Lodging is a major constraint on the stable production of high-quality japonica rice in the Yangtze River Delta. This study evaluated whether different concentrations of prohexadione calcium (Pro-Ca) could improve lodging resistance while maintaining grain yield in high-quality japonica rice. Field experiments were conducted in the 2024 and 2025 growing seasons, with TA 1 cultivated in 2024 and TA 1, SY 28, and HR 1212 cultivated in 2025. Pro-Ca was applied at the jointing stage at four concentrations: CK (water spray), P1 (15 mg L−1), P2 (30 mg L−1) and P3 (45 mg L−1). Rice yield and its components, lodging parameters, culm morphological traits, and non-targeted metabolomic profiles were analyzed. Compared with CK, the P1 treatment significantly reduced the lodging index without a significant reduction in grain yield. In contrast, the P2 and P3 treatments further decreased the lodging index by 14.0–48.1% but decreased grain yield by 6.7–17.9%, mainly due to reductions in effective panicle number and spikelets per panicle. Pro-Ca treatment significantly increased internode diameter and culm wall thickness by 4.9–29.3% and 11.7–76.5%, respectively, and promoted the accumulation of lignin by 5.4–17.7% and cellulose by 3.0–8.6%, thereby enhancing the structural reinforcement of the rice stem. A metabolomic analysis showed that Pro-Ca treatment was associated with changes in carbon- and nitrogen-related metabolites, including metabolites linked to the tricarboxylic acid (TCA) cycle and amino acid biosynthesis. These changes were accompanied by increased accumulation of phenylpropanoid pathway intermediates and lignin-related precursors, including sinapyl alcohol and coniferyl aldehyde. Therefore, in our study, 15 mg L−1 Pro-Ca showed the most favorable balance between lodging resistance and yield, indicating its potential for further evaluation; however, its agronomic and economic feasibility requires additional investigation before practical recommendation.
Wang et al. (Thu,) studied this question.