10 March 2024, Volume 38 Issue 2 Previous Issue   

Review and Special Topic
Research Papers
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Review and Special Topic
Research Progress in Mechanism Behind Heat Damage and Its Regulatory Techniques During Flowering in Rice
XU Yongqiang, JIANG Ning, FENG Baohua, XIAO Jingjing, TAO Longxing, FU Guanfu
2024, 38(2): 111-126.  DOI: 10.16819/j.1001-7216.2024.230601
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In recent years, extremely high temperatures have significantly impacted rice growth, yield, and quality. The flowering stage of rice is particularly sensitive to high temperatures, making it crucial to study their effects on spikelet fertility and cultivation techniques. To mitigate high-temperature damage to rice and enhance food security, this paper reviews the characteristics and mechanisms of rice floret opening, anther dehiscence, pollen scattering, pollen germination, and pollen tube elongation under high-temperature stress. It clarifies the regulatory mechanisms of heat tolerance during rice flowering and proposes cultivation measures to alleviate high-temperature damage. This paper offers new insights into heat resistance mechanisms and cultivation technologies at the rice flowering stage, with promising implications for future research.

Research Progress on the Damage and Management of Apple Snails(Ampullariider: Pomacea) in Paddy Fields
LÜ Haitao, LI Jianzhong, LU Yanhui, XU Hongxing, ZHENG Xusong, LÜ Zhongxian
2024, 38(2): 127-139.  DOI: 10.16819/j.1001-7216.2024.230807
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Rice is a widely cultivated food crop in China and around the world, with over half of the global population depending on it as their primary food source. The golden apple snail, Pomacea canaliculata, as an invasive species, poses a significant threat to rice production, garnering extensive attention in China. From sowing to field sundrying, rice is susceptible to being bitten by P. canaliculata. During sowing, it bites the embryo of rice seeds, and at the seedling stage, it attacks the entire seedling, leading to a reduction in rice seedlings and effective tillers, significantly impacting rice yield. This paper reviews the species, biological characteristics, damage patterns in paddy fields, field prevention and control technology, and resource utilization of apple snails. The aim is to lay a foundation for further prevention and control measures in paddy fields, ultimately increasing rice yield and quality and minimizing economic losses for farmers.

Research Papers
Map-based Cloning and Functional Analysis of a New Allele of D1, a Gene Controlling Plant Height in Rice (Oryza sativa L.)
GAO Junru, QUAN Hongyu, YUAN Liuzhen, LI Qinying, QIAO Lei, LI Wenqiang
2024, 38(2): 140-149.  DOI: 10.16819/j.1001-7216.2024.230502
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【Objective】Plant height is an important agronomic trait in rice breeding. Identification of genes controlling plant height and their functional characterization can provide useful genetic resources for high-yield breeding.【Methods】A dwarf mutant, d1-11, was screened from the rice variety Nipponbare by EMS mutagenesis. Phenotypic and cytological observations, gene expression, hormone content and drought resistance were analyzed. The d1-11 mutant gene was identified through map-based cloning.【Results】The d1-11 mutant exhibits dwarfism, with more shortened and widened leaves, and more rounded grains compared to the wild type. The d1-11 mutant leaf has a smaller midvein, reduced number and area of large and small veins, resulting in abnormal leaf morphology in the d1-11 mutant. The d1-11 gene is genetically mapped between two molecular markers on rice chromosome 5. Map-based cloning reveals that a single base substitution at the junction of the ninth exon-intron in the D1 gene results in the loss-of-function mutation of d1-11. The D1 gene has a higher expression level in various tissues at the seedling stage, but the expression levels decrease from the tillering stage. Exogenous abscisic acid (ABA) treatment for 24 hours induces D1 gene expression, exogenous gibberellin (GA) treatment inhibits D1 gene expression, and salt stress treatment for 24 hours can strongly induce D1 gene expression. The contents of several hormones such as GA, brassinosteroid (BR), and indole-3-acetic acid (IAA) were increased in the d1-11 mutant. The d1-11 mutant shows a significant increase in relative water content (RWC) and a reduced rate of water loss in leaves. Furthermore, d1-11 mutant plants exhibit stronger resistance to drought stress.【Conclusion】The d1-11, a novel allele in D1 locus was identified in the present study. It was showed that the d1-11 mutant had increased levels of various endogenous hormones, increased leaf water content, and enhanced resistance to drought stress. This study will further enrich the genetic resources related to dwarfism and reveals some new biological roles of the D1 gene in rice.

Genome-wide Association Analysis of Rice Seed Dehydration Rate at Maturity Stage
LIU Zhongqi, ZHANG Haiqing, HE Jiwai, GUI Jinxin
2024, 38(2): 150-159.  DOI: 10.16819/j.1001-7216.2024.230305
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【Objective】The dehydration rate of grains directly influences the safe harvesting and rapid drying of seeds. Therefore, to ensure seed quality and reduce production costs, varieties with low grain moisture content and fast dehydration rates were selected for production. 【Method】A total of 165 rice core germplasms from 82 different countries and regions were used as experimental materials. Genome-wide association analysis (GWAS) was conducted by combining the phenotype and genotype of seed dehydration rates at the maturity stage. This aimed to explore key genes sensitive to dehydration and their regulatory roles in rice germplasm, laying a foundation for cultivating and developing fast dehydration varieties. 【Results】1) Descriptive statistical analysis of dehydration rate traits of the rice core germplasm population showed that these traits exhibited continuously skewed normal distributions over two years, with significant correlations between years for rapid dehydration rates. Rapid dehydration rates were positively correlated with slow dehydration rates across different subgroups. 2) GWAS analysis identified 170 SNPs and 36 QTLs associated with dehydration rates. LD analysis revealed six QTLs closely related to dehydration rates: qGDR2.3, qGDR4.1, qGDR4.2, qGDR6.1, qGDR6.4, and qGDR10.1. 【Conclusion】 The main candidate genes within these QTL intervals, including OsPIP1;1, OsTIFY9, OsbZIP48, OsATG8b, OsDREB1C, OsSCP46, are closely associated with water transport activity, signal transduction, transcriptional regulation, and antioxidant defense. It is speculated that they play roles in seed dehydration rates and can serve as optimal candidate genes.

Super-high Yield Characteristics of Two-line Hybrid Rice Zhuoliangyou 1126
LIU Huimin, ZHOU Jieqiang, HU Yuanyi, TIAN Yan, LEI Bin, LI Jianwu, WEI Zhongwei, TANG Wenbang
2024, 38(2): 160-171.  DOI: 10.16819/j.1001-7216.2024.230307
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【Objective】Uncovering the yield potential of hybrid rice and cultivating ultra-high-yielding varieties is both a scientific challenge and a strategic approach for ensuring food security through “innovative application of agricultural technology to increase farmland productivity”. The focus is on analyzing the formation pattern of super-high yield in hybrid rice Zhuoliangyou 1126, with the small-grain sterile line Zhuo 201S as the female parent, aiming to lay theoretical support for breeding high-quality and high-efficiency super hybrid rice.【Method】In 2022, Zhuoliangyou 1126 and three super rice varieties (Liangyoupeijiu, Y Liangyou 900, and Xiangliangyou 900) were cultivated in Longhui County, Shaoyang City, Hunan Province. A systematic comparison was conducted on yield, yield components, dry matter accumulation, root system development, and lodging resistance between Zhuoliangyou 1126 and the three control varieties.【Result】Zhuoliangyou 1126 exhibited a significantly higher yield, with a 35.07% increase compared to Liangyoupeijiu, 17.84% compared to Y Liangyou 900, and 14.52% compared to Xiangliangyou 900. On the basis of stable 1,000-grain weight and seed setting rate, the yield increase in Zhuoliangyou 1126 was attributed to an increase in the total number of spikelets by striking a balance in the effective panicles and grains per panicle. Aboveground dry weight per stem, root dry weight, and root-shoot ratio of Zhuoliangyou 1126 were significantly higher than controls, indicating superior root system growth contributes to super-high yield formation. Zhuoliangyou 1126 exhibited moderate plant height, the total length of the basal three internodes, the length of the internodes under the panicle were both significantly higher than those of the controls, with the differences in the bending moment and bending resistance of the second node from the bottom between Zhuoliangyou 1126 and Xiangliangyou 900 being insignificant. Zhuoliangyou 1126 maintained strong lodging resistance together with increased plant height. Rice quality was rated Ministry Standard High Quality Grade 2, with a 5.53% yield increase under extreme high temperature compared to control Y Liangyou 1928. 【Conclusion】Zhuoliangyou 1126, maintaining stable thousand-grain weight and seed setting rate, significantly increases the total number of spikelets for super-high yield. The significant difference in grain size between the parents of Zhuoliangyou 1126 facilitates mechanized seed production through mixed sowing and harvesting, reducing seed production costs. Additionally, the 1,000-grain weight of small-grain sterile lines is only half that of conventional sterile lines. With the same seed production, the seeding area is doubled compared to conventional sterile lines, significantly cutting down the seed cost of hybrid rice. Therefore, Zhuoliangyou 1126, as a representative combination, exemplifies the “small grain seed, big grain rice” mode in its parentage, offering innovative solutions to current hybrid rice challenges and signaling a new development direction.

Relationship Between Embryo Survival and Glucose Supply of Rice Seed and Embryo Under Flooding Stress
ZHENG Guangjie, YE Chang, ZHU Junlin, TAO Yi, XIAO Deshun, XU Yanan, CHU Guang, XU Chunmei, WANG Danying
2024, 38(2): 172-184.  DOI: 10.16819/j.1001-7216.2024.230902
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【Objective】To investigate varietal differences in germ glucose supply under flooded conditions and its relationship with rice germ survival.【Method】Germinated seeds of four rice varieties with different flooding tolerance were used as material and subjected to flooding and wet (control) conditions. Dynamic changes of non-structural carbohydrate contents in seed and germ tissue, seed α-amylase activities, and germ antioxidant enzyme activities over time were analyzed, along with their correlation with seed survival rates.【Result】Under flooding stress, the glucose content and the activities of SOD and POD in the germs of the flooding-sensitive rice materials, Zhongjiazao 8(S1) and Zhongjiazao 17(S2), decreased significantly after 72 hours of flooding, leading to stagnation of germ growth and death. However, the embryo glucose content and the activities of SOD and POD remained stable in the germs of the flooding-tolerant variety Nipponbare(T1) and Yunliangyoujiu 48(T2) after 96 hours of flooding treatment, allowing the germs to continue growing and elongating. Analysis of seed α-amylase activities showed that while short-term flooding (0-48h) enhanced seed α-amylase activities in all four materials, only flooding-tolerant varieties T1 and T2 maintained high α-amylase activity under prolonged flooding (72-96h), leading to a decline in starch content within their seeds and an increase in glucose content. In contrast, the α-amylase activities of flood-sensitive varieties S1 and S2 declined after 48 and 72 hours of flooding treatment, respectively, with relatively stable starch content in the seeds but substantial declines in glucose content of the seeds and the germ. Correlation analysis revealed that germ survival was highly positively correlated with germ and seed glucose content, and POD activity of germ, while highly negatively correlated with seed starch content.【Conclusion】Under flooding stress, the germ tissue consumes a large amount of glucose to maintain its physiological metabolic balance, and the ability of seeds to supply glucose to the embryo is directly related to its survival. Changes in seed α-amylase activity play a pivotal role in the glucose supply to the germ, which is crucial for the survival and emergence of the seed under flooding stress.

Effects of Variety and Seeding Rate Interaction on Nutrient Competition Between Mechanized Dry Direct Seeded Rice and Weeds
YANG Yonggang, YUAN Xiaojuan, CAO Yun, CHEN Xuefang, YIN Huilai, WANG Zhiqiang, WEN Yanfang, YANG Zhiyuan, SUN Yuanyuan, JIA Xianwen, MA Jun, SUN Yongjian
2024, 38(2): 185-197.  DOI: 10.16819/j.1001-7216.2024.230803
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【Objective】To clarify the effect of mechanical dry direct seeded rice varieties and sowing rates on weed growth inhibition, laying a theoretical basis for achieving high-quality, high-yield, green, and efficient cultivation techniques in mechanical direct seeded rice.【Method】Using the three-line hybrid rice Chuankangyou 6308 (C1) and the two-line hybrid rice Jingliangyou 534 (C2) as test materials, three sowing rates of 15 kg/hm2 (S1), 22.5 kg/hm2 (S2), and 37.5 kg/hm2 (S3) were set to study their effects on dry matter accumulation, nutrient accumulation, and transport of the main weeds in the rice field during the critical growth period. The study also explored the relationship between rice and weed nutrient competition under the interaction of varieties and sowing rates.【Results】1) At 29 days after direct seeding, the density of weeds in the paddy fields increased significantly by 39.29% to 47.16% compared with that of rice, with the dry weight ratio and nutrient accumulation ratio of weed to rice population being higher than 1∶1, necessitating weed control. 2) Before weeding, weed density of variety C1 significantly decreased by 91.34% to 96.54% compared to C2, with dry matter accumulation of rice increasing by 19.21% to 30.24%, and nitrogen, phosphorus, and potassium accumulation increasing by 7.17% to 34.59%. For the same variety, increasing the sowing rate significantly reduced weed amount by 21.95-109.69%, increasing rice dry matter accumulation by 39.78-94.52%, and nitrogen, phosphorus, and potassium accumulation by 10.11-50.79% compared to S1 treatment. 3) After weeding and 43 days of direct seeding, weed number significantly decreased. The dry matter accumulation of C1 increased by 54.12% to 66.97% compared to C2, with nitrogen, phosphorus, and potassium nutrients increasing by 15.56% to 47.45%. For the same variety, S2 and S3 treatments significantly increased rice density by 14.94-32.34%, dry matter accumulation by 24.45-85.07%, and nitrogen, phosphorus, and potassium nutrients by 21.62-98.34% compared to S1 treatments. However, with the increase of sowing amount, nitrogen, phosphorus, and potassium nutrient transport amount and rate during the filling period, as well as rice yield, showed an increasing-decreasing trend, with S2 treatment being the highest.【Conclusions】Based on comprehensive inhibition of weed growth and rice yield characteristics, this experiment selected Chuankangyou 6308 for mechanical dry direct seeding with a seeding rate of 22.5 kg/hm2. Considering the higher total density of weeds in the rice field compared to rice, and the 1∶1 dry weight and nutrient ratio of weeds to rice population, optimal weeding timing can be achieved. This leverages the advantages of the interaction between rice varieties and seeding rates to control weed growth, reduce herbicide use, and improve yield.

Effects of Straw Return Rate on Soil Reducing Substances and Rice Growth Under Different Soil Conditions
PENG Xianlong, DONG Qiang, ZHANG Chen, LI Pengfei, LI Bolin, LIU Zhilei, YU Cailian
2024, 38(2): 198-210.  DOI: 10.16819/j.1001-7216.2024.230404
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【Objective】The study investigates the formation of reductive substances following rice straw incorporation and its impact on rice growth across different soil types.【Method】A two-year pot experiment simulated full straw incorporation at low (RL), medium (RM), and high (RH) rates on sandy loam (S1) and silty loam (S2) soils, with no straw incorporation (R0) as the control. Total soil reducing substances, Eh, ferrous ions, manganese ions, and ammonium nitrogen contents were measured, alongside analyses of rice tillering, root dry weight, root vigor, and rice yield.【Results】Soil Eh decreased significantly, and the concentrations of reducing substances increased after straw incorporation, with S2 exhibiting higher levels than S1. Compared to the control, straw incorporation up to 56 days after transplanting in 2021 increased the levels of total reducing substances, Fe, and Mn by 8.36%−199.64%, 1.43%−160.03%, and 8.43%− 57.68%, respectively. Similar increases occurred before 45 days after transplanting in 2022, ranging from 2.95% to 163.61%, 0.77% to 19.74%, and 3.28% to 64.96%. There was a positive correlation between straw incorporation and the levels of total reducing substances, Fe, and Mn. Straw incorporation significantly elevated soil ammonium N content by 11.28%−50.67% and 10.79%−351.53% before 56 days (2021) and 35 days (2022) after transplanting, respectively. Root dry weight at the tillering and jointing stages decreased by 15.06%−45.80% due to straw incorporation. In S1 soil, RL and RM increased root vigor at the jointing stage, while RH decreased root vigor on S2 soil. The number of rice tillers and dry matter accumulation decreased by 7.23%−48.44% and 3.59%−43.57%, respectively, during the rice reproductive period after straw incorporation. Rice yield was not significantly affected in the second year of RL and RM treatments, whereas RH treatment significantly reduced yield in both years. S1 exhibited higher oxidation-reduction potential than S2, with S2 displaying higher levels of reducing substances, manganese ions, ammonium nitrogen, root dry weight, root activity, tiller number, dry matter accumulation, and yield.【Conclusion】Straw incorporation increases the early-stage content of reducing substances and inhibits rice growth in cold areas. The impact of straw return on rice yield varies with soil type, with significant yield reductions observed on sticky soil following straw incorporation. Medium straw incorporation does not significantly affect the number of tillers but promotes the formation of larger panicle without reducing yield significantly. Optimizing straw incorporation technology requires effective measures to mitigate the negative effects of reducing substances.

Effects of Green Manure Planting and Lime Application on Cadmium Content in Double-cropping Rice Under Controlled Irrigation
TANG Zhiwei, ZHU Xiangcheng, ZHANG Jun, DENG Aixing, ZHANG Weijian
2024, 38(2): 211-222.  DOI: 10.16819/j.1001-7216.2024.231005
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【Objective】Cadmium (Cd) pollution in farmland is a major environmental challenge affecting the development of high-quality rice production in China, impacting both rice commodity value and human health. This study conducted a large-area field trial to investigate the effects of green manure planting and lime application on rice yield and Cd content in grain under controlled irrigation, aiming to provide technical references for rice production safety. 【Method】Early and late rice varieties used in the experiment were Xiangzaoxian 24 and Huarun 2, respectively. The field experiment was conducted in Yiyang City, Hunan Province, where five treatments were set up: conventional cultivation (CK), controlled irrigation (W), green manure + controlled irrigation (GW), lime + controlled irrigation (LW), and green manure + lime + controlled irrigation (GLW). 【Result】Compared with the CK treatment, the average cadmium content in brown rice in the early and late rice under the W, GW, and LW treatments was significantly reduced by 34.5%, 83.5%, and 83.3%, respectively. The average cadmium content in rice grain was significantly reduced by 26.3%, 82.5%, and 83.4%, respectively. As for GLW, compared to CK, the cadmium content in brown rice of late rice was only significantly reduced by 43.7%, and that of rice grain was significantly reduced by 40.8% correspondingly. Compared with the CK treatment, the average cadmium content in rice husk in early rice and late rice under GW and LW treatments was significantly reduced by 71.3% and 74.2%, respectively. However, in GLW, it was significantly reduced by 38.5% only in the late-season rice. The average cadmium content in stems and leaves in early rice and late rice under GW and LW treatments was significantly reduced by 85.3% and 79.1%, respectively, but that of GM was significantly reduced by 51.9% only in the late rice. Compared with the CK treatment, the soil pH value in the early and late rice under the W, GW, and LW treatments was significantly increased by 6.2%, 23.7%, and 20.0%, respectively. The average soil effective Cd content in the early and late rice under the GW treatment was significantly reduced by 20.0% to 22.6% during the filling period. Compared to CK, the GW and LW treatments significantly reduced Cd translocation from early rice hulls to brown rice. Except for the W treatment, where the differences between early rice hulls and late rice stems and leaves were not significant, other treatments significantly reduced the enrichment of soil Cd in stems and leaves, brown rice, and rice hulls. There was no significant difference in rice yield among treatments.【Conclusion】Under flooding irrigation after panicle differentiation, planting leguminous green manure in winter or lime application in spring could ensure rice production safety in lightly cadmium-polluted paddy fields without affecting rice yield.