Effects of photoperiod and abscisic acid hormone on Cannabis sativa L. morphological and chemical characteristics

Light is one of the environmental factors influencing the growth and development of plants. In recent years, the attention of agricultural experts has been directed to plant growth regulators in order to improve the quality and stability of the cultivation system. The current research was carried out in the year 2021 in the greenhouse of Shahid Fozveh Biological Research Center in a factorial format in the form of a completely randomized design in 5 replications. For this purpose, the effect of test factors including four concentrations of abscisic acid (0, 5, 10 and 20 mg/liter) and 5 day lengths (16, 14, 12, 10 and 8 hours of light) on the growth characteristics and content of photosynthetic pigments. The cannabis plant was evaluated. The results showed that the highest plant height, stem diameter, number of leaves, root length, fresh and dry weight of roots, fresh and dry weight of aerial parts and fresh and dry weight of leaves were obtained under the lighting duration of 14 hours, while the lowest amount of this the traits were observed during the lighting period of 16 hours. Also, the highest amounts of chlorophyll a, b, total and carotenoid were obtained in the treatment of 16 hours of light duration without the use of abscisic acid hormone. While the highest amount of anthocyanin was observed in the treatment of 16 hours of light duration under the treatment of abscisic acid hormone with concentrations of 10 and 20 ppm. Also, the highest amount of total phenol was obtained during the lighting period of 16 hours under the treatment of abscisic acid with a concentration of 20 ppm. Considering the importance and many uses of secondary metabolites in today's human life, investigating the existence of a relationship between environmental conditions and the production and accumulation of secondary metabolites in plants can be very useful. Therefore, it is recommended to use LED light with lighting durations of 14 and 16 hours to increase the growth characteristics and content of photosynthetic pigments of hemp plant.