Yield potential and radiation use efficiency of “super” hybrid rice grown under subtropical conditions

China's “super” hybrid rice breeding project has developed many new varieties using a combination of the ideotype approach and intersubspecific heterosis. It is controversial whether these “super” hybrid varieties have increased the yield potential of irrigated rice. This study was conducted to compare grain yield and yield attributes among “super” hybrid, ordinary hybrid, and inbred varieties. Field experiments were done in Liuyang (moderate-yielding site) and Guidong (high-yielding site) counties, Hunan Province, China, in 2007 and 2008. Two varieties from each varietal group were grown in each field experiment under moderate and high N rates. Grain yield, yield components, aboveground total dry weight, harvest index, total N uptake, and crop radiation use efficiency (RUE) were measured for each variety. A significant difference in grain yield was observed among the varieties and varietal groups but not between the two N rates. “Super” hybrid varieties have increased rice yield potential by 12% compared with ordinary hybrid and inbred varieties. The higher grain yield of “super” hybrid varieties was attributed to improvement in both source and sink. “Super” hybrid varieties produced more biomass than ordinary hybrid and inbred varieties. Long growth duration and high accumulated incident radiation were partially responsible for high biomass production for the “super” hybrid varieties. “Super” hybrid varieties had significantly larger panicle size (spikelets per panicle) than ordinary hybrid and inbred varieties, which resulted in larger sink size (spikelets per m²). Crop RUE did not explain the yield superiority of “super” hybrid rice. Our study suggests that “super” hybrid rice varieties do not necessarily require more N fertilizer to produce high grain yield.     

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.     

超级稻高产栽培生理研究进展

 我国于1996年启动了理想株型与亚种间杂种优势相结合为技术路线的超级稻育种计划,目前已育成约80个超级稻品种。这些品种产量高,兼顾品质与抗性,在试验示范区或特定气候条件下产量可达到12～21 t/hm2,展示了超级稻的巨大增产潜力。对于超级稻品种高产的原因,可概括为以下几个方面：与常规高产品种相比,超级稻品种每穗颖花数多、库容量大(即单位面积颖花数多);叶面积指数大、绿叶面积持续期长、光合速率高、茎秆抗倒性强;  抽穗前干物质累积量高, 结实期茎叶中碳水化合物转运到籽粒中的量大;  根量大、根系活性强。但是,超级稻品种在生产上也存在一些问题,突出地表现在两个方面：一是强势粒(着生在穗子中上部、开花较早的籽粒)、弱势粒(着生在穗子基部、开花较迟的籽粒)充实整齐性差;二是结实率低且不稳定。综述了超级稻的生物特性、产量结构、群体质量特征以及相关生理机理方面的研究进展,提出深入开展超级稻栽培生理研究的建议。     

Hybrid rice heterosis and genetic diversity of IRRI and Lao rice

Glutinous and non-glutinous rice hybrids derived from IRRI and Lao PDR rice germplasm were evaluated for yield heterosis and genetic diversity based on SSR markers. Pollen and spikelet fertilities of the hybrids showed absence of effective restorer and maintainer genes in the Lao varieties for WA-CMS cytoplasm. Positive heterosis over better or male parent (Lao varieties) was observed. Hybrids derived from an IRRIs TGMS line with Lao varieties showed a great potential in hybrid rice application. Genetic diversity among the rice lines was assessed by COP and SSR markers. Cluster analysis based on the molecular markers generated three parental groups in agreement with parental pedigree information. Significant linear relation was detected between yield heterosis and marker-based genetic distance of parents.     

Pre-anthesis non-structural carbohydrate reserve in the stem enhances the sink strength of inferior spikelets during grain filling of rice

Sink strength plays an important role in grain filling of cereals but how it is related to the pre-anthesis non-structural carbohydrate (NSC) reserves is not clear. This study investigated if and how an increase in NSC reserves could enhance sink strength, and consequently improve grain filling of later-flowering inferior spikelets (in contrast to the earlier flowering superior spikelets) for rice varieties with large panicles. Two “super” rice varieties (the recently bred high-yielding rice) and two New Plant Type (NPT, named in IRRI for the extra-large panicle) rice lines were compared with two elite inbred varieties under field-grown conditions. Three nitrogen (N) treatments, applied at the stages of panicle initiation, spikelet differentiation or both, were adopted with no N application during the mid-season as control. Both super rice and NPT rice showed a greater yield capacity as a result of a larger panicle than the elite inbred rice. However, a lower percentage of filled grains limited the realization of higher yield potential in super rice and especially in NPT rice, due to their lower grain filling rate and the smaller grain weight of their inferior spikelets. The low grain filling rate and small grain weight of inferior spikelets are mainly attributed to a poor sink strength as a result of small sink size (small number of endosperm cells) and low sink activity, e.g. low activities of sucrose synthase (SuSase) and adenosine diphosphoglucose pyrophosphorylase (AGPase). The amounts of NSC in the stem and NSC per spikelet at the heading time are significantly and positively correlated with sink strength (number of endosperm cells and activities of SuSase and AGPase), grain filling rate, and grain weight of inferior spikelets. Nitrogen application at the spikelet differentiation stage significantly increased, whereas N application at the panicle initiation or at both panicle initiation and spikelet differentiation stages, significantly reduced, NSC per spikelet at the heading time, sink strength, grain filling rate, and grain weight of inferior spikelets in super rice. The results suggest that pre-anthesis NSC reserves in the stem are closely associated with the sink strength during grain filling of rice, and N application at the spikelet differentiation stage would be a good practice to increase pre-anthesis NSC reserves, and consequently to enhance sink strength for rice varieties with large panicles, such as super rice varieties.     

Practice and Thought on Developing Hybrid Rice for Super High Yield by Exploiting Inter-subspecific Heterosis

Since the breakthrough of grain yield owing to the development of dwarf rice and three-line system hybrid rice, rice breeding for high yield hardly had showed significant progress in the next successive two decades. It was considered that utilizing heterosis between subspecific varieties (Oryza sativa L.) would be an effective approach to increase yield further. During 1987-1993,an indica-japonica hybrid Yayou 2 yielded as high as 10.5 t/ha; however, it failed to be commercialized because of seed purity problem due to non-uniform emasculation by chemical agent in seed production, and sensitivity of seed setting in F1 plants to environmental conditions. In the past decade, two inter-subspeific hybrids, Liangyoupeijiu (Peiai 64S/9311, javanica/indica) and Liangyou E32 (Peiai 64S/E32, javanica/japonica); both of them exhibited grain yield higher than 10.5 t/ha, and were widely judged as the pioneers of super hybrid rice. Liangyoupeijiu has been successfully popularized over 4 million hectare in wide climatic areas, while Liangyou E32 made a yield record and offered a model of plant ideotype for super hybrid rice. It was considered that in combination with plant ideotype, active physiological functions, and wide-range adaptability to ecological conditions, exploitation of indica-japonica heterosis would be the key approach for super hybrid rice breeding.     

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”。     

水稻广亲和系的选育

水稻广亲和基因的发现及其遗传研究 ,揭开了籼粳稻亚种间杂种一代半不育现象的遗传本质 ,为利用水稻亚种间杂种优势指明了方向。但是 ,已知的广亲和材料 ,绝大多数为古老的农家品种 ,农艺性状不良 ,如植株太高 ,株叶形披散和生育期很长等 ;不能直接作为选配优良组合的亲本加以利用。因此 ,培育具有优良农艺性状和经济性状、可供实用的水稻广亲和系就显得非常重要 ,这是开展亚种间杂种优势育种的首要任务之一。普通栽培稻有籼稻、粳稻和爪哇稻三个亚种 ,所以亚种间的杂交可分为籼粳交、籼爪交和粳爪交三种形式。初步研究表明 ,水稻杂种优势强弱的程度 ,具有籼粳交 >籼爪交 >粳爪交 >籼籼交 >粳粳交的一般趋势。也就是说 ,亚种间的杂种优势一般要强于品种间的。为了能充分利用各种形式的亚种间杂种优势 ,提高育成强优组合的几率 ,就有必要建立籼、粳、爪三个亚种类型的优良广亲和系。我们在以前工作的基础上 ,近年来开展了水稻广亲和系选育的研究 ,已取得一些进展和结果 ,育成了粳型广亲和系培C3 11,爪哇型广亲和系轮回 4 2 2 ,籼型广亲和系培矮 64以及广亲和光敏核不育系培矮 64S。     

Morphological and physiological traits of roots and their relationships with shoot growth in “super” rice

Success in “super” rice breeding has been considered a great progress in rice production in China. This study aimed to test the hypothesis that an improved root system may contribute to better shoot growth and consequently to higher grain yield in “super” rice. Two “super” rice varieties Liangyoupeijiu (an indica hybrid) and Huaidao 9 (a japonica inbred) and two elite check varieties Yangdao 6 (an indica inbred) and Yangfujiang 8 (a japonica inbred) were field-grown at Yangzhou, China in 2006 and 2007. Root and shoot dry weight (DW) was significantly greater in “super” rice varieties than in check ones throughout the growth season in both years, so was the root length density. Root oxidation activity (ROA) and root zeatin (Z) zeatin riboside (ZR) content, in per plant basis, were significantly greater in “super” rice than check varieties before and at heading time. However, both ROA and root Z + ZR content, either in per plant basis or per unit root DW basis, were significantly lower in ‘super’ rice than in check varieties at the mid- and late grain filling stages. Grain yield of the two ‘super’ rice varieties, on average, was 10.2 t ha⁻¹ in 2006 and 11.4 t ha⁻¹ in 2007, and was 13% and 21% higher than that of check varieties, respectively. The high grain yield was mainly due to a larger sink size (total number of spikelets) as a result of a larger panicle. The percentage of filled grains of the two “super” rice varieties, on average, was 72.9% in 2006 and 79.0% in 2007, and was 19.4% and 12.9%, respectively, lower than that of the check varieties. The mean ROA and root Z + ZR content during the grain filling period significantly correlated with the percentage of filled grains. Collectively, the data suggest that an improved root and shoot growth, as showing a larger root and shoot biomass and greater root length density during the whole growing season and higher ROA and root Z + ZR content per plant at early and mid-growth stages, contributes to the large sink size and high grain yield in the “super” rice varieties. The data also suggest the yield of “super” rice varieties can be further increased by an increase in filled grains through enhancing root activity during grain filling.     

广亲和系配制的杂种产量潜力分析

通过对以国内新育成的优良广亲和系为母本，典型籼、粳品种为父本配制的8个杂种F1的产量潜力分析，结果表明杂种一代具有库容、物质生产和产量优势，特别是亚种间杂种优势突出。亚种间杂交组合抽穗后叶片衰老缓慢，功能期长，存在抽穗后干物质积累优势，但大多数亚种间杂交组合物质转运不良，限制了其产量潜力的发挥。     

亚种间重穗型杂交稻冈优881的选育与应用

首先用密阳４６作母本与明恢６３杂交选育出恢复系６３２３;然后从恢复系６３２３与粳稻天然杂交后代选育成籼粳亚种间重穗型恢复系蜀恢８８１,其穗平重可达４．３１ｇ,它与三系不育系冈４６配组,培育出了籼粳亚种间重穗型杂交稻强优势组合冈优８８１。该组合产量高,米质好,抗瘟性强,适应性广,１９９５年５月通过四川省品种审定。     

光身杂交稻选育研究进展

利用美国光身稻种质资源,培育出野败型三系光身杂交稻配套亲本光香A、B和光身R及光身光温敏核不育系光S,并用其配组率先育成一批三系光身杂交稻组合,如光香优德87、光香优602、光香优613等;还选配出一批非光身的优质高产三系杂交稻新组合如光香优7号、光香优13和光香优6号以及两系杂交稻组合光两优113和光两优193等.光身杂交稻及其配套亲本的选育成功,将进一步促进水稻亚种间杂种优势利用,可望实现我国杂交稻育种在米质、产量、抗性和适应性方面新的突破.     

我国杂交籼稻选育进展

自水稻杂种优势被利用以来,我国杂交籼稻育种取得显著进展,在保障我国粮食安全中发挥着重要作用。本文根据国家水稻数据中心水稻品种审定数据信息,对我国籼型水稻不育系研究进展、杂交籼稻品种审定情况、籼型超级稻品种发展现状和几个籼稻育种大省的杂交籼稻国审情况进行了对比和分析,并对杂交籼稻的发展进行了展望。     

三系法籼粳亚种杂交水稻研究的初步进展

笔者自１９８５年开始三系法籼粳亚种间杂交水稻研究工作,至１９８９年已初步育成了一 批籼粳亚种杂交水稻的早、中、晚稻组合,其穗型大小、结实率和千粒重等,比同熟期的当家常 规稻和品种间杂交稻都有大幅度超出。在轮回４２２／选１０－１９组合分离后代中,选育了多种熟期和生态类型的广亲和恢复系。     

安徽省三系杂交籼稻育种现状与展望

综述了安徽省２０ａ来三系杂交籼稻的育种成就和存在问题,指出今后的育种目标应主攻早熟、优质、超高产,并选育适于机械化制种和耐旱的组合;技术路线上早杂以选育早熟恢复系,中晚杂以选育优质不育系,亚种间组合以选育广亲和不育系为主。     

Research Advances in High-Yielding Cultivation and Physiology of Super Rice

In 1996,China launched a program to breed super rice or super hybrid rice by combining intersubspecific heterosis with ideal plant types.Today,approximately 80 super rice varieties have been released and some of them show high grain yields of 12-21 t/hm2 in field experiments.The main reasons for the high yields of super rice varieties,compared with those of conventional varieties,can be summarized as follows:more spikelets per panicle and larger sink size (number of spikelets per square meter);larger leaf area index,longer duration of green leaf,greater photosynthetic rate,higher lodging resistance,greater dry matter accumulation before the heading stage,greater remobilization of pre-stored carbohydrates from stems and leaves to grains during the grain-filling period;and larger root system and greater root activity.However,there are two main problems in super rice production:poor grain-filling of the later-flowering inferior spikelets (in contrast to earlier-flowering superior spikelets),and low and unstable seed-setting rate.Here,we review recent research advances in the crop physiology of super rice,focusing on biological features,formation of yield components,and population quality.Finally,we suggest further research on crop physiology of super rice.     

提高水稻杂种优势水平的可能途径

杂交水稻的单产处于徘徊状态。提高单产的可靠途径在于扩大双亲的遗传差异, 进一步提高杂种优势水平。培育“杂交水稻超高产群体理想型”, 应用分子标记辅助相互轮回选择法累加不同组群的优势基因和应用分子标记技术挖掘与利用野生稻中的远缘优势基因, 有可能大幅度地提高杂交水稻的单产潜力。     

辽宁杂交粳稻育种有关问题探讨

针对目前北方杂交粳稻发展中存在的问题，笔者结合自己多年的育种实践，提出了杂交粳稻育种的研究方向和技术路线。     

几个粳稻品种穗部性状杂种优势及遗传分析

以8个粳稻品种为试验材料,利用4×4不完全双列杂交方式,对16个粳稻杂交组合F1穗部性状的杂种优势及遗传参数进行了分析。结果表明,在杂种F1的穗部性状中,总粒数、一次枝梗数和一次枝梗粒数的增加是杂种优势的普遍表现,选择结实率高的组合是实现杂种优势的主要途径。在杂交育种后代选择的早期世代对总粒数、一次枝梗数和一次枝梗粒数进行选择会有较好的效果,把二次枝梗数、二次枝梗结实率和一次枝梗结实率放在高代进行选择会有较好的效果。同时,对后代亲本选择进行了探讨。     

两系杂交早稻杂种优势的初步研究

对安农Ｓ－１配制的１１７个杂交早稻组合的杂种优势分析，阐述了两系杂交稻在产量、生育期和经济性状上的优势表现；论述了杂种与父本、杂种产量与产量性状及各产量性状之间的相互关系，提出了在选育两系杂交早稻组合时应注意的一些问题。