Spectral manipulation of growth and physiology of gerbera jamesonii bolus

Abstract

Gerbera (African daisy) is one of the most important commercial flower grown throughout the world under a wide range of climatic conditions. Gerbera requires high light intensities for good vegetative growth and flower yield. The average sunshine hours in open condition in the central zone of Kerala during January to May goes upto 8.1 h/day while during June- September is only 3h/day as per 33 year mean data available with the Agro Meteorology Observatory COH, Vellanikkara. This shortage in the sun shine hours can be substituted by the use of external light in polyhouse. When light is provided at the optimal levels it can significantly increase growth rate, health and yield of the crop. The experiment was conducted during the period from July 2018 to September 2019 in polyhouses, at, College of Horticulture, Vellanikkara, to study the influence of spectral light intensities and UV on the morphological, phenological, physiological characters, yield and flower quality of Gerbera (Gerbera Jamesonii Bolus) Tissue culture plants of Gerbera variety Julia developed and marketed by LJ International (AVT Biotechnology) in two leaf stage were directly planted in pots of size 9-inch depth at the rate of one plant per pot. The pots were placed under LED lights of red, blue, green, white and yellow colours kept at a height of one meter from the ground. Plants were illuminated for 10 hours from 09.00 am to 07.00 pm daily from July 28th to September 25 th (2018 to 2019). Observations on morphological characters such as plant height, leaf length, leaf breadth, plant spread, number of lobes, specific leaf area and petiole length were significantly influenced by spectral colors and UV. Among the spectral color’s plants under red and blue showed significant higher morphological attributes compared to other colors. Also, plants under non-UV condition showed greater growth characters as compare to UV condition. Floral evocation was observed when the plants reached five leaf stage. Under red and blue light exposure, plants came to flower in September (49 days from planting) while plants in all other treatments started flowering in October (60 days from planting). Evaluation of photosynthetic rate under different color regimes indicated that maximum photosynthetic rate was under red light. Gas exchange parameters like stomatal conductance, transpiration rate and stomatal frequencies were higher under blue light followed by red light. Also, plants under non-UV condition showed better physiological characters as compare to those under UV condition. Estimation of GA, IAA and chlorophyll content revealed that all the three components were higher in red light followed by blue under non-UV condition. Nitrate reductase enzyme plays a major role in nitrogen metabolism of plants. In the present study, the nitrate reductase enzyme activity was found to be higher in plants grown under red light in non-UV condition. Flower pigments like anthocyanin, xanthophyll, flavonoids were found higher in plants grown under blue light and under UV condition rather than non-UV condition. These constituents are products of secondary metabolic pathway in plants. Flower number and flower quality parameters like number of flowers, flower head diameter, flower stalk length, flower stalk girth and vase life was better under non UV condition than UV condition. These quality characters were seen to be better in plants grown under red and blue light. The study indicated that UV stabilized sheets would be more beneficial than normal polythene sheets and red and blue LED’s can be used to supplement light requirement in polyhouses for commercial cultivation of Gerbera jamesoni Bolus