Purpose: This study aimed to assess the effects of the sowing date and nitrogen application rate on the grain yield, nitrogen use efficiency (NUE), 2-acetyl-△1-pyrroline (2-AP) contents and biochemical parameters related to 2-AP formation in fragrant rice. Methods: A factorial split-plot arrangement of treatments was set up in a split-zone experiment with two factors and three levels carried out for 3 years. The main plots included two sowing dates: April 1st and May 1st. Subplots contained three different nitrogen levels i.e., 0 kg N ha⁻¹ (N0), 120 kg N ha⁻¹ (N1) and 180 kg N ha⁻¹ (N2). Results: The results indicated that compared with April 1st, the delay in the sowing date (May 1st) decreased the number of grains per panicle, 1000-grain weight, grain yield, NUE and contents of 2-AP, △1-pyrroline, proline and pyrroline-5-carboxylic acid (P5C), as well as the proline dehydrogenase (ProDH) activity. Furthermore, compared with N0, higher-N (N1 and N2) applications increased the panicle number, the number of grains per panicle, grain yield and contents of 2-AP, △1-pyrroline, proline and P5C, as well as the activities of ProDH and ornithine aminotransferase (OAT). The seed-setting rate, 1000-grain weight and NUE were decreased under N2 compared to N1, but the 2-AP content and yield were higher under the high-N application N2 (180 kg ha⁻¹) compared to N1 (120 kg ha⁻¹). Conclusions: Sowing on April 1st and the N2 (180 kg ha⁻¹) application improved the yield and promoted 2-AP biosynthesis, while sowing on May 1st reduced the yield and 2-AP content. Therefore, sowing on April 1st with 180 kg ha⁻¹ of nitrogen is the best, which can not only ensure the yield but also improve the fragrant quality of rice.

Studying the evolutionary patterns of rice agronomic traits in South China and analyzing the characteristics of rice improvement can provide insights into the developmental trajectory of rice breeding in South China and can guide further enhancement of variety yield. In this study, widely promoted varieties and core parents developed through dwarf breeding in the southern region, as well as landraces, were collected and planted in three different ecological regions. A total of 18 agronomic traits were investigated related to heading date, plant type, panicle type, grain type, and yield, and multiple comparisons, a correlation analysis, and a path analysis were conducted. The results indicate that dwarf breeding has significantly increased the yield of inbred indica rice varieties in South China. However, a reduction in plant height has also resulted in a reduction in flag leaf, shorter panicles, and decreased biomass, which have led to metabolic source and storage capacity deficiencies and limited yield potential. To address these limitations, breeders have employed strategies such as increasing flag leaf width, spikelet density, number of primary branches, and grain number per panicle. These measures have led to a gradual increase in yield. Additionally, starting from the 1980s, high-quality rice breeding has been pursued in South China, resulting in slender grain shape and reduced thousand grain weight. Given that total grain number per panicle has already increased significantly and the thousand grain weight cannot be reduced further, enhancing the effective tiller number, which decreases year by year, becomes an important approach to increasing the yield of inbred indica rice varieties in South China.

Salinity is one of the main environmental factors influencing rice production. Many genes affecting salt tolerance (ST) have been cloned in rice so far. In the present study, four genes negatively regulating ST, including HST1, LRRK1, STRK2, and PC1, were edited by CRISPR-Cas9 technology in six rice varieties (three in indica (xian) and three in japonica (geng) backgrounds), and three two-gene editing combinations, including hst1-lrrk1, hst1-strk2, and hst1-pc1, were created. All combinations of hst1-pc1, hst1-lrrk1, and hst1-strk2 significantly improved the ST of all the tested materials in both xian and geng backgrounds and had much better ST than single-gene editing lines. The combination of hst1-pc1 had the poorest ST in CH70 and 8TX23 backgrounds but showed almost the same level of ST as the combinations of hst1-strk2 and hst1-lrrk1 in the C199S background for 17 days after salinization, which clearly brought out the background effect on ST and its utilization in ST breeding. As a comparison of the recipient varieties, almost all gene-edited lines except hst1-pc1 in the CH70 background showed significantly reduced grain weight owing to reduced seed setting rate in normal conditions. The hst1-strk2 showed the highest level of ST at the seedling stage and a relatively higher grain yield among all the lines; thus, it is feasible to enhance the ST of high-yielding rice varieties by simultaneously gene-editing against the two loci or pyramiding these two alleles with the other major ST genes of rice. Our results provide valuable gene resources and germplasms for improving rice salt tolerance and high yield.

This study explored the effects of the sowing stage and nitrogen application rate on the grain yield and its allocation of light-temperature resources over a 9-year experiment from 2011 to 2019. Measurement indicators include the effective accumulative temperature on different growth durations, leaf area index (LAI), above-ground biomass production, and harvest index (HI). Methods: A split-plot design was arranged in the treatment, with N supply as the main plot and the sowing stage as the subplot. The main plots consisted of two nitrogen treatments: low nitrogen (LN: 120 kg ha⁻¹) and high nitrogen (HN: 180 kg ha⁻¹). The subplots contained two sowing stages: the early sowing stage (ES) and the late sowing stage (LS). Results: Compared with LNLS, LNES, and HNLS from 2011 to 2019, HNES of HHZ increased the grain yield by 9.5%, 2.5%, and 5.3%, while the difference in grain yield in YY8 was higher than HHZ, especially under HNES. Compared with LNLS, LNES, and HNLS from 2011 to 2019, HNES of HHZ increased the panicle number by 6.0%, 5.9%, and 1.0%, and HNES of YY8 increased by 12.7%, 11.4%, and 3.8%. Compared with HNLS of HHZ, LNES, LNLS, and HNES decreased the spikelets per panicle by 2.3%, 2.9%, and 1.1%, and decreased by 3.5%, 1.9%, and 2.2% in YY8. The early sowing or increasing N supply significantly increased the dry matter accumulated, grain weight, LAI, and HI. The higher grain yield in LNES was more closely related to the average temperature and the number of spikelets per panicle. The grain yield in HNES was more dependent on the effective accumulative temperature. Conclusions: Sowing in mid-May and increasing the N application (180 kg ha⁻¹) are beneficial to the allocation of light temperature and the increase in yield. Therefore, this research provides a theoretical basis for improving rice yield and optimizing the utilization of light-temperature resources in the future.

As a temperature-loving crop, rice is sensitive to low temperatures. With the popularization of direct-seeded rice, cold tolerance (CT) at the bud burst stage has become an important breeding goal. Here, we evaluated CT for 513 rice accessions at the bud burst stage. A total of 13 QTLs were detected by genome-wide association analysis using the severity of damage (SD) and survival rate of seedlings (SR) as indicators of CT. Based on analyses of LD blocks, GO enrichment, gene expression and haplotype, we identified five genes, LOC_Os01g35184, LOC_Os01g56150, LOC_Os01g73410, LOC_Os02g36740, and LOC_Os09g28180, as the most likely candidates for qSD1-1, qSD1-4, qSD1-5, qSD2-1, and qSR9-1, respectively, for CT. The accumulative effects of favorable haplotypes for the above five most likely candidate genes played an important role in the improvement of the CT of rice cultivars. Hence, this study has furnished valuable insights for advancing gene cloning and pyramiding breeding, aiming to enhance cold tolerance during the bud burst stage in rice.

With the endless growth of the population and development of the economy and living standards, a high yield with good grain quality has become the prime objective of breeding. However, lodging is a major factor leading to a significant decline in rice (Oryza sativa L.) production and quality. We conducted genome-wide association analysis to detect quantitative trait loci (QTL)-related lodging resistance, using 395 temperate geng accessions. A total of 50 QTL affecting the six traits were detected, using 1,438,279 high-quality single nucleotide polymorphism markers. Five important QTL clusters were detected affecting the lodging resistance-related traits. The ten candidate genes were detected by performing gene differential expression analysis and haplotype analysis. Among them, LOC_Os07g48570 (OsDof-23) for qLA7.2, qSA7.2 and qPR7.3, LOC_Os08g29110 (wp2) for qLA8 and qSA8, and LOC_Os11g36440 (MHZ5) for qPR11 and qBR11.1 were considered the most likely candidate genes based on functional annotations. The results may facilitate the breeding of rice varieties resistant to lodging, to overcome the adverse effects of climate change.