Effects of Exogenous Salicylic Acid on the Physiological Characteristics of Luffa acutangula Seedlings Under Waterlogging Stress

In order to explore the regulatory effect of exogenous salicylic acid (SA) on the waterlogging tolerance of Luffa acutangula Roxb. seedlings, 0.5, 1.0, 1.5, and 2.0 mmol·L⁻¹ salicylic acid solution was sprayed on the leaves of Luffa acutangula Jinfu No.15. Then, the effects of salicylic acid solution on the seedling growth and physiological metabolism under the waterlogging stress were studied. The results showed that: the root length, plant height and fresh weight of Luffa acutangula seedlings under the waterlogging stress were significantly lower than those of the control group CK (non flooding + no external application of SA). After spraying the exogenous salicylic acid, the decreasing range of various agronomic traits decreased. The root length and plant height of seedlings sprayed with 1.5 mmol·L⁻¹ SA were increased by 19.0% and 12.3% compared with the control group CK1 (flooding + no external application of SA), respectively. The fresh weight and dry weight of seedlings sprayed with 2.0 mmol·L⁻¹ SA were increased by 9.0% and 19.2% compared with the control group CK1, respectively. The content of membrane lipid peroxide in the leaves of seedlings increased under the waterlogging stress, while spraying the salicylic acid could significantly reduce the content of MDA and H₂O₂. Compared with CK1 (flooding+no external application of SA), the activities of SOD and CAT in the leaves of seedlings sprayed with 1.5 mmol·L⁻¹ SA were the highest, which were increased by 37.5% and 52.18%, respectively. The activity of POD in the leaves of seedlings sprayed with 2.0 mmol·L⁻¹ SA was the highest, which was increased by 78.1% compared with CK1. Combined with the comprehensive evaluation of the subordinate function values of each index, the order of spraying different concentrations of SA on the waterlogging resistance was as follows: SA1.5 > SA2.0 > SA1.0 > SA0.5 > CK1, and the scores of the two treatments sprayed with 1.5 mmol·L⁻¹ and 2.0 mmol·L⁻¹ SA were relatively close, indicating that the two treatments performed similarly in terms of waterlogging resistance. The comprehensive comparison showed that, the effect of spraying 1.5 mmol·L⁻¹ SA was the best.