted plants with single stems, consistent with prior research highlighting the advantages of grafting in tomato cultivation.

Conclusion

The study found that light treatments (red, blue, white, red-blue mix) post-grafting didn't affect tomato plant growth or fruit quality significantly. Future research should explore light effects during graft establishment or adjust light intensity/wavelengths from grafting to pre-flowering. Moreover, grafting methods (two or three stems) significantly influenced tomato growth and fruit biochemistry compared to non-grafted single-stem plants. Further investigations using diverse rootstock/scion combos and training methods (single-stem, two-stem, three-stem) are needed to better understand their interactions and impact on tomato physiology and fruit quality.