Can ‘relative culm wall thickness’ be used to evaluate the lodging resistance of rice?

Many indexes have been demonstrated to evaluate the lodging resistance of rice, but most of them are complex or not representative. Thus, we propose a simple and low-cost index, called relative culm wall thickness (RCWT), which can be calculated as the ratio of the basal internode wall thickness to its diameter, to measure the lodging characteristics of rice. A field experiment with 20 indica hybrid rice varieties was conducted in Dayi, Sichuan, China, in 2017 and 2018. The results show that RCWT was significantly negatively correlated with the lodging index, visual lodging rate, plant inclination angle, and bending moment, while it was significantly positively correlated with culm wall thickness, breaking resistance, cellulose, and lignin. Compared with the middle and low RCWT types, the high RCWT type had a lower plant height and center of gravity. Meanwhile, the short basal internodes, thick culm wall thickness, and small pith diameter increased the fullness of the stem, which increased the content of cellulose and lignin in the stem, and thus enhanced the bending resistance and decreased lodging index of the stem. These results indicate that the RCWT can be used as an important index to evaluate the lodging resistance of rice.