Four Decades of Breeding for Varietal Improvement of Irrigated Lowland Rice in the International Rice Research Institute

Abstract

Since the establishment of the International Rice Research Institute (IRRI) in 1960, IRRI’s breeding effort in varietal improvement for irrigated lowland has passed four decades. Breeding of semi-dwarf rice varieties such as IR8 at IRRI during first decade from 1960 to 1969 resulted in quantum leaps in yield potential, which marked the green revolution in Asia. During the second decade from 1970 to 1979, the primary emphasis of rice improvement has been directed towards incorporation of multiple disease and insect resistance and shortening of growth duration. Grain quality was the main target of crop improvement at IRRI during the third decade from 1980 to 1989. The fourth decade from 1990 to 1999 and beyond was focused again on the improvement of yield potential by developing hybrid rice and new plant type. Up to 1999, 46 indica inbred varieties and 2 indica/indica hybrid rice varieties were developed by IRRI and released in the Philippines for the irrigated lowland rice systems. Large-scale adoption of these improved varieties under modern crop management practices has resulted in a dramatic increase in rice production in major rice-growing countries. The hybrid varieties between indicas increased yield potential by 9% under the tropical conditions. New plant type (NPT) breeding has not yet resulted in an increase in yield potential. The second generation NPT developed by crossing tropical japonica with indica has demonstrated some promising results in terms of improvements in yield potential, disease and insect resistance, and grain quality.     

Scientific Breakthroughs and Plant Breeding

SUMMARY

This article highlights the historical developments in genetics since the rediscovery of Mendelian laws of heredity, decade-by-decade, that have contributed to increases in food production. Two phases of plant breeding-evolutionary and evaluation-are briefly discussed. Scientific breakthroughs will continue to advance plant breeding in the coming decades. Genes identified through functional genomics should be useful in crop improvement. Plant breeding has a bright future. More plant breeders need to be equipped with the knowledge and training to utilize new advances in molecular biology.     

Improving Rice to Meet Food and Nutritional Needs: Biotechnological Approaches

SUMMARY

The livelihood and calorie needs of large populations based in developing countries is dependent on rice cultivation. More than three billion people consume rice as a staple food. To meet the future demands of the human population, innovative tools such as genomics are being used to improve rice yield increase, for the incorporation of stress resistance/tolerance in rice varieties, and for the improvement of the nutritional quality of rice. These new tools include: sequencing, large-scale analysis of expressed sequence tags, high throughout microarray analysis and genetic transformation. Rice now serves as a model for a science based crop design for the agronomic, nutritional, and economic benefit of farmers. This article discusses the use of biotechnology as a tool to improve the rice plant for the benefit of mankind.     

Effects of High Water Table and Short-Term Flooding on Growth,Yield, and Seed Quality of Sunflower

Abstract

Sunflower, a major edible oil crop producing a high-quality and healthful oil for human consumption and also recycled for use as feedstock to produce biodiesel fuel, is recently being cultivated in rotation with rice in the paddy field. The oil of cultivars with a high oleic acid content has higher oxidation stability and better nutritional properties than the standard cultivars, which have a high linoleic acid content. In this study, we evaluated the effects of excess water on plant growth, seed yield, and oil quality. Seed yield, the major yield components, the oleic acid content and the total oil content were negatively affected by a shallow water table. In particular, waterlogging at the establishment stage decreased the growth and seed yield severely. In addition, waterlogging during the flowering and maturation stages tended to decrease the oleic acid content and to increase the linoleic acid content. These results will be useful for improving management practices to increase the seed yield and improve the oil quality of sunflower in rotation with upland paddy rice.     

Drought Resistance Improvement in Rice: An Integrated Genetic and Resource Management Strategy

Abstract

Drought is the major constraint to rice production in rainfed areas across Asia and sub-Saharan Africa. In the context of current and predicted water scarcity, increasing irrigation is generally not a viable option for alleviating drought problems in rainfed rice-growing systems. It is therefore critical that genetic management strategies for drought focus on maximum extraction of available soil moisture and its efficient use in crop establishment and growth to maximize biomass and yield. Extensive genetic variation for drought resistance exists in rice germplasm. However, the current challenge is to decipher the complexities of drought resistance in rice and exploit all available genetic resources to produce rice varieties combining drought adaptation with high yield potential, quality, and resistance to biotic stresses. The strategy described here aims at developing a pipeline for elite breeding lines and hybrids that can be integrated with efficient management practices and delivered to rice farmers. This involves the development of high-throughput, high-precision phenotyping systems to allow genes for yield components under stress to be efficiently mapped and their effects assessed on a range of drought-related traits, and then moving the most promising genes into widely grown rice mega-varieties, while scaling up gene detection and delivery for use in marker-aided breeding.     

我国水稻重要农艺性状分子遗传研究进展及在育种上的应用

水稻是我国的主要粮食作物,在人口快速增长和自然环境不断恶化的今天,传统的育种技术已经很难满足当前水稻育种的需求,分子育种技术逐渐成为育种工作者解决当前困境的主要方法。经过几十年的努力,中国科学家不仅在水稻遗传学和功能基因组学领域取得了令世界瞩目的成就,还在水稻分子育种方面为提高粮食产量、营养质量和环境效益方面做出了巨大努力。本文主要综述了我国科学家在水稻分子遗传和分子育种方面取得的成就并进行讨论。     

西南稻区重穗型杂交稻发展现状及分子设计育种策略

水稻是我国重要的粮食作物,全国有60%以上人口以大米为主食。西南稻区是我国六大稻区之一,对保障我国粮食安全具有重要的战略意义。针对西南稻区“寡日照、高湿度、小温差”的生态条件,周开达院士等经历了艰苦的探索和反复实践,提出发展“重穗型”杂交稻是西南稻区实现水稻超高产的重要途径。本文总结了西南稻区重穗型杂交稻发展现状,列举了可用于重穗型杂交稻分子设计育种的基因资源,提出了重穗型杂交稻的分子设计育种策略,以期为培育新的高产优质“重穗协调型”品种提供参考,致力于打造更高水平的“天府粮仓”。     

中国水稻育种百年发展与展望

水稻是中国最重要的口粮作物,新品种的培育与推广对水稻生产作出了重大贡献。中国现代水稻育种起步于20世纪20年代,已有百年历程,期间纯系育种、杂交育种、诱变育种和分子育种等技术成为技术主体,成就了矮化育种、杂交稻育种和超级稻育种三次突破,推进了全国水稻平均单产从20世纪50年代的200 kg/667 m²平台跃上了当前的470 kg/667 m²平台。展望未来百年的水稻产业需求,培育C4水稻、固氮水稻、耐盐碱水稻、耐旱水稻和一系杂交稻是水稻育种面临的重大任务。     

稻米品质调控的分子基础及非生物胁迫对稻米品质的影响

水稻是世界上最重要的粮食作物之一，为全球超过半数人口提供食物来源。近些年来，随着温饱问题的解决，稻米品质日益受到关注。随着现代生物技术和生物信息技术的发展，控制稻米品质的基因相继被克隆并应用于水稻育种。本文综述了稻米品质调控分子机制，并对干旱、低温、高温、盐胁迫对稻米品质的影响进行了概述，以期为改善非生物胁迫下的稻米品质提供参考。     

Making a Greener Revolution: A Nutrient Delivery System for Food Production to Address Malnutrition through Crop Science

Abstract

During the 1970s, the Green Revolution basically used dwarfing genes in wheat and rice that allowed greater water and fertilizer efficiency which dramatically increased the cereal productivity and thus, increased human caloric intake of the developing world. However, having met caloric intake, there is a need to address the issues of malnutrition through a holistic food production system. For example Ca-deficient induced rickets was found in 9% of children in SE Bangladesh, illustrating the failure of that food production system to address this vital nutrient, calcium. A clinical trial has shown a minimum of increase in calcium intake of 250 mg Ca per child per day was enough to prevent rickets. In Bangladesh, a consortium of universities and other medical institutions and the International Center for Wheat and Maize Improvement (CIMMYT) has developed strategies to infuse calcium within the food delivery system. For treatment of ricketic children, a strategy was developed to use live and video drama to create community awareness of the production and/or consumption of highcalicum crops/food and calcium supplement added to the cooking rice (in this case, highly edible CaCO3 readily available throughout the country). Though this represents a very specific case study, this is a useful example of how collaboration based around crop science can address the ‘hidden’ hunger of malnutrition throughout the world.     

Characterization of Aroma and Agronomic Traits in Afghan Native Rice Cultivars

Abstract

In this study, we collected native aromatic rice cultivars from north, east and northeast of Afghanistan, and check cultivars from Japan, Thailand and India. We characterized some important agronomic characters such as plant height, panicle number per plant, grain number per panicle, 1,000-grain weight, grain length and grain width to find the desirable characters for breeding programs. Many of them were classified into tall culm rice according to IRRI index, but had thin and slender grain, and strong aroma which are favorable characteristics in Afghanistan and surrounding regions. The aromatic character was characterized by three methods, 1.7% KOH sensory test, gas chromatography-mass spectrometry-selected ion monitoring (GC-MS-SIM), and polymerase chain reaction (PCR) analysis. These three methods gave similar results. Six out of 10 Afghan native rice cultivars were aromatic and four non-aromatic. Among the check cultivars, Basmati 370, Jasmine 85, Izayoi, Oitakoutou and Jakouine were aromatic and Nipponbare non-aromatic. Improvement of aromatic and high yielding rice and reduction of plant height are the important objectives for rice breeding in Afghanistan. The results showed that Pashadi Konar from Afghanistan has the intermediate plant height, heavier 1,000-grain weight (32 g), longer grain (11 mm) and favorable aroma. Therefore, this cultivar may be a good source of aromatic rice germplasm in Afghanistan. To clarify the genetic nature of aroma in rice, we crossed non-aromatic cultivar Nipponbare with aromatic cultivar Jasmine 85, and examined the aromatic character in the F₂ generation by 1.7% KOH sensory test and PCR analysis. Non-aromatic and aromatic characters were segregated at a ratio of 3:1, showing that aroma is controlled by a single recessive gene.     

Breeding efforts to mitigate damage by heat stress to spikelet sterility and grain quality

Global warming is predicted to aggravate the risk of unstable crop production. It is of great concern that damage to rice spikelet sterility and grain quality will increase, resulting in yield and economic losses. To secure the global food supply and farmers’ income, the development of rice cultivars with heat resilience is a pressing concern. Regarding spikelet sterility, rice cultivars with heat tolerance at different growth stages have been identified in recent years. The early-morning flowering (EMF) trait is effective in heat escape because it shifts the time of day of flowering to earlier in the morning when it is cooler. Although varietal differences are very small, there are some genetic resources for EMF in wild rice accessions. Regarding heat-induced grain chalkiness, heat-tolerant japonica cultivars for mitigating white-back type of chalky grains (WBCG) were found. Quantitative trait loci for heat tolerance at flowering, EMF, and for WBCG in grain quality have been mapped on the rice chromosomes. Further genetic efforts have been successfully connected to the development of near-isogenic lines for each trait with tagged molecular markers. These breeding materials are quite unique and useful in facilitating marker-assisted breeding toward the development of heat-resilient rice in terms of spikelet sterility and grain quality.     

In-vitro Androgenesis in Rice: Advantages,Constraints and Future Prospects

In vitro androgenesis is an important component of plant biotechnology when the pollen grains are forced to switch from their normal pollen developmental pathway towards an embryogenic route. Haploid and doubled haploid produced through androgenesis have long been recognized as a valuable tool in plant breeding as it can shorten the breeding cycle, fix agronomic characters in homozygous state and enhance the selection efficiency of useful recessive agronomic traits. Recently, doubled haploids have been largely recognized as an important component of crop improvement through genome mapping, quantitative trait locus analysis, and genetic mutation, and as targets for genetic transformation programs. Thus, this review is focused mainly on various facets of doubled haploid in the chief staple food crop rice and sights its recent applications in plant breeding, genetics and genomics.     

Saline-Alkali Tolerance in Rice: Physiological Response,Molecular Mechanism,and QTL Identification and Application to Breeding

Salinity-alkalinity is incipient abiotic stress that impairs plant growth and development. Rice (Oryza sativa) is a major food crop greatly affected by soil salinity and alkalinity, requiring tolerant varieties in the saline-alkali prone areas. Understanding the molecular and physiological mechanisms of saline-alkali tolerance paves the base for improving saline-alkali tolerance in rice and leads to progress in breeding. This review illustrated the physiological consequences, and molecular mechanisms especially signaling and function of regulating genes for saline-alkali tolerance in rice plants. We also discussed QTLs regarding saline-alkali tolerance accordingly and ways of deployment for improvement. More efforts are needed to identify and utilize the identified QTLs for saline-alkali tolerance in rice.     

水稻镉积累影响因素与低镉稻米生产策略

镉是一种生物毒性极强且分布广泛的重金属元素。农田中的镉不仅影响作物的生长发育,而且可通过食物链进入人体内,当富集到一定程度会危害人体健康。水稻是我国重要的粮食作物之一,在保障我国粮食安全中的地位举足轻重,但水稻同时也是对镉吸收和积累最强的大宗谷类作物之一。近些年“镉大米”事件在我国频繁发生,稻米镉污染已成为一个备受社会关注的严峻问题,治理稻米镉污染迫在眉睫。本文从低镉水稻品种筛选与培育、优化水分管理、调节土壤pH值、施用叶面阻隔剂等方面对稻米镉污染治理技术的研究进展进行了综述,旨在为技术的集成、推广和应用提供理论依据,同时为新技术的研发提供新的思路。     

Increasing Crop Competitiveness to Weeds Through Crop Breeding

Abstract

Increasing the ability of crops to compete against weeds, through either enhancing crop tolerance or crop interference to weeds, provides an attractive addition to current weed control practices and could be an integral component of weed management systems. Research has shown that considerable variability exists among crop culti-vars with respect to their ability to compete with weeds. Despite this evidence, directed research on competitive crops has been minimal. Reasons for this lack of emphasis in plant breeding programs include the effectiveness of current weed management with tillage and herbicides, and the lack of easily identifiable crop characteristics that are indicative of weed competitiveness. Expanded knowledge of specific crop-weed interactions would facilitate crop competitiveness to weeds through either crop management practices or plant breeding. Plant breeders need basic and applied information to identify favorable crop-weed competitive traits in order to enhance or incorporate those traits into crop cultivars. Accelerated research on weed competitive crops should lead to more economical, effective, and feasible integrated weed management programs for all crops.     

Nitrogen Dynamics in Lowland Rice as Affected by Crop Establishment and Nitrogen Management

Abstract

Information on the dynamics of nitrogen as influenced by crop establishment method and N management strategy is meager, but such information is necessary in optimizing nitrogen input for lowland rice (Oryza sativa L.). A field experiment was conducted at the experimental farm of the International Rice Research Institute (IRRI), Philippines, during the wet and dry seasons of 2003 and 2004 to evaluate the effects of crop establishment and nitrogen management strategies for lowland rice on the dynamics of mineral N. The experiment was laid out in a split-plot design with four crop establishment methods as main plots and two N management techniques as subplots with three replications. Zero-N fertilizer (N-omission) micro-plots were embedded in each plot. Crop establishment method did not significantly influence uptake of indigenous mineral N during the wet (44-55 kg ha-1) and dry (43-50 kg ha-1) seasons. Apparently, NH4+-N and NO3～-N accumulated in the top 20-cm layer of the soil during the wet season, resulting in relatively high initial N during the dry season. Crop establishment and N management strategies did not influence crop removal of N during a one-year period. Actual N balance across crop establishment methods during the one-year period ranged from 10 to 16 kg ha-1, whereas the apparent N balance ranged from 45 to 99 kg ha-1. A fertilizer recommendation should be developed based on the actual N balance along with the assessment of crop N requirement for a given yield potential.     

Agronomic performance of rice breeding lines selected based on plant traits or grain yield

Selection for yield per se has greatly contributed to yield improvement in many crops. It is expected that selection based on plant traits is more effective in increasing crop yield potential. This study was conducted to compare the effectiveness of trait-based and yield-based selection in increasing rice yield and to determine whether lines with ideotype traits have the potential to express higher yield under optimal crop management conditions. Lines were selected based on plant traits or on grain yield measured in a breeder's replicated yield trial. The main target traits for selection were plant height, leaf and panicle morphology, grain size, total dry weight, and grain-filling percentage. Yield performance of trait-based selection was compared with that of yield-based selection in an agronomic trial with optimum crop management for three seasons. Trait-based selection increased leaf area index and total dry weight but reduced spikelet number per m² and harvest index compared with yield-based selection. Consequently, selection based on plant traits did not increase grain yield compared with selection based on yield per se. In one of the three seasons, yield of trait-based selection was significantly lower than that of yield-based selection. Among all tested breeding lines, maximum yield was produced by yield-based selection and minimum yield came from trait-based selection. These results suggest that lines with ideotype traits did not express higher grain yield than lines selected based on yield per se under optimal crop management conditions, and yield-based selection was as effective in increasing rice grain yield as trait-based selection in the late generations of the breeding cycle.     

Making Rice a Perfect Food

Abstract

Despite a significant increase in food production during the last century, world production will need to be doubled or tripled by the year 2050 to meet the needs of an expected 10 billion global population. Fortunately, a second revolution in agriculture appears to be taking place from advances in biotechnology. Worldwide in 1999, about 40 million hectares of transgenic plants were grown, and this area is expected to increase significantly for years to come. Rice (Oryza sauva L.) is the staple food of the majority of 3.5 billion people in Asia. Increases in population in the rice growing regions of Asia will require 70% more rice in 2025 than is consumed today. In addition, rice, in its milled form, is poor in essential amino acids and a range of vitamins and micronutri-ents, which creates malnutrition. With the increasing number of genes discovered in plants and other organisms, transgenic research is being utilized to improve agronomic traits of rice, such as resistance to biotic and abiotic stress, and to increase photosynthetic efficiency which collectively increase yield. Research is also moving toward improvement of grain quality traits, including amino acids, micronutrients, and vitamins. Genome sequencing and the techniques for rice transformation have been developed. Thus, collaborative efforts in genomics, transformation, and molecular breeding of rice are expected to lead to a significant contribution to global food security. In this article, we review the current status of genetic improvement of rice. Improved methods for transgene expression in rice and potential modifications that will significantly improve yield and grain quality of rice are also discussed.