Effect of Chloride Salicylic Acid Ionic Liquids on Cotton Topping and High-Temperature Resistance

Chemical topping involves using plant growth regulators to facilitate the rapid transition of cotton into reproductive growth, similar to manual topping (MT), thereby enhancing cotton yield. Despite its benefits, high-temperature stress following cotton topping often reduces cotton yield. Therefore, developing an effective formula capable of not only inhibiting cotton top growth but also alleviating high-temperature stress is of critical importance. In this study, chlormequat chloride salicylic acid ionic liquids (CSILs) were synthesized via the acid-base neutralization of salicylic acid (SA) and 2-chloro-N,N,N-trimethyl ethanaminium hydroxide, obtained from the reaction between potassium hydroxide and chlormequat chloride (CCC). The resulting CSILs were characterized using various techniques, including nuclear magnetic resonance (NMR), Fourier transformation infrared spectroscopy (FTIR), and ultraviolet-visible light (UV-vis) spectroscopy. The characterization results confirmed the successful synthesis of CSILs as a novel water-soluble cotton-topping agent. Notably, compared with CCC treatment, CSILs at the same concentration exhibited a more sustainable and stable inhibition effect on cotton tip growth, resulting in an 11% increase in cotton yield. These findings suggest that CSILs have a greater potential for use in cotton chemical topping compared with CCC. Furthermore, compared with MT, the MDA content of cotton leaves treated with CSILs was reduced, and the activities of POD and SOD were increased under high-temperature stress. Moreover, these effects became more pronounced with an increasing CSIL concentration, highlighting the positive impact of CSILs in alleviating high-temperature stress on cotton. Notably, no significant difference in cotton yield was observed between the CSIL treatment at 120 g AI ha-1 and the MT treatment. Thus, this study underscores the significant potential of CSILs in both cotton topping and enhancing resistance to high-temperature stress.