Diploid Crosses Research Articles

Cannabis Triploids Exhibit Reduced Fertility and Similar Growth and Flower Production Compared to Diploids

Cannabis (Cannabis sativa) grown for flowers containing cannabinoids requires all female plants, which are susceptible to seed set from exposure to pollen. Created triploids demonstrated reduced seed production compared with diploids in field and greenhouse studies in which plants were challenged with pollen from males. In the field, seed production as a percent of floral biomass ranged from 6.7% to 18.0% for triploids and from 52.6% to 57.1% for diploids. The photoperiod-insensitive triploid genotype ‘Purple Star’ × ‘Wilhelmina’ had 98.5% fewer filled (containing a developed embryo) seeds than the photoperiod-insensitive diploid genotype ‘Tsunami’ × ‘Wilhelmina’. In the greenhouse, triploid ‘Wife’ had 99.5% fewer filled seeds than diploid ‘Wife’. Plant growth and flower production were similar with eight triploid and seven diploid genotypes evaluated over three greenhouse studies. There were a few superior triploid and diploid genotypes; however, their performance was more likely attributable to the parental cultivar combination than ploidy level. The optimal cross direction for producing triploid seed in large quantities is tetraploid × diploid because the diploid × tetraploid cross exhibits triploid block caused by endosperm paternal excess. Colchicine-induced tetraploid parent plants should be tested over a prolonged period to eliminate cryptic chimeral mixoploids or tetraploid plants should be derived from seed produced by crossing two colchicine-induced putative tetraploid plants to ensure that seeds from tetraploid × diploid crosses will be triploid. The latter approach is necessary for photoperiod-insensitive cultivars because a prolonged period of ploidy testing is not possible for these plants. These findings indicate that triploid plants have significantly reduced fertility and are a suitable alternative to diploids in situations in which pollen exposure is possible.

All-triploid offspring in the yellowtail tetra Astyanax altiparanae Garutti & Britski 2000 (Teleostei, Characidae) derived from female tetraploid × male diploid crosses.

This study aimed to evaluate the ploidy and survival of larvae resulting from crosses between tetraploid females and diploid males of yellowtail tetra Astyanax altiparanae, both females (three diploids and three tetraploids) and males (n = 3 diploids). Breeders were subjected to hormonal induction with pituitary gland extract from common carp fish (Cyprinus carpio). Females received two doses at concentrations of 0.3 and 3.0 mg/kg -1 body weight and at intervals of 6 h. Males were induced with a single dose of 3.0 mg/kg -1 applied simultaneously with the second dose in females. Oocytes from each diploid and tetraploid female were fertilized with semen from the same male, resulting in two crosses: cross 1 (diploid male and diploid female) and cross 2 (diploid male and tetraploid female). The procedures were performed with separate females (diploid and tetraploid) and diploid males for each repetition (n = 3). For ploidy determination, 60 larvae from each treatment were analyzed using flow cytometry and cytogenetic analyses. As expected, flow cytometry analysis showed that progenies from crosses 1 and 2 presented diploid and triploid individuals, respectively, with a 100% success rate. The same results were confirmed in the cytogenetic analysis, in which the larvae resulting from cross 1 had 50 metaphase chromosomes and those from cross 2 had 75 chromosomes. The oocytes have a slightly ovoid shape at the time of extrusion. Diploid oocytes had a size of 559 ± 20.62 μm and tetraploid of 1025.33 ± 30.91 μm. Statistical differences were observed between eggs from crosses 1 and 2 (P = 0.0130). No significant differences between treatments were observed for survival at the 2-cell stage (P = 0.6174), blastula (P = 0.9717), gastrula (P = 0.5301), somite (P = 0.3811), and hatching (P = 0.0984) stages. In conclusion, our results showed that tetraploid females of the yellowtail tetra A. altiparanae are fertile, present viable gametes after stripping and fertilization using the 'dry method', and may be used for mass production of triploids. This is the first report of these procedures within neotropical characins, and which can be applied in other related species of economic importance.

THERMAL TOLERANCE PHENOTYPE IN CDC13-1 EXO1 HETEROZYGOUS DIPLOIDS OF S. CEREVISIAE IS A DOMINANT TRAIT

Background: Telomeric DNA is found at the end of eukaryotic chromosomes, where they play a role in protecting the chromosome and the integrity of the genome of the organism through the activity of telomerase. Saccharomyces cerevisiae exists in two genotypes: haploid and diploid. Temperature sensitive point mutation on the cdc13 gene of each genotype and deletion of exo1 gene (cdc13-1Exo1 mutants) give rise to mutant survivors at enhanced temperatures. The mode of inheritance of the thermal tolerance allele in the heterozygous diploid genotype is not known. Materials and Methods: We constructed diploids by mating temperature sensitive haploid strains of opposite mating type cdc13-1 exo1: LEU with temperature resistant strains of cdc13-1 exo1::HIS. The crosses were 1296x3182 (D) and 2561x3181 (C). Using a sterile stick, smear of one haploid strain was made on each YEPD plates labelled C2, C8, C10, D4, D10, and D113. A smear of another opposite mating type was made on the previous strain. They were mixed and allowed to mate for six hours, before culturing on media lacking Luecine and Histidine (–L and –H) to purify and confirm that they are diploids. After confirmation, a loop full aliquot of the diploids were streaked on sterile media lacking leucine and histidine (-L, -H) and on YEPD and cultured at 370C to check thermal tolerance and number of viable colonies from each diploid crosses in (cfu). Result: The heterozygous diploid D thrived at the enhanced temperature of 370C and there is a significant difference in the yield of viable colonies by the D diploids when compared to the yield of the C diploids with P-value of 0.05. Conclusion: The growth of diploid D10 as shown in plate 3.1 establishes that, temperature resistant allele inherited by cdc13-1 exo1heterozygous diploids is a dominant phenotype, and its mode of inheritance is dominant as the heterozygous diploid thrived at the enhanced temperature of 370C.

Survival and growth of triploid eastern oysters, Crassostrea virginica, produced from wild diploids collected from low-salinity areas

Triploid Eastern oysters have been reported to suffer greater mortalities than diploids when exposed to low-salinity (<5) conditions in the U.S. Gulf of Mexico and Atlantic estuaries. As such, the effect of broodstock parentage was investigated on the low-salinity tolerance of triploid progeny produced by mating diploid females (collected from three Louisiana estuaries differing in salinity regimes) with male tetraploids at two hatcheries. Diploid crosses were also produced using the wild broodstocks to verify expected differences in low-salinity tolerance among diploid progeny and between ploidy levels. All progeny were deployed at low and moderate-salinity (averages of 9.3 and 19.4) field sites to monitor monthly growth and mortality. Sex ratio, gametogenic stage, gonad-to-body ratio, condition index, and Perkinsus marinus infection were also measured periodically at both field sites Although high triploid mortality at the low-salinity site prevented complete analysis, results indicated that diploid parentage had little effect on triploid survival at low salinity. Broodstock parentage affected diploid mortality and growth, although results did not match with predictions made based on historical salinity at broodstock collection sites. Ploidy level had the largest effect on triploid survival and growth followed by the hatchery site where the oysters were produced.

Estimating heterosis and heterobeltiosis in phenological and vegetative traits and correlations in Musa diploid x diploid crosses

This study was conducted to determine the extent of heterosis and heterobeltiosis in phenological and vegetative traits in Musa diploid by diploid crosses. The experimental design was RCB with two replications of 6 plants per genotype. Planting was done in alleys of multispecies hedgerows in an area of 2,880 m2 at a spacing of 3 m x 2 m. The study was conducted at the International Institute of Tropical Agriculture (IITA) High Rainfall Station, Onne, Rivers State, Nigeria for 3 years. Six female diploid banana and plantain clones (maternal/ seed parents) were crossed with a single diploid male plantain accession, TMP2x 2829-62 (paternal/pollen parent). The resulting diploid F1 embryos were cultured in vitro for 6 weeks and their seedlings along with the parental clones, vegetatively propagated from the parents of each genotype, were planted in the field. Data collected included days to flowering, time to fruit filling, plant height, plant girth, and height of next tallest sucker. Data subjected to ANOVA in RCB was tested at 5% level of significance. Heterosis (Ht) and heterobeltiosis (Hbt) were estimated. The degree of heterosis and heterobeltiosis differed for different traits, different crosses and genotype. Overall, 66.7% of the progenies showed heterosis and heterobeltiosis for days to flowering and time to fruit filling; 66.7% exhibited heterosis and 50% heterobeltiosis for plant height; 33% heterosis and heterobeltiosis for plant girth and 16.7% heterosis and heterobeltiosis for height of next tallest sucker. Correlations between the levels of heterosis for different traits between the progeny and the female parents were generally weak except for time to fruit filling (r = 0.816) which showed a significant correlation. Heterosis and heterobeltiosis occur in phenological and vegetative traits in diploid x diploid crosses indicating their importance in further possibilities for breeding.

Growth, survival and gonad development of two new types of reciprocal triploid hybrids between Crassostrea gigas and C. angulata

The allotriploid technology has been widely applied to aquaculture worldwide. To overcome the deficiency of low growth, poor taste and high mortality of diploid hybrids between Crassostrea gigas and C. angulata in summer, two new types of triploid hybrids were produced by inhibiting the polar body II using cytochalasin B. The growth, survival and gonad traits of triploid hybrids (TGA – C. gigas ♀ × C. angulata ♂ and TAG – C. angulata ♀ × C. gigas ♂), diploid hybrids (GA – C. gigas ♀ × C. angulata ♂ and AG – C. angulata ♀ × C. gigas ♂) and purebred crosses (GG – C. gigas ♀ × C. gigas ♂ and AA – C. angulata ♀ × C. angulata ♂) were evaluated. A high triploidy induction rate (> 95%) was found by ploidy analysis. The fertilization and hatch rates of triploid hybrids were significantly (P < 0.05) lower than that of diploid crosses. During the larval stage, the triploid advantage (TA) was positive in growth, despite was negative in survival. The triploid hybrids exhibited superior performance during the grow-out stage. Across three culture environments (Rongcheng, Rushan and Huangdao), triploid hybrids performed better than diploid hybrids in growth with an increasing value of TA over time. The incremental survival rates of triploid hybrids, especially that of TGA, were significantly (P < 0.05) higher than that of diploid hybrids at Rushan and Huangdao in summer. The TA in cumulative survival rate ranged from 13.80% to 36.04% among environments. A positive yield advantage for diploid and triploid hybrids was observed at Rongcheng (mid-parent heterosis H: 114.11%; TA: 35.76%), Rushan (H: 148.22%; TA: 48.78%) and Huangdao (H: 138.96%; TA: 60.22%). Additionally, most of the triploid hybrids exhibited high sterility during reproduction phase. These findings demonstrated that triploid hybrids between C. gigas × C. angulata had obvious advantage in growth, survival and yield, which have important application value for commercial oyster cultivation in northern China.

Identification of Parental Genome Construction and Inherited Morphological Characteristics in Triploid and AneuploidIntergeneric Hybrids from a Diploid−Diploid Cross between Citrus and Fortunella

We previously obtained two intergeneric hybrids with different ploidies, i.e., aneuploid (2n = 28) and eutriploid, from diploid−diploid crosses between ‘Kiyomi’ tangor (Citrus unshiu Marcow. × C. sinensis (L.) Osbeck) and Meiwa kumquat (Fortunella crassifolia Swingle) as novel breeding materials for a seedless kumquat. In this study, we attempted to clarify the construction of the parental genomes of these hybrids by SSR genotyping and genomic in situ hybridization (GISH)−chromomycin A3 (CMA) analysis. SSR genotyping in NSX43 (LG5) and CiBE2227 (LG8) loci revealed that both hybrids inherited one allele from ‘Kiyomi’ tangor and two heterozygous alleles from Meiwa kumquat. The GISH analysis failed due to the high genomic homology between Citrus and Fortunella. At the same time, the CMA karyotype compositions of the two intergeneric hybrids (H15-701: 2A + 1B + 3C + 13D + 7E + 1F + 1Dst; H15-702: 3A + 1B + 2C + 15D + 4E +1F + 1Dst) and both parents (‘Kiyomi’ tangor: 1A + 2B + 2C + 6D + 7E; Meiwa kumquat: 2A + 2C + 12D + 1F + 1Dst) were completely revealed. We identified the parental genome construction and polyploidization processes in both intergeneric hybrids on the basis of these SSR genotypes and CMA karyotype compositions according to the following theory: the SSR genotypes and chromosome compositions were the same as those of the somatic chromosome and two-fold after the first division (even number) in unreduced gametes caused by first-division restitution (FDR) and second-division restitution (SDR), respectively. Consequently, we determined that both intergeneric hybrids may have had two genomes derived from the 2n male unreduced gamete as a result of the FDR of the Meiwa kumquat. In addition, most horticultural traits of the leaves, flowers, and fruits of both hybrids showed intermediate traits of the parents, but the fruit sizes and flowering habits were more like those of the two inherited genomes of Meiwa kumquat.

Identification of Parental Genome Construction and Inherited Morphological Characteristics in Triploid and Aneuploid Intergeneric Hybrids from a Diploid−Diploid Cross between Citrus and Fortunella

Identification of Parental Genome Construction and Inherited Morphological Characteristics in Triploid and Aneuploid Intergeneric Hybrids from a Diploid−Diploid Cross between Citrus and Fortunella

Identification of Parental Genome Construction and Inherited Horticultural Traits in Triploid and Aneuploid Intergeneric Hybrids from a Diploid−Diploid Cross between Citrus and Fortunella

Identification of Parental Genome Construction and Inherited Horticultural Traits in Triploid and Aneuploid Intergeneric Hybrids from a Diploid−Diploid Cross between Citrus and Fortunella

A field test investigating the influence of brood stock origin and ploidy on the susceptibility of Crassostrea virginica to “triploid mortality” in the Chesapeake Bay

Mass mortalities of cultured triploid Crassostrea virginica in late spring, or “triploid mortality,” have been reported on farms in the Chesapeake Bay since 2012. Typical causes, such as disease or poor husbandry, were not responsible, and mortalities occurred without clear signs of biological or physical stressors. Previous comparisons of the effects of genetic origin on triploid mortality have been uncontrolled, initiating this investigation of the effect of brood stock source and ploidy on triploid mortality. Four triploid and four diploid crosses, produced by crossing different combinations of brood stock of Virginia, Louisiana, and Maine origin in early 2015, were tested at four commercial oyster farms in Virginia throughout 2016. From February to November, oysters from all crosses and sites were regularly sampled, and growth (shell height), condition (meat weight), and pathology were monitored, as were environmental conditions. Compared to diploids made from Virginia brood stock, diploids with Maine genetic origin had high mortality, and diploid Virginia-Maine hybrids exhibited mid-parent heterosis. A triploid mortality event occurred in late spring at only one site and only affected the triploid crosses. Evidence for substantial disease pressure from Haplosporidium nelsoni or Perkinsus marinus or of especially stressful environmental conditions based on temperature, salinity, pH, and dissolved oxygen was absent during the triploid mortality event. At 18 months, shell height was similar in the diploids and triploids with the most similar genetic origin. Triploids maintained meat weight through the summer, while meat weight in diploids dropped sharply. Triploids may be especially susceptible to late spring mortality events in the Chesapeake Bay, which justifies their classification as “triploid mortality” and warrants further investigation on traits in triploids that may affect susceptibility.

Identification of the High Frequency of Triploid Potato Resulting from Tetraploid × Diploid Crosses

Conventional wisdom regarding potato breeding indicates that a strong triploid block prevents the development of viable triploid seeds from crosses between tetraploid and diploid clones. However, in a recent set of crosses between elite tetraploid potatoes and an improved diploid hybrid population derived from group Stenotomum and group Phureja, 61.5% of the resulting clones were found to be triploid. If clones derived from one diploid parent suspected of producing a high frequency of unreduced gametes were excluded, then the frequency of triploid clones increased to 74.4%. Tubers of these triploids are generally intermediates of the two parental groups. Our findings indicate the possibility of using triploid potatoes in potato variety development programs and in genetic and genomic studies.

Genome-wide Inference of Somatic Translocation Events During Potato Dihaploid Production.

Potato ( L.) breeders often use dihaploids, which are 2× progeny derived from 4× autotetraploid parents. Dihaploids can be used in diploid crosses to introduce new genetic material into breeding germplasm that can be integrated into tetraploid breeding through the use of unreduced gametes in 4× by 2× crosses. Dihaploid potatoes are usually produced via pollination by haploid inducer lines known as in vitro pollinators (IVP). In vitro pollinator chromosomes are selectively degraded from initially full hybrid embryos, resulting in 2× seed. During this process, somatic translocation of IVP DNA may occur. In this study, a genome-wide approach was used to identify such events and other chromosome-scale abnormalities in a population of 95 dihaploids derived from a cross between potato cultivar Superior and the haploid inducing line IVP101. Most Superior dihaploids showed translocation rates of <1% at 16,947,718 assayable sites, yet two dihaploids showed translocation rates of 1.86 and 1.60%. Allelic ratios at translocation sites suggested that most translocations occurred in individual cell lineages and were thus not present in all cells of the adult plants. Translocations were enriched in sites associated with high gene expression and H3K4 dimethylation and H4K5 acetylation, suggesting that they tend to occur in regions of open chromatin. The translocations likely result as a consequence of double-stranded break repair in the dihaploid genomes via homologous recombination during which IVP chromosomes are used as templates. Additionally, primary trisomy was observed in eight individuals. As the trisomic chromosomes were derived from Superior, meiotic nondisjunction may be common in potato.

Comparison of Methods to Distinguish Diploid and Tetraploid Potato in Applied Diploid Breeding

Diploid (2n = 2x = 24) and tetraploid (2n = 4x = 48) germplasm are commonly used in potato breeding programs. Potato breeders need to efficiently and inexpensively differentiate between diploid and tetraploid progeny in dihaploid induction crosses as well as 2x-2x crosses where 2n gametes may occur in the parents. In this study, we compared the chloroplast count, genome-wide SNP genotyping and flow cytometry methods to determine ploidy. Twenty-eight clones were used as reference samples (14 diploid lines (2n = 2x = 24), 14 tetraploid (2n = 4x = 48) varieties and advanced breeding lines) to compare the three ploidy determination methods. The chloroplast count method was used to determine the ploidy level in the 28 reference samples, and 102 potato breeding lines derived from diploid (2x-2x) crosses. The Infinium 12 K V2 Potato Single Nucleotide Polymorphism (SNP) Array was used to examine the 28 reference samples and the 102 breeding lines. The results obtained from both chloroplasts counts and SNP genotyping techniques determined that there was a total of 84 diploid lines and 18 tetraploid lines. Flow cytometry was also used to determine ploidy level in a subset of 42 lines (28 reference lines set and 14 breeding lines). All three methods of ploidy determination (chloroplast counting, SNP genotyping and flow cytometry) agreed for all samples evaluated. These results demonstrate the usefulness of chloroplast counting as an efficient and inexpensive method for breeders to differentiate ploidy between diploid and tetraploid potato in applied breeding programs.

Limonium homoploid and heteroploid intra‐ and interspecific crosses unveil seed anomalies and neopolyploidy related to sexual and/or apomictic reproduction

AbstractApomixis is a form of asexual reproduction that consists in cloning through seeds. In Limonium (Plumbaginaceae) species present a pollen–stigma dimorphism linked to a sporophytic self‐incompatibility system associated with sexual and/or apomictic reproductive modes. Previous work in other genera suggests that the emergence of apomixis is associated with hybridization and/or polyploidy. In this study, our goal was to test the ability of diploid and tetraploid species to hybridize and to evaluate the variate outcomes from these crosses. To achieve this, sexual diploid (L. nydeggeri, L. ovalifolium) and facultative apomict tetraploid (L. binervosum, L. dodartii) plants from cultivated material, previously cytogenetically and reproductively characterized, were used for experimental intra‐ and interspecific crosses. Genome sizes, ploidy levels and morphology were examined in the resulting progenies. Results showed a high production of viable seeds in particular in plants from tetraploid × diploid (heteroploid) crosses. In these crosses, some seedlings exhibited pleiocotyly (tricotyl, tetracotyl), while others showed polyembryony. In both homoploid (diploid × diploid) and heteroploid (tetraploid × diploid) crosses, most of the offspring plants were morphologically and in their ploidy similar to the female receiver, although some morphological abnormalities were found. Molecular progeny tests using the nrDNA ITS1‐ITS2 sequence demonstrated an astounding range of diploid offspring plants originated from diploid × diploid crosses that were either genetically similar or distinct from parental plants. Although in intraspecific crosses most of the resulting progeny was diploid, one triploid plant was formed. Moreover, in homoploid interspecific crosses, neopolyploids (two tetraploid plants) were produced. Progeny plants from heteroploid crosses always showed nrDNA ITS1‐ITS2 sequences identical to the parental plant used as female receiver. In conclusion, diploid homoploid crosses presented genetically diverse offspring arising from sexual reproduction. By contrast, heteroploid crosses generated clonal, maternal (apomictic) offspring.

Attack of the clones: reproductive interference between sexuals and asexuals in the Crepis agamic complex.

Negative reproductive interactions are likely to be strongest between close relatives and may be important in limiting local coexistence. In plants, interspecific pollen flow is common between co‐occurring close relatives and may serve as the key mechanism of reproductive interference. Agamic complexes, systems in which some populations reproduce through asexual seeds (apomixis), while others reproduce sexually, provide an opportunity to examine effects of reproductive interference in limiting coexistence. Apomictic populations experience little or no reproductive interference, because apomictic ovules cannot receive pollen from nearby sexuals. Oppositely, apomicts produce some viable pollen and can exert reproductive interference on sexuals by siring hybrids. In the Crepis agamic complex, sexuals co‐occur less often with other members of the complex, but apomicts appear to freely co‐occur with one another. We identified a mixed population and conducted a crossing experiment between sexual diploid C. atribarba and apomictic polyploid C. barbigera using pollen from sexual diploids and apomictic polyploids. Seed set was high for all treatments, and as predicted, diploid–diploid crosses produced all diploid offspring. Diploid–polyploid crosses, however, produced mainly polyploidy offspring, suggesting that non‐diploid hybrids can be formed when the two taxa meet. Furthermore, a small proportion of seeds produced in open‐pollinated flowers was also polyploid, indicating that polyploid hybrids are produced under natural conditions. Our results provide evidence for asymmetric reproductive interference, with pollen from polyploid apomicts contributing to reduce the recruitment of sexual diploids in subsequent generations. Existing models suggest that these mixed sexual–asexual populations are likely to be transient, eventually leading to eradication of sexual individuals from the population.

Aneuploid progeny of the American oyster, Crassostrea virginica, produced by tetraploid × diploid crosses: another example of chromosome instability in polyploid oysters.

The commercial production of triploids, and the creation of tetraploid broodstock to support it, has become an important technique in aquaculture of the eastern oyster, Crassostrea virginica. Tetraploids are produced by cytogenetic manipulation of embryos and have been shown to undergo chromosome loss (to become a mosaic) with unknown consequences for breeding. Our objective was to determine the extent of aneuploidy in triploid progeny produced from both mosaic and non-mosaic tetraploids. Six families of triploids were produced using a single diploid female and crossed with three mosaic and non-mosaic tetraploid male oysters. A second set of crosses was performed with the reciprocals. Chromosome counts of the resultant embryos were tallied at 2-4 cell stage and as 6-hour(h)-old embryos. A significant level of aneuploidy was observed in 6-h-old embryos. For crosses using tetraploid males, aneuploidy ranged from 53% to 77% of observed metaphases, compared to 36% in the diploid control. For crosses using tetraploid females, 51%-71% of metaphases were aneuploidy versus 53% in the diploid control. We conclude that somatic chromosome loss may be a regular feature of early development in triploids, and perhaps polyploid oysters in general. Other aspects of chromosome loss in polyploid oysters are also discussed.

Induction and viability of tetraploids in brook trout (Salvelinus fontinalis)

Brook trout (Salvelinus fontinalis) populations are threatened by introduction of invasive species, habitat loss, and habitat degradation in their native range and are a problem invasive species in western Unites States and Canada and in Europe. Stocking sterile triploids has been promoted as an approach to reduce negative effects of stocking of brook trout for recreational fishing on native fish populations. Crossing a tetraploid with a diploid is a method of triploid production that may help hatcheries meet demand. We induced tetraploidy in brook trout by application of 633 kg·cm−2 of hydrostatic pressure for 8 min at 70%–72.5% of the first cleavage interval. Yields of above 50% tetraploid progeny at hatching were readily achieved, although few animals reached 1 year of age. We crossed a male tetraploid with female diploid fish and produced interploid-triploids with eyeing rates in excess of 50%, demonstrating male tetraploids are fertile and capable of siring triploid progeny. Female tetraploid fish were reared to 16 months posthatching and possessed follicles in secondary vitellogenesis, suggesting tetraploid females are also fertile. Tetraploid induction rates in excess of 96% were achieved applying the same hydrostatic pressure treatment to zygotes of tetraploid × diploid crosses at 30 min postfertilization.

Phenotypic trait analysis of diploid and triploid hybrids from female Crassostrea hongkongensis×male C. gigas

The allotriploid induction is one of effective tools used for animal breeding in aquaculture. To improve the growth weakness of diploid hybrids between female Crassostrea hongkongensis and male Crassostrea gigas, allotriploid induction by inhibiting the second polar body of fertilized eggs of C. hongkongensis was conducted using a hypotonic treatment. Three replicates were successfully performed, and each replicate consisted of two intraspecific crosses (GG—C. gigas ♀ × C. gigas ♂ and HH—C. hongkongensis ♀ × C. hongkongensis ♂), a diploid cross HG (C. hongkongensis ♀ × C. gigas ♂) and a triploid cross HHG (C. hongkongensis ♀ × C. gigas ♂). The phenotypic traits of these crosses were evaluated in the aspects of survival, growth, gonad development and ploidy estimation. The egg cleavage rate of the HHG cross was similar to that of HG, and that of both crosses were significantly lower than that of the two intraspecific crosses (P < 0.05). The D larval rate of HHG was the lowest in all the groups. The survival heterosis of the diploid hybrids was always positive, despite the growth weakness. The allotriploid advantages of survival and growth were both negative in the larval stages and then converted to positive in the spat and adult stages. Most of the triploid hybrids exhibited sterility, with atrophic gonads and abnormal gametogenesis as observed in the diploid hybrids. Our finding suggests that triploid hybrids are viable, fast growing (in terms of the diploid hybrids), and highly sterile, and promise potential utilization in aquaculture as a new oyster stock.

Interploid and intraploid hybridizations to produce polyploid Haskap (Lonicera caerulea var. emphyllocalyx) plants

We produced polyploid Haskap (Lonicera caerulea var. emphyllocalyx) plants by performing interploid and intraploid crosses of wild accessions. Embryo rescue in a tetraploid (4x) × diploid (2x) cross produced triploid plants; reciprocal 2x × 4x cross failed to produce viable seeds. Intraploidy crosses of 4x × 4x produced mostly tetraploids but also several hexaploid (6x) and octoploid (8x) plants. Using hexaploids obtained from this cross, we examined reciprocal 4x–6x crosses and found that both produced pentaploid plants. An octoploid was produced by applying colchicine to a tetraploid; a 4x × 8x cross using this plant and aided by embryo rescue culture produced three hexaploid plants, with an aneuploid number of chromosomes. Several plants obtained in this study flowered and set fruits. We discuss the overall efficiency of producing polyploid plants in interploid and intraploid crosses.

A Dense Linkage Map for Chinook salmon (Oncorhynchus tshawytscha) Reveals Variable Chromosomal Divergence After an Ancestral Whole Genome Duplication Event

Comparisons between the genomes of salmon species reveal that they underwent extensive chromosomal rearrangements following whole genome duplication that occurred in their lineage 58−63 million years ago. Extant salmonids are diploid, but occasional pairing between homeologous chromosomes exists in males. The consequences of re-diploidization can be characterized by mapping the position of duplicated loci in such species. Linkage maps are also a valuable tool for genome-wide applications such as genome-wide association studies, quantitative trait loci mapping or genome scans. Here, we investigated chromosomal evolution in Chinook salmon (Oncorhynchus tshawytscha) after genome duplication by mapping 7146 restriction-site associated DNA loci in gynogenetic haploid, gynogenetic diploid, and diploid crosses. In the process, we developed a reference database of restriction-site associated DNA loci for Chinook salmon comprising 48528 non-duplicated loci and 6409 known duplicated loci, which will facilitate locus identification and data sharing. We created a very dense linkage map anchored to all 34 chromosomes for the species, and all arms were identified through centromere mapping. The map positions of 799 duplicated loci revealed that homeologous pairs have diverged at different rates following whole genome duplication, and that degree of differentiation along arms was variable. Many of the homeologous pairs with high numbers of duplicated markers appear conserved with other salmon species, suggesting that retention of conserved homeologous pairing in some arms preceded species divergence. As chromosome arms are highly conserved across species, the major resources developed for Chinook salmon in this study are also relevant for other related species.