Mapping a Novel Gene of Cold Tolerance at Booting Stage by Using Near-Isogenic Lines in japonica Rice

Genetic analysis showed that cold tolerance at booting stage of near-isogenic lines （NILs） of Kunmingxiaobaigu was controlled by a gene with large phenotypic variance. One hundred and sixty-four simple sequence repeats （SSR） distributed over 12 chromosomes were used to screen polymorphism between Towata （recurrent parent, RP） and near-isogenic line pool （NILP）, and two SSR markers at the long arm of chromosome 5 showed polymorphism in comparison with RP genome. Of the two markers, RM31 was found possibly linked with the cold tolerance gene at booting stage through one-way ANOVA. Twelve SSR markers around RM31 were then used to detect polymorphism between RP and NIL, and only RM7452 had polymorphism. The gene of cold tolerance at booting stage was further mapped on chromosome 5 between RM7452 and RM31 with genetic distances of 4.8 cM and 8.0 cM, respectively. This gene explained 10.50% of phenotypic variance and 5.10% of phenotypic variance of fully filled grains, and was tentatively designated as Ctb（t）.

Virulence of Xanthomonas oryzae pv. oryzae on Rice Near-Isogenic Lines with Single Resistance Gene and Pyramiding Lines in China

Ninety one isolates of Xanthomonas oryzae pv. oryzae were collected from different rice- growing regions in China and determined for their virulence on 24 rice near-isogenic lines containing single resistance gene and 2-4 genes: IRBB1 (Xa1), IRBB2 (Xa2), IRBB3 (Xa3), IRBB4 (Xa4), IRBB5 (xa5), IRBB7 (Xa7), IRBB8 (xa8), IRBB10 (Xa10), IRBB11 (Xa11), IRBB13 (xa13), IRBB14 (Xa14), IRBB21 (Xa21), IR24 (Xa18), IRBB50 (Xa4 + xa5), IRBB51 (Xa4 + xa13), IRBB52 (Xa4 + Xa21), IRBB53 (xa5 + xa13), IRBB54 (xa5 + Xa21), IRBB55 (xa13 + Xa21), IRBB56 (Xa4 + xa5 + xa13), IRBB57 (Xa4 + xa5 + Xa21), IRBB58 (Xa4 + xa13 + Xa21), IRBB59 (xa5 + xa13 + Xa21) and IRBB60 (Xa4 + xa5 + xa13 + Xa21). The results showed that most isolates were less virulent on lines with more than one genes pyramided than those with single resistance gene. The isolates tested were more virulent on IR24 and IRBB10, less virulent on IRBB5, IRBB7 and IRBB21. Based on interactions between isolates and rice near-isogenic lines, 7 cultivars with single gene (IRBB5, IRBB4, IRBB3, IRBB14, IRBB2, IRBB1 and IR24) were chosen as the differentials, and the tested isolates were classified into 7 virulence groups. The reaction patterns of the 7 groups in order were: RRRRRRR, RRRRRRS, RRRRRSS, RR/SRRSSS, RRRSSSS, RRSSSSS, RSSSSSS. The virulence frequencies were 7.69, 6.59, 14.29, 12.09, 14.29, 28.57 and 16.48% respectively. The elementary system for races identification has been established in China based on the results. It will be possible to compare with races in other countries, and the results will facilitate the development of rice resistance breeding to bacterial blight in China.

Physiological Macro-lesions Enhanced Resistance to Blast (Magnaporthe grisea) in Rice Near-isogenic Lines

Roll-leaf-1 （rl-1） and spot-leaf-1 （spl-1） were two near-isogenic lines, which were obtained after 3 to 4 backcrosses with early season indica rice Zhefu 802 as recurrent parent. Henna macro-lesions, referred as physiological or morphological markers, began to appear on leaves at 4.5- to 6.0-leaf stage. The rice seedlings were inoculated at 3.5-, 5.0- and 7.0-leaf stages with high pathogenic races Zhong A1 and Zhong B1 of Magnaporthe grisea, respectively. The resistance of rl-1, spl-1 and Zhefu 802 against blast was significantly different. The seedlings of Zhefu 802 at 3.5- to 7.0-leaf stage were susceptible to races Zhong A1 and Zhong B1 of M. grisea, whereas those of rl-1 and spl-1 at 3.5-, 5.0- and 7.0-leaf stages were susceptible, moderately resistant and resistant, respectively. These results suggested that the enhanced resistance of rl-1 and spl-1 related to the appearance of their morphological marker lesions. The experiment provided a basis for studying lesion mimic and hypersensitive response in association with disease resistance.

Analysis of Introgressed Segments in Near-isogenic Lines for F_1 Pollen Sterility in Rice (Oryza sativa)

One hundred and fifty-eight microsatellite markers showing polymorphism among parents were used to survey the introgressed segments in the 50 near-isogenic lines of F_1 pollen sterility. Two hundred and sixty introgressed segments were detected in 50 near-isogenic lines, each carrying 5.2 introgressed segments on an average. Among the 260 segments, one hundred carrying F_1 pollen sterility loci concentrated on the region of F_1 pollen sterility genes, and the remaining one hundred and sixty without F_1 pollen sterility loci distributed randomly over 12 chromosomes. Both the average number and length of the introgressed segments decreased along with the increase of backcross generations. The number of introgressed segments was less than four and the length was less than 20 cM in the near-isogenic lines after backcrossing for four or more times.

Breeding of near-isogenic japonica rice lines with three major genes for resistance to bacterial blight

From 1986 to 1993, a set of near-isogenic japonicarice Iines with three major genes Xα-3, Xα - 4,and Xα-12 for resistance to bacterial blight(Xan-thomonas oryzae pv.oryzae)were developed anddesignated as CBB3, CBB4, and CBB12 respective-

Development of Chinese Near-isogenic Line of Rice and Their Differentiating Ability of Pathogenic Races of Blast Fungus

The rice( Oryza L. ) variety, Lijiangxintuanheigu(LTH), is a universally susceptible variety. A set of near-isogenic lines (NILs) of rice which has single resistance gene for each line was developed by use of LTH as recurrent parent and Kusabue,Tsuyuake, K1, PiNo. 4, K60 and BL1, which are from Kiyosawa's differential varieties(KDV), as donor parents. Differentiating ability of these NILs to Philippine isolates was compared with that of their donor parents, KDV and IRRI' s NILs. The results of comparative studies were as follows: (1) Differentiating ability of Chinese NILs to Philippine isolates was much stronger than that of their donor parents and that of KDV. (2) Chinese NILs had similar ability to differentiate races to IRRI's NILs or higher differentiating ability than them. But IRRI's NILs almost had no differentiating ability to isolates from japonica rice-growing regions. They can not be used to differentiate races of isolates from japonica ricegrowing regions. Whereas, Chinese NILs can be used to differentiate races of isolates from both japonica ricegrowing regions and indica rice-growing regions. It was concluded that the set of Chinese NILs can be used as international differentials.

Effect of high-molecular-weight glutenin subunit deletion on soft wheat quality properties and sugar-snap cookie quality estimated through near-isogenic lines

High-molecular-weight glutenin subunits（HMW-GSs） play a critical role in determining the viscoelastic properties of wheat dough. The HMW-GSs are encoded by Glu-A1, Glu-B1, and Glu-D1 loci on the long arms of chromosomes 1A, 1B, and 1D, respectively. In the present study, four near-isogenic lines with different HMW-GS deletions and compositions at the Glu-A1 and Glu-D1 loci in Yangmai 18 background were used for quality analysis. Deletion in Glu-D1 showed much weaker gluten quality and dough strength than null Glu-A1 genotype and wild genotype（WT）, based on the measurements of sodium dodecyl sulfate（SDS）-sedimentation, lactic acid solvent retention capacity（SRC）, gluten index, development time, stability time, and alveograph P and L values. The deletion of Glu-D1 did not significantly affect grain hardness, grain protein content, water SRC, sodium carbonate SRC, and sucrose SRC. Double null genotype in Glu-A1 and Glu-D1 and single null genotype in Glu-D1 showed significantly higher cookie diameter, crispness, and lower cookie height compared with single null genotype in Glu-A1 and WT. These indicate that the null Glu-D1 genotype is useful for improvement of biscuit quality, and use of this germplasm would be a viable strategy to develop new wheat varieties for biscuit processing.

Characterization of Fertility Alteration in 8 Environment-sensitive Genic Male-sterile Lines of indica Rice

Eight indica ( Oryza sativa L.) environment-sensitive genic male-sterile (EGMS) lines, 2-2S, K1405S, F131S, 2136S, Pei-Ai 64S, 1290S, GD-IS and N17S, were sequentially seeded with 10-15 d interval at three sites, Wuhan in 1997, Guiyang in 1997 and Sanya in 1997 and 1998, China. The results of investigations on self-sterilities showed that all of eight EGMS lines had stable sterile periods of longer than 30 d at Wuhan. They can be used for seed production of two-line hybrid rice, but can not reproduce themselves. Their stable sterile periods were shorter than 30 d at Guiyang, they can reproduce themselves and can not be used for hybrid seed production. In Sanya, their stable sterile periods were longer than 150 d, all of eight lines can be used for seed production in summer and autumn and reproduce themselves in winter. The fertility of all eight lines were sensitive to temperature. The sensitive stages, sensitive duration and critical point of temperatures (CPT) of fertility alteration in various lines were different. The sensitive stages of 2-2S and K1405S were from 18 d to 9 d before heading, the sensitive durations were 7-10 d and the CPTs were 23.7-24.5 degreesC. The sensitive stage, sensitive duration and CPT of F131S were from 17 to 5 d before heading, 13 d and 24.3-24.7 degreesC, respectively. The sensitive stage, sensitive duration and CPT of 2136S were from 18 to 12 d before heading, 7 d and 24.6-25.1 degreesC:, respectively. The sensitive stages, sensitive durations of Pei-Ai 64S, 1290S, N17S and GD-1S were from 24 to 13 d before heading and 10-13 d. And their CPTs were 24.6-25.1 degreesC, 25.5-26.2 degreesC, 25.4-26.1 degreesC,, and 24.1-24.7 degreesC, respectively.

Development of Isogenic Lines of Morphological Markers in Indica Rice

A total of 28 accessions of rice (Oryza sativa L.) germplasms were collected from International Rice Research Institute (IRRI), Philippine and Gene Pool of China National Rice Research Institute (CNRRI). These germplasms were attributed as a Donor Gene Pool, consisting of 27 diverse morphological marker lines with each having a unique valuable trait (gene), and the recurrent parent-Zhefu 802, an early-season indica cultivar in south of China in the 1980s and 1990s. A set of 27 isogenic lines with 2-3 markers on every chromosome were obtained after more than 10 successive backcrosses. Moreover, 15 accessions of double-marker isogenic lines were developed by further pyramiding markers on the same chromosome. Key agronomic traits such as heading date, plant height, tillering number and panicle length in this set of lines were similar to that of Zhefu 802 except the marker traits.

Correlation between Stigma Characteristics and Outcrossing Rate of Five Photo-thermo Sensitive Genic Male Sterile(PTGMS) Rice Lines

[Objective] This study aimed to investigate the correlation between stigma characteristics and outcrossing rate of photo-thermo sensitive genic male sterile（PTGMS） rice lines. [Method] The stigma exsertion rate, stigma size and stigma vitality of Chuang 5S, Yun 9S, Peiai 64 S, P88 S and Y58 S were analyzed. Using R608 as a male parent, outcrossing rate of these five PTGMS lines was determined. [Result]There were differences in stigma exsertion rate, stigma size and stigma vitality among five PTGMS lines. P88 S exhibited the best stigma characteristics and relatively strong stigma vitality, with the stigma exsertion rate of 95.94%, stigma vitality coefficient of 2.71, outcrossing rate of 84.02% in the field. Peiai 64 s had the minimum stigma length（2.41 mm） and stigma width（1.10 mm） and the weakest stigma vitality, with the stigma exsertion rate of 93.04%, outcrossing rate of 65.47%. Yun 9S,Y58 S and Chuang 5S displayed medium stigma characteristics, among which Yun9 S exhibited higher outcrossing rate than other two PTGMS lines. Correlation analysis showed that stigma exsertion rate, stigma length, stigma width, stigma area and stigma volume were significantly correlated to outcrossing rate（P〈0.05）, with correlation coefficients of 0.897, 0.934, 0.934, 0.939 and 0.937, respectively. However,there was no significant correlation between stigma vitality coefficient and outcrossing rate. [Conclusion] Based on stigma characteristics of five PTGMS lines, auxiliary pollination measures should be adopted reasonably to save production costs and improve hybrid rice seed yield.

Mapping of QTLs Related to Grain Weight Using Chromosome Single Segment Substitution Lines in Rice

Grain weight, one of the major factors determining rice yield, is a typical quantitative trait control ed by multiple genes. With Guangluai 4 as recipient and Nipponbare as donor, a population of 119 chromosome single segment substitution lines had been developed. Correlation analysis between grain weight and grain shape by SPSS revealed that 1 000-grain weight shared extremely significant posi-tive correlation with grain length and length-width ratio, but no significant correlation with grain width and thickness. The QTL analysis of grain weight was carried out using one-way analysis of variance and Dunnett＇s test. Nineteen stable QTLs re-sponsible for grain weight were identified over two years. Al 19 QTLs were identi-fied on al chromosomes except for chromosome 10 and 12 at a significance level of P≤0.001. Among them, 10 QTLs had a positive effect and were derived from the Nipponbare al ele, the additive effect of these QTLs ranged from 0.49 to 2.74 g, and the contributions of the additive effects ranged from 2.00% to 11.05%. Another 9 QTLs had a negative effect and were al derived from Guangluai 4 al ele, the ad-ditive effect of these QTLs ranged from 0.60 to 2.35 g, and the contributions of the additive effects ranged from 2.40% to 9.84%. The results provide a basis for the fine mapping and gene cloning of novel locus associated with rice grain weight.

Combining Ability Analysis on Yield Traits of Recombinant Inbred Lines in Hybrid Rice

A population of 140 recombinant inbred lines at F8 generation were obtained after seven successive generations of self-pollination using single seed descent（SSD） method from the F2 hybrids of three-line restorers Luhui 8258 with high combining ability and Yanghui 34. Then, the 140 inbred lines obtained above and their parents Luhui 8258 and Yanghui 34 were crossed with three different types of cyto-plasmic male sterile（CMS） lines（Gang 46 A, Ⅱ-32 A and Lu 98A） according to NCⅡ design. The resulting 426 combinations were planted at Deyang and Suining bases to test the combining ability and inheritance of five yield traits： yield per plant, panicle number per plant, filled grain number per panicle, seed setting rate and 1 000-grain weight. The results showed that the variances of both general and specific combining abilities of the five traits all reached a significant or extremely significant level at the two sites. The broad and narrow heritability of the yield traits（except 1 000-grain weight whose broad and narrow heritability were both over70%） were all below 50% at the two experimental bases, suggesting that the four traits were easily subjected to environment influence. Very significant positive correlation of general combining ability was found between yield per plant and other traits except 1 000-grain weight. The general combining ability variance showed a normal distribution among the recombinant inbred lines at two sites, right in line with inheritance of quantitative traits. So, the genes controlling rice general combining ability can be targeted by QTL mapping.

Flowering Characteristics of Japonica Rice Male Sterile Lines Adaptive to High Temperature and Summer Drought

[Objective] This study was conducted to screen japonica rice male sterile lines with good flowering characteristics under high temperature and summer drought. [Method] The flowering habits of 23 japonica male sterile lines, such as flowering peak, single-panicle flowering duration, single-plant flowering duration, en- closed glume rate, glume-opening angle, the distance between glumes, stigma exer- tion rate and sigma vitality, were compared with II-32A as a control under above weather condition. [Result] The flowering characteristics had significant difference a- mong the tested rice lines. Compared with the control, three japonica rice male ster- ile lines 35478A, 35489A and 35502A had better flowering traits, such as earlier flowering peak, longer single-panicle flowering duration, longer single-plant flowering duration, lower rate of enclosed glumes, larger glume angle and larger distance be- tween glumes. 35478A performed its flowering peak from 10：00-11：00 am, 1.5 h earlier than the control; 35489A exhibited higher stigma exertion rate, up to 76.23%; and 35502A had higher stigma vitality, up to 84.68%, which kept longer time than that of the CK. [Conclusion] The results will provide high-quality resources for the breeding of new japonica rice varieties with high-yield and high-temperature toler- ance.

Effect of Enhanced UV-B Radiation on Seed Setting Rate and 1 000-grain Weight of Indica Hybrid Rice Restorer Lines

[Objective] This study was to investigate the effect of enhanced UV-B radiation on seed setting rate and 1 000-grain weight of hybrid rice combinations. [Method] The seed setting rate and 1 000-grain weight of 10 new sterile indica restorer lines planted in pots under enhanced UV-B radiation and fluorescent lamps （control） were respectively measured, and the differences were compared. [Result] The enhanced UV-B radiation significantly reduced the seed setting rate of indica restorer lines, and the differences between that UV-B radiation treatment and control all reached extremely significant level. In addition, the enhanced UV-B radiation reduced the 1 000-grain weight of most indica restorer lines, and compared with that of control the difference achieved significant or very significant level. However, the effect of enhanced UV-B radiation on seed setting rate and 1 000-grain weight differed to different indica restorer lines, and the differences among restorer lines tested were significant or very significant, which indicated the possibility to screen antiUV-B radiation rice materials and combinations. Finally, the indica restorer lines 09R-14, Luhui 37 and 10R-7703 which were strongly resistant to UV-B radiation were screened out. [Conclusion] This study laid foundation for breeding hybrid rice varieties resistance to UV-B radiation.

Effect of High Temperature on Outcrossing Characteristics at the Fertility Sensitive Period of Photo-thermo Sensitive Genic Male Sterile (PTGMS) Rice Lines

Four sterile lines （Peiai64S, Y58S, Guangzhan 63-2S and H638S） and the restoring line R527 were used as materials. Five temperature gradients （24, 27, 30, 33 and 36 ℃ in artificial climate chamber） and the natural temperature （as control） were treated to the four sterile lines for 6 d in the fertility sensitive period of heading to flowering stage, respectively, to study the effects of temperature on physiological biochemical characteristics of young panicles and outcrossing characteristics. The results showed that the percentages of exerted stigma of Peiai 64S and Y58S were the highest at 27 ℃, which were 86.81% and 86.06%, respectively, while the percentages of exerted stigma of Guangzhan 63-2S and H638S were the highest at 24 ℃, which were 76.24% and 81.76%, respectively; the stigma viability of Peiai 64S, Y58S, Guangzhan 63-2S and H638S were the best at 24 ℃, which were 1.96, 2.12, 1.74 and 1.94, respectively; the outcrossing rates of Peiai 64S, Guangzhan 63-2S and H638S were the highest at 24 ℃, which were 58.87%, 54.22% and 50.50%, respectively, while the outcrossing rate of Y58S was the highest at 27 ℃, which was 58.96%; and the contents of peroxidase （POD） of the four sterile lines increased significantly at 33 ℃ compared with the control, while the contents of malondialdehyde （MDA） and proline increased significantly at 36 ℃ compared with the control. There were differences in temperature sensitivity between the male sterile lines, and the 24 ℃ treatment during the sensitive period was the best for the fertility sensitive period of Peiai 64S, while 27 ℃ was the best temperature for Y58S, Gangzhan 63-2S and H638S.

QTLs Mapping for Salinity Tolerance at Seedling Stage or Rice(Oryza sativa L.) Using Chromosome Segment Substitution Lines

In this study, a population of chromosome segment substitution lines （CSSLs） derived from the cross between 9311 （indica） and Nipponbare （japonica） was employed to map the quantitative trait loci （QTLs） for salt tolerance under the salt stress simulated with 0.5% NaCI, using survival rate as the index. The data were analyzed by QTL IciMapping v3.1, and the results showed that one QTL （QSsr3） related to salt tolerance was located in the vicinity of the marker RM1350 on chromosome 3, into a genetic interval of 113.2-132.8 cM, with a contribution rate of 17.75%. The additive effect was 10.9, indicating that the QTL derived from the parent Nipponbare improved the salt tolerance of rice at seedling stage. This study will provide a theoretical basis for the selection of salt tolerant rice germplasm.

Mapping QTLs Associated with Sheath Blight Resistance Using Chromosome Segment Substitution Lines of Rice(Oryza sativa L.)

In this study, a population of 119 chromosome segment substitution lines （CSSLs） derived from backcross between indica 9311 and japonica Nipponbare was employed to map quantitative trait loci （QTL） associated with sheath blight resis-tance in rice with toothpick inoculation method. A total of three sheath blight resis-tance-associated QTLs （qsb8-1, qsb8-2 and qsb8-3） were identified, which were lo-cated on adjacent molecular markers RM3262, RM5485 and RM3496 of chromo-some 8; the genetic interval was 81.7cM-91.7cM, 91.7cM-108.1cM and 108.1cM-119.6cM, respectively. The additive effect of qsb8-2 was negative, indicating that sheath blight resistance of susceptible parent harboring qsb8-2 fragment was en-hanced; additive effects of qsb8-1 and qsb8-3 were positive, indicating that sheath blight resistance of susceptible parent harboring qsb8-1 and qsb8-3 fragments was reduced.

Characterization and evaluation of rice blast resistance of Chinese indica hybrid rice parental lines

The development of resistant varieties and hybrid combinations has been the most effective and economical strategy to control blast disease caused by Magnaporthe oryzae.However, the distribution of major R genes and blast resistance characterization in hybrid rice parents has not been well investigated, resulting in their limited use in hybrid rice blast-resistance breeding. In the present study, 88 elite indica hybrid rice parental lines were evaluated with 30 isolates of M. oryzae collected from the main planting area of indica hybrid rice in China and were characterized for the presence of 11 major resistance genes using molecular markers. The pathogenicity assays showed that four types of hybrid rice parent line showed some resistance to M. oryzae. However, the proportions of highly resistant lines and the mean resistance frequency(RF) varied among the four types, with resistance in decreasing order shown by three-line restorer lines, three-line maintainer lines, two-line sterile lines, and two-line restorer lines. All 88 hybrid rice parental lines carried more than one R gene, but none carried the R genes Pi1 and Pi2. Although Pid3 and Pi9 were present only in three-line restorer lines and Pigm only in three-line maintainer lines, the remaining six R genes(Pib, Pid2, Pi5, Pia, Pi54, and Pita) were present in the four types of hybrid rice parent with significantly different distribution frequencies. The correlation between R genes and resistance reactions was investigated. The results are expected to provide useful information for rational utilization of major R genes in hybrid rice breeding programs.

Characterization of QTL for unique agronomic traits of new-plant-type rice varieties using introgression lines of IR64

To enhance the yield potential of an elite indica rice cultivar,an introgression(BC_3-derived) line of IR64,YTH288,was developed using a new-plant-type cultivar,IR66215-44-2-3,as a donor parent.YTH288 has agronomically valuable characteristics such as large panicles,few unproductive tillers,and large leaves inherited from NPT.To identify the genetic basis of these traits,we used 167 F_2 plants derived from a cross between IR64 and YTH288 to conduct QTL analysis for five agronomic traits:days to heading(DTH),culm length(CL),flag leaf length(FLL),flag leaf width(FLW),and filled spikelet number per panicle(FSN).Six putative QTL were detected:four on chromosome4(for CL,FLL,FLW,and FSN) and two on chromosome 2(for DTH and FLL).All QTL with the IR66215-44-2-3 allele,except that for FLL on chromosome 2,had positive effects on each trait.To confirm the effects of these putative QTL,we developed NILs with the IR64 genetic background by marker-assisted selection.We observed significant differences in several agronomic traits between IR64 and NILs that carried these QTL on chromosomes2 and 4.Additionally,four IR64-NILs carrying chromosomal segments derived from different NPT varieties on the long arm of chromosome 4 exhibited similar pleiotropic To enhance the yield potential of an elite indica rice cultivar, an introgression(BC3-derived) line of IR64, YTH288, was developed using a new-plant-type cultivar,IR66215-44-2-3, as a donor parent. YTH288 has agronomically valuable characteristics such as large panicles, few unproductive tillers, and large leaves inherited from NPT.To identify the genetic basis of these traits, we used 167 F2 plants derived from a cross between IR64 and YTH288 to conduct QTL analysis for five agronomic traits: days to heading(DTH), culm length(CL), flag leaf length(FLL), flag leaf width(FLW), and filled spikelet number per panicle(FSN). Six putative QTL were detected: four on chromosome4(for CL, FLL, FLW, and FSN) and two on chromosome 2(for DTH and FLL). All QTL with the IR66215-44-2-3 allele, except that for FLL on chromosome 2, had positive effects on each trait. To confirm the effects of these putative QTL, we developed NILs with the IR64 genetic background by marker-assisted selection. We observed significant differences in several agronomic traits between IR64 and NILs that carried these QTL on chromosomes2 and 4. Additionally, four IR64-NILs carrying chromosomal segments derived from different NPT varieties on the long arm of chromosome 4 exhibited similar pleiotropiceffects for unique agronomic traits. These NILs can be used as research materials for studying each trait and as breeding materials for yield improvement of indica rice cultivars.

Thermal Resistance of Common Rice Maintainer and Restorer Lines to High Temperature During Flowering and Early Grain Filling Stages

Fifteen common rice maintainer lines and 26 high-yielding restorer lines were used to evaluate their thermal resistance and fertility during flowering and early grain filling stages. The rice plants were subjected to high temperature stress （39-43 ℃） for 1-15 d from main stem flowering. Based on the heat stress index, they were divided into thermal resistant lines, semi-thermal resistant lines, semi-thermal sensitive lines and thermal sensitive lines. Therefore, the maintainer lines K22B, Bobai B and V20B belonged to thermal resistant lines, whereas 11-32B, Zhongzhe B and Zhong 9B belonged to thermal sensitive lines. For rice restorer lines, Minghui 63 had the highest thermal resistance, followed by R207, P32, P929, and the lowest thermal resistant lines P62-2-2, R8006 and P51. The correlation analysis indicated that the heat stress index was significantly correlated with seed-setting rate and abortive grain rate under heat stress, but not under natural conditions. This indicated that heat stress occurred during flowering and early grain filling stages mainly decreased the seed- setting rate and significantly increased the abortive grain rate in both rice maintainer and restorer lines.