Retrospective and perspective of rice breeding in China

Breeding is the art and science of selecting and changing crop traits for the benefit of human beings. For several decades, tremendous efforts have been made by Chinese scientists in rice breeding in improving grain yield, nutrition quality, and environmental performance, achieving substantial progress for global food security. Several generations of crop breeding technologies have been developed, for example, selection of better performance in the field among variants (conventional breeding), application of molecular markers for precise selection (molecular marker assisted breeding), and development of molecular design (molecular breeding by rational design). In this review, we briefly summarize the advances in conventional breeding, functional genomics for genes and networks in rice that regulate important agronomic traits, and molecular breeding in China with focuses on high yield, good quality, stress tolerance, and high nutrient-use efficiency. These findings have paved a new avenue for rational design of crops to develop ideal varieties with super performance and productivity.     

Toward understanding genetic mechanisms of complex traits in rice

Rice is the primary carbohydrate staple cereal feeding the world population. Many genes, known as quantitative trait loci (QTLs), con-trol most of the agronomically important traits in rice. The identification of QTLs controlling agricultural traits is vital to increase yield and meet the needs of the increasing human population, but the progress met with challenges due to complex QTL inheritance. To date,many QTLs have been detected in rice, including those responsible for yield and grain quality; salt, drought and submergence tolerance;disease and insect resistance; and nutrient utilization efficiency. Map-based cloning techniques have enabled scientists to successfully fine map and clone approximately seventeen QTLs for several traits. Additional in-depth functional analyses and characterizations of these genes will provide valuable assistance in rice molecular breeding.     

中国水稻遗传育种历程与展望

我国的水稻育种经历了矮化育种、杂种优势利用和绿色超级稻培育3次飞跃,其间伴随矮化育种(第一次绿色革命)、三系杂交稻培育、二系杂交稻培育、亚种间杂种优势利用、理想株型育种和绿色超级稻培育等6个重要历程。育种目标从唯产量是举到高抗、优质和高产并重,育种理念从高产优质逐步提升为“少投入,多产出,保护环境”。水稻功能基因组研究为第二次绿色革命准备了大量的有重要利用价值的基因,水稻育种正迈向设计育种的新时代。基因组选择技术和转基因技术将为培育“少打农药,少施化肥,节水抗旱,优质高产” 绿色超级稻保驾护航。本文对我国水稻遗传育种的发展历程进行了概括,指出了各种育种方法和育种技术的优缺点,系统介绍了水稻细胞质雄性不育和光温敏雄性核不育以及籼粳杂种不育的分子机制的研究进展,综述了水稻株型、穗型、粒形和养分高效利用相关的重要功能基因,阐明了产量与开花期联动的关系,凸显了我国水稻基础研究在国际上的重要地位。特别指出,近年来,我国水稻生产方式发生了或正在发生巨大变革,育种理念也要与时俱进。未来,杂交育种技术要与现代育种技术紧密结合,选育水稻品种不仅要满足市场需求,而且更要具备绿色健康的特点,同时还要适应新耕作制度和新耕作方法。     

Yield-related QTLs and Their Applications in Rice Genetic Improvement

Grain yield is one of the most important indexes in rice breeding,which is governed by quantitative trait loci (QTLs).Different map-ping populations have been used to explore the QTLs controlling yield related traits.Primary populations such as F 2 and recombi-nant inbred line populations have been widely used to discover QTLs in rice genome-wide,with hundreds of yield-related QTLs detected.Advanced populations such as near isogenic lines (NILs) are efficient to further fine-map and clone target QTLs.NILs for primarily identified QTLs have been proposed and confirmed to be the ideal population for map-based cloning.To date,20 QTLs directly affecting rice grain yield and its components have been cloned with NIL-F 2 populations,and 14 new grain yield QTLs have been validated in the NILs.The molecular mechanisms of a continuously increasing number of genes are being unveiled,which aids in the understanding of the formation of grain yield.Favorable alleles for rice breeding have been ’mined’ from natural cultivars and wild rice by association analysis of known functional genes with target trait performance.Reasonable combination of favorable alleles has the potential to increase grain yield via use of functional marker assisted selection.     

水稻卷叶细胞学与分子机制研究进展

卷叶性状是水稻(Oryza sativa)重要的育种指标之一。研究表明,水稻叶片适度卷曲对植株的光合作用、株型及增产等均具有重要作用。该文综述了水稻叶片卷曲的相关研究进展,对水稻叶片卷曲的细胞学形成机制和相关调控基因的分子机制进行了阐述,以期深入阐明水稻叶片卷曲的细胞学和分子机制,促进卷叶性状在水稻育种中的应用。     

鱼和熊掌的选择:反向重复序列变异介导的玉米环境适应与产量平衡

作物育种的目标是找到产量和抗性的最佳平衡点,其中涉及“鱼和熊掌”二者兼得的选择策略。哪些逆境负调控位点影响产量性状,以及如何调控等是突破育种瓶颈的重要科学问题。近百年来,高产玉米(Zeamays)育种使玉米单产不断提高,同时现代玉米品种对干旱的敏感性也呈现出增强趋势,故而存在高产稳产的潜在风险。可对于这一现象背后确切的遗传机制却知之甚少,从而限制了既高产又高抗玉米新品种的培育。玉米的非生物胁迫抗性与产量性状均为多基因控制的复杂数量性状,涉及全基因组范围内大量基因的表达与调控。玉米基因组内存在大量的小RNA (sRNA),其对基因表达起精细调控作用,但人们对sRNA调控作物环境胁迫应答与产量性状机制的理解仍然有限。近日,华中农业大学代明球课题组与李林和李峰两个课题组合作,基于对338份玉米关联群体在不同环境下的sRNA表达组分析,鉴定到大量干旱应答的sRNA,以及调控这些sRNA表达的遗传位点(eQTL);并克隆了8号染色体上1个干旱特异性eQTL热点DRESH8。生物信息学分析显示, DRESH8是1个由转座子组成的长度约为21.4 kb的反向重复序列(TE-IR)。DRESH8通过产...     

Progress in research and development on hybrid rice: a super-domesticate in China

BACKGROUND: China has been successful in breeding hybrid rice strains, but is now facing challenges to develop new hybrids with high-yielding potential, better grain quality, and tolerance to biotic and abiotic stresses. This paper reviews the most significant advances in hybrid rice breeding in China, and presents a recent study on fine-mapping quantitative trait loci (QTLs) for yield traits. SCOPE: By exploiting new types of male sterility, hybrid rice production in China has become more diversified. The use of inter-subspecies crosses has made an additional contribution to broadening the genetic diversity of hybrid rice and played an important role in the breeding of super rice hybrids in China. With the development and application of indica-inclined and japonica-inclined parental lines, new rice hybrids with super high-yielding potential have been developed and are being grown on a large scale. DNA markers for subspecies differentiation have been identified and applied, and marker-assisted selection performed for the development of restorer lines carrying disease resistance genes. The genetic basis of heterosis in highly heterotic hybrids has been studied, but data from these studies are insufficient to draw sound conclusions. In a QTL study using stepwise residual heterozygous lines, two linked intervals harbouring QTLs for yield traits were resolved, one of which was delimited to a 125-kb region. CONCLUSIONS: Advances in rice genomic research have shed new light on the genetic study and germplasm utilization in rice. Molecular marker-assisted selection is a powerful tool to increase breeding efficiency, but much work remains to be done before this technique can be extended from major genes to QTLs.     

水稻籽粒灌浆速率的分子机制与遗传调控研究进展

水稻(Oryza sativa)的高产优质是我国粮食安全的重要保障,也是育种家一直追求的目标。水稻籽粒灌浆速率(GFR)是一个重要而复杂的农艺性状,直接影响籽粒充实度、粒重和米质。目前,快速灌浆的优良水稻品种缺乏,可供育种利用的相关优异基因资源有限,已成为制约水稻产量和品质进一步提高的瓶颈。相对于水稻的其它农艺性状,G...     

水稻抗病性基因的克隆和功能研究进展

抗病性是水稻遗传改良的主要目标, 是水稻高产、优质的重要保证。近年来, 水稻的抗病机制研究取得实质性进展, 鉴定并克隆了一批重要的抗性基因。文章综述了这些基因的鉴定、克隆和生物学功能研究进展, 探讨了抗病基因的有效利用。     

Striga infestation of cereal crops - an unsolved problem in resource limited agriculture

The parasitic weed Striga causes devastating losses in cereal yields in sub-Saharan Africa. The parasite lifecycle is intimately linked with its host via a complex interchange of signals. Understanding the molecular basis of these interactions and of host resistance to Striga is essential for the identification of genes for improving crop yield via biotechnological or marker assisted breeding strategies. Cloning and sequencing of ESTs from the 'model' parasite Triphysaria versicolor is facilitating the identification of parasitism genes. The identification of resistance to Striga in sorghum and rice germplasm is allowing molecular dissection of these traits using genomic platforms and quantitative trait loci (QTL) analysis. QTL underlying different resistance phenotypes have been identified and the use of advanced backcross populations is allowing the exploitation of sources of resistance in wild relatives of cereals.     

Mapping QTLs for Plant Phenology and Production Traits Using Indica Rice (Oryza sativa L.) Lines Adapted to Rainfed Environment

Drought is a major abiotic stress limiting rice production and yield stability in rainfed ecosystems. Identifying quantitative trait loci (QTL) for rice yield and yield components under water limited environments will help to develop drought resilient cultivars using marker assisted breeding (MAB) strategy. A total of 232 recombinant inbred lines of IR62266/Norungan were used to map QTLs for plant phenology and production traits under rainfed condition in target population of environments. A total of 79 QTLs for plant phenology and production traits with phenotypic variation ranging from 4.4 to 72.8% were detected under non-stress and drought stress conditions across two locations. Consistent QTLs for phenology and production traits were detected across experiments and water regimes. The QTL region, RM204-RM197-RM217 on chromosome 6 was linked to days to 50% flowering and grain yield per plant under both rainfed and irrigated conditions. The same genomic region, RM585-RM204-RM197 was also linked to harvest index under rainfed condition with positive alleles from Norungan, a local landrace. QTLs for plant production and drought resistance traits co-located near RM585-RM204-RM197-RM217 region on chromosome 6 in several rice genotypes. Thus with further fine mapping, this region may be useful as a candidate QTL for MAB, map-based cloning of genes and functional genomics studies for rainfed rice improvement.     

Advances in Drought Resistance of Rice

Water deficit is a serious environmental stress and the major constraint to rice productivity. Losses in rice yield due to water shortage probably exceed losses from all other causes combined and the extent of the yield loss depends on both the severity and duration of the water stress. Drought affects rice at morphological, physiological, and molecular levels such as delayed flowering, reduced dry matter accumulation and partitioning, and decreased photosynthetic capacity as a result of stomatal closure, metabolic limitations, and oxidative damage to chloroplasts. Small-statured rice plants with reduced leaf area and short growth duration are better able to tolerate drought stress, although the mechanisms are not yet fully understood. Increased water uptake by developing larger and deeper root systems, and the accumulation of osmolytes and osmoprotectants are other important mechanisms for drought resistance. Drought resistance in rice has been improved by using plant growth regulators and osmoprotectants. In addition, several enzymes have been found that act as antioxidants. Silicon has also improved drought resistance in rice by silicification of the root endodermis and improving water uptake. Seed priming improves germination and crop stand establishment under drought. Rice plants expressing HVA1, LEA proteins, MAP kinase, DREB and endo-1, 3-glucanase are better able to withstand drought stress. Polyamines and several enzymes act as antioxidants and reduce adverse effects of drought stress in rice. Drought resistance can be managed by developing and selecting drought-tolerant genotypes. Rice breeding and screening may be based on growth duration, root system, photosynthesis traits, stomatal frequency, specific leaf weight, leaf water potential, and yield in target environments. This review discusses recent developments in integrated approaches, such as genetics, breeding and resource management to increase rice yield and reduce water demand for rice production.     

赤霉素生物合成与信号传递对植物株高的调控

植物株高是影响作物产量和品质的重要农艺性状。赤霉素(Gibberellins,GAs)是调控植物株高的重要激素,GA相关株高基因的克隆与分子机制研究对于合理调控作物生长发育和农业生产具有极其重要的利用价值,在水稻、小麦等粮食作物育种中得到了广泛应用。为了促进GA在果树、花卉等园艺作物育种中的有效利用,文中在分子生物学水平上介绍GA生物合成和GA信号传递途径对植物株高的调控。     

Assessment of yield based selection under managed field stress condition for breeding for rice yield improvement under drought

The progress in development and dissemination of drought tolerant lines has been slow as compared to the increasing drought prevalence in the rice growing regions. Significant amount of work has been done in the past on drought resistance traits in rice crop, still the benefit of improved drought tolerant rice cultivars reaching the farmer’s field is not very high and ways to expedite the development of drought tolerant and productive rice cultivars needs to be addressed. In this article, an assessment of easily practicable approach of managed stress screening and prospect of direct selection for yield under drought stress is discussed. Also the large effect yield QTLs identified for grain yield under drought stress field conditions is being reviewed for successful introgression into elite genetic background for developing drought tolerant cultivars with improved yield for the drought prone target environment.     

Marker assisted selection in crop plants

Genetic mapping of major genes and quantitative traits loci (QTLs) for many important agricultural traits is increasing the integration of biotechnology with the conventional breeding process. Exploitation of the information derived from the map position of traits with agronomical importance and of the linked molecular markers, can be achieved through marker assisted selection (MAS) of the traits during the breeding process. However, empirical applications of this procedure have shown that the success of MAS depends upon several factors, including the genetic base of the trait, the degree of the association between the molecular marker and the target gene, the number of individuals that can be analyzed and the genetic background in which the target gene has to be transferred. MAS for simply inherited traits is gaining increasing importance in breeding programs, allowing an acceleration of the breeding process. Traits related to disease resistance to pathogens and to the quality of some crop products are offering some important examples of a possible routinary application of MAS. For more complex traits, like yield and abiotic stress tolerance, a number of constraints have determined severe limitations on an efficient utilization of MAS in plant breeding, even if there are a few successful applications in improving quantitative traits. Recent advances in genotyping technologies together with comparative and functional genomic approaches are providing useful tools for the selection of genotypes with superior agronomical performancies.     

Transmission of important chromosomal regions under selection revealed in rice pedigree breeding programs

Genetic analysis across a whole plant genome based on pedigree information offers considerable potential for enhancing genetic gain from plant breeding programs through quantitative trait loci (QTL) mapping and marker-assisted selection. Here, we report its application for graphically genotyping varieties used in Chinese japonica rice (Oryza sativa L.) pedigree breeding programs. We identified 34 important chromosomal regions from the founder parent that are under selection in the breeding programs, and by comparing donor genomic regions that are under selection with QTL locations of agronomic traits, we found that QTL clustered in important genomic regions, in accordance with association analyses of natural populations and other previous studies. The convergence of genomic regions under selection with QTL locations suggests that donor genomic regions harboring key genes/QTL for important agronomic traits have been selected by plant breeders since the 1950s from the founder rice plants. The results provide better understanding of the effects of selection in breeding programs on the traits of rice cultivars. They also provide potentially valuable information for enhancing rice breeding programs through screening candidate parents for targeted molecular markers, improving crop yield potential and identifying suitable genetic material for use in future breeding programs.     

辐射诱变创制水稻新种质研究进展及浙粳99突变体库的建立

辐射诱变育种所需年限短、变异率高、后代性状稳定快,在作物遗传育种中已广泛应用.本文统计了我国近10年来利用辐射诱变技术培育的在生产应用上发挥重要作用的部分优良新品种18个,说明通过辐射诱变可加速水稻变异,丰富水稻遗传图谱,为培育高产、优质、抗病水稻新品种提供更多类型种质资源.此外总结了利用辐射诱变获得的各种类型突变,包...     

水稻非生物胁迫相关QTL研究进展

培育优质高产水稻品种是水稻育种工作者的首要目标。近年来,不断恶化的环境条件使水稻生长面,临更多的逆境胁迫。其中,非生物胁迫严重影响水稻产量提高和品质改善。从QTL角度研究水稻对非生物胁迫的适应机理,对于提高水稻产量、品质和抗逆性等方面具有重要的意义。本文综述了近年来水稻非生物胁迫相关QTL的研究进展,以及通过分子辅助育种手段创制多目标性状聚合的优良水稻品种的主要策略,为实现水稻优质高产和广适性的综合改良提供思路。     

Breeding for abiotic stresses for sustainable agriculture

Using cereal crops as examples, we review the breeding for tolerance to the abiotic stresses of low nitrogen, drought, salinity and aluminium toxicity. All are already important abiotic stress factors that cause large and widespread yield reductions. Drought will increase in importance with climate change, the area of irrigated land that is salinized continues to increase, and the cost of inorganic N is set to rise. There is good potential for directly breeding for adaptation to low N while retaining an ability to respond to high N conditions. Breeding for drought and salinity tolerance have proven to be difficult, and the complex mechanisms of tolerance are reviewed. Marker-assisted selection for component traits of drought in rice and pearl millet and salinity tolerance in wheat has produced some positive results and the pyramiding of stable quantitative trait locuses controlling component traits may provide a solution. New genomic technologies promise to make progress for breeding tolerance to these two stresses through a more fundamental understanding of underlying processes and identification of the genes responsible. In wheat, there is a great potential of breeding genetic resistance for salinity and aluminium tolerance through the contributions of wild relatives.     

抗旱相关基因在烟草中的应用研究进展

干旱是影响烟草正常生长、发育、产量和烟叶品质的一个重要逆境因子。在干旱胁迫下,植物体内会通过激发一些抗旱基因的表达来增强植物的抗旱能力。目前,很多抗旱相关的功能蛋白基因和调控蛋白基因已被克隆并在烟草中实现了遗传转化,外源抗旱基因的表达提高了转基因烟草的抗旱能力。抗旱基因的克隆为烟草抗旱新品种的培育奠定了良好的分子基础,系统深入地研究抗旱相关基因在干旱胁迫条件下的表达与调控,可为通过基因工程手段提高烟草的抗旱能力开辟新途径,同时也能为其他农作物的抗旱分子育种和品种改良提供基因资源。