Heterosis in inter and intrasubspecific crosses over three-environments in rice

Moderate to high heterosis for yield and ten related characters was studied in 45 crosses involving six indica (I) and four tropical japonica (J) varieties of rice under three (E₁-optimum sowing and high fertility, E₂-both optimum sowing and fertility and E₃- late sowing and high fertility) environments. Trends of magnitude of heterosis for grain yield and plant height were I/J > I/I > J/J and for days to 50% flowering I/J > J/J > I/I hybrids. Estimates of standard heterosis (%) for grain yield were –64.5 to 146.1 in E₁, –70.4 to 82.2 in E₂ and –67.2 to 63.8 in E₃. Environment E₁ seemed to be more favorable for higher heterosis expression than others. Higher heterosis in yield also accompanied heterosis in panicle number, dry matter and spikelet and grain number per panicle. Most estimates for days to flower were negative. Heterotic I/J hybrids also recorded maximum heterosis for earliness. Moderate to low standard heterosis for plant height across environments (2.0 to 13.7%) was recorded. Hybrids were identified in specific environments for direct exploitation in hybrid breeding. Hybrids B4116 / Sarjoo 52, B4122 / Pant Dhan 4 and B4122 / Narendera 359 were more stable than others over three environments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Indica-Japonica differentiation of paddy rice and its relationship with heterosis

The Indica‐Japonica differentiation of three photoperiod‐sensitive and/or thermosensitive genetic male‐sterile rice (PGMS or TGMS, respectively) lines and 47 male parental lines from seven ecotypes were studied for their restriction fragment length polymorphism marker data to determine which ecotype crosses with the three PGMS and/or TGMS lines could lead to higher yield potential, and to estimate the relationship between the Indica‐Japonica differentiation of parents and heterosis in grain yield and its components. The results indicated that hybrids derived from ‘N422s’ and the early‐middle ripening Indica varieties from southern China, and hybrids between ‘Pei'ai64s’ and three Japonica ecotypes, including North‐eastern Japonica varieties, restoring lines of Japonica hybrid rice and north China Japonica varieties, showed the highest grain yields. There was less variation of yield among the F1s between ‘108s’ and the seven ecotypes than among the other F₁s. Highly significant positive correlations between heterosis of the F₁ yield and genetic distance of the parents were detected, although the correlation between F₁ yield performance and genetic distance did not reach a significant level. Considerable variation of correlation between heterosis and genetic distance was also detected in the Indica × Indica crosses and Indica × Japonica crosses. There was much higher correlation (r = 0.63) between the F₁ yield performance and the genetic distance of parents in the Indica × Indica crosses than in the others. It is proposed that a genetic distance of 0.4‐0.8 between the two parents of hybrid rice might be appropriate not only for F₁ performance, but also for heterosis.     

水稻籼爪交和粳爪交杂种优势的研究Ⅱ.农艺性状的杂种优势分析

研究了籼爪交和粳爪交杂种在长沙、三亚的农艺性状和干物质产量的杂种优势.在长沙的籼爪交杂种在结实率和每穗实粒数方面具有负向超亲优势,在每穗实粒数、结实率、单株粒重和理论产量方面存在负向对照优势,其余性状均为正向优势;粳爪交杂种在千粒重和结实率方面存在负向超亲优势,其余性状为正向超亲优势, 在始穗期、秆高和单     

Relationship between heterosis and genetic divergence in 'Tongil'-type rice

Improving grain yield and quality of ‘Tongil’‐type rice (indica/japonica) continues to be a major breeding objective in Korea. In this study, genetic divergence among 13‘Tongil’‐type rice cultivars was evaluated and the relationship between genetic distance and hybrid performance in all possible nonreciprocal crosses between them assessed. The 78 F₁ hybrids together with the 13 parents were evaluated for eight traits of agronomic importance, including yield, in a replicated field trial. The 13 parents were examined for DNA polymorphism using 71 micro‐satellite or simple sequence repeats and 46 random decamer oligonucleotide primers. A total of 319 polymorphic variants were generated and, based on the polymorphism data, genetic distances (GDs) ranged from 0.021 to 0.437. Cluster analysis based on GDs revealed associations among cultivars which was in agreement with the pedigree data. Heterosis was observed in hybrids for most of the traits, and yield exhibited the highest heterosis among the eight traits examined. The correlation values of GDs with F₁ performance were mostly nonsignificant, except for yield, culm length and spikelets per panicle. The correlations of GDs with midparent and better‐parent heterosis were not significant enough to be of predictive value. These results indicate that GDs based on the microsatellite and random amplified polymorphic DNA (RAPD) markers may not be useful for predicting heterotic combinations in ‘Tongil’‐type rice and support the idea that the level of correlation between hybrid performance and genetic divergence is dependent on the germplasm used.     

杂交粳稻亲本产量性状优异配合力的标记基因型筛选

提高杂交粳稻竞争优势的关键是改良其恢复系产量性状的配合力。为使之更富成效,选用115个SSR引物扩增6个粳稻BT型不育系和12个恢复系的标记基因型,并按NCII遗传设计配制72个F1组合,分析18个亲本的单株日产量、单株有效穗数、每穗总粒数、每穗实粒数、千粒重5个性状的配合力,结合亲本SSR分子标记数据和性状配合力数据筛选了5个性状优异配合力的标记基因型。结果发现20个SSR标记基因型与亲本产量及其构成性状配合力显著相关。其中8个与亲本单个性状配合力相关;6个同时与亲本2个性状配合力相关;4个同时与亲本3个性状配合力相关;2个同时与亲本4个性状配合力相关。同时与多个性状配合力相关的标记基因型,对各性状的作用方向有正有负。RM152-165/170是单株日产量和单株有效穗数优异配合力效应最大的标记基因型,可使F1的相应性状值增加20.6%和12.7%。优异配合力的标记基因型可直接用于粳稻恢复系配合力的分子标记辅助改良。     

Development of TGMS lines for developing two-line rice hybrids for the tropics

A breeding program was initiated at the International Rice Research Institute (IRRI) in 1990 to develop thermosensitive genic male sterile (TGMS) rice lines for developing two-line rice hybrids for the tropics. The TGMS trait was transferred from a temperate japonica TGMS mutant, Norin PL 12, to indica and tropical japonica rice varieties using the pedigree selection procedure. Six new TGMS rice lines adapted to tropical conditions were developed which showed complete pollen and spikelet sterility when maximum temperature was higher than 30 ^°C 1–2 week after panicle initiation. However, up to 85.5% spikelet fertility was observed when these lines were exposed to 26–29 ^°C during the critical stage. Using two of these TGMS lines, some heterotic rice hybrids showing 1–1.6 t/ha higher grain yield than the inbred check varieties were identified in unreplicated observational yield trial conducted at IRRI. Two of the six two-line hybrids yielded significantly higher than the check variety in a replicated preliminary yield trial. This revised version was published online in July 2006 with corrections to the Cover Date.     

甬优系列籼粳杂交稻氮肥群体最高生产力的优势及形成特征

以长江下游地区大面积种植的4种类型(籼粳杂交稻、常规粳稻、杂交粳稻和杂交籼稻)水稻品种中有代表性的品种为材料,设置6个氮肥水平(0、187.5、225.0、262.5、300.0、337.5 kg hm–2),比较研究其氮肥群体最高生产力及其产量构成、关键生育阶段天数、主要生育时期的叶面积指数和干物重。结果表明:(1)杂交籼稻获得最高生产力对应的施氮量为225.0~262.5 kg hm–2,常规粳稻为300.0 kg hm–2,杂交粳稻和籼粳杂交稻为262.5~300.0 kg hm–2。(2)氮肥群体最高生产力以籼粳杂交稻最高,达12.2(12.0~12.3)t hm–2,较杂交粳稻、常规粳稻和杂交籼稻分别高出6.6%、9.8%和19.6%(两年平均值)。群体颖花量和每穗粒数均以籼粳杂交稻最高,但其每穗粒数年度间波动较大。穗数和结实率以常规粳稻最高。(3)播种至抽穗期天数以杂交粳稻最长,抽穗至成熟期天数则以籼粳杂交稻最长,达60 d左右。全生育期天数呈杂交粳稻常规粳稻籼粳杂交稻杂交籼稻。两年中日产量以籼粳杂交稻最高。(4)籼粳杂交稻在抽穗、抽穗后20 d和成熟期的叶面积指数和干物重均显著高于另外3种类型品种,且抽穗至成熟期的干物质积累量也最高。此外,籼粳杂交稻在拔节至抽穗期以及抽穗至成熟期的光合势显著高于另外3种类型品种。较多的每穗粒数、较长的灌浆期天数以及较高的日产量、生育后期(抽穗至成熟期)较强的光合物质生产能力是籼粳杂交稻氮肥群体最高生产力形成的重要原因和基础。     

A Novel Breeding Approach in Quest of Temperature Sensitive Genic Male Sterile Lines Among Rice Intersubspecies Derivatives

Summary An investigation was made to exploit an innovative tool viz., thermosensitive genic male sterile (TGMS) system in twoline inter-subspecies rice hybrids using 132 hybrids involving four TGMS lines viz., TS15, TS16, TS18 and TS29 and thirty three testers viz., 17 indicas, 7 japonicas and 9 javanicas by line × tester method at Paddy Breeding Station, Tamil Nadu Agricultural University, India. Pre-ponderence of non-additive gene action for yield and yield attributing traits was observed by analysing combining ability. TGMS lines TS18, TS29 and the testers CB96073, CB96026, CB94247, TNAU 94241 (indicas), Gohykumangoku (japonica), Dular, PRR16 (javanicas) were good general combiners. The hybrids TS29 × TNAU 94241 (indica/indica), TS 18 × Yamadanishiki (indica/japonica) and TS29 × Dular, TS29 × PRR16 (indica/javanica) were promising for heterosis breeding programme. The japonica tester Gohykumangoku and javanica testers Dular and CPSL0-17 exhibited strong heterosis for spikelet fertility when crossed with TGMS lines TS 16, TS 18, TS 29 indicated that these lines may possess wide compatible gene (WCG) for spikelet fertility. Based on mean performance, standard heterosis and sca for yield and yield traits, the inter – subspecies hybrids viz., TS29 × TNAU 94241, TS18 × TNAU 94241, TS29 × CB96073, TS29 × CB94247, TS29 × CB96026 (indica/indica) TS18 × Yamadanishiki, TS29 × Gohykumangoku (indica/japonica), TS29 × Dular, TS29 × PRR16 (indica/javanica) exhibited high heterosis over check hybrid CORH2 and the above hybrids can be exploited commercially. The present investigation revealed that the TGMS system may utilized as an innovative tool for developing inter subspecies two line hybrids with strong heterosis in rice.     

Heterosis and combining ability for grain yield and other agronomic traits in winter triticale

Hybrid breeding is a widely discussed alternative for triticale. Heterosis as well as general (GCA) and specific combining ability (SCA) effects were estimated for eight agronomic traits. The experiment comprised 24 F₁ hybrids, produced by a chemical hybridizing agent, together with their six female and four male parents, grown in drilled plots in two locations. In comparison with the mid‐parent values, hybrids averaged a 6.4 dt/ha (10.1%) higher grain yield, 8.4% more kernels per spike, a 6.8% higher 1000‐kernel weight, 9.7% lower falling number (FN) and 4.4% greater plant height. SCA effects for grain yield were significant and ranged from 4.5 to 6.9 dt/ha for grain yield. Together with GCA x location interactions, they explained most of the variation. For 1000‐kernel weight, GCA effects were predominant. SCA and interactions with location accounted for most of the variation in FN, whereas interactions were negligible for plant height. Correlations between mid‐parent and hybrid performance and between GCA and per se performance of parents were tight for all traits except grain yield, which allows for pre‐selection of parental lines. Although the amount of heterosis in triticale at present is closer to wheat than to rye, by selecting parents for combining ability and identifying heterotic patterns, grain yield heterosis of up to 20% appears sufficiently encouraging to embark on hybrid breeding.     

Construction of chromosomal segment substitution lines and genetic dissection of introgressed segments associated with yield determination in the parents of a super‐hybrid rice

Heterosis is a phenomenon whereby hybrids of inbred lines produce favourable phenotypes that exceed those of their parents. Traits of interest are higher yield and stronger stress tolerance. The two‐line super‐hybrid rice ‘Liangyoupei9’ (LYP9) shows superiority to both its elite inbred line ‘93‐11’ and ‘Pei'ai64s’ (‘PA64s’) parents and conventional hybrids. However, the genetic basis of its hybrid vigour, especially yield determination, remains elusive. In the present study, a set of 156 chromosome segment substitution lines (CSSLs) carrying overlapping segments from ‘PA64s’ in a genetic background of ‘93‐11’ were constructed and planted in six environments. Three major agronomic traits, viz. panicle length (PL), heading date (HD) and plant height (PH), and five yield‐related traits, viz. grain weight per panicle (GWP), number of grains per panicle (GPP), 1000‐grain weight (TGW), seed set (SS) and number of panicles of per plant (PPP), were evaluated over 3 years. Quantitative trait loci (QTL) analysis was conducted using a likelihood ratio test based on stepwise regression. Forty‐six putative QTL distributed on 11 chromosomes were detected in more than one year. Remarkably, GWP of four CSSLs carrying positive yield QTL outperformed the recurrent parent ‘93‐11’ by more than 15%, in at least two environments. These results indicate that CSSLs are effective in identifying yield‐associated traits, and lines harbouring such QTL will be rich in resources for future molecular breeding programmes.     

Use of androgenesis in intersubspecific hybrid rice breeding

Significant differences of callus induction, green plant regeneration and culture efficiency were observed among restorer lines and their hybrids in rice. Average callus induction percentage of F₁, hybrids was about twice that of their parents. Twenty doubled haploid (DH) lines that showed normal fertility with both indica and japonica CMS lines, were selected as widely compatible restorers (WCRs). TG8 derived from CPSLO17/Minghui 63 not only showed normal fertility to both indica and japonica test varieties and CMS lines, but also exhibited superior agronomic traits, in particular short plant, desired plant type, high tillerability, large panicles, good grain quality and resistance to rice blast disease. Strong heterosis for yield was observed in crosses between indica or japonica CMS lines and TG8. TG8 possessed a dominant, widely compatible gene (WCG) that was inherited from the variety CPSLO17. Results confirmed that the anther culture technique is a quick and effective way of developing widely compatible restorers in rice and that it is applicable to the direct use of intersubspecific heterosis with the three-line method.     

江淮稻区杂交粳稻骨干亲本产量性状配合力的SSR标记位点鉴定

鉴定杂交粳稻亲本产量性状配合力的标记位点有助于利用分子标记辅助选择技术改良亲本配合力、提高杂交粳稻竞争优势水平。利用9个粳稻BT型不育系和10个恢复系, 按照北卡罗林那设计II (North Carolina Design II)配制90个F₁组合,在南京和盱眙两个环境下种植,测定了各亲本产量性状的配合力和SSR分子标记基因型;结合二者数据鉴定了6个产量性状配合力的标记位点。结果表明,在两个环境下综合评价配合力较优的不育系是BT-18A和武羌A,恢复系是C418。与亲本单株有效穗数、每穗总粒数、每穗实粒数、结实率、千粒重和单株日产量性状配合力显著相关的SSR标记位点,南京环境下分别检测到8、13、11、6、6和2个;盱眙环境下分别检测到12、21、8、15、10和7个;2个环境下都检测到的分别有4、11、5、3、5和1个。标记位点杂合基因型显示正向优势的,南京环境下占74% (34/46);盱眙环境下占53% (39/73)。2个环境下都检测到的标记位点中,有3个各自与3个产量性状配合力共相关;另有3个各自与2个产量性状配合力共相关;其余的只与单个产量性状配合力显著相关。数据库检索发现两环境下都检测到的标记位点中,有10个其附近存在控制相应性状的基因/QTL。讨论了利用鉴定出的标记位点改良粳稻恢复系产量性状配合力的策略。     

水稻超高产育种的实践与思考

20世纪50年代末广东的籼稻矮化育种，60年代IRRI的“绿色革命”和70年代我国三系杂交籼稻的培育成功，都使水稻每公顷产量成吨增加。前两者高产育种的成功主要是利用了矮秆基因，后者则是利用了杂种优势。在尔后的10～20年里，有利基因的发掘利用和育种途径没有很大的突破，单产徘徊不前。笔者认为，利用籼粳亚种间有利性状的     

苏南地区晚熟粳稻杂种优势及其亲本配合力分析

用7个BT型晚粳不育系和7个粳稻恢复系按NCⅡ交配设计配成49个杂交组合，研究10个重要农艺性状的杂种优势及亲本的配合力。结果表明,各性状的优势有正有负，其中每穗总粒数的优势最为明显，竞争优势和超高亲优势平均值分别为22.6%和8.6%；产量性状的超高亲优势最大，平均值为9.5%，变幅为－38.0%～43.9%，竞争优势平均值变幅为－54.8%～10.3%。在产量性状上配合力较优的不育系有852-77A、后36A和9522A，恢复系有161-10、3402、HP121，优良组合有9522A/161-10、9522A/C166、852-77A/3402。     

Hybrid performance and heterosis in strawberry (Fragaria × ananassa Duchesne), regarding acidity,soluble solids and dry matter content in fruits

A top‐cross‐mating design among 29 S₄ inbred lines and tester (cultivar ‘Dukat’) was carried out to study their breeding value in terms of general combining ability (GCA). The objectives of this study were to evaluate the acidity, soluble solids and dry matter contents in fruits of progeny F₁ in comparison with S₄ inbred lines as well as the cultivars (S₀); identify strawberry genotypes with high value of GCA for use in cultivar development; and determine mid‐parent heterosis regarding S₄ inbred lines and cultivated strawberry. The 2‐year observations showed statistically significant differences between tested genotypes in terms of the studied traits. The highest breeding value based on GCA was estimated for Chandler 123‐5 for soluble solids and dry matter content, and Kent 7‐6 for acidity. Estimated mid‐parent heterosis had positive and negative values. The highest heterosis in terms of extract and dry matter content (26.71% and 17.50%, respectively) occurred in the offspring Chandler 123‐5 × ‘Dukat’, but as regards acidity in hybrid Chandler 123‐22 with cv. ‘Dukat’. The study of genetic divergence by dendrograms may help to identify parents suitable for obtaining hybrids with higher heterosis effects.     

Prediction of hybrid performance based on the genetic distance of parental lines in two-line rice (Oryza sativa L.) hybrids

A total of six TGMS (thermosensitive genic male sterile lines) and nine pollinator lines were subjected to molecular characterization using 48 genome-wide SSR (simple sequence repeat) markers. Cluster analysis revealed clear differentiation among the TGMS lines according to their source of origin. The SSR-based genetic distance between the hybrids of the parental lines ranged from 0.36 to 0.79 suggesting a high degree of genetic divergence. Among a set of 54 hybrids generated using parental lines, 32 showed better parent heterosis (+21.7%) while 19 showed mid-parent heterosis (+15.0%). For the trait yield per plant genetic distance (GD) was negatively correlated with F₁ performance (r = ?0.202), mid-parent heterosis (r = ?0.325*; P < 0.05), and better parent heterosis (r = ?0.261), while it was positively correlated with specific combining ability (r = 0.042). Based on the grouped genetic distance (GGD), the hybrid combinations were divided into four groups. The GGD showed linear correlation with hybrid performance within the group (GGD = 40–50: r = ?0.07; GGD = 70–80: r = 0.32). This information can be utilized in the development of higher yielding, two-line rice hybrids through selection of intermediately diverse parental lines using GGD.     

General combining ability and heterosis regarding the phytochemical properties in strawberry (Fragaria × ananassa) hybrids

Strawberries are a common and important fruit in human diet because of their high content of essential nutrients and beneficial phytochemicals, which have relevant biological activity in human health. In this study, six cultivars and 15 selected F₁ hybrids between S₄ inbred lines and tester (cv. ‘Dukat’) were evaluated in a field trial over a period of two consecutive years. The amounts of total anthocyanin, phenolics and vitamin C in fruits and antiradical activity were analysed. General combining ability (GCA) and mid‐parent heterosis were also determined for those characteristics. Among all the genotypes tested, the inbred lines of ‘Senga Sengana’ 17 showed the highest breeding value based on GCA for all studied traits. Estimated heterosis varied among genotypes tested. The highest heterosis in terms of vitamin C occurred in the offspring of clone 1387 18‐15 × ‘Dukat’, but with regard to phenols and antiradical activity in hybrid ‘Teresa’ 18‐15 with cv. ‘Dukat’. This study revealed that the differentiation in chemical composition of strawberry fruits between genotypes is clearly dependent on individual genotype combinations and demonstrated the presence of heterosis in phytochemical contents in some specific genotypic combinations.     

水稻籼粳亚种间杂种不育性的研究进展

克服杂种不育性是利用籼粳亚种间杂种优势的关键。由此对水稻亚种间杂种不育性的原因、细胞学基础及两种主要基因遗传模式进行了总结,并详细综述了利用“亲和基因”克服籼粳杂种不育性的两种有代表性的学说-广亲和基因和特异亲和基因分子定位的最新研究进展,并提出了两“亲和基因”共同利用的初步设想:将聚合了Si等位基因的粳型亲籼系与聚合了不同广亲和基因(中性亲和基因的广亲和力强、亲和谱广泛的粳型品种进行杂交和回交,选育出聚合不同广亲和基因和Si等位基因的粳型亲籼系,再与籼稻品种杂交,真正实现直接利用籼粳亚种间杂种优势。     

Diallel analysis of combining ability and heterosis for yield and yield components in rice by using positive loci

Diallel crosses have been widely used for analysis of general combining ability (GCA), specific combining ability (SCA) and heterosis. In the present research, 12 lines were selected from 60 inbred rice bred by International Rice Research Institute with extremely-high or -low yielding records according to the previous three consecutive seasons of yield trial experiments, to construct a half diallel cross. The genetic distances (GDs) revealed by molecular markers for the 12 lines ranged from 0.2288 to 0.7169, averaging at 0.5882; clustering analysis showed the 12 lines were divided into four groups maintaining the original cluster structure of the 60 lines. The positive loci (PLs) including effective-increasing loci (ILs) and effective-decreasing loci (DLs) were screened. The results showed that hybrids derived from those parents with higher GCA effects had better performance for traits of yield and yield components. The SCA effects were strongly correlated to F₁ performance as well as heterosis; the GDs based on ILs were significantly positive correlated to SCA effects and heterosis for yield and yield components while the GDs based on DLs showed the significant negative correlations. Based on this research, a new conception, i.e. general sum of combining ability (GSCA) was conceived, which is defined as the sum of GCAs for two parents of a hybrid. The GSCA and SCA showed similar correlations with traits of yield and yield components. The results illustrated that ILs could be used for further study on prediction of heterosis for traits of yield and yield components; and GSCA may be another considerable parameter combined with ILs for breeders in selecting elite hybrid.     

Dissection of component QTL expression in yield formation in rice

Yield and its components were investigated by using a population of 241 recombinant inbred lines (F₉ RILs) derived from an elite hybrid rice cross of ‘Zhenshan 97’בMinghui 63′. Quantitative trait loci (QTLs) for causal analysing of yield traits were detected at different yield component (YC) influences by conditional and unconditional QTL mapping methods. The number of QTLs significantly affecting yield was different at component‐special influence. Some QTLs controlling yield identified in one component influence were undetectable at the others. More QTLs for yield could be detected at different YC influences. It is possible to reveal that causal gene expression for yield could be different at different YC influences. Mapping QTLs for component effects of yield could help us in understanding the nature of cause‐effect traits for the formation of grain yield.