Effects of jasmonic acid in foliar spray and an humic acid amendment to saline soils on forage sorghum plants’ growth and antioxidant defense system

Salinity is one of the primary abiotic stresses that cause negative physiological and biochemical changes due to the oxidative stress caused by the generation of reactive oxygen species (ROS). The effect of jasmonic acid (JA) as foliar spray and humic acid (HA) as soil amendment on the growth and biochemical attributes of forage sorghum plants exposed to salinity stress was investigated. Soil treated with NaCl at levels of 0, 2, and 4 g NaCl kg(−1) dry soil (designated as S0, S1, and S2) and soil amendment with humic acid at 0, 3, and 6 g HA kg(−1) dry soil (designated as HA0, HA1, and HA2). The plants were sprayed with three JA levels, including 0, 5, and 10 mM JA. Salinity stress increased carotenoid and soluble protein content, superoxide dismutase (SOD) activity, and malondialdehyde (MDA) content. In contrast, salinity stress reduced plant height, leaf area, relative growth rate, proline content, and the activity of peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). At the S2 salinity level, HA2 rate increased plant high by 9.7%, relative growth rate by 70.8% and CAT by 45.5, while HA1 increased leaf area by 12.5%, chlorophyll content by 22.3%, carotenoid content by 38.1%, SOD activity by 20.9%, MDA content by 18.0%, POD activity by 24.6% and APX value by 21.7%. At the S2 salinity level, the highest plant height, chlorophyll content, soluble protein content and APX value were recorded at 5 mM JA, while the highest leaf area, the content of carotenoid, proline, and MDA, and the activity of POD and CAT were achieved at 10 mM JA. Generally, 10 mM JA and 3 g HA kg(−1) dry soil produced the best positive effects on forage sorghum plants physiological responses. Our study suggested that jasmonic acid and humic acid at appropriate rates can successfully mitigate the adverse effects of salinity stress on forage sorghum.