Effects of amino acid foliar fertilizer on Cry1Ac protein and yield in Bt cotton during flowering

Background Achieving a synergistic enhancement in both the yield and insect resistance of Bt cotton holds substantial importance for boosting farmers' income and ecological advantages. This study investigated the impact of amino acid foliar fertilizer (AAF) on the yield and Cry1Ac protein (CP) content, providing valuable insights for enhancing its productivity and insect-resistance capabilities. In 2021, Sikang 1 and Sikang 3 were treated with AAF once (A1) and water (CK) during the peak flowering stage. In 2022, AAF was sprayed one (A1), two (A2), and three (A3) times, respectively, with CK serving as the control. Results Compared with the control, the A3 treatment increased seed cotton yield (SCY) by 16.0% and CP by 40.98% at 30 days after flowering. AAF application enhanced soluble protein content (SP) and glutamate pyruvate transaminase (GPT) activity, while suppressing protease and peptidase activities. Concurrently, AAF improved sucrose metabolism through elevated sucrose content and increased activities of sucrose synthase (SS) and sucrose conversion enzyme (SCE), which were also positively correlated with yield. A lower ratio of carbon-to-nitrogen (C/N) was linked to higher yields and CP content. Path analysis confirmed that SP, GPT, SS, and SCE demonstrated positive effects on CP content and SCY, respectively. Peptidase activity had negative effects on CP and SCY. The C/N ratio had negative effects on SCY and CP, respectively. Conclusions Triple foliar application of AAF maintained lower C/N ratios with enhanced carbon metabolism and protein synthesis capacity, thereby simultaneously increasing both Cry1Ac protein content and yield in Bt cotton. These findings provide critical insights for improving both pest resistance and agronomic performance in Bt cotton cultivation.