抗除草剂杂交籼稻亲本的配合力分析

本试验以6份新育成的抗除草剂籼型恢复系为父本,5份生产上广泛应用的不育系为母本,采用不完全双列杂交设计配制了30份杂交组合,对其苗期除草剂抗性和主要农艺性状配合力进行了分析。除草剂抗性鉴定表明,亲本恢复系及三系杂交组合抗性接近完全,两系杂交组合抗性达90%以上。配合力分析表明,不育系除单株有效穗数外其他农艺性状的一般配合力均达到极显著差异;恢复系间一般配合力在所有性状中均达到显著或极显著差异;杂交组合间特殊配合力方差仅在单株产量、结实率、播始历期和千粒重4个性状中达到显著或极显著差异。不育系中,金科1A在单株产量、结实率等7个性状上的一般配合力均为最高,但其特殊配合力方差最小;广占63-4S在千粒重性状上具有最高的一般配合力、最大的特殊配合力方差,在播始历期上具有最高的一般配合力负效应;C815S在株高上的一般配合力负效应最大,同时特殊配合力方差较高。恢复系中,华抗恢101在单株有效穗数上具有最高的一般配合力和特殊配合力方差;华抗恢104在穗长上具有最高的一般配合力,在播始历期上具有最高的一般配合力负效应;华抗恢105在单株产量、结实率等性状上具有最高的一般配合力,在株高上具有最高的一般配合力负效应;华抗恢106在千粒重性状上具有最高的一般配合力和特殊配合力效应方差。利用抗除草剂恢复系配制杂交组合,不仅可以改良其除草剂抗性,也可以通过广泛测配,选择一般配合力强、特殊配合力方差大的亲本配组育成强优势组合。     

Genetic distances revealed by morphological characters,isozymes, proteins and RAPD markers and their relationships with hybrid performance in oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

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 (GD_total, indicating general heterozygosity), significant markers (GD_sign, indicating specific heterozygosity) and favoring markers (GD_favor, indicating favoring-marker heterozygosity) were calculated. The correlation between GD_favor or GD_sign and hybrid performance was higher than the correlation between GD_total and hybrid performance. GD_sign and GD_favor 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.     

Differentiation and classification of parental lines and favorable genic interactions affecting F1 fertility in distant crosses of rice (Oryza sativa L.)

 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     

Interacted QTL Mapping in Partial NCII Design Provides Evidences for Breeding by Design

The utilization of heterosis in rice, maize and rapeseed has revolutionized crop production. Although elite hybrid cultivars are mainly derived from the F₁ crosses between two groups of parents, named NCII mating design, little has been known about the methodology of how interacted effects influence quantitative trait performance in the population. To bridge genetic analysis with hybrid breeding, here we integrated an interacted QTL mapping approach with breeding by design in partial NCII mating design. All the potential main and interacted effects were included in one full model. If the number of the effects is huge, bulked segregant analysis were used to test which effects were associated with the trait. All the selected effects were further shrunk by empirical Bayesian, so significant effects could be identified. A series of Monte Carlo simulations was performed to validate the new method. Furthermore, all the significant effects were used to calculate genotypic values of all the missing F₁ hybrids, and all these F₁ phenotypic or genotypic values were used to predict elite parents and parental combinations. Finally, the new method was adopted to dissect the genetic foundation of oil content in 441 rapeseed parents and 284 F₁ hybrids. As a result, 8 main-effect QTL and 37 interacted QTL were found and used to predict 10 elite restorer lines, 10 elite sterile lines and 10 elite parental crosses. Similar results across various methods and in previous studies and a high correlation coefficient (0.76) between the predicted and observed phenotypes validated the proposed method in this study.     

DNA divergence as a criterion of a sweet pepper (Capsicum annuum L.) selection for heterosis

The identification of perspective parental lines for the creation of high-yield hybrids is the most labor-consuming stage of selection, because it needs extensive trials of combining ability. Based on evaluation of the genetic divergence of the parental lines, the prediction accuracy of F₁ hybrids performance was investigated. The value of the divergence was calculated using biometric and molecular methods, such as inter simple sequence repeats (ISSR) and random amplified polymorphic DNA (RAPD). Based on estimates of divergence, 10 lines were chosen for cyclic cross (scheme I) and testcross (scheme II). In most crosses, the F₁ hybrids were significantly superior to the parents in the main economically valuable traits. The level of heterosis was higher among hybrids of scheme I. Analysis of the relationship between parental divergence and F₁ performance showed that the hybrid productivity of scheme I was predetermined by ISSR divergence in 86%, and productivity was caused by RAPD divergence in 69%, whereas the F₁ yield of scheme II was not related to the value of genetic distances. Since the values of DNA divergence were closely associated both with midparent level and F₁ performance, we assumed that part of the polymorphic DNA fragments of the parental lines of scheme I is related to heterotic loci (HTL), which may be considered potential key markers for the heterotic selection of the sweet pepper.     

Genetic diversity and its relationship to hybrid performance and heterosis in rice as revealed by PCR-based markers

Ten elite inbred lines (four japonica, six indica), chosen from those widely used in the hybrid rice breeding program at Human Hybrid Rice Research Center in China, were crossed to produce all possible hybrids excluding reciprocals. The 45 F₁ hybrids along with the ten parents were evaluated for eight traits of agronomic importance, including yield potential, in a replicated field trial. The ten parents were analyzed with 100 arbitrary decamer oligonucleotide primers and 22 microsatellite (simple sequence repeats, SSRs) primer sets via polymerase chain reaction (PCR). Out of the 100 random primers used, 74 were informative and amplified 202 non-redundant bands (variants) with a mean of 2.73 bands per polymorphic primer. All 22 microsatellite primer sets representing 23 loci in the rice genome showed polymorphisms among the ten parents and revealed 90 alleles with an average of 3.91 per SSR locus. Cluster analysis based on Nei's genetic distance calculated from the 291 (202 RAPDs, 89 SSRs) non-redundant variants separated the ten parental lines into two major groups that corresponds to indica and japonica subspecies, which is consistent with the pedigree information. Strong heterosis was observed in hybrids for most of the traits examined. For the 43 diallel crosses (excluding 2 crosses not heading), yield potential, its components (including panicles per plant, spikelets per panicle and 1000-grain weight) and their heterosis in F₁ hybrids showed a significant positive correlation with genetic distance. When separate analyses were performed for the three subsets, yield potential and its heterosis showed significant positive correlations with genetic distance for the 15 indica x indica crosses and the 6 japonica x japonica crosses; however, yield potential and its heterosis were not correlated with genetic distance for the 22 indica x japonica crosses. Results indicated that genetic distance measures based on RAPDs and SSRs may be useful for predicting yield potential and heterosis of intra-subspecific hybrids, but not inter-subspecies hybrids.     

Heterotic patterns in rapeseed (<Emphasis Type="Italic">Brassica napus</Emphasis> L.): I. Crosses between spring and Chinese semi-winter lines

Chinese semi-winter rapeseed is genetically diverse from Canadian and European spring rapeseed. This study was conducted to evaluate the potential of semi-winter rapeseed for spring rapeseed hybrid breeding, to assess the genetic effects involved, and to estimate the correlation of parental genetic distance (GD) with hybrid performance, heterosis, general combining ability (GCA) and specific combining ability (SCA) in crosses between spring and semi-winter rapeseed lines. Four spring male sterile lines from Germany and Canada as testers were crossed with 13 Chinese semi-winter rapeseed lines to develop 52 hybrids, which were evaluated together with their parents and commercial hybrids for seed yield and oil content in three sets of field trials with 8 environments in Canada and Europe. The Chinese parental lines were not adapted to local environmental conditions as demonstrated by poor seed yields per se. However, the hybrids between the Chinese parents and the adapted spring rapeseed lines exhibited high heterosis for seed yield. The average mid-parent heterosis was 15% and ca. 50% of the hybrids were superior to the respective hybrid control across three sets of field trials. Additive gene effects mainly contributed to hybrid performance since the mean squares of GCA were higher as compared to SCA. The correlation between parental GD and hybrid performance and heterosis was found to be low whereas the correlation between GCA_{(f + m)} and hybrid performance was high and significant in each set of field trials, with an average of r = 0.87 for seed yield and r = 0.89 for oil content, indicating that hybrid performance can be predicted by GCA_{(f + m)}. These results demonstrate that Chinese semi-winter rapeseed germplasm has a great potential to increase seed yield in spring rapeseed hybrid breeding programs in Canada and Europe.     

Molecular mapping and inheritance of restoration of fertility (<Emphasis Type="Italic">Rf</Emphasis>) in A4 hybrid system in pigeonpea (<Emphasis Type="Italic">Cajanus cajan</Emphasis> (L.) Millsp.)

Key message

We report molecular mapping and inheritance of restoration of fertility (Rf) in A4 hybrid system in pigeonpea. We have also developed PCR-based markers amenable to low-cost genotyping to identify fertility restorer lines.

Abstract

Commercial hybrids in pigeonpea are based on A4 cytoplasmic male sterility (CMS) system, and their fertility restoration is one of the key prerequisites for breeding. In this context, an effort has been made to understand the genetics and identify quantitative trait loci (QTL) associated with restoration of fertility (Rf). One F₂ population was developed by crossing CMS line (ICPA 2039) with fertility restorer line (ICPL 87119). Genetic analysis has shown involvement of two dominant genes in regulation of restoration of fertility. In parallel, the genotyping-by-sequencing (GBS) approach has generated ~?33 Gb data on the F₂ population. GBS data have provided 2457 single nucleotide polymorphism (SNPs) segregating across the mapping population. Based on these genotyping data, a genetic map has been developed with 306 SNPs covering a total length 981.9 cM. Further QTL analysis has provided the region flanked by S8_7664779 and S8_6474381 on CcLG08 harboured major QTL explained up to 28.5% phenotypic variation. Subsequently, sequence information within the major QTLs was compared between the maintainer and the restorer lines. From this sequence information, we have developed two PCR-based markers for identification of restorer lines from non-restorer lines and validated them on parental lines of hybrids as well as on another F₂ mapping population. The results obtained in this study are expected to enhance the efficiency of selection for the identification of restorer lines in hybrid breeding and may reduce traditional time-consuming phenotyping activities.

     

Bayesian QTL mapping using genome-wide SSR markers and segregating population derived from a cross of two commercial F<Subscript>1</Subscript> hybrids of tomato

Key message

Using newly developed euchromatin-derived genomic SSR markers and a flexible Bayesian mapping method, 13 significant agricultural QTLs were identified in a segregating population derived from a four-way cross of tomato.

Abstract

So far, many QTL mapping studies in tomato have been performed for progeny obtained from crosses between two genetically distant parents, e.g., domesticated tomatoes and wild relatives. However, QTL information of quantitative traits related to yield (e.g., flower or fruit number, and total or average weight of fruits) in such intercross populations would be of limited use for breeding commercial tomato cultivars because individuals in the populations have specific genetic backgrounds underlying extremely different phenotypes between the parents such as large fruit in domesticated tomatoes and small fruit in wild relatives, which may not be reflective of the genetic variation in tomato breeding populations. In this study, we constructed F₂ population derived from a cross between two commercial F₁ cultivars in tomato to extract QTL information practical for tomato breeding. This cross corresponded to a four-way cross, because the four parental lines of the two F₁ cultivars were considered to be the founders. We developed 2510 new expressed sequence tag (EST)-based (euchromatin-derived) genomic SSR markers and selected 262 markers from these new SSR markers and publicly available SSR markers to construct a linkage map. QTL analysis for ten agricultural traits of tomato was performed based on the phenotypes and marker genotypes of F₂ plants using a flexible Bayesian method. As results, 13 QTL regions were detected for six traits by the Bayesian method developed in this study.

     

普通小麦1BL—1RS K,V型雄性不育体系育性恢复的研究

对１ＢＬ－１ＲＳ Ｋ,Ｖ型雄性不育系及其保持素与中国春及其第一部分同源群染色体全部６个缺－四体杂种Ｆ１的育性恢复进行了研究。结果表明：Ｋ型杂种的育笥恢复主要受１ＢＳ上Ｒｆｖ１基因的控制;而Ｖ杂种则受Ｒｆｖ１的１Ｄ染色上育性恢复基因的共同控制;在保持１Ｄ正常剂量的情况下,使恢复系中载有Ｒｆｖ１的１Ｂ染色体（片段）加倍,如１Ａ缺体－１Ｂ四体能使Ｋ,Ｖ型杂种1Ｆ的育性完全恢复。     

Conversion of a rice CMS maintainer into a photo- or thermo-sensitive genetic male sterile line

A maintainer line of 3-line hybrid rice commonly presents a certain genetic distance to a 2-line restorer line, but in many cases, 2-line restorer lines present defects upon recovery of the object cytoplasmic male sterile (CMS) line of the maintainer line, which impedes the utilization of their heterosis. Here, we report a strategy and an example of converting a maintainer into a photoperiod/temperature-sensitive genic male sterile (P/TGMS) line with an almost identical genetic background, thus maximizing the heterosis. Firstly, through treatment of maintainer line T98B with ⁶⁰C_O-γ irradiation, we identified the TGMS line T98S, which is sterile at higher temperatures and fertile at lower temperatures. Secondly, the T98S line was proven to be identical to T98B with regard to genetic background via an examination of 48 parental polymorphous SSR markers and exhibited excellent blossom traits similar to those of T98B, with an extensive forenoon flowering rate of 75.92% and a high exertion rate of 64.59%. Thirdly, in a combination test, three out of six hybrids from T98S crossed with 2-line restorer lines showed a yield increase of 6.70–15.69% for 2 consecutive years. These results demonstrated that the strategy can generate a new P/TGMS line with strong general combining ability (converted from a maintainer line), thus helping to increase the genetic diversity of male sterile heterotic groups.     

Allelic compositions at polymorphic gene loci in maize inbred and hybrid lines and their associations with levels of heterosis

We analyzed polymorphism in the parental lines GK26 and Mo17 and testers Od221MV, Od308MV, and Od329 using SSR-analysis. Recombinant inbred lines (RILs) from populations F₄ and F₆ were genotyped at ten polymorphic loci. Allelic compositions and allele frequencies at microsatellite loci were investigated in parental lines and testers, and the best highly heterotic hybrids and their molecular genetic formulae were derived. The allelic composition of microsatellites were investigated in RILs and high-yield hybrids for the best combining ability parameters.     

Relationship of Parental Genetic Distance with Heterosis and Specific Combining Ability in Sesame (<Emphasis Type="Italic">Sesamum indicum</Emphasis> L.) Based on Phenotypic and Molecular Marker Analysis

The genetic distance analysis for selection of suitable parents has been established and effectively used in many crops; however, there is dearth of conclusive report of relationship of genetic distance analysis with heterosis in sesame. In the present study, an attempt was made to estimate the associations of genetic distances using SSR (GDSSR), seed-storage protein profiling (GDSDS) and agro-morphological traits (GDMOR) with hybrid performance. Seven parents were selected from 60 exotic and Indian genotypes based on genetic distance from clustering pattern based on SSR, seed-storage protein, morphological traits and per se performance. For combining ability analysis, 7 parents and 21 crosses generated from 7 × 7 half diallel evaluated at two environments in a replicated field trial during pre-kharif season of 2013. Compared with the average parents yield (12.57 g plant^?1), eight hybrids had a significant (P < 0.01) yield advantage across environments, with averages of 26.94 and 29.99% for better-parent heterosis (BPH) and mid-parent heterosis (MPH), respectively, across environments. Highly significant positive correlation was observed between specific combining ability (SCA) and per se performance (0.97), while positive non-significant correlation of BPH with GDSSR (0.048), and non-significant negative correlations with GDMOR (? 0.01) and GDSDS (? 0.256) were observed. The linear regressions of SCA on MPH, BPH and per se performance of F₁s were significant with R² value of 0.88, 0.84 and 0.95 respectively. The present findings revealed a weak association of GDSSR with F₁’s performance; however, SCA has appeared as an important factor in the determination of heterosis and per se performance of the hybrids. The present findings also indicated that parental divergence in the intermediate group would likely produce high heterotic crosses in sesame.     

Identification of simple sequence repeat markers for utilizing wide-compatibility genes in inter-subspecific hybrids in rice (Oryza sativa L.)

Although pronounced heterosis in inter-subspecific hybrids was known in rice for a long time, its utilization for hybrid rice breeding has been limited due to their hybrid sterility (HS). For the last two decades, however, a few inter-subspecific hybrids have been developed by incorporating wide-compatibility genes (WCG) that resolve HS, into parental lines of these inter-subspecific hybrids. For effective use of WCG, it is necessary to find convenient markers linked to WCG of practical importance. In this paper, initially a set of simple sequence repeat (SSR) markers in the vicinity of known WCG loci identified based on comparative linkage maps have been surveyed in a population derived from the three-way cross- IR36/Dular//Akihikari, where a known donor of WCG Dular was crossed to a representative indica and japonica cultivar. Of the five parental polymorphic markers, RM253 and RM276 were found to be closely linked to the WCG locus S5 at a distance of 3.0 and 2.8 cM, respectively. Later, loci for HS were examined in three F₂ populations derived from inter-subspecific crosses, with same set of SSR markers. The locus S8 was confirmed to have major influence on HS in the F₂ population derived from CHMRF-1/Taichung65 since two SSR markers in its vicinity, RM412 and RM141, co-segregated with HS at a map distance of 7.6 and 4.8 cM, respectively. In the F₂ population derived from the cross BPT5204/Taipei309, three SSR markers in the vicinity of S5, RM50, RM276 and RM136 co-segregated with HS at a map distance of 4.2, 3.2 and 7.8 cM, respectively. In the third F₂ population derived from Swarna/Taipei309, the SSR markers in the vicinity of S5, RM225, RM253, RM50, RM276 and RM136 were identified to co-segregate with HS at a map distance of 3.2, 2.6, 3.4, 2.6 and 6.6 cM, respectively. These results indicated a clear picture of WCG in Dular as well as the predominant role of HS alleles at S5 locus. The identified SSR markers are expected to be used for incorporation of WCG into parental lines in hybrid rice breeding to solve HS in inter-subspecific hybrids.S.P. Singh , R.M. Sundaram contributed equally     

The extent of parental genotypic divergence determines maximal heterosis by increasing fertility in inter-subspecific hybrids of rice (Oryza sativa L.)

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.     

First draft genome sequencing of fennel (<Emphasis Type="Italic">Foeniculum vulgare</Emphasis> Mill.): identification of simple sequence repeats and their application in marker-assisted breeding

The development of F₁ hybrid varieties benefits from the synergistic effect of conventional and molecular marker-assisted breeding schemes. A sequencing run was carried out in Foeniculum vulgare (2n?=?2x?=?22) to develop the first genome draft and to identify microsatellites suitable for implementing multilocus SSR marker assays. A preliminary cytometric analysis allowed us to estimate the genome size (2C?=?2.64–2.86 pg), equal to about 1.34 Mbp for 1C genome, and to calculate the sequencing coverage (53×). The genome draft assembly into 300,408 scaffolds and its bioinformatic analysis enabled the annotation of coding and non-coding regions across the genome, including 103,306 SSR elements. A total of 100 microsatellites were randomly chosen among those with dinucleotide and trinucleotide repeat motifs and with a repeat motif length?≥?25 times and were preliminarily tested. Of these, 27 SSR markers, classified as suitable for genetic diversity analyses, were efficiently organized in five PCR multiplex assays and validated using a core collection of 100 fennel individuals potentially useful for the development of inbred lines and F₁ hybrids. All SSR loci were found to be polymorphic, scoring an observed number of marker alleles Na?=?207 and an average polymorphism information content PIC?=?0.69. The SSR data were used to calculate (i) the degree of homozygosity for the individual inbred lines (0.35?<?Ho?<?0.96), to eventually plan additional selfing or sibling cycles, and (ii) the degree of genetic similarity for all possible pair-wise comparisons between parental inbred lines (GS?=?0.55–0.77), to identify the most divergent combinations for the constitution of experimental F₁ hybrids. The integration of genotypic and phenotypic data was useful for implementing guidelines for precision hybrid breeding schemes in fennel.     

Rapid Evolution of Simple Sequence Repeat Induced by Allopolyploidization

Microsatellite evolution normally occurs in diploids. Until now, there has been a lack of direct experimental evidence for microsatellite evolution following allopolyploidization. In the present study, F₁ hybrids and newly synthesized allopolyploids were derived from Triticum aestivum Chinese Spring × Secale cereale Jinzhou-heimai. One hundred and sixty-three wheat simple sequence repeat (SSR) markers were used to investigate the variation of wheat microsatellites after allopolyploidization and variation of the PCR products of 29 of the SSR markers was observed. Of these 29 SSR markers, 15 were unable to produce products from amphiploids. The other 14 SSR markers did produce products from parental wheat, F₁ hybrids and amphiploids. However, the length of the products amplified from amphiploids was different from the length of the products amplified from parental wheat and F₁ hybrids. Sequencing indicated that the length variation of the 14 microsatellites stemmed mainly from variation in the number of repeat units. The alteration of repeat units occurred in both perfect and compound repeats. In some compound SSR loci, one motif was observed to expand whereas another to contract. Almost all the microsatellite evolution observed in this study could be explained by the slipped-strand mispairing model. The results of this study seem to indicate that stress caused by allopolyploidization might be one of the factors that induce microsatellite evolution. In addition, the findings of present study provided an instance of how simple sequence repeats evolved after allopolyploidization.     

Mean, genetic variance, and usefulness of selfing progenies from intra- and inter-pool crosses in faba beans (Vicia faba L.) and their prediction from parental parameters

 Determining the genetic potential of a base population from the properties of their parental lines would improve the efficiency of a breeding program. In the present study, we investigated whether the means of the parents and the genetic distance determined from RAPD data (GD) or multivariate analysis (Mahalanobis D²), mid-parent heterosis (MPH), and the absolute difference between means of the parents (∣P₁−P₂∣) can be used for predicting the means and genetic variances (σ^² _g ) of F_3:4 lines derived from different crosses in faba beans. The material comprised 18 intra- and 18 inter-pool crosses among lines from the Minor, Major, and Mediterranean germplasm pools. Fifty F_3:4 lines from each cross were evaluated for days to anthesis, plant height, seeds per plant, and seed yield in German (GE) and Mediterranean (ME) environments. GD estimates between parent lines ranged from 0.38 to 0.58, while D² ranged from 45.5 to 134.7. Correlations between means of the parents and F_3:4 lines were highly significant for most traits. Estimates of σ² _g for all traits showed non-significant correlations with MPH, GD, D². In one ME, ∣P₁−P₂∣ had significant associations with σ^² _g for seed yield and days to anthesis. The predicted usefulness of crosses, defined as the sum of the population mean and selection responses, was most closely associated with the means of F_3:4 lines. We conclude from this study that the means of F_3:4 lines can be predicted from the means of the parents, whereas the prediction of genetic variance is still an unsolved problem Received: 12 December 1997 / Accepted: 13 July 1998     

Performance of recombinant inbred lines in Brussels sprouts (Brassica oleracea var. gemmifera)

Summary Performance of a random array of recombinant inbred lines derived by single seed descent from five different source populations of Brussels sprouts (Brassica oleracea var. gemmifera) is presented. A total of 2,356 lines were tested in trials during 1985 and 1986. Three of the source populations were derived from double crosses between F₁ hybrids. These hybrids show a considerable heterotic advantage over their inbred parents for the most important agronomic traits. The recombinant inbred lines performed, on average, less well than the parental inbred material, indicating that additive x additive genie interactions may make a significant contribution to the performance of current inbred material. Nevertheless, the very large variation among the recombinant inbred lines permitted many lines to be identified which outperformed the best parental inbred for all traits. Two lines outperformed the reference F₁ hybrid, Gower, for an index that included marketable yield and quality. Consideration was also given to the dangers of misinterpreting phenotypically based proportions. Accordingly, response equations were used to ascertain the real genetic progress that was made. Advance seemed small when compared with the large heterotic effect, which is consistent with the segregation of a large number of loci. The distribution of the recombinant inbred lines was compared to predictions made from early generation trials. There was broad agreement but significant discrepancies existed which, it is suggested, may arise from the effects of genotype-environment interactions.