Ameliorative Effects of Jasmonic Acid and Humic Acid on Antioxidant Enzymes and Salt Tolerance of Forage Sorghum under Salinity Conditions

Salinity is one of the most important factors that reduce the growth and antioxidant defense of plants. A controlled pot experiment was conducted to investigate the ameliorative effects of jasmonic acid (JA) priming (0, 5, and 10 mM) and humic acid (HA) (0, 3, and 6 g HA kg−1 soil) amendment on antioxidant enzymes and salt tolerance of forage sorghum seedling (Sorghum bicolor L.) grown under three salinity conditions (0, 100, and 200 mM NaCl). Salinity stress reduced emergence seedling index (ESI), promptness index (PI), emergence stress tolerance index (ESTI), dry weight stress tolerance index (DWSTI), and the activities of the peroxidase (POD) and catalase (CAT) enzymes. The activity of superoxide dismutase (SOD) and malondialdehyde (MDA) content increased with salinity. Application of JA positively affected all parameters except CAT and MDA. Humic acid significantly increased all measured parameters except ESTI, DWSTI, and SOD activity. At the 200 mM NaCl level, JA and HA increased CAT, POD, SOD, ESI, DWSTI, ESTI, PI, and MDA as compared with the control. The application of HA at 6 g kg−1 soil decreased SOD and ESI relative to the control at high salinity. The application of 10 mM JA combined with HA at 6 g kg−1 soil was most effective in alleviating salinity stress. Therefore, the combined application of JA and HA on forage sorghum may improve salt tolerance and increase antioxidant enzymes that alleviate damages caused by salinity stress. Core Ideas Application of jasmonic acid and humic acid (HA) mitigated salinity stress. Jasmonic acid (JA) and HA increased the antioxidant enzymes. Applying a combination of JA and HA at high levels of salinity improved salt tolerance.