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To investigate the differential responses of super rice grain filling to low filling stage temperature (LT) and the regulative effect of nitrogen panicle fertilizer (NPF), physiological and molecular experiments were conducted with two super rice varieties (Nanjing 7th: N7 and Nanjing 9108th: N9108) on two different filling stage temperature treatments implemented by applying two sowing dates [Normal filling stage temperature (CK): Sowed on May 30, Tmean = 24.7°C and low filling stage temperature (LT): Sowed on July 1, Tmean = 20.3°C], and two NPF levels (0 and 150 kg N ha−1). In this study, LT, NPF, and simultaneous LT and NPF treatments suppressed the grain filling in all varieties with different levels. Under LT or NPF treatments, the reduction of grain weight, seed setting rate, and filling rate were closely associated with suppressed starch biosynthesis rate in inferior seeds, suggesting that reduced starch biosynthesis rate, expression, and activities of enzymes encoded by related genes, Floury endosperm-4 (FLO4), Starch branching enzyme-I (SBE1), and Starch phosphorylase-L (PHO-l), were responsible for the grain filling reduction. Under LT or NPF treatments, significantly higher grain filling rates and lower variance were found in N9108 compared to that in N7, which were closely related to their higher starch biosynthesis ability, related gene expression, and enzymes activities. One of the probable explanations of the grain filling difference was the variation in the relative amount of key regulative hormones, Abscisic acid (ABA) and 1-aminocyclopropane-1-carboxylic acid (ACC). These results raise a possibility that super rice with higher sink activities has superior adaptability to LT and NPF due to their higher sink activities. [ABSTRACT FROM AUTHOR]

Climate change threatens rice production by increasing the frequency of extreme temperatures during grain-filling stage (T GF). Nitrogen application can significantly affect rice yield and quality. However, the effects of interaction between T GF and nitrogen application rate on yield and quality of rice remains unclear. The objectives of this study were to comprehensively evaluate the quantitative regulatory mechanism between T GF and nitrogen application rate on rice yield and quality formation. A two-year field experiment with three varieties, five sowing dates, and three nitrogen application rates was conducted at four ecological sites in the middle and lower reaches of the Yangtze River, China in 2019 and 2020. Grain yield, milling, appearance, and eating quality were quantified for each treatment. This study demonstrated that T GF varied from 17.8 ℃ to 31.4 ℃ in different sites and sowing dates and decreased by an average of 2.1 ℃ for every 15 days the sowing date was delayed. The grain yield, head rice rate, chalky grain rate, chalkiness and taste value were all related to T GF through a quadratic function. The optimum T GF for both yield and quality of indica hybrid rice was 24.2–26.5 ℃. In terms of grain yield, nitrogen agronomic efficiency increased linearly with T GF , and nitrogen application could only confer a small increase in yield or even reduce yield under extreme low T GF. Nitrogen application alleviated the adverse effects of high T GF on rice quality, but exacerbated the deterioration of quality under low T GF. For milling and appearance quality and eating quality, the critical T GF leading to such opposite regulatory effect were identified as 23.4 ± 0.4 ℃ and 29.5 ± 0.5 ℃, respectively. The variations of the ratio of amylopectin to amylose and protein content altered texture and starch gelatinization properties, mainly explaining the differences in eating quality caused by T GF and nitrogen application rate. The present study suggests that T GF should be considered when formulating nitrogen management strategies for high-quality rice, which is crucial for alleviating the deterioration of rice quality caused by extreme T GF under global climate change. [Display omitted] • The optimum temperature during grain filling stage (T GF) for indica hybrid rice was 24.2–26.5 ℃. • Nitrogen agronomic efficiency was significantly positively correlated with T GF. • Nitrogen application could alleviate the adverse effects of high T GF on rice quality. • Nitrogen application exacerbated the deterioration of quality under low T GF. [ABSTRACT FROM AUTHOR]

The responses of rice quality including milling, appearance, and eating quality between superior (SG) and inferior grains (IG) to temperature during grain filling stage (T GF) remained poorly understood, especially for eating quality. Therefore, the regulation of T GF (17.6−30.4 °C) on quality of three indica hybrid varieties (IHs) was investigated by setting multiple sowing dates and the mechanism underlying taste difference was explored by monitoring chemical compositions, rapid visco analyser (RVA) profiles, and texture properties. Results suggested that T GF ranging from 23.3 to 25.2 °C could comprehensively improve the milling, appearance and eating quality of IHs, and the optimal T GF of SG was 2.3–4.2 °C lower than that of IG. Compared with chemical compositions and RVA profiles, texture properties were better for evaluating the eating quality of IHs. When T GF was higher than 24.0 °C, the taste value of IG was higher than that of SG mainly due to higher elasticity. The findings indicate that T GF had differential regulatory effects on SG and IG, which could provide a useful reference for cultivation of high-quality rice varieties under global climate change. Besides, the determination of texture properties was a reliable method for taste evaluating of IHs in the breeding process. [Display omitted] • T GF had a significant quadratic function relationship with quality of IHs. • T GF ranging from 23.3 to 25.2 °C could improve the quality of IHs. • The optimal T GF of IG was 2.3–4.2 °C higher than that of SG. • Texture properties can effectively evaluate the eating quality of IHs. • The TV of IG was higher than SG at T GF greater than 24 °C, mainly due to higher elasticity. [ABSTRACT FROM AUTHOR]