Impact of biparental mating on correlation coefficients in bread wheat

Summary Phenotypic and genotypic correlation coefficients and path-coefficients were studied in the biparental (BIPs) and F₃ self progenies of the two wheat crosses. A comparison of correlation coefficients in the BIPs and the F₃'s revealed that as many as twelve new significant correlations were noticed in case of the BIPs in cross I although some of them occurred in the undesirable direction. On the other hand, only three new correlations were observed in the BIPs of cross II, although as many as fifteen correlations were not significant. Results suggested that intermating in the F₂ was effective in breaking the linkages. Path-coefficient analysis further revealed that the direct effect of tillers/ plant on grain yield was important and remained unchanged in both populations of cross I. In cross II, the direct effect of tillers/plants on grain yield was also high and it increased in the BIPs. Intermating seemed to have influenced considerably both the direct and indirect effects.     

A comparative analysis of biparental mating and selfing in pearl millet (Pennisetum typhoïdes) S & H

Summary A study was made of the nature of variation and changes in association for characters related to yield, development and disease resistance in two sets of progenies one set derived through biparental mating (A-series) and the other by traditional inbreeding (selfing) from the F₂ onwards (T-series), in a 22 × 22 diallel of dwarf derivatives of Pennisetum typhoides S & H. Comparison of means and variances within and between the two groups of progenies (A and T-series) and with those of released hybrids (HB-1, HB-2, HB-3, HB-4) for seventeen characters (six related to development, six to productivity, three to vegetative growth and one each to earliness and disease incidence) showed significant variation among the lines of the two series for synchrony of tillering, earliness, disease incidence, chlorophyll depth, grain hairiness, tiller number, plant height, length of earhead, grain yield and grain weight. The A-series selections were significantly superior to the T-series for most of the characters, indicating the effectiveness of selection in biparental matings compared with selection in selfed progenies for these traits. Many of the A-series (220 out of 800) selections were also superior to the existing released hybrids.Changes in the magnitude and nature of association among twelve important characters in the two populations were more favourable in the biparental matings: of 66 possible correlation coefficients examined, 25 cases were found with changes in favour of selections from biparental matings (A-series). These changes were probably due to the breakage of unfavourable linkages and changes in phase of linkage, and indicate the usefulness of biparental matings in the simultaneous improvement of the population for several attributes.     

Effect of population structure on protein-yield improvements in spring wheat (Triticum aestivum L. em Thell)

Summary In a study designed to develop a more efficient breeding method for concurrent protein-yield improvements in wheat (Triticum aestivum L. em. Thell), 7 base populations [2 F₂'s, 1 intermated F₂ (IF₂) and 4 partial backcross (PBC) populations] developed from biparental crosses involving 2 Canadian hard red spring (CHRS) and 2 Canadian utility (CU) wheat cultivars were evaluated in Winnipeg, Manitoba, Canada. The IF₂ and PBC populations were generated for comparison with conventional F₂ populations and to determine which of the 4 methods of population development would provide a more efficient means of producing potentially superior genetic recombinants. Parameters pertaining to means, variances, correlations, heritabilities and frequencies of desirable and undesirable progenies were used to evaluate the limitations to genetic gain that may be expected from selection for GY and GPC in F₂, IF₂, CHRS-PBC and CU-PBC populations. Analysis of protein and yield data from 105 S₁ lines derived from each of the 7 populations showed the CU-PBC's to have the highest grain yield (GY) and the lowest grain protein concentration (GPC) means; and the CHRS-PBC's, the lowest GY and the highest GPC means. The F₂ and IF₂ populations were intermediate for both characteristics. Populations developed from the same biparental cross did not differ significantly with respect to the majority of genetic parameters. However, desirable progenies combining high GY with high GPC were more frequent in the CU-PBC, and least frequent in the CHRS-PBC populations. The observed superiority of the CU-PBC populations appeared to be related to the advantage the system has in preserving the genetic integrity of a proven cultivar, while adding desirable genetic factors from another cultivar, thus capitalizing on introgression and upgrading simultaneously.Contribution No. 549 from Agriculture Canada, Lacombe Research Station. Research was supported by a grant from the Natural Sciences and Engineering Research Council of Canada     

Genome-Wide High-Resolution Mapping by Recurrent Intermating Using Arabidopsis Thaliana as a Model

We demonstrate a method for developing populations suitable for genome-wide high-resolution genetic linkage mapping, by recurrent intermating among F(2) individuals derived from crosses between homozygous parents. Comparison of intermated progenies to F(2) and ``recombinant inbred' (RI) populations from the same pedigree corroborate theoretical expectations that progenies intermated for four generations harbor about threefold more information for estimating recombination fraction between closely linked markers than either RI-selfed or F(2) individuals (which are, in fact, equivalent in this regard). Although intermated populations are heterozygous, homozygous ``intermated recombinant inbred' (IRI) populations can readily be generated, combining additional information afforded by intermating with the permanence of RI populations. Intermated populations permit fine-mapping of genetic markers throughout a genome, helping to bridge the gap between genetic map resolution and the DNA-carrying capacity of modern cloning vectors, thus facilitating merger of genetic and physical maps. Intermating can also facilitate high-resolution mapping of genes and QTLs, accelerating map-based cloning. Finally, intermated populations will facilitate investigation of other fundamental genetic questions requiring a genome-wide high-resolution analysis, such as comparative mapping of distantly related species, and the genetic basis of heterosis.     

Variation of the parental genome contribution in segregating populations derived from biparental crosses and its relationship with heterosis of their Design III progenies

The variation of the parental genome contribution (PGC) and its relationship with the genetic architecture of heterosis have received little attention. Our objectives were to (1) derive formulas for the variance of PGC in selfing, backcross (BC) or intermated generations produced from biparental crosses of homozygous parents, (2) investigate the correlation r(Z₂ ,\Uppsi_M ) r(Z_{2} ,\Uppsi_{M} ) of the PGC (\Uppsi_M ) (\Uppsi_{M} ) estimated by a set M of markers, with Z ₂ (half the trait difference between each pair of BC progenies) in the Design III, and (3) interpret experimental results on this correlation with regard to the genetic basis of heterosis. Under all mating systems, the variance of PGC is smaller in species with a larger number and more uniform length of chromosomes. It decreases with intermating and backcrossing but increases under selfing. The ratio of variances of PGC in F₁DH (double haploids), F₂ and BC₁ populations is 4:2:1, but it is smaller in advanced selfing generations than expected for quantitative traits. Thus, altering the PGC by marker-assisted selection for the genetic background is more promising (i) in species with a smaller number and/or shorter chromosomes and (ii) in F₂ than in progenies of later selfing generations. The correlation r(Z₂ ,\Uppsi_M ) r(Z_{2} ,\Uppsi_{M} ) depends on the linkage relationships between M and the QTL influencing Z₂ as well as the augmented dominance effects d_i^* d_{i}^{*} of the QTL, which include dominance and additive × additive effects with the genetic background, and sum up to mid-parent heterosis. From estimates of r(Z₂ ,\Uppsi_M ) r(Z_{2} ,\Uppsi_{M} ) as well as QTL studies, we conclude that heterosis for grain yield in maize is caused by the action of numerous QTL distributed across the entire genome with positive d_i^* d_{i}^{*} effects.     

Comparison of linkage maps from F2 and three times intermated generations in two populations of European flint maize (Zea mays L.)

Intermated mapping populations are expected to result in high mapping resolution for tightly linked loci. The objectives of our study were to (1) investigate the consequences of constructing linkage maps from intermated populations using mapping methods developed for F₂ populations, (2) compare linkage maps constructed from intermated populations (F₂Syn3) with maps generated from corresponding F₂ and F₃ base populations, and (3) investigate the advantages of intermated mapping populations for applications in plant breeding programs. We constructed linkage maps for two European flint maize populations (A × B, C × D) by mapping 105 SSR markers in generations F₂ and F₂Syn3 of population A × B, and 102 SSR markers in generations F₃ and F₂Syn3 of population C × D. Maps for F₂Syn3 were constructed with mapping methods for F₂ populations (Map A) as well as with those specifically developed for intermated populations (Map B). Both methods relate map distances to recombination frequencies in a single meiosis and, therefore, did not show a map expansion in F₂Syn3 compared with maps constructed from the respective F₂ or F₃ base populations. Map A and B differed considerably, presumably because of theoretical shortcomings of Map A. Since loosely linked markers could not unambiguously be mapped in the F₂Syn3 populations, they may hamper the construction of linkage maps from intermated populations.     

Chloroplast DNA inheritance in theStellaria longipes complex (Caryophyllaceae)

Inheritance of chloroplast DNA (cpDNA) was examined in F₁ progenies derived from three crosses and three corresponding reciprocal crosses betweenStellaria porsildii andS. longifolia. Chloroplast DNA restriction fragments were analyzed using methods of nonradioactive digoxigenin-11-dUTP labeling and chemiluminescent detection with Lumi-Phos 530. Distinct interspecific restriction fragment polymorphisms were identified and used to demonstrate the mode of cpDNA inheritance. Mode of cpDNA inheritance differed among crosses. Two crosses in whichS. porsildii, SP2920-21, was the maternal parent exhibited three different types of plastids, maternal, paternal and biparental, among the F₁ hybrids, suggesting a biparental cpDNA inheritance and plastid sorting-out inStellaria.     

Breeding Potential of Introgression Lines Developed from Interspecific Crossing between Upland Cotton (Gossypium hirsutum) and Gossypium barbadense: Heterosis,Combining Ability and Genetic Effects

Upland cotton (Gossypium hirstum L.), which produces more than 95% of the world natural cotton fibers, has a narrow genetic base which hinders progress in cotton breeding. Introducing germplasm from exotic sources especially from another cultivated tetraploid G. barbadense L. can broaden the genetic base of Upland cotton. However, the breeding potential of introgression lines (ILs) in Upland cotton with G. barbadense germplasm integration has not been well addressed. This study involved six ILs developed from an interspecific crossing and backcrossing between Upland cotton and G. barbadense and represented one of the first studies to investigate breeding potentials of a set of ILs using a full diallel analysis. High mid-parent heterosis was detected in several hybrids between ILs and a commercial cultivar, which also out-yielded the high-yielding cultivar parent in F₁, F₂ and F₃ generations. A further analysis indicated that general ability (GCA) variance was predominant for all the traits, while specific combining ability (SCA) variance was either non-existent or much lower than GCA. The estimated GCA effects and predicted additive effects for parents in each trait were positively correlated (at P<0.01). Furthermore, GCA and additive effects for each trait were also positively correlated among generations (at P<0.05), suggesting that F₂ and F₃ generations can be used as a proxy to F₁ in analyzing combining abilities and estimating genetic parameters. In addition, differences between reciprocal crosses in F₁ and F₂ were not significant for yield, yield components and fiber quality traits. But maternal effects appeared to be present for seed oil and protein contents in F₃. This study identified introgression lines as good general combiners for yield and fiber quality improvement and hybrids with high heterotic vigor in yield, and therefore provided useful information for further utilization of introgression lines in cotton breeding.     

Biochemical genetics of powdery mildew resistance in pea

Summary A biochemical study on phenolic (total phenols and orthodihydroxy phenols) content and on the activities of phenol oxidizing enzymes (peroxidase and polyphenol oxidase) in pea cultivars resistant and susceptible to powdery mildew infection revealed that the resistant cultivars contained higher levels of phenolics and phenol-oxidizing enzymes than the susceptible ones. A further study of their F₁s, F₂s and backcross progenies suggested a high heritability for all biochemical traits. The correlation coefficients between the biochemical parameters and the disease index were also high. Both additive (d) and dominant () components were found to contribute to the inheritance of these constituents.Associate Professor (Genetics), Department of Basic Sciences     

Partial Dominance,Overdominance and Epistasis as the Genetic Basis of Heterosis in Upland Cotton (Gossypium hirsutum L.)

Determination of genetic basis of heterosis may promote hybrid production in Upland cotton (Gossypium hirsutum L.). This study was designed to explore the genetic mechanism of heterosis for yield and yield components in F_{2: 3} and F_{2: 4} populations derived from a hybrid ‘Xinza No. 1’. Replicated yield field trials of the progenies were conducted in 2008 and 2009. Phenotypic data analyses indicated overdominance in F₁ for yield and yield components. Additive and dominance effects at single-locus level and digenic epistatic interactions at two-locus level were analyzed by 421 marker loci spanning 3814 cM of the genome. A total of 38 and 49 QTLs controlling yield and yield components were identified in F_{2: 3} and F_{2: 4} populations, respectively. Analyses of these QTLs indicated that the effects of partial dominance and overdominance contributed to heterosis in Upland cotton simultaneously. Most of the QTLs showed partial dominance whereas 13 QTLs showing overdominance in F_2:3 population, and 19 QTLs showed overdominance in F_2:4. Among them, 21 QTLs were common in both F_{2: 3} and F_{2: 4} populations. A large number of two-locus interactions for yield and yield components were detected in both generations. AA (additive × additive) epistasis accounted for majority portion of epistatic effects. Thirty three complementary two-locus homozygotes (11/22 and 22/11) were the best genotypes for AA interactions in terms of bolls per plant. Genotypes of double homozygotes, 11/22, 22/11 and 22/22, performed best for AD/DA interactions, while genotype of 11/12 performed best for DD interactions. These results indicated that (1) partial dominance and overdominance effects at single-locus level and (2) epistasis at two-locus level elucidated the genetic basis of heterosis in Upland cotton.     

Linkage disequilibrium in two European F<Subscript>2</Subscript> flint maize populations under modified recurrent full-sib selection

According to quantitative genetic theory, linkage disequilibrium (LD) can hamper the short- and long-term selection response in recurrent selection (RS) programs. We analyzed LD in two European flint maize populations, KW1265 × D146 (A × B) and D145 × KW1292 (C × D), under modified recurrent full-sib selection. Our objectives were to investigate (1) the decay of initial parental LD present in F₂ populations by three generations of intermating, (2) the generation of new LD in four (A × B) and seven (C × D) selection cycles, and (3) the relationship between LD changes and estimates of the additive genetic variance. We analyzed the F₂ and the intermated populations as well as all selection cycles with 104 (A × B) and 101 (C × D) simple sequence repeat (SSR) markers with a uniform coverage of the entire maize genome. The LD coefficient D and the composite LD measure Δ were estimated and significance tests for LD were performed. LD was reduced by intermating as expected from theory. A directional generation of negative LD between favorable alleles could not be observed during the selection cycles. However, considerable undirectional changes in D were observed, which we attributed to genetic sampling due to the finite population size used for recombination. Consequently, a long-term reduction of the additive genetic variance due to negative LD was not observed. Our experimental results support the hypothesis that in practical RS programs with maize, LD generated by selection is not a limiting factor for obtaining a high selection response.     

Population genetic structure of the gynodioecious Thymus vulgaris L. (Labiatae) in southern France

In a self-compatible gynodioecious species, the abundance of female plants (which are obligate outcrossers) relative to hermaphrodites (which may self and outcross) may be a critical factor influencing genetic diversity and population structure. In the gynodioecious Thymus vulgaris L., female frequency varies from 5 to 95%, providing a suitable model to examine this issue. In this study, we use allozyme markers to (1) evaluate the relationship between female frequency, genetic diversity and population structure, (2) determine whether females and hermaphrodites vary in heterozygote deficiency and (3) examine whether other factors such as plant density are related to heterozygote deficiency. Twenty three natural populations, with female frequencies ranging from 11 to 92%, were sampled in and around the St-Martin-de-Londres basin in southern France. Based on four polymorphic allozyme loci, we found no significant correlation between female frequency and heterozygote deficiency. A significant (P < 0.05) F_IS value over loci and over populations of 0.11 was detected. The F_IS value per population showed a significant heterozygote deficiency in 11 of the 23 populations. However, no significant difference between female and hermaphrodite F_IS values was found. A significant heterozygote deficiency only occurred in populations of intermediate density. There was little differentiation among populations (F_ST = 0.038) nor among subpopulations within each population. The significant F_IS values are thus mostly due to inbreeding effects. The lack of a correlation between F_IS values and female frequency may be due to outcrossing in hermaphrodites and/or restoration of male fertility which may occur to a greater extent at low female frequency. The similarity of female and hermaphrodite F_IS values indicates that females may occasion high levels of biparental inbreeding.     

Combining ability analysis over F1-F5 generations in diallel crosses of bread wheat

Summary Combining ability studies for grain yield and its primary component traits in diallel crosses involving seven diverse wheat cultivars of bread wheat (Triticum aestivum L.) over generations F₁-F₅ are reported. The general and specific combining ability variances were significant in all generations for all the traits except specific combining ability variance for number of spikes per plant in the F₅. The ratio of general to specific combining ability variances was significant for all the traits except grain yield in all the generations. This indicated an equal role of additive and non-additive gene effects in the inheritance of grain yield, and the predominance of the former for its component traits. The presence of significant specific combining ability variances in even the advanced generations may be the result of an additive x additive type of epistasis or evolutionary divergence among progenies in the same parental array. The relative breeding values of the parental varieties, as indicated by their general combining ability effects, did not vary much over the generations. The cheap and reliable procedure observed for making the choice of parents, selecting hybrids and predicting advanced generation (F₅) bulk hybrid performance was the determination of breeding values of the parents on the relative performance of their F₂ progeny bulks.     

Early generation selection for agronomic characters in a potato breeding programme

Summary A random sample of seedlings representing high, medium and poor vigour was studied for tuber colour, tuber shape, eye depth, tuber cracking, tuber yield per plant, average tuber weight and number of tubers per plant in four successive generations (F₁, F₁, F₁C₂, and F₁C₃). Based on the performance of vigour groups in various generations and inter-generation correlation coefficients, we propose a procedure for the elimination of unproductive genotypes early in the breeding programme. The data indicates that seedlings of poor vigour can be discarded at the seedling stage prior to transplantation in the field. The rejection of clones on the basis of tuber colour, tuber shape, eye depth and tuber cracking can also be initiated at the seedling stage. For tuber yield and average tuber weight a negative selection (rejection of poor phenotypes) is suggested from the first clonal generation and for number of tubers, from second clonal generation, until statistically sound replicated trials can be conducted for carrying out positive selection.     

Breeding for reduced seed coat fuzz in Upland cotton (Gossypium hirsutum)

The inheritance of seed coat fuzz was studied in two half diallel sets of crosses of Upland cotton. One with F₄ selections from an inter-varietal cross showed a significant level of non-additive variance attributable to dominance and non-allelic interaction. In the other, using inbred varieties of diverse origin, the genetic control of seed fuzz was adequately accounted for by an additive-dominance model with no interaction. Genotypic correlations between seed coat fuzz, yield and lint quality characters, calculated for both diallel sets and for two other groups of breeding material, showed good agreement within each experiment between parents and hybrids or between parents and progenies but no consistent pattern between experiments. The results serve to emphasize the risks in extrapolating correlations from one group of breeding material to another. A useful level of reduced fuzz has been obtained in selections from the AH breeding programme and the genetical investigations indicate that a further reduction may be possible, thereby leading to easier handling of seed, speedier and cheaper ginning, low levels of seed coat nep and better seed germination.     

Efficiency of early generation selections for yield and related characters in safflower (Carthamus tinctorius L.)

The efficiency of early generation selection for yield and related characters in safflower (Carthamus tinctorius L.) was studied in the F₂, F₃ and F₄ generations. Twenty-five F₂ progenies derived from various crosses were studied. In the F₂ generation, number of capitula per plant (CNSP), number of seeds per capitulum (SPSP), test weight (SWSP), and seed yield (SYSP) were the criteria used for single plant selection. The analysis of variance showed significant differences for all of the characters in the F₂, F₃, and F₄ generations. The analysis of variance in each of the selection classes showed highly significant genotypic differences. A large number of selections in the CNSP and SYSP classes showed greater yield than the check variety. In each class the mean for that particular character showed a positive shift. The observed F₃ and F₄ means for seed yield per plant was higher in SYSP, indicating the effectiveness of single plant selection for yield. Correlated response showed that selection for number of capitula per plant was effective for improvement of yield.     

转大肠杆菌过氧化氢酶基因棉花的抗旱生理研究

以导入大肠杆菌过氧化氢酶基因KatE的T3代转基因棉花为供试材料,经卡那霉素检测和PCR鉴定,将筛选出的阳性转基因植株与对照棉花进行整个生育期的持续水分胁迫处理直至收获,比较材料间的生理生化指标的差异,鉴定转基因植株的耐旱能力。结果显示:(1)干旱胁迫持续至初蕾期时,转基因棉花与对照植株间各项抗旱生理指标差异均未达到显著水平。(2)水分胁迫持续至盛蕾和盛花期时,转基因棉花叶片相对含水量、光系统Ⅱ最大光化学效率(Fv/Fm)、CAT活性,以及叶片的净光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)均显著或极显著高于对照植株,叶绿素含量也都明显高于对照植株。干旱胁迫持续至吐絮期时,转基因棉花的株高、果枝数和铃数均显著或极显著高于对照植株,且转基因棉花和对照的籽棉产量分别比正常灌溉处理降低57.5%和60.1%,全生育期的水分胁迫严重影响了棉花籽棉产量,但转基因棉花的籽棉产量仍显著高于对照。研究表明,在新疆石河子当地自然降水(干旱胁迫)条件下,转KatE基因棉花表现出了较好的生理和生长优势,KatE基因有助于提高棉花的抗旱性。     

Molecular marker heterozygosity and hybrid performance in indica and japonica rice

An essential assumption underlying markerbased prediction of hybrid performance is a strong linear correlation between molecular marker heterozygosity and hybrid performance or heterosis. This study was intended to investigate the extent of the correlations between molecular marker heterozygosity and hybrid performance in crosses involving two sets of rice materials, 9 indica and 11 japonica varieties. These materials represent a broad spectrum of the cultivated rice gene pool including landraces, primitive cultivars, historically important cultivars, modern elite cultivars and parents of superior hybrids. Varieties within each set were intermated in all possible nonreciprocal pairs resulting in 36 crosses in the indica set and 55 in the japonica set. The F₁s and their parents, 111 entries in total, were examined for performance of seven traits in a replicated field trial. The parents were surveyed for polymorphisms using 96 RFLP and ten SSR markers selected at regular intervals from a published molecular marker linkage map. Molecular marker genotypes of the F₁ hybrids were deduced from the parental genotypes. The analysis showed that, with very few exceptions, correlations in the indica dataset were higher than in that of their japonica counterparts. Among the seven traits analyzed, plant height showed the highest correlation between heterozygosity and hybrid performance and heteorsis in both indica and japonica datasets. Correlations were low to intermediate between hybrid performance and heterozygosity (both general and specific) in yield and yield component traits in both indica and japonica sets, and also low to intermediate between specific heterozygosity and heterosis in the indica set, whereas very little correlation was detected between heterosis and heterozygosity (either general or specific) in the japonica set. In comparison to the results from our previous studies, we concluded that the relationship between molecular marker heterozygosity and heterosis is variable, depending on the genetic materials used in the study, the diversity of rice germplasms and the complexity of the genetic basis of heterosis.     

Association of AFLP and SSR markers with agronomic and fibre quality traits in <Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L.

Molecular markers linked to QTL contributing to agronomic and fibre quality traits would be useful for cotton improvement. We have attempted to tag yield and fibre quality traits with AFLP and SSR markers using F₂ and F₃ populations of a cross between two Gossypium hirsutum varieties, PS56-4 and RS2013. Out of 50 AFLP primer combinations and 177 SSR primer pairs tested, 32 AFLP and four SSR primers were chosen for genotyping F₂ individuals. Marker-trait associations were studied for eight agronomic and five fibre quality traits through simple and multiple regression analysis (MRA) using a set of 92 AFLP polymorphic loci and four SSR markers. Simple linear regression analysis (SLRA) identified 23 markers for eight different traits whereas multiple regression analysis identified 30 markers for at least one of the 13 traits. SSR marker BNL 3502 was consistently identified to be associated with fibre strength. While all the markers identified in SLRA were also detected in MRA, as many as 16 of the 30 markers were identified to be associated with respective traits in both F₂ and F₃ generations. The markers explained up to 41 per cent of phenotypic variation for individual traits. A number of markers were found to be associated with multiple traits suggesting clustering of QTLs for fibre quality traits in cotton.     

Development of synthetic Brassica amphidiploids by reciprocal hybridization and comparison to natural amphidiploids

In a previous study we proposed that cytoplasmic genomes have played an important role in the evolution of Brassica amphidiploid species. Based on this and other studies, we hypothesized that interactions between the maternal cytoplasmic genomes and the paternal nuclear genome may cause alterations in genome structure and/or gene expression of a newly synthesized amphidiploid, which may play an important role in the evolution of natural amphidiploid species. To test this hypothesis, a series of synthetic amphidiploids, including all three analogs of the natural amphidiploids B. napus, B. juncea, and B. Carinata and their reciprocal forms, were developed. These synthetic amphidiploids were characterized for morphological traits, chromosome number, and RFLPs revealed by chloroplast, mitochondrial, and nuclear DNA clones. The maternal transmission of chloroplast and mitochondrial genomes was observed in all of the F₁ hybrids examined except one hybrid plant derived from the B. rapa x B. oleracea combination, which showed a biparental transmission of organelles. However, the paternal chloroplast and mitochondrial genomes were not observed in the F₂ progeny. Nuclear genomes of synthetic amphidiploids had combined RFLP patterns of their parental species for all of the nuclear DNA clones examined. A variation in fertility was observed among self-pollinated progenies of single amphidiploids that had completely homozygous genome constitutions. Comparisons between natural and synthetic amphidiploids based on restriction fragment length polymorphism (RFLP) patterns indicated that natural amphidiploids are considerably more distant from the progenitor diploid species than the synthetic amphidiploids. The utility of these synthetic amphidiploids for investigating the evolution of amphidiploidy is discussed.