Sterile F1 Hybrids Research Articles

Abnormal expression of LiASY1 and LiDMC1 is the main cause of sterility in F1 hybrids developed from Lagerstroemia speciosa and Lagerstroemia indica ‘Ebony Embers’

Lagerstroemia × ‘Xiaoxiang Huaxiu’ (an F1 hybrid of Lagerstroemia speciosa and Lagerstroemia indica ‘Ebony Embers’) exhibits significant sterility. Cytological studies have revealed numerous abnormal chromosomal behaviors during the meiotic division of pollen mother cells in L. × ‘Xiaoxiang Huaxiu’. Transcriptome sequencing identified that LiDMC1 and LiASY1 were expressed at very low levels in ‘Xiaoxiang Huaxiu’. To further verify whether the abnormal expression of LiDMC1 and LiASY1 was the fundamental cause of sterility in ‘Xiaoxiang Huaxiu’, we cloned the full-length gene sequences of LiDMC1 and LiASY1 from ‘Ebony Embers’. Using VIGS (virus-induced gene silencing) technology, pTRV1 and pTRV2 gene silencing vectors were employed to silence LiDMC1 and LiASY1 in the paternal parent ‘Ebony Embers’. The results indicated that in the double-silenced lines of ‘Ebony Embers’, the cytoplasm sizes of different tetrads during the tetrad stage varied significantly. There was a notable proportion of polyads, binucleate cells with micronuclei, and pentads. Additionally, pollen diameter varied significantly, closely resembling the sterility observed in ‘Xiaoxiang Huaxiu’. Pollen viability in the double-silenced ‘Ebony Embers’ decreased by 22.8%. This study demonstrates that the low expression of LiDMC1 and LiASY1 leads to abnormal microspore development in ‘Ebony Embers’, and their low expression is the cause of sterility in ‘Xiaoxiang Huaxiu’.

Identification, Elucidation and Deployment of a Cytoplasmic Male Sterility System for Hybrid Potato.

Recent advances in diploid F1 hybrid potato breeding rely on the production of inbred lines using the S-locus inhibitor (Sli) gene. As a result of this method, female parent lines are self-fertile and require emasculation before hybrid seed production. The resulting F1 hybrids are self-fertile as well and produce many undesirable berries in the field. Utilization of cytoplasmic male sterility would eliminate the need for emasculation, resulting in more efficient hybrid seed production and male sterile F1 hybrids. We observed plants that completely lacked anthers in an F2 population derived from an interspecific cross between diploid S. tuberosum and S. microdontum. We studied the antherless trait to determine its suitability for use in hybrid potato breeding. We mapped the causal locus to the short arm of Chromosome 6, developed KASP markers for the antherless (al) locus and introduced it into lines with T and A cytoplasm. We found that antherless type male sterility is not expressed in T and A cytoplasm, proving that it is a form of CMS. We hybridized male sterile al/al plants with P cytoplasm with pollen from al/al plants with T and A cytoplasm and we show that the resulting hybrids set significantly fewer berries in the field. Here, we show that the antherless CMS system can be readily deployed in diploid F1 hybrid potato breeding to improve hybridization efficiency and reduce berry set in the field.

Spontaneous hybridization among invasive Poaceae in Hawai‘i: Chloris × pseudosagrana nothosp. nov. and Cenchrus × peregrinus nothosp. nov.

During grass surveys across the islands of Hawai‘i in 2022, two novel hybrids among non-native Poaceae were found growing on roadsides. Spontaneous hybridization was observed among Chloris barbata and C. divaricata on O‘ahu and among Cenchrus clandestinus and C. setaceus on Hawai‘i island. Morphological evidence initially suggested these plants may be hybrids and molecular analysis using the ITS and rpl32-trnL regions confirmed that the plants are hybrids and identified their parentage. These hybrids are named Chloris × pseudosagrana nothosp. nov. and Cenchrus × peregrinus nothosp. nov. No developed seeds could be found on either of these hybrids and they are suspected to be sterile F1 hybrids. The occurrence of hybridization events among other non-native species are also discussed.

Genomic mechanisms and consequences of diverse postzygotic barriers between monkeyflower species.

The evolution of genomic incompatibilities causing postzygotic barriers to hybridization is a key step in species divergence. Incompatibilities take two general forms - structural divergence between chromosomes leading to severe hybrid sterility in F1 hybrids and epistatic interactions between genes causing reduced fitness of hybrid gametes or zygotes (Dobzhansky-Muller incompatibilities). Despite substantial recent progress in understanding the molecular mechanisms and evolutionary origins of both types of incompatibility, how each behaves across multiple generations of hybridization remains relatively unexplored. Here, we use genetic mapping in F2 and RIL hybrid populations between the phenotypically divergent but naturally hybridizing monkeyflowers Mimulus cardinalis and M. parishii to characterize the genetic basis of hybrid incompatibility and examine its changing effects over multiple generations of experimental hybridization. In F2s, we found severe hybrid pollen inviability (< 50% reduction vs. parental genotypes) and pseudolinkage caused by a reciprocal translocation between Chromosomes 6 and 7 in the parental species. RILs retained excess heterozygosity around the translocation breakpoints, which caused substantial pollen inviability when interstitial crossovers had not created compatible heterokaryotypic configurations. Strong transmission ratio distortion and inter-chromosomal linkage disequilibrium in both F2s and RILs identified a novel two-locus genic incompatibility causing sex-independent gametophytic (haploid) lethality. The latter interaction eliminated three of the expected nine F2 genotypic classes via F1 gamete loss without detectable effects on the pollen number or viability of F2 double heterozygotes. Along with the mapping of numerous milder incompatibilities, these key findings illuminate the complex genetics of plant hybrid breakdown and are an important step toward understanding the genomic consequences of natural hybridization in this model system.

The contribution of sex chromosome conflict to disrupted spermatogenesis in hybrid house mice.

Incompatibilities on the sex chromosomes are important in the evolution of hybrid male sterility, but the evolutionary forces underlying this phenomenon are unclear. House mice (Mus musculus) lineages have provided powerful models for understanding the genetic basis of hybrid male sterility. X chromosome-autosome interactions cause strong incompatibilities in M. musculus F1 hybrids, but variation in sterility phenotypes suggests a more complex genetic basis. In addition, XY chromosome conflict has resulted in rapid expansions of ampliconic genes with dosage-dependent expression that is essential to spermatogenesis. Here, we evaluated the contribution of XY lineage mismatch to male fertility and stage-specific gene expression in hybrid mice. We performed backcrosses between two house mouse subspecies to generate reciprocal Y-introgression strains and used these strains to test the effects of XY mismatch in hybrids. Our transcriptome analyses of sorted spermatid cells revealed widespread overexpression of the X chromosome in sterile F1 hybrids independent of Y chromosome subspecies origin. Thus, postmeiotic overexpression of the X chromosome in sterile F1 mouse hybrids is likely a downstream consequence of disrupted meiotic X-inactivation rather than XY gene copy number imbalance. Y chromosome introgression did result in subfertility phenotypes and disrupted expression of several autosomal genes in mice with an otherwise nonhybrid genomic background, suggesting that Y-linked incompatibilities contribute to reproductive barriers, but likely not as a direct consequence of XY conflict. Collectively, these findings suggest that rapid sex chromosome gene family evolution driven by genomic conflict has not resulted in strong male reproductive barriers between these subspecies of house mice.

Unraveling patterns of disrupted gene expression across a complex tissue.

Whole tissue RNASeq is the standard approach for studying gene expression divergence in evolutionary biology and provides a snapshot of the comprehensive transcriptome for a given tissue. However, whole tissues consist of diverse cell types differing in expression profiles, and the cellular composition of these tissues can evolve across species. Here, we investigate the effects of different cellular composition on whole tissue expression profiles. We compared gene expression from whole testes and enriched spermatogenesis populations in two species of house mice, Mus musculus musculus and M. m. domesticus, and their sterile and fertile F1 hybrids, which differ in both cellular composition and regulatory dynamics. We found that cellular composition differences skewed expression profiles and differential gene expression in whole testes samples. Importantly, both approaches were able to detect large-scale patterns such as disrupted X chromosome expression, although whole testes sampling resulted in decreased power to detect differentially expressed genes. We encourage researchers to account for histology in RNASeq and consider methods that reduce sample complexity whenever feasible. Ultimately, we show that differences in cellular composition between tissues can modify expression profiles, potentially altering inferred gene ontological processes, insights into gene network evolution, and processes governing gene expression evolution.

Stage-specific disruption of X chromosome expression during spermatogenesis in sterile house mouse hybrids.

Hybrid sterility is a complex phenotype that can result from the breakdown of spermatogenesis at multiple developmental stages. Here, we disentangle two proposed hybrid male sterility mechanisms in the house mice, Mus musculus domesticus and M. m. musculus, by comparing patterns of gene expression in sterile F1 hybrids from a reciprocal cross. We found that hybrid males from both cross directions showed disrupted X chromosome expression during prophase of meiosis I consistent with a loss of meiotic sex chromosome inactivation (MSCI) and Prdm9-associated sterility, but that the degree of disruption was greater in mice with an M. m. musculus X chromosome consistent with previous studies. During postmeiotic development, gene expression on the X chromosome was only disrupted in one cross direction, suggesting that misexpression at this later stage was genotype-specific and not a simple downstream consequence of MSCI disruption which was observed in both reciprocal crosses. Instead, disrupted postmeiotic expression may depend on the magnitude of earlier disrupted MSCI, or the disruption of particular X-linked genes or gene networks. Alternatively, only hybrids with a potential deficit of Sly copies, a Y-linked ampliconic gene family, showed overexpression in postmeiotic cells, consistent with a previously proposed model of antagonistic coevolution between the X- and Y-linked ampliconic genes contributing to disrupted expression late in spermatogenesis. The relative contributions of these two regulatory mechanisms and their impact on sterility phenotypes await further study. Our results further support the hypothesis that X-linked hybrid sterility in house mice has a variable genetic basis, and that genotype-specific disruption of gene regulation contributes to overexpression of the X chromosome at different stages of development. Overall, these findings underscore the critical role of epigenetic regulation of the X chromosome during spermatogenesis and suggest that these processes are prone to disruption in hybrids.

Insights on life cycle and cell identity regulatory circuits for unlocking genetic improvement in Zygosaccharomyces and Kluyveromyces yeasts.

ABSTRACTEvolution has provided a vast diversity of yeasts that play fundamental roles in nature and society. This diversity is not limited to genotypically homogeneous species with natural interspecies hybrids and allodiploids that blur species boundaries frequently isolated. Thus, life cycle and the nature of breeding systems have profound effects on genome variation, shaping heterozygosity, genotype diversity and ploidy level. The apparent enrichment of hybrids in industry-related environments suggests that hybridization provides an adaptive route against stressors and creates interest in developing new hybrids for biotechnological uses. For example, in the Saccharomyces genus where regulatory circuits controlling cell identity, mating competence and meiosis commitment have been extensively studied, this body of knowledge is being used to combine interesting traits into synthetic F1 hybrids, to bypass F1 hybrid sterility and to dissect complex phenotypes by bulk segregant analysis. Although these aspects are less known in other industrially promising yeasts, advances in whole-genome sequencing and analysis are changing this and new insights are being gained, especially in the food-associated genera Zygosaccharomyces and Kluyveromyces. We discuss this new knowledge and highlight how deciphering cell identity circuits in these lineages will contribute significantly to identify the genetic determinants underpinning complex phenotypes and open new avenues for breeding programmes.

Wolbachia and host intrinsic reproductive barriers contribute additively to postmating isolation in spider mites.

Wolbachia are maternally-inherited bacteria that induce cytoplasmic incompatibility in many arthropod species. However, the ubiquity of this isolation mechanism for host speciation processes remains elusive, as only few studies have examined Wolbachia-induced incompatibilities when host populations are not genetically compatible. Here, we used three populations of two genetically differentiated colour forms of the haplodiploid spider mite Tetranychus urticae to dissect the interaction between Wolbachia-induced and host-associated incompatibilities, and their relative contribution to postmating isolation. We found that these two sources of incompatibility act through different mechanisms in an additive fashion. Host-associated incompatibility contributes 1.5 times more than Wolbachia-induced incompatibility in reducing hybrid production, the former through an overproduction of haploid sons at the expense of diploid daughters (ca. 75% decrease) and the latter by increasing the embryonic mortality of daughters (by ca. 49%). Furthermore, regardless of cross direction, we observed near-complete F1 hybrid sterility and complete F2 hybrid breakdown between populations of the two forms, but Wolbachia did not contribute to this outcome. We thus show mechanistic independence and an additive nature of host-intrinsic and Wolbachia-induced sources of isolation. Wolbachia may contribute to reproductive isolation in this system, thereby potentially affecting host differentiation and distribution in the field.

Hybrid Sterility, Genetic Conflict and Complex Speciation: Lessons From the Drosophila simulans Clade Species.

The three fruitfly species of the Drosophila simulans clade— D. simulans, D. mauritiana, and D. sechellia— have served as important models in speciation genetics for over 40 years. These species are reproductively isolated by geography, ecology, sexual signals, postmating-prezygotic interactions, and postzygotic genetic incompatibilities. All pairwise crosses between these species conform to Haldane’s rule, producing fertile F1 hybrid females and sterile F1 hybrid males. The close phylogenetic proximity of the D. simulans clade species to the model organism, D. melanogaster, has empowered genetic analyses of their species differences, including reproductive incompatibilities. But perhaps no phenotype has been subject to more continuous and intensive genetic scrutiny than hybrid male sterility. Here we review the history, progress, and current state of our understanding of hybrid male sterility among the D. simulans clade species. Our aim is to integrate the available information from experimental and population genetics analyses bearing on the causes and consequences of hybrid male sterility. We highlight numerous conclusions that have emerged as well as issues that remain unresolved. We focus on the special role of sex chromosomes, the fine-scale genetic architecture of hybrid male sterility, and the history of gene flow between species. The biggest surprises to emerge from this work are that (i) genetic conflicts may be an important general force in the evolution of hybrid incompatibility, (ii) hybrid male sterility is polygenic with contributions of complex epistasis, and (iii) speciation, even among these geographically allopatric taxa, has involved the interplay of gene flow, negative selection, and positive selection. These three conclusions are marked departures from the classical views of speciation that emerged from the modern evolutionary synthesis.

Gene and Transposable Element Expression Evolution Following Recent and Past Polyploidy Events in Spartina (Poaceae).

Gene expression dynamics is a key component of polyploid evolution, varying in nature, intensity, and temporal scales, most particularly in allopolyploids, where two or more sub-genomes from differentiated parental species and different repeat contents are merged. Here, we investigated transcriptome evolution at different evolutionary time scales among tetraploid, hexaploid, and neododecaploid Spartina species (Poaceae, Chloridoideae) that successively diverged in the last 6–10 my, at the origin of differential phenotypic and ecological traits. Of particular interest are the recent (19th century) hybridizations between the two hexaploids Spartina alterniflora (2n = 6x = 62) and S. maritima (2n = 6x = 60) that resulted in two sterile F1 hybrids: Spartina × townsendii (2n = 6x = 62) in England and Spartina × neyrautii (2n = 6x = 62) in France. Whole genome duplication of S. × townsendii gave rise to the invasive neo-allododecaploid species Spartina anglica (2n = 12x = 124). New transcriptome assemblies and annotations for tetraploids and the enrichment of previously published reference transcriptomes for hexaploids and the allododecaploid allowed identifying 42,423 clusters of orthologs and distinguishing 21 transcribed transposable element (TE) lineages across the seven investigated Spartina species. In 4x and 6x mesopolyploids, gene and TE expression changes were consistent with phylogenetic relationships and divergence, revealing weak expression differences in the tetraploid sister species Spartina bakeri and Spartina versicolor (<2 my divergence time) compared to marked transcriptome divergence between the hexaploids S. alterniflora and S. maritima that diverged 2–4 mya. Differentially expressed genes were involved in glycolysis, post-transcriptional protein modifications, epidermis development, biosynthesis of carotenoids. Most detected TE lineages (except SINE elements) were found more expressed in hexaploids than in tetraploids, in line with their abundance in the corresponding genomes. Comparatively, an astonishing (52%) expression repatterning and deviation from parental additivity were observed following recent reticulate evolution (involving the F1 hybrids and the neo-allododecaploid S. anglica), with various patterns of biased homoeologous gene expression, including genes involved in epigenetic regulation. Downregulation of TEs was observed in both hybrids and accentuated in the neo-allopolyploid. Our results reinforce the view that allopolyploidy represents springboards to new regulatory patterns, offering to worldwide invasive species, such as S. anglica, the opportunity to colonize stressful and fluctuating environments on saltmarshes.

Profitability of cultivation of onion interspecific hybrids

Based on interspecific plant crossing of the genus Allium L., with the overcoming of species incompatibility by embryo culture invitro and sterility of F1 hybrids using polyploidy, backcrossing and inbreeding of hybrid forms, cytological analysis, selection evaluation and selection of recombinant forms, highly effective technological processes for creating initial forms of onion interspecific hybrids were developed. The aim of obtaining onion interspecific hybrids is to create resistant forms of onions to false mildew. The paper shows the possibility of growing onion interspecific hybrids that are relatively resistant to false mildew without the use of fungicides to increase the economic efficiency of onion production, as well as to obtain more environmentally friendly and high-quality products.

Development of Fertility-Restoring Lines for 9E Type CMS of Sorghum Using Environmentally Induced Fertility Revertants

Development of reliable fertility-restoring lines is the most important prerequisite for using cytoplasmic male sterility (CMS) in plant breeding. Sorghum 9E type CMS is characterized by unstable expression of fertility-restoring genes, which require high levels of water availability for plants during microsporogenesis and flowering. In order to create reliable male-fertility-restoring lines for 9E type CMS, the progeny of test crosses of fertile revertant lines in 9E cytoplasm, which were obtained as a result of reversions in sterile F1 hybrids induced by conditions of high water availability, with CMS lines in this cytoplasm were grown in selective backgrounds: in the dry plots and in the plots with additional watering as well as in the field under natural moisture supply. In the majority of hybrid combinations, fertile plants were observed only when additionally watered during the flowering period. F1 hybrids with different CMS lines with 9E cytoplasm significantly differed in terms of the degree of restored fertility and the response to water availability conditions. Fertile plants predominated in the F2 families; in different hybrid combinations, the ratio of restored and sterile plants corresponded to 3 : 1 or 13 : 3 segregation. After selection in the drought conditions of the fertile plants from the offspring of hybrids from the cross of the CMS line 9E Pishchevoe 614 and male-fertile revertants, two lines were obtained that were able to restore fertility of F1 hybrids in field conditions.

Genomic Structure of Hstx2 Modifier of Prdm9-Dependent Hybrid Male Sterility in Mice.

F1 hybrids between mouse inbred strains PWD and C57BL/6 represent the most thoroughly genetically defined model of hybrid sterility in vertebrates. Hybrid male sterility can be fully reconstituted from three components of this model, the Prdm9 gene, intersubspecific homeology of Mus musculus musculus and Mus musculus domesticus autosomes, and the X-linked Hstx2 locus. Hstx2 modulates the extent of Prdm9-dependent meiotic arrest and harbors two additional factors responsible for intersubspecific introgression-induced oligospermia (Hstx1) and meiotic recombination rate (Meir1). To facilitate positional cloning and to overcome the recombination suppression within the 4.3 Mb encompassing the Hstx2 locus, we designed Hstx2-CRISPR and SPO11/Cas9 transgenes aimed to induce DNA double-strand breaks specifically within the Hstx2 locus. The resulting recombinant reduced the Hstx2 locus to 2.70 Mb (chromosome X: 66.51-69.21 Mb). The newly defined Hstx2 locus still operates as the major X-linked factor of the F1 hybrid sterility, and controls meiotic chromosome synapsis and meiotic recombination rate. Despite extensive further crosses, the 2.70 Mb Hstx2 interval behaved as a recombination cold spot with reduced PRDM9-mediated H3K4me3 hotspots and absence of DMC1-defined DNA double-strand-break hotspots. To search for structural anomalies as a possible cause of recombination suppression, we used optical mapping and observed high incidence of subspecies-specific structural variants along the X chromosome, with a striking copy number polymorphism of the microRNA Mir465 cluster. This observation together with the absence of a strong sterility phenotype in Fmr1 neighbor (Fmr1nb) null mutants support the role of microRNA as a likely candidate for Hstx2.

Genetic structure of Spartina hybrids between native Spartina maritima and invasive Spartina densiflora in Southwest Europe

Interspecific hybridization represents an evolutionary force resulting in novel genotypes. The genomic changes that occur as a result of hybridization affect both genome structure and gene expression and consequently determine hybrid phenotypes and ecology. This study provides new data on the dynamics of hybrid invasions, integrating effects of the genetic, phenotypic, geographical and environmental scenarios with hybridization following invasion of a halophyte community by an exotic plant species. We analyzed the spatial genetic structure of sterile Spartina F1 hybrid populations established at the Gulf of Cadiz (Southwest Iberian Peninsula) and that of their parental species native S. maritima and invasive S. densiflora using nuclear DNA (Simple Sequence Repeats) and chloroplast DNA sequences. We also analyzed the relationships between the spatial genetic structure of the hybrids, their phenotypic variability and their marsh environment. The studied populations of Spartina hybrids were establishing hybrid zones with a spatial genetic structure inherited from both parental species. The hybrids were genetically more similar to the native than to the invasive species. The hybrid populations with greater genetic differentiation were those more spatially separated from each other and that were present in more contrasted sedimentary environments, revealing respective isolation processes by distance and by environment. The hybrids in the Guadiana Estuary were the most genetically differentiated and with the highest transgressive behavior in terms of tiller height.

Population structure, genetic diversity and downy mildew resistance among Ocimum species germplasm

BackgroundThe basil (Ocimum spp.) genus maintains a rich diversity of phenotypes and aromatic volatiles through natural and artificial outcrossing. Characterization of population structure and genetic diversity among a representative sample of this genus is severely lacking. Absence of such information has slowed breeding efforts and the development of sweet basil (Ocimum basilicum L.) with resistance to the worldwide downy mildew epidemic, caused by the obligate oomycete Peronospora belbahrii. In an effort to improve classification of relationships 20 EST-SSR markers with species-level transferability were developed and used to resolve relationships among a diverse panel of 180 Ocimum spp. accessions with varying response to downy mildew.ResultsResults obtained from nested Bayesian model-based clustering, analysis of molecular variance and unweighted pair group method using arithmetic average (UPGMA) analyses were synergized to provide an updated phylogeny of the Ocimum genus. Three (major) and seven (sub) population (cluster) models were identified and well-supported (P < 0.001) by PhiPT (ΦPT) values of 0.433 and 0.344, respectively. Allelic frequency among clusters supported previously developed hypotheses of allopolyploid genome structure. Evidence of cryptic population structure was demonstrated for the k1 O. basilicum cluster suggesting prevalence of gene flow. UPGMA analysis provided best resolution for the 36-accession, DM resistant k3 cluster with consistently strong bootstrap support. Although the k3 cluster is a rich source of DM resistance introgression of resistance into the commercially important k1 accessions is impeded by reproductive barriers as demonstrated by multiple sterile F1 hybrids. The k2 cluster located between k1 and k3, represents a source of transferrable tolerance evidenced by fertile backcross progeny. The 90-accession k1 cluster was largely susceptible to downy mildew with accession ‘MRI’ representing the only source of DM resistance.ConclusionsHigh levels of genetic diversity support the observed phenotypic diversity among Ocimum spp. accessions. EST-SSRs provided a robust evaluation of molecular diversity and can be used for additional studies to increase resolution of genetic relationships in the Ocimum genus. Elucidation of population structure and genetic relationships among Ocimum spp. germplasm provide the foundation for improved DM resistance breeding strategies and more rapid response to future disease outbreaks.

Two New Species of Pristionchus (Nematoda: Diplogastridae) from Taiwan and the Definition of the pacificus Species-Complex Sensu Stricto.

Pristionchus pacificus Sommer, Carta, Kim, and Sternberg, 1996 is an important model organism in evolutionary biology that aims to integrate developmental biology and evo-devo with population genetics and ecology. Functional studies in P. pacificus are supported by a well-established phylogenetic framework of around 30 species of the genus Pristionchus that have been described in the last decade based on their entomophilic and necromenic association with scarab beetles. Biogeographically, East Asia has emerged as a hotspot of Pristionchus speciation and recent samplings have therefore focused on Islands and mainland settings in East Asia. Here, we describe in a series of three publications the results of our sampling efforts in Taiwan, Japan, and Hongkong in 2016 and 2017. We describe a total of nine new species that cover different phylogenetic species-complexes of the Pristionchus genus. In this first publication, we describe two new species, Pristionchus sikae sp. n. and Pristionchus kurosawai sp. n. that are closely related to P. pacificus . Together with five previously described species they form the " pacificus species-complex sensu stricto" that is characterized by all species forming viable, but sterile F1 hybrids indicating reproductive isolation. P. sikae sp. n. and P. kurosawai sp. n. have a gonochorist mode of reproduction and they are described using morphology, morphometrics, mating experiments, and genome-wide sequence analysis. We discuss the extreme diversification in the pacificus species-complex sensu stricto in East Asia and its potential power to study speciation processes.

Breeding value of parents for creation of simple and three-line sunflower hybrids

The article presents the results of evaluating parents of F1 sunflower hybrids for valuable economic features. Morphological traits of the crop initial forms were established. The levels of the general and specific combining abilities of sunflower lines and sterile hybrids were determined by yield capacity. Promising starting material was selected for heterosis breeding.The aim and tasks of the study. The purpose of the experiments was to establish the value of sunflower parents in terms of levels of morphological and economic characteristics and to determine their combining ability.Material and methods. The experiments were conducted in the breeding crop rotation fields of the Plant Production Institute nd a VYa Yuryev of NAAS by the preliminary testing method of randomized blocksin 3 replicas in 2014-2016.The test material was 208 female forms, of which 38 were self-pollinated lines bred at three research institutes of Ukraine (Plant Production Institute nd a VYa Yuryev of NAAS, Kharkiv; Plant Breeding and Genetics Institute - National Center for Seed and Cultivar Investigations, Odesa; Institute of Oil Crops of NAAS, Zaporizhzhia), and 170 were simple sterile hybrids created on their basis.The test material was evaluated for the growing season length, yield capacity, oil content, plant height, and calathidium diameter.To test starting material for combining ability and to create experimental sunflower hybrids on this basis, a 62/5 tester crossing design was planned and implemented. Five lines-fertility pollen restorers of different morphotypes were taken as testers.Results and discussion. The diversity of parents of sunflower hybrids by economic features was studied. Strong effects of the combining ability were noticed for two sunflower lines - pollen fertility restorers − Kh06134V and Kh06135V. Hybrid combinations derived from crossed with these lines gave high yields: on average 3.16 t/ha and 3.24 t/ha, respectively, in 2014; 3.47 t/ha and 3.58 t/ha, respectively, in 2015.Analysis of the effects of the combining ability of female lines by yield capacity distinguished two lines, Od4301A and Skh12A, with high combining ability effects. Hybrid combinations derived from crosses with them gave high yields: 2.88 t/ha and 2.65 t/ha, respectively, in 2014; 3.78 t/ha and 3.64 t/ha, respectively, in 2015.The combining ability of simple sterile hybrids, which were used in crossing as female components, was established. Sterile hybrid Zl42A/Kh51B was singled out; the resulting three-line hybrids with it gave consistently high yields of 3.06 t/ha in 2014 and 3.48 t/ha in 2015. The two-year data show that female forms Od391A/Kh1002B and Zl10A/Mkh524B had consistently strong effects of the GCA by yield capacity.Conclusions. Analysis of the data demonstrate advantages of the distinguished lines with high yield capacity and strong effects of the combining ability. Parent lines Kh06134V, Kh06135V, Od4301A, Skh12A and sterile F1 hybrids Zl42A/Kh51B, Od391A/Kh1002B, Zl10A /Mkh524B are recommended to use in breeding programs as starting material for obtaining high-yielding interline simple and tree-line sunflower hybrids

Pentaploid Wheat Hybrids: Applications, Characterisation, and Challenges.

Interspecific hybridisation between hexaploid and tetraploid wheat species leads to the development of F1 pentaploid hybrids with unique chromosomal constitutions. Pentaploid hybrids derived from bread wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum spp. durum Desf.) crosses can improve the genetic background of either parent by transferring traits of interest. The genetic variability derived from bread and durum wheat and transferred into pentaploid hybrids has the potential to improve disease resistance, abiotic tolerance, and grain quality, and to enhance agronomic characters. Nonetheless, pentaploid wheat hybrids have not been fully exploited in breeding programs aimed at improving crops. There are several potential barriers for efficient pentaploid wheat production, such as low pollen compatibility, poor seed set, failed seedling establishment, and frequent sterility in F1 hybrids. However, most of the barriers can be overcome by careful selection of the parental genotypes and by employing the higher ploidy level genotype as the maternal parent. In this review, we summarize the current research on pentaploid wheat hybrids and analyze the advantages and pitfalls of current methods used to assess pentaploid-derived lines. Furthermore, we discuss current and potential applications in commercial breeding programs and future directions for research into pentaploid wheat.

Chromosomal rearrangements in holocentric organisms lead to reproductive isolation by hybrid dysfunction: The correlation between karyotype rearrangements and germination rates in sedges.

Understanding the drivers of speciation is a central task of evolutionary biology. Chromosomal rearrangements are known to play an important role in species diversification, but the role of rearrangements of holocentric chromosomes-chromosomes without localized centromeres-is poorly understood. We made numerous artificial crosses between Carex scoparia individuals of different diploid chromosome numbers and, for comparison, between individuals of the same chromosome number. We studied chromosome pairing and chromosomal rearrangements in the F1 individuals using light microscopy. We then estimated germination rates as a function of geographic distance, genetic distance, chromosome number differences in parents, and pairing irregularities in F1 individuals, using generalized least squares to fit alternative regression models. The most informative predictors of germination rates in the F1 generation are chromosome number differences and minimum number of chromosome pairing irregularities in the F1 individuals. Genetic and geographic distances between parents are not significant predictors. Holocentric chromosomal rearrangements play an important role in postzygotic reproductive isolation in Carex through F1 hybrid inviability and sterility. Hybrid dysfunction seems to be a suitable model for chromosomal speciation when there are several chromosomal rearrangements between parents. However, we have not tested the hypothesis that genome rearrangements may also play an important role in suppressing recombination between cytogenetically divergent populations.