Yield Of Hybrid Rice Research Articles

Achieving higher grain yield in hybrid rice through the promotion of individual growth and development

AbstractEnsuring rice (Oryza sativa) self‐sufficiency in China relies significantly on achieving high grain yields in hybrid rice production. This study conducted field experiments across two site‐years, comparing grain yield per unit of land area, grain yield generated per seedling, and associated yield traits for a hybrid rice variety under two combinations of hill spacing and the number of seedlings per hill. The combinations included a hill spacing of 30 cm × 14 cm with one seedling per hill (H14S1) and a hill spacing of 30 cm × 24 cm with three seedlings per hill (H24S3). The results revealed that H14S1 consistently outperformed H24S3, demonstrating a 7%–16% increase in grain yield per unit of land area and an impressive 88%–104% higher grain yield generated per seedling. H14S1 exhibited 56%–77% more panicles formed per seedling and 10%–15% more spikelets per panicle compared to H24S3. H14S1 produced 78%–115% higher biomass at heading and maturity per seedling and 8%–25% higher biomass at heading and maturity per tiller than H24S3. This study underscores the importance of promoting the individual growth and development of seedlings as a crucial strategy for achieving higher grain yield in hybrid rice production.

Exploring strategies for agricultural sustainability in super hybrid rice using the food-carbon-nitrogen-water-energy-profit nexus framework

The breakthrough in super hybrid rice yield has significantly contributed to China's and global food security. However, the inherent conflict between high productivity and environmentally sustainable agriculture poses challenges. Issues like water scarcity, energy crises, escalating greenhouse gas emissions, and diminishing farm profitability all threaten agricultural sustainability. In response to these challenges, we applied a holistic food-carbon-nitrogen-water-energy-profit (FCNWEP) nexus framework to comprehensively evaluate sustainability of distinct crop management strategies across three sub-sites in central China. Field experiments were conducted in Hubei and Hunan Provinces from 2017 to 2021, with a widely adopted elite super hybrid rice (Y-liangyou900). Four crop management treatments were implemented: a control (CK, 0 kg N ha-1), conventional crop management (CCM, 210-250 kg N ha-1, 7:3 basal: mid-tiller fertilizer ratio), and two integrated crop management treatments (ICM1, 180-210 kg N ha-1, 5:2:3 basal: mid-tiller: panicle initiation fertilizer ratio; ICM2, 240-270 kg N ha-1, 5:2:2:1 basal: mid-tiller: panicle initiation: flowering fertilizer ratio). Grain yield, carbon footprint, nitrogen footprint, energy footprint, nitrogen use efficiency and economic benefits were among the assessed variables. Our results showed that significant yield variations were observed, with ICM2 consistently outperforming CCM and ICM1 across the three sites. In Jingzhou, Suizhou, and Changsha, ICM2’s grain yield was 30.2, 24.7, and 13.3% higher than CCM, respectively. Additionally, net profits for ICM2 exceeded those of CCM and ICM1 by 31.8 and 115.2% in Jingzhou, 32.2 and 109.9% in Suizhou, and 15.4 and 34.0% in Changsha. Integrated crop managements, specifically ICM2, demonstrated improved nitrogen and energy use efficiency, resulting in reduced carbon, nitrogen, water, and energy footprints. Overall, composite sustainability scores, calculated using the FCNWEP framework, indicated that both ICM2 and ICM1 generally exhibited higher sustainability levels compared to CCM. This study offers valuable insights into practical management methodologies and provides recommendations for enhancing agricultural sustainability.

Impact of Agronomic Zinc Biofortification on Yield Attributes, Yield and Micronutrient Uptake of Rice (Oryza sativa L.) in Southern Odisha

Cereal crops are low in micronutrients primarily due to Iron and Zinc deficiency in soil. Iron, being the cofactor of various enzymes, performs basic functions in the human body, while its absence causes anaemia. Symptoms of Zn-deficiency appearing in the human body includes retarded growth, hypogonadism, immune dysfunction and cognitive impairment. In rice plants, their deficiency results in stunted growth and poor plant development, leading to yield reduction. Consumption of milled rice containing very low levels of iron and zinc, is one of the principal reasons for widespread malnutrition among rice consumers. Health of millions of people around the world, including India, is directly or indirectly affected due to ‘Hidden Hunger’ or ‘Malnutrition’ of iron and zinc. The current study was conducted in the summer season of 2022 at the Post Graduate Research Farm, M.S. Swaminathan School of Agriculture, comprising 8 treatments of zinc (foliar and basal) applications on rice. Influence of these treatments on grain and straw yield of rice was ascertained by measuring Pearson correlation coefficient and different multivariate tests viz., Multiple Regression, Multilayer Perceptron Neural Analysis (MPN) and Principal Component Analysis (PCA), which indicated that grain zinc and iron content, was highly influenced by the zinc application. Analysis of generated data indicated that basal application of 5 kg Zn ha−1 along with foliar application of 0.25% Zn at maximum tillering and at booting stage produced the highest grain yield (6.80 t ha-1) and superior outcomes on different yield attributes, nutrient uptake and straw yield of hybrid rice as compared to other treatments, (MARVEL 1011) in the soil of Southern Odisha.

Rapid improvement of grain appearance in three-line hybrid rice via CRISPR/Cas9 editing of grain size genes

Key messageGenetic editing of grain size genes quickly improves three-line hybrid rice parents to increase the appearance quality and yield of hybrid rice.Grain size affects rice yield and quality. In this study, we used CRISPR/Cas9 to edit the grain size gene GW8 in the maintainer line WaitaiB (WTB) and restorer line Guanghui998 (GH998). The new slender sterile line WTEA (gw8) was obtained in the BC2F1 generation by transferring the grain mutation of the maintainer plant to the corresponding sterile line WantaiA (WTA, GW8) in the T1 generation. Two slender restorer lines, GH998E1 (gw8(II)) and GH998E2 (gw8(I)), were obtained in T1 generation. In the early stage, new sterile and restorer lines in grain mutations were created by targeted editing of GS3, TGW3, and GW8 genes. These parental lines were mated to detect the impact of grain-type mutations on hybrid rice yield and quality. Mutations in gs3, gw8, and tgw3 had a minimal impact on agronomic traits except the grain size and thousand-grain weight. The decrease in grain width in the combination mainly came from gw8/gw8, gs3/gs3 increased the grain length, gs3/gs3-gw8/gw8 had a more significant effect on the grain length, and gs3/gs3-gw8/gw8(I) contributed more to grain length than gs3/gs3-gw8/gw8(II). The heterozygous TGW3/tgw3 may not significantly increase grain length. Electron microscopy revealed that the low-chalky slender-grain variety had a cylindrical grain shape, a uniform distribution of endosperm cells, and tightly arranged starch grains. Quantitative fluorescence analysis of endospermdevelopment-related genes showed that the combination of slender grain hybrid rice caused by gs3 and gw8 mutations promoted endosperm development and improved appearance quality. An appropriate grain size mutation resulted in hybrid rice varieties with high yield and quality.

Increasing Hybrid Rice Yield, Water Productivity, and Nitrogen Use Efficiency: Optimization Strategies for Irrigation and Fertilizer Management.

Water and fertilizer are crucial in rice growth, with irrigation and fertilizer management exhibiting synergies. In a two-year field study conducted in Yiyang City, Hunan Province, we examined the impact of three irrigation strategies-wet-shallow irrigation (W1), flooding irrigation (W2), and the "thin, shallow, wet, dry irrigation" method (W3)-in combination with distinct fertilizer treatments (labeled F1, F2, F3, and F4, with nitrogen application rates of 0, 180, 225, and 270 kg ha-1, respectively) on rice yield generation and water-fertilizer utilization patterns. The study employed Hybrid Rice Xin Xiang Liang you 1751 (XXLY1751) and Yue Liang you Mei Xiang Xin Zhan (YLYMXXZ) as representative rice cultivars. Key findings from the research include water, fertilizer, variety, and year treatments, which all significantly influenced the yield components of rice. Compared to W2, W1 in 2022 reduced the amount of irrigation water by 35.2%, resulting in a 42.0~42.8% increase in irrigation water productivity and a 25.7~25.9% increase in total water productivity. In 2023, similar improvements were seen. Specifically, compared with other treatments, the W1F3 treatment increased nitrogen uptake and harvest index by 1.4-7.7% and 5.9-7.7%, respectively. Phosphorus and potassium uptake also improved. The W1 treatment enhanced the uptake, accumulation, and translocation of nitrogen, phosphorus, and potassium nutrients throughout the rice growth cycle, increasing nutrient levels in the grains. When paired with the F3 fertilization approach, W1 treatment boosted yields and improved nutrient use efficiency. Consequently, combining W1 and F3 treatment emerged as this study's optimal water-fertilizer management approach. By harnessing the combined effects of water and fertilizer management, we can ensure efficient resource utilization and maximize the productive potential of rice.

Optimal seeding rate enhances seedling quality, mechanical transplanting quality, and yield in hybrid rice.

To determine the appropriate seeding rate for machine-transplanted hybrid rice, field experiments were conducted during 2022-2023 using the hybrid rice variety Huazhe You 210 as the material. Four seeding rate treatments were set up: 40 (T1), 60 (T2), 80 (T3) and 100g tray-1 (T4), to investigate the effects of seeding rate on the seedling quality, transplanting quality, yield formation, and economic benefits of high-quality indica hybrid rice seedlings. The results showed that with increasing seeding rate, the seedling base stem diameter and seedling plumpness of hybrid rice seedlings decreased, but the root entwining force gradually increased, leading to a deterioration in individual seedling quality but an improvement in collective characteristics. As the seeding rate increased, the missing hill rate during mechanical planting of hybrid rice significantly decreased, while the number of seedlings per hill and the damaged seedling rate showed an upward trend. The growth volume of tillers, tillering spikelet rate, and harvest index of hybrid rice in the field showed an overall downward trend with increasing seeding rate, while the accumulation of dry matter initially increased and then decreased. The yield and economic benefits of hybrid rice grains showed an initial increase followed by a decrease with increasing seeding rate, with the highest yield and economic benefits achieved with the T2 treatment. In conclusion, the appropriate seeding rate for machine-transplanted hybrid rice is T2 (60g tray-1), which can maintain good seedling quality and improve transplanting quality, coordinate larger collective growth and appropriate harvest index, contributing to high yield and good economic benefits.

Modulation of histone acetylation enables fully mechanized hybrid rice breeding.

Hybrid rice has achieved high grain yield and greatly contributes to food security, but the manual-labour-intensive hybrid seed production process limits fully mechanized hybrid rice breeding. For next-generation hybrid seed production, the use of small-grain male sterile lines to mechanically separate small hybrid seeds from mixed harvest is promising. However, it is difficult to find ideal grain-size genes for breeding ideal small-grain male sterile lines without penalties in the number of hybrid seeds and hybrid rice yield. Here we report that the use of small-grain alleles of the ideal grain-size gene GSE3 in male sterile lines enables fully mechanized hybrid seed production and dramatically increases hybrid seed number in three-line and two-line hybrid rice systems. The GSE3 gene encodes a histone acetyltransferase that binds histones and influences histone acetylation levels. GSE3 is recruited by the transcription factor GS2 to the promoters of their co-regulated grain-size genes and influences the histone acetylation status of their co-regulated genes. Field trials demonstrate that genome editing of GSE3 can be used to immediately improve current elite male sterile lines of hybrid rice for fully mechanized hybrid rice breeding, providing a new perspective for mechanized hybrid breeding in other crops.

A higher-yield hybrid rice is achieved by assimilating a dominant heterotic gene in inbred parental lines.

The exploitation of heterosis to integrate parental advantages is one of the fastest and most efficient ways of rice breeding. The genomic architecture of heterosis suggests that the grain yield is strongly correlated with the accumulation of numerous rare superior alleles with positive dominance. However, the improvements in yield of hybrid rice have shown a slowdown or even plateaued due to the limited availability of complementary superior alleles. In this study, we achieved a considerable increase in grain yield of restorer lines by inducing an alternative splicing event in a heterosis gene OsMADS1 through CRISPR-Cas9, which accounted for approximately 34.1%-47.5% of yield advantage over their corresponding inbred rice cultivars. To achieve a higher yield in hybrid rice, we crossed the gene-edited restorer parents harbouring OsMADS1GW3p6 with the sterile lines to develop new rice hybrids. In two-line hybrid rice Guang-liang-you 676 (GLY676), the yield of modified hybrids carrying the homozygous heterosis gene OsMADS1GW3p6 significantly exceeded that of the original hybrids with heterozygous OsMADS1. Similarly, the gene-modified F1 hybrids with heterozygous OsMADS1GW3p6 increased grain yield by over 3.4% compared to the three-line hybrid rice Quan-you-si-miao (QYSM) with the homozygous genotype of OsMADS1. Our study highlighted the great potential in increasing the grain yield of hybrid rice by pyramiding a single heterosis gene via CRISPR-Cas9. Furthermore, these results demonstrated that the incomplete dominance of heterosis genes played a major role in yield-related heterosis and provided a promising strategy for breeding higher-yielding rice varieties above what is currently achievable.

Shading at the Booting Stage Improved the Grain Quality of Hybrid Rice Due to Reduced Spikelet Production

As a growing abiotic stress, light deficient conditions seriously affect the yield and quality of rice. However, few studies focus on the effects of shading on grain quality at the booting stage and the responses of different hybrid rice cultivars to shading. Field experiments involving four representative rice (Oryza sativa L.) cultivars across no shading (CK) and 40% shading at the booting (S) and grain filling stages (SS) were conducted in 2021 and 2022. Compared with CK, S reduced grain yield by 53.0% but increased the head rice rate by 11.4% averaged across varieties and years. The chalkiness degree (CD) and chalky grain percentage (CR) were reduced by 73.0% and 61.6% in S due to its 45.3% lower total spikelets m–2, 44.0% lower grain–leaf ratio and 23.5% lower dry weight spikelet production efficiency, compared with CK. The CD and CR in SS were 49.5% and 41.0% higher and HR was 7.1% lower than that in CK. Shading significantly reduced amylose content, peak viscosity and breakdown value, but increased protein content and setback value, and the effects of SS were greater than S. Y-liangyou900 and Liangyoupeijiu showed better milling quality, while Y-liangyou900 and Chuanyou6203 obtained a better appearance and eating quality than the other varieties under both S and SS. In conclusion, shading at the booting stage significantly improved the milling, appearance and nutritional quality, and did not reduce the cooking and eating quality, but led to a significant decline in the grain yield of hybrid rice. Moreover, Y-liangyou900 exhibited better rice quality but lower yield under shading treatments. Therefore, more attention needs to be focused on screening shade-tolerant varieties using both yield and quality to cope with climate change in the future.

Post-heading dry-matter transport and nutrient uptake differentiate hybrid and inbred indica rice in the double-cropping system in South China.

Hybrid rice demonstrated superior performance in enhancing yield and efficiency in rice production compared to inbred rice. Nevertheless, the underlying mechanism responsible for the increased yield and efficiency of hybrid rice in South China's double-cropping rice region remains understudied. Field experiments over two consecutive years were conducted. Firstly, yield variations among 20 inbred and 15 hybrid rice cultivars prevalent in South China's double-cropping rice system were examined. Secondly, selecting representative hybrid and inbred rice cultivars with significant yield disparities were carried out on further analyzing dry-matter production, source-sink relationships, and nutrient absorption and utilization in both rice types. Hybrid rice displayed an average grain yield of 8.07 and 7.22t hm-2 in the early and late seasons, respectively, which corresponds to a 12.29% and 13.75% increase over inbred rice with statistically significant differences. In comparison to inbred rice, hybrid rice exhibited enhanced nitrogen concentration in leaves at the heading stage (15.48-16.20%), post-heading dry matter accumulation (52.62-73.21%), post-heading dry matter conversion rate (29.23-34.12%), and harvest index (17.31-18.37%). Additionally, grain nitrogen and phosphorus uptake in hybrid rice increased by 11.88-22.50% and 16.38-19.90%. Hybrid rice mainly improved post-heading nitrogen and phosphorus uptake and transport, while not total nitrogen and phosphorus uptake. Internal nitrogen and phosphorus use efficiency enhanced by 9.83%-14.31% and 10.15%-13.66%, respectively. Post-heading dry matter accumulation, harvest index, grain nitrogen and phosphorus uptake, and internal nitrogen and phosphorus use efficiency exhibited significant positive linear correlations with grain yield. The period from heading to maturity is critical for enhancing hybrid rice yield and efficiency. Improving photosynthetic capacity during this period and promoting nutrient transport to grains serve as crucial pathways for increasing grain yield and efficiency. This study is of great significance for further improvement grain yield and breeding rice cultivars with high-yield and high nutrients use efficiency for South China's double-cropped rice system.

Utilizing differences in bTH tolerance between the parents of two-line hybrid rice to improve the purity of hybrid rice seed.

Two-line hybrid rice based on Photoperiod/thermo-sensitive genic male sterile (P/TGMS) lines has been developed and applied widely in agriculture due to the freedom in making hybrid combinations, less difficulty in breeding sterile lines, and simpler procedures for breeding and producing hybrid seed. However, there are certain risks associated with hybrid seed production; if the temperature during the P/TGMS fertility-sensitive period is lower than the critical temperature, seed production will fail due to self-pollination. In a previous study, we found that the issue of insufficient purity of two-line hybrid rice seed could be initially addressed by using the difference in tolerance to β-triketone herbicides (bTHs) between the female parent and the hybrid seeds. In this study, we further investigated the types of applicable herbicides, application methods, application time, and the effects on physiological and biochemical indexes and yield in rice. The results showed that this method could be used for hybrid purification by soaking seeds and spraying plants with the bTH benzobicylon (BBC) at safe concentrations in the range of 37.5-112.5 mg/L, and the seeds could be soaked in BBC at a treatment rate of 75.0 mg/L for 36-55 h without significant negative effects. The safe concentration for spraying in the field is 50.0-400.0 mg/L BBC at the three-leaf stage. Unlike BBC, Mesotrione (MST) can only be sprayed to achieve hybrid purification at concentrations between 10.0 and 70.0 mg/L without affecting yield. The three methods of hybrid seed purification can reach 100% efficiency without compromising the nutritional growth and yield of hybrid rice. Moreover, transcriptome sequencing revealed that 299 up-regulated significant differentially expressed genes (DEGs) in the resistant material (Huazhan) poisoned by BBC, were mainly enriched in phenylalanine metabolism and phenylpropanoid biosynthesis pathway, it may eliminate the toxic effects of herbicides through this way. Our study establishes a foundation for the application of the bTH seed purification strategy and the three methods provide an effective mechanism for improving the purity of two-line hybrid rice seeds.

Effect of nitrogen level on growth, yield attributes and yield of hybrid varieties of rice (Oryza sativa L.)

A field experiment was conducted during two consecutive seasons of kharif 2020 and 2021 at Agronomy Research Farm, Acharya Narendra Deva University of Agriculture and Technology, Kumarganj Ayodhya (U.P.) to evaluate the effect of nitrogen level on growth, yield attributes and yield of different hybrid varieties of rice (Oryza sativa L.). The experiment was conducted in factorial randomized block design which comprised of 4 levels of nitrogen viz., 0 % RDN, 50 % RDN, 75 % RDN and 100 % RDN and 4 varieties viz., Arize-6444 Gold, Ankur-7576, 27P31 and Shahi-Dawat. Experiment was replicated three times. Results revealed significantly higher growth parameters, yield attributes and yield at 100% of RDN (150 kg N ha-1) which is at par with 75 % RDN (112 kg N ha-1) and significantly superior over 0 % RDN and 50 % RDN (75kg N ha-1) were increased at all stages except days taken to 50% flowering. The growth parameters, yield attributes and yield were increased significantly with Ankur-7576 variety except for length of the panicle (cm) and test weight (g). Ankur-7576 gave a good response in low level of nitrogenous fertilizer and showed good efficiency in utilization of available and applied nitrogen to the crop and is best suitable for obtaining higher yield of hybrid rice.

Base Editing of EUI1 Improves the Elongation of the Uppermost Internode in Two-Line Male Sterile Rice Lines

The use of male sterile lines (MSLs) of rice is essential for heterosis utilization. However, MSLs have a common defect in the elongation of the uppermost internode, eventually leading to incomplete panicle exsertion, blocking pollination, and reducing the hybrid rice seed yield. Previously, the elongated uppermost internode 1 (EUI1) was identified as an active gibberellin-deactivating enzyme that plays a key role in panicle exsertion from the flag leaf sheath in rice (Oryza sativa L.). We used an adenine base editor to edit EUI1 and obtained two types of homozygous transgenic plants (eui1-1 and eui1-2). The transcription and translation levels of EUI1 in the two mutants were significantly lower than in the wild type, as was the oxidation activity of EUI1 to active gibberellins (GAs), which also decreased. The contents of the plant hormones GA1, GA3, and GA4 in eui1-1 (1.64, 1.55, and 0.92 ng/g) and eui1-2 (0.85, 0.64, and 0.65 ng/g) panicles were significantly higher than the wild type (0.70, 0.57, and 0.42 ng/g). The uppermost internode lengths of the mutant were 26.5 and 23.6 cm, which were significantly longer than that of the wild type (18.0 cm), and the cell lengths of the mutant were 161.10 and 157.19 μm, which were longer than that of the wild type (89.28 μm). Our results indicate that the adenine base editing system could increase the content of endogenous bioactive GAs in young panicles by fine-tuning EUI1 activity, reduce the defect of panicle enclosure in MSLs and increase the yield of hybrid rice seed production.

Effect of phosphate solubilizing bacteria and blue green algae on yield and NPK content in hybrid rice

A pot experiment was conducted during kharif season of 2020 on sandy loam soil in texture and classified as mixed hyperthermic typic haplustepts to investigate the impact of phosphate solubilizing bacteria (PSB) and blue green algae (BGA) on crop yield and NPK nutrient uptake in hybrid rice cultivation. Thirteen treatments laid in completely randomized design with two different doses of chemical fertilizers (100% and 75%), two isolates of PSB (Enterobacter cloacae strain BAU3 and Bacillus aryabhattai strain BAUMS8) and blue green algae had been used in the study. The grain and straw yield of hybrid rice and nutrient uptake in both grain and straw increased significantly when supplied with 100% recommended dose of inorganic fertilizers (RDF) + PSB @ 750 ml ha-1 + BGA @ 10 kg ha-1 as compared to 100% RDF. It had been observed that combined application of PSB and BGA along with 100% RDF, enhanced grain and straw yield upto 11.17 and 6.53 percent, respectively in comparison to 100% RDF. Increase in the concentration of grain and straw N in treatment T8 was 8.65% and 11.42%, respectively, when compared with treatment T2 (100% RDF). The concentration of grain P in treatment T8 were 5.80% when compared with treatment T2 (100% RDF) while the magnitude of increase in rice straw was 7.28 percent. A similar trend of result was obtained in the case of K content in grain and straw of hybrid rice but the K concentration was higher in straw. Finally, application of 100% RDF along with PSB @ 750 ml ha-1 + BGA @ 10 kg ha-1 significantly augmented the yield and nutrient content in hybrid rice.

Overexpression of OsNF-YB4 leads to flowering early, improving photosynthesis and better grain yield in hybrid rice

For cereal crops, such as rice, the grain yield mainly comes from the accumulation of carbohydrates in the seed, which depends ultimately on photosynthesis during the growth period. To create early ripen variety, higher efficiency of photosynthesis is thus necessary to get higher grain yield with shorter growth period. In this study, flowering early was observed in the hybrid rice with overexpression of OsNF-YB4. Along with the flowering early, the hybrid rice also was shorter in plant height with less of leaves and internodes, but no changes of panicle length and leaf emergence. The grain yield was kept or even increased in the hybrid rice with shorter growth period. Transcription analysis revealed that Ghd7-Ehd1-Hd3a/RFT1 was activated early to promote the flowering transition in the overexpression hybrids. RNA-Seq study further showed that carbohydrate-related pathways were significantly altered in addition to circadian pathway. Notably, up-regulation of three pathways related to plant photosynthesis was observed, as well. Increased carbon assimilation with alteration of chlorophyll contents was subsequently detected in the following physiological experiments. All these results demonstrate that overexpression of OsNF-YB4 in the hybrid rice activates flowering early and improves photosynthesis resulting in better grain yield with shorter growth period.

Modelling nitrogen management in hybrid rice for coastal ecosystem of West Bengal, India.

Hybrid rice requires adequate nitrogen (N) management in order to achieve good yields from its vegetative and reproductive development. With this backdrop, a field experiment was conducted at Regional Research Station (Coastal Saline Zone), Bidhan Chandra Krishi Viswavidyalaya, Kakdwip, West Bengal (India) to record growth and yield performance of hybrid rice (cv. PAN 2423) under varied N-fertilizer doses. A modelling approach was adopted for the first time in hybrid rice production system under coastal ecosystem of West Bengal (India). In the present study, the Agricultural Production Systems Simulator (APSIM) model was calibrated and validated for simulating a hybrid rice production system with different N rates. The APSIM based crop simulation model was found to capture the physiological changes of hybrid rice under varied N rates effectively. While studying the relationship between simulated and observed yield data, we observed that the equations developed by APSIM were significant with higher R2 values (≥0.812). However, APSIM caused an over-estimation for calibrate data but it was rectified for validated data. The RMSE of models for all the cases was less than respective SD values and the normalized RMSE values were ≤20%. Hence, it was proved to be a good rationalized modelling and the performance of APSIM was robust. On the contrary, APSIM underestimated the calibrated amount of N (kg ha-1) in storage organ of hybrid rice, which was later rectified in case of validated data. A strong correlation existed between the observed and APSIM-simulated amounts of N in storage organ of hybrid rice (R2 = 0.94** and 0.96** for the calibration and validation data sets, respectively), which indicates the robustness of the APSIM simulation study. Scenario analysis also suggests that the optimal N rate will increase from 160 to 200 kg N ha-1 for the greatest hybrid rice production in coming years under elevated CO2 levels in the atmosphere. The APSIM-Oryza crop model had successfully predicted the variation in aboveground biomass and grain yield of hybrid rice under different climatic conditions.

Effects of Mixed Planting on Machine Transplanting Adaptability and Grain Yield of Hybrid Rice

Because the current hybrid rice machine transplanting sowing quantity is too large and the high rate of missing hills or poor seedling quality during mechanical transplanting, the mechanized planting of hybrid rice is limited, which results in significant hindrance of large-scale planting of hybrid rice in China. In this study, a mixed sowing technology (replacement of a portion of hybrid rice seeds with conventional rice seeds) in seedling cultivation was adopted to determine the appropriate variety combinations and conventional rice sowing quantity using a variety combination experiment and sowing quantity experiments, respectively. The results of the variety combination experiment showed that combinations of Changyou 4 mixed with Nanjing 5055, and Yuanliangyou mixed with Yangdao 6 could reduce the sowing quantity of hybrid rice, improve the quality of machine transplanting, and not reduce the grain yield. The results of the conventional rice sowing quantity experiment showed that with the increase in conventional rice sowing quantity, the seedling quality, spikelet per panicle, and filled kernel percentage decreased, and the mechanical transplanting quality improved. Compared with pure sowing hybrid rice, the grain yield was not significantly different in the japonica rice treatment when the sowing quantity of Nanjing 5055 was more than 75 g/tray and Yangdao 6 was more than 60 g/tray. With the increase in conventional rice sowing quantity, the missing hill rate decreased significantly and the seedling density increased significantly, so that the panicle number was also improved, which might have compensated the reduction in seedling quality, spikelet per panicle, and filled kernel percentage. As a whole, 90 g Nanjing 5055 seeds mixed with 30 g Changyou 4 seeds per tray and 75 g Yangdao 6 seeds mixed with 30 g Yuanliangyou seeds per tray were suitable sowing quantities for mixed planting that could ensure strong seedlings and better mechanical transplanting quality, while reducing the cost (reduce the sowing quantity of hybrid rice and conventional rice) without reducing the grain yield.

Yuan Longping, a great world hunger fighter

Yuan Longping, a great world hunger fighter

Effect of Nitrogen and Zinc fertilization on Growth and Yield of Hybrid Rice (Oryza sativa L.)

Effect of Nitrogen and Zinc fertilization on Growth and Yield of Hybrid Rice (Oryza sativa L.)

Optimizing Agronomy Improves Super Hybrid Rice Yield and Nitrogen Use Efficiency through Enhanced Post-Heading Carbon and Nitrogen Metabolism

The super hybrid rice breeding program in China has raised genetic yield ceilings through morphological improvements and inter-subspecific heterosis. Despite this, little information on the physiological basis underlying this yield transformation exists, and less so on the genotype x environment x management conditions enabling consistent yield gains. Here, we assess grain yield, photosynthetic physiology, and leaf carbon and nitrogen (N) metabolic properties of super rice (Y-liangyou900) under four management practices (i.e., zero-fertilizer control, CK; farmers’ practice, FP; high-yield and high-efficiency management, OPT1; and super-high-yield management, OPT2) using a field experiment conducted over five years. Grain yield and agronomic N use efficiency (AEN) of OPT2 were 15% and 10% higher than OPT1, and 30% and 78% higher than FP, respectively. The superior yields of OPT2 were attributed to higher source production capacity, that is, higher leaf photosynthetic rate, carbon metabolic enzyme activity (i.e., AGP and SPS), nitrogen metabolic enzyme activity (i.e., NR, GS, and GOGAT), soluble protein and sugar content, and delayed leaf senescence (the latter due to elevated activity of protective enzyme systems) during grain filling. The higher AEN of OPT2 was associated with higher activity of leaf carbon metabolic enzyme (i.e., AGP and SPS), nitrogen metabolic enzyme (i.e., NR, GS, GDH, and GOGAT) and protective enzyme (POD) after heading, and lower C/N ratio in grains. We conclude that optimized management (optimized water and fertilizer management with appropriate dense planting) improved grain yield and N use efficiency simultaneously by enhancing post-heading leaf carbon and N metabolism and delayed leaf senescence.