Morphological and Biochemical Responses of Basil Plant Under Ultraviolet Radiation-B and Deficit Irrigation Under Greenhouse Conditions

Environmental stresses such as deficit irrigation and ultraviolet radiation can influence plant growth and development. Among the environmental variables, ultraviolet radiation is an important factor in plant response to other stresses, such as deficit irrigation. The purpose of this study was to investigate the effects of ultraviolet B radiation (UV-B), irrigation stress and combined effects of UV-B radiation and deficit irrigation on the morphological and biochemical responses of two basil species. Five treatments of UV-B radiation duration (0, 5, 10, 15 and 20 minutes per day) as well as four irrigation levels (100, 75, 50 and 30% of field capacity), two green and violet types of basil, based on a factorial experiment in a completely randomized design, were considered. Results indicated that the effects of duration of UV-B radiation, drought stress and basil type as well as their interaction on morphological and biochemical responses of both basil types were significant. At the highest level of UV-B radiation (i.e., 20 min/day), the measured traits such as photosynthetic pigments decreased by 18.2%, stem height by 11.2% and root length by 10.1% as compared to control, and the other traits such as leaf thickness increased significantly by 32.3%, malondialdehyde (MDA) content by 7.6%, anthocyanin by 40.6% and proline content by 19.1% as compared to control. While leaf area, number of leaves, root and shoot dry weights were firstly increased by radiation duration and then were reduced as compared to control. Five-minute irradiation treatment increased the stem dry weight (5.8%), leaf area (9.3%) and number of leaves (10.0%) as compared to the control. Deficit irrigation stress had 46.3% greater effect than UV-B radiation in reducing the measured basil characteristics. Simultaneous use of UV-B radiation and deficit irrigation prevented the reduction of growth factors due to low irrigation stress, indicating a synergistic state.