| In order to investigate the effects of chlormequat chloride (CCC) spraying on the lodging resistance characteristics and yield of foxtail millet, this study took ''Shaangu 1'' as the test material and conducted a two-year field experiment. In 2022, spraying was carried out at the early jointing stage, with six treatments set at different CCC concentrations: clear water (CK), 0.625 mL/L (T1), 1.25 mL/L (T2), 2.5 mL/L (T3), 5 mL/L (T4), and 10 mL/L (T5). Based on the 2022 results, T3 and T4 were retained in 2023, with two spraying periods added: seedling stage (M) and early jointing stage (B). The effects of different treatments on stem mechanical strength, microstructure, lignin content, activities of lignin-related metabolic enzymes, and yield of foxtail millet were studied. The results showed that: (1) After CCC spraying, the increasein the number of vascular bundles and total vascular bundle area in foxtail millet stems were 25.88%~84.14% and 11.27%~28.87%, respectively, while the decrease ranges of xylem vessel area and aerenchyma area were 5.62%~44.19%. Therefore, spraying CCC at concentrations of 2.5 mL/L or 5 mL/L at the early jointing stage could enable foxtail millet stems to obtain the optimal mechanical support capacity. (2) Changes in stem chemical components and metabolic enzyme activities indicated that the T3 treatment in 2022 and the BT3 treatment (T3 sprayed at early jointing stage) in 2023 had the most significant effects on promoting the synthesis and accumulation of stem lignin. (3) Compared with the control, the plant height showed the greatest decrease in the T5 and BT4 treatments, reducing by 22.66% and 11.95% respectively. For the basal second internode stem diameter (the key determination index for lodging resistance), the most obvious increases were found in the T4 and BT3 treatments, with an increase of 12.31% and 36.51% respectively. (4) Among the yield components, the T3 and T4 treatments in 2022 and the BT4 treatment in 2023 had positive effects on improving yield-related traits of foxtail millet. (5) Correlation analysis results showed that both the lodging resistance and grain yield of foxtail millet stems were significantly positively correlated with vascular bundle area (VbA), phloem area (PA), lignin content (LC), cellulose content (CC), as well as the activities of phenylalanine ammonia-lyase (PAL), tyrosine ammonia-lyase (TAL), and 4-coumarate:coenzyme A ligase (4CL) (p<0.05). In conclusion, spraying CCC at concentrations of T3 (2.5 mL/L) and T4 (5 mL/L) at the early jointing stage of foxtail millet can enhance stem mechanical strength and reduce plant height by increasing stem lignin content and the activities of related metabolic enzymes, thereby significantly improving the lodging resistance of foxtail millet and ultimately achieving yield improvement. Therefore, it is recommended to spray CCC at concentrations of 2.5 mL/L or 5 mL/L at the early jointing stage in foxtail millet production, so as to provide technical support for lodging-resistant cultivation and high and stable yield of foxtail millet. |