Abstract: To investigate the alleviating effects of spraying Nengbaiwang 2.0 (0.16% 14-hydroxylated brassinosteroid·thidiazuron+polyglutamic acid) at different stages on rice growth and yield under salt stress, hybrid rice ‘Xiangliangyou 900’ and commonly cultivated rice ‘Huanghuazhan’ were used as the experimental materials to examine the effects of continuous spraying Nengbaiwang for 2 (sprayed once at tillering stage and heading stage) or 3 (sprayed once at tillering stage, heading stage, and grain filling stage) times on photosynthetic characteristics, antioxidant metabolism, osmotic regulation, and yield of rice under 0.3% salt stress. The results showed that salt stress inhibited the growth of both rice varieties, significantly decreased net photosynthetic rate (Pn), and reduced yield by 33.7% and 43.2% in Xiangliangyou 900 and Huanghuazhan, respectively. Foliar spraying Nengbaiwang could alleviate the negative effects of salt stress on rice growth. Spraying Nengbaiwang twice significantly increased the effective tillers of Xiangliangyou 900 and Huanghuazhan, and spraying three times significantly increased plant height, stem diameter, total leaf number, flag leaf length, and inverted second leaf length of Huanghuazhan under salt stress compared with the single salt treatment. Foliar spraying Nengbaiwang for two or three times significantly increased the P_n, stomatal conductance (G_s), chlorophyll content, the activities of antioxidant enzymes (SOD, CAT, POD, and APX), the levels of non-antioxidants (AsA and GSH), and proline accumulation. However, it decreased the contents of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) under salt stress compared to the single salt treatment. The yield loss of Xiangliangyou 900 and Huanghuazhan was alleviated by 20.0% and 14.3%, respectively, after spraying twice Nengbaiwang, and 14.5% and 28.6%, respectively, after spraying three times Nengbaiwang. In conclusion, foliar spraying Nengbaiwang could reduce the damage caused by salt stress on rice by enhancing photosynthetic activity, antioxidant system, and osmotic regulation potential, thus alleviating yield loss under salt stress.

Key words: rice, Nengbaiwang, salt stress, antioxidant metabolism, yield.