Genetic and Molecular Insights into the Enhancement of Rice Yield Potential

Rice is one of the most important global food crops and a primary source of calories for more than half of the world's population. Rice production increased steadily during the green revolution era primarily as a result of introducing high-yielding rice varieties. World rice production increased at a rate of 2.3–2.5% per year during 1970s and 1980s, but this rate of growth was only 1.5% per year during the 1990s. The yield growth rate for rice has further declined during the first decade of this century. However, the populations in the major rice-consuming countries continue to grow at a rate of more than 1.5% per year. According to various estimates, world rice production must increase at the rate of 2 million tons per year. To meet this challenge, rice varieties with higher yield potential and greater yield stability are needed. Various strategies for increasing the yield potential of rice include; (1) conventional hybridization and selection, (2) F₁ hybrid breeding, (3) modification of plant architecture, and (4) enhancement of photosynthesis. Many genes and QTLs have recently been identified which will assist with rice breeding objectives.     

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。     

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.     

Advances to improve the eating and cooking qualities of rice by marker-assisted breeding

The eating and cooking qualities of rice are heavily emphasized in breeding programs because they determine market values and they are the appealing attributes sought by consumers. Conventional breeding has developed traditional varieties with improved eating and cooking qualities. Recently, intensive genetic studies have pinpointed the genes that control eating and cooking quality traits. Advances in genetic studies have developed molecular techniques, thereby allowing marker-assisted breeding (MAB) for improved eating and cooking qualities in rice. MAB has gained the attention of rice breeders for the advantages it can offer that conventional breeding cannot. There have been successful cases of using MAB to improve the eating and cooking qualities in rice over the years. Nevertheless, MAB should be applied cautiously given the intensive effort needed for genotyping. Perspectives from conventional breeding to marker-assisted breeding will be discussed in this review for the advancement of the eating and cooking qualities of fragrance, amylose content (AC), gel consistency (GC) and gelatinization temperature (GT) in rice. These four parameters are associated with eating and cooking qualities in rice. The genetic basis of these four parameters is also included in this review. MAB is another approach to rice variety improvement and development in addition to being an alternative to genetic engineering. The MAB approach shortens the varietal development time, and is therefore able to deliver improved rice varieties to farmers within a shorter period of time.     

Newer and select maize,wheat, and rice varieties can help mitigate N footprint while producing more grain

Sustainably feeding the growing population amid a changing climate and dwindling resources is a grand challenge facing mankind. Decades‐long advancement in crop breeding has progressively elevated yield potential, markedly enhancing global food production capacity. However, relevant impact on reactive N (Nr) emissions associated with crop variety improvement has not been explicitly described. Here, we report multitiered evidence that newer and select maize, wheat, and rice varieties developed in China have the capacity to substantially lower Nr losses while producing more grain. First, we pooled studies featuring side‐by‐side comparison of different varieties, totaling 269 paired observations, to demonstrate that collectively, relatively newer varieties of maize, wheat, and rice had less Nr emissions (9.6%–23.5%) while yielding more grains (7.3%–11.2%) compared to older varieties under wide‐ranging conditions. Next, we built an extended database (142 field studies with 833 observations) and comprehensively evaluated the Nr‐loss reduction potential of newer varieties (2000 and after) versus older ones (1985–1999). We found that newer varieties had Nr emission factors (N loss as a percentage of N applied after correcting for background emissions) 18.2%–75.7% less for N₂O, 18.3%–75.7% less for , and ?8.5% to 22.8% less for NH₃, while producing more grains (16.0%–24.4%). Individual varieties differed markedly in yield‐emission scores. A nationwide farmer survey (2.47 million responses) indicated tremendous opportunities for a new way of management intervention. Coupling variety selection with sound N and other agronomic management can help lower N footprint while producing more grain.     

转C4光合固碳相关基因水稻的研究进展

近10年来,转C4光合固碳相关基因水稻的研究取得了长足进展,已受到国内外科学界的广泛关注。本文简要介绍并评述了有关方面的研究进展,包括水稻的C4光合固碳基因工程、转C4固碳相关基因水稻光合和光氧化的生理特性及转C4光合固碳相关基因水稻的生理育种3个方面：提出以常规育种和生物技术相结合,开展转C4光合固碳相关基因水稻的生理育种,是培育优质、高产超级稻的有效途径。     

Bt水稻杂交育种中转基因的遗传分析

利用PCR、GUS染色和Western印迹杂交技术检测了Bt水稻杂交后代群体,发现在394株GUS阳性株中,共有392株表达Bt蛋白,协同表达株率达99.49%。由此表明,在杂交后代中报告基因Gus和目的基因crylAb紧密连锁遗传与表达。本试验还发现,在BC1、BC1F2和粳粳交F2群体中转基因呈单基因显性遗传,而在籼粳交F2群体中偏离3:1分离。 Abstract:Improved histochemical staining for GUS activity,PCR and Western blotting were used to detect the population of Bt rice crossed to conventional rice varieties.A total of 392 plants expressing Bt toxin protein were found in 394 GUS positive plants.The result demonstrated that cry1Ab gene closely inherited and expressed with reporter gene gus.Therefore,it is possible to develop GUS-assisted-selection to preliminarily identify the Bt gene and study the inheritance of transgenes in (back)cross breeding.Mendelian segragation of reporter gene Gus was observed in F2,BC1 and BC1F2 progenies.Thus indicated that transgenes inherited as a single dominant gene in the progenies of Bt rice crossed to conventional rice varieties.     

Genomics-based precision breeding approaches to improve drought tolerance in rice

Rice (Oryza sativa L.), the major staple food crop of the world, faces a severe threat from widespread drought. The development of drought-tolerant rice varieties is considered a feasible option to counteract drought stress. The screening of rice germplasm under drought and its characterization at the morphological, genetic, and molecular levels revealed the existence of genetic variation for drought tolerance within the rice gene pool. The improvements made in managed drought screening and selection for grain yield under drought have significantly contributed to progress in drought breeding programs. The availability of rice genome sequence information, genome-wide molecular markers, and low-cost genotyping platforms now makes it possible to routinely apply marker-assisted breeding approaches to improve grain yield under drought. Grain yield QTLs with a large and consistent effect under drought have been indentified and successfully pyramided in popular rice mega-varieties. Various rice functional genomics resources, databases, tools, and recent advances in “-omics” are facilitating the characterization of genes and pathways involved in drought tolerance, providing the basis for candidate gene identification and allele mining. The transgenic approach is successful in generating drought tolerance in rice under controlled conditions, but field-level testing is necessary. Genomics-assisted drought breeding approaches hold great promise, but a well-planned integration with standardized phenotyping is highly essential to exploit their full potential.     

高产早籼稻产量构成因素初析

1998年早季在广州研究了3个两系法杂交水稻组合和2个常规稻品种的产量构成因素,初步认为:两系法杂交稻新组合培矮64s/E32的产量最高,它单穗湿重和穗长亦最大,分别达5.42g和24.7cm;而常规稻品种粤香占亩有效穗数最高和谷/秆比值最大,分别达23.3万穗/亩和1.53。如果把这些性状有机地组合起来后再加上粤杂122的优质特性,这种结构模式将为华南地区水稻超高产或超级稻育种,展示了一种美好的前景。     

A whole‐genome SNP array (RICE6K) for genomic breeding in rice

The advances in genotyping technology provide an opportunity to use genomic tools in crop breeding. As compared to field selections performed in conventional breeding programmes, genomics‐based genotype screen can potentially reduce number of breeding cycles and more precisely integrate target genes for particular traits into an ideal genetic background. We developed a whole‐genome single nucleotide polymorphism (SNP) array, RICE6K, based on Infinium technology, using representative SNPs selected from more than four million SNPs identified from resequencing data of more than 500 rice landraces. RICE6K contains 5102 SNP and insertion–deletion (InDel) markers, about 4500 of which were of high quality in the tested rice lines producing highly repeatable results. Forty‐five functional markers that are located inside 28 characterized genes of important traits can be detected using RICE6K. The SNP markers are evenly distributed on the 12 chromosomes of rice with the average density of 12 SNPs per 1 Mb and can provide information for polymorphisms between indica and japonica subspecies as well as varieties within indica and japonica groups. Application tests of RICE6K showed that the array is suitable for rice germplasm fingerprinting, genotyping bulked segregating pools, seed authenticity check and genetic background selection. These results suggest that RICE6K provides an efficient and reliable genotyping tool for rice genomic breeding.     

A Pyramid Breeding of Eight Grain-yield Related Quantitative Trait Loci Based on Marker-assistant and Phenotype Selection in Rice （Oryza sativa L.）

1000-Grain weight and spikelet number per panicle are two important components for rice grain yield.In our previous study,eight quantitative trait loci(QTLs)conferring spikelet number per panicle and 1000-grain weight were mapped through sequencing-based genotyping of 150 rice recombinant inbred lines(RILs).In this study,we validated the effects of four QTLs from Nipponbare using chromosome segment substitution lines(CSSLs),and pyramided eight grain yield related QTLs.The new lines containing the eight QTLs with positive effects showed increased panicle and spikelet size as compared with the parent variety 93-11.We further proposed a novel pyramid breeding scheme based on marker-assistant and phenotype selection(MAPS).This scheme allowed pyramiding of as many as 24 QTLs at a single hybridization without massive cross work.This study provided insights into the molecular basis of rice grain yield for direct wealth for high-yielding rice breeding.     

Improving Salinity Tolerance in Cereals

Cereals are grown in almost every region of the world and are exposed to a variety of environmental stresses that severely affect their growth and grain yield. Of various abiotic stresses, salinity is one of the more significant threats to cereal crops. To ensure food security, there is a need to adopt strategies to overcome this specific threat. Undoubtedly, plant scientists have been exploiting a variety of approaches to achieve enhanced crop productivity on salt affected soils. Of the various biotic approaches, conventional breeding, marker-assisted selection and genetic engineering to develop salt-tolerant lines/cultivars of cereals all seem plausible. Some success stories have been reported for improvement in salt tolerance of wheat and rice, but are scarce for other cereals. A number of barriers to the development of salt-tolerant cultivars/lines have been identified and include a lack of knowledge about the genetics of crops, their physiological and biochemical behavior, wide variation in environmental conditions, and the complex polygenic nature of the salt tolerance character. This review focuses on how improvements have been made in salt tolerance in cereals through different biotic means, such as conventional breeding, marker assisted selection and genetic engineering.     

Domestication, genomics and the future for banana

BACKGROUND: Cultivated bananas and plantains are giant herbaceous plants within the genus Musa. They are both sterile and parthenocarpic so the fruit develops without seed. The cultivated hybrids and species are mostly triploid (2n = 3x = 33; a few are diploid or tetraploid), and most have been propagated from mutants found in the wild. With a production of 100 million tons annually, banana is a staple food across the Asian, African and American tropics, with the 15 % that is exported being important to many economies. SCOPE: There are well over a thousand domesticated Musa cultivars and their genetic diversity is high, indicating multiple origins from different wild hybrids between two principle ancestral species. However, the difficulty of genetics and sterility of the crop has meant that the development of new varieties through hybridization, mutation or transformation was not very successful in the 20th century. Knowledge of structural and functional genomics and genes, reproductive physiology, cytogenetics, and comparative genomics with rice, Arabidopsis and other model species has increased our understanding of Musa and its diversity enormously. CONCLUSIONS: There are major challenges to banana production from virulent diseases, abiotic stresses and new demands for sustainability, quality, transport and yield. Within the genepool of cultivars and wild species there are genetic resistances to many stresses. Genomic approaches are now rapidly advancing in Musa and have the prospect of helping enable banana to maintain and increase its importance as a staple food and cash crop through integration of genetical, evolutionary and structural data, allowing targeted breeding, transformation and efficient use of Musa biodiversity in the future.     

中国野生稻遗传资源的保护及其在育种中的利用

我国有三种野生稻,即普通野生稻(Oryza rufipogon)、药用野生稻(O.officinalis)和瘤粒野生稻(O.meyeriana)。这三种野生稻均被列为国家二级保护植物(渐危种)。调查结果表明,野生稻由于其自然群落大量丧失而濒危,濒危程度为普通野生稻>药用野生稻>瘤粒野生稻。造成濒危的主要原因是人为的破坏活动。人类的经济活动导致了野生稻生境丧失、生境质量不断恶化、栖息地越来越少;人类的活动也导致了外来种的入侵。目前,对野生稻的保护措施主要有就地保护(原地保护或原位保护)和迁地保护(易地保护或异位保护)。易地保护包括以种子保存的种质厍、以种茎保存的种质圃和以器官培养物作为材料的超低温保存。野生稻具有许多优良特性,如特强的耐寒性、高的抗病虫性、优质蛋白质含量高、功能叶片耐衰老的特异性、特强的再生性、良好的繁茂性及生长优势等等,这些优良特性已被广泛用于水稻常规育种和杂交育种中,并取得了巨大的社会效益和经济效益。有关野生稻生物技术方面的研究,如花药培养、原生质培养、体细胞杂交和基因工程等方面已取得了较大的进展。野生稻将在水稻育种中发挥越来越重要的作用。     

我国杂交水稻基因工程育种策略探讨

杂交水稻在我国水稻及粮食生产中占有突出地位 ,基因工程可在杂交水稻育种中发挥重要作用。针对杂交水稻育种存在的主要问题 ,指出应将优质、抗虫和抗病作为当前基因工程育种的研究重点。同时提出基因工程育种与常规育种紧密结合 ,优质基因工程着重改良保持系及聚合转基因等策略 ,以培育出超高产优质抗病虫转基因聚合杂交稻新组合。     

Cryopreservation of sweetpotato (Ipomoea batatas) and its pathogen eradication by cryotherapy

Sweetpotato (Ipomoea batatas) ranks as the seventh most important staple crop in the world and the fifth in developing countries after rice, wheat, maize and cassava. Sweetpotato is mainly grown in developing countries, which account for more than 95% of total production of the whole world. Genetic resources, including cultivated varieties and wild species, are a prerequisite for novel sweetpotato breeding in both conventional and genetic engineering programs. Various cryopreservation protocols have been developed for shoot tips and embryogenic tissues. The former explants are preferred for long-term conservation of sweetpotato genetic resources, while the latter are valuable for sweetpotato genetic improvement. This review provides update comprehensive information on cryopreservation of sweetpotato shoot tips and embryogenic tissues.Plant pathogens such as viruses and phytoplasma severely hamper high yield and high quality production of sweetpotato. Thus, usage of pathogen-free planting materials is pivotal for sustainable sweetpotato production. Cryotherapy of shoot tips can efficiently eradicate sweetpotato pathogens such as viruses and phytoplasma. The mechanism behind pathogen eradication by cryotherapy of shoot tips has been elucidated. Pathogen eradication by cryotherapy provides an alternative, efficient strategy for production of pathogen-free plants. In addition, cryopreserved tissues may also be considered to be safer for exchange of germplasm between countries and regions.     

近年来国内外橡胶树育种研究新进展

从常规育种、高产育种和抗性育种方面综述近年来国外橡胶树育种研究的新进展,并结合我国橡胶树育种现状,提出我国橡胶树育种的方向,以期为我国橡胶树产量性状、遗传改良和抗逆性育种等提供借鉴.     

Integration of genomic tools to assist breeding in the <Emphasis Type="Italic">japonica</Emphasis> subspecies of rice

The cultivated rice (Oryza sativa L.) has two subspecies, indica and japonica. The japonica rice germplasm has a narrower genetic diversity compared to the indica subspecies. Rice breeders aim to develop new varieties with a higher yield potential, with enhanced resistances to biotic and abiotic stresses, and improved adaptation to environmental changes. In order to face some of these challenges, japonica rice germplasm will have to be diversified and new breeding strategies developed. Indica rice improvement could also profit from more “genepool mingling” for which japonica rice could play an important role. Interesting traits such as low-temperature tolerance, and wider climate adaptation could be introgressed into the indica subspecies. In the past decade, huge developments in rice genomics have expanded our available knowledge on this crop and it is now time to use these technologies for improving and accelerating rice breeding research. With the full sequence of the rice genome, breeders may take advantage of new genes. Also new genes may be discovered from the genepool of wild relatives, or landraces of the genus Oryza, and incorporated into elite japonica cultivars in a kind of “gene revolution” program. Expectedly, new technologies that are currently being optimized, aiming for novel gene discovery or for tracking the regions under selection, will be suggested as new breeding approaches. This paper revisits breeding strategies successfully employed in indica rice, and discusses their application in japonica rice improvement (e.g. ideotype breeding, wide hybridization and hybrid performance).     

Rice genetic resources: history,conservation, investigative characterization and use in Japan

Rice has been grown in Japan for about 3000 years. Although both japonica and indica varieties have been grown in Japan, now japonica rices are grown. Japanese rice breeding has used an ecological breeding approach. While emphasis in rice breeding in the 1940's and 1950's focussed on yield in recent decades quality has been of major importance. Consumer preference and name recognition of high quality varieties, such as Koshihikari, has resulted in slow acceptance of new varieties.Rice germplasm was systematically collected throughout Japan between 1962 and 1963. Subsequent acquisition and collecting, in Japan and other countries, has resulted in 28,000 accessions being conserved in the National Genebank, based at the National institute of Agrobiological Resources (NIAR).Research on genetic diversity of rice using a range of techniques, for example esterase isozymes, has revealed clinal variation in rice radiating from the center of diversity of rice in and around southwest China. Newly found genes in traditional rice germplasm, such as genes for non-elongating mesocotyl, are now routinely identified on the rice genome. Pioneering studies on eco-genetic differentiation of species in the genus Oryza in Japan has revealed much about the complex genepool for which rice evolved.Pest and disease resistance sources, particularly to blast, bacterial blight and brown plant hopper, from many countries have been incorporated into Japanese varieties. Cold tolerance at the booting stage was found in the Indonesian variety Silewah. In the future in characterisation of rice germplasm and interaction between rice germplasm specialists and rice molecular scientists, both in Japan and internationally, will be corner stones to securing rice genetic diversity and rice improvement in the next century.