The Effect of Light Quality and Cultivar on some Physiological and Vegetative Characteristics of Melon (Cucumis melo Gr. Inodorus) Transplant

Transplant production is one of the most important commercial production of melon. Transplanting of seedlings with strong and healthy stems and roots will be successful. Environmental conditions, such as light, affect the proper growth of healthy transplants. The light provides the necessary energy for photosynthesis. Due to the stimulation of the activity of photosynthetic pigments and light receptor pigments, it can be expected that plant performance increase by improving the quality and quantity of light. High pressure sodium and fluorescent lamps are common artificial light sources in greenhouses but because of their high power consumption, heat generation and the light spectrum that the plant does not use, application of LED is taken into consideration. The production of specific spectrum of light and the possibility of spectral composition are advantages of LED lamps. The aim of this experiment was to investigate the effect of light quality and cultivar on some physiological and vegetative characteristics of two melon cultivar seedlings, Ghasri and Khatooni, which are among the most important melon cultivars in Iran. To investigate the effect of light quality and cultivar on vegetative characteristics of melon (Cucumis melo Gr. Inodorus) transplants, a research was conducted from April 4 to May 10, 2016 as split plot experiment in completely randomized design with five replications and the seedlings of Khatoonia and Ghasri cultivars were treated under different light quality include two combinations of blue and red spectrum with ratios of 15%B : 85%R , 30%B : 70%R, fluorescent lamp and HPS lamp. In order to set spectra combinations, LED lamps of Red (R625nm )  and Blue (B476nm)  were used. The 85%R: 15%B ratio was obtained through using of 340 R lamps plus 60 B lamps and the 70%R: 30%B ratio was obtained by the usage of 280 R lamps plus 120 B lamps on separate Plexiglass plate. Closed growth chambers without natural light were used. The size of LED growth chambers were 70×60×60 cm3 and the size of HPS lamp growth chamber was 120×60×60 cm3. The seeds were planted at a depth of 4 cm and were transplanted to growth chamber equipped with the desired light compounds. Light intensity was 65 mmol    and duration of light was 16 hours. Data was collected when transplant had four leaves. Emergence speed index, mean time for emergence of  transplants, fresh and dry weights of foliage and root, root volume, leaf area and thickness, leaf number, height, height to diameter ratio, stem caliper, chlorophyll a, chlorophyll b, chlorophyll total and carotenoids contents were measured. The result showed that the interaction effect of light quality and cultivar was significant on fresh and dry weights of foliage and root, root volume, leaf area and thickness, height to diameter ratio, chlorophyll a, chlorophyll b, chlorophyll total and carotenoids contents. The fresh and dry weights of foliage of Ghasri cultivar and fresh weight of root of Khatooni cultivar under 15%B: 85%R ratio, the dry weight and root volume of Ghasri cultivar under, 30%B: 70%R ratio, the chlorophyll a and carotenoids contents of Ghasri cultivar under, 30%B: 70%R ratio, the chlorophyll b and chlorophyll total contents of Khatooni cultivar under, 30%B: 70%R ratio were superior. The results of this study showed that the use of compounds of blue and red lights increased the dry matter and development of roots in studied plants. Proper dry matter and root development are important because they make the plant resistant to environmental stress. However, the effect of light quality was affected by the cultivar. For example, Ghasri cultivar showed the highest fresh and dry weights of foliage under 15%B: 85%R ratio and with the increase of blue light level, these two traits decrease significantly, but this results was not obtained in Khatooni cultivar. The results showed that the light quality affected leaf area and thickness of two cultivars in a different way. In Ghasri cultivar the highest leaf area and thickness were obtained under, 30%B: 70%R ratio. In Khatooni cultivar, under, 30%B: 70%R ratio, the highest leaf area and under fluorescent light, the highest leaf thickness were observed. The effect of blue light on the variation of leaf area among plants has been reported differently. The leaf area plays an important role in photosynthesis in plants and with its increase, photosynthesis and plant growth improved. The result showed that the interaction effect of light quality and cultivar was not significant on emergence speed index, mean time for emergence of transplants, leaf number, stem caliper and height. The highest emergence speed index and mean time for emergence of transplants were obtained under, 30%B: 70%R ratio without significant difference with 15%blue: 85%red ratio. Leaf number was lowest under HPS lamp and there is no significant difference in leaf number among 15%B: 85%R ratio, 30%B: 70%R ratio and fluorescent lamp. The highest stem caliper and lowest height were obtained under, 30%B: 70%R ratio. Interaction of phytochromes and cryptochromes due to different levels of blue and red lights lead to the formation of different concentrations of gibberellins and this affects the height of the plants. In some plants, increasing the amount of blue light leads to a decrease in the secretion of this hormone and as a result, plant heights are reduced. The results showed that the blue light had a positive effect on the increase of stem caliper and increasing transplant diameter has a positive effect on its establishment and development after their transfer  to the main planting site. The result showed that the application of the blue and red spectra compared to fluorescent and HPS lamps improved the quality of transplants growth. Improve or mitigate results and the performance in traits such as fresh and dry weights of foliage and root, root volume, leaf area and thickness, height to diameter ratio, chlorophyll a, chlorophyll b, chlorophyll total and carotenoids contents depend on  light quality and cultivar.