Effect of Gibberellic Acid and Different Spectra of LED Lights on Quality of Cyclamen persicum Mill. Seedlings

 Cyclamen persicum is a genus of Primulaceae family and is a winter pot plant that can be marketed within seven months under proper growing conditions. In recent years, the rapid development of lighting technology has increased the use of several types of LED lamps because of their efficient roles to generate visible light via a lot of wavelengths. Application of some plant growth regulators (PGRs) like GA3 is well-known as an environment-friendly growth regulatorwhich is extensively employed to increase the productivity and and changing the phenotypic features of several ornamental plants.

 In this experiment, cyclamen large red flower seeds, i.e. the Halios series, were planted in early May, and then kept in a dark and cool greenhouse for one month. After germination and the emergence of cotyledonary leaves, transplants exposed to two levels of the LED light spectrum for 4 months consisting of the ratios of 70:20:10 and 40:40:20 via white:red and blue with the same intensity 100 µmol/m2/s subjected to a 16-hour photoperiodic conditions. At the end of the third month of growth, GA3 was sprayed on the leaves at four concentrations of 0, 20, 40, and 60 mg/l three times around the experiment. NPK fertilizer with a ratio of 10-52-10 was then applied once a week and a ratio of 20-19-19 fertilizer until the roots were fully established. Afterwards, the leaf area was measured using Digimizer version 5.4.3 software, in which the flowering date was calculated from of transferring time the plants of each treatment under light. In the following, chlorophyll and carotenoid contents were measured using Lichtenthaler and Wellburn method. Leaf soluble sugar was measured using the Oregon method and the chlorophyll fluorescence indices were measured using FluorPen FP 100.

 According to the results, the highest leaf number of cyclamen seedlings in the treatment of 40:40:20 was equal to seven, whereas the highest leaf area (9.8 cm2) observed under the light treatment of 70:20:10. the blue LED light can affects on differentiation of leaf mesophilic cells as well as the development of intercellular spaces, and the red light affects the production of a plant hormone so-called Meta-Topolin, which stimulates cell division and leaf expansion. Here, it should be noted that adding white LED light to the composition spectrum increases both growth and photosynthesis because of its deeper penetration into the plant canopy. The maximum root length was achieved at a concentration of 60 mg/l GA3 equal to 5.1 cm. It should be mentioned that GA3 is effective to increase the growth of cells in different parts of the plant (such as roots) by stimulating mitotic division. The closest date to cyclamen flowering time (90 days) was obtained in 70:20:10 treatment. . The highest amount of chlorophyll b was achieved from the interaction of light treatment 40:40:20 and concentration of 0 mg/l GA3 equal to 0.35 mg/g. Results showed that the red light is needed for the photosynthesis, whereas the blue light is needed for chlorophyll and chloroplast synthesis, stomatal opening, and photomorphogenesis. The highest amount of leaf soluble sugar of cyclamen seedlings was achieved from the interaction of 40:40:20 and the concentration of 0 mg/l GA3 equal to 0.53 mg/ml. Carbohydrates mostly accumulate in the leaves under blue light, whereas the red light can cause them to accumulate by preventing the transferring the photosynthetic products from the leaves. Among chlorophyll fluorescence indices, the highest VJ index was obtained from 40 mg/l GA3 concentration equal to 0.51. VJ was measured from the first light pulse, in which its increase via increasing the performance of the photosynthetic apparatus reveal the ability of seedlings to make better use of environmental conditions applied to produce more carbohydrates as well as to enhance the growth quality. The highest values of φ-E0 and Ψ-0 indices in GA3 0 treatment were 0.44 and 0.54, respectively, indicating that increasing them improves the performance index of the photosynthetic apparatus. The external GA3 increases only the amount of chlorophyll and soluble protein content in the leaves of some plants, and interferes with the greater light reflection, chlorophyll fluorescence and eventually the performance of photosystem II. In this regard, the highest amount of ABS/RC index was observed in the interaction of 40:40:20 and concentration of 60 mg/l GA3 equal to 2.27, which is equal to increasing the performance index of photosynthetic device. During the plant growth, the use of monochromatic LED light compared to the full visible spectrum or red + blue lights would lead to creating some defects in the electron transport chain.

 An increase in PI (Plant Photosynthetic Performance Index) means that the plant is operating under conditions of normal photosynthesis. In general, an increase in this index indicates the ability of seedlings or mature plants to make better use of environmental conditions to produce more carbohydrates and improve growth quality. The relationship between increasing the amount of chlorophyll b, leaf soluble sugar and ABS / RC index all in 40:40: 20 treatment while confirming this correlation, shows that since most of the light absorption by chlorophyll is in the red and blue light spectrum. 40: 40: 20 is better than 70: 20: 10 with more red and blue light. The effect of light of any quality or GA3 at any concentration on the qualitative traits of seedling or adult plant growth is directly related to plant genotype and no specific effects can be determined for them. The use of complementary LED light may in some respects lead to a further increase in the quality of Cyclamen seedlings, but it is only reasonable to use them if it compensates for other production costs, including electricity consumption. Finally, chlorophyll fluorescence indices are also independent of each other in terms of their effect on the performance of the photosynthetic apparatus.