2n Cross Research Articles

Triploid brown trout, Salmo trutta, develop functional gonads with age and are able to interbreed with diploid counterparts.

The study investigated if gonad maturation in triploid brown trout, Salmo trutta, was entirely suppressed or only delayed, and if triploids could interbreed with diploid counterparts. Ten percent of the total number of 3-year-old triploid S. trutta, 15% of 4-year-old fish, and 17% of 5-year-old fish produced semen. Three and 4 years old triploid fish did not produce eggs, but 15% of the 5-year-old fish did so. The quantity and sperm motility of triploid semen did not differ from diploids, but the sperm concentration was significantly lower. When diploid eggs were fertilized with triploid semen (3n × 2n crosses), the percentage of eyed stage embryos, of hatched larvae, and of normal-shaped larvae did not differ from the diploid controls. Circa 90% of 3n × 2n crosses had a ploidy level of 2.4n. In the remaining percentage of 3n × 2n crosses, the ploidy level was ≥2n and <2.4n. In sperm competition experiments where diploid eggs were fertilized with a mixture of diploid and triploid semen, 52% of the originating larvae had a ploidy level of 2n, 43% of 2.4n, and 5% of the fish were not exactly classified. From the start of feeding to an age of 248 days, the mortality rate of 3n × 2n interploid crosses and of 2n × 2n controls was similar. The growth of interploid crosses was significantly higher than that of controls. In triploid mature females, the egg mass per kilogram of body weight was significantly lower than in diploids. The mass of the non-hardened eggs and the percentile weight increase during hardening did not differ from diploid eggs. When triploid eggs were fertilized with diploid semen (2n × 3n crosses), the development rate to normal hatched larvae was less than 10%. All originating larvae had a ploidy level of 3n. From the start of feeding to an age of 248 days, 2n × 3n crosses had a higher mortality rate (15%) than diploid controls (<5%). Growth of this type of interploid crosses was reduced in comparison to controls. Therefore, triploids introduced into natural waters for recreational fisheries or escaping from farms may interbreed with diploid counterparts. This not only alters the genotypes of local populations but also changes the ploidy levels.

ORIGIN OF RECOGNITION COMPLEX 3 controls the development of maternal excess endosperm in the Paspalum simplex agamic complex (Poaceae).

Pseudogamous apomixis in Paspalum simplex generates seeds with embryos genetically identical to the mother plant and endosperms deviating from the canonical 2(maternal):1(paternal) parental genome contribution into a maternal excess 4m:1p genome ratio. In P. simplex, the gene homologous to that coding for subunit 3 of the ORIGIN OF RECOGNITION COMPLEX (PsORC3) exists in three isogenic forms: PsORC3a is apomixis specific and constitutively expressed in developing endosperm whereas PsORCb and PsORCc are up-regulated in sexual endosperms and silenced in apomictic ones. This raises the question of how the different arrangement and expression profiles of these three ORC3 isogenes are linked to seed development in interploidy crosses generating maternal excess endosperms. We demonstrate that down-regulation of PsORC3b in sexual tetraploid plants is sufficient to restore seed fertility in interploidy 4n×2n crosses and, in turn, its expression level at the transition from proliferating to endoreduplication endosperm developmental stages dictates the fate of these seeds. Furthermore, we show that only when being maternally inherited can PsORC3c up-regulate PsORC3b. Our findings lay the basis for an innovative route-based on ORC3 manipulation-to introgress the apomictic trait into sexual crops and overcome the fertilization barriers in interploidy crosses.

Measurement of (n, f) and (n, xn) cross sections with surrogate reaction method

Surrogate reaction method is an important approach to overcome the difficulties meet in the direct measurement of neutron induced nuclear reaction. The current existing surrogate reactions generally employ the peripheral reactions such as inelastic excitation and transfer reaction where the involved angular momenta are much larger than the neutron capture reaction, which causes a difficulty in theoretical correction of spin of compound nucleus. We proposed to use capture reaction of light charged particle as the surrogate reaction, thus the spin distributions of compound nucleus in two reactions are quite similar and therefore the spin correction is not strongly desired. Based on this idea, the 239Pu(n, f) and (n, 2n) cross sections were successfully extracted by using 236U(α,, f) and (α, 2n) reactions as the surrogate reactions. The well coincidence of the present results with the data of ENDFB7 within the error bars shows the reliability of the proposed surrogate capture reaction method.

New Data on Photoneutron Reaction Cross Sections for 76,78,80,82Se Nuclei

The problem of reliability of the cross section data obtained for partial photoneutron reactions on 76,78,80,82Se nuclei in beams of quasimonoenergetic annihilation photons by means of neutron multiplicity sorting is discussed by employing objective physical criteria. It is shown that, because of substantial systematic uncertainties, experimental data on the (γ, 1n) and (γ, 2n) cross sections are unreliable. New data satisfying the reliability criteria are obtained for the partial photoneutron reaction cross sections for 76,78,82Se nuclei by an experimental—theoretical method for evaluating such cross sections and are compared with experimental data and with data evaluated earlier for the isotope 80Se. The evaluated integrated cross sections for the total photoneutron reactions on 76,78,80,82Se nuclei are compared with the predictions of the Thomas-Reiche-Kuhn classical dipole sum rule.

Studies on the synthesis of isotopes of superheavy element Lv (Z = 116)

The probable projectile-target combinations for the synthesis of superheavy nucleus 296Lv found in the cold valley of 296Lv have been identified by studying the interaction barrier of the colliding nuclei, probability of compound nucleus formation, \(P_{CN}\), and survival probability \(W_{sur}\). At energies near and above the Coulomb barrier, the capture, fusion and evaporation residue (ER) cross sections for the probable combinations for the hot and cold fusion reactions are systematically investigated. By considering intensities of the projectile beams, availabilities of the targets and half lives of the colliding nuclei, the combination 48Ca+248Cm is found to be the most probable projectile-target pair for the synthesis of 296Lv. The calculated maximum value of 2n, 3n, 4n and 5n channel cross section for the reaction 48Ca+248Cm are 0.599 pb, 5.957 pb, 4.805 pb, and 0.065 pb, respectively. Moreover, the production cross sections for the synthesis of isotopes 291-295,298Lv using 48Ca projectile on 243-247,250Cm targets are calculated. Among these reactions, the reactions 48Ca+247Cm \(\rightarrow\) 295Lv and 48Ca+250Cm \(\rightarrow\) 298Lv have maximum production cross section in 3n (10.697 pb) and 4n (12.006 pb) channel, respectively. Our studies on the SHE Lv using the combinations 48Ca+245Cm \( \rightarrow\) 293Lv and 48Ca+248Cm \( \rightarrow\) 296Lv are compared with available experimental data and with other theoretical studies. Our studies are in agreement with experimental data and we hope that these studies will be a guide for the future experiments to synthesize the isotopes of Lv.

Parental Genome Imbalance Causes Post-Zygotic Seed Lethality and Deregulates Imprinting in Rice.

BackgroundReproductive isolation between rice of different ploidy levels is manifested as endosperm and embryo abortion in seeds produced by interploidy crosses. Genomic imprinting is considered to be the underlying mechanism establishing the post-zygotic hybridization barrier. We characterized disrupted seed development in reciprocal crosses between a diploid Japonica rice and a tetraploid Indica rice.ResultsTriploid seeds from these crosses had aborted development and could not germinate in soil but could be rescued in culture medium with significantly more seeds developing to seedlings in the 4n × 2n (♀-♂) cross with excess maternal genomes than in the 2n × 4n cross with excess paternal genome. Consistent with previous findings, precocious endosperm cellularization and bigger embryos were observed in the seeds from the maternal excess cross, whereas absence of cellularization and arrested globular embryos were found in the seeds from the paternal excess cross, supporting the idea that endosperm cellularization is an important transition for embryo development. Moreover, we found that starch granules were persistently deposited in the pericarp parenchyma cells of the paternal excess cross, while pericarp starch gradually decreased and relocated to the developing endosperm in balanced and maternal excess crosses in which cellularization and starch deposition occur in endosperm, suggesting that parental genome balance influences pericarp starch relocation via cellularization and starch deposition. Loss of imprinting, or altered expression of imprinted genes and epigenetic regulators, OsFIE2 and OsMET1b were observed, implying the potential role of imprinting and epigenetic mechanisms in regulating the differential parental genome dosage effects on endosperm development.ConclusionsOur results support the hypothesis that the maternal genome dosage promotes endosperm cellularization and the paternal genome dosage delays or inhibits cellularization via contributing different sets of imprinted genes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-016-0115-4) contains supplementary material, which is available to authorized users.

Genetic and environmental influence on triploid Crassostrea virginica grown in Chesapeake Bay: Growth

Aquaculture of triploid Crassostreavirginica in the Chesapeake Bay, USA is popular with the majority of growers raising mostly triploids. This choice stems from improved growth and survival relative to diploids. Triploids are made commercially by crossing tetraploid males and diploid females, thus either or both parent could influence the performance of the triploid. We examined the influence of the female (diploid) parent in an experiment comparing nine diploid (2n×2n) and nine triploid (4n×2n) crosses across three environments. The diploid genotypes consisted of wild populations and selectively bred lines and the environments ranged from low salinity with no disease pressure to higher salinity with consistent disease pressure. Growth metrics (shell height and wet tissue weight) are reported. In the low salinity environment, triploidy seemed disadvantageous for any genotype at least when gauged by final tissue weight. In moderate salinity with low disease pressure, selectively bred diploids performed equivalently to their triploid counterparts showing that breeding efforts can improve diploid field performance to rival triploids. In high salinity with constant disease pressure, triploids offered the greatest advantage for growth. Genotype×environmental response of triploids indicates that breeders may have to tailor crosses to suit particular areas interested in using triploids. Statement of relevanceWe address factors of commercial triploid oyster performance.

Application of Neutron Activation Techniques for the Measurement of 238U (n, γ) and 238U (n, 2n) Cross Section at Neutron Energies of 13.5 and 17.28 MeV

Application of Neutron Activation Techniques for the Measurement of 238U (n, γ) and 238U (n, 2n) Cross Section at Neutron Energies of 13.5 and 17.28 MeV

Evaluation of 54Fe(n, 2n) Cross Sections and Their Covariance Data below 20 MeV

Experimental data of 54Fe(n, 2n) cross sections below 20 MeV were analyzed and evaluated with corrections and normalization. The data were processed in terms of a fitting by a spline code with the consideration of correlation errors. Also, the corresponding covariance matrices of the experimental data were constructed with the information on experimental errors and correlation errors.

Measurements of (n, 2n) Reaction Cross Sections at 14 MeV for Several Nuclei

Measurements of (n, 2n) reaction cross sections to produce 84Rb, 86Rb, 88Y, 139Ce, 141Ce, 168Tm, 174m+gLu, 180mTa, 184m+gRe, 196n+gAu, and 237U were carried out in the range of 13.4 to 14.8 MeV. The samples were irradiated at various positions on the surface of a two-ring orientation instrument with a 20-cm radius centered at the deuterium-tritium neutron source. The 27Al(n,α)24Na reaction was used to monitor the neutron fluence in the target samples. The neutron energies of different directions were determined using the ratio of 89Zr to 92mNb specific activities induced in Zr and Nb foils by (n, 2n) reactions. The (n, 2n) products were measured using a calibrated Ge detector. Experimental uncertainty was within ±4%. The results are presented and compared with the results of references and ENDF/B-VII.0 evaluations. Cross sections of 85Rb(n, 2n)84Rb, 140Ce(n, 2n)139Ce, and 89Y(n, 2n)88Y were in good agreement with those of ENDF/B-VII.0 evaluations; however, disagreements were observed for 175Lu(n, 2n)174Lu and 142Ce(n, 2n)141Ce between the present data and the ENDF/B-VII.0 evaluation file. The present data showed improvement in accuracy in comparison with previously reported data; therefore, the results should be offered for evaluations of neutron (n, 2n) cross sections.

Investigation of Some Structural Fusion Materials for (n, 2n) Reactions up to 40 MeV

The knowledge of (n, 2n) cross section is very important and necessary in the reactor technology since a significant portion of the fission neutron spectrum lies above the threshold of (n, 2n) reaction for the most of the reactor materials. The (n, 2n) cross section is neutron multiplier reaction in fusion reactor design. Therefore, (n, 2n) reactions of the selected blanket materials can play a key role for multiplying neutrons in reactor environment. In this study, for some structural fusion materials (n, 2n) reactions such as 27Al(n, 2n)26Al, 51V(n, 2n)50V, 52Cr(n, 2n)51Cr, 55Mn(n, 2n)54Mn, 56Fe(n, 2n)55Fe and 58Ni (n, 2n)57Ni have been carried out up to 40 MeV incident neutron energy. In these calculations, the pre-equilibrium and equilibrium effects have been investigated. Also in the present work, the (n, 2n) reaction cross-sections have calculated by using evaluated empirical formulas developed by Tel et al. at 14–15 MeV energy. The calculated results are discussed and compared with the experimental data taken from EXFOR database.

Cytogenetic studies on microsporogenesis and male gametophyte development in autotriploid cucumber (Cucumis sativus L.): implication for fertility and production of trisomics

To understand the correlation between chromosomes behavior and fertility in autotriploid cucumber (Cucumis sativus L.), microsporogenesis in pollen mother cells (PMCs) and male gametophyte development were studied using improved staining and chromosome preparation techniques. Meanwhile, for more efficient selection of trisomics from the progeny of autotriploid-diploid crosses, fertilization rates of ovules from reciprocal crosses were counted to observe the transfer rate of gametes in the autotriploid cucumber. Variable chromosome configurations, e.g. multivalents, quadrivalents, trivalents, bivalents and univalents were observed in the most PMCs of the autotriploids at metaphase I. Chromosome lagging and bridges at anaphase in both meiotic divisions resulted from irregular chromosome separation and asynchronization was frequently observed as well, which led to formation of micronuclei and inviable gametes. The frequency of normal PMCs in autotriploids at the stage of tetrad was only 40.6%. Among those normal microspores, most of them (91.2%) could develop into normal gametophytes with 2 cells and 3 germ pores. Stainability and germination rate of pollen grains were only 18.8 and 13.5%, respectively. However, chromosomes separated to form gametes with 8 chromosomes at anaphase I, suggesting a possible method for the production of primary trisomics from the progeny of autotriploid-diploid crosses. Fruit set of 3n × 2n and 2n × 3n were 80 and 70%, respectively. It obtained an average of 6.2 plump seeds per fruit in 3n × 2n, while 4.9 in 2n × 3n crosses. Transfer rates of gametes through the gastrula or the pollen in autotriploids were 13.4 and 10.4%, respectively. Some aneuploid gametes (n + 1 = 8, n + 2 = 9) also have capability of setting seed and sexual reproduction besides normal gametes containing whole chromosome sets (n = 7, 2n = 14). Further, some primary trisomic plants were selected from the progeny of autotriploid-diploid crosses. Based on the results obtained we suggest that abnormal meiosis in PMCs was the cytogenetic reason for low fertility of autotriploid cucumber pollen. 3n × 2n cross was more efficient for selecting primary trisomic plants in cucumber.

Agronomic Performance of 4n x 2n–derived Plantain (&lt;i&gt;Musa&lt;/i&gt; sp. AAB group) Hybrids in a Humid Agro-ecological Zone of Nigeria

A field experiment was conducted on thirteen (13) Musa hybrids derived from 4n x 2n crosses, three (3) checks and two (2) plantain landraces to evaluate phenology, growth characteristics and yield performance in a humid agro ecological zone of Nigeria. Fifteen (15) phenotypic characters were significantly different (P

239Pu and 241Am (n, 2n) cross-section measurements near E n = 14 MeV

Summary We measured the (n, 2n) cross sections for neutron energies from 13.7 to 15.1 MeV on 239Pu and 241Am by α- and γ-spectroscopy measurements of the post–irradiation 238Pu/239Pu and 240Am/241Am ratios relative to the (n, 2n) cross sections of 196Au and other calibration reactions. Statistical errors on the measurements were not more than a few percent. Cross–section values ranged from 228 to 214 millibarns for the reaction on 239Pu and from 260 to 222 millibarns for the 241Am reaction for neutron energies from 13.7 to 15.1 MeV.

Occurrence and cytological mechanism of 2n pollen formation in a tetraploid accession of Ipomoea batatas (sweet potato).

We evaluated a 4x accession of Ipomoea batatas (L.) Lam. and four 2x accessions of Ipomoea triloba for 2n pollen production. Approximately 90% of the genotypes of accession 81.2 (I. batatas, 4x) produced 2n pollen with different frequencies. In contrast, none of the genotypes of I. triloba produced 2n pollen. The diameter of the 2n pollen was approximately 30% ((3) sqrt 2) larger than that of the n pollen, making it easy to identify, measure, and quantify. The correlation (r = 0.93**) between the frequency of giant pollen and the frequency of dyads and triads was highly significant, strongly suggesting that the giant pollen grains were 2n pollen. The 2n pollen producers presented either a parallel or tripolar spindle arrangement (Y shaped) at anaphase II instead of the normal 60 degrees crossed spindle orientation. These two abnormal spindle configurations produced dyads and triads, with different frequencies (13-67%), instead of tetrads. Occasionally a metaphase II spindle variation was found with a single fused spindle, which also forms a dyad. The correlation (r = 0.89**) between the frequency of 2n pollen and the frequency of parallel, fused, and tripolar spindle arrangements was also highly significant, suggesting that these abnormal spindle configurations are involved in the production of 2n pollen in I. batatas. When we evaluated the efficiency of 2n pollen in polyploidization using 4x x 4x (2n) crosses, all progenies were 4x, suggesting the existence of barriers to crossability between 4x genotypes and their 2n pollen-producer counterparts.

Benchmark experiment on LiAlO 2, Li 2TiO 3 and Li 2ZrO 3 assemblies with D–T neutrons–leakage neutron spectrum measurement

For the three materials LiAlO 2, Li 2TiO 3 and Li 2ZrO 3, known as advanced breeder materials for a fusion reactor, D–T neutron benchmark experiments have been conducted at fusion neutronics source (FNS) of Japan Atomic Energy Research Institute (JAERI), Japan, to validate five nuclear data files, i.e. JENDL-3.2, JENDL fusion file, ENDF/B-VI, FENDL/E-1.0 and FENDL/E-2.0. From the result, all the nuclear data files were confirmed to be fairly reliable with respect to the prediction of neutron spectrum in the use of LiAlO 2 and Li 2TiO 3. However, it was recommended that the inelastic scattering neutron spectra of oxygen, lithium and aluminium in the five nuclear data files had to be re-examined. As for zirconium, it was pointed out that the natZr(n, 2n) cross section could be overestimated for the five nuclear data files.

049 Thickness and Weight of Watermelon Seed Produced from a Cross Between Tetraploid and Diploid Plants

Triploid watermelon seed are produced by crosses between tetraploid female and diploid male plants. When open-pollinated, the resultant seed can be either tetraploid due to self-pollination or triploid from pollination by a diploid. This work was done to test if triploid and tetraploid seed can be separated on the basis of seed thickness and weight. Open-pollinated seed from a 4n × 2n cross were separated by either thickness (grouped into 0.1-mm increments) or weight (5-mg increments). Seed were germinated in a greenhouse and transplanted into the field. Plants were scored as either triploid or tetraploid by use of a genetic marker system. When separated by either thickness or weight, triploid and tetraploid seed were found in essentially each size category. There were no significant differences between populations for thickness, and the mean weights were essentially equal between triploid and tetraploid seed.

230 Seed Priming of Triploid Watermelon Seed

Triploid watermelon seed does not germinate in cold, wet soils as well as diploids; germination is slower due to reduced embryo size and thicker seed coat; fissures on the seed coat provide safe harbour for fungal spores; and triploid fruit set is later than most diploid cultivars. Because of these problems producers often transplant rather than direct-seed seedless watermelons. Seed priming has been shown to improve germination in other crops and would be an attractive method allowing for direct seeding of seedless watermelons. Seed from open-pollinated 4n × 2n crosses were primed in solutions of H2O, polyethylene glycol 8000, KNO3, or left untreated. Treatment times were 1, 3, or 6 days, and treated seed were subsequently dried for either 1 or 7 d. Seed were scored for germination in the laboratory and emergence under field conditions. Germination was better using H2O than KNO3 and PEG but not always better than the untreated control. Treatment time of 1 day was superior to 3 or 6 days, but length of drying time was insignificant. In the field trial, treatments did not differ in emergence.

The measurement and calculation of the correlated neutron production rate from [formula omitted] sources

The production of time-correlated neutrons from six 241 AmO 2 Be(α, n) neutron sources has been measured using a high level neutron coincidence counter (HLNCC-II). Five of the sources were contained in standard Amersham X.2 capsules while the sixth was in the larger X.3 format. The results quantitatively support the hypothesis that the predominant source of time-correlated neutrons arises from the Be(n, 2n) process initiated by the primary 241AmO 2/Be(α, n) neutrons. On this basis, analysis of the experimental data yields an (n, 2n) (α, n) ratio of ≈ 1.8% for the X.2 sources and ≈ 2.1% for the X.3 source. This work suggests that passive neutron coincidence counters could be used to good effect in the measurement and testing of integral (n, 2n) cross section data. Tentative conclusions are that the EFF-2 evaluation of the Be(n, 2n) double differential cross section is to be preferred over the ENDF/B-VI evaluation and that the integrated-over-angle Be(n, 2n) cross sections appearing in these evaluations may be approximately 20% low.

Viability and Freshwater Performance of Atlantic Salmon (Salmo salar) × Brown Trout (Salmo trutta) Triploid Hybrids

Survival to initiation of feeding and early freshwater growth were measured for both diploid (2N) and triploid (3N) Atlantic salmon (Salmo salar) and 2N and 3N hybrids between female Atlantic salmon and male brown trout (Salmo trutta) to evaluate the triploid hybrid's potential for commercial culture. Crosses were made in 1990 and 1991 and triploidy was induced by heat shock. Average survival to initiation of feeding generally did not differ among the 2N Atlantic salmon and hybrids within years, nor between the 3N crosses within years. Average survival to initiation of feeding of the 3N Atlantic salmon and hybrids relative to the corresponding 2N crosses was reduced by 2 and 9%, respectively, in 1990, and by 55 and 62%, respectively, in 1991. Five freshwater growth trials were conducted to compare the different crosses. Results indicated no consistent differences in relative growth rates, although the hybrids demonstrated greater variability in growth at age 0+.