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.

The effect of machine transplanting density on grain starch synthesis in good taste rice cultivars (GTRC) is still unclear. In the experiment, three representative GTRC of Nanjing 9108, Nanjing 5055, and Nanjing 46 in Jiangsu province were used as materials. Five machine transplanting densities of 33.3 × 10⁴, 27.8 × 10⁴, 23.8 × 10⁴, 20.8 × 10⁴, and 18.5 × 10⁴ hills hm^-2 were formed with the row spacing at 30 cm and the plant spacing of 10, 12, 14, 16, and 18 cm, respectively. The effects of machine transplanting density on yield and grain starch synthesis in above three rice cultivars were studied, and the regulation mechanism of halving normal nitrogen (N) rate of panicle nitrogen fertilizer on the starch synthesis was also observed. The results were as follows: (1) The grain yield of the three GTRC were highest at the transplanting density of 27.8 × 10⁴ hills hm^-2. The amylose content at mature stage of the three GTRC decreased first and then increased with the increase in machine transplanting density, while the amylopectin content continued to decrease. When the machine transplanting density was controlled at 27.5 × 10⁴-29.9 × 10⁴hills hm^-2, it was beneficial to improve the taste value of the above-mentioned GTRC. (2) With the increase in machine transplanting density, the activities of granule-bound starch synthase (GBSS) and ADP-glucose pyrophosphorylase (AGP) were increased in the early and middle stages of grain filling (8-20 days after heading), and were decreased rapidly at later grain filling stage. Machine transplanting density had no significant effect on starch branching enzyme (SBE) activity. Among them, the activities of GBSS and AGP in grains at 12-16 days after heading were significantly and positively correlated with the contents of amylose and total starch. (3) Compared with normal N rate of panicle nitrogen fertilizer, half normal N rate could significantly decrease the activities of GBSS and AGP in grains during the early and middle stages of grain filling, reduce the amylose content of rice, and further improve the taste value of GTRC. These results indicated that machine transplanting density could regulate the amylose content due to the activities variations of key enzymes involved in starch synthesis (GBSS and AGP) in the grains during the early and middle stages of grain filling, thus resulting in the difference of rice taste value. Reasonable machine transplanting density and panicle nitrogen fertilizer rate are helpful to further improve the eating quality of GTRC.

Rice (Oryza sativa L.) is a staple crop for over half of the global population; however, pathogenic infections pose significant threats to its sustainable production. Although chemical pesticides are commonly employed for disease control, their prolonged usage has led to pathogen resistance, reduced effectiveness, and non-target toxicity, rendering them unsustainable for agricultural practices. Nanomaterials (NMs) present a promising alternative due to their small size, tunable release properties, and diverse mechanisms for disease resistance. This review examines how NMs can enhance rice disease management through (1) direct pathogen suppression; (2) the activation of plant defense pathways; (3) the formation of nanoscale barriers on leaves to obstruct pathogens; (4) targeted delivery and controlled release of fungicides; and (5) modulation of the microbiome to bolster resilience. Moreover, we critically analyze the agricultural potential and environmental implications of NMs, develop optimized application strategies, and, for the first time, propose the innovative ‘NMs-Rice-Soil’ Ternary System framework. This groundbreaking approach integrates nanotechnology, plant physiology, and soil ecology. The pioneering framework offers transformative solutions for sustainable crop protection, illustrating how strategically engineered NMs can synergistically enhance rice productivity, grain quality, and global food security through science-based risk management and interdisciplinary innovation.