Backcross Progeny Research Articles

Introgression of Herbicide-Resistant Gene from Genetically Modified Brassica napus L. to Brassica rapa through Backcrossing.

Interspecific hybridization between two different Brassicaceae species, namely Brassica rapa ssp. pekinensis (♀) (AA, 2n = 2x = 20) and genetically modified Brassica napus (♂) (AACC, 2n = 4x = 38), was performed to study the transmission of a herbicide resistance gene from a tetraploid to a diploid Brassica species. Initially, four different GM B. napus lines were used for hybridization with B. rapa via hand pollination. Among the F1 hybrids, the cross involving the B. rapa (♀) × GM B. napus (♂) TG#39 line exhibited the highest recorded crossability index of 14.7 ± 5.7. However, subsequent backcross progenies (BC1, BC2, and BC3) displayed notably lower crossability indices. The F1 plants displayed morphological characteristics more aligned with the male parent B. napus, with significant segregation observed in the BC1 generation upon backcrossing with the recurrent parent B. rapa. By the BC2 and BC3 generations, the progeny stabilized, manifesting traits from both parents to varying degrees. Cytogenetic analysis revealed a substantial reduction in chromosome numbers, particularly in backcrossing progenies. BC1 plants typically exhibited 21-25 chromosomes, while BC2 progenies showed 21-22 chromosomes, and by the BC3 generation, stability was achieved with an average of 20 chromosomes. SSR marker analysis confirmed the progressive reduction of C-genome regions, retaining minimal C-genome-specific bands throughout successive backcrossing. Despite the extensive elimination of C-genome-specific genomic regions, the glyphosate resistance gene from the male parent B. napus was introgressed into BC3 progenies, suggesting that the glyphosate resistance gene located and introgressed in A-chromosome/genome regions of the Brassica plants.

Glyphosate resistance and no fitness cost in backcross offspring of wild soybean and transgenic soybean with epsps gene

BackgroundThe commercial utilization of genetically modified soybeans has yielded substantial economic advantages. Nevertheless, the genetic drift towards wild soybeans is one of the main ecological risks that needs to be addressed. Previous experiments demonstrated the absence of fitness cost or florescence overlap in hybrid offspring resulting from the crossbreeding of transgenic soybean GTS40-3-2 and Zhengzhou wild soybeans. In this study, hybrid progeny was systematically crossed with wild soybeans to establish a backcross progeny system. This system was employed to evaluate the ecological risk associated with the backcross progeny of transgenic and wild soybeans.ResultsThe findings indicated that the offspring from the backcross exhibited glyphosate tolerance. Furthermore, the expression of foreign proteins in the backcross offspring was notably lower than in the transgenic soybean, and there was no significant difference when compared to the hybrid progeny. Parameters such as germination rate, aboveground biomass, pods per plant, full seeds per plant, and 100-grain weight exhibited no significant differences between the negative and positive lines of the backcross progenies, and no fitness cost was identified in comparison to wild soybeans. These results underscore the potential for foreign genes to propagate within other wild soybeans, which requires continuous attention.ConclusionsThe widespread adoption of genetically modified soybeans has undeniably led to substantial economic gains. However, the research findings emphasize the critical importance of addressing the ecological risks posed by genetic drift towards wild soybeans. The backcross progeny system established in this study indicates that the potential for foreign gene dissemination to wild soybean populations warrants continued attention and mitigation strategies.

Hybridization between Aedes aegypti and Aedes mascarensis mosquitoes leads to disruption of male sex determination

Understanding the sex determination pathway and its disruptions in mosquitoes is critical for the effective control of disease vectors through genetic manipulations based on sex separation. When male hybrids of Aedes aegypti females and Ae. mascarensis males are backcrossed to Ae. aegypti females, a portion of the backcross progeny manifests as males with abnormal sexual differentiation. We discovered a significant correlation between pupal abnormalities and the feminization of subsequent adults exemplified by the relative abundance of ovarian and testicular tissues. All intersex individuals were genetic males as they expressed a male determining factor, Nix. Further, our analysis of the sex-specific splicing of doublesex and fruitless transcripts demonstrated the presence of both male and female splice variants indicating that sex determination is disrupted. A comparative transcriptomic analysis revealed similar expression levels of most female-associated genes in reproductive organs and carcasses between intersexual males and normal females. Moreover, intersexes had largely normal gene expression in testes but significant gene downregulation in male accessory glands when compared with normal males. We conclude that evolving hybrid incompatibilities between Ae. aegypti and Ae. mascarensis involve disruption of sex determination and are accompanied by changes in gene expression associated with sexual differentiation.

Pyramiding of bacterial blight resistance genes into promising restorer BRRI31R line through marker-assisted backcross breeding and evaluation of agro-morphological and physiochemical characteristics of developed resistant restorer lines.

BRRI31R is one of the Bangladesh's most promising restorer lines due to its abundant pollen producing capacity, strong restoring ability, good combining ability, high outcrossing rate and genetically diverse from cytoplasmic male sterile (CMS) line. But the drawback of this line is that it is highly susceptible to bacterial blight (BB) disease of rice caused by Xanthomonas oryzae pv. oryzae. The present study highlighted the pyramiding of effective BB resistance genes (xa5, xa13 and Xa21) into the background of BRRI31R, through marker-assisted backcrossing (MABC). Backcross progenies were confirmed and advanced based on the foreground selection of target genes. Pyramided lines were used for pathogenicity test against five Bangladeshi Xanthomonas oryzae (BXo) races (BXo93, BXo220, BXo822, BXo826, BXo887) and confirmed the dominant fertility restore genes, Rf3 and Rf4 and further validated against SNP markers for more confirmation of target resistance genes. All pyramided restorer lines consisted of Xa4 (in built), xa5, xa13, Xa21, and Chalk5 with two fertility restorer genes, Rf3, Rf4. and these restorer lines showed intermediate amylose content (<25%). Restorer lines BRRI31R-MASP3 and BRRI31R-MASP4 showed high levels of resistance against five virulent BXo races and SNP genotyping revealed that these lines also contained a blast resistance gene Pita races. Gene pyramided restorer lines, BRRI31R-MASP3 and BRRI31R-MASP4 can directly be used as a male parent for the development of new BB resistant hybrid rice variety or could be used as a replacement of restorer line of BRRI hybrid dhan5 and 7 to enhance the quality of hybrid seeds as well as rice production in Bangladesh.

Genetic analysis and identification of SSR marker linked topowdery mildew resistance in bitter gourd (&lt;i&gt;Momordica charantia &lt;/i&gt;L.)

The inheritance of powdery mildew resistance in bitter gourd resistant line IIHR-144-1 was studied in cross with two susceptible lines Arka Harit and IIHR Sel-5-8. The segregation ratios in F2 and backcross progenies indicated that resistance is governed by dominant-recessive epistasis or dominant inhibitory epistasis, indicating the involvement of more than one pairs of genes, one dominant and one recessive for resistance along with other background minor genes in the resistant line IIHR-144-1. Bulk segregant analysis of F2 population of cross between IIHR-144-1 and Arka Harit using SSR markers identified McSSR 57 produced a polymorphic DNA fragment that co-segregated with disease reaction. Considering the cross compatibility between Momordica charantia L. and M. charantia var. muricata (IIHR-144-1) the resistance trait can be transferred to cultivated species through hybridization and selection.

Growth Evaluation of Backcross Progenies BC2F1 Experiencing Submerg-ence and Non-submergence at BC1F1 and its Parents

The utilization of dual-resistant varieties that are resistant to soaking and drought in certain periods is an alternative to rice cultivation in swampy land. Inpara 8 is a variety that is confirmed to have SUB 1 gene, resistant to submerged stress and Inpago 5 is identified to be resistant to drought stress. Crosses were made between Inpara 8 (donor parent) with Inpago 5 (recipient parent), resulting in F1, then F1 was crossed back with Inpago 5 and produced BC1F1, then crossed back with Inpago 5 to become BC2F1. This paper contains an evaluation of the growth of BC2F1, which in the BC1F1 stage experienced submerged stress in the vegetative phase and which did not experience submerged stress. The research was carried out in August 2021 - January 2022 at the Greenhouse of the Department of Agricultural Cultivation, Faculty of Agriculture, Sriwijaya University. The results showed that in the vegetative phase, progeny BC2F1 TR has an average value of the highest per plant (113.64 cm) and the average per plant height Inpara 8 (3.93). In the generative phase, the fastest flowering time on the accession of BC2F1 TR (68 days), the fastest harvest time on Inpara 8 (122.93 days), while for the amount of grain per panicle, the amount of grain per clump, and dry weight on Inpago 5 (529.60 g, 2648 g, and 11.62 g). The average yield of BC2F1 progeny is more similar to Inpago 5 as the recipient parent. Both progeny have the same Sub 1 gene in them and can survive to produce, but Accessions that have experienced previous submerged stress are more vulnerable to growth so they have an impact on the resulting production.

Mutations in the dwarf3 gene confer height stability in sorghum.

Dwarfism is a useful trait in many crop plants because it contributes to improved lodging resistance and harvest index. The mutant allele dw3-ref (dwarf3-reference) of sorghum [Sorghum bicolor (L.) Moench] is characterized by an 882bp tandem duplication in the fifth exon of the gene that is unstable and reverts to wild-type at a frequency greater than 0.001 in many genetic backgrounds. The goal of this research was to identify stable alleles of dw3 (dwarf3) that could be backcrossed into elite parent lines to improve height stability of the crop. To discover new alleles of dw3, a panel consisting mostly of sorghum conversion lines (SC-lines) was screened by polymerase chain reaction for the 882bp tandem duplication in the fifth exon of dw3-ref. Sanger sequencing was used to characterize the DNA sequence of this fragment in genotypes that did not contain the 882bp tandem duplication. Sequence analysis identified three indel mutations, including an 82bp deletion, a 6bp duplication, and a 15bp deletion in this region of the gene. Field trials of the donor genotypes with these new alleles indicated no wild-type revertants of dw3-sd3 (dwarf3-stable dwarf), dw3-sd4, and dw3-sd5. These alleles were backcrossed into Tx430. Field trials of backcross progeny (BC2F4) with the dw3-sd3, dw3-sd4, and dw3-sd5 alleles indicated no revertants. The plant height and flowering time characteristics of the backcross progeny were similar or slightly shorter and earlier than the recurrent parent. These findings demonstrate that dw3-sd3, dw3-sd4, and dw3-sd5 alleles will be useful in breeding for the stable dwarf trait.

Genomewide marker estimates of the level of dominance in maize heterosis

AbstractHeterosis is the superiority of an F1 hybrid over its parents, and overdominance and dominance are the two main hypotheses for the genetic basis of heterosis. Our objectives were to determine if genomewide marker effects accurately reflect the level of dominance at quantitative trait loci (QTL) and assess the distribution of per‐marker estimates of the level of dominance in maize (Zea mays L.). We simulated different levels of dominance at QTL that were in coupling, repulsion, and random linkage phases. Genomewide marker effects from ridge regression‐best linear unbiased prediction led to accurate estimates of the level of dominance when all linkages were in coupling phase, but repulsion and random linkage phases led to an upward bias. We then estimated levels of dominance from genomewide marker effects in a reciprocal testcross experiment with 1642 hybrids genotyped with 4805 single nucleotide polymorphism markers, and in a legacy Design III experiment with 351 backcross progenies (subjected to three generations of random mating to dissipate linkages) genotyped with 160 simple sequence repeats. In both experiments, the level of dominance was higher for yield than for moisture. For each trait, some loci showed little or no dominance, others showed partial to complete dominance, and others showed overdominance. A high level of dominance was typically due to a small difference between homozygote values. Overall, the results were consistent with previous QTL mapping results indicating that heterosis in maize is due to varying levels of dominance rather than a prevalent level of dominance.

Mapping QTLs and candidate genes introgressed from Sinapis alba for siliquae related traits in second backcross progeny of allohexaploid brassica

Mapping QTLs and candidate genes introgressed from Sinapis alba for siliquae related traits in second backcross progeny of allohexaploid brassica

Interbiotype hybridization between biotypes A and B of Liriomyza chinensis (Diptera: Agromyzidae).

Liriomyza chinensis (Kato) is a formidable pest of Allium species, especially the Japanese bunching onion Allium fistulosum L. Recently, a novel biotype of L. chinensis (biotype B) has emerged, which causes more severe damage than the native biotype A. It has been reported that biotype B has frequently displaced biotype A in the Japanese bunching onion fields in Japan. As interbiotype hybridization is a possible factor that influences such displacement, interbiotype hybridization was conducted between L. chinensis biotypes A and B. Eggs were not laid under one-by-one crossing conditions; however, adult hybrid progeny of both sexes emerged from no-choice mating combinations-when multiple males and females were present. The fertility of F1 hybrid adults was also investigated, and backcrossed adults emerged from F1 females in both mating combinations. F1 males might have exhibited reproductive abnormalities because only a small number of backcross progeny emerged from the mating combinations using F1 males. Additionally, 3 representative endosymbionts (Wolbachia, Spiroplasma, and Cardinium) were investigated, and both biotypes were found to be infected by the same strain of Wolbachia. In addition, the courtship signals (tapping) of male adults differed between biotypes A and B as well as between F1 hybrids; the F1 males exhibited tapping behavior that was intermediate between biotypes A and B. Therefore, mating sounds serve as a form of premating reproductive isolation between biotypes A and B.

Fitness of the first backcross generations from the second to the sixth progenies of glyphosate-resistant transgenic Brassica napus and wild Brassica juncea in absence of the herbicide

Abstract Successful introgression of a transgene from a transgenic crop into a wild or weedy relative is determined by the fitness of backcross generations carrying the transgene. To provide insight for ecological risk assessment of gene flow between transgenic Brassica napus and wild Brassica juncea, this study investigated the fitness of the first backcross generations from the second to the sixth progenies (BC1F2R–BC1F6R) between glyphosate-resistant transgenic B. napus and wild B. juncea at low density (5 plants/m2) and high density (10 plants/m2), and monoculture and mixed planting (wild B. juncea: BC1F2R–BC1F6R = 1:1). Correlations between the fitness components of backcross progeny, planting density and planting patterns were analyzed. In the monoculture at low density, compared with B. juncea, earlier generations BC1F2R and BC1F3R had low composite fitness, while later generations from BC1F4R to BC1F6R were more fit. At high density, whatever monoculture or mixed planting, all backcrossed generations had lower composite fitness than B. juncea. Correlation analysis indicated that both planting density and pattern significantly affected the fitness components of the first backcross generations from the second to the sixth progenies (BC1F2R–BC1F6R). These results indicate that the probability of transgene introgression from cultivated B. napus to weedy B. juncea is likely to be highly contingent on the specific growing conditions of their backcross descendants.

Testing a candidate meiotic drive locus identified by pool sequencing.

Meiotic drive biases the transmission of alleles in heterozygous individuals, such that Mendel's law of equal segregation is violated. Most examples of meiotic drive have been discovered over the past century based on causing sex ratio distortion or the biased transmission of easily scoreable genetic markers that were linked to drive alleles. More recently, several approaches have been developed that attempt to identify distortions of Mendelian segregation genome wide. Here, we test a candidate female meiotic drive locus in Drosophila melanogaster, identified previously as causing a ∼54:46 distortion ratio using sequencing of large pools of backcross progeny. We inserted fluorescent visible markers near the candidate locus and scored transmission in thousands of individual progeny. We observed a small but significant deviation from the Mendelian expectation; however, it was in the opposite direction to that predicted based on the original experiments. We discuss several possible causes of the discrepancy between the 2 approaches, noting that subtle viability effects are particularly challenging to disentangle from potential small-effect meiotic drive loci. We conclude that pool sequencing approaches remain a powerful method to identify candidate meiotic drive loci but that genotyping of individual progeny at early developmental stages may be required for robust confirmation.

Esterase Profile in Distinguishing Inbreeds F1 And Backcross Hybrids in Indian Major Carps

Esterase was surveyed in four different tissues namely skeletal muscle, heart, liver and kidney obtained from two Indian major carps viz.., rohu (Labeo rohita) and catla (Catla catla) pair crossed F1 hybrids of catla (y) x rohu (6), and back crossed hybrid progenies of (catla x rohu) (?) x catla (J) (BC1C) and of (catla x rohu) (?) x rohu (6) (BC1R). The enzyme was found to be highly polymorphic in different tissues of the inbred as well as in hybrids. Detailed scanning of different activity zones in the zymograms revealed that amidst 15 bands, band numbers 4 and 12 of liver and kidney tissues were found to be common in both the inbreeds and hybrids were probably characteristics bands to these two species and their hybrid progenies. Band 4 of rohu and 6/7 of catla were diagnostic bands of pure rohu and catla, respectively, regardless of the nature of the tissue. However, both the bands were present in F 1 hybrid and BC1C backcross progenies only. Another backcross i.e. BC1R could not manifest shared bandings of the parents perhaps because of cleavage into or fusion with other sister esterase isomorphs through homo- or hetero-polymerization. Only band 4 was found to be present across all the tissues in BC 1R renders its demarcation difficult from rohu inbreed. However, band 9 and 13 of liver in BC1R can distinguishit from F1and inbreeds. They are likely to be instrumental in distinguishing inbreeds from hybrids reliably. The mean pair wise similarity (S) based on esterase profile, between the parents (catla and rohu) and the developed progenies (F, hybrids, BC1C and BC1R) showed BC1C was genetically more diverse than the F 1hybrids and BC1R for esterase which may be used in carp breeding and improvement programme if it is found to be tightly linked with any characters of economic importance.

Homoeologous Chromosome Pairing and Alien Introgression in Backcrossing Progenies Derived from Hybrids Solanum tuberosum (+) Mexican 2x (1 EBN) B-Genome Potato Species

We applied a genomic in situ hybridization (GISH) to analyze the genomic constitution of and meiotic pairing in interspecific somatic hybrids, and in a wide subset of backcrossing derivatives (BC1–BC5), from three interspecific combinations involving the cultivated potato, Solanum tuberosum (AAAA genome), and three diploid (1 EBN) wild Mexican potato species (genome BB)—S. tarnii, S. pinnatisectum, and S. bulbocastanum. The theoretically expected genomic composition was detected in the somatic hybrids (AAAABB) and in the BC1 progeny (AAAAB), whereas in the subsequent BC2–BC4 generations, the partial loss of alien chromosomes was observed and almost all the BC5 genotypes showed a complete chromosome elimination of wild species. GISH revealed a homoeologous pairing between the chromosomes of the A- and the B-genomes in each of the hybrid progenies. Using GISH, we selected introgression lines with a single chromosome of the wild species in a potato genome background, as well as introgression lines with intergenomic recombinant chromosomes. Moreover, via molecular screening, BC hybrids with diagnostic markers for the R-genes conferring resistance to late blight disease and to the quarantine pest of the potato–Columbia root-knot nematode—were selected. The potential application of the results obtained for the planning of introgressive schemes directed to the breeding of advanced lines with multiple disease and pest resistance is discussed.

Development of alloplasmic male sterile lines and their assessment for heterotic potential in eggplant (Solanum melongena L.)

ABSTRACT The use of Solanum aethiopicum as the female parent with S. melongena led to the development of a cytoplasmic-genic male sterility system (CGMS) in eggplant. The male sterility was complete and expressed as rudimentary anthers with no pollen grains. Ten backcross progenies of male sterile lines in diverse genetic backgrounds of S. melongena were characterised after BC7 generation for 14 horticultural traits. It was observed that male sterile lines and their respective maintainer parents were isogenic for all the traits, except stamen size and days to 50% flowering. The fertility of male sterile lines was restored after hybridising with plants derived from an S. melongena × S. aethiopicum cross. The fertility restoration was governed by a single dominant gene. The maternal cytoplasm of S. aethiopicum in male sterile lines and of S. melongena in maintainers and restorers was confirmed with mitochondria and chloroplast DNA-specific molecular markers. Further, to assess the heterotic potential, 10 cytoplasmic male sterility lines were crossed with three restorers to develop 30 F1 hybrids, out of which D−67A × R−6 and D−104A × R−6 were found consistently better than the standard check for yield plant−1 over two years. In this manuscript a comprehensive study on development and utilisation of an alloplasmic CGMS system in eggplant has been discussed.

Specifics of Transfer of DNA Markers of Wild Allotetraploid Potato Species Solanum stoloniferum to Backcross Progenies Depending on Their Subgenomic Location and Used Schemes of Introgression

Specifics of Transfer of DNA Markers of Wild Allotetraploid Potato Species Solanum stoloniferum to Backcross Progenies Depending on Their Subgenomic Location and Used Schemes of Introgression

The effect of inheritance of IgE responsiveness on the susceptibility of mice to Trichinella spiralis infection.

IgE antibodies are likely involved in host protection. Trichinella spiralis is a helminth that induces protection through IgE antibodies. The present study examined T. spiralis susceptibility in high and low IgE responder mice, with a specific focus on the inheritance of IgE responsiveness, which controls IgE production specific for the IgE isotype and non-specific for antigens. Furthermore, low IgE responsiveness is inherited as a recessive trait under a single gene, which is not linked to the H-2 gene. This study determined the total IgE and anti-T. spiralis IgE antibody levels after T. spiralis infection in low IgE responder SJL/J mice were several times lower than those in high IgE responders, such as the BALB/c mice. An IgE-dependent susceptibility to T. spiralis, evaluated in mice treated with anti-IgE antibodies and in control mice, was observed in high IgE responder mice but not in low IgE responder mice. The inheritance of IgE responsiveness and susceptibility to T. spiralis was investigated using crosses of SJL/J with high IgE responders. All of the (BALB/c × SJL/J) F1 and half of the (BALB/c × SJL/J) F1 × SJL backcross progenies were high IgE responders after T. spiralis infection. Total IgE and antigen-specific IgE antibody levels were correlated and not linked to H-2. It should be noted that high IgE responders always exhibited low susceptibility, suggesting that the trait of IgE responsiveness functions as a trait of susceptibility to T. spiralis.

Mode of inheritance of field-evolved resistance to pirimiphos-methyl in Sitophilus oryzae (Linnaeus) (Coleoptera: Curculionidae)

Sitophilus oryzae is an economic pest of stored grain worldwide with the ability to transmit mycotoxigenic fungi in the infested commodities. Recently this pest has shown field-evolved resistance to pirimiphos-methyl in Pakistan. Understanding mode of inheritance of insecticide resistance is of prime importance in order to implement a successful resistance management program. Here, we studied the mode of inheritance of resistance to pirimiphos-methyl in two field-evolved resistant strains (LR-SO and HR-SO) of S. oryzae. LR-SO and HR-SO strains exhibited 31.05 and 219.18 fold resistance to pirimiphos-methyl compared with an insecticide susceptible reference strain (Lab-SO). Reciprocal progenies revealed an indistinguishable difference in their response (LC50s) to pirimiphos-methyl pointing out the absence of maternal effects or sex-linkage and autosomal inheritance pattern. The degree of dominance values for all the reciprocal and pooled progenies ranged from −0.47 to −0.78 suggesting that resistance to pirimiphos-methyl was expressed as an incompletely recessive trait. Chi-square and log-dose probit line analyses of self-bred and backcross progenies exhibited significant variation between the expected and observed mortality, which suggest that resistance was governed by more than one gene. In conclusion, field-evolved resistance to pirimiphos-methyl in S. oryzae was autosomal, incompletely recessive, and multigenic. Our results provide basic information about the nature of resistance to pirimiphos-methyl that will be helpful to formulate successful management strategies for controlling S. oryzae and to alleviate the allied threats to environment and human health.

Microsporogenesis in the triploid hybrid ‘Beilinxiongzhu 1#’ and detection of primary trisomy in 2x × 3 × Populus hybrids

BackgroundPrimary trisomy is a powerful genetic tool in plants. However, trisomy has not been detected in Populus as a model system for tree and woody perennial plant biology.ResultsIn the present study, a backcross between Populus alba × Populus glandulosa ‘YXY 7#’ (2n = 2x = 38) and the triploid hybrid ‘Beilinxiongzhu 1#’ (2n = 3x = 57) based on the observation of microsporogenesis and an evaluation of the variations in pollen was conducted to create primary trisomy. Many abnormalities, such as premature migration of chromosomes, lagging of chromosomes, chromosome bridges, asymmetric separation, micronuclei, and premature cytokinesis, have been detected during meiosis of the triploid hybrid clone ‘Beilinxiongzhu 1#’. However, these abnormal behaviors did not result in completely aborted pollen. The pollen diameter of the triploid hybrid clone ‘Beilinxiongzhu 1#’ is bimodally distributed, which was similar to the chromosomal number of the backcross progeny. A total of 393 progeny were generated. We provide a protocol for determining the number of chromosomes in aneuploid progeny, and 19 distinct simple sequence repeat (SSR) primer pairs covering the entire Populus genome were developed. Primary trisomy 11 and trisomy 17 were detected in the 2x × 3 x hybrid using the SSR molecular markers and counting of somatic chromosomes.ConclusionsNineteen distinct SSR primer pairs for determining chromosomal number in aneuploid individuals were developed, and two Populus trisomies were detected from 2x × 3 x hybrids by SSR markers and somatic chromosome counting. Our findings provide a powerful genetic tool to reveal the function of genes in Populus.

Reference genomes of channel catfish and blue catfish reveal multiple pericentric chromosome inversions

BackgroundChannel catfish and blue catfish are the most important aquacultured species in the USA. The species do not readily intermate naturally but F1 hybrids can be produced through artificial spawning. F1 hybrids produced by mating channel catfish female with blue catfish male exhibit heterosis and provide an ideal system to study reproductive isolation and hybrid vigor. The purpose of the study was to generate high-quality chromosome level reference genome sequences and to determine their genomic similarities and differences.ResultsWe present high-quality reference genome sequences for both channel catfish and blue catfish, containing only 67 and 139 total gaps, respectively. We also report three pericentric chromosome inversions between the two genomes, as evidenced by long reads across the inversion junctions from distinct individuals, genetic linkage mapping, and PCR amplicons across the inversion junctions. Recombination rates within the inversional segments, detected as double crossovers, are extremely low among backcross progenies (progenies of channel catfish female × F1 hybrid male), suggesting that the pericentric inversions interrupt postzygotic recombination or survival of recombinants. Identification of channel catfish- and blue catfish-specific genes, along with expansions of immunoglobulin genes and centromeric Xba elements, provides insights into genomic hallmarks of these species.ConclusionsWe generated high-quality reference genome sequences for both blue catfish and channel catfish and identified major chromosomal inversions on chromosomes 6, 11, and 24. These perimetric inversions were validated by additional sequencing analysis, genetic linkage mapping, and PCR analysis across the inversion junctions. The reference genome sequences, as well as the contrasted chromosomal architecture should provide guidance for the interspecific breeding programs.