Multigenerational outbreeding effects in Chinook salmon (Oncorhynchus tshawytscha)

Outbreeding, mating between genetically divergent individuals, may result in negative fitness consequences for offspring via outbreeding depression. Outbreeding effects are of notable concern in salmonid research as outbreeding can have major implications for salmon aquaculture and conservation management. We therefore quantified outbreeding effects in two generations (F₁ hybrids and F₂ backcrossed hybrids) of Chinook salmon (Oncorhynchus tshawytscha) derived from captively-reared purebred lines that had been selectively bred for differential performance based on disease resistance and growth rate. Parental lines were crossed in 2009 to create purebred and reciprocal hybrid crosses (n = 53 families), and in 2010 parental and hybrid crosses were crossed to create purebred and backcrossed hybrid crosses (n = 66 families). Although we found significant genetic divergence between the parental lines (F_ST = 0.130), reciprocal F₁ hybrids showed no evidence of outbreeding depression (hybrid breakdown) or favorable heterosis for weight, length, condition or survival. The F₂ backcrossed hybrids showed no outbreeding depression for a suite of fitness related traits measured from egg to sexually mature adult life stages. Our study contributes to the current knowledge of outbreeding effects in salmonids and supports the need for more research to better comprehend the mechanisms driving outbreeding depression.     

Linkage analysis of quantitative trait loci in multiple line crosses

Simple line crosses, for example, backcross and F₂, are commonly used in mapping quantitative trait loci (QTL). However, these simple crosses are rarely used alone in commercial plant breeding; rather, crosses involving multiple inbred lines or several simple crosses but connected by shared inbred lines may be common in plant breeding. Mapping QTL using crosses of multiple lines is more relevant to plant breeding. Unfortunately, current statistical methods and computer programs of QTL mapping are all designed for simple line crosses or multiple line crosses but under a regular mating system. It is not straightforward to extend the existing methods to handle multiple line crosses under irregular and complicated mating designs. The major hurdle comes from irregular inbreeding, multiple generations, and multiple alleles. In this study, we develop a Bayesian method implemented via the Markov chain Monte Carlo (MCMC) algorithm for mapping QTL using complicated multiple line crosses. With the MCMC algorithm, we are able to draw a complete path of the gene flow from founder alleles to their descendents via a recursive process. This has greatly simplified the problem caused by irregular mating and inbreeding in the mapping population. Adopting the reversible jump MCMC algorithm, we are able to simultaneously search for multiple QTL along the genome. We can even infer the posterior distribution of the number of QTL, one of the most important parameters in QTL study. Application of the new MCMC based QTL mapping procedure is demonstrated using two different mating designs. Design I involves two inbred lines and their derived F₁, F₂, and BC populations. Design II is a half-diallel cross involving three inbred lines. The two designs appear different, but can be handled with the same robust computer program.     

Improved resistance to bacterial soft rot by protoplast fusion between Brassica rapa and B. oleracea

Erwinia soft rot is a destructive disease of Brassica rapa vegetables. Reliable sources of resistance and control methods are limited, so development of highly resistant breeding lines is desirable. Protoplasts from B. rapa and B. oleracea genotypes selected for resistance to soft rot were fused in order to combine different sources of resistance. Twelve somatic hybrids (synthetic B. napus) were obtained and confirmed by morphology, nuclear DNA content, and RAPD analysis. They were normal looking plants that easily set seeds following self-pollination and backcrossing to B. rapa. Assays of detached leaves or seedlings inoculated in a mist-chamber showed that most somatic hybrids had lower disease severity ratings than the B. rapa fusion partner and a commercial variety of B. napus. Some progeny from selfing or backcrossing of somatic hybrids to B. rapa showed much more resistance than either fusion partner. The offspring populations of the somatic hybrids (F₁–S₁ and F₁–BC₁) clearly moved to the resistant direction compared to the parents; the percentage of resistant plants increased from 21% (average of parents) to 36% (F₁–S₁) and 48% (F₁–BC₁). These results suggest that it may be possible to obtain highly resistant B. rapa lines by further backcrossing and selection. Received: June 1999 / Accepted: 29 July 1999     

Integrated transcript and metabolite profiling reveals coordination between biomass size and nitrogen metabolism in Arabidopsis F1 hybrids

Heterosis refers to the improved agronomic performance of F₁ hybrids relative to their parents. Although this phenomenon is widely employed to increase biomass, yield, and stress tolerance of plants, the underlying molecular mechanisms remain unclear. To dissect the metabolic fluctuations derived from genomic and/or environmental differences contributing to the improved biomass of F₁ hybrids relative to their parents, we optimized the growth condition for Arabidopsis thaliana F₁ hybrids and their parents. Modest but statistically significant increase in the biomass of F₁ hybrids was observed. Plant samples grown under the optimized condition were also utilized for integrated omics analysis to capture specific changes in the F₁ hybrids. Metabolite profiling of F₁ hybrids and parent plants was performed using gas chromatography-mass spectrometry. Among the detected 237 metabolites, 2-oxoglutarate (2-OG) and malate levels were lower and the level of aspartate was higher in the F₁ hybrids than in each parent. In addition, microarray analysis revealed that there were 44 up-regulated and 12 down-regulated genes with more than 1.5-fold changes in expression levels in the F₁ hybrid compared to each parent. Gene ontology (GO) analyses indicated that genes up-regulated in the F₁ hybrids were largely related to organic nitrogen (N) process. Quantitative PCR verified that glutamine synthetase 2 (AtGLN2) was upregulated in the F₁ hybrids, while other genes encoding enzymes in the GS-GOGAT cycle showed no significant differences between the hybrid and parent lines. These results suggested the existence of metabolic regulation that coordinates biomass and N metabolism involving AtGLN2 in F₁ hybrids.     

Frequency dependent selection: I. Rare male phenomenon in D. subobscura dependent on the proportion of Amy genotypes and substrate composition

Analysis of the rare male mating advantage in D. subobscura, as a type of frequency dependent selection on maltose and starch media, was done by applying different statistical approaches (χ², cross-product ratio, variance and regression analysis). They reveal that mating occurs at random when proportions of prospective mates are equal, and that mating success of the males homozygous for Amy-locus genotypes (S/S and F/F) depends on their proportion. Regression analysis showed that the F/F males are sexually more active (have higher vigour) than S/S males. Rare male effect is one-sided and appears in F/F males that partake in more heterogamic matings. Comparison of the number of observed and expected homo- and heterogamic matings shows that homogamic matings are more frequent. Multifactorial analysis of variance shows that the number of matings are different for nine pairs of lines and four possible mating types (S_fS_m, S_fF_m, F_fS_m, F_fF_m). The rare male phenomenon is not dependent on different food composition, but is associated with variations in individual genotypes.     

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。     

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.     

Isolation mechanisms in closely related grasshopper species <Emphasis Type="Italic">Chorthippus albomarginatus</Emphasis> and <Emphasis Type="Italic">Ch. oschei</Emphasis> (Orthoptera: Acrididae)

Two closely related grasshopper species Chorthippus albomarginatus and Ch. oschei are known to hybridize in the narrow contact zone at the territory of Ukraine and Moldova. Different isolaton mechanisms providing reproductive isolation between the two species were studied. In choice mating experiments, females of the both species demonstrated a strong assortative mating (80–90% preference for the conspecific males). Comparison of the parental and hybrid viability revealed a reduced hatching and increased larval mortality in F₁ and F₂ hybrids. In choice mating experiments, the hybrid females mated less assortatively than the parental females. An assymmetry was found in mating preferences and in viability of hybrids. The results demonstrate the existence of pre-and post-mating isolation between Ch. albomarginatus and Ch. oschei. A possible fate of the hybrid zone is discussed.     

Inheritance studies with inbred lines of maize having different activity levels of the AP 1 controlled acid phosphatase isozymes

Summary The genetic control of acid phosphatase-1 (AP ₁) activity in pollen of maize was studied by crossing inbred lines having different AP ₁ isozymes and different activity levels of the A P ₁ enzyme. Usually, the intensities of the SS and FF isozyme bands were not equal in pollen of A P ₁ ^S /A P ₁ ^F heterozygous F ₁ hybrids, but the relative intensities of the two bands were not correlated to the activity levels of the parental lines. The A P ₁ ^S /A P ₁ ^S and A P ₁ ^F /A P ₁ ^F F ₂ populations differed in their mean level of activity. Both populations showed segregation in the activity levels indicating single gene control. The intensity ratios of the SS and FF bands in the different heterozygous A P ₁ ^S /A P ₁ ^F F ₂ plants did not segregate. The results support the competition model for gene regulation proposed by Schwartz (1971).     

Genetic variance and drift in selfed and intermated populations derived from backcrossing

Summary The genetic variance among random-mated lines derived from backcrossing (BC_gS₁ lines) depends upon the backcross generation (g) and the number (n) of BC_gF₁ plants crossed in generations 1 through g. There is little effect of n on genetic variance for n > 6. The genetic variance among BC_gF₂-derived lines is greater than that among BC_gS₁ lines for all g. If either BC_gF₂-derived or BC_gS₁ lines are used as a base population for recurrent selection, 8, 16, 32, and 64 BC₁F₁, BC₂F₁, BC₃F₁, and BC₄F₁ plants, respectively, should be used to avoid loss of donor alleles to drift.Joint contribution of USDA-ARS and Journal Paper No. J-11224 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 2471Formerly Research Geneticist, USDA-ARS, Ames, Iowa, USA     

S-alleles are retained and expressed in a self-compatible cultivar of Petunia hybrida.

Summary We identified two S-allele-associated proteins (S-proteins) in a self-compatible cultivar of Petunia hybrida based on their segregation in F₁ hybrids between P. hybrida and its self-incompatible relative, Petunia inflata (with S₂S₂ genotype), and in selfed progeny of P. hybrida. These two S-proteins, designated S_x-protein (24 kDa) and S_o- protein (31 kDa), are pistil specific, and their expression follows a temporal and spatial pattern similar to that of S-proteins characterized in self-incompatible solanaceous species. Their amino-terminal sequences also share a high degree of similarity with those of solanaceous S-proteins. Selfing of P. hybrida yielded plants with S_oS_o, SxSo, and S_xS_x genotypes in an approximately 1:2:1 ratio, indicating that the S_x- and S_o-alleles, though expressed in the pistil, failed to elicit a self-incompatibility response. The S₂-allele of P. inflata is expressed in all the F₁ hybrids, rendering them capable of rejecting pollen bearing the S₂-allele. The S_o-allele is not functional in the F1 hybrids, because all the F₁ progeny with S₂S_o genotype are self-compatible. However, in F₁ hybrids with S₂S_x genotype, approximately half are self-incompatible and half are self-compatible, indicating that the function of the S_x-allele depends on the genetic background. These results strongly suggest that the presence of functional S-alleles alone is not sufficient for expression of a self-incompatibility phenotype, and reaffirm the multigenic nature of gametophytic self-incompatibility suggested by earlier genetic studies.     

Permanent genetic variability in the introgressive lines and amphidiploids of Triticeae

The hybrid origin of an organism’s genome has been regarded in recent years as the cause for a certain genetic instability inherent in such genomes. Using the model of amphidiploids and introgressive Aegilops wheat lines, evidence is given for confirming the facts of permanent alterations in their genomes, which were revealed at the phenotypic level in studies of morphological traits and biochemical character in successive generations of certain genotypes, as well as those of F₁ and F₂ hybrids. The actions of both transposons and intrachromosomal rearrangements caused by the 4S^sh gametocidal chromosome may be considered as the causes of such variability.     

Assessing hybrid sterility in <Emphasis Type="Italic">Oryza glaberrima</Emphasis> × <Emphasis Type="Italic">O. sativa</Emphasis> hybrid progenies by PCR marker analysis and crossing with wide compatibility varieties

Interspecific crossing of the African indigenous rice Oryza glaberrima with Oryza sativa cultivars is hindered by crossing barriers causing 100% spikelet sterility in F₁ hybrids. Since hybrids are partially female fertile, fertility can be restored by back crossing (BC) to a recurrent male parent. Distinct genetic models on spikelet sterility have been developed predicting, e.g., the existence of a gamete eliminator and/or a pollen killer. Linkage of sterility to the waxy starch synthase gene and the chromogen gene C, both located on chromosome 6, have been demonstrated. We selected a segregating BC₂F₃ population of semi-sterile O. glaberrima × O. sativa indica hybrid progenies for analyses with PCR markers located at the respective chromosome-6 region. These analyses revealed that semi-sterile plants were heterozygous for a marker (OSR25) located in the waxy promoter, whereas fertile progenies were homozygous for the O. glaberrima allele. Adjacent markers showed no linkage to spikelet sterility. Semi-sterility of hybrid progenies was maintained at least until the F₄ progeny generation, suggesting the existence of a pollen killer in this plant material. Monitoring of reproductive plant development showed that spikelet sterility was at least partially due to an arrest of pollen development at the microspore stage. In order to address the question whether genes responsible for F₁ sterility in intraspecific hybrids (O. sativa indica × japonica) also cause spikelet sterility in interspecific hybrids, crossings with wide compatibility varieties (WCV) were performed. WCV accessions possess "neutral" S-loci (Sⁿ) improving fertility in intraspecific hybrids. This experiment showed that the tested Sⁿ-loci had no fertility restoring effect in F₁ interspecific hybrids. Pollen development was completely arrested at the microspore stage and grains were never obtained after selfing. This suggests that distinct or additional S-loci are responsible for sterility of O. glaberrima × O. sativa hybrids.Communicated by H.C. Becker     

Spawning and fertility of F<Subscript>1</Subscript> hybrids of the coral genus <Emphasis Type="Italic">Acropora</Emphasis> in the Indo-Pacific

The role of hybridization through multi-specific synchronous spawning in the evolution of reef-building corals has been discussed since the 1990s, particularly for the genus Acropora. However, F₁ hybrids have been reported as common in only one case in the Caribbean, with no evidence of mechanisms that would allow continuous reproduction of the hybrids. In this study, we report for the first time the fecundity of two F₁ hybrid colonies produced experimentally from two Indo-Pacific species, A. intermedia and A. florida. These F₁ hybrids spawned at the same time as the parental corals. Backcrossing and F₁ hybrid crossing were successful in both directions. Furthermore, more than 90% self-fertilization was achieved in an F₁ hybrid, although it was negligible in the parental corals. While it is possible that the F₁ hybrid was a chimera, these results suggest that some products of interspecific hybridization may persist as the offspring of self-fertilizing F₁ hybrids.     

Increase in photosynthesis of maize hybrids (<Emphasis Type="Italic">Zea mays</Emphasis> L.) at suboptimal temperature (15 °C) by selection of parental lines on the basis of chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence measurements

We tested the usefulness of chlorophyll a fluorescence quenching analysis for the selection of maize parental inbred lines able to produce F₁ hybrids with a high CO₂ assimilation rate during growth at suboptimal temperature. Fifty inbred lines, grown at 15 °C, showed at 6 °C a broad genetic variability regarding the quantum yield of photosynthetic electron transport (_PS2). A decrease of _PS2 in sensitive lines was caused more by reduction of the efficiency of excitation energy capture by open photosystem 2 (PS2) reaction centres (F_v'/F_m') than by a drop in photochemical quenching (q_P). Selected inbred lines with the highest (H) and the lowest (L) values of _PS2 were used for separate crossings in a diallelic arrangement. Twenty-one of H×H hybrids and 21 of the L×L hybrids were grown at 15 °C. The H×H hybrids showed at suboptimal temperature a significantly higher transport of photosynthetic electrons than the L×L hybrids at lower (400) as well as at higher [800 mol(photon) m^–2 s^–1] irradiance. The mean net photosynthetic rate (P _N) in H×H and L×L hybrids amounted to 8.4 and 5.8 (second leaf) and 8.5 and 7.6 mol(CO₂) m^–2 s^–1 (third leaf), respectively. Among the best 20 hybrids with regard to P _N (values larger than the average) of second leaves, as many as 15 were derived from H lines (75 % of hybrids), whereas among the best 21 hybrids with regard to P _N of the third leaves, 16 were derived from H lines (76 % of hybrids). The intensive P _N of H×H hybrids was most often accompanied by less water lost via transpiration in relation to photosynthesis than in the hybrids of L lines. Hence an analysis of chlorophyll a fluorescence quenching enables the selection of inbred lines, which can produce hybrids with improved CO₂ fixation and with efficient water management during growth at suboptimal temperature.     

The use of replicated progenies in marker-based mapping of QTL's

Summary Seven types of progeny are described which can be used in detection of linkage between marker loci and quantitative trait loci (QTL) in a cross between two inbred lines. Three types of progeny: recombinant inbred lines (RI); doubled haploid lines (DH); and S₁ lines can be used to detect linked main effects, d. DH and RI lines can be used to detect smaller effects than S₁ lines. However, S₁ lines can also be used to detect within-population dominance effects, h. The smallest d detectible is in the range of 1/2 to 1/12 the size of the corresponding LSD_(0.05) for the quantitative trait, using 100 lines and 6 replicates. The smallest h detectible is 3–4 times this size. Four types of progeny can be used to detect differences in the dominance behavior of alleles within the population relative to an allele in another inbred line (P₄: DH lines x P₄; RI lines x P₄; either F₂ x P₄ or S₁ lines x P₄; and progeny generated by crossing (F₁ x P₃) x P₄. Dominance differences in the range of 1 1/4 to 1/6 the size of the corresponding LSD_(0.05) are routinely detectible using 100 lines and 6 replicates. Increasing the numbers of progeny evaluated or the number of replicates allows for the detection of relatively smaller linked effects.Contribution of United AgriSeeds, Inc.     

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.     

Maternal and Reciprocal Effects on Seedling Characters in ARABIDOPSIS THALIANA (L.) Heynh

Five early growth characters were examined in six races of Arabidopsis thaliana (L.) Heynh, their reciprocal F₁ hybrids (1974) and F₁ by tester hybrids, using a seventh race as a paternal tester. Three of the five characters were also examined at two nutrient levels in reciprocal F₁ hybrids (1972) of all seven races. Analyses of F₁ and F₁ by tester hybrids revealed significant maternal effects in all characters examined in F₁ hybrids (1972) and in root length and plant weight of F₁ (1974) and F₁ by tester hybrids. Significant reciprocal effects were found for plant weight in F₁ by tester hybrids and for seed weight, percentage of germination and root length in F₁ (1974) and F₁ by tester hybrids. The presence of significant maternal and/or reciprocal components in both F₁ (1974) and F₁ by tester diallels suggests that differences in maternal cytoplasm rather than maternal genotype per se were responsible for much of the variation resulting from these non-direct genetic effects.     

Durum wheat as a candidate for the unknown female progenitor of bread wheat: an empirical study with a highly fertile F<Subscript>1</Subscript> hybrid with <Emphasis Type="Italic">Aegilops tauschii</Emphasis> Coss.

Hexaploid bread wheat was derived from a hybrid cross between a cultivated form of tetraploid Triticum wheat (female progenitor) and a wild diploid species, Aegilops tauschii Coss. (male progenitor). This cross produced a fertile triploid F₁ hybrid that set hexaploid seeds. The identity of the female progenitor is unknown, but various cultivated tetraploid Triticum wheats exist today. Genetic and archaeological evidence suggests that durum wheat (T. turgidum ssp. durum) may be the female progenitor. In previous studies, however, F₁ hybrids of durum wheat crossed with Ae. tauschii consistently had low levels of fertility. To establish an empirical basis for the theory of durum wheat being the female progenitor of bread wheat, we crossed a durum wheat cultivar that carries a gene for meiotic restitution with a line of Ae. tauschii. F₁ hybrids were produced without using embryo rescue techniques. These triploid F₁ hybrids were highly fertile and spontaneously set hexaploid F₂ seeds at the average selfed seedset rate of 51.5%. To the best of our knowledge, this is the first example of the production of highly fertile F₁ hybrids between durum wheat and Ae. tauschii. The F₁ and F₂ hybrids are both similar morphologically to bread wheat and have vigorous growth habits. Cytological analyses of F₁ male gametogenesis showed that meiotic restitution is responsible for the high fertility of the triploid F₁ hybrids. The implications of these findings for the origin of bread wheat are discussed.     

SEXUAL SELECTION AGAINST HYBRIDS BETWEEN SYMPATRIC STICKLEBACK SPECIES: EVIDENCE FROM A FIELD EXPERIMENT

Sexual selection against viable, fertile hybrids may contribute to reproductive isolation between recently diverged species. If so, then sexual selection may be implicated in the speciation process. Laboratory measures of the mating success of hybrids may underestimate the amount of sexual selection against them if selection pressures are habitat specific. Male F₁ hybrids between sympatric benthic and limnetic sticklebacks (Gasterosteus aculeatus complex) do not suffer a mating disadvantage when tested in the laboratory. However, in the wild males choose different microhabitats and parental females tend to be found in the same habitats as conspecific males. This sets up the opportunity for sexual selection against male hybrids because they must compete with parental males for access to parental females. To test for sexual selection against adult F₁ hybrid males, we examined their mating success in enclosures in their preferred habitat (open, unvegetated substrate) where limnetic males and females also predominate. We found significantly reduced mating success in F₁ hybrid males compared with limnetic males. Thus, sexual selection, like other mechanisms of postzygotic isolation between young sister species, may be stronger in a wild setting than in the laboratory because of habitat-specific selection pressures. Our results are consistent with, but do not confirm, a role for sexual selection in stickleback speciation.