Effects of mechanical and physicochemical properties on the lodging resistance of hybrid japonica rice

Lodging has posed a serious threat to the yield and quality of rice. This study aims to explore the effect of mechanical and physicochemical properties on the lodging resistance of hybrid japonica rice. The test subjects were selected as the curved panicle hybrid japonica rice Liaoyou 2006 (LY2006), Liaoyou 5218 (LY5218), and Liaoyou 5273 (LY5273) in northern China. The control object was selected as the conventional japonica rice Nonglin 313 (NL313(CK)) easy to fall. Then the agronomic characters and microstructure of the plant were measured to establish the mechanical evaluation index for the lodging resistance of japonica hybrid rice, including the maximum bending force, breaking moment, bending section coefficient, single stem weight mass moment, bending strength, Young's elastic modulus and inertia moment, according to the bending and tensile test. Finally, the correlation between the physicochemical and mechanical properties and lodging index was also studied to investigate the effects of mechanical and physicochemical properties on the lodging resistance of hybrid japonica rice under natural cultivation conditions in the field. Four results were obtained. 1) The type of plant was used to improve the structure of rice plants. Thus, ventilation and light transmission were provided for the plants to create a microclimate, thereby strengthening the individual stems and their lodging resistance. The plant height and panicle weight of hybrid japonica rice LY2006, LY5218, and LY5273 were significantly higher than those of conventional japonica rice NL313, whereas, their lodging resistance was greater than that of NL313. Therefore, the shorter the plant height was, and the lighter the panicle was, the stronger the lodging resistance was under suitable cultivation conditions. The structure of the rice plant type was optimized for the unity of high-stem and high-yield. 2) The length of the basal internodes and leaf sheaths of hybrid japonica rice shared a significant impact on the lodging resistance. The lengths of the second and third internodes of hybrid japonica rice LY2006, LY5218, and LY5273 were significantly lower than those of conventional japonica rice NL313, while the lengths of the second and third leaf sheaths were significantly higher. Therefore, the short basal internodes and the long leaf sheaths effectively enhanced the lodging resistance of rice plants. 3) The lodging resistance depended on the thickness of cells and tissues, the area of vascular bundles, as well as the content of cellulose, lignin, and potassium in the stems of hybrid japonica rice. The hybrid japonica rice LY2006, LY5218, and LY5273 presented the strong lodging resistance, indicating the relatively larger cell and tissue thickness, vascular bundle area, as well as the higher content of cellulose, lignin, and potassium. The cultivation and genetic regulation were optimized during rice growth. 4) The mechanical properties of hybrid japonica rice stems also played a decisive role in the lodging resistance of rice plants. The breaking resistance, bending moment, bending section coefficient, single stem weight mass moment, bending strength, Young's modulus, and inertia moment were used as the evaluation indexes for the lodging resistance of hybrid japonica rice. It was found that there was a significant positive correlation between lodging resistance and the maximum breaking resistance, bending moment, bending section coefficient, bending strength, and Young's modulus (P<0.01). There was a significant negative correlation between single stem weight mass moment and inertia moment (P<0.01). The finding can provide comprehensive data support and theoretical support to improve the lodging resistance varieties and agronomic traits in northern japonica hybrid rice.