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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. [ABSTRACT FROM AUTHOR]

Few studies have tested the influence of climatic factors on yields by adjusting sowing dates at both low and high altitudes. We investigated the influence of the synergistic effects of temperature and solar radiation by conducting field experiments using different rice varieties and sowing dates in the low-altitude plains of Chongzhou and the high-altitude mountainous region of Hanyuan, Sichuan Province, China, in 2017 and 2018. The results showed that from transplanting to maturity, biomass yield and grain yield were significantly (p < 0.01) correlated with the average daily temperature and solar radiation. The Hanyuan site experienced higher solar radiation and lower temperature than those of Chongzhou, which contributed to higher dry matter accumulation (DMA) and crop growth rate values pre- and post-anthesis and more panicles per m2, leading to higher biomass yields and grain yields at Hanyuan. The rice sowed earlier was subjected to higher solar radiation and lower temperature at Chongzhou and Hanyuan, resulting in increased DMA post-anthesis, panicles per m2, and spikelet filling, improving biomass yield and grain yield. These results indicate that the high potential yield from the early sowing date in the high-altitude region was primarily due to increased solar radiation and decreased temperatures. [ABSTRACT FROM AUTHOR]