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1.
 The partial sterility of hybrids between the indica and japonica rice subspecies of Asian cultivated rice is a serious constraint for utilizing inter-subspecific heterosis in hybrid rice breeding. In this study, we have investigated the relationship between molecular-marker polymorphism and indica-japonica hybrid fertility using a diallel set involving 20 rice accessions including 9 indica and 11 japonica varieties. Spikelet fertility of the resulting 190 F1s and their parents was examined in a replicated field trial. Intra-subspecific hybrids showed much higher spikelet fertility than inter-subspecific hybrids except in crosses involving wide-compatibility varieties. The parents were surveyed for DNA polymorphism using 96 RFLP and ten SSR markers, which revealed extensive genetic differentiation between indica and japonica varieties. A large number of markers detected highly significant effects on hybrid fertility. The chromosomal locations for many of the positive markers coincided well with previously identified loci for hybrid sterility. The correlation between hybrid fertility and parental distance was low in both intra- and inter-subspecific crosses. The results suggest that the genetic basis of indica-japonica hybrid sterility is complex. It is the qualitative, rather than the quantitative, difference between the parents that determines the fertility of hybrids. Received: 3 January 1997/Accepted: 17 January 1997  相似文献   

2.
The most important concerns of hybrid rice breeders are selection of donors to improve parental lines and prediction of hybrid performance. In this study, SSR molecular marker technology and a half-diallel method were used to address these related hybrid production issues. The results show that genetic diversity among the parental lines is certainly related to heterosis. The heterozygosity of each parental pair is significantly associated with the general combining ability, not with the specific combining ability. However, neither genetic diversity nor heterozygosity is a good indicator for predicting heterosis. From these results, it is suggested that donors for improving parents of hybrids be selected from the improved inbred lines by conventional breeding programs. In this investigation, we also discovered that four favorable alleles and six favorable heterogenic patterns on the parental lines significantly contribute to the heterosis of their hybrids in grain yield, whereas six unfavorable alleles and six unfavorable heterogenic patterns significantly reduce heterosis. These noticeable findings could be, in practice, useful for hybrid rice breeding programs with SSR marker-assisted selection. It is suggested that the optimal combinations with the superior grain yield could be bred out by assembling those favorable alleles into their parental lines and by removing the unfavorable alleles from the parental lines. This study also indicates that there is still a great heterosis potential to be exploited in indica/indica hybrids by the same strategy. In indica/japonica hybrid breeding programs, it may also be important to remove unfavorable alleles rather than broaden genetic diversity or heterozygosity of the parents.  相似文献   

3.
Molecular divergence and hybrid performance in rice   总被引:42,自引:0,他引:42  
This study was undertaken to determine the relationship between genetic distance of the parents based on molecular markers and F1 performance in a set of diallel crosses involving eight commonly used parental lines in hybrid rice production. The F1s and their parents were measured for five traits including heading date, plant height, straw weight, grain yield and biomass. The parental lines were assayed for DNA polymorphisms using two classes of markers: 140 probes for restriction fragment length polymorphisms (RFLPs) and 12 simple sequence repeats (SSRs), resulting in a total of 105 polymorphic markers well spaced along the 12 rice chromosomes. SSRs detected more polymorphism than RFLPs among the eight lines. A cluster analysis based on marker genotypes separated these eight lines into three groups which agree essentially with the available pedigree information. Correlations were mostly low between general heterozygosity based on all the markers and F1 performance and heterosis. In contrast, very high correlations were detected between midparent heterosis and specific heterozygosity based on the markers that detected significant effects for all the five traits; these correlations may have practical utility in predicting heterosis. The analyses also suggest the existence of two likely heterotic groups in the rice germplasm represented by these eight lines.  相似文献   

4.
Li ZK  Luo LJ  Mei HW  Wang DL  Shu QY  Tabien R  Zhong DB  Ying CS  Stansel JW  Khush GS  Paterson AH 《Genetics》2001,158(4):1737-1753
To understand the genetic basis of inbreeding depression and heterosis in rice, main-effect and epistatic QTL associated with inbreeding depression and heterosis for grain yield and biomass in five related rice mapping populations were investigated using a complete RFLP linkage map of 182 markers, replicated phenotyping experiments, and the mixed model approach. The mapping populations included 254 F(10) recombinant inbred lines derived from a cross between Lemont (japonica) and Teqing (indica) and two BC and two testcross hybrid populations derived from crosses between the RILs and their parents plus two testers (Zhong 413 and IR64). For both BY and GY, there was significant inbreeding depression detected in the RI population and a high level of heterosis in each of the BC and testcross hybrid populations. The mean performance of the BC or testcross hybrids was largely determined by their heterosis measurements. The hybrid breakdown (part of inbreeding depression) values of individual RILs were negatively associated with the heterosis measurements of their BC or testcross hybrids, indicating the partial genetic overlap of genes causing hybrid breakdown and heterosis in rice. A large number of epistatic QTL pairs and a few main-effect QTL were identified, which were responsible for >65% of the phenotypic variation of BY and GY in each of the populations with the former explaining a much greater portion of the variation. Two conclusions concerning the loci associated with inbreeding depression and heterosis in rice were reached from our results. First, most QTL associated with inbreeding depression and heterosis in rice appeared to be involved in epistasis. Second, most ( approximately 90%) QTL contributing to heterosis appeared to be overdominant. These observations tend to implicate epistasis and overdominance, rather than dominance, as the major genetic basis of heterosis in rice. The implications of our results in rice evolution and improvement are discussed.  相似文献   

5.
 This study was intended to investigate the extent of genetic differentiation in parental lines of rice hybrids and to analyze the genetic basis underlying the fertility phenomenon in distant crosses. Two subsets of rice material (111 entries in total) were used, including 81 doubled-haploid (DH) lines and 30 Indica and Japonica rice varieties or lines (as a control). The DH lines was derived from a heterotic Indica/Japonica cross (Gui630/02428) by anther culture. The materials in the control represent a broad spectrum of the Asian cultivated rice gene pool including landraces, primitive cultivars, historically important cultivars, modern elite cultivars, super rice and parents of superior hybrids. In accordance with the NC II design, 57 out of the DH lines were test-crossed to two important wide compatibility lines: photoperiod-sensitive genetic male sterile (PGMS) line N422s and thermo-sensitive genetic male sterile (TGMS) line Peiai64s. The F1s and their parents, 182 entries in total, were examined for the performance of seven traits in a replicated field trial. All the rice materials was surveyed for polymorphisms using 92 RFLP markers selected from two published molecular marker linkage maps. Genotypes of the F1 hybrids at the molecular-marker loci were deduced from the parental genotypes. The analysis showed that there were two types of genetic differentiation in the two subsets of rice material; that is, qualitative differentiation in the control and quantitative differentiation in the DH lines. In addition, favorable genic interactions (both intra- or inter-locus) contributed to better increase the fertility in hybrids of distant crosses through incorporation of a wide-compatibility line as the female parent. Favorable genic interactions can be applied in hybrid rice breeding programs by selecting parents with an appropriate extent of genetic differentiation. Received: 5 June 1997 / Accepted: 10 September 1997  相似文献   

6.
The magnitude of heterosis in F1 hybrids is related not only to the performance of parents per se but also to the genetic diversity between two parents. The extent of genotypic divergence between hybrid rice parents was investigated at the molecular level, using two subsets of rice materials: a subset of doubled haploid (DH) lines derived from an Indica × Japonica cross (Gui630/02428) and another subset of Indica or Japonica lines representative of a broad spectrum of the Asian cultivated rice gene pool, including landraces, primitive cultivars, historically important cultivars, modern elite cultivars, super rice and parents of superior hybrids. 57 entries deliberately selected from the 81-DH lines (in total) were testcrossed to two widely used rice lines in China, photoperiod-sensitive genic male sterile (PGMS) N422s and thermo-sensitive genic male sterile (TGMS) Peiai64s. Results of the two sets of test-cross F1 populations showed congruently that parental genotypic divergence has a relatively low impact on heterosis for the two yield components, i.e., panicle number and 1000-grain weight, but it has a great bearing on fertility parameters, i.e., filled grains per plant and seedset. Heterosis for grain yield in the two test-cross populations exhibited a sharp maximum when the proportion of Japonica alleles in the male parent was between 50 and 60%, so was the heterosis for fertility parameters correspondingly. Thus fertility parameters were the most sensitive and important factors which were influenced by the extent of parental genotypic divergence. Moreover, our results showed that parents with moderate extent of genotypic divergence played an important role in the use of inter-subspecific rice heterosis.  相似文献   

7.
Hybrid rice has contributed significantly to the dramatic increase of rice production in the world. Despite this, little attention has been given to studying the genetic basis of heterosis in rice. In this paper, we report a diallel analysis of heterosis using two classes of molecular markers: restriction fragment length polymorphisms, (RFLPs) and microsatellites. Eight lines, which represent a significant portion of hybrid rice germ plasm, were crossed in all possible pairs, and the F1s were evaluated for yield and yield component traits in a replicated field trial. The parental lines were surveyed for polymorphisms with 117 RFLP probes and ten microsatellites, resulting in a total of 76 polymorphic markers well-spaced in the rice RFLP map. The results indicated that high level heterosis is common among these crosses: more than 100% midparent and 40% better-parent heterosis were observed in many F1s, including some crosses between maintainer lines. Heterosis was found to be much higher for yield than for yield component traits, which fits a multiplicative model almost perfectly. Between 16 and 30 marker loci (positive markers) detected highly significant effects on yield or its component traits. Heterozygosity was significantly correlated with several attributes of performance and heterosis. Correlations based on positive markers (specific heterozygosity) were large for midparent heterosis of yield and seeds/panicle and also for F1 kernel weight. These large correlations may have practical utility for predicting heterosis.  相似文献   

8.

Key message

Two heterotic groups and four heterotic patterns were identified for IRRI hybrid rice germplasm to develop hybrid rice in the tropics based on SSR molecular data and field trials.

Abstract

Information on heterotic groups and patterns is a fundamental prerequisite for hybrid crop breeding; however, no such clear information is available for tropical hybrid rice breeding after more than 30 years of hybrid rice commercialization. Based on a study of genetic diversity using molecular markers, 18 parents representing hybrid rice populations historically developed at the International Rice Research Institute (IRRI) were selected to form diallel crosses of hybrids and were evaluated in tropical environments. Yield, yield heterosis and combining ability were investigated with the main objectives of (1) evaluating the magnitude of yield heterosis among marker-based parental groups, (2) examining the consistency between marker-based group and heterotic performance of hybrids, and (3) identifying foundational hybrid parents in discrete germplasm pools to provide a reference for tropical indica hybrid rice breeding. Significant differences in yield, yield heterosis and combining ability were detected among parents and among hybrids. On average, the hybrids yielded 14.8 % higher than the parents. Results revealed that inter-group hybrids yielded higher, with higher yield heterosis than intra-group hybrids. Four heterotic patterns within two heterotic groups based on current IRRI B- and R-line germplasm were identified. Parents in two marker-based groups were identified with limited breeding value among current IRRI hybrid rice germplasm because of their lowest contribution to heterotic hybrids. Heterotic hybrids are significantly correlated with high-yielding parents. The efficiency of breeding heterotic hybrids could be enhanced using selected parents within identified marker-based heterotic groups. This information is useful for exploiting those widely distributed IRRI hybrid rice parents.  相似文献   

9.
Genetic distances (GDs) based on morphological characters, isozymes and storage proteins, and random amplified polymorphic DNAs (RAPD) were used to predict the performance and heterosis of crosses in oilseed rape (Brassica napus L.). Six male-sterile lines carrying the widely used Shaan2A cytoplasm were crossed with five restorer lines to produce 30 F1 hybrids. These 30 hybrids and their parents were evaluated for seven agronomically important traits and their mid-parent heterosis (MPH) at Yangling, Shaanxi province in Northwest China for 2 years. Genetic similarity among the parents based on 34 isozyme and seven protein markers was higher than that based on 136 RAPDs and/or 48 morphological markers. No significant correlation was detected among these three sets of data. Associations between the different estimates of GDs and F1 performance for some agronomic traits were significant, but not for seed yield. In order to enhance the predicting efficiency, we selected 114 significant markers and 43 favoring markers following statistical comparison of the mean values of the yield components between the heterozygous group (where the marker is present only in one parent of each hybrid) and the homozygous group (where the marker is either present or absent in both parents of each hybrid) of the 30 hybrids. Parental GD based on total polymorphic markers (GDtotal, indicating general heterozygosity), significant markers (GDsign, indicating specific heterozygosity) and favoring markers (GDfavor, indicating favoring-marker heterozygosity) were calculated. The correlation between GDfavor or GDsign and hybrid performance was higher than the correlation between GDtotal and hybrid performance. GDsign and GDfavor significantly correlated with plant height, seeds per silique and seed yield, but not with the MPH of the other six agronomic traits with the exception of plant height. The information obtained in this study on the genetic diversity of the parental lines does not appear to be reliable for predicting F1 yield and heterosis.  相似文献   

10.
Using differential display analysis, we assessed the patterns of differential gene expression in hybrids relative to their parents in a diallel cross involving 8 elite rice lines. The analysis revealed several patterns of differential expression including: (1) bands present in one parent and F1 but absent in the other parent, (2) bands observed in both parents but not in the F1, (3) bands occurring in only one parent but not in the F1 or the other parent, and, (4) bands detected only in the F1 but in neither of the parents. Relationships between differential gene expression and heterosis and marker heterozygosity were evaluated using data for RFLPs, SSRs and a number of agronomic characters. The analysis showed that there was very little correlation between patterns of differential expression and the F1 means for all six agronomic traits. Differentially expressed fragments that occurred only in one parent but not in the other parent or in F1 in each of the respective crosses were positively correlated with heterosis and heterozygosity. And conversely, fragments that were detected in F1s but in neither of the respective parents were negatively correlated with heterosis and heterozygosity. The remaining patterns of differential expression were not correlated with heterosis or heterozygosity. The relationships between the patterns of differential expression and heterosis observed in this study were not consistent with expectations based on dominance or overdominance hypotheses.  相似文献   

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