Tetraploid Populations Research Articles

The Role of Polyploidy in the Genetic Structure and Expansion of Lepisorus clathratus in the Qinghai–Tibetan Plateau and Hengduan Mountains

Polyploidy plays a crucial role in plant evolution, particularly in shaping genetic diversity and geographic distribution. This study investigates the genetic diversity and distribution of Lepisorus clathratus (C. B. Clarke) Ching, a polyploid fern species endemic to the Qinghai–Tibetan Plateau and Hengduan Mountains. We sampled 586 individuals from 66 populations and identified three ploidy levels: diploid, tetraploid, and hexaploid. Flow cytometry and chloroplast DNA sequencing were used to assess ploidy variation and genetic structure. Tetraploid populations dominated the Hengduan Mountains and exhibited wider geographic ranges, while diploids were largely confined to the Qinghai–Tibetan Plateau. Molecular variance analysis revealed significant genetic differentiation among regions, with polyploid populations demonstrating higher cross-region migration rates compared with diploids, as evidenced by the historical gene flow analysis. Ecological niche modeling suggested that polyploids expanded more successfully in post-glacial periods, likely due to their greater ecological flexibility and capacity for long-distance colonization. These findings highlight the critical role of polyploidy in shaping genetic structure and species expansion, contributing to the understanding of plant adaptation in response to historical climatic changes.

Aegilops crassa Cytotypes in Some Regions of Türkiye.

A new hexaploid cytotype of Aegilops crassa has been identified in Türkiye. To assess the ploidy levels of native populations, 50 samples from Adıyaman, Batman, Bitlis, Diyarbakır, Hakkari, Mardin, Siirt, Şanlıurfa, Şırnak, and Van were analyzed using flow cytometry and cytogenetic techniques. DNA content was determined by comparison with standard plants. Results confirmed two cytotypes in Türkiye: tetraploid populations from Batman, Bitlis, Diyarbakır, Hakkari, Mardin, Siirt, Şanlıurfa, and Şırnak, and hexaploid accessions from Adıyaman and Van. Ten metaphase plates were analyzed. The tetraploid cytotype exhibited chromosome lengths of 8.95 ± 0.27 to 13.96 ± 0.13 µm, a total genome length of 165.51 ± 0.34 µm, and nuclear DNA content of 18.53 ± 0.29 to 20.37 ± 0.49 pg. Most chromosomes were metacentric, except for chromosomes 7, 8, 10, and 12, which were submetacentric. Two satellite pairs were found on chromosomes 4 and 10. The hexaploid cytotype showed chromosome lengths of 8.90 ± 0.16 to 14.06 ± 0.06 µm, a total genome length of 230.47 ± 0.23 µm, and nuclear DNA content of 33.40 ± 0.52 to 35.01 ± 0.31 pg. Most chromosomes were also metacentric, with three satellite pairs on chromosomes 3, 6, and 10. In conclusion, both tetraploid (2n = 2x = 28) and hexaploid (2n = 6x = 42) cytotypes of Ae. crassa exist in Türkiye, with the hexaploid cytotype having potential for wheat breeding programs.

Chromosome Study of Six Populations of Trifolium tumens Stev. ex M. B. in IRAN

Trifolium tumens Stev. ex M. B is a perennial legume with long‐lived and deep rooting from the Vesicaria section in Trifolium genus. It is distributed in Iran. The base chromosome number (x = 8) in the population, confirmed the views of the previous researchers. In this study, the number of chromosomes in the mitotic metaphase stage in the meristematic cells of the root ends were counted in six populations of Trifolium tumens. Also, chloroplast count of stomata guard cells, morphological studies, pollen grain size and flowcytometry were studied in six accessions. Our results showed that this species has ploidy level (2n=16, 2n=32). and the tetraploid state in the species T. tumens is reported. Through flowcytometry, chloroplast count of stomata guard cells and compare the pollen grain, different characters were showed between diploid and tetraploid populations, too. Based on the results, this new cytotype is reported from Iran.

Ice age-driven range shifts of diploids and expanding autotetraploids of Biscutella laevigata within a conserved niche.

Early studies of the textbook mixed-ploidy system Biscutella laevigata highlighted diploids restricted to never-glaciated lowlands and tetraploids at high elevations across the European Alps, promoting the hypothesis that whole-genome duplication (WGD) is advantageous under environmental changes. Here we addressed long-held hypotheses on the role of hybridisation at the origin of the tetraploids, their single vs multiple origins, and whether a shift in climatic niche accompanied WGD. Climatic niche modelling together with spatial genetics and coalescent modelling based on ddRAD-seq genotyping of 17 diploid and 19 tetraploid populations was used to revisit the evolution of this species complex in space and time. Diploids differentiated into four genetic lineages corresponding to allopatric glacial refugia at the onset of the last ice age, whereas tetraploids displaying tetrasomic inheritance formed a uniform group that originated from southern diploids before the last glacial maximum. Derived from diploids occurring at high elevation, autotetraploids likely inherited their adaptation to high elevation rather than having evolved it through or after WGD. They further presented considerable postglacial expansion across the Alps and underwent admixture with diploids. Although the underpinnings of the successful expansion of autotetraploids remain elusive, differentiation in B. laevigata was chiefly driven by the glacial history of the Alps.

A low-cost dpMIG-seq method for elucidating complex inheritance in polysomic crops: a case study in tetraploid blueberry.

Next-generation sequencing (NGS) library construction often requires high-quality DNA extraction, precise adjustment of DNA concentration, and restriction enzyme digestion to reduce genome complexity, which results in increased time and cost in sample preparation and processing. To address these challenges, a PCR-based method for rapid NGS library preparation, named dpMIG-seq, has been developed and proven effective for high-throughput genotyping. However, the application of dpMIG-seq has been limited to diploid and polyploid species with disomic inheritance. In this study, we obtained genome-wide single nucleotide polymorphism (SNP) markers for tetraploid blueberry to evaluate genotyping and downstream analysis outcomes. Comparison of genotyping qualities inferred across samples with different DNA concentrations and multiple bioinformatics approaches revealed high accuracy and reproducibility of dpMIG-seq-based genotyping, with Pearson's correlation coefficients between replicates in the range of 0.91 to 0.98. Furthermore, we demonstrated that dpMIG-seq enables accurate genotyping of samples with low DNA concentrations. Subsequently, we applied dpMIG-seq to a tetraploid F1 population to examine the inheritance probability of parental alleles. Pairing configuration analysis supported the random meiotic pairing of homologous chromosomes on a genome-wide level. On the other hand, preferential pairing was observed on chr-11, suggesting that there may be an exception to the random pairing. Genotypic data suggested quadrivalent formation within the population, although the frequency of quadrivalent formation varied by chromosome and cultivar. Collectively, the results confirmed applicability of dpMIG-seq for allele dosage genotyping and are expected to catalyze the adoption of this cost-effective and rapid genotyping technology in polyploid studies.

Mapping of a novel locus Ra conferring extreme resistance against potato virus A in cultivated potato (Solanum tuberosum L.).

The Ra extreme resistance against potato virus A was mapped to the upper of chromosome 4 in tetraploid potato. Potato virus A (PVA) is one of the major viruses affecting potato worldwide and can cause serious disease symptoms and yield losses. Previously, we determined that potato cultivar Barbara harbors Rysto (genotype: Ryryryry) and Ra (genotype: Rararara) that each independently confer extreme resistance to PVA. In this study, employing a combination of next-generation sequencing and bulked-segregant analysis, we further located this novel Ra on chromosome 4 using a tetraploid BC1 potato population derived from a Ry-free progeny (Rararararyryryry) of Barbara (RarararaRyryryry) × F58050 (rararararyryryry). Using 29 insertion-deletion (InDel) markers spanning chromosome 4, Ra was delimited by the InDel markers M8-83 and M10-8 within a genetic interval of 1.46cM, corresponding to a 1.86-Mb genomic region in the potato DM reference genome. The InDel marker M10-8, which is closely linked with the resistance against PVA in the Ry-free segregating populations, was then used to screen 43 selected Rysto-free tetraploid potato breeding clones. The phenotype to PVA was significantly correlated with the present/absent of the marker, albeit with a 9.3% false positive rate and a 14.0% false negative rate. These findings are of importance in furthering the cloning of Ra and employing the marker-assisted selection for PVA resistance.

QTL mapping of fruit quality traits in tetraploid kiwiberry (Actinidia arguta)

Fruit quality traits play an important role in consumption of kiwiberry (Actinidia arguta). The genetic basis of fruit quality traits in this woody, perennial and dioecious fruit crop remains largely unknown. This study aimed to identify the underlying genetic basis of fruit quality traits in A. arguta, using a single nucleotide polymorphism (SNP) genetic linkage map previously developed in a tetraploid F1 population of ‘Ruby-3’ × ‘KuiLv-M’. The F1 population was phenotyped over three years (2020–2022) for fruit quality traits, including skin color, flesh color, fruit weight, fruit diameter, total soluble solids, fruit longitudinal diameter and fruit shape index. A total of nine QTLs were detected for five traits, explaining 10%–32% of the trait variation. For fruit color, the support interval of a major QTL on LG9 contained an MYB transcription factor MYB110, which was previously demonstrated to control color regulation in kiwifruit, thus suggesting that the MYB110 is the candidate gene for fruit color in kiwiberry. The linked marker for fruit color was validated in an F1 population and 25 kiwiberry cultivars. In conclusion, the knowledge obtained through the QTL mapping is applicable to improve the efficiency and cost-effectiveness in kiwiberry breeding.

QTL identified that influence tuber length-width ratio, degree of flatness, tuber size, and specific gravity in a russet-skinned, tetraploid mapping population.

Potato tuber shape, size, and specific gravity are important agronomic traits in the russet market class of potatoes with an impact on quality, consistency, and product recovery of processed foods such as French fries. Therefore, identifying genetic regions associated with the three traits through quantitative trait locus/loci (QTL) analysis is a crucial process in the subsequent development of marker-assisted selection for use in potato breeding programs. QTL analysis was conducted on a tetraploid mapping population consisting of 190 individuals derived from the cross between two russet-skinned parents, Palisade Russet and the breeding clone ND028673B-2Russ. Field data collected over a 2-year period and used in the QTL analyses included tuber length-width and width-depth ratios that were obtained using a digital caliper. The width-depth ratio provided an assessment of the "flatness" of a tuber, which is of importance in potato processing. To cross-validate the accuracy and differences among tuber shape measurement methods, a trained evaluator also assessed the identical tubers based on 1-5 scale (compressed to long) visual assessment method. Furthermore, the weights of analyzed tubers and specific gravities were also collected during the phenotyping process for each mapping clone. A major tuber shape QTL was consistently observed on chromosome 10 with both the length-width ratio and visual assessments. On chromosome 4, a significant QTL for tuber shape from the visual assessment phenotypic data was also detected. Additionally, a tuber shape-related QTL on chromosome 6 was also detected from the length-width ratio data from 2020. Chromosome 2 was also identified as having a significant QTL for the width-depth ratio, which is of importance in influencing the flatness of a tuber. One significant QTL for tuber weight (i.e., tuber size) was observed on chromosome 5, and a significant QTL for specific gravity was found on chromosome 3. These significant and major QTL should be useful for developing marker-assisted selection for more efficient potato breeding.

Evidence of conservative range in mountain grasses during past climate change: Only contractions or local expansions possible

The ongoing biodiversity crisis associated with anthropogenic global warming has especially severe effects on mountain and cold-adapted species. The lesson from the postglacial period can provide examples for future predictions, but scenarios of the range shift of mountain species are not fully explored. Different stories could happen if a species achieved long-distance dispersal and reached lowland locations or if survived only in mountains, during the ice age. In the case of grasses, a key role in range dynamics is played also by polyploidy. Due to their enhanced genetic and physiological plasticity, polyploids are thought to be less likely to become extinct during global changes.The present study explores the postglacial range shifts in two Festuca species, which differ in range size (endemic vs widespread) and in ploidy level (diploid vs mixed-ploidy). We used phylogeography and distribution models to analyze changes in potential range during global warming. We achieved a sophisticated prediction by using modeling based on climate and edaphic factors.Our findings indicate a low level of gene flow between populations, irrespective of variation in distance, range size and ploidy. Slightly shorter genetic distances were observed between the tetraploid populations compared to the diploids. Our data indicates that diploids adapted to cold conditions were restricted to mountains during glaciations, while polyploids spread more widely during cold periods. Nevertheless, since the LGM it appears that all studied ranges have been rather conservative, with maybe some local contractions and expansions, especially in tetraploids. Moreover, tetraploids demonstrated the most stable potential range during climate warming.The studied cases are characterized by individual and complex range dynamics dependent on local conditions and cytotype behaviour. However, generally speaking, studied mountain species demonstrate a conservative range, which places them at risk of extinction during global warming due to the lack of effective means of escape.

Morphological and habitat differentiation between diploids and tetraploids of a Drakensberg near‐endemic taxon, Rhodohypoxis baurii var. platypetala (Hypoxidaceae)

AbstractEnvironmental factors may shape the spatial distribution of ploidy levels. Here, we undertook a cytogeographical study of Rhodohypoxis baurii var. platypetala (Hypoxidaceae), a Drakensberg near‐endemic taxon. We addressed the following questions: (1) Are there mixed‐ploidy populations or is each population represented by a single ploidy level? (2) Is there a pattern in the environmental distribution of ploidy levels? (3) Are there specific environmental variables associated with each ploidy level locality? (4) Are plant traits similar or different within and among ploidy levels across populations that experience different environmental factors? We measured leaf and flower traits of individuals that were sampled for flow cytometry from 17 populations across the KwaZulu‐Natal and Free State provinces in South Africa. We extracted daily climate data for 13 variables and collected soil samples to evaluate pH and nutrient properties to characterize the sampled populations to test for relationships with ploidy level distributions. Twelve populations were found to contain only diploids, four populations contained only tetraploids, and only one population was ‘mixed ploidy’ (both diploid and triploid individuals present). There was an overlap in the altitudinal range of diploid and tetraploid populations, but diploids reached the highest altitudes recorded for the current study. We also found that R. baurii var. platypetala occurs in acidic soils and that tetraploids occurred in soils with marginally higher nitrogen and phosphorus than soils where diploids occur. Tetraploids generally occurred in warmer conditions, in drier soils, and possessed broader leaves and larger flowers than diploids. Our study suggests that soil factors and temperature at a small (within localities) spatial scale likely shape ploidy level distributions in the Drakensberg grasslands.

Chromosome evolution screens recapitulate tissue-specific tumor aneuploidy patterns.

Whole chromosome and arm-level copy number alterations occur at high frequencies in tumors, but their selective advantages, if any, are poorly understood. Here, utilizing unbiased whole chromosome genetic screens combined with in vitro evolution to generate arm- and subarm-level events, we iteratively selected the fittest karyotypes from aneuploidized human renal and mammary epithelial cells. Proliferation-based karyotype selection in these epithelial lines modeled tissue-specific tumor aneuploidy patterns in patient cohorts in the absence of driver mutations. Hi-C-based translocation mapping revealed that arm-level events usually emerged in multiples of two via centromeric translocations and occurred more frequently in tetraploids than diploids, contributing to the increased diversity in evolving tetraploid populations. Isogenic clonal lineages enabled elucidation of pro-tumorigenic mechanisms associated with common copy number alterations, revealing Notch signaling potentiation as a driver of 1q gain in breast cancer. We propose that intrinsic, tissue-specific proliferative effects underlie tumor copy number patterns in cancer.

Persistence of Chronic Lymphocytic Leukemia Stem-like Populations under Simultaneous In Vitro Treatment with Curcumin, Fludarabine, and Ibrutinib: Implications for Therapy Resistance.

Leukemic stem cells (LSCs) possess similar characteristics to normal hematopoietic stem cells, including self-renewal capacity, quiescence, ability to initiate leukemia, and drug resistance. These cells play a significant role in leukemia relapse, persisting even after apparent remission. LSCs were first described in 1994 by Lapidot et al. Although they have been extensively studied in acute leukemia, more LSC research is still needed in chronic lymphocytic leukemia (CLL) to understand if reduced apoptosis in mature cells should still be considered as the major cause of this disease. Here, we provide new evidence suggesting the existence of stem-like cell populations in CLL, which may help to understand the disease as well as to develop effective treatments. In this study, we identified a potential leukemic stem cell subpopulation using the tetraploid CLL cell line I83. This subpopulation is characterized by diploid cells that were capable of generating the I83 tetraploid population. Furthermore, we adapted a novel flow cytometry analysis protocol to detect CLL subpopulations with stem cell properties in peripheral blood samples and primary cultures from CLL patients. These cells were identified by their co-expression of CD19 and CD5, characteristic markers of CLL cells. As previously described, increased alkaline phosphatase (ALP) activity is indicative of stemness and pluripotency. Moreover, we used this method to investigate the potential synergistic effect of curcumin in combination with fludarabine and ibrutinib to deplete this subpopulation. Our results confirmed the effectiveness of this ALP-based analysis protocol in detecting and monitoring leukemic stem-like cells in CLL. This analysis also identified limitations in eradicating these populations using in vitro testing. Furthermore, our findings demonstrated that curcumin significantly enhanced the effects of fludarabine and ibrutinib on the leukemic fraction, exhibiting synergistic effects (combination drug index, CDI 0.97 and 0.37, respectively). Our results lend support to the existence of potential stem-like populations in CLL cell lines, and to the idea that curcumin could serve as an effective adjuvant in therapies aimed at eliminating these populations and improving treatment efficacy.

Synthetic polyploid induction influences morphological, physiological, and photosynthetic characteristics in Melissa officinalis L.

Melissa officinalis L., a well-known herb with diverse industrial and ethnopharmacological properties. Although, there has been a significant lack in the breeding attempts of this invaluable herb. This study aimed to enhance the agronomical traits of M. officinalis through in vitro polyploidization. Nodal segments were micropropagated and subjected to oryzalin treatment at concentrations of 20, 40, and 60 mM for 24 and 48 hours. Flow cytometry, chromosome counting, and stomatal characteristics were employed to confirm the ploidy level of the surviving plants. The survival rate of the treated explants decreased exponentially with increasing oryzalin concentration and duration. The highest polyploid induction rate (8%) was achieved with 40 mM oryzalin treatment for 24 hours. The induced tetraploid plants exhibited vigorous growth, characterized by longer shoots, larger leaves, and a higher leaf count. Chlorophyll content and fluorescence parameters elucidated disparities in photosynthetic performance between diploid and tetraploid genotypes. Tetraploid plants demonstrated a 75% increase in average essential oil yield, attributed to the significantly larger size of peltate trichomes. Analysis of essential oil composition in diploid and tetraploid plants indicated the presence of three major components: geranial, neral, and citronellal. While citronellal remained consistent, geranial and neral increased by 11.06% and 9.49%, respectively, in the tetraploid population. This effective methodology, utilizing oryzalin as an anti-mitotic agent for polyploid induction in M. officinalis, resulted in a polyploid genotype with superior morpho-physiological traits. The polyploid lemon balm generated through this method has the potential to meet commercial demands and contribute significantly to the improvement of lemon balm cultivation.

Polyploidy in the history of breeding at the Yaltushkiv Experimental Breeding Station: new methods of differentiation and stabilisation of sugar beet tetraploids

Purpose. To analyse the history of the polyploid breeding at the Yaltushkiv Experimental Breeding Station, in particular the improvement of genetic models of new hybrids, new methods of induction of meiotic tetraploids, differentiation and selection of breeding genotypes by genome ploidy.
 Methods. Cytological analysis of metaphase chromosomes of the apical meristems of the growth points of seed plants and beets of the first year for the selection of tetraploid plants 4x = 36 chromosomes; cytophotometric analysis using computer programs AP Partec to study ploidy based on the quantitative content of nuclear DNA; field methods (selection of tetraploid seed plants according to the types of pollen grains, formation of synthetic populations of tetraploid multigerm plants on a cytogenetic basis according to the structure of bivalent conjugation of homologous chromosomes in meiosis.
 Results. In the process of tetraploid induction, cytological methods of ploidy analysis at the station were improved using computer programs of AP Partec for the selection of sugar beets 4x by the quantitative content of nuclear DNA in the cell on plants of the first year of vegetation and for the formation of tetraploid populations after colchicine induction in seed plants. In the process of studying the structure of polyploid populations by ploidy, the percentage of tetraploids varied from 82.0±2.22% in Ya/Hen pollinator to 58.1±2.81% in Ya/Man pollinator. It was established that the selection for fertility and pollen uniformity depends on the genetic characteristics of the breeding genotypes and affects the pollen-forming ability in the first generations after induction with colchicine, reducing the number of 4x IIa and IIb biotypes according to cytological classification. Using the example of the multigerm pollinator Ya/Roi, it was established that selection for sugar content and productivity had, to a certain extent, a stabilising effect on the degree of ploidy. The biotechnological methods used to deposit 4x genotypes with a high percentage of bivalent conjugation of homologous chromosomes in metaphase I of meiosis (70–90%) contributed to the cytogenetic stability of polyploid gametes and their high yield – 92.9% of 4x in the next generation of seeds. It was investigated that the productivity of triploid hybrids obtained with the use of the tetraploid pollinator Ya/DA 4x based on the germplasm of the wild species Beta patula at the early stages of vegetative development varied in triploid plants from 325 to 465 g, and the sugar content in some numbers reached 21.5%.
 Conclusions. The development of polyploid selection at the Yaltushkiv Experimental Breeding Station evolved from the development polyhybrids to the development of triploid hybrids based on CMS using tetraploid multigerm pollinators. For the formation of populations of tetraploid multigerm pollinators, the methods of fluorescent cytophotometry and computer programs AP Partec were used, as well as biotechnological methods for creating synthetic populations of tetraploid multigerm pollinators on a cytogenetic basis, which ensure the yield of tetraploids in seeds up to 92.9%.

1078. Solidago nemoralis Aiton: Compositae

SummarySolidago nemoralis Aiton (Compositae: Astereae: Solidagininae) is illustrated and described, and its extensive synonymy provided (covering both proposed subspecies), together with full type citations and location of known types and relevant commentary. The position of the somewhat daunting genus Solidago L., and its position within the tribe Astereae is discussed. Solidago nemoralis is placed with a small cluster of species (with just S. decemflora and S. nana) in its own subgenus and subsection, Solidago subgen. Nemorales (Mack.) Semple & J. B. Beck subsect. Nemorales (Mack.) G. L. Nesom. Cultivation, propagation, pests and diseases and availability of S. nemoralis are commented on. Differences between S. nemoralis, a predominantly diploid species with a few tetraploid populations, and S. decemflora, a tetraploid species throughout its range, are noted, and the two maintained as distinct species.

Identification of QTL associated with plant vine characteristics and infection response to late blight, early blight, and Verticillium wilt in a tetraploid potato population derived from late blight-resistant Palisade Russet.

Potato late blight (causal agent Phytophthora infestans) is a disease of potatoes with economic importance worldwide. Control is primarily through field monitoring and the application of fungicides. Control of late blight with fungicides and host plant resistance is difficult, with documented cases of such control measures failing with the advent of new pathotypes of P. infestans. To better understand host plant resistance and to develop more durable late blight resistance, Quantitative Trait Locus/Loci (QTL) analysis was conducted on a tetraploid mapping population derived from late blight-resistant potato cultivar Palisade Russet. Additionally, QTL analyses for other traits such as Verticillium wilt and early blight resistance, vine size and maturity were performed to identify a potential relationship between multiple traits and prepare genetic resources for molecular markers useful in breeding programs. For this, one hundred ninety progenies from intercrossing Palisade Russet with a late blight susceptible breeding clone (ND028673B-2Russ) were assessed. Two parents and progenies were evaluated over a two-year period for response to infection by the US-8 genotype of P. infestans in inoculated field screenings in Corvallis, Oregon. In Aberdeen, Idaho, the same mapping population was also evaluated for phenotypic response to early blight and Verticillium wilt, and vine size and maturity in a field over a two-year period. After conducting QTL analyses with those collected phenotype data, it was observed that chromosome 5 has a significant QTL for all five traits. Verticillium wilt and vine maturity QTL were also observed on chromosome 1, and vine size QTL was also found on chromosomes 3 and 10. An early blight QTL was also detected on chromosome 2. The QTL identified in this study have the potential for converting into breeder-friendly molecular markers for marker-assisted selection.

Creation of doubled haploid lines of maize <i>Zea mays</i> L. by resynthesis from a tetraploid population

The search for new, effective methods for broadening the genetic polymorphism of the original breeding material remains one of important problems of hybrid maize breeding. Globally, breeding of commercial maize varieties and hybrids is carried out using diploid genotypes, whereas tetraploid sources of initial material and wild relatives of maize are poorly involved in the breeding process. The direct heteroploid crosses between diploid and tetraploid genotypes lead to the formation of weakly fertile or completely sterile triploid hybrids, which are cytologically unstable in subsequent generations. Tetraploid maize (2n=40), as well as some wild relatives with tetraploid genome, such as Zea perennis Hitchk. (2n=40) and Tripsacum dactiloides (L.) L. (2n=72), are attractive to breeders as sources for improving economically valuable traits. The attractiveness of resynthesized diploid lines is explained by the fact that unequal crossing over between homologous chromosomes forming polyvalent associations of chromosomes, more chromosomal rearrangements occur in tetraploids than in diploid genotypes, the chromosomes of which form bivalents. Synthetic tetraploid populations of maize and its tetraploid wild relatives have great potential of variability for improving diploid maize. The authors proposed a direct method for the resynthesis of doubled haploid lines using haploid induction and an indirect method for obtaining diploid lines by heteroploid crossing and subsequent segregation of a triploid hybrid in the progeny. The method of resynthesizing the tetraploid maize genome to diploid serves as an ideal model for studying the processes of crossing over in meiosis between multivalent associations of homologous chromosomes; it is promising for obtaining diploid lines with an increased frequency of recombination between the homologous chromosomes of different genomes, combined into a common one, and can serve as a source for obtaining aneuploid series.

Pollen Variability of Alnus glutinosa (L.) Gaerth. (Betulaceae) from Southern Range Edge Populations in Northern Morocco

Moroccan populations of Alnus glutinosa (L.) Gaerth. (Betulaceae) are found at the southern limit of the species’ range and are represented by tetraploid cytotypes with no available pollen data. The objective of this study was to assess the morphological and morphometric variability of the pollen, specifically focusing on pollen diameters and the number of apertures. To achieve this, we sampled 11 populations that are representative of the Moroccan distribution area of this species. We employed a hierarchical sampling design (11 populations, 10 trees per population, and from 30 to 300 pollen grains per tree, depending on the character measured) to examine different levels of variability: interpopulation, intrapopulation, and intraindividual. The results demonstrate that there is no discernible difference in the morphology or size of the pollen among the Moroccan tetraploid populations. However, we observed a high degree of intraspecific variability in pollen morphometric traits, but most of this variability is associated with the intraindividual level.

Interploidy gene flow via a 'pentaploid bridge' and ploidy reduction in Cystopteris fragilis fern complex (Cystopteridaceae: Polypodiales).

Our results indicate the existence of interploidy gene flow in Cystopteris fragilis, resulting in sexual triploid and diploid gametophytes from pentaploid parents. Similar evolutionary dynamics might operate in other fern complexes and need further investigation. Polyploidization and hybridization are a key evolutionary processes in ferns. Here, we outline an interploidy gene flow pathway operating in the polyploid Cystopteris fragilis complex. The conditions necessary for the existence of this pathway were tested. A total of 365 C. fragilis individuals were collected covering representatives of all three predominant ploidy levels (tetraploid, pentaploid, and hexaploid), cultivated, had their ploidy level estimated by flow cytometry, and their spores collected. The spores, as well as gametophytes and sporophytes established from them, were analysed by flow cytometry. Spore abortion rate was also estimated. In tetraploids, we observed the formation of unreduced (tetraploid) spores (ca 2%). Collected pentaploid individuals indicate ongoing hybridization between ploidy levels. Pentaploids formed up to 52% viable spores, ca 79% of them reduced, i.e. diploid and triploid. Reduced spores formed viable gametophytes, and, in the case of triploids, filial hexaploid sporophytes, showing evidence of sexual reproduction. Some tetraploid sporophytes reproduce apomictically (based on uniform ploidy of their metagenesis up to filial sporophytes). Triploid and diploid gametophytes from pentaploid parents are able to mate among themselves, or with "normal" reduced gametophytes from the sexual tetraploid sporophytes (the dominant ploidy level in the sporophytes in this populations), to produce tetraploid, pentaploid, and hexaploid sporophytes, allowing for geneflow from the pentaploids to both the tetraploid and hexaploid populations. Similar evolutionary dynamics might operate in other fern complexes and need further investigation.

Effect of Lolium perenne population differences on shoot tissue nitrogen concentrations when grown on a peat soil

AbstractGrass nitrogen (N) concentrations of dairy grasslands are higher on peat soil than on mineral soils. This can lead to increased N losses to air and water from dairy farming systems on peat soils. Our hypothesis was that the use of low-N perennial ryegrass (Lolium perenne L.) genotypes could be a means to lower grass N concentrations, when grown on peat soils. Our objective was to determine whether perennial ryegrass populations with different shoot tissue N concentrations, recorded on a sandy soil, would show different shoot tissue N concentrations and N use efficiencies (NUE) or N uptake efficiencies (NUptE) when grown on a peat soil. First, a pot experiment lasting 62 days was carried out with nine diploid and seven tetraploid populations, followed by a field experiment with two diploid and two tetraploid populations and a control lasting 30 months. Both experiments had three N fertilization levels. In the pot experiment, populations explained 3% of the variation in shoot tissue N concentration among tetraploids, 5 and 7% of the variation in NUE among diploids and tetraploids and 12% of the variation in NUptE among diploids. In the field experiment, populations explained 44% of the variation in NUptE. A higher NUE coincided with lower shoot tissue N concentrations among tetraploid populations in the pot experiment. We conclude that there is potential to alter the shoot tissue N concentrations of perennial ryegrass grown on peat soil, via selection for shoot tissue N concentrations and NUE.