Study on the growth performances of sweet orange (Citrus sinensis L.) in effect of indole acetic acid on the salt tolerance of sweet orange (Citrus sinensis L.) under in vitro salinity stress

Sweet orange (Citrus sinensis L.) is a fruit that has nutritional and medicinal value because this plant contains natural compounds with high biological activities which are widely used as antibacterial, antidiabetic, antioxidant, antitoxic, and analgesic agents. Climate change, which causes drought and affects seed germination, growth, flowering, and fruiting of trees, is currently affecting the production and quality of Citrus plants. Therefore, finiding a solution for enhancing this plant’s growth is necesarry. This study investigated the effects of IAA at different concentrations (0, 0.1, 0.3, and 0.5 mg/L) on the growth of sweet orange plants under in vitro saline stress. Seeds were cultured in MS medium supplemented with 0 g/L NaCl (positive control), 6 g/L (negative control), and IAA at different concentrations. After 8 weeks of culture, the plants significantly improved their germination, growth, biochemical, and micro-morphology compared to the control. The plant's best germination ability reached 80% at an IAA concentration of 0.3 mg/L, significantly improving growth indicators (plant height, number of leaves, leaf length, leaf width, number of roots, root length, fresh biomass, and dry biomass) and biochemical indicators (photosynthesis intensity, proline) compared to the remaining treatments. The results of anatomical morphology observations showed that IAA significantly improved the structure and anatomical morphology of leaves and roots. Compared with the control experiment, the vascular bundle sheath cells of roots and leaves were thicker, and the parenchyma cells of the cortex and endodermis of the roots were less ligninized.