Enhance Rice Yield Research Articles

Global analysis of yield benefits and risks from integrating trees with rice and implications for agroforestry research in Africa

While agroforestry is a well-established approach for agroecological intensification, rice is less often integrated with trees than other annual staple crops. The benefits and risks from rice agroforestry practices have not been systematically explored. Considering the need for strategies that may address low fertility and high degradation of arable soils and contribute to smallholder farm productivity, livelihoods and climate resilience, such exploration would both be timely and relevant. This study, therefore, reviews the published literature on integrating trees in rice production worldwide and provides perspectives for future research, with special attention to Africa, where the potential for sustainable productivity enhancement is deemed highest. Worldwide, six improved rice agroforestry practices are distinguished: hedgerow alley-cropping, short-term (0.5–4 years) improved fallows, pre-rice green manuring, biomass transfer, systematically arranged rice – tree intercropping and irregularly dispersed trees in fields. The rice agroforestry practices in the 87 publications reviewed were associated with 204 woody perennial species world-wide. Rice agroforestry practices provide a range of products and services to farmers but rice yield is the only quantitative performance indicator reported widely enough to enable meta-analysis. Frequently reported comparative or additional effects of fertilizer application, made it possible to include this aspect in the analyses. Across all types of agroforestry practices enumerated, the average effect of adding trees compared to a no-fertilizer and no-tree control is + 38%. The most beneficial practices in terms of enhancing rice yield were biomass transfer, pre-rice green manuring (100% of data points showing positive responses for both practices) and hedgerow alley-cropping (21% positive cases overall but 64% where fertilizer was not applied). Yield reductions occurred with fertilized intercropping compared to a fertilized mono-crop (in 95% of cases) and with the unfertilized short fallow practice (50% of data points showed yield reduction due to competition in the relay intercropping stage). Tree species that combined rice yield enhancements (alongside other products and services) with wide environmental adaptability across the African continent, include Sesbania rostrata, Aeschynomene afraspera , Acacia auriculiformis , Gliricidia sepium and Gmelia arborea . Yield benefits and risks from integrating trees with smallholder rice cropping depend on the type of agroforestry practice used and how each practice interacts with fertilizer application. Further research is needed to investigate the impact of different ways of integrating trees with rice cropping on wider environmental, social and economic sustainability aspects, that are driving increasing interest in rice agroforestry. • World-wide, 204 woody perennial species were used in 6 types of rice agroforestry. • Pre-rice green manure, biomass transfer and hedgerows increased rice yield most. • Sesbania rostrata and Aeschynomene afraspera are effective as pre-rice green manure. • A broad range of tree species are useful for biomass transfer. • Gliricidia sepium and Gmelia arborea benefit rice yield in hedgerow alley-cropping.

OsCOMT, encoding a caffeic acid O-methyltransferase in melatonin biosynthesis, increases rice grain yield through dual regulation of leaf senescence and vascular development.

SummaryMelatonin, a natural phytohormone in plants, plays multiple critical roles in plant growth and stress responses. Although melatonin biosynthesis‐related genes have been suggested to possess diverse biological functions, their roles and functional mechanisms in regulating rice grain yield remain largely unexplored. Here, we uncovered the roles of a caffeic acid O‐methyltransferase (OsCOMT) gene in mediating rice grain yield through dual regulation of leaf senescence and vascular development. In vitro and in vivo evidence revealed that OsCOMT is involved in melatonin biosynthesis. Transgenic assays suggested that OsCOMT significantly delays leaf senescence at the grain filling stage by inhibiting degradation of chlorophyll and chloroplast, which, in turn, improves photosynthesis efficiency. In addition, the number and size of vascular bundles in the culms and leaves were significantly increased in the OsCOMT‐overexpressing plants, while decreased in the knockout plants, suggesting that OsCOMT plays a positive role in vascular development of rice. Further evidence indicated that OsCOMT‐mediated vascular development might owe to the crosstalk between melatonin and cytokinin. More importantly, we found that OsCOMT is a positive regulator of grain yield, and overexpression of OsCOMT increase grain yield per plant even in a high‐yield variety background, suggesting that OsCOMT can be used as an important target for enhancing rice yield. Our findings shed novel insights into melatonin‐mediated leaf senescence and vascular development and provide a possible strategy for genetic improvement of rice grain yield.

Effects of Biochar Amendment and Nitrogen Fertilizer on RVA Profile and Rice Grain Quality Attributes.

Improving rice production in modern agriculture relies heavily on the overuse of chemical fertilizer, which adversely affects grain quality. Biochar (BC) application is well known for enhancing rice yield under reduced nitrogen (N) application. Therefore, we conducted a two-year field experiment in 2019 and 2020 to evaluate RVA profile characteristics, grain milling, and appearance qualities under four BC rates (0, 10, 20, 30 t ha−1) in combination with two N levels (135 and 180 kg ha−1). The results showed that BC at 30 t ha−1 along with 135 kg N ha−1 improved rapid visco-analyzer (RVA) profile attributes, including peak viscosity (4081.3), trough viscosity (3168.0), break down (913.3), final viscosity (5135.7), and set back (1967.7). Grain yield, grain rain length, milled rice rate, percent grains with chalkiness, amylose, and starch content were improved by 27%, 23%, 37%, 24%, 14%, and 8%, respectively, in the plots treated with the combination of 30 t BC ha−1 and 180 kg N ha−1. A positive coefficient of correlation was observed in RVA profile, milling, and apparent quality of rice with soil properties. These results suggested that BC at 20 to 30 t ha−1 in combination with 135 kg N ha−1 is a promising option for enhancing grain yield, RVA profile, appearance, and milling quality.

Genetic diversity reveals synergistic interaction between yield components could improve the sink size and yield in rice

AbstractIntensive breeding programs have increased rice yields, strongly contributing to increasing global food security during the post‐green revolution period. However, rice productivity has reached a yield barrier where further yield improvement is restricted by inadequate information on the association of yield components, and morphological and physiological traits with yield. We conducted a field experiment to evaluate (i) the contribution of morphological and physiological traits to yield and (ii) quantify the trade‐off effect between the yield components in rice, using a mini‐core collection of 362 rice genotypes comprising geographically distinct landraces and breeding lines. Our data point towards multiscale coordination of physiological and morphological traits associated with yield and biomass. Considerable trait variations across the genotypes in yield ranging from 0.5 to 78.5 g hill−1and harvest index ranging from 0.7% to 60.7% highlight enormous diversity in rice across the globe. The natural elimination of trade‐off between yield components revealed the possibility to enhance rice yield in modern cultivars. Furthermore, our study demonstrated that genotypes with larger sink sizes could fix more carbon to achieve a higher yield. We propose that the knowledge thus generated in this study can be helpful for (a) trait‐based modeling and pyramiding alleles in rice‐breeding programs and (b) assisting breeders and physiologists in their efforts to improve crop productivity under a changing climate, thus harnessing the potential for sustainable productivity gains.

Characteristics of root‐associated bacterial community and nitrogen biochemical properties of twoJaponicarice cultivars with different yields

AbstractRoot‐associated microbiomes play pivotal roles in rice plant nutrition and productivity. We studied how the Liaoxing 1 and Akitakomachi rice cultivars, which are characterized by high and low yields, respectively, modified the nutrient content, enzymatic activities in the rhizosphere, and bacterial community structure in the root endosphere, rhizosphere, and bulk soil with and without nitrogen application. Rice genotype and nitrogen application amount are both essential driving factors for changes in the nutrient content, enzymatic activities, and bacterial community. Bacterial community structure varied significantly across the three root‐associated compartments, and rhizosphere and bulk soil harbored significantly higher diversity and richness of bacteria than root endophytes. Bacterial communities in the root endosphere are mainly structured by rice cultivars. Nitrogen fertilization application influenced the compositions and functions of bacterial groups across the three compartments.Prolixibacteriaceae, as nitrogen‐fixing bacteria, were significantly enriched in the rhizosphere, and the relative abundance in the rhizosphere of the high‐yield cultivar was higher than that of the low‐yield cultivar. Rice genotype and nitrogen application amount are both essential driving factors for changes in nutrient content and enzymatic activities. In this study, it was found that the higher available nitrogen content and soil enzymatic activities in the rhizosphere of the high‐yield rice cultivar promoted rice nitrogen use, and they ultimately formed a positive feedback loop. Our results indicated that root‐associated bacterial communities combined with soil enzymatic activities strengthen the transformation of nitrogen nutrients, suggesting that the interactions could represent a mechanism for enhancing rice yield.

The Effect of Zinc Oxide Nanoparticles for Enhancing Rice (Oryza sativa L.) Yield and Quality

Zinc oxide nanoparticles (ZnO NPs) have been applied widely in agriculture, and many studies were conducted to evaluate the effect of ZnO NPs on plant growth. So far, few studies have been investigated with regard to the potential effect of ZnO NPs on cereal yield formation or Zn content in grains. Herein, we used a pot experiment, which was conducted involving five dosages of Zn (0.3, 0.6, 1.2, 2.4, and 4.8 g Zn pot−1), to evaluate the impacts which ZnO NPs made in rice yield, dry matter accumulation, rice quality and grain Zn contents. The results demonstrated that ZnO NPs increased the production of grain, dry matter accumulation and particulate Zn content. Compared with control treatment, ZnO NPs application presented higher rice yield with more panicle number (4.83–13.14%), spikelets per panicle (4.81–10.69%), 1000-grain weight (3.82–6.62%) and filled grain rate (0.28–2.36%). Additionally, the dry jointing, heading and mature periods, LAI, SPAD values, and photosynthetic potentials of ZnO NPs were all significantly higher relative to treatment without ZnO NPs. The more photosynthetic substances and higher dry matter accumulated in the whole rice growing stage resulted in higher rice grain yield. Furthermore, ZnO NPs increased brown rice rate, milled rice rate, head rice rate, chalkiness size, chalkiness grain rate, chalkiness degree, amylose content and protein content, improving rice processing and appearance qualities. For the Zn nutrition in rice grain, ZnO NPs application significantly increased the Zn content of edible polished rice and promoted the relocation of Zn from the aleurone layer. This study effectively demonstrated that ZnO NPs could be a potential high-performed fertiliser for enhancing rice yield and quality.

Combined biochar and double inhibitor application offsets NH3 and N2O emissions and mitigates N leaching in paddy fields

The effects of combined biochar and double inhibitor application on gaseous nitrogen (N; nitrous oxide [N2O] and ammonia [NH3]) emissions and N leaching in paddy soils remain unclear. We investigated the effects of biochar application at different rates and double inhibitor application (hydroquinone [HQ] and dicyandiamide [DCD]) on NH3 and N2O emissions, N leaching, as well as rice yield in a paddy field, with eight treatments, including conventional urea N application at 280 kg N ha−1 (CN); reduced N application at 240 kg N ha−1 (RN); RN + 7.5 t ha−1 biochar (RNB1); RN + 15 t ha−1 biochar (RNB2); RN + HQ + DCD (RNI); RNB1 + HQ + DCD (RNIB1); RNB2 + HQ + DCD (RNIB2); and a control without N fertilizer. When compared with N leaching under RN, biochar application reduced total N leaching by 26.9–34.8% but stimulated NH3 emissions by 13.2–27.1%, mainly because of enhanced floodwater and soil NH4+-N concentrations and pH, and increased N2O emission by 7.7–21.2%, potentially due to increased soil NO3−-N concentrations. Urease and nitrification inhibitor addition decreased NH3 and N2O emissions, and total N leaching by 20.1%, 21.5%, and 22.1%, respectively. Compared with RN, combined biochar (7.5 t ha−1) and double inhibitor application decreased NH3 and N2O emissions, with reductions of 24.3% and 14.6%, respectively, and reduced total N leaching by up to 45.4%. Biochar application alone or combined with double inhibitors enhanced N use efficiency from 26.2% (RN) to 44.7% (RNIB2). Conversely, double inhibitor application alone or combined with biochar enhanced rice yield and reduced yield-scaled N2O emissions. Our results suggest that double inhibitor application alone or combined with 7.5 t ha−1 biochar is an effective practice to mitigate NH3 and N2O emission and N leaching in paddy fields.

Genetic Analysis of Yield Attributes in Rice for Water Deficit Under Egyptian Conditions التحليل الوراثى لصفات المحصول فى الارز للاجهاد المائى تحت الظروف المصرية

Rice parental genotypes with good combining abilities provide an efficient tool to enhance rice yield under water deficit conditions. Using 15 F1 hybrids derived from a half diallel mating involving six parental genotypes, two experiments were carried out during 2019 and 2020 growing seasons to investigate the genetic analysis and combining ability for yield and its components under irrigated (E I) and water stress (E II) environments. Eight agronomic traits were studied over a period of two seasons, and cluster analysis based on 16 SSR primers found that the genotypes under study differed greatly in terms of variation. Overall, all yield attributes have been significantly affected by water deficit and was governed by both additive and non-additive gene actions. Based on the mean values and GCA effects, Gaori and IET1444 are suitable for incorporation of earliness and drought tolerance traits. Obviously that Gaori, IET1444, IRAT 170 and WAB 450 would serve as good general combiners for grain yield attributes under (E II) conditions. Due importance should be given for six combinations viz, Giza 177 x IRAT 170, Giza 177x Gaori, Sakha 101x IRAT 170, Sakha 101x IET 1444, Gaori x WAB 450 and IET 1444x WAB 450 to identify as new genotypes with high grain yield under water deficit condition. There might be a great possibility to get the best new combinations through crossing genotypes with highest genetic distance. Therefore, these findings should be considered when selecting elite genotypes for developing superior new rice crosses under water-stress conditions.

Weather Forecast Based Rice Advisory Services in Bangladesh

Strengthening the early warning system to forecast extreme weather and provide action-oriented advisories may increase rice yield as well as enhance the income of the farmers through minimizing risks and losses, if proper use of the generated advisory is ensured. This study assessed the importance and impact of weather forecast based advisory service (WFBAS) in Bangladesh. Literature review and field experimental data were used in a sensitivity analysis to show the impact of WFBAS on rice production. Available literatures suggested that the weather based advisory service would enhance rice yield by around 6.7-10%, but the experimental findings revealed that yield advantage could be 21.48%. Besides, the adoption of this technology would reduce the cost of cultivation by 12%, whereas the aggregate impact would increase the farmers’ profit by 25%. In the sensitivity study, we considered the production and price of Aman and Boro seasons (actual and government procured prices for 2018-19) and assumed only 6.70% yield increase with 5% farmers adopting of WFBAS. As such, additional 0.172 million tons will be added to the national rough rice production and thus the nation will be benefited by 3143 million Bangladeshi taka (BDT) at the actual farmgate price and it would be 4478 million BDT at the government procured price. The return on one BDT investment in this technology would be 51-73 BDT based on actual and procured prices. The projection showed enhenced production of the rough rice at 0.119 million tons and 0.214 million tons by 2025 and 2030, on which the additional return would be BDT 2441 and BDT 5223 million at the projected actual farmgate price and BDT 3522 and BDT 6979 million at the projected Government procured price, respectively. Hence, the successful implementation of the WFBAS will help to develop resilient rice farming communities, minimize livelihood risk, reduce the cost of production, utilize resources efficienty, and enable the farmers to take maximum benefit from favorable weather conditions through improved agricultural extension services. Finally, the enhanced yield and loss reduction will help to achieve the target of Sustainable Development Goal (SDG) by 2030 through sustaining rice production in Bangladesh under changing climate. Bangladesh Rice J. 25 (1) : 51-74, 2021

Impact of management practices on weed infestation, water productivity, rice yield and grain quality in irrigated systems in Côte d'Ivoire

• AWD reduced weed biomass due to reduction of lowland and broad-leaved weeds. • AWD increased water productivity without yield penalty compared to CF. • Soil pH and N fertilization affected rice yield and water productivity in AWD fields. • Choice of rice variety largely determined grain quality. Management practices that simultaneously enhance rice yield, water productivity, labor productivity, and grain quality are needed for improving crop production and mitigating the negative impact of water scarcity on food security. The objectives of this on-farm study were to evaluate the effects of water management practices including the safe alternate wetting and drying (AWD) method of irrigation on rice yield, water productivity, weed biomass, and grain quality, and identify the factors associated with their variabilities in the fields with AWD. On-farm trials were conducted over two years in 30 fields within two irrigation schemes in the region of Bouake, central Côte d’Ivoire. Before rice cultivation, in each field, three plots consisting of water management practices were established: continuous flooding (CF), safe AWD, and farmers’ practice (FP). Lowland weeds were dominant in rice fields in this study area. Large variations in weed biomass, rice yield, and water productivity were found across fields for each water management practice. Weed biomass and irrigation water input were lower under safe AWD than CF due to higher soil drying while there was no significant difference in rice yield between safe AWD and CF. Water productivity was higher under safe AWD than CF and FP. Rice milling recovery, head yield, and chalkiness were not significantly different among water management practices. Higher rice yield and water productivity in the safe AWD fields were associated with higher soil pH and nitrogen (N) fertilizer rate and better congruence between nitrogen fertilizer application and crop N demand. Milling recovery, head yield, and chalkiness in the safe AWD fields were strongly affected by the choice of rice variety. Combination of safe AWD with varieties having good grain quality characteristics and improved nutrient management practices could be recommended to the smallholder rice farmers to improve rice yield, water productivity, and grain quality and reduce labour requirement for irrigation and weeding particularly in schemes where lowland weeds are dominant.

Ginger Essential Oils-Loaded Nanoemulsions: Potential Strategy to Manage Bacterial Leaf Blight Disease and Enhanced Rice Yield.

The bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most serious rice diseases, causing huge yield losses worldwide. Several technologies and approaches have been opted to reduce the damage; however, these have had limited success. Recently, scientists have been focusing their efforts on developing efficient and environmentally friendly nanobactericides for controlling bacterial diseases in rice fields. In the present study, a scanning electron microscope (SEM), transmission electron microscope (TEM), and a confocal laser scanning microscope (CLSM) were utilized to investigate the mode of actions of ginger EOs on the cell structure of Xoo. The ginger EOs caused the cells to grow abnormally, resulting in an irregular form with hollow layers, whereas the dimethylsulfoxide (DMSO) treatment showed a typical rod shape for the Xoo cell. Ginger EOs restricted the growth and production of biofilms by reducing the number of biofilms generated as indicated by CLSM. Due to the instability, poor solubility, and durability of ginger EOs, a nanoemulsions approach was used, and a glasshouse trial was performed to assess their efficacy on BLB disease control. The in vitro antibacterial activity of the developed nanobactericides was promising at different concentration (50–125 µL/mL) tested. The efficacy was concentration-dependent. There was significant antibacterial activity recorded at higher concentrations. A glasshouse trial revealed that developed nanobactericides managed to suppress BLB disease severity effectively. Treatment at a concentration of 125 μL/mL was the best based on the suppression of disease severity index, AUDPC value, disease reduction (DR), and protection index (PI). Furthermore, findings on plant growth, physiological features, and yield parameters were significantly enhanced compared to the positive control treatment. In conclusion, the results indicated that ginger essential oils loaded-nanoemulsions are a promising alternative to synthetic antibiotics in suppressing Xoo growth, regulating the BLB disease, and enhancing rice yield under a glasshouse trial.

Climatic constraints to yield and yield components of temperate japonica rice

AbstractAlthough temperate japonica rice (Oryza sativa L.) production is limited by both low‐ and high‐temperature stresses, the primary constraint was reported to be cold stress in the past. However, the magnitudes of low‐ and high‐temperature stresses may have been altered by global warming. In this study, the major climatic constraints to the yield and yield components of temperate japonica rice grown in field conditions under the current climates were assessed using the random forests method with 14‐yr field trial data (n = 499). Low temperatures had negligible impacts on rice yield under the current climates (2005–2018) in South Korea. Meanwhile, high‐temperature stress was most significant during the ripening stage, followed by the reproductive stage. Yield losses by high temperatures were primarily associated with reduced filled‐grain percentage, followed by reduced 1,000‐grain weight. During the vegetative stage, higher temperature (or higher growing degree days, GDD) decreased the number of panicles per m2 and increased the number of spikelets per panicle, resulting in negligible changes in the number of spikelets per m2 and yield. The effect of solar radiation was most significant during the ripening stage. More solar radiation during the ripening stage enhanced rice yield by increasing filled‐grain percentage and 1,000‐grain weight. This study highlights that the primary constraints to temperate japonica rice grown under the current climates are high‐temperature stresses during the ripening and reproductive stages rather than low‐temperature stresses. Thus, there is an urgent need to explore options for improving the adaptation of temperate japonica rice to anticipated global warming.

Enhancing Rice Yield and Weed Management in Direct Seeded Rice Using Ammonium Sulfate as Adjuvant with Lower Dose of Early Postemergence Herbicides

A field experiment was conducted in 2016 to find out the sequential use of different herbicides with adjuvants (a substance which enhances pesticides efficiency) towards improved rice production and weed management in direct-seeded rice crop. The early postemergence herbicides (Kelion 50 WG, Ryzelan 240 SC, and Nominee 100 SC were applied at full or 75% of the full dose with and without adjuvants i.e. 2% solution of ammonium sulfate (AS) and alkyl ether sulfate (AES) at 14 days after sowing (DAS), followed by late postemergence herbicides i.e. Puma super (7.5 EW) and Sunstar 60 WG at 28 DAS. Application of herbicides with and without adjuvant substantially suppressed weed with weed dry weight at 40 and 60 DAS and improved rice yield attributes over a weedy check. It was found that a combination of 75% of Nominee 100 SC along with adjuvant i.e. AS (2% v/v) resulted in higher biological yield (9.16 t/ha), harvest index (30.65%), more grains per panicle (98.13), 1000 grain weight (21.32 g) with improved seed yield (3.86 t/ha). Also, abortive kernel (5.33), chalky kernels (5.66), opaque kernels (5.00), normal kernel (70.66), water absorptive ratio (4.28), and kernel length (10.13).

Application of Exogenous KH2PO4 and Salicylic Acid and Optimization of the Sowing Date Enhance Rice Yield Under High-Temperature Conditions

Application of Exogenous KH2PO4 and Salicylic Acid and Optimization of the Sowing Date Enhance Rice Yield Under High-Temperature Conditions

Rotation with oilseed rape as the winter crop enhances rice yield and improves soil indigenous nutrient supply

Crop yield and soil fertility are significantly influenced by crop rotation practices and plant nutrition management. A 3-year field experiment testing different fertilizer inputs under oilseed rape–rice (OR), wheat–rice (WR), and fallow–rice (FR) rotations was performed to investigate the effects of different rotations on rice yield and soil indigenous nutrient supply. Rice yield under the OR rotation was significantly higher than yields under the other two rotations, especially when no fertilizer was applied (control treatment) or when the applied fertilizer lacked N (no-N treatment). The rice grain yields of the control and no-N treatments under OR rotation exceeded those under the WR and FR rotations by 20.5 % and 14.5 % (control), and by 16.2 % and 14.9 % (no-N), respectively. The increase in rice yield was significantly related to the soil indigenous nutrient supply. Linear regression analysis showed that for every 1.0 kg increase in soil N supply, the rice yield increased by 86.2–136.8 kg ha–1. The indigenous N supply in the rice season under OR rotation was 22.0 % and 19.5 % higher than supplies under WR and FR rotations, respectively. The indigenous P and K supplies under OR were 21.9 % and 12.8 % higher, respectively, than those under WR. The highest N and P surpluses and lowest K deficits occurred under OR rotation. These effects were significantly correlated with the soil indigenous nutrient supply. Thus, a surplus of 1.0 kg N ha–1 increased the soil indigenous N supply by 0.04–0.29 kg N ha–1. Consequently, the use of oilseed rape as a previous crop in a rotation protocol could significantly increase rice yield and soil indigenous nutrient supply capacity. Inclusion of this rotation practice into agronomic systems that currently use wheat-rice and fallow-rice rotations should bring significant benefits.

Idealizing inflorescence architecture to enhance rice yield potential for feeding nine billion people in 2050

Rice serves as the staple food in meeting the energy needs of more than half of the global population. Several high-yielding, semi-dwarf rice varieties, including the milestone variety IR8 that was developed by the International Rice Research Institute (IRRI) through the introduction of the semi-dwarf1 (sd1) allele of GA20-ox-2 gene and the beneficial allele of HIGH TILLERING AND DWARF 1/DWARF17 (Wang et al., 2020), doubled the yield over traditional germplasm and contributed to the Green Revolution in Asia.

History and progress in genetic improvement for enhancing rice yield in sub-Saharan Africa

Abstract Genetic improvement has been given high priority in rice research for development in sub-Saharan Africa (SSA). This paper provides an overview of historical efforts of genetic improvement in SSA focused on improving rice productivity. It further describes yield gain of new rice varieties evaluated in recent field experiments in four selected breeding target domains, and summarizes adoption studies on rice varieties. Efforts to develop rice varieties adapted to diverse rice production systems in SSA have been made by several research organizations, including national agricultural research institutes, bilateral organizations, and three CGIAR centers. The efforts have resulted in the release of around 570 rice varieties in 10 major rice-producing SSA countries by 2020. Among these varieties, the most well-known are interspecfic upland rice varieties “New Rice for Africa (NERICA)” that were developed from crosses between improved Oryza sativa tropical japonica and Oryza glaberrima varieties. However, recent field assessements demonstrated that upland rice yield can be further improved through introduction of upland indica materials from Asia. In contrast, lowland interspecific rice varieties out-yielded the previously released improved O. sativa varieties in selected SSA countries. Field assessments in Senegal and Madagascar did not demonstrate the yield advantage of the recently-developed varieties including hybrids over best performing ones released before. The adoption level of improved varieties in terms of share of area occupied by improved varieties in 18 SSA countries was 40 % in 2008 with old varieties that were released before 2000 being dominant and 7% of the total rice area occupied by NERICA varieties. Especially in irrigated and rainfed lowland rice systems, the majority of dominant varieties were still those introduced from Asia. Panel data between 2002 and 2019 from the Senegal River Valley also confirmed this, and Sahel 108, which was introduced from Asia and released in Senegal in 1994, accounted for >70 % of the total rice area in both the wet and dry seasons in 2019. The implications of this review for future rice genetic improvement and varietal replacement in SSA are discussed.

Additional Nitrogen Application Under Different Water Regimes at Tillering Stage Enhanced Rice Yield and 2-Acetyl-1-Pyrroline (2AP) Content in Fragrant Rice

Water (W) and nitrogen (N) management at tillering stage could largely affect aroma biosynthesis in fragrant rice. In the present study, three rice cultivars, i.e., Basmati, Nongxiang 18, and Yungengyou 14, were applied with three N levels, i.e., 0, 30, and 60 kg N ha−1 regarded as N0, N1, and N2, respectively, and three water levels, i.e., well-watered treatment with water layer of 4–6 cm, 0 kPa (W1), soil water potential of ‒10 kPa (W2), and soil water potential of ‒20 kPa (W3), were applied at tillering stage during 2012 and 2013 under field conditions. Results depicted that application of N fertilizer and less irrigation water at tillering stage increased head milled rice yield and 2 acetyle-1-pyrroline (2AP) content in grain. The N2 and W3 treatments were found effective regarding grain yield and aroma improvements than other levels of nitrogen and water. The head milled rice yield (HMRY) in Nongxiang 18 and Yungengyou 14 was remained than Basmati during both years, whereas the trend for HMRY and 2AP content in mature grain was found as W1 < W2 < W3 and N1 < N2 < N3 for water and nitrogen treatments, respectively. Moreover, the 2AP, 1-pyrroline-5-carboxylic acid content, and pyrroline-5-carboxylic acid synthetase activity were significantly associated with the grain 2AP content at MS. Overall, additional N application at tillering stage with intermittent irrigation could improve rice yield and aroma of fragrant rice.

Genome-wide association study and Mendelian randomization analysis provide insights for improving rice yield potential

Rice yield per plant has a complex genetic architecture, which is mainly determined by its three component traits: the number of grains per panicle (GPP), kilo-grain weight (KGW), and tillers per plant (TP). Exploring ideotype breeding based on selection for genetically less complex component traits is an alternative route for further improving rice production. To understand the genetic basis of the relationship between rice yield and component traits, we investigated the four traits of two rice hybrid populations (575 + 1495 F1) in different environments and conducted meta-analyses of genome-wide association study (meta-GWAS). In total, 3589 significant loci for three components traits were detected, while only 3 loci for yield were detected. It indicated that rice yield is mainly controlled by minor-effect loci and hardly to be identified. Selecting quantitative trait locus/gene affected component traits to further enhance yield is recommended. Mendelian randomization design is adopted to investigate the genetic effects of loci on yield through component traits and estimate the genetic relationship between rice yield and its component traits by these loci. The loci for GPP or TP mainly had a positive genetic effect on yield, but the loci for KGW with different direction effects (positive effect or negative effect). Additionally, TP (Beta = 1.865) has a greater effect on yield than KGW (Beta = 1.016) and GPP (Beta = 0.086). Five significant loci for component traits that had an indirect effect on yield were identified. Pyramiding superior alleles of the five loci revealed improved yield. A combination of direct and indirect effects may better contribute to the yield potential of rice. Our findings provided a rationale for using component traits as indirect indices to enhanced rice yield, which will be helpful for further understanding the genetic basis of yield and provide valuable information for improving rice yield potential.

Comprehensive analysis of SUSIBA2 rice: The low-methane trait and associated changes in soil carbon and microbial communities

Rice cultivation is the primary source of anthropogenic methane (CH4), which dramatically impacts global climate change. A growing body of evidence shows that optimizing photosynthate distribution is important for increasing rice yields and mitigating CH4 emissions. Therefore, the molecular rice breeding with a barley HvSUSIBA2 gene that confers elevated photosynthate flux to grains, is predicted to enhance rice yield and mitigate CH4 emissions in paddies. Here, in a series of field experiments with differences in growing season and rice variety, we show that SUSIBA2 rice reduced CH4 emissions from paddies. SUSIBA2 rice grown in the early rice season and late rice season showed similar mitigation effects, with reduction rates of 50.98% for early rice and 50.97% for late rice. The reduction rate of SUSIBA2 rice during the winter rice season was significantly lower (22.26%) than those of other rice seasons. The reduction rates also varied between rice varieties, and SUSIBA2 japonica rice showed a more significant CH4 mitigation effect than SUSIBA2 indica rice. Further yield-scaled CH4 emission analyses indicated that the SUSIBA2 effect did not mitigate CH4 emissions at the expense of yield. Compared with the wild type, SUSIBA2 rice significantly reduced soil organic carbon properties and the abundance of CH4-related microbes, and altered methanogenic and methanotrophic communities, indicating that SUSIBA2 rice released less carbon to the soil, which reduced CH4 production. Furthermore, a comparison of microbial communities between SUSIBA2 japonica and indica rice revealed different responses of methanogenic and methanotrophic communities, which may partly explain their differences in growth performance and CH4 mitigation effect. Thus, our results show that SUSIBA2 rice substantially reduces CH4 emissions and that SUSIBA2 can potentially mitigate the CH4 emissions of japonica and indica rice under distinct cultivation conditions.