High-yielding Rice Research Articles

Identification and verification of grain shape QTLs by SNP array in rice.

Grain shape strongly influences the economic value and grain yield of rice. Thus, identifying quantitative trait loci (QTLs) for grain shape has been a longstanding goal in rice genetic research and breeding programs. Single nucleotide polymorphism (SNP) markers are ubiquitous in the rice genome and are more abundant and evenly distributed on the 12 rice chromosomes than traditional markers. An F2 population was genotyped using the RICE6K SNP array to elucidate the mechanisms governing grain shape. Thirty-five QTLs for grain shape were detected on 11 of 12 chromosomes over 2 years. The major QTL cluster qGS7 was detected in both years and displayed strong genetic effects on grain length and width, showing consistency with GL7/GW7. Some minor QTLs were also detected, and the effects of four QTLs on seed size were then validated using BC1F6 populations with residual heterozygous lines in each QTL region. Our findings provide insights into the molecular basis of grain shape as well as additional resources and approaches for producing hybrid high-yield rice varieties.

Identification of QTLs for cold tolerance at the booting and flowering stages in rice (Oryza sativa L.)

Rice growth and productivity are greatly affected by cold stress, which is likely to become more of a hindrance for high and stable rice yields. To identify cold tolerance at the booting and flowering stages in rice, a recombinant inbred line was developed by crossing a cold-tolerant japonica cultivated variety, Jileng1, with a cold-sensitive indica cultivated variety, Milyang23. The seed setting rate (SST) of the parents and RIL population were investigated under different temperature environments, and the SST and cold stress tolerance index under natural low temperature were used to evaluate cold tolerance and quantitative trait locus (QTL) mapping. Fifteen QTLs were detected on chromosomes 1, 2, 3, 5, 7, 11 and 12, with log-likelihood values ranging from 2.64 to 4.76. These QTLs account for 3.34% to 12.02% of the phenotypic variance explained. Three QTLs, qCtb1, qCtb5 and qCtb12, were repeatedly detected in different conditions, and they were considered stably expressed QTLs. qCtb5 was localized to chromosome 5 marker between CMB0526.3 and ID5014265. In this interval or nearby, many cold-resistance QTLs have been identified in previous studies, so qCtb5 is considered a major cold-tolerance QTL. Thirteen QTLs with environmental interactions were also detected, and QTLs detected in single environment were all found to be involved in environmental interactions. These results show that environmental interactions have a significant effect on cold tolerance in rice. Stable expression of major QTLs will help to fine mapping cold-tolerance genes and provide gene resources to cultivate cold-tolerance rice varieties.

Characteristics and Influencing Factors of Cadmium Accumulation in Different Rice Varieties Under Cadmium Contaminated Field Conditions

Eight rice varieties suitable for local cultivation were selected and field tests were carried out to compare the accumulation, absorption, and transport characteristics of Cd. The rice varieties with low Cd accumulation were screened, and the factors affecting the accumulation degree and stability of rice were analyzed. The results showed that:①According to the comprehensive accumulation index(PN) evaluation method, the rice varieties with low PN ability for Cd were selected as follows:Chuanyou 3203, Chuanyou 6203, Dejing 6, and Shenyou 17. ②Considering the Cd content and yield of rice, Chuanyou 3203 and Chuanyou 6203 are suitable for planting in this region, which guarantees a safe Cd content in and high yield of rice. ③The contents of Cd in Chuanyou 3203 and Chuanyou 6203 were significantly lower than those of other rice varieties and stable under different pH and total Cd ranges and soil conditions. ④The difference between rice varieties had a significant effect on rice enrichment ability, but little effect on translocation from stem to leaf. The low enrichment coefficient of Chuanyou 3203 and Chuanyou 6203, combined with low translocation, demonstrated the low Cd enrichment capacity of rice. ⑤Correlation analysis showed that the Cd content was most affected by the enrichment coefficient of rice, and least affected by the total Cd content of rhizosphere soil.

Cross-locational experiments to reveal yield potential and yield-determining factors of the rice cultivar ‘Hokuriku 193’ and climatic factors to achieve high brown rice yield over 1.2kg m-2 at Nagano in central inland of Japan

ABSTRACT Understanding the yield potential and yield-determining factors of recent high-yielding cultivars is essential for further increasing rice yield. In this study, a cross-locational field experiment was conducted across 3 years using ‘Hokuriku 193ʹ (H193), a high-yielding cultivar, at four sites including one in Nagano Prefecture, which is the highest-yielding region in Japan. The highest mean yields of 3 years, 1214 g m−2 for brown rice grains and 1586 g m−2 for rough grains, were recorded at the Nagano site. The yields from the 17 environments were strongly correlated with spikelet number per square meter while percentage of filled grain was relatively stable, suggesting that sink capacity is the primary determining factor for grain yield of H193. The climatic factors for high spikelet number at the Nagano site can be explained by the high cumulative radiation before heading associated with longer duration until heading by low night temperature. In addition, a large increase in shoot dry weight during grain filling (ΔW) and high radiation use efficiency (ΔW/rad) at the Nagano site could satisfy large source demand by the large sink size. The high ΔW/rad at the Nagano site associated with low night temperature. This study demonstrated high yield potential of H193 and revealed an environment that achieves extra-high yields in H193, which provided insight to attain further increase in rice yield.

Increasing pit‐planting density of rice varieties with different panicle types to improves sink characteristics and rice yield under alternate wetting and drying irrigation

AbstractThe Chinese government regards ensuring food security and developing water‐saving agriculture as an important national strategy and that carrying out relevant research has important practical significance and production application value. A two‐year field experiment was conducted to explore the compensation potential in rice yield by using rice varieties with different panicle size under two water management regimes (conventional water management or CWM and alternate wetting and drying or AWD). The results showed that the large panicle rice variety resulted in greater yield, crop water productivity, spikelet density, dry matter accumulation and translocation, and photosynthesis. Compared with the CWM, the AWD had little effect on rice yield. However, with an appropriate planting density, the AWD achieved a greater grain yield compared with the CWM. Moreover, the AWD increased crop water productivity and the grain‐filling efficiency. The loss of spikelets under the AWD could be compensated by increasing the planting density. Although AWD reduced tillering number, it increased the photosynthetic rate, dry matter accumulation and its translocation to grain, and leaf area index. In addition, the adverse effects on rice growth and the yield caused by the AWD could be alleviated by increasing planting density of rice. Therefore, an appropriate planting density can be used to save water and maintain high grain yield of rice under alternate wetting and drying.

The combination of straw return and appropriate K fertilizer amounts enhances both soil health and rice yield in Northeast China

AbstractTo identify the ideal potassium (K) fertilization rate in fields with continuous straw return to maintain soil potassium supply and increase yield in the rice‐producing regions of Northeast China, we studied the effect of different K fertilizer application amounts (0, 30, 60, 90, 120, 150, and 180 kg K2O ha−1 yr−1) on rice yield, K use efficiency, and soil K availability in straw‐returned and straw‐removed plots from 2017 to 2019. Results showed that the highest rice yield in straw‐returned plots (60 K2O ha−1) was 3.3% higher than that in the straw‐removed plots (90 K2O ha−1), and the straw‐return treatment attained higher K use efficiencies under low K fertilizer application conditions (30 and 60 kg K2O ha−1). Compared with straw‐removed plots, straw‐returned plots had increased exchangeable K and nonexchangeable K contents in the top 20 cm of soil. The ranges of K fertilizer application amount required to maintain soil K balance (K input–K output) in straw‐returned plots and straw‐removed plots were 48–53 kg ha−1 and 127–140 kg ha−1, respectively. Continuous straw return in rice‐producing regions in Northeast China can decrease K fertilizer application needs by 62.2% compared with straw‐removed plots while simultaneously maintaining soil K balance. Straw return plays an important role in increasing crop yield, preventing soil K depletion, and keeping the development of K resources sustainable.

Genomic insight into balancing high yield, good quality, and blast resistance of japonica rice

BackgroundBalancing the yield, quality and resistance to disease is a daunting challenge in crop breeding due to the negative relationship among these traits. Large-scale genomic landscape analysis of germplasm resources is considered to be an efficient approach to dissect the genetic basis of the complex traits. Central China is one of the main regions where the japonica rice is produced. However, dozens of high-yield rice varieties in this region still exist with low quality or susceptibility to blast disease, severely limiting their application in rice production.ResultsHere, we re-sequence 200 japonica rice varieties grown in central China over the past 30 years and analyze the genetic structure of these cultivars using 2.4 million polymorphic SNP markers. Genome-wide association mapping and selection scans indicate that strong selection for high-yield and taste quality associated with low-amylose content may have led to the loss of resistance to the rice blast fungus Magnaporthe oryzae. By extensive bioinformatic analyses of yield components, resistance to rice blast, and taste quality, we identify several superior alleles for these traits in the population. Based on this information, we successfully introduce excellent taste quality and blast-resistant alleles into the background of two high-yield cultivars and develop two elite lines, XY99 and JXY1, with excellent taste, high yield, and broad-spectrum of blast resistance.ConclusionsThis is the first large-scale genomic landscape analysis of japonica rice varieties grown in central China and we demonstrate a balancing of multiple agronomic traits by genomic-based strategy.

Yield-scaled greenhouse gas emissions from the use of common urea and controlled-release nitrogen fertiliser in a subtropical paddy rice field

Suitable nitrogen (N) fertilisation is key for economic and environmental sustainability of croplands, and little is known on the potential of slow-release N sources to mitigate nitrous oxide (N2O) and methane (CH4) emissions in paddy rice growing in subtropical lowlands. We assessed the impact of controlled-released N fertiliser (CRNF) on partial global warming potential (pGWP) and yield-scaled greenhouse gas (GHG) emissions (GHG emission per unit of yield) in comparison to common urea in irrigated rice growing in a Typic Albaqualf in southern Brazil. The field experiment comprised four treatments: (1) control; (2) common urea applied into three splits, and CRNF applied at rice sowing; (3) on soil surface; and (4) in the seeding furrow. The N fertilisers did not increase N2O emissions when compared to control with exception of CRNF at the seeding furrow. However, N fertilisation increased CH4 emissions, with exception of the CRNF applied to the seeding furrow. Rice grain yields (7954–8637 kg ha−1) were not affected by N sources. The pGWP (11 683–14 297 kg CO2 eq ha−1) and the yield-scaled GHG (1.47–1.74 kg CO2 eq kg−1 grain) were similar among N sources. N fertilisation is a crucial practice to obtain high rice yields, which did not affect negatively the yield-scaled GHG emissions in this subtropical environment under continuous flood irrigation. CRNF applied at rice sowing provides rice grain productivity and agronomic efficiency similar to common urea applied into three splits.

Climate risk and agricultural technology adaption: evidence from rice farmers in the Ayeyarwady River delta of Myanmar

Crop income can be raised in two ways: one way is to increase crop productivity and the other is to grow high-value crops that could be sold at high prices in the market. This study evaluated the adoption determinants of high-yielding varieties (HYVs) and high-value varieties (HVVs) of rice and their associations on crop income using data collected in coastal areas of the Ayeyarwady River delta, which is prone to climate shocks such as saltwater intrusion and cyclones. We used cross-sectional data on 298 rice-producing households and 393 rice plots to conduct multinomial logit estimates, which revealed that the heights of the plots, and past exposure to saltwater intrusion negatively affected the adoption of HVVs. Our estimates also suggest that while the adoption of HYVs is not associated with high rice yield, income, or profit, HVV adoption is associated with high income and profit.

Metabolic factors restricting sink strength in superior and inferior spikelets in high-yielding rice cultivars

Many high-yielding rice cultivars with large sink size (total number of spikelet per unit area × mean grain weight) have been developed, but some japonica cultivars developed in Japan often fail to attain the expected high yield due to low sink strength of spikelets. Although there is natural variation in sink strength of spikelets among high-yielding cultivars, metabolic factors involved in the natural variation and relationships of sink strength in spikelets with final percentage of filled spikelets are not fully understood. In the present study, we examined cultivar differences in sink strength for superior and inferior spikelets (i.e. earlier fertilizing spikelets with faster growth and later fertilizing ones with slower growth, respectively) in a panicle, using each spikelet at 10 d after the onset of development (10 DAD) when starch accumulation in endosperm was actively proceeding. Nine high-yielding cultivars were used: five japonica-dominant and four indica-dominant cultivars. Cultivar differences were observed in starch contents at 10 DAD in each spikelet type, and indica cultivars had higher starch contents than japonica cultivars in both superior and inferior spikelets. In addition, starch contents at 10 DAD were closely related to percentage of filled grains at maturity in both spikelet types. The activities of sucrose synthase (SUS) and uridine diphosphoglucose pyrophosphorylase (UGP), and the protein levels of phosphorylase 1 (Pho1), were higher in indica than japonica cultivars, and were positively correlated with starch contents at 10 DAD for both superior and inferior spikelets; although metabolic states, revealed from relations between intermediate metabolites and starch contents, differed among spikelet types. Consequently, it was considered that SUS and UGP at the step from sucrose cleavage to adenosine diphosphoglucose synthesis, and Pho1 at the starch biosynthesis step, were key metabolic factors involved in cultivar differences of sink strength (ability to synthesize starch).

Identifying agronomic practices with higher yield and lower global warming potential in rice paddies: a global meta-analysis

Rice agriculture faces the dual challenge of increasing grain production while reducing global warming potential (GWP). Yield-scaled GWP, a commonly employed indicator, is not sufficient to identify smart agronomic practices that can address this dual challenge. Thus, practices that can increase yield while simultaneously reducing GWP in rice paddies have not yet been clearly defined. In this study, we synthesised independent experiments by meta-analyses to identify agronomic management practices with higher rice yield and lower GWP. The results showed that the application of nitrification inhibitors (NI) and biochar significantly increased rice yield by an average of 9.5% and 9.1%, and simultaneously reduced GWP by 24% and 14%, respectively. Overall, controlled-release nitrogen (N) fertilisers did not affect GWP despite increasing rice yield (+9.2%). In contrast, conventional N application enhanced both rice yield (+44%) and GWP (+27%). No-tillage reduced GWP (˗23%) but did not significantly affect rice yield. Non-continuous flooding in rice paddies significantly reduced GWP (˗48%) but also reduced the yield (˗4.2%). The rice yield and GWP outcomes were similar for rice-animal co-culture and rice monoculture systems. In conclusion, both NI and biochar application are promising practices for increasing yield while simultaneously reducing GWP in rice paddies. In addition, we suggest that individual agronomic practices should be combined to increase rice yield while mitigating climate warming.

Effects of Selenium Fertilizer Application on Yield and Selenium Accumulation Characteristics of Different Japonica Rice Varieties

In this study, three japonica rice varieties—Nanjing 9108, Jiahua 1 and Wuyunjing 29—were supplied with different levels of nano-foliar selenium fertilizers (0, 40 and 80 kg Se ha−1) under field conditions. Their rice yield and absorption, accumulation, transportation and utilization of selenium were studied to find suitable selenium-rich rice cultivars and optimal selenium supply levels, while providing references for the development of selenium-rich rice. On an average basis, the Nanjing 9108, Jiahua 1 and Wuyunjing 29 yielded 8755 ± 190, 8200 ± 317 and 9098 ± 72.7 kg ha−1, respectively. The selenium content in polished rice of the three rice varieties is between 0.210 and 0.933 mg kg−1. When 40 g Se ha−1 nano-selenium fertilizer was used, the selenium accumulation in the shoots of Nanjing 9108, Jiahua 1 and Wuyunjing 29 was, respectively, 11.4 g Se ha−1, 12.3 g Se ha−1 and 12.2 g Se ha−1, and when 80 g Se ha−1 selenium fertilizer was applied, the total selenium accumulation of three rice varieties was, respectively, 2.45, 1.75 and 2.40 times that of 40 g Se ha−1 selenium fertilizer. No evident diversity was observed in the selenium transport coefficient and the apparent utilization rate of selenium among the three varieties. The three rice varieties in this experiment had a strong selenium enrichment capacity, and they could be planted as selenium-enriched and high-yield rice varieties. Further, the amount of selenium fertilizer should not exceed 40 g Se ha−1.

Optimization of the Water and Fertilizer of Rice in the Cold Field and the Biochar Application Amount Based on RAGA Model

This paper proposes an optimization method based on the RAGA model. Taking rice from a cold area as the research object, this article selects irrigation volume, nitrogen application volume, and biochar application volume as experimental factors, and rice yield, water use efficiency, greenhouse gas emission comprehensive warming potential as influencing indicators. The research design is D311 Field trials by 3 factors of 5 levels of saturation. Hence, we can obtain the data on rice yield, water use efficiency, greenhouse gas emissions and comprehensive warming potential under different levels of water and fertilizer, and biochar application, and regression equations were established respectively. The RAGA model was used to simulate the regression equations. The optimal combination of water and fertilizer, and biochar was obtained as follows: irrigation amount is 7230 m3.hm-2, nitrogen fertilizer application amount is 92.13 kg.hm-2, and biochar application amount is 30 t.hm-2. The optimal rice yield obtained under this combination is 9452.20 kg.hm-2. The water use efficiency is 1.94 kg.m-3, and the comprehensive warming potential of greenhouse gas emissions is 4546.73 kg.hm-2. The combined application of water and fertilizer, and biochar optimized by this model can provide a theoretical basis for achieving high yield, water-saving, and emission reduction of rice in cold areas, and it can also provide a reliable calculation method and idea for solving similar optimization problems in the field of agricultural production.

Blended Amendments: A Sustainable Approach for Managing Nutrient Deficiency in Rice Fields

The application of chemical fertilizer provides absorbable soluble macronutrients for increasing rice yield while reducing the availability of micronutrients and occasionally halting nitrogen mineralisation in the soil. To lessen some of these undesirable effects of chemical fertilization, an effort has been made to prepare blended soil organic amendments by mixing organic materials like rice straw, dried cow-dung and compost prepared from eco-friendly wastes from the kitchen, backyard garden and dried cow-dung mixed in the ratio 1:2:2. Such prepared amendments were applied in the rice field by growing three high-yielding rice cultivars Dikhow, Chandrama and Naveen, in three different rice cropping seasons, pre-monsoon (Ahu), monsoon (Sali) and summer (Boro) during 2015-2016 and 2016-2017 for studying soil properties, crop growth and yield. The key finding of the investigation was that the soil amended with chemical fertilizer showed improvement in soil moisture compared to unamended soil in all three rice fields. However, chemically fertilized soil exhibited lower amounts of available phosphorus, available potassium, diethylenetriaminepentaacetic acid (DTPA) extracted iron and copper in Ahu field, DTPA extracted iron, copper and zinc in Sali field and immobilizing nitrogen in Boro field than blended amendments. Overall, chemical fertilizer + rice straw displayed more available nitrogen and yield in Ahu field, whereas, chemical fertilizer + dried cow dung showed the highest amount of zinc and copper along with the highest yield in Sali rice field and chemical fertilizer+compost had better moisture and soil organic carbon amounts with an ideal acidic pH supporting maximum yield in Boro rice field.

Cover crops as green mulching for weed management in rice

A field study was carried out in 2017 and 2018 in two Italian rice farms (at Livorno Ferraris and Rovasenda) to assess the effect of using cover crops as green mulching on weed control and rice yield. Three different rice fields were sown in each site after rice harvest with either Vicia villosa, Lolium multiflorum, or a mixture of both (V. villosa 40% + L. multiflorum 60%); at Rovasenda, a small percentage of Brassica napus and Triticale was also present in the mixture. An additional field at both sites without cover crop was considered as a control reference. Rice was broadcasted sown within the cover crop in May. After few days, the cover crop was terminated in half of each field using a roller-crimper, while in the other half, it was terminated by shredding. Within 10 days, the fields were flooded for about a week to promote the degradation of the cover crop biomass. Then, the fields were cultivated in flooding conditions without further weed control. Weed density and weed cover were evaluated three times during the growing season. At harvest, rice yield and harvest index were determined. Mixed nested Mixed nested ANOVAs were performed for each site to assess the effect of cover crop species, termination technique, and the interaction between cover crop and year. L. multiflorum showed high biomass before termination, while V. villosa had a more variable development. At Rovasenda, V. villosa growth was limited because of the combination of scarce emergence due to sod-seeding and frost damage. In general, green mulching significantly affected weed density. The best weed suppression was observed with L. multiflorum and mix at Rovasenda, with values of weed density <40 plants m–2 recorded in 2018. At both sites, rice yield was variable in the two years. The highest rice yield (>5 t ha–1) was observed in 2018 in the shredded mixture at Rovasenda and in V. villosa at Livorno Ferraris in 2017. Generally, control fields showed lower yields (1-3 t ha–1) at both sites. The termination methods did not significantly affect both weed density and rice yield. The results highlighted that green mulching could reduce weed infestations, even though alone is not able to avoid weed development completely. Some critical issues of the technique were observed, such as the need for a good cover crop establishment which eventually results in abundant biomass production and significant weed suppression. Highlights - Green mulching reduces weed pressure, but it should be integrated with other weed control techniques. - Hairy vetch showed poor establishment because of the combination of scarce emergence due to sod-seeding and low temperatures. - Italian ryegrass was more tolerant to low temperatures and showed a good cover that contained weed growth. - Cover crop mixture showed variable results with higher suppression probably related to the number of cover crop species present in the mixture. - The termination methods (crimping and shredding) did not affect weed density and rice yield.

Screening salt-tolerant rice at the seedling and reproductive stages: An effective and reliable approach

Screening salt-tolerant rice genotypes is important to develop salt-tolerant high-yielding cultivars. To categorize salt-tolerant genotypes, we used a comprehensive collection of morpho-physiological parameters, yield-contributing characteristics, and molecular and biochemical markers with multivariate analysis in this study. A total of 20 rice genotypes were screened at seedling stages in a hydroponic system at three different salinity levels (8, 10, and 12 dS m−1). Furthermore, at the reproductive stage, 12 genotypes were evaluated at 4 and 6 dS m−1 salinity conditions. The seedlings growth of the most rice genotypes were severely reduced by salinity stress, however, some genotypes (M-12, M-20, IR-10, IR-8, and M-19) showed the lowest growth reduction. Total salt stress response index revealed that the genotypes M-12 was the most salt-tolerant. Though the genotype M-12 acquired the highest position in seedling stage screening but unfortunately failed to show sufficient yield potential at reproductive stage, in which M-19 was qualified with highest yield response. Therefore, only seedling stage screening may provide misleading results. M-19 also showed the highest antioxidant activity with lower Na+/ K+ ratio, hydrogen peroxide, and malondialdehyde content, indicating a strong defense mechanism against salt-induced oxidative and osmotic stress. Overall, M-19 was selected as the most appropriate candidate genotypes for salinity tolerance. The accuracy and reliability of these methods were superbly assured by principal component analysis and seedling stage molecular assay. Therefore, the identified salt-tolerant genotypes could be further utilized as a source of appropriate donor parents in breeding of salt-tolerant high-yielding rice varieties.

Restriction of soil bacteria promoting high yield of super hybrid rice in the Huaihe Valley in central China by conventional ploughing intensity

Fields used to grow ‘Super rice’ rice bred to meet the rising food demand in China are typically ploughed before seedling transplantation. However, conventional tillage, i.e. shallow ploughing (SP) to < 15 cm depth, limits further improvements in yield and fertiliser use efficiency in paddy soils of central China. Microorganisms drive soil nutrient transformation and can be manipulated by cultivation practices. However, little is known about the extent and biological mechanisms of the soil microbes responsible for the rice yield limitation. Our results showed that tillage was a primary factor affecting paddy soil microbial communities. Shallow ploughing affected the diversity and composition of soil bacteria communities, while deep ploughing resulted in closer, more competitive soil bacterial networks with 1.64-folder higher negative connection among bacterial taxa. Shallow ploughing resulted in 10.5 % lower relative abundance of Nitrospirae and higher abundances of denitrification pathway genes (nirS, nirK, and nosZ) of soil microbes, as well as greater nitrogen loss through N2O, leading to a lower rice yield. Our results indicated that the conventional tillage intensity has negative effects on the composition and network of soil bacteria, particularly affecting nitrification and limiting the achievement of high yield in rice paddies. This finding provides a theoretical basis underlying a microbiological mechanism that will be useful in proposing a novel tillage practice for high-yield rice cultivation in the Huaihe Valley in central China.

Multi-locus genome-wide association studies for five yield-related traits in rice

BackgroundImproving the overall production of rice with high quality is a major target of breeders. Mining potential yield-related loci have been geared towards developing efficient rice breeding strategies. In this study, one single-locus genome-wide association studies (SL-GWAS) method (MLM) in conjunction with five multi-locus genome-wide association studies (ML-GWAS) approaches (mrMLM, FASTmrMLM, pLARmEB, pKWmEB, and ISIS EM-BLASSO) were conducted in a panel consisting of 529 rice core varieties with 607,201 SNPs.ResultsA total of 152, 106, 12, 111, and 64 SNPs were detected by the MLM model associated with the five yield-related traits, namely grain length (GL), grain width (GW), grain thickness (GT), thousand-grain weight (TGW), and yield per plant (YPP), respectively. Furthermore, 74 significant quantitative trait nucleotides (QTNs) were presented across at least two ML-GWAS methods to be associated with the above five traits successively. Finally, 20 common QTNs were simultaneously discovered by both SL-GWAS and ML-GWAS methods. Based on genome annotation, gene expression analysis, and previous studies, two candidate key genes (LOC_Os09g02830 and LOC_Os07g31450) were characterized to affect GW and TGW, separately.ConclusionsThese outcomes will provide an indication for breeding high-yielding rice varieties in the immediate future.

Effect of Elevated CO2 on N2O Emissions from Different Rice Cultivars in Rice Fields

Using the free air CO2 enrichment (FACE) platform, an in-situ field experiment was conducted to explore the impacts of elevated CO2 mole fraction (x[CO2]) on N2O emissions from strongly and weakly responsive rice cultivars. Under elevated x[CO2], grain yield of the strongly responsive rice cultivars increased significantly, by more than 30%, whereas the weakly responsive cultivars showed a growth rate of 10%-15%. The four treatments comprised A-W (normal x[CO2]+weakly responsive cultivar), F-W (elevated x[CO2]+weakly responsive cultivar), A-S (normal x[CO2]+strongly responsive cultivar), and F-S (elevated x[CO2]+strongly responsive cultivar). Compared to the normal x[CO2] treatments (A-S and A-W), when the strongly and weakly responsive cultivars were exposed to elevated x[CO2](F-S and F-W), N2O emissions decreased by 52.54% (P<0.05) and 38.40% (P<0.05), rice yield increased by 22.96% (P<0.05) and 12.11% (P>0.05), and N2O emission intensity decreased by 61.68% (P<0.05) and 45.13% (P<0.05), respectively. Moreover, N2O emissions of all treatments were significantly positively correlated with NH4+-N content (P<0.05), whereas not correlated with NO2--N content. Soil temperature is an important factor affecting the N2O emissions of the strongly responsive cultivar in rice fields under elevated x[CO2] conditions. Through comprehensive consideration of climate conditions, in the future, priority should be given to planting the strongly responsive cultivar, ensuring high rice yield and significant reduction in N2O emissions.

The Flower-Infecting Fungus Ustilaginoidea virens Subverts Plant Immunity by Secreting a Chitin-Binding Protein.

Ustilaginoidea virens is a biotrophic fungal pathogen specifically colonizing rice floral organ and causes false smut disease of rice. This disease has emerged as a serious problem that hinders the application of high-yield rice cultivars, by reducing grain yield and quality as well as introducing mycotoxins. However, the pathogenic mechanisms of U. virens are still enigmatic. Here we demonstrate that U. virens employs a secreted protein UvCBP1 to manipulate plant immunity. In planta expression of UvCBP1 led to compromised chitin-induced defense responses in Arabidopsis and rice, including burst of reactive oxygen species (ROS), callose deposition, and expression of defense-related genes. In vitro-purified UvCBP1 protein competes with rice chitin receptor OsCEBiP to bind to free chitin, thus impairing chitin-triggered rice immunity. Moreover, UvCBP1 could significantly promote infection of U. virens in rice flowers. Our results uncover a mechanism of a floral fungus suppressing plant immunity and pinpoint a universal role of chitin-battlefield during plant–fungi interactions.