Thermo-sensitive Genic Male Sterile Line Research Articles

Influence of Genetic Drift of Restoring Gene ( Rf) on Seed Purity of Yuetai A, a Honglian-Type Cytoplasmic Male Sterile Line in Hybrid Rice

The seed samples of Yuetai A, a Honglian (HL) type cytoplasmic male sterile (CMS) line in hybrid rice were investigated to assess the seed purity and to analyze the cause of off-type plants by imitating the biological contaminant to Yuetai A in Nanjing, Jiangsu Province and Lingshui, Hainan Province during 2004–2006. The seed impurity of Yuetai A mainly resulted from the genetic drift of restoring fertility gene ( Rf) after biological contamination but not from its sterility unstability. All of the ten maintainer lines, five restorer lines and three thermo-sensitive genic male sterile lines used in the study could pollinate Yuetai A and Yuetai B to produce F 1 plants, directly or indirectly resulting in Rf-gene drifting into Yuetai A and generating ‘iso-cytoplasm restoring-generations’. Furthermore, high outcrossing rate and similar heading date of Yuetai A with many varieties used in rice production might easily result in the biological contamination. After removing all plants with Rf-gene mixed in Yuetai A and preventing Rf-gene drifting into Yuetai A, the seed purity of Yuetai A and Yuetai B had been raised to 100%.

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.)

AbstractPresence 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.

Strategy and utilization of a herbicide resistance gene in two-line hybrid rice

Hybrid rice plays an important role in China's aim to improve rice production as it accounts for some 50% of rice planting area but produces about 60% of the total rice grain. However, the existing three-line system used in hybrid rice production has its limitations. The two-line system, which makes use of photoperiod-sensitive genic male-sterile (PGMS) and thermo-sensitive genic male-sterile (TGMS) lines to generate the male-sterile parental line, was developed to overcome some of these limitations. The sterility of the male-sterile line of two-line hybrid rice, however, fluctuates when the temperature-sensitive phase of fertility encounters abnormal low temperatures during hybrid seed production, which induces selfing and decreases the purity of hybrid. We describe here the strategy of utilizing a herbicide resistance gene in two-line hybrid rice to eliminate this fluctuation in the sterility of the P/TGMS lines during hybrid seed production and reports the development of the herbicide resistance restorer line Bar68-1 and its herbicide-resistant early season hybrid rice Xiang125s/Bar68-1. When the restorer line and its derived hybrid are herbicide resistant, the selfed seeds can be removed easily from the hybrid by herbicide spraying. A herbicide resistance gene bar was transferred into a restorer line by particle bombardment. The resulting transgenic restorer line Bar68-1 and its hybrid Xiang125 s/Bar68-1 inherited stable herbicide resistance. The purity of Xiang125s/Bar68-1 was increased by spraying the seed bed with herbicide, which resulted in a significant increase in yield, grain quality, and disease resistance in comparison to the controls in a regional trial.

Identification of a cytochrome P450 hydroxylase, CYP81A6, as the candidate for the bentazon and sulfonylurea herbicide resistance gene, Bel, in rice

Bentazon and sulfonylureas have been used for selective control of broadleaf weeds and sedges in rice fields for more than 20 years. A bentazon and sulfonylurea susceptible mutant, bel, was previously identified for the purpose of allowing these herbicides to be used for removing false hybrids from hybrid rice. While this mutation has been used successfully in rice breeding, the genetic nature of bel is not known. Using 1,776 susceptible plants from a population of 10,000 F2 individuals, we constructed a fine map for the Bel locus and delimited it to a 36-kb DNA fragment between two restriction fragment length polymorphism markers, L5 and P17. Bioinformatic analysis indicated that there are five genes within this interval, an ethylene-responsive OsER33 gene and four tandem repeats of cytochrome P450 genes designated as CYP81A5, CYP81A6, CYP81A7, and CYP81A8. Comparative sequencing could not find any differences in the coding regions of the OsER33, CYP81A5, CYP81A7, and CYP81A8 genes between the mutant bel and its wild-type progenitor W6154S, but did identify a single base guanine deletion at position +1,332 bp downstream from the translation start codon of CYP81A6. This deletion introduces a premature stop codon and leads to the loss of the heme-binding motif, which is essential for cytochrome P450 function because it contains an absolutely conserved cysteine that serves as the fifth ligand to the heme iron. CYP81A6 presumably functions as a hydroxylase for the detoxification of bentazon and sulfonylurea herbicides in rice. A gene-specific cleaved amplified polymorphic sequence marker and tightly linked flanking markers were developed that will be very useful for selection of the bel allele when transferred to photoperiod-/thermo-sensitive genic male sterility and CMS lines in hybrid rice breeding programs.

Characterization and identification of the candidate gene of rice thermo-sensitive genic male sterile gene tms5 by mapping

Previous research has demonstrated that the thermo-sensitive genic male-sterile (TGMS) gene in rice was regulated by temperature. TGMS rice is important to hybrid rice production because the application of the TGMS system in two-line breeding is cost-effective, simple, efficient and overcomes the limitations of the cytoplasmic male sterility (CMS) system. AnnongS is the first discovered and deeply studied TGMS rice line in China. Previous studies have suggested that AnnongS-1 and Y58S, two derivative TGMS lines of AnnongS, were both controlled by a single recessive gene named tms5, which was genetically mapped on chromosome 2. In the current study, three populations (AnnongS-1 x Nanjing11, Y58S x Q611, and Y58S x Guanghui122) were developed to investigate the tms5 gene molecular map. Analysis of recombination events of sterile samples, utilizing 125 probes covering the tms5 region, suggested that the tms5 gene was physically mapped to a 19 kb DNA fragment between two markers, 4039-1 and 4039-2, located on the BAC clone AP004039. Following the construction of a physical map between the two markers, ONAC023, a member of the NAC (NAM-ATAF-CUC-related) gene family, was identified as the candidate of the tms5 gene.

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

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.

Genetic analyses and mapping of a new thermo-sensitive genic male sterile gene in maize

The present study describes a novel thermo-sensitive genic male sterile (TGMS) line, Qiong68ms. To analyse the mode of fertility inheritance and tag the TGMS gene, a set of F2, BC1 and F(2:3) populations derived from a cross between Qiong68ms and K12 were evaluated for a period of 2 years. Classical genetic analyses and QTL mapping using the mean restoration percentage of the F(2:3) populations revealed that the fertility of Qiong68ms was likely to be governed by a single recessive gene, which was named tms3; the tms3 gene was mapped to a location between SSR markers umc2129 and umc1041, at a distance of 3.7 cM form umc2129 and 1.5 cM form umc1041. The molecular markers tightly linked with tms3 gene will aid in the transfer of the TGMS gene to various background inbred lines using the MAS method.

Gene expression profiling under different photoperiod/temperature conditions in a photoperiod-/thermo-sensitive genic male sterile line of rice (Oryza sativa L.)

Peiai 64S is a photoperiod-and thermosensitive genic male sterile (PTSGMS) line of rice, which is male sterile at long day/high temperature and partial fertile at short day/low temperature. A cDNA array representing 3328 unique rice genes was used to profile the gene expression patterns in the young panicles of Peiai 64S under these two conditions. The statistical data showed that up to 14.60% of genes exhibited up-or down-regulated expressions in the plants at long day/high temperature compared with plants at short day/low temperature. Only four genes were up-regulated while 482 genes down-regulated. Real-time PCR with all the up-regulated and 9 randomly selected down-regulated genes confirmed the differential expressions detected by the array, indicating that the constructed cDNA array is reliable. These differently expressed genes participated in almost all cell biological responses. Analysis of up-and down-regulated genes revealed distinctive changes between the mRNA abundances of MMK1 and MMK2, both of which are analogs of MAPK, and significant down-regulation of several transcription factors. It was suggested that changes that occurred in the MAPK signal transduction pathway might disturb the transcription control necessary for morphogenesis of pollens and corresponding physiological functions.

Effect of Growth Regulators and Chemicals on Pollen Sterility in TGMS Lines of Rice

Thermosensitive genic male sterility (TGMS) in rice is a widely adopted technique for successful hybrid rice production in Asia. TGMS lines remain male sterile when daily mean temperature is above the critical sterility temperature and are therefore used as female parents. The same line will remain fertile when mean temperature is below the critical sterility temperature. Achievement of 100% male sterility in TGMS lines is important for the successful utilization of TGMS lines as female parents in hybrid rice production. This study examined the external application of some growth regulators and chemicals and their effect on pollen sterility. Among the various treatments, ethrel (800 ppm), salicylic acid (600 ppm) and maleic hydrazide (0.2%) induced a significantly higher percentage of male sterility in the TGMS lines. The sprayed plants also showed higher total phenol accumulation in their flag leaves. The results suggest that it is possible to achieve 100% male sterility in TGMS lines with the external application of growth regulators and chemicals.

Genetics, fertility behaviour and molecular marker analysis of a new TGMS line, TS6, in rice

AbstractThe thermosensitive genic male sterility (TGMS) system has great potential for revolutionizing hybrid rice production through simple, less expensive and more efficient seed production technology. For the successful utilization of this novel male sterility system, knowledge of the breeding and fertility behaviour of a TGMS line is essential. In this study, the fertility transformation behaviour, the critical fertility and sterility temperatures and the mode of inheritance of male sterility were studied for a new TGMS line, TS6, identified at Tamil Nadu Agricultural University, Coimbatore, India. The pollen and spikelet fertilities recorded on plants raised at fortnightly intervals revealed that this line was completely sterile for 78 consecutive days (35/22 to 32/23°C, maximum/minimum temperatures) and reverted to fertile when the temperature was 30/18°C. It remained fertile continuously for 69 days and the maximum pollen and spikelet fertilities recorded were 75 and 70%, respectively. The fertility was highly influenced by daily maximum temperature followed by average and minimum temperatures. It was not influenced by relative humidity, sunshine hours or photoperiod. The critical temperature inducing sterility and fertility was 26.7 and 25.5°C, respectively. The male sterility in TS6 was inherited as a monogenic recessive in the F2 and BC1 populations of TS6 × MRST9 as well as TS6 × IR68281B. Using bulked segregant analysis on an F2 population of TS6 × MRST9, an RAPD marker, OPC052962, was identified to be associated with TGMS in TS6.

HPLC profiles of polyamines in the leaves and anthers of a new thermosensitive genic male sterile rice line

Hybrid rice is successfully cultivated in India and, in recent years, the country has released commercial rice hybrids having at least 1 t ha -1 higher yield than inbred checks. The cytoplasmic male sterility (CMS) system, also known as the three-line system, is presently the most widely used system for producing F 1 rice hybrids. Although effective, the system is cumbersome because CMS lines require specific maintainer and restorer lines and possess wild abortive (WA) cytoplasm that is vulnerable to biological stresses. On the other hand, the thermosensitive genic male sterility (TGMS) system does not require restorer lines, and the seeds of TGMS lines are multiplies by selfing when exposed to the right temperature at the critical growth stage (in the tropics, 5-15 d after panicle initiation) (Maruyama et al 1990).

Sterility of Thermo-Sensitive Genic Male Sterile Line, Heterosis for Grain Yield and Related Characters in F1 Hybrid Rice (Oryza sativa L.)

The thermo-sensitive genic male sterile (TGMS) T29s line was sterile when exposed to daily mean temperatures of 24.1°C or above during the critical stage (from 15 to 11 days before heading). It was completely sterile for both pollen and spikelet when the plant headed from June 16 to November 7 in Okinawa, because the temperature exceeded 24.1°C. The heterosis of the F1 hybrids between the T29s line and seven indica cultivars was examined. Most of the F1 hybrids showed positive heterosis over the male parent for grain yield per plant and the number of spikelets per panicle, and one of them manifested heterosis for grain yield over a F1 hybrid from a cytoplasmic male sterile (CMS) line. Dry matter accumulation per plant at the panicle initiation stage in most F1 hybrids was higher than that in the respective male parent or mid-parent, and it was correlated with a larger number of tillers and leaf area per plant. All F1 hybrids produced a larger number of panicles per plant than their respective male parent. Positive heterosis over the male parent for the number of filled grains per panicle, 1000-grain weight and harvest index was obtained in several F1 hybrids. A positive correlation was found between grain yield and the dry matter accumulation per plant in F1 hybrids. Both the larger number of panicles per plant and the larger number of spikelets per panicle were more important for the positive heterosis for grain yield in F1 hybrids rather than the higher 1000-grain weight. Among the yield attributes, a larger number of filled grains per panicle mainly contributed to a higher grain yield of F1 hybrids.

Identification of critical sterility temperature (CST) and thermo sensitive stage in selected TGMS lines in rice (OryZa sativa L.)

Thermosensitive genic male sterility (TGMS) is a type of genetic male sterility expression regulated by certain temperature conditions. The knowledge of the critical sterility temperature and the critical thermosensitive stage for fertility alteration of TGMS lines is useful to determine most suitable time of their planting for multiplication or hybrid seed production. The experiment was conducted in mini phytotron. The critical sterility temperature of three TGMS lines viz. TGMS 6, TGMS 16 and TGMS 29 was assessed by subjecting them to different temperatures during reproductive stage. The pollen sterility percentage increased as the daily mean temperature increased and the genotypes behaved differently before they attain complete pollen sterility. The results that the CST of TGMS 6 was 28.0°C, TGMS 16 was 27.0°C and TGMS 29 was 27.5°C with 34.0, 33.0°C and 34.0°C the maximum temperatures respectively. Three TGMS lines were exposed to CST for different durations coinciding the various stages of panicle development to understand the critical stage of thermosensitivity for fertility alteration. In this study, 10-25 DBH was identified as critical thermosensitive stage for fertility alteration, which corresponds to differentiation of secondary branch primordiam, differentiation of pistil and stamen, formation of PMC and early meiosis stages (Stage 111 to IV).

Development of TGMS lines and two-line rice hybrids through a shuttle breeding program between IRRI and China

Based on the discovery of photoperiod-sensitive genic male sterile (PGMS) rice mutant Nongken 58S (Shi 1981), rice scientists in China began work on the two-line system of hybrid rice breeding in the early 1980s. Subsequently, some thermosensitive genic male sterile (TGMS) rice mutants, such as Annong S-1 and 5460S, were developed in 1988 through screening of breeding materials and radiation, respectively (Lu et al 1998). The two-line system was established in China by using PGMS and TGMS lines. This method was considered more efficient than the thre-line system in exploiting heterosis to increase yield.

Cytological screening of rice TGMS lines

AbstractAn 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.

Heterosis for Photosynthesis, Dry Matter Production and Grain Yield in F1 Hybrid Rice (Oryza sativa L.) from Thermo-Sensitive Genic Male Sterile Line Cultivated at Different Soil Nitrogen Levels

This study was conducted to determine the effects of soil nitrogen levels (0.22, 0.44 and 0.88gN pot-1) on the heterosis for photosynthetic characters, dry matter production and grain yield in F1 hybrid rice obtained from thermo-sensitive genic male sterile line. Net CO2 exchange rate (CER) and other related characters viz., SPAD reading, leaf N content, soluble protein content and ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) activity increased significantly with increasing N level in all the F1 hybrid and parental cultivars. With increasing N level, the number of tillers, leaf area, root weight, wholeplant dry weight and grain yield also increased. Under the low N level, the F1 hybrid did not show heterosis for most photosynthetic characters. However, at high N level, heterosis for CER over both the male parent and the mean of parents was ascribed to high leaf N content and several characters related to CER. The F1 hybrid exhibited substantial heterosis over the male parent for whole-plant dry weight, number of panicles per plant, number of spikelets per panicle and grain yield in all N levels. Among the yield components, the strengthening of heterosis for number of filled grains per panicle was the major cause of greater heterosis for grain yield in the F1 hybrid at high N level.

A bentazon and sulfonylurea sensitive mutant: breeding, genetics and potential application in seed production of hybrid rice.

The use of a thermosensitive genic male sterility (TGMS) system in two-line hybrid rice breeding is affected greatly by the sterility instability of TGMS lines caused by temperature fluctuation beyond their critical temperatures for fertility reversion. To prevent seed production from self contamination, we have developed a system to secure seed purity using a herbicide-sensitive TGMS mutant, M8077S, obtained by radiation. Genetic analysis, using the F(1), F(2) and F(3) populations derived from this mutant and other normal varieties, revealed that bentazon lethality/sensitivity was controlled by a single recessive gene, which was named bel. The mutant can be killed at the seedling stage by bentazon at 300 mg/l or higher, a dosage that is safe for its F(1) hybrids and all other normal varieties. This mutant is also sensitive to all the tested sulfonylurea herbicides. Response of segregating plants to these two types of herbicide indicated that sulfonylurea sensitivity was also controlled by bel. By crossing this mutant with Pei-Ai 64S, an F(2) population was developed for genetic mapping. Surveying the two DNA pools from sensitive and non-sensitive F(2) plants identified four markers that were polymorphic between the pools. The putative linked markers were then confirmed with the F(2) population. The bel locus was located on chromosome 3, 7.1 cM from the closest microsatellite marker RM168. Phenotypic analysis indicated that the bel gene had no negative effect on agronomic traits in either a homozygous or heterozygous status. The mutant M8077S is valuable in the development of a TGMS breeding system for preventing impurity resulting from temperature fluctuation of the TGMS. Several two-line hybrid rice crosses using this system are under development.

Molecular mapping of the reverse thermo-sensitive genic male-sterile gene (rtms1) in rice

TGMS (thermo-sensitive genic male-sterile) rice is widely used in hybrid rice production. Because of a specific temperature requirement, it can be used only in a narrow rice-growing zone in Asia. A newly discovered reverse thermo-sensitive genic male-sterile line, J207S, has an opposite phynotype compared to the normal TGMS lines. J207S is completely sterile when the temperature is lower than 31°C. Thus, it can be widely used in a larger area. Genetic analysis indicated that the sterility of J207S was controlled by a single recessive gene which was first named as rtms1. An F2 population from the cross between J207S and E921 was developed and used for molecular mapping of the rtms1 gene. The AFLP (amplified fragment length polymorphism) technique, combined with BSA (bulked segregant analysis), was used to screen markers linked to the target gene, and eight polymorphic AFLP loci were identified. Co-segregating analysis using the F2 population showed that two of them, Rev1 and Rev7, were closely linked to the target gene with a recombinant rate of 3.8% and 7.7%, respectively. Both Rev1 and Rev7 were found to be single-copy sequences through Southern analysis. Rev1 was subsequently mapped on chromosome 10 with a doubled-haploid mapping populations derived from the cross CT9993 × IR62266 available at Texas Tech University. RM222 and RG257 were linked to Rev1 at a distance of 11.8 cM and 4.6 cM, respectively. Additional SSR markers from the rice map of Cornell University, RFLP markers from the map of RGP in Japan and the map of Texas Tech University were selected from the region surrounding Rev1 on chromosome 10 to conduct the fine-mapping of the rtms1 gene. Presently, rtms1 was mapped between RM239 and RG257 with genetic distance of 3.6 cM and 4.0 cM, respectively. The most-closely linked AFLP marker, Rev1, 4.2 cM from the rtms1 gene, was sequenced and converted into a SCAR (sequence characterized amplified region) marker which could facilitate marker-assisted selection of the rtms1 gene.

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.

Genetics of thermosensitive genic male sterile lines in rice

Genetics of thermosensitive genic male sterile lines in rice