Exogenous Choline Chloride Increases Rice Yield Under NaCl Stress by Enhancing the Seedling Index

The aim of this study was to determine the mechanism by which exogenous choline chloride (CC) improves the strength of rice seedlings under salt stress and to evaluate the correlation between the seedling index (SI) and rice yield. To this end, the effects of foliar spraying of 500 mg L-1 CC at the three-leaf stage on the salt tolerance, yield, and yield components of the salt-tolerant rice Wanshengyou Tianhong 4 (WSY) and the salt-sensitive rice Huanghuazhan (HHZ) were investigated. CC application remarkedly increased the SI of WSY and HHZ under NaCl stress compared with NaCl treatment, and this was positively correlated with the rice yield. These phenomena were more pronounced when CC was applied to HHZ under NaCl stress as an exogenous spray. The CC application also enhanced the ROS scavenging ability by upregulating antioxidant enzyme activities, enhancing the ascorbate-glutathione (AsA-GSH) cycle, inhibiting Na+ uptake, and promoting osmotic solute accumulation. Meanwhile, CC increased the levels of indole-3-acetic acid (IAA), salicylic acid (SA), and zeatin (ZT) and decreased the abscisic acid (ABA) level in HHZ under NaCl stress. Furthermore, the exogenous application of CC notably increased the yield of NaCl-stressed WSY by 11.17% in 2021 and the yield of NaCl-stressed HHZ by 27.12% and 17.76% in 2021 and 2022, respectively, as compared with NaCl treatment alone. Overall, CC supplementation can effectively improve the SI by enhancing the plant's antioxidant defence, promoting osmoregulation, and modulating mineral uptake and hormone dynamic balance. This, in turn, increases the rice yield under NaCl stress.