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10 September 2024, Volume 38 Issue 5 Previous Issue   
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Reviews and Special Topics

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Sterility Mechanism of Photoperiod/Thermo-sensitive Genic Male Sterile Lines and Development and Prospects of Two-line Hybrid Rice WANG Yichen, ZHU Benshun, ZHOU Lei, ZHU Jun, YANG Zhongnan 2024, 38(5): 463-474.  DOI: 10.16819/j.1001-7216.2024.231008 Abstract ( )   HTML ( )   PDF (1010KB) ( )   This review documented the research progress of two-line hybrid rice in China, and introduced germplasm resources of photoperiod/thermo-sensitive genic male sterile (P/TGMS) lines in two-line hybrid rice breeding. We also summarized various genetic and cellular mechanisms of P/TGMS in plants, and suggestions were proposed for the genetic resource optimization and breeding strategies of P/TGMS lines in two-line hybrid rice breeding.

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Research Progress in Influencing Factors of Methane Production and Emission as Well as Emission Reduction Measures in Paddy Fields XIE Xianzhi, LIU Qihua, LI Xinhua, LI Weiping 2024, 38(5): 475-494.  DOI: 10.16819/j.1001-7216.2024.231102 Abstract ( )   HTML ( )   PDF (1684KB) ( )   The emission of methane from paddy fields is regarded as one of the most significant sources of carbon emissions in agricultural production. Consequently, modern agricultural researchers are focusing on how to effectively reduce methane emissions without sacrificing grain yield in rice production. This review summarizes recent advances in understanding methane production, emission, and strategies for reducing emissions in paddy fields, based on current research findings. It clarifies the processes of methane production, oxidation, and emission, as well as the key influencing factors. The production and emission of methane are closely correlated with the physicochemical properties of soil (including pH, key enzyme activities, water content, temperature, oxidation-reduction potential, and texture), rice varieties (including root morphology and activity, root exudation, aerenchyma, harvest index, and plant height), cultivation techniques (including crop rotation patterns, irrigation and fertilization management practices, and planting methods), and climate factors (including air temperature, atmospheric carbon dioxide concentration, and UV-B radiation). In this review, management practices aiming at decreasing methane emissions are summarized from the perspectives of new variety breeding and comprehensive regulation methods: 1) Selecting evaluation parameters based on the differences in methane emission levels among various rice varieties and breeding new rice varieties that achieve high grain yield with low methane emissions; 2) Exploring new substances that can reduce methane emissions in paddy fields; 3) Investigating innovative technologies for low-carbon cycled cultivation and breeding of rice and fish systems that promote low-carbon circulation, enhance carbon fixation capacity, and reduce methane emissions in paddy soil, as well as the integration of multiple cultivation methods. Additionally, we should explore the pathways for reducing methane emissions in paddy fields according to different production environments in rice-growing regions and establish a high-efficiency comprehensive cultivation regulation system. Reasonable suggestions for future research directions regarding the reduction of methane emissions in paddy fields are presented. It is hoped that this paper will provide not only theoretical evidence for high-yield rice cultivation with lower methane emissions but also technical references for achieving the national "dual carbon" goals.

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Research Progress of Pollen Tube Growth in Pistil of Rice and Its Response to Abiotic stress XU Yongqiang, XU Jun, FENG Baohua, XIAO Jingjing, WANG Danying, ZENG Yuxiang, FU Guanfu 2024, 38(5): 495-506.  DOI: 10.16819/j.1001-7216.2024.231107 Abstract ( )   HTML ( )   PDF (618KB) ( )   Rice, a vital food crop in China and globally, is susceptible to abiotic stresses such as extreme high temperatures, drought, cold, and low light which can impair rice production and threaten worldwide food security, including in China. The growth of pollen tubes in the pistil is crucial for successful fertilization, however abiotic stress can disrupt signaling transport and energy metabolism in the pistils, leading to spikelet sterility. Therefore, it is essential to investigate the impact of abiotic stress on pollen tube growth in pistils and to understand the underlying regulatory mechanisms. This review focuses on the process of pollen tube growth in pistils, encompassing signal transduction, and energy metabolism. Furthermore, it explores the effects of abiotic stress on pollen tube growth in pistils and describes strategies to mitigate stress-induced inhibition of pollen tube growth. This research provides a theoretical foundation for developing cultivation techniques aimed at enhancing spikelet fertility in rice under abiotic stress. Finally, the paper outlines future research directions for studying pollen tube growth in rice pistils under abiotic stress.

Research Papers

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Creation of Rice Grain Size Mutants by Editing OsOFP30 via CRISPR/Cas9 System HE Yong, LIU Yaowei, XIONG Xiang, ZHU Danchen, WANG Aiqun, MA Lana, WANG Tingbao, ZHANG Jian, LI Jianxiong, TIAN Zhihong 2024, 38(5): 507-515.  DOI: 10.16819/j.1001-7216.2024.231002 Abstract ( )   HTML ( )   PDF (1986KB) ( )   【Objective】To study the role of OsOFP30, a transcription factor of the rice OFP family, in regulating grain size and to create new mutant materials of grain size, thereby providing a new reference for the improvement of rice grain size.【Method】The japonica rice line Zhonghua 11 was utilized as a transgenic recipient to generate OsOFP30 mutants using the CRISPR/Cas9 system. Through continuous screening of the T0, T1, and T2 generations, three types of homozygous mutants without foreign fragment insertions were obtained: the long segment deletion mutation OsOFP30−89, the single base insertion mutation OsOFP30+1G, and OsOFP30+1A. Grain size was measured at maturity stages, and the potential reasons for the different grain sizes were analyzed through bioinformatics and sequencing.【Results】 Compared with the wild-type, the grain width and 1000-grain weight of all three types of mutants were significantly reduced. For OsOFP30−89 and OsOFP30+1G, only the grain length and grain thickness are significantly reduced, with no obvious differences in panicle shape indicators from the wild type. The grain length and grain thickness of OsOFP30+1A show no obvious differences from the wild type, and only the number of primary branches is significantly lower than that of the wild type. Bioinformatics analysis revealed that the three types of mutants introduced premature translation termination due to a frameshift mutation. The OsOFP30−89 mutant protein consists of 252 amino acids, while the OsOFP30+1G and OsOFP30+1A mutant proteins consist of 282 amino acids. Sequence analyses showed that OsOFP30+1G and OsOFP30+1A differ by a single base, with G and A at the 323rd position, respectively. This variation resulted in a change between serine and asparagine at the 108th position of the mutant protein. 【Conclusion】The OsOFP30 gene plays a crucial role in regulating rice grain size. This study successfully created new mutant materials affecting grain size, which will provide valuable references for the improvement of rice grain size.

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Identification of Candidate Genes for Rice Nitrogen Use Efficiency by Genome-wide Association Analysis LÜ Yang, LIU Congcong, YANG Longbo, CAO Xinglan, WANG Yueying, TONG Yi, Mohamed Hazman, QIAN Qian, SHANG Lianguang, GUO Longbiao 2024, 38(5): 516-524.  DOI: 10.16819/j.1001-7216.2024.231010 Abstract ( )   HTML ( )   PDF (2255KB) ( )   【Objective】 The exploration of germplasm and gene resources in rice for high nitrogen efficiency, along with the elucidation of their molecular mechanisms and genetic effects, represents a significant focus and goal within current research efforts on rice nitrogen use efficiency (NUE).【Method】 To identify the variant loci and candidate genes associated with rice NUE, we collected 190 Asian rice accessions as an association population. After thorough filtering and screening, we obtained 3,934,195 high-quality single nucleotide polymorphisms (SNPs). Under field conditions, two nitrogen treatment levels were established: low nitrogen (N1, 90 kg/hm²) and normal nitrogen (N2, 180 kg/hm²). We investigated the phenotypic data of rice leaf width in response to both low and normal nitrogen treatments at the maturity stage. Genome-wide association analysis (GWAS) was conducted by integrating the FarmCPU and MLM models. 【Result】By calculating the phenotypic ratio Q (N1/N2) of leaf width under low and normal nitrogen levels, we found that the Q value exhibited a normal distribution. A total of 100 significant loci were identified on 12 chromosomes through GWAS for the Q value, leading to the determination of 39 candidate QTLs. This included the cloned NUE-related genes OsNR1.2 and OsNAC42. Additionally, we identified superior haplotypes and potential advantageous haplotype combinations of the candidate genes OsNR1.2 and OsNAC42, which provide valuable resources and information for enhancing rice NUE. 【Conclusion】This study elucidated the genetic basis of rice leaf width under varying nitrogen treatments using GWAS and haplotype analysis. We identified candidate QTLs and genes associated with NUE, including OsNR1.2 and OsNAC42. Through haplotype analysis, we recognized advantageous haplotype combinations of these two genes, offering valuable resources and insights for the improvement of rice NUE.

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Development and Application of Specific Molecular Markers for Eight Rice Blast Resistance Genes in Rice YANG Hao, HUANG Yanyan, WANG Jian, YI Chunlin, SHI Jun, TAN Chutian, REN Wenrui, WANG Wenming 2024, 38(5): 525-534.  DOI: 10.16819/j.1001-7216.2024.230811 Abstract ( )   HTML ( )   PDF (2859KB) ( )   【Objective】To elucidate the composition of blast resistance genes in rice parents and facilitate their effective utilization in rice resistance breeding, it’s crucial to develop molecular markers that transcend genetic background limitations. These molecular markers can accurately discern resistance genes in parents, serving as essential tools for marker-assisted breeding.【Method】By comparing the coding sequence of each Resistance gene with allelic genes in 155 rice resources, nucleotide polymorphism sites within each resistance gene were identified. Primer pairs for molecular markers were then developed targeting the most specific polymorphism sites.【Results】Effective molecular markers were successfully developed for eight resistance genes: Pit, Pish, Pib, Pid3, Pi5, Pia, Pi54, and Pita2/Ptr. These markers were validated through examination using multiple positive and negative controls or gene sequencing. Subsequently, these markers were utilized to identify the resistance gene composition in 109 breeding parent lines commonly used in the Sichuan Basin. Results revealed that the Pia gene was absent in these parent lines, while Pit, Pish, Pi54, Pid3, Ptr/Pita2, Pi5, and Pib genes were present in 3.67%, 13.76%, 14.68%, 18.35%, 24.77%, 26.61%, and 38.53% of lines, respectively. Furthermore, 21.10% of the rice parent lines lacked these resistance genes, 35.78% possessed one resistance gene, and 43.12% harbored two to four resistance genes.

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Analysis of Nitrogen-response Related Loci in japonica Rice Varieties from Jiangsu Province TANG Weijie, CHEN Haiyuan, ZHANG Suobing, TANG Jun, LIN Jing, FANG Xianwen, ZHANG Shunan, XIAO Ning, WU Yunyu, LI Aihong, ZHANG Yunhui 2024, 38(5): 535-543.  DOI: 10.16819/j.1001-7216.2024.231004 Abstract ( )   HTML ( )   PDF (7199KB) ( )   【Objective】In order to identify nitrogen-response related traits and genes, the study was carried out in Jiangsu Province, a region with a long history of rice breeding and a wide range of germplasm sources, screening nitrogen efficient lines, and finally reducing the amount of nitrogen fertilizer.【Method】We used 76 japonica rice varieties bred in 1983-2014 from different regions of Jiangsu Province as experimental materials. We investigated nitrogen-response related traits at the maturity stage at three nitrogen fertilizer levels, as well as the nitrogen-response related loci. The GATK4 and Admixture software were used for population variations calling and population structure analysis.【Result】 We selected nitrogen insensitive varieties such as Huajing 5 and Ningjing 5. By using association analysis, we identified neighboring loci of known or reported nitrogen related genes (OsAMT1.2, OsNRT2.4 and Fd-GOGAT1, etc.); Further analysis focused on the favorable variation of these loci and the varieties carrying advantageous loci. 【Conclusion】 This study identified the differences in nitrogen response and excellent loci carried by japonica rice varieties in Jiangsu Province. The findings provide both genetic materials and superior loci for breeding nitrogen responsive varieties.

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Yield Formation Characteristics of Ratooning Hybrid Rice Under Simplified Cultivation Practices in Winter Paddy Fields JIANG Peng, ZHANG Lin, ZHOU Xingbing, GUO Xiaoyi, ZHU Yongchuan, LIU Mao, GUO Chanchun, XIONG Hong, XU Fuxian 2024, 38(5): 544-554.  DOI: 10.16819/j.1001-7216.2024.231205 Abstract ( )   HTML ( )   PDF (349KB) ( )   【Objective】Simplified cultivation practices in rice production have attracted significant attention due to their social, economic, and environmental benefits. This study aimed to investigate the impact of simplified cultivation practices on yield formation characteristics of hybrid rice in both the main crop season and ratoon season within a rice-ratoon rice system. The goal was to lay a theoretical foundation for simplified rice cultivation in such a system.【Method】Field experiments were conducted in Luzhou City, Sichuan Province, in 2021 and 2022, involving eight rice varieties, including seven hybrid rice varieties (Yiliangyou 94, Deyou 6699, Taiyou 1060, Rong 7 you 680, Le 3 you 2275, Deyou 727, Jinfengyou 727) and one high-yield inbred rice variety, Jinnongsimiao (JNSM). Each year, the eight rice varieties were cultivated using two methods: NTDS (no-tillage direct seeding) and NTST (no-tillage and seedling throwing). Various parameters such as grain yield, yield components, biomass production, and harvest index were measured for each rice variety in both years.【Result】The results indicated that the main season yield, ratoon season yield, and annual grain yields were significantly influenced by the cultivation method and rice variety. Main season yield, ratoon season yield, and annual grain yields under NTDS were 3.52%－7.37%, 18.94%－47.37%, and 7.04%－14.93% higher than those under NTST, respectively. The higher yields under NTDS were attributed to factors such as increased panicle number, grain filling, biomass production, and harvest index. Among the eight rice varieties, Taiyou 1060 and Jinfengyou 727 exhibited high grain yields in the main season, with Taiyou1060 achieving the highest ratoon season yield and annual grain yields. On average over the two years, high-yielding hybrid rice varieties (Taiyou 1060, Deyou 6699, Deyou 727, Jinfengyou 727) reached main season yields of 8.80 t/hm2, ratoon season yields of 2.53 t/hm2, and annual grain yields of 11.33 t/hm2, representing increases of 13.54%, 6.03%, and 11.76% compared to medium and low-yielding hybrid rice varieties (Yiliangyou 94, Rong 7 you 680, Le 3 you 227). High-yielding hybrid rice also outperformed the high-yield inbred rice (Jinnongsimiao) by 9.97%, 21.87%, and 12.41% in main season yield, ratoon season yield, and annual grain yield, respectively. Medium and low-yielding hybrid rice varieties had slightly lower main season yields but higher ratoon season yields and annual grain yields compared to high-yield inbred rice.In terms of yield components, high-yielding hybrid rice varieties exhibited higher panicle numbers and grain weights in both main and ratoon seasons compared to high-yield inbred rice. Regarding dry matter production, high-yielding hybrid rice showed higher dry matter production and harvest index at maturity compared to high-yield inbred rice, with differences of 3.82% and 5.45% for the main season and 11.16% and 5.70% for the ratoon season, respectively. The lower biomass production at maturity in medium and low-yielding hybrid rice varieties contributed to their lower main season yields compared to high-yielding inbred rice.【Conclusion】The study highlighted the superiority of rice yields under NTDS compared to NTST in a rice-ratoon rice system, which can be attributed to the effective coordination of source and sink size in NTDS. To achieve high rice yields in simplified cultivation techniques for rice-ratoon rice systems in winter paddy fields in Sichuan Province, breeding rice varieties with strong tillering ability and high grain weight through breeding programs may be a viable approach.

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Effects of Nitrogen Reduction Combined with Biochar Application on Stem and Sheath Assimilate Translocation and Yield Formation in Rice Under Tobacco-rice Rotation YANG Mingyu, CHEN Zhicheng, PAN Meiqing, ZHANG Bianhong, PAN Ruixin, YOU Lindong, CHEN Xiaoyan, TANG Lina, HUANG Jinwen 2024, 38(5): 555-566.  DOI: 10.16819/j.1001-7216.2024.231203 Abstract ( )   HTML ( )   PDF (2078KB) ( )   【Objective】In the tobacco-rice multiple and continuous cropping system, the responses of the translocation of stem and sheath assimilates and the yield of rice were explored to lay a scientific basis for soil improvement. 【Method】The hybrid rice “Yongyou 1540” was used as the material, with conventional nitrogen application as the control (T0). Under the premise of applying 30 t/hm2 biochar in the whole soil layer after the harvest of flue-cured tobacco, the relationships between rice yield and the accumulation and translocation of assimilates in stem and sheath and their regulatory mechanisms were analyzed by setting treatments of no reduction in nitrogen (T1), 10% reduction in nitrogen (T2), 20% reduction in nitrogen (T3), and 30% reduction in nitrogen (T4).【Result】The results revealed that the yield of treatments showed a trend of T1>T2>T3>T0>T4 in the 2-year field trial. The differences between the T2 and T3 treatments with 10%, 20% nitrogen reduction and the T1 treatment without nitrogen reduction were not significant, but they were all significantly higher than that of the T0 and T4 treatments. The average actual yield of T2 and T3 treatments increased by 13.94% and 13.46%, respectively compared with the control in 2 years. In terms of harvest index, T2 and T3 treatments were significantly higher than other treatments, and the ratio of grain to grass in each treatment was T3>T2>T4>T1>T0. The net photosynthetic rate and SPAD value of leaves at the heading stage under biochar treatment with appropriate nitrogen reduction were significantly higher than those of the control. The peak tiller number of T1 treatment was the highest, but the productive tiller rate was significantly lower than that under nitrogen reduction with biochar treatments. There was no significant difference between T3 and T2 treatments in the export percentage and translocation percentage of stem-sheath assimilates, but they were significantly higher than other treatments. The transport capacity, transport rate, and grain contribution rate of non-structural carbohydrate (NSC) in stems and sheathes were consistent with the export percentage and translocation percentage of stem-sheath assimilates. Analysis of sucrose-related enzyme activities in stem and sheath showed that the activities of α-Amylase, β-Amylase, sucrose synthase (SS), and sucrose phosphate synthase (SPS) in T3 and T2 treatments at pre- and mid-grain filling stages were the highest. However, these enzyme activities were highest in the T1 treatment at 20 days after heading.【Conclusion】The application of biochar can improve the photosynthetic performance of rice leaves during the grain filling period. Reducing the application of 10%, 20% nitrogen fertilizer was conducive to improving the activities of sucrose synthesis and transport enzymes in the stem and sheath at the heading stage, promoting the accumulation and translocation of stem sheath matter, improving the rice harvest index, and achieving the cultivation goal of “reducing nitrogen and maintaining yield”.

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Effect of Biochar-based Fertilizer Application on Rice Yield and Nitrogen Utilization in Film- mulched PaddyFields XIONG Jiahuan, ZHANG Yikai, XIANG Jing, CHEN Huizhe, XU Yicheng, WANG Yaliang, WANG Zhigang, YAO Jian, ZHANG Yuping 2024, 38(5): 567-576.  DOI: 10.16819/j.1001-7216.2024.230901 Abstract ( )   HTML ( )   PDF (790KB) ( )   【Objective】To investigate the impact of biochar-based fertilizers and increased biochar application on grain yield and nitrogen utilization of film-mulched rice, aiming to provide a theoretical foundation for sustainable rice mulching technology.【Methods】Utilizing the high-quality conventional japonica rice variety Zhehexiang 2(ZHX2) and the indica-japonica hybrid rice Yongyou 538(YY538), film-mulched mechanical transplanting experiments were conducted in 2021 with CK (no nitrogen application), T1 (slow-release fertilizers), and T2 (biochar-based fertilizers) treatments. In 2022, similar experiments were conducted with CK, T2, T3 (biochar-based fertilizers with an additional 6 t/hm2 biochar), and T4 (biochar-based fertilizers with an additional 12 t/hm2 biochar) treatments. The study assessed the effects of biochar-based fertilizer application on dry matter accumulation, yield, yield components, and nitrogen uptake and utilization in mulched rice fields. 【Result】 Biochar-based fertilizers enhanced the growth and yield of mulched rice. They significantly increased dry matter accumulation by 5.40% to 29.69% compared to T1, and additional biochar application further increased dry matter accumulation by 9.28% to 46.91% compared to T2. The impact was consistent throughout ZHX2's growth duration, with YY538 showing more significant effects in the later stages. Biochar-based fertilizers significantly boosted rice yield by 3.84% to 4.65% compared to T1. Increased biochar application led to a 7.97% to 15.06% yield increase compared to T2. Biochar-based fertilizers enhanced nitrogen uptake and utilization, improving nitrogen utilization efficiency. They increased nitrogen accumulation in critical growth periods by 4.87% to 31.68%, with higher accumulation observed with additional biochar application. The highest nitrogen accumulation was achieved in T4, showing an 11.87% to 40.59% increase compared to T2. Biochar-based fertilizers reduced nitrogen dry matter productivity and nitrogen grain production efficiency but enhanced nitrogen partial factor productivity, nitrogen agronomic efficiency, and nitrogen recovery efficiency. Increased biochar application further improved nitrogen utilization and reduced losses.【Conclusion】 Applying biochar-based fertilizers in mulched rice fields enhances dry matter mass and nitrogen accumulation, with additional biochar application further improving these effects, leading to increased yield and nitrogen utilization efficiency. The yield increase in ZHX2 was primarily due to panicle number and grain number per panicle, while in YY538, it was due to panicle number, with the best effect observed in T4.

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Effects of Crop Rotation Patterns and Nitrogen Fertilizer Levels on Storage and Structure of Soil Organic Carbon in Paddy Fields ZHOU Ziyu, WANG Mengjia, FENG Xiangqian, QIN Jinhua, WANG Aidong, MA Hengyu, CHU Guang, LIU Yuanhui, XU Chunmei, ZHANG Xiufu, WANG Danying, ZHENG Xi, CHEN Song 2024, 38(5): 577-590.  DOI: 10.16819/j.1001-7216.2024.230912 Abstract ( )   HTML ( )   PDF (1056KB) ( )   【Objective】The aim of this study is to clarify the role of paddy-upland crop rotation patterns and nitrogen fertilizer levels in carbon sequestration (organic carbon storage and chemical functional group characteristics) in paddy soils.【Method】Relying on the long-term paddy-upland crop rotation experiments in the China National Rice Research Institute (2003 to present), we investigated the effects of four paddy-upland crop rotation patterns: rice-fallow (RF), rice-green manure (Chinese milk vetch; RC), rice-wheat (RW), and rice-potato with rice straw mulch (RP) at two nitrogen levels during the rice growing season: no nitrogen application (N0, 0 kg/hm2) and normal nitrogen application (N1, 135 kg/hm2) on soil organic carbon stocks (0－50 cm) and the characteristics of soil organic carbon functional groups (0－20 cm) in paddy fields. 【Result】1) Within the shallow tillage layer (0－20 cm) of the soil, crop rotation was able to enhance soil organic carbon content to some extent, with the order of effectiveness being RP > RC > RW or RF. However, for soil organic carbon stocks in the full tillage layer (0－50, 0－40, and 0－30 cm), there were no significant differences between the winter crop rotations (RP, RC, and RW) and RF. In contrast, nitrogen application was found to be more favorable for soil carbon sequestration. 2) In the N0 treatment during the rice growing season after winter cropping, compared to RF, winter crop rotations (RP, RC, and RW) significantly increased the stable forms of carbon, including Alkyl C and Aromatic C, while suppressing the labile form of carbon dominated by O-Alkyl C. This treatment also significantly increased the soil humification index (HI), aromaticity (fa), and hydrophobicity, contributing to an increase in total soil organic carbon reserves in the surface layer (0－20 cm). It is noteworthy that the HI and hydrophobicity are closely associated with the C/N ratio of returned straw, which is important for promoting soil carbon sequestration in shallow soils. 【Conclusion】In comparison to crop rotation, moderate nitrogen application has shown to be more favorable for soil organic carbon reserves throughout the soil profile. On the other hand, the impact of full straw return on soil organic matter accumulation in the annual upland-paddy rotation was primarily observed in the shallow tillage layer, indicating that the effect of straw return on soil organic carbon accumulation might be overestimated when considering the entire soil profile. Therefore, further exploration is needed to better understand the fate and destination of straw carbon in paddy fields.