Combining ability and heterosis over environments for yield and yield components in two-line hybrids involving thermosensitive genic male sterile lines in rice (Oryza sativa L.)

Presence of substantial heterosis and economic hybrid seed production are two most desirable components for success of any commercial hybrid breeding programme. Thermosensitive genic male sterile (TGMS) lines of rice, in this regard, have tremendous potential in realizing further quantum jump in yield and economical hybrid seed cost. Analyses for combining ability and heterosis over optimum (120N : 60P₂O₅ : 40K₂O kg/ha) and high (200N : 90P₂O₅ : 60K₂O kg/ha) fertility environments for six traits were made in 2 years (2001 and 2002) using 120 hybrids of inter‐ and intra‐subspecific nature derived from hybridization of 30 elite indica TGMS lines and four cultivars, viz., ‘Pant Dhan 4’ and ‘Ajaya’ (I = indica), ‘Taichung 65’ (J = japonica) and ‘IR 65598‐112‐2’ (TJ = tropical japonica) in line × tester mating design. Predominance of non‐additive genetic variance suggested good prospects of hybrid breeding. Pooled analysis revealed highly significant variances for lines, general combining ability (GCA), specific combining ability (SCA) and line x tester. TGMS line 365‐8S was the best general combiner for all the six traits including grain yield. Trend of relative mid‐parent heterosis for grain yield, panicle length, grain number per panicle and earliness in flowering was I/TJ > I/J > I/I. For panicle number per plant and 1000‐grain weight, trends were I/TJ > I/I > I/J and I/I > I/TJ > I/J, respectively. Grain yield recorded heterosis of 49.3%, 71.9% and 92.7% for I/I, I/J and I/TJ hybrid groups respectively. Effect of environments on the hybrid performance indicated better response of hybrids at high fertilizer dose. Study suggests greater prospects of combining improved japonica and tropical japonica germplasms having wide compatible gene with indica TGMS lines for exploitation of intersubspecific heterosis.     

Cytological screening of rice TGMS lines

An investigation was undertaken to develop new stable thermo‐sensitive genic male sterility (TGMS) rice lines in intermated progenies (IMPs) of TGMS lines by using an anther clearing technique. The results indicate that both pre‐ and post‐meiotic genetic systems operate during anther development for the expression of sterility in TGMS lines. In all the TGMS lines, sterile anthers were small with empty pollen grains of irregular shape, except for TS 16, which showed pollen‐free anthers. This indicates that the sensitive stage of TS 16 is around stage IV (stamen and pistil primordia) of panicle development. Distinct differences were observed between sterile and fertile phases with respect to anther size, shape and colour of the pollen grains in TS 18 and TS 29. The pollen grains at the sterile phase were small and irregular in shape while in the fertile phase they were plump and larger with a yellow colour, establishing that the occurrence of sterility in TS 18 and TS 29 is post‐meiotic. Three distinct classes of pollen fertility percentage viz. <20%, 50‐70% and >90% were observed in IMPs. Anther clearing in IMPs showed distinct developmental patterns of pollen production with respect to distinct classes of pollen fertility. Less than 20% pollen fertility was observed in hybrids such as TS 15 × TS 16, TS 15 × Co 47, TS 18 × TS 16 and TS 18 × Co 47 which hold promise for developing new TGMS lines with a good plant type and acceptable quality.     

Genetics of thermosensitive genic male sterility in rice

Summary Inheritance of thermosensitive genic male sterility (TGMS) in Norin PL12 and IR32364TGMS and their allelic relationship were studied from F₁, F₂ testcross (TC) and F₃ generations of the crosses made with the two mutants and several fertile tester parents. F₂, TC and F₃ segregation behavior for pollen and spikelet fertility indicated that the TGMS trait in the two mutants was controlled by a single recessive gene. Allelic relationship studies indicated that TGMS genes of the two mutants were different. Since TGMS gene in Norin PL12 has been designated as tms ₂ , the TGMS gene present in IR32364TGMS is tentatively designated as tms ₃ (t) until allelic test is done with another TGMS gene (tms ₁ ) reported from China in a line 5460S seeds of which were not available.     

Development of new cytoplasmic source of male sterile lines in rice for shallow lowland

Two shallow lowland male sterile lines, MotiA and PadminiAwith Miz.4 cytoplasmic source were developed throughintervarietal hybridization and recurrent backcrossing withtheir respective parents. In all probability, MotiA and PadminiA of Miz.4 source may be genetically different from the Wild abortive CMS source (V.20A). These two CMS lines are semitall in stature, photosensitive, of late duration in flowering with easy fertility restoration ability, and thus could be useful for developing hybrid rice suitable for shallow lowland areas.     

Development of new sources of cytoplasmic male-sterile lines in rice

Two male-sterile lines, KalashreeA and PadminiA, with a Miz.21 cytoplasm source were developed through indica/indica hybridization followed by repeated backcrossing with their respective recurrent male parents (Kalashree and Padmini) up to the BC₆ generation. These two cytoplasmic male-sterile lines are suitable for use in the development of hybrids for lowland situations owing to their intermediate to semi-tall stature, late flowering duration, good grain quality and easy fertility restoration ability.     

Identification of restorers and maintainers for developing basmati and non-basmati hybrids in rice, Oryza sativa

Twenty‐seven improved aromatic lines of germplasm and 18 non‐aromatic disease‐resistant genotypes of rice were test‐crossed with four cytoplasmic male‐sterile lines (IR 58025A, IR 62829A, PMS 3A and PMS 10A). Thirteen aromatic and 10 non‐aromatic genotypes were selected based on pollen fertility, and crosses were repeated to confirm sterility‐maintaining and fertility‐restoring ability. Genotypes were categorized as effective restorers (> 80% spikelet fertility), partial restorers (21‐79% spikelet fertility) and maintainers (< 1% spikelet fertility). The effective basmati restorers identified were Basmati 385, Chandan, P1031‐8‐5‐1, HKR 241‐IET‐12020, SAF Khalsa 7 and Karnal Local. The basmati maintainers identified were Basmati 370, Pusa basmati 1, P615‐K‐167‐13 and P1173‐4‐1. The frequency of restorers obtained was higher for the non‐aromatic than the aromatic basmati type. The performance of restorers varied with cytoplasmic male‐sterile (CMS) line, location and season of testing. The differential ability to restore fertility in the CMS lines that have the wild abortive (WA) cytosterile system could result from different nuclear backgrounds of the CMS lines. These restorers and maintainers possess acceptable grain dimensions, a desirable degree of aroma, volume expansion through linear kernel elongation and cooking quality characteristics of basmati rice. These genotypes will contribute to developing basmati hybrids and provide restorers and maintainers with acceptable key basmati quality characteristics.     

Cytological observations in some hybrids between the rice species Oryza sativa L. and O. glaberrima Steud.

Summary Several hybrids between Oryza sativa and O. glaberrima and their backcrosses with O. sativa were studied. Their seed sterility was very different; large differences were also observed in the level of pollen sterility and in the earliness of microspore failure. The proportion of aborted embryo sacs was much lower than the rate of sterile male gametophytes. The backcross populations were much more sterile than the corresponding F₁ hybrids. On the base of our observations and according to the literature, we may conclude that genic unbalance is the main cause of sterility of these hybrids, but that physiological factors may also be involved. Thus a restoration of fertility is generally possible by selection. On the other hand, male-sterile lines could be bred from some of these hybrids.     

粳型两系杂交稻品质性状的遗传分析

选择有代表性的11个优良粳型两系杂交稻亲本,包括6个光敏核不育系和5个粳稻恢复系,采用p×q不完全双列杂交模式对4个品质性状的配合力进行分析并估算其遗传参数.结果表明,4个品质性状的一般配合力(GCA)和特殊配合力(SCA)均达到了显著或极显著水平.在垩白度、直链淀粉含量性状上,以加性效应占主导地位;在胶稠度两性状上则以非加性效应为主,而在整精米率上加性效应和非加性效应的作用相当.     

Production and testing of plants regenerated from protoplasts of photoperiod sensitive genic male sterile rice (Oryza sativa L.)

Plants were regenerated from protoplasts isolated from embryonic suspension cultures of N5047S, a photoperiod sensitive genic male sterile (PGMS) Japonica rice line. Flow cytometric analyses of nuclear DNA content identified some tetraploid regenerates whose agronomic traits could be distinguished from diploid regenerates. Pollen and female fertility of diploid protoplast-derived clones grown under different light and temperature conditions was compared. A promising PGMS protoplast clone, ZAU11S, was developed from these clones. Its male sterility was confirmed as a photoperiod × temperature interaction type. This revised version was published online in July 2006 with corrections to the Cover Date.     

Expression of thermosensitive genic male sterility in rice under varying temperature situations

Response of thermosensitive genic male sterility in rice to varying temperature situations was studied by using four TGMS lines. In three sets of maximum, minimum and their combined temperatures, it was observed that maximum temperature played a predominant role in influencing sterility/fertility of TGMS lines under the combined regimes. Expression of a TGMS gene was found to be influenced by the genetic background of the recipient lines. Exposure for more than 8 hours of 32 ^°C was found necessary to induce complete male sterility in indica TGMS lines: IR68945-4-33-4-14 and IR68949-11-5-31 while, more than 4 hours of such exposure was enough to induce sterility in case of their japonica donor Norin PL 12. Sudden interruption with 27 ^°C even for 2 hours under the sterility inducing regime of 32/24 ^°C could induce partial fertility in the line IR68945-4-33-4-14. However, the line ID 24 remained completely sterile even with 10 hours of interruption with 27 ^°C. An interruption with lower temperature of 27 ^°C for 4 hours for even one day induced partial fertility in IR68945-4-33-4-14. The period of four to eight days after panicle initiation was the stage most sensitive to temperature variations. Hybrid rice breeders need to develop numerous genetically diverse TGMS lines, which possess critical sterility inducing temperature of 28 ^°C and are not affected by sudden interruptions with a lower temperature for few hours daily for a couple of days. This revised version was published online in August 2006 with corrections to the Cover Date.     

Heterosis in rice hybrids

Summary One hundred and thirtysix hybrids were developed utilizing four cytoplasmic genetic male sterile lines (V 20A, Zhen Shan 97A, IR 46829A and IR 46830A) and 34 effective restorers. Heterosis, heterobeltiosis and standard heterosis were found to be significant for grain yield and other yield attributing characters in most of the hybrids. The heterosis for grain yield was mainly due to the significant heterosis for the number of spikelets per panicle, test weight and total dry matter accumulation. Interestingly, it was found that most of the higher yielding hybrids were accompanied by significant negative heterosis for harvest index. Hybrids shorter than the shortest parent and earlier than the earliest parent were not observed; hybrids with intermediate to tall plant height having nonlodging habit could be developed. Eighteen hybrids gave more than 20% grain yield than the standard checks. These were evaluated for their stable and consistent yield performance over four seasons. The results on analysis for stability parameters indicated that the hybrids V 20A × Himdhan and Zhen Shan 97A × Mahsuri were stable over environments.     

两系杂交稻干物质积累与运转特性研究

根据湘西山区生态环境特点,分析比较了4个两系杂交中稻与2个三系杂交中稻的干物质积累与运转情况,结果表明：两系杂交组合前中期叶片、茎鞘养分积累较多,后期向穗部转移亦比较充分,供试组合剑叶展开期平均干重为39.7g/蔸,齐穗期茎鞘叶平均干重为41.0g/蔸,分别比三系杂交组合高14.41%和23.88%;茎鞘叶干物质向穗部的平均运转量为16.4 g/蔸,比三系杂交组合高18.84%;平均运转率为40.00%,与三系杂交组合平均值40.18%相近;对产量的贡献率为43.27%,比三系杂交组合平均值高近5个百分点。     

应用群体改良技术选育水稻温敏核不育系的研究

应用随机多交加混合选择的方法,不仅可以改良单个性状柱头外露率,而且可以改良配合力、品质、抗性等综合性状。从用N8S、怀早4号、香2B和早优1号构建的两次随机多交加混合选择的群体中选育出一个柱头外露率高、配合力、品质和抗性都较对照V20A有明显改善的实用温敏核不育系准S。准S柱头外露率达78.6%,比对照V20A高72.4%。     

The transformation of the photo-thermo sensitive genic male-sterile line 261S of rice via an expression vector containing the anti-Waxy gene

Transgenic photo-thermo sensitive genic male sterility Oryza sativa L. cv. “261S” plants with the anti-Waxy gene were successfully obtained using an Agrobacterium tumefaciens-mediated co-transformation method. Marker-free homozygous transgenic lines with the anti-Waxy gene were obtained. The setting seed rates of the transgenic plants via self-pollination or via crossing with the restorer line WX99075 rice and the 1000-grain weight of the transgenic plants and the F₂ hybrid seeds obtained by crossing the transgenic or non-transgenic plants with the restorer line WX99075 rice, and the number of panicles of the transgenic plants and yields of the F₂ hybrid rice, were analysed. Quality indexes of the transgenic plants and of the F₂ hybrid seeds were analysed. Our researches results indicate that hybrid female and hybrid descendant edibility could be improved via the introduction of the anti-Waxy gene, but the grain yields of the reserve seeds via self-pollination of the transgenic photo-thermo sensitive genic sterile lines and of the hybrid rice were not affected.     

甘蓝型油菜光、温敏雄性不育系Huiyou50S花粉败育的细胞学观察

Huiyou50S是从甘蓝型油菜品种汇油50中发现的半不育株选育而成的光、温敏雄性不育系,育性受隐性核基因控制,在高温、长光周期下不育而在低温、短光周期条件下可育。本文通过半薄树脂切片、扫描电镜、花粉压片染色、花药整体透明方法对Huiyou50S及其近等基因系Huiyou50F的花药发育过程及花粉形态观察比较。结果表明, Huiyou50S的花药造孢细胞、花粉母细胞、减数分裂、四分体阶段均正常,在单核期出现明显异常,虽然能形成花粉壁,但小孢子细胞质收缩、解体,最终只剩余空瘪的花粉壳; Huiyou50S的花药绒毡层在单核后期提前降解,绒毡层解体速度快于可育株Huiyou50F。Huiyou50S的小孢子的完全败育主要发生在单核时期,绒毡层发育与小孢子异常有某种关联,该结论为油菜光、温敏雄性不育类型划分及育种应用提供了依据。     

中国西南温光型两系杂交小麦研究进展

为深入西南温光型两系杂交小麦研究,综述了中国西南温光型两系杂交小麦研究历程,包括温光型不育系的发现和温光型两系杂交小麦研究的起始,温光型不育系育性稳定性研究,生理变化,温光条件对育性的影响,外源化学物质对‘C49S’育性的影响;总结了应用研究成果,包括对原始温光型不育系的改造,恢复系的选育,温光型两系杂交小麦强优势组合筛选,中国西南温光型两系杂交小麦配套栽培技术研究及其生产示范;提出了西南温光型两系杂交小麦研究中存在的问题:(1)对条锈病抗性的丧失影响杂交小麦的应用,(2)如何提高制种纯度的问题,(3)如何降低制种成本的问题。文章最后介绍了西南温光型两系杂交小麦研究的新动向,提出了应对方法。     

Developing rice lines possessing neutral alleles at sterility loci to improve the width of compatibility

To improve the width of compatibility for overcoming various sterilities in inter‐subspecific hybrid rice, some elite lines combining several sterility‐neutral genes were developed and the effects on mitigating various hybrid sterilities were tested. From Akihikari// IR36/Dular, neutral genes at ga11 and six sterility loci, S5, S7, S8, S9, S15 and S16, were combined and elite lines were obtained in their successive progeny. Four of the lines tested were confirmed to combine the neutral alleles S5‐n, S7‐n, S8‐n, S9‐n, S15‐n and S16‐n at the sterility loci and, among them, two harboured an additional gamete abortion‐neutral allele, ga11‐n. F₁s, which used the lines and various testers as parents, mitigated the spikelet sterilities by six sterility loci and gamete abortion by a gametophyte gene, ga11. These lines could be selectively used as parents or donors to increase the width of compatibility of rice varieties for improving fertility in inter‐subspecific hybrid rice breeding.     

A proposed mechanism for loss of heterozygosity in rice hybrids

A phenomenon, loss of heterozygosity (LOH), was discovered in hybrid plants involving a selected plant (named AMR) of the Chinese rice cultivar ‘ZhongxinNo. 1’ as one parent. In these hybrids and some of their progenies, somatic variations were manifested by molecular genotypes and/or morphological phenotypes in vegetative parts of the same plant. Random amplified polymorphic DNA (RAPD) markers for the parents have been followed through the F₃ generation. RAPD markers were uniformly present or absent in all plants within some or all F₂ panicle rows derived from F₁ hybrids involving AMR. In contrast, RAPD markers segregated in the Mendelian manner for dominant markers in panicle rows derived from control hybrids. Certain F₂ panicle rows from F₁hybrids involving the special rice became fixed for all assayed RAPD markers. Genotype fixation was confirmed by molecular assays and field observations of the F₃ progenies. We propose a new biological mechanism, called ‘assortment mitosis,’ as being responsible for the observed phenomenon. The use of this mechanism in plant hybrids allows the development of uniform progenies as early as the F₂ generation. Therefore, the time required to obtain fixed non-parental type progenies for subsequent performance trials can be drastically shortened. Utilizing this mechanism in plant breeding represents a new approach and requires the modification of conventional plant breeding procedures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification and characterization of new sources of cytoplasmic male sterility in rice

Search for male sterility-inducing cytoplasm in wild species of the genus Oryza was attempted with a view to diversify the base of the cytoplasmic genetic male sterility system currently used in the development of commercial rice hybrids. A total of 132 interspecific crosses were made involving accessions of four wild and two cultivated species, all belonging to the A genome. Wild accessions possessing sterility-inducing cytoplasms were identified following reciprocal and sterile F₂ backcross methods. Sterile segregants were pursued through substitution backcrosses to develop cytoplasmic male-sterile (CMS) lines. CMS lines were developed with the cytoplasm of either O. rufipogon (VNI) or O. nivara (DRW 21018, DRW 21001, DRW 21039, DRW 21030 and RPW 21111). Based on shape, staining, and abortive pattern of pollen and also on type of interaction with a set of restorers and maintainers for known cytoplasmic male steriles of WA source (V 20A), the newly-developed CMS lines were grouped into four classes. Of these, RPMS 1 and RPMS 2 showed gametophytic male sterility with a restorer reaction different from WA cytoplasmic male-sterile stocks.