An essential feature of modern high‐yielding rice varieties is the production of numerous spikelets, but the physiological mechanism underlying spikelet formation in these varieties remains unclear. In this study, we explored the characteristics of spikelet differentiation and degeneration and the relevant physiological characteristics of rice varieties with different panicle sizes. The regulatory effects of alternate wetting and moderate soil drying (AWMD) on spikelet formation were also measured. We determined that the high spikelet number per panicle and grain yields of large‐panicle rice varieties were primarily due to a higher number of differentiated and surviving secondary spikelets. Furthermore, shoot dry weight, plant nitrogen (N) uptake, plant N concentration, non‐structural carbohydrate (NSC) accumulation in stems, leaf area, and leaf photosynthetic rate from branch differentiation stage (BDS) to spikelet differentiation stage (SDS) were positively correlated with the number of differentiated secondary spikelets per panicle. Plant N concentration, NSC accumulation in stems, and leaf photosynthetic rate at pollen mother cell meiosis (PMC) were negatively correlated with the number of degenerated secondary spikelets. Finally, the number of differentiated secondary spikelets of Huaidao 5 (small panicle size) and Yongyou 2640 (large panicle size) varieties was promoted by 19.2% and 6.6%, and the number of degenerated secondary spikelets was reduced by 14.4% and 6.3%, respectively, under AWMD treatment compared to continuously flooded treatment. Prominent spikelet formation under AWMD resulted from the shoot dry weight, plant N uptake, plant N concentration, NSC accumulation in stems, leaf area, and leaf photosynthetic rate. Collectively, improvements in these key aboveground indices mentioned above during the BDS to SDS and the plant N concentration, NSC accumulation in stems, and leaf photosynthetic rate at the PMC stage would benefit spikelet formation by promoting differentiation and reducing degeneration of secondary spikelets, thereby enhancing yield of large‐panicle rice varieties.

Nitrogen (N) fertilizer is a critical element that affects rice yield. However, its effects on dry matter accumulation (DMA), N accumulation, and their physiological mechanisms with grain yield and N utilization efficiency still lack in-depth study. Three large-scale japonica rice varieties—Jinxiangyu 1, Nanjing 46, and Huaidao 5—were used in two field experiments with varying N fertilizer application rates to examine grain yield and N utilization efficiency. The results showed that: (1) In the range of 0~360 kg ha⁻¹ total N application rate (TNAR), the rice yields of the three cultivars were maximum under the TNAR at 270 kg ha⁻¹. The optimal TNAR for the highest yield of Jinxiangyu 1, Nanjing 46, and Huaidao 5 were calculated based on quadratic regressions with values of 305.5 kg ha⁻¹, 307.6 kg ha⁻¹, and 298.0 kg ha⁻¹, and the corresponding yields were 10.3 t ha⁻¹, 10.6 t ha⁻¹ and 10.2 t ha⁻¹, respectively. The N utilization efficiency decreased gradually with the increase in TNAR, and the recovery efficiency decreased from 35.7~38.19% to 29.61~31.59%. (2) The yield was significantly positively correlated with DMA and N accumulation from the heading stage (HD) to the maturity stage (MA). The DMA and N accumulation of HD-MA were significantly positively correlated with leaf photosynthetic rate, non-structural carbohydrate (NSC) accumulation in stems, root oxidation activity, zeatin (Z) + zeatin riboside (ZR) contents in roots, and nitrate reductase (NR) and glutamate synthase (GOGAT) activity in HD. (3) In the range of 0~216 kg ha⁻¹ panicle N application rate (PNAR), the rice yield was maximum under the PNAR at 108 kg ha⁻¹. The optimal PNAR for the highest yield of Jinxiangyu 1 was calculated based on the quadratic regression with values of 139.5 kg ha⁻¹, and the highest yield was 9.72 t ha⁻¹. The leaf photosynthetic rate, NSC accumulation in stems, root oxidation activity, Z + ZR contents in roots, and NR activity in leaves in rice were higher under 108 kg ha⁻¹ PNAR. Excessive application of panicle fertilizer reduced the above physiological indicators and rice yield. The above results showed that optimizing N fertilizer could increase the leaf photosynthetic rate, NSC accumulation in stems, root oxidation activity, Z + ZR contents in roots, and NR activity from HD to MA, which was beneficial to improving DMA and N uptake during HD-MA, thus improving grain yield and N utilization efficiency in rice.

Cultivar renewal (CR) contributes greatly to rice yield increase in China and even in the world. However, few studies were focused on the impact and mechanism of CR on field methane (CH₄) emissions. A 2-year field experiment was conducted using 14 typical japonica rice cultivars released in the Yangtze River Basin of China during the last 70 years. The grain yield, root morphophysiological traits and their relationships with CH₄ emissions were examined. The results showed that the grain yields of cultivars in the 1960–2010s increased by 18.8–93.9% while the CH₄ emissions decreased by 9.5–41.2% compared with the 1950’s cultivars. The daily and cumulative CH₄ emissions during the panicle differentiation stage (PD) were reduced significantly, which contributed greatly to the CH₄ mitigation of the whole growing season. The CR notably increased root biomass, root/shoot ratio, root oxidation activity, and the total organic carbon in root exudates (ETOC), and decreased the ratios of ETOC/yield, ETOC/root biomass and ETOC/shoot biomass. Nitrogen fertilizer applied during panicle differentiation could improve the root physiology and decrease the ETOC/yield and ETOC/root, therefore reducing CH₄ emissions. Our findings illustrated that CR reduced CH₄ emissions by improving root traits and by optimizing the photosynthate allocation to biomass and grain yields. Applying nitrogen fertilizer during panicle differentiation could further mitigate the CH₄ emissions in paddies.

Maximizing rice yield potential has always been the focus of high-yield rice cultivation research. For high-yield rice cultivation and breeding, more research into the link between yield and yield components is essential. In this experiment, 38 rice varieties with different yield types and 185 rice varieties as materials were chosen. The relationships between yield and yield components were studied. The regulation effects of total nitrogen application rate (TNAR) on yield and yield components were observed. The results showed that (1) the grain yield of high-yield varieties was 189.3−195.6%, 76.1−77.7%, and 27.0−28.7% higher than that of super-low-yield, low-yield, and medium-yield varieties, respectively. Compared with rice varieties with other yield types, rice varieties with high-yield type have a higher total number of spikelets. (2) The spikelet number per panicle and total number of spikelets were significantly positively linked with grain yield, but significantly negatively correlated with filled grains and grain weight. (3) With an increase in TNAR (0−340 kg ha⁻¹), the panicles, spikelet number per panicle, and total spikelets of rice varieties with different yield types increased gradually, and the filled grains and grain weight decreased gradually. The higher the TNAR, the more obvious the decrease in filled grains and grain weight. The grain yield of rice varieties with different yield types was the highest under the TNAR at 250 kg ha⁻¹. The main factor contributing to its high yield was the substantial increase in total spikelets. The above results showed that increasing the spikelet number per panicle and total spikelets played a material role in improving rice yield.

Of all the crops, rice is the one that consumes the most water. Rice yields and quality are significantly influenced by irrigation. However, it is still unknown how different irrigation practices would affect the grain yield and quality of water-saving and drought-resistant rice. Hyou 518 (high-yielding rice variety) and Hanyou 73 (water-saving and drought-resistant rice variety) were employed as materials. Three irrigation regimes were set up in the field: conventional flooding irrigation (CF), alternate wetting and moderate soil drying irrigation (AWD), and dry cultivation (D). It was investigated how various irrigation regimes affected the two varieties’ yield and quality. The results revealed the following: 1. D considerably increased water-use efficiency while drastically reducing the yield, compared to CF and AWD. In comparison to other irrigation regimes, the grain yield and water use efficiency of Hanyou 73 enhanced synergistically under AWD treatment. 2. In contrast to CF treatment, AWD and D (especially) treatments decreased perfect rice kernel, total starch content, amylose content, amylopectin content, amylose/amylopectin, gel consistency, and breakdown, but increased green rice kernel, chalky kernel, protein content, and setback. 3. After heading, AWD and D lowered, and D treatment decreased more, the activities of ADP-glucose pyrophosphorylase (AGP), soluble starch synthase (SSS), and starch branching enzyme (SBE). AGP, SSS, and SBE were strongly inversely linked with perfect rice kernel, amylopectin content, gel consistency, and breakdown, but significantly negatively correlated with green rice kernel, chalky kernel, protein content, and setback. The results indicate that with AWD treatment, Hanyou 73 might provide a synergistic boost grain production, water-use efficiency, and quality. D treatment could significantly improve water-use efficiency. Compared with Hyou518, Hanyou 73 could maintain higher AGP, SSS, and SBE activities, head milled rice, perfect rice kernel, amylopectin content, and gel consistency under AWD and D treatment.