Early-maturing japonica/indica hybrids (EJIH) have recently been released, performing a yield potential of 13.5 t ha⁻¹ and greater yield increase over conventional japonica rice (CJ) and hybrid indica rice (HI) in production. More spikelets per panicle and improved grain-filling efficiency underlined the basis for the superior yield performance of EJIH. However, few studies are available on the panicle traits and grain-filling characteristics of EJIH, as well as their differences to CJ and HI. In our study, two EJIH, two CJ, and two HI cultivars with similar growth patterns were grown in the same fields. EJIH had a 12.2–18.8% increased (p < 0.05) grain yield relative to CJ and HI, mainly attributed to their higher daily grain yield. Although it had a lower panicle per m², EJIH exhibited 28.0–38.3% more (p < 0.05) spikelets per m² from an increase of 58.0–87.8% (p < 0.05) in spikelets per panicle than CJ and HI. Compared with CJ and HI, EJIH had a higher single panicle weight and more grains in the six parts of the panicle, especially in the upper secondary branches (US) and middle secondary branches (MS). EJIH exhibited a higher leaf area index (LAI), leaf area duration (LAD), leaf photosynthetic rate, and SPAD values after heading, which helped increase shoot biomass weight at heading and maturity and post-heading biomass accumulation. For CJ and HI, the grain-filling dynamics of grains in the six parts were all well simulated by the Richards equation. For EJIH, the grain-filling dynamics of grains in the lower secondary branches (LS) were well fitted by the logistics equation, with the Richards equation simulating grain positioning on the other five parts. EJIH had a lower mean grain-filling rate (GR_mean) and longer days and grain filling amounts (GFA) during early, middle, and late stages than CJ and HI. Our results suggest EJIH gave a yield advantage over CJ and HI through a higher daily grain yield. The panicle traits and grain-filling characteristics differed greatly among the three cultivar types. Compared with CJ and HI, EJIH had lower GR_mean and higher days and more grains in the panicle during early, middle, and late stages, which contributed to an increased GFA after heading, improved filled-grain efficiency, and higher grain yield.

Understanding the agronomic and physicochemical characteristics related to grain yield and grain quality is an ongoing hotspot. In 2018 and 2019, high-yielding rice with good palatability (HYGP), high-yielding rice with poor palatability (HYPP), and low-yielding rice with good palatability (LYGP) were grown in paddy fields to explore the main traits underlying the better grain yield and overall palatability of HYGP. HYGP and HYPP demonstrated a 18.1–20.7% higher grain yield (p < 0.05) than LYGP; HYGP and LYGP gave an overall palatability from 75.2 to 77.0, higher (p < 0.05) than HYPP. The higher grain yield of HYGP compared to that of LYGP resulted from a larger sink size because of the spikelets per panicle and the higher total shoot biomass weight (p < 0.05). HYGP exhibited more (p < 0.05) panicles per m² but lower spikelets per panicle and 1000-grain weight than HYPP and maintained a similar grain yield to HYPP. Compared with HYPP and LYGP, HYGP exhibited more (p < 0.05) biomass accumulation from heading to maturity, supported by the higher leaf area index, post-heading leaf photosynthetic rate, and SPAD values. HYGP had higher (p < 0.05) adenosine diphosphate glucose pyrophosphorylase and starch branching enzyme activities at the middle and late grain-filling stages than HYPP and LYGP. HYGP and LYGP had a lower (p < 0.05) chalky area, chalky degree, amylose content, setback, grain protein content, and prolamin content than HYPP, while it had a higher (p < 0.05) gel consistency, breakdown, and ratio of glutelin content to prolamin content. Our results suggested that optimized yield components, more biomass accumulation through improved leaf photosynthetic capacities, a lower amylose content with coordinated enzyme activities involved in starch synthesis, and a lower grain protein content with a better composition were the main traits facilitating the better grain yield and overall palatability of rice in east China.

A decreased nitrogen (N) rate with increased planting density (DNID) is recommended as a feasible method to maintain rice grain yield and N-utilization efficiency. However, it is still unclear whether DNID could improve grain quality, particularly the edible quality of rice. Three high-yield rice with superior palatability (HYSP) and three high-yield rice with inferior palatability (HYIP) were grown under DNID and local cultivation practices (LCP) in the same paddy fields during the 2018 and 2019 rice planting seasons. HYSP exhibited similar grain yields to HYIP under both cultivation treatments. HYSP had more spikelets per m² through panicles per m², while having lower spikelets per panicle and 1000-kernel weight than HYIP. DNID increased panicles per m² and 1000-kernel weight and decreased spikelets per panicle of HYSP and HYIP compared with LCP. HYSP exhibited more biomass accumulation during heading to maturity under NDID and LCP (p < 0.05), which is supported by a higher leaf area index (LAI) and SPAD values after heading. DNID reduced shoot biomass weight and non-structural carbohydrate, while increasing harvest index and NSC remobilization reserve, especially for HYSP (p < 0.05). HYSP had a higher amylopectin content, total starch content, gel consistency, stickiness, and overall palatability (p < 0.05), while it had a lower hardness (p < 0.05) than HYIP. Compared with LCP, DNID increased the amylose content, amylopectin content, total starch content, gel consistency, stickiness, and overall palatability, while it decreased grain protein content and hardness of HYSP and HYIP. HYSP showed consistently higher peak viscosity, breakdown, and gelatinization temperatures (p < 0.05), while it showed lower setback (p < 0.05) than HYIP. For HYSP and HYIP, DNID increased the peak viscosity, breakdown, and gelatinization temperatures (p < 0.05), while it decreased the setback compared with LCP. Generally, the results indicated that coordinated yield components, more post-heading biomass accumulation, lower amylose content, higher peak viscosity and breakdown with lower setback, and higher gelatinization temperatures facilitated high-level grain yield and excellent cooked rice palatability of HYSP. DNID is a feasible method to maintain rice grain yield and enhance the quality of cooked rice for edible properties.

Since genetic improvement greatly promoted an increased yield japonica inbred rice in east China after the 1990s, better root characteristics were certainly expected. In 2018 and 2019, nine japonica inbred rice released in the 1990s, 2000s, and 2010s were investigated to evaluate the changes in root morpho-physiology and identify root traits that contributed to the positive yield trends during the genetic process. The 2010’s rice had 8.0 and 4.3% higher grain yield than the 1990’s and the 2000’s rice, respectively (p < 0.05). Genetic yield gain was mainly attributed to the increased spikelets per panicle. Compared with the 1990’s and the 2000’s rice, the 2010’s rice had higher shoot biomass at heading and maturity (p < 0.05), as well as root biomass (p < 0.05), especially for root biomass of 15–30 cm soil depth. Leaf area index (LAI), soil-plant analysis development (SPAD) values, and leaf photosynthetic rate at middle grain-filling period (MGP) and late grain-filling period (LGP) were all increased. The 2010’s rice had consistently higher root length and volume, root oxidation activity, and root bleeding rate at MGP and LGP than the 1990’s and the 2000’s rice (p < 0.05). Positive correlations were detected between root length and volume, root oxidation activity, and root bleeding rate at MGP, LGP, and SPAD values, leaf photosynthetic rate at MGP and LGP, and higher shoot biomass accumulation after heading and grain yield (p < 0.05 or p < 0.01). The present study implied that genetic improvement optimized post-heading root morphology and physiology, which maintained shoot stay-green and facilitated biomass accumulation and yield increase in japonica inbred rice during the genetic process since the 1990s.