Challenge and Opportunity in Improving Fertilizer-nitrogen Use Efficiency of Irrigated Rice in China

Today, about 30% of world nitrogen (N) fertilizer is consumed by China. Rice crops in China consume about 37% of the total N fertilizer used for rice production in the world. Average rate of N application for rice production in China is high and fertilizer-N use efficiency is low compared with other major rice growing countries. Research progresses have been made internationally and domestically on the application method, fertilizer-N sources, computer-based decision support systems, and real-time N management in order

Effect of irrigation regime on grain yield,water productivity,and methane emissions in dry direct-seeded rice grown in raised beds with wheat straw incorporation

Dry direct-seeded rice grown in raised beds is becoming an important practice in the wheat–rice rotation system in China.However,little information has been available on the effect of various irrigation regimes on grain yield,water productivity(WP),nitrogen use efficiency(NUE),and greenhouse gas emission in this practice.This study investigated the question using two rice cultivars in 2015 and 2016 grown in soil with wheat straw incorporated into it.Rice seeds were directly seeded into raised beds,which were maintained under aerobic conditions during the early seedling period.Three irrigation regimes:continuous flooding(CF),alternate wetting and drying(AWD),and furrow irrigation(FI),were applied from 4.5-leaf-stage to maturity.Compared with CF,both AWD and FI significantly increased grain yield,WP,and internal NUE,with greater increases under the FI regime.The two cultivars showed the same tendency in both years.Both AWD and FI markedly increased soil redox potential,root and shoot biomass,root oxidation activity,leaf photosynthetic NUE,and harvest index and markedly decreased global warming potential,owing to substantial reduction in seasonalThe results demonstrate that adoption of either AWD or FI could increase grain yield and resource-use efficiency and reduce environmental risks in dry direct-seeded rice grown on raised beds with wheat straw incorporation in the wheat–rice rotation system.

Genetic mapping of QTL for agronomic traits and grain mineral elements in rice

Malnutrition is one of the prevailing health problems worldwide, affecting a large proportion of the populations in rice-consuming countries. Breeding rice varieties with increased concentrations of elements in the grain is considered the most cost-effective approach to alleviate malnutrition. Development of molecular markers for high grain concentrations of essential elements, particularly Zn, for use in marker-assisted selection (MAS) can hasten breeding efforts to develop rice varieties with nutrient-dense grain. We performed QTL mapping for four agronomic traits: days to 50% flowering, plant height, number of tillers, grain yield, and 13 grain elements: As, B, Ca, Co, Cu, Fe, K, Mg, Mn, Mo, Na, P, and Zn, in two doubled-haploid populations derived from the crosses IR64 × IR69428 and BR29 × IR75862. These populations were phenotyped during 2015DS and 2015WS at IRRI, Los Ba os, The Philippines, and genotyped them with a 6 K SNP chip. Inclusive composite interval mapping revealed 15 QTL for agronomic traits and 50 QTL for grain element concentration. Of these, eight QTL showed phenotypic variance of >25% and 11 QTL were consistent across seasons. There were seven QTL co-localization regions containing QTL for more than two traits. Twenty five epistatic interactions were detected for two agronomic traits and seven mineral elements. Several DH lines with high Fe and Zn in polished rice were identified. These lines can be used as donors for breeding high-Zn rice varieties. Some of the major QTL can be further validated and used in MAS to improve the concentrations of nutritive elements in rice grain.

Molecular Improvement of Grain Weight and Yield in Rice by Using GW6 Gene

Molecular design breeding is one of straightforward approaches to break yield barriers in rice. In this study, GW6 gene for grain length and width from Baodali was transferred into an indica recurrent parent 9311 and a japonica variety Zhonghua 11 （ZH11） using marker-assisted backcross （MAB）. One and three introgression lines were selected for phenotypic analysis from 9311 and ZH11 genetic backgrounds, respectively. SSL-1, an improved 9311 near isogenic line with GW6 performed 11%, 19% and 6.7%higher of grain length, 1000-grain weight and single plant yield, respectively, as compared with 9311. All the three improved ZH11-GW6 lines, R1, R2 and R3, had more than 30% increase in grain weight and about 7%higher in grain yield. Seed plumpness of R1, R2 and R3 was improved synchronously because the three ZH11-GW6 lines contained GIF1 （Grain Incomplete Filling 1）, a dominant grain filling gene. Thus, GW6 has high potential in increasing the yield of inbred lines through MAB, making it an important genetic resource in super hybrid rice breeding. This study provides insights in the utilization of GW6 for large grain and high yield rice breeding via molecular design breeding.

Breeding by selective introgression: Theory, practices, and lessons learned from rice

Future demands for increased productivity and resilience to abiotic/biotic stresses of major crops require new technologies of breeding by design(BBD)built on massive information from functional and population genomics research.A novel strategy of breeding by selective introgression(BBSI)has been proposed and practiced for simultaneous improvement,genetic dissection and allele mining of complex traits to realize BBD.BBSI has three phases:a)developing large numbers of trait-specific introgression lines(ILs)using backcross breeding in elite genetic backgrounds as the material platform of BBD;b)efficiently identifying genes or quantitative trait loci(QTL)and mining desirable alleles affecting different target traits from diverse donors as the information platform of BBD;and c)developing superior cultivars by BBD using designed QTL pyramiding or marker-assisted recurrent selection.Phase(a)has been implemented massively in rice by many Chinese research institutions and IRRI,resulting in the development of many new green super rice cultivars plus large numbers of ILs in 30+elite genetic backgrounds.Phase(b)has been demonstrated in a series of proof-of-concept studies of high-efficiency genetic dissection of rice yield and tolerance to abiotic stresses using ILs and DNA markers.Phase(c)has also been implemented by designed QTL pyramiding,resulting in a prototype of BBD in several successful cases.The BBSI strategy can be easily extended for simultaneous trait improvement,efficient gene and QTL discovery and allele mining of complex traits using advanced breeding lines from crosses between a common"backbone"parent and a set of elite parents in conventional pedigree breeding programs.BBSI can be relatively easily adopted by breeding programs with small budgets,but the BBSI-based BBD strategy can be fully and more efficiently implemented by large seed companies with sufficient capacity.

Developing green super rice varieties with high nutrient use efficiency by phenotypic selection under varied nutrient conditions

The development of green super rice varieties with improved nutrient use efficiency(NuUE)is a vital target area to increase yield and make it more stable under rainfed conditions.In the present study, we followed an early backcross(BC) breeding approach by using a highyielding and widely adapted Xian variety, Weed Tolerant Rice 1(WTR-1), as a recipient and a Geng variety, Hao-An-Nong(HAN), as a donor.Starting from the BC1F2 generation, the BC population went through one generation of selection under irrigated, low-input, and rainfed conditions, followed by four consecutive generations of screening and selection for high grain yield(GY) under six different nutrient conditions(NPK, 75 N,-N,-P,-NP, and-NPK), leading to the development of 230 BC1F6 introgression lines(ILs).These 230 ILs were evaluated under the same six nutrient conditions for 13 agro-morphological and grain yield component traits in comparison to four checks and parents.Significant trait variations were observed between the treatments and ILs.Positive correlations were identified for GY with biomass, panicle length, flag-leaf area, flag-leaf width, filled grain number per panicle,1000-grain weight, and tiller number under-N,-P,-NP, and-NPK conditions.Out of 230 ILs,12 were identified as promising under two or more nutrient deficiency conditions.The results demonstrated an efficient inter-subspecific BC breeding procedure with a first round of selection under rainfed-drought conditions, followed by four generations of progeny testing for yield performance under six nutrient conditions.The promising ILs can be useful resources for molecular genetic dissection and understanding the physiological mechanisms of NuUE.

The Rice Processing Industry in Nepal: Constraints and Opportunities

A rice mill survey covering diverse rice processing companies in terms of their milling output, type of technology and year of establishment was conducted to understand the current situation of the rice milling industry and to identify enablers and barriers to its growth in Nepal. Coarse rice varieties dominate Nepal’s rice processing industry, with a 42% share by total weight, followed by medium rice (34%) and fine varieties (less than 7%). Polished white rice (Arwa) was the dominant rice type in Nepal in the survey, followed by parboiled and steamed rice. The price and profit margins increased from coarse to fine rice varieties and from Arwa to parboiled and steamed rice. The cost of milling also followed a similar trend. The rice milling industry in Nepal largely influences the adoption or non-adoption of any specific type of rice variety by dictating specific brands in the market and this has important implications for rice research and development. The rice processing industry of Nepal was unable to compete with the Indian rice milling industry because of: 1) low profit margins due to the high cost of rice production and procurement, 2) a lack of economies of scale, 3) a lack of milling technologies for long and extra-long and steamed rice in the country and a lack of investment to modernize rice milling technology, and 4) unavailability of paddy throughout the year locally. Millers were willing to upgrade their rice milling technology to include high throughput parboiling, steamed rice as well as long and extra-long grain rice. This will be a strategic decision in counteracting the ever-increasing rice imports in Nepal. We believe that the findings of the study will be vital for formulating an appropriate rice research, development and rice processing strategy for Nepal to achieve food and nutritional security and the Sustainable Development Goals.

Weedy Rice(Oryza sativa L.)Problem in Rice(Oryza sativa L.)Based Cropping Systems in the Philippines

A study was undertaken in February 2012 to understand the knowledge and practices of rice farmers about weedy rice in two municipalities of Iloilo, Philippines. The specific objectives of the study were to establish what rice farmers know about weedy rice, examine rice farmers’ practices in managing weedy rice, and recommend policies on weedy rice management based on the results of the study. Farmers’ knowledge of weedy rice did not differ much between two villages. Results showed that 41% from the second most affected village and 33% from the most affected village thought that weedy rice cannot reduce the market value of the harvested rice. Majority of the farmers (68%) responded that awns can be absent in some weedy rice and about 40% of the farmers did not know that seeds of weedy rice have dormancy. Cutting the weedy rice panicles at harvest, as the best way of reducing weedy rice, was practiced by majority of the respondents (82%) from the most affected village. Our study suggests that there is a need to increase awareness about weedy rice among Asian farmers.

Identification of Potential Zinc Deficiency Responsive Genes and Regulatory Pathways in Rice by Weighted Gene Co-expression Network Analysis

Zinc(Zn)malnutrition is a major public health issue.Genetic biofortification of Zn in rice grain can alleviate global Zn malnutrition.Therefore,elucidating the genetic mechanisms regulating Zn deprivation response in rice is essential to identify elite genes useful for breeding high grain Zn rice varieties.Here,a meta-analysis of previous RNA-Seq studies involving Zn deficient conditions was conducted using the weighted gene co-expression network analysis(WGCNA)and other in silico prediction tools to identify modules(denoting cluster of genes with related expression pattern)of co-expressed genes,modular genes which are conserved differentially expressed genes(DEGs)across independent RNA-Seq studies,and the molecular pathways of the conserved modular DEGs.WGCNA identified 16 modules of co-expressed genes.Twenty-eight and five modular DEGs were conserved in leaf and crown,and root tissues across two independent RNA-Seq studies.Functional enrichment analysis showed that 24 of the 28 conserved modular DEGs from leaf and crown tissues significantly up-regulated 2 Kyoto Encyclopedia of Genes and Genomes(KEGG)pathways and 15 Gene Ontology(GO)terms,including the substrate-specific transmembrane transporter and the small molecule metabolic process.Further,the well-studied transcription factors(OsWOX11 and OsbHLH120),protein kinase(OsCDPK20 and OsMPK17),and miRNAs(OSA-MIR397A and OSA-MIR397B)were predicted to target some of the identified conserved modular DEGs.Out of the 24 conserved and up-regulated modular DEGs,19 were yet to be experimentally validated as Zn deficiency responsive genes.Findings from this study provide a comprehensive insight on the molecular mechanisms of Zn deficiency response and may facilitate gene and pathway prioritization for improving Zn use efficiency and Zn biofortification in rice.

Global wild rice germplasm resources conservation alliance:World Wild-Rice Wiring

Wild relatives of crop are key genetic resources serving as diversity reservoirs for crop improvement under changing environments.Rice(Oryza sativa)is one of the most important crops in the world,providing staple food for half of the world's population.Wild rice is thus a critical germplasm resource for sustained global food security,ensuring high production yields,improved quality,and stress resistance in the face of climate change.Wild rice is closely related to domesticated rice and has a rich genetic diversity and exceptional adaptability to extreme environments.It has played a pivotal role in the history of rice hybridization and has become a key resource for rice breeding programs.The identification of wild-type cytoplasmic male sterility resources paved the way for the achievement of the“three lines”goal in hybrid rice,leading to a significant increase in rice yields.In addition,the use of resistance alleles found in wild rice is making rice production more resilient to losses caused by environmental stresses.However,wild rice germplasm resources are threatened due to habitat destruction and other anthropogenic factors.At the same time,the lack of centralized distribution of wild rice has hampered the sharing of basic information on wild rice resources and the utilization and conservation of wild rice in each country,as well as collaboration among scientists.

不同耕作方式对杂交水稻根系特性及产量的影响

目的探明不同耕作方式下杂交水稻根系特性及增产的机制。方法在田间试验条件下,研究不同耕作方式(翻耕和免耕)对直播稻和移栽稻根系特性和产量的影响。结果无论直播或移栽,免耕稻最高分蘖期的根冠比、单蔸根干重、根系总吸收表面积和活跃吸收表面积均高于翻耕稻,其成熟期0～5cm土层的根重、根重密度和5～10cm、10～20cm土层的比根长也比翻耕稻高。在移栽条件下,免耕稻成熟期0～5cm土层的根长、根长密度和根表面积高于翻耕稻,其最高分蘖期的根系32P吸收总量和根系氧化力分别比翻耕稻平均增加40.72%、13.81%;在直播条件下,免耕稻最高分蘖期、孕穗期、齐穗期的根系32P吸收总量和根系氧化力分别比翻耕稻平均增加54.56%、19.53%、2.80%和12.59%、24.06%、74.19%,其孕穗期的地上部32P的转运率比翻耕稻平均增加13.68%,而其根系残留率比翻耕稻平均降低10.22%。无论移栽或直播,免耕稻的有效穗数比翻耕稻低,但其每穗粒数高于翻耕稻。在直播和移栽条件下,免耕稻的产量平均分别为8979.0kg·ha-1和8588.0kg·ha-1,比翻耕稻分别增产2.30%和1.19%,但未达到5%的显著水平。结论免耕稻相对于翻耕稻有明显的增产优势,是其根系特性的一种响应。

提高中国稻田氮肥利用率的研究策略

介绍了中国水稻生产氮肥使用及利用率概况。中国氮肥消费量占世界氮肥总量的 30 %,水稻生产所消耗的氮肥占世界水稻氮肥总消耗量的 37%。与主要产稻国相比 ,中国水稻生产氮肥施用量较高而利用率较低 ;介绍了国际上公认的氮肥利用率的概念和相应的定量方法 ;总结了国内外水稻氮肥的施用方法 ,肥料种类 ,计算机推荐施肥以及实时施氮管理模式等对降低氮素损失 ,提高氮肥利用率的研究概况和研究进展 ;从水稻品种耐肥性、土壤供肥能力、施肥技术及水分管理等多方面分析了中国水稻氮肥利用率低的可能原因 ;提出了通过改善水稻品种对氮肥的敏感反应 ,以作物氮素状况为指导适时和适量施用氮肥 ,以及合理调节土壤背景氮来降低氮素损失 ,提高水稻的氮肥利用率的研究策略。

Intellectual Property Rights and the Development of Transgenic Products:Practical Experience

As has happened in the history of many technological advances that have led to important products, many of the initial advances in what we now know as agricultural biotechnology were made in academic research labs.

Rice Gene Index:A comprehensive pan-genome database for comparative and functional genomics of Asian rice

Dear Editor,Asian rice(Oryza sativa)is the staple food for half the world and is a model crop that has been extensively studied.It contributes20%of calories to the human diet(Stein et al.,2018).With the increase in global population and rapid changes in climate,rice breeders need to develop new and sustainable cultivars with higher yields,healthier grains,and reduced environmental footprints(Wing et al.,2018).Since the first gold-standard reference genome of rice variety Nipponbare was published(International Rice Genome Sequencing Project,2005),an increasing number of rice accessions have been sequenced,assembled,and annotated with global efforts.Nowadays,a single reference genome is obviously insufficient to perform the genetic difference analysis for rice accessions.Therefore,the pan-genome has been proposed as a solution,which allows the discovery of more presence-absence variants compared with single-reference genome-based studies(Zhao et al.,2018).Over the past years,several databases,such as RAP-db(https://rapdb.dna.affrc.go.jp),RGAP(http://rice.uga.edu),and Gramene(https://www.gramene.org),have long-term served rice genomic research by providing information based on one or a series of individual reference genomes.To integrate and utilize the genomic information of multiple accessions,we performed comparative analyses and established the user-friendly Rice Gene Index(RGI;https://riceome.hzau.edu.cn)platform.RGI is the first gene-based pan-genome database for rice.

Quantitative Trait Loci Mapping for Leaf Length and Leaf Width in Rice cv.IR64 Derived Lines

The present study was conducted to identify quantitative trait loci （QTLs） for leaf size traits in IR64 introgression lines （INLs）. For this purpose, selected F2 populations derived from crosses between recurrent parent IR64 and its derived INLs, unique for leaf length and leaf width, were used to confirm QTLs. A total of eight QTLs, mapped on three chromosomes, were identified for the four leaf size traits in six F2 populations. A QTL for leaf length, qLLnpt-1, in HKL69 was identified around simple sequence repeat （SSR） marker RM3709 on chromosome 1. Two QTLs for flag leaf length, qFLLnpt-2 and qFLLnpt-4, in HFG39 were indentified on chromosomes 2 and 4, respectively. For flag leaf width, a QTL, qFLWnpt-4, in HFG39 was identified around RM17483 on chromosome 4. While another QTL for flag leaf width, qFLWnpt-1, in HFG27 was identified around RM3252 on chromosome 1. A QTL for leaf width, qLWnpt-2, in HKL75 was identified around RM7451 on chromosome 2. For leaf width, two QTLs, qLWnpt-4a, qLWnpt-4b, in HKL48 and HKL99 were identified around RM7208 and RM6909, respectively on chromosome 4. Results from this study suggest the possibilities to use marker-assisted selection and pyramiding these QTLs to improve rice water productivity.

Two gap-free reference genomes and a global view of the centromere architecture in rice

Rice(Oryza sativa),a major staple throughout the world and a model system for plant genomics and breeding,was the first crop genome sequenced almost two decades ago.However,reference genomes for all higher organisms to date contain gaps and missing sequences.Here,we report the assembly and analysis of gap-free reference genome sequences for two elite O.sativa xian/indica rice varieties,Zhenshan 97 and Minghui 63,which are being used as a model system for studying heterosis and yield.Gap-free reference genomes provide the opportunity for a global view of the structure and function of centromeres.We show that all rice centromeric regions share conserved centromere-specific satellite motifs with different copy numbers and structures.In addition,the similarity of CentO repeats in the same chromosome is higher than across chromosomes,supporting a model of local expansion and homogenization.Both genomes have over 395 non-TE genes located in centromere regions,of which∼41%are actively transcribed.Two large structural variants at the end of chromosome 11 affect the copy number of resistance genes between the two genomes.The availability of the two gap-free genomes lays a solid foundation for further understanding genome structure and function in plants and breeding climate-resilient varieties.

Genetic diversity for mycorrhizal symbiosis and phosphate transporters in rice

Phosphorus （P） is a major plant nutrient and developing crops with higher P-use efficiency is an important breeding goal. In this context we have conducted a comparative study of irrigated and rainfed rice varieties to assess genotypic differences in colonization with arbuscular mycorrhizal （AM） fungi and expression of different P trans- porter genes. Plants were grown in three different soil samples from a rice farm in the Philippines. The data show that AM symbiosis in all varieties was established after 4 weeks of growth under aerobic conditions and that, in soil derived from a rice paddy, natural AM populations recovered within 6 weeks. The analysis of AM marker genes （AM1, AM3, AM14） and P transporter genes for the direct Pi uptake （PT2, PT6） and AM-mediated pathway （PTll, PT13） were largely in agreement with the observed root AM colonization providing a useful tool for diversity studies. Interestingly, delayed AM colonization was observed in the aus-type rice varieties which might be due to their different root structure and might confer an advantage for weed competition in the field. The data further showed that P-starvation induced root growth and expression of the high-affinity P transporter PT6 was highest in the irrigated variety IR66 which a]so maintained grain yield under P-deficient field conditions.

Development of an inflatable solar dryer for improved postharvest handling of paddy rice in humid climates

Rice is the staple food for more than three billion people worldwide.Although considerable progress has been made with respect to improved breeds and production practices,losses during postharvest handling remain considerable.Drying and storage of paddy are two key stages where management can be improved.For rice,grain moisture content of 14%prevents microbiological activity,while a level of about 12%minimizes quality losses over prolonged storage periods.Due to the need for simple and economical technologies,an inflatable solar dryer(ISD)was developed based on adaptations of the Hohenheim-type solar tunnel dryer.To form a drying tunnel,transparent polyethylene(PE)film attaches by zipper to a reinforced black polyvinyl chloride(PVC)film.To reduce heat loss,a flexible multilayer floor was used along the drying area.The tunnel does not need a substructure as it is stabilized adequately from pressure created by two axial flow ventilators.During experiments,paddy was spread on the floor and mixed with a special roller bar.The ISD has been evaluated for paddy in the Philippines during both rainy and dry seasons and was subsequently optimized.Sun drying and shade drying were carried out in parallel for comparison and product was evaluated for moisture content and quality in terms of milling recovery and head rice yield.Moisture content was reduced from 23%to 14%within 26-52 h of continuous operation during the rainy season and 16%to 14%within 4-26 h of drying during the dry season.In both seasons,the final moisture content of 12%was reached after prolonged drying periods.Quality was not found to be affected with respect to drying treatment.The ISD showed advantages over sun drying,despite longer drying periods.

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.In the subsequent decades,breeding efforts targeted ideal plant architecture to increase grains per panicle,reduce unproductive tillers,and improve grain quality by lowering chalkiness and enhancing palatability(Khush,2001).

Review of the wolf spiders from Hainan Island,China(Araneae:Lycosidae)

Twenty-eight species in 14 genera of the family Lycosidae Sundevall,1833 are documented from Hainan Island,China,including five new species:Allotrochosina huangi Wang,Li&Zhang,sp.nov.(♂♀),Al.limu Wang,Li&Zhang,sp.nov.(♂),Arctosa hainan Wang,Li&Zhang,sp.nov.(♂♀),Ar.tangguoi Wang,Li&Zhang,sp.nov.(♂)and Zoica hainan Wang,Li&Zhang,sp.nov.(♂♀).Eight new synonyms are proposed:Arctosa danzhounensis Barrion,Barrion-Dupo&Heong,2012 syn.nov.=Ar.springiosa Yin,Wang,Xie&Peng,1993;Hippasa sinsiloides Barrion,Barrion-Dupo&Heong,2012 syn.nov.=H.holmerae Thorell,1895;Lycosa hawigvittata Barrion,Barrion-Dupo&Heong,2012 syn.nov.=L.vittata Yin,Bao&Zhang,1995;Pardosa daxiansongi Barrion,Barrion-Dupo&Heong,2012 syn.nov.=P.pusiola(Thorell,1891);P.tieshinglii Barrion,Barrion-Dupo&Heong,2012 syn.nov.=P.sumatrana(Thorell,1890);P.villarealae Barrion,Barrion-Dupo&Heong,2012 syn.nov.=P.sumatrana(Thorell,1890);Pirata sanya Barrion,Barrion-Dupo&Heong,2012 syn.nov.=Lysania pygmaea Thorell,1890;Pirata catindigae Barrion,Barrion-Dupo&Heong,2012 syn.nov.=Pi.subpiratica(Bösenberg&Strand,1906).The genus Allotrochosina Roewer,1960 and the species Wadicosa okinawensis(Tanaka,1985)are newly recorded from China,and Pardosa aciculifera Chen,Song&Li,2001 is recorded from Thailand for the first time.Females of Arctosa tridentata Chen&Song,1999 and Ocyale qiongzhongensis Yin&Peng,1997 are described for the first time.Morphological illustrations and photos of all species are given.