Regulation of Wheat Lodging Resistance Through Culm Structure Optimization and Synergistic by Uniconazole and Prohexadione Calcium

The mechanical physicochemical properties of wheat culms are key intrinsic determinants of lodging resistance. This study aimed to determine the relationships between plant growth regulator-induced changes in culm physicochemical traits and improvements in mechanical properties.

Two wheat varieties with different lodging resistance, Yangmai 22 and Ningmai 13, were selected. The experiment included four foliar spray treatments: water (control), uniconazole (20 mg·L^-1), prohexadione- calcium (4.5 g·L^-1) and a combination of uniconazole and prohexadione-calcium, applied at key growth stages. Culm morphological characteristics, mechanical traits, structural carbohydrate content, and yield components were systematically measured to analyze the regulatory effects of different treatments on culm lodging resistance and grain yield.

Plant growth regulator treatments significantly reduced plant height and center of gravity height, shortened basal the first and second internodes, while increasing basal internode culm diameter, culm wall thickness, dry matter accumulation, and culm filling degree, with increased cell wall structural carbohydrate content. In 2022-2023, lignin content in the second basal internode at maturity stage of Yangmai 22 and Ningmai 13 increased by 21.17%-25.52% and 5.87%-8.61%, respectively. This optimization of morphology and matter accumulation further improved culm mechanical properties, as evidenced by significantly increased breaking force, section modulus, and breaking moment of the second basal internode, along with significantly reduced lodging index and markedly improved field lodging conditions. In 2023-2024, field lodging rate at maturity stage decreased by 7.81%, 8.94%, and 11.95%, respectively. Correlation analysis showed that breaking strength and breaking moment were significantly positively correlated with section modulus and culm wall thickness, while significantly negatively correlated with bending stress, center of gravity height, and basal internode length. The lodging index was significantly negatively correlated with breaking strength, breaking moment, section modulus, culm diameter, and wall thickness of the basal internodes, but significantly positively correlated with bending stress, plant height, center of gravity height, and internode length. In terms of yield, foliar application of uniconazole, prohexadione-calcium, and their combination increased grain yield. In 2022-2023, grain yield increased by 4.03%-28.40% in Yangmai 22 and by 9.35%-22.48% in Ningmai 13 compared with the control, respectively. In 2023-2024, spray treatments of Yangmai 22 increased by 15.71%, 14.97%, and 12.33% compared with the control, respectively.

Foliar application of uniconazole, prohexadione-calcium, and their combination significantly enhanced wheat culm lodging resistance by optimizing the morphological structure of basal internodes, including reducing plant height, shortening internodes, and increasing culm diameter; promoting dry matter accumulation, culm filling, and lignin deposition; and improving culm mechanical properties. These treatments also maintained or increased grain yield.