Tetraploid Populations Research Articles

Cardiac interstitial tetraploid cells can escape replicative senescence in rodents but not large mammals

Cardiomyocyte ploidy has been described but remains obscure in cardiac interstitial cells. Ploidy of c-kit+ cardiac interstitial cells was assessed using confocal, karyotypic, and flow cytometric technique. Notable differences were found between rodent (rat, mouse) c-kit+ cardiac interstitial cells possessing mononuclear tetraploid (4n) content, compared to large mammals (human, swine) with mononuclear diploid (2n) content. In-situ analysis, confirmed with fresh isolates, revealed diploid content in human c-kit+ cardiac interstitial cells and a mixture of diploid and tetraploid content in mouse. Downregulation of the p53 signaling pathway provides evidence why rodent, but not human, c-kit+ cardiac interstitial cells escape replicative senescence. Single cell transcriptional profiling reveals distinctions between diploid versus tetraploid populations in mouse c-kit+ cardiac interstitial cells, alluding to functional divergences. Collectively, these data reveal notable species-specific biological differences in c-kit+ cardiac interstitial cells, which could account for challenges in extrapolation of myocardial from preclinical studies to clinical trials.

Role of ploidy in colonization of alpine habitats in natural populations of Arabidopsis arenosa.

Polyploidy is an important driver of plant diversification and adaptation to novel environments. As a consequence of genome doubling, polyploids often exhibit greater colonizing ability or occupy a wider ecological niche than diploids. Although elevation has been traditionally considered as a key driver structuring ploidy variation, we do not know if environmental and phenotypic differentiation among ploidy cytotypes varies along an elevational gradient. Here, we tested for the consequences of genome duplication on genetic diversity, phenotypic variation and habitat preferences on closely related diploid and tetraploid populations that coexist along approx. 2300 m of varying elevation. We sampled and phenotyped 45 natural diploid and tetraploid populations of Arabidopsis arenosa in one mountain range in Central Europe (Western Carpathians) and recorded abiotic and biotic variables at each collection site. We inferred genetic variation, population structure and demographic history in a sub-set of 29 populations genotyped for approx. 36 000 single nucleotide polymorphisms. We found minor effects of polyploidy on colonization of alpine stands and low genetic differentiation between the two cytotypes, mirroring recent divergence of the polyploids from the local diploid lineage and repeated reticulation events among the cytotypes. This pattern was corroborated by the absence of ecological niche differentiation between the two cytotypes and overall phenotypic similarity at a given elevation. The case of A. arenosa contrasts with previous studies that frequently showed clear niche differentiation between cytotypes. Our work stresses the importance of considering genetic structure and past demographic processes when interpreting the patterns of ploidy distributions, especially in species that underwent recent polyploidization events.

Comparative Subsequence Sets Analysis (CoSSA) is a robust approach to identify haplotype specific SNPs; mapping and pedigree analysis of a potato wart disease resistance gene Sen3

BackgroundStandard strategies to identify genomic regions involved in a specific trait variation are often limited by time and resource consuming genotyping methods. Other limiting pre-requisites are the phenotyping of large segregating populations or of diversity panels and the availability and quality of a closely related reference genome. To overcome these limitations, we designed efficient Comparative Subsequence Sets Analysis (CoSSA) workflows to identify haplotype specific SNPs linked to a trait of interest from Whole Genome Sequencing data.ResultsAs a model, we used the resistance to Synchytrium endobioticum pathotypes 2, 6 and 18 that co-segregated in a tetraploid full sib population. Genomic DNA from both parents, pedigree genotypes, unrelated potato varieties lacking the wart resistance traits and pools of resistant and susceptible siblings were sequenced. Set algebra and depth filtering of subsequences (k-mers) were used to delete unlinked and common SNPs and to enrich for SNPs from the haplotype(s) harboring the resistance gene(s). Using CoSSA, we identified a major and a minor effect locus. Upon comparison to the reference genome, it was inferred that the major resistance locus, referred to as Sen3, was located on the north arm of chromosome 11 between 1,259,552 and 1,519,485 bp. Furthermore, we could anchor the unanchored superscaffold DMB734 from the potato reference genome to a synthenous interval. CoSSA was also successful in identifying Sen3 in a reference genome independent way thanks to the de novo assembly of paired end reads matching haplotype specific k-mers. The de novo assembly provided more R haplotype specific polymorphisms than the reference genome corresponding region. CoSSA also offers possibilities for pedigree analysis. The origin of Sen3 was traced back until Ora. Finally, the diagnostic power of the haplotype specific markers was shown using a panel of 56 tetraploid varieties.ConclusionsCoSSA is an efficient, robust and versatile set of workflows for the genetic analysis of a trait of interest using WGS data. Because the WGS data are used without intermediate reads mapping, CoSSA does not require the use of a reference genome. This approach allowed the identification of Sen3 and the design of haplotype specific, diagnostic markers.

Transference of natural diversity from the apomictic germplasm of Paspalum notatum to a sexual synthetic population

AbstractGenetic improvement in apomictic forage species has been restricted because of the absence of genetic variability in sexual germplasm with the same ploidy level. Following a new breeding scheme, a sexual synthetic tetraploid population (SSTP) of Paspalum notatum has been generated. The objectives of this work were: (a) to evaluate the genetic variability in SSTP by means of molecular markers, morphologic and agronomic traits, and seed fertility and quality traits and (b) to assess the transference of genetic variability from the apomictic germplasm to the sexual one. Molecular markers revealed a twofold higher level of variability in the SSTP in comparison with the sexual germplasm utilised for its generation, and similar levels with the apomictic ones; moreover, markers showed that most of the variability was inherited from the apomictic germplasm. Morphologic and agronomic traits and seed fertility and quality traits showed high levels of variation in the three groups of genotypes indicating that the new breeding scheme was effective in transferring variability from the apomictic germplasm to the SSTP. This new population will be useful in breeding of P. notatum, and the breeding scheme used for its generation may be used in other apomictic species.

Polyploid breeding strategies for developing hop cultivars in New Zealand

The main objective of the New Zealand hop breeding programme is to develop triploid cultivars with unique brewing properties. Created from crosses between diploid and tetraploid parents, these genotypes have the advantage of being seedless as well as high yielding. Population improvement procedures are used independently for both diploid and tetraploid populations. Restricted maximum likelihood statistical procedures are used for the selection of both male and female genotypes for tetraploid and diploid parental material. In this regard, particular emphasis is placed on identifying sexually derived tetraploids to widen the gene pool. Crosses using tetraploids, as both female and male parents, hybridised with diploid genotypes, are described. Gender segregation ratios from recent triploid seedling populations vary considerably. The statistical analysis of triploid seedling female genotypes from these populations for several key traits is presented. A summary of main chemistry features of New Zealand bred polyploid cultivars is presented. Future breeding strategies for triploid hops are discussed.

Mapping QTL underlying tuber starch content and plant maturity in tetraploid potato

Tuber starch content and plant maturity are two important agronomic traits of potato. To investigate the complex genetic basis of these traits in the cultivated potato, as well as the relationship between them, we developed a linkage map in a tetraploid population of 192 clones derived from the cross Longshu 8 × Zaodabai and mapped quantitative trait loci (QTL) for tuber starch content and plant maturity using data collected in three diverse environments over two years. We detected eleven QTL for tuber starch content distributed on seven chromosomes, of which four, on chromosomes I, II, and VIII, were expressed in at least three environments. For plant maturity, we identified six QTL on chromosomes II, IV, V, VII, and XI, one of which, on chromosome V, showed LOD peaks ranging from 45.2 to 62.5 cM and explained 21.6%–26.6% of phenotypic variation was expressed in five of the six environments. Because the reproducible QTL for plant maturity and tuber starch content mapped to different chromosomes and neither overlapping QTL, nor any genetic interaction between QTL were detected, we infer that tuber starch content and plant maturity are controlled by independent genetic loci. This inference supports the prospect of breeding potato for both early maturity and high starch content.

Development of molecular marker for nitrate reductase (NR) gene to improve nitrogen use efficiency in potato

Two diverse potato varieties Kufri Jyoti (N inefficient) and Kufri Gaurav (N efficient) were used to amplify, clone and analyze the sequence of nitrate reductase (NR) gene, involved in N metabolism in plants. Only single, distinct and un-fractioned two fragments amplified by the NR gene-based primers were cloned and sequence analyzed. Following sequence analysis, non-redundant sequences with uninterrupted open reading frames of NR homologues were identified to the known N metabolism. A cleaved amplified polymorphic sequence (CAPS) marker of the NR gene was developed for marker-assisted selection (MAS) in potato. The CAPS marker was validated in a tetraploid mapping population of 123 individuals and 48 potato varieties for its polymorphism. Thus, the development of new CAPS marker would be useful for MAS with better nitrogen use efficiency (NUE) in potato.

Genetic Mapping of Water Use Efficiency and Carbon and Nitrogen Metabolism in Drought‐Stressed Alfalfa

Identifying quantitative trait loci (QTL) associated with alfalfa (Medicago sativa L.) shoot biomass (SB), water use efficiency, and C and N metabolism can resolve potential target sites for selection and provide new insight into genetic relationships that may exist between key traits in water‐limited environments. The goal of this study was to utilize a tetraploid (2n = 4x = 32) BC1 mapping population and a genetic map based on 334 molecular markers to detect QTL associated with SB, C isotope discrimination (CID), and C and N content during drought stress. Half‐sib families derived from 96 BC1 individuals were evaluated for the SB trait in seeded plots near Las Cruces, NM, during two water‐stressed forage regrowth cycles in each of 3 yr (2005–2007). High costs associated with CID phenotyping precluded evaluation of the entire population. Therefore, in 2006 and 2007, shoot tissue samples for CID, C content, and N content measurements were collected from a subset of 29 families that exhibited extreme SB phenotypes in 2005. Significant genotype effects were observed among these families for SB and CID in both years and C and N content in 2006. Interval mapping identified QTL for all traits. Phenotypic effects of QTL supported significant positive genetic correlations detected between SB and CID, and between C and N content. Estimated QTL positions within the M. truncatula Gaertn. genome sequence assembly encompassed multiple candidate genes affiliated with stomatal development, cuticular wax biosynthesis, C and N metabolism, and abiotic stress response.

Climatic niche modeling reveals divergence between cytotypes in Eutrema edwardsii (Brassicaceae)

Polyploidy among plants is most frequent in the arctic, where glaciation cycles put selective pressures on populations by repeated fragmentation and fluctuation in climate. Polyploids should have been more fit in the novel habitats created as glaciers receded because of increased genetic material and novel gene products, which results in phenotypic plasticity and rapid adaptation. Higher ploidy is then expected to confer a broader tolerance of environmental conditions. Eutrema edwardsii R. Br. (Brassicaceae) is an arctic-alpine mustard with a near circumpolar distribution that occurs as a tetraploid, hexaploid, and octaploid. We used flow cytometry to document the distribution of polyploid cytotypes using herbarium tissue, and modeled the niche of each cytotype to test for niche differentiation. Flow cytometry revealed four cytotypes among 85 individuals. Notably, 60% of the herbarium tissue assays were successful using tissue up to 50 years old. Principle components analysis was performed on 20 climatic variables, of which, the first four axes were used as environmental variables for niche modeling. Niche models were created for tetraploid and hexaploid populations and used to calculate niche overlap (Shoener’s D). Overlap between tetraploid and hexaploid models (D = 0.534) is lower than the null distribution (D = 0.681–0.944) supporting the hypothesis of niche divergence.

Mapping and QTL Analysis of Early-Maturity Traits in Tetraploid Potato (Solanum tuberosum L.).

Early maturity is one of the most important agronomical traits in potato breeding. To identify the DNA segment that codes for early maturity, a tetraploid potato segregation population of “Zhongshu 19” × “Zhongshu 3” was genetically analyzed, using a combination of high throughput simplified genome sequencing (2b-RAD) and bulked segregant analysis (BSA). The DNA segment related to the early-maturity trait was identified at the 3.7~4.2 Mb locus on the short arm of chromosome 5. Eight molecular markers were developed, of which five were closely linked to the early-maturity trait loci. Additionally, 42 simple sequence repeats (SSR) markers were constructed based on the reference sequence of Solanum tuberosum group Phureja DM1-3 516 R44 (DM). Using the TetraploidMap software, the linkage map of chromosome 5 was constructed with 50 markers. The total map length was 172 centiMorgan (cM), with an average genetic distance of 3.44 cM. Correlating molecular and phenotypic data of the segregating population, the mapped Quantitative Trait Loci (QTL) on the short arm of chromosome 5 contributed to 33.55% of the early-maturity phenotype. The early-maturity QTL was located at 84 cM, flanked by the SSR5-85-1 and SCAR5-8 markers. The QTL was fine-mapped to 471 kb. Using DNA sequence annotation, 34 genes were identified in this region, 12 of them with unknown function. Among the other 22 annotated genes, E3 ubiquitin ligase gene PUB14 could be related to maturity and regulation of tuber formation. The constructed QTL map is a useful basic tool for the cloning of early-maturity related genes in tetraploid potatoes.

Linkage analysis and QTL mapping in a tetraploid russet mapping population of potato

BackgroundGenome-wide single nucleotide polymorphism (SNP) markers coupled with allele dosage information has emerged as a powerful tool for studying complex traits in cultivated autotetraploid potato (Solanum tuberosum L., 2n = 4× = 48). To date, this approach has been effectively applied to the identification of quantitative trait loci (QTLs) underlying highly heritable traits such as disease resistance, but largely unexplored for traits with complex patterns of inheritance.ResultsIn this study, an F1 tetraploid russet mapping population (162 individuals) was evaluated for multiple quantitative traits over two years and two locations to identify QTLs associated with tuber sugar concentration, processing quality, vine maturity, and other high-value agronomic traits. We report the linkage maps for the 12 potato chromosomes and the QTL location with corresponding genetic models and candidate SNPs explaining the highest phenotypic variation for tuber quality and maturity related traits. Significant QTLs for tuber glucose concentration and tuber fry color were detected on chromosomes 4, 5, 6, 10, and 11. Collectively, these QTLs explained between 24 and 46% of the total phenotypic variation for tuber glucose and fry color, respectively. The QTL on chromosome 10 was associated with apoplastic invertases, with ‘Premier Russet’ contributing the favorable allele for fry processing quality. On chromosome 5, minor-effect QTLs for tuber glucose concentration and fry color co-localized with various major-effect QTLs, including vine maturity, growth habit, tuber shape, early blight (Altenaria tenuis), and Verticillium wilt (Verticillium spp.).ConclusionsLinkage analysis and QTL mapping in a russet mapping population (A05141) using SNP dosage information successfully identified favorable alleles and candidate SNPs for resistance to the accumulation of tuber reducing sugars. These novel markers have a high potential for the improvement of tuber processing quality. Moreover, the discovery of different genetic models for traits with overlapping QTLs at the maturity locus clearly suggests an independent genetic control.

PI3K blockage synergizes with PLK1 inhibition preventing endoreduplication and enhancing apoptosis in anaplastic thyroid cancer

Anaplastic thyroid cancer (ATC) is among the most lethal malignancies. The mitotic kinase PLK1 is overexpressed in the majority of ATCs and PLK1 inhibitors have shown preclinical efficacy. However, they also cause mitotic slippage and endoreduplication, leading to the generation of tetraploid, genetically unstable cell populations.We hypothesized that PI3K activity may facilitate mitotic slippage upon PLK1 inhibition, and thus tested the effect of combining PLK1 and PI3K inhibitors in ATC models, in vitro and in vivo. Treatment with BI6727 and BKM120 resulted in a significant synergistic effect in ATC cells, independent of the levels of AKT activity. Combination of the two drugs enhanced growth suppression at doses for which the single drugs showed no effect, and led to a massive reduction of the tetraploid cells population. Furthermore, combined treatment in PI3Khigh cell lines showed a significant induction of apoptosis.Finally, combined inhibition of PI3K and PLK1 was extremely effective in vivo, in an immunocompetent allograft model of ATC.Our results demonstrate a clear therapeutic potential of combining PLK1 and PI3K inhibitors in anaplastic thyroid tumors.

Assessment of Genetic Diversity, Population Structure, and Evolutionary Relationship of Uncharacterized Genes in a Novel Germplasm Collection of Diploid and Allotetraploid Gossypium Accessions Using EST and Genomic SSR Markers.

This study evaluated the genetic diversity and population structures in a novel cotton germplasm collection comprising 132 diploids, including Glossypium klotzschianum and allotetraploid cotton accessions, including Glossypium barbadense, Glossypium darwinii, Glossypium tomentosum, Glossypium ekmanianum, and Glossypium stephensii, from Santa Cruz, Isabella, San Cristobal, Hawaiian, Dominican Republic, and Wake Atoll islands. A total of 111 expressed sequence tag (EST) and genomic simple sequence repeat (gSSR) markers produced 382 polymorphic loci with an average of 3.44 polymorphic alleles per SSR marker. Polymorphism information content values counted 0.08 to 0.82 with an average of 0.56. Analysis of a genetic distance matrix revealed values of 0.003 to 0.53 with an average of 0.33 in the wild cotton collection. Phylogenetic analysis supported the subgroups identified by STRUCTURE and corresponds well with the results of principal coordinate analysis with a cumulative variation of 45.65%. A total of 123 unique alleles were observed among all accessions and 31 identified only in G. ekmanianum. Analysis of molecular variance revealed highly significant variation between the six groups identified by structure analysis with 49% of the total variation and 51% of the variation was due to diversity within the groups. The highest genetic differentiation among tetraploid populations was observed between accessions from the Hawaiian and Santa Cruz regions with a pairwise FST of 0.752 (p < 0.001). DUF819 containing an uncharacterized gene named yjcL linked to genomic markers has been found to be highly related to tryptophan-aspartic acid (W-D) repeats in a superfamily of genes. The RNA sequence expression data of the yjcL-linked gene Gh_A09G2500 was found to be upregulated under drought and salt stress conditions. The existence of genetic diversity, characterization of genes and variation in novel germplasm collection will be a landmark addition to the genetic study of cotton germplasm.

The association of genomic lesions and PD-1/PD-L1 expression in resected triple-negative breast cancers

BackgroundElevated PD-L1 expression on tumor cells, a context associated with an adaptive immune response, has been linked to the total burden of copy number variants (CNVs) in aneuploid tumors, to microsatellite instability (MSI), and to specific genomic driver lesions, including loss of PTEN, MYC amplification, and activating mutations in driver oncogenes such as KRAS and PIK3CA. Triple-negative breast cancers (TNBCs) typically have high levels of CNVs and diverse driver lesions in their genomes. Thus, there is significant interest in exploiting genomic data to develop predictive immunotherapy biomarkers for patients with TNBC.MethodsWhole tissue samples from 55 resected TNBCs were screened by immunohistochemistry (IHC) for PD-1 and PD-L1 by using validated antibodies and established scoring methods for staining of tumor and non-tumor cells. In parallel, we interrogated biopsies from each resection with DNA content flow cytometry and sorted the nuclei of diploid, tetraploid, and aneuploid cell populations. CNVs were mapped with CNV oligonucleotide arrays by using purified (>95%) tumor populations. We generated whole exome data for 12 sorted tumor samples to increase the resolution within loci of interest and to incorporate somatic mutations into our genomic signatures.Results and ConclusionsPD-L1 staining was detected on tumor cells in 29 out of 54 (54%) evaluable cases and was associated with increased overall survival (P = 0.0024). High levels of PD-1 and PD-L1 (IHC ≥4) were present in 11 out of 54 (20%) and 20 out of 54 (37%) cases with staining of PD-L1 primarily on tumor cells for 17 out of 20 (85%) cases. The latter included tumors with both high (>50) and low (<20) numbers of CNVs. Notably, homozygous deletion of PTEN (n = 6) or activating mutation in PIK3CA (n = 1) was not associated with increased expression of either immune checkpoint activator in TNBC. In contrast, two treatment-naïve cases with EGFR driver amplicons had high PD-L1 tumor staining. High mutational load and predicted neoepitopes were observed in MSI+ and high CNV burden TNBCs but were not associated with high PD-L1 expression on tumor cells. Our results challenge current models of genomic-based immunotherapy signatures yet suggest that discrete genomic lesions may complement existing biomarkers to advance immune checkpoint therapies for patients with TNBC.

QTL analysis reveals quantitative resistant loci for Phytophthora infestans and Tecia solanivora in tetraploid potato (Solanum tuberosum L.).

Late blight and Guatemalan potato tuber moth caused by Phytophthora infestans and Tecia solanivora, respectively, are major phytosanitary problems on potato crops in Colombia and Ecuador. Hence, the development of resistant cultivars is an alternative for their control. However, breeding initiatives for durable resistance using molecular tools are limited due to the genome complexity and high heterozygosity in autotetraploid potatoes. To contribute to a better understanding of the genetic basis underlying the resistance to P. infestans and T. solanivora in potato, the aim of this study was to identify QTLs for resistance to P. infestans and T. solanivora using a F1 tetraploid potato segregant population for both traits. Ninety-four individuals comprised this population. Parent genotypes and their progeny were genotyped using SOLCAP 12K potato array. Forty-five percent of the markers were polymorphic. A genetic linkage map was built with a length of 968.4 cM and 1,287 SNPs showing good distribution across the genome. Severity and incidence were evaluated in two crop cycles for two years. QTL analysis revealed six QTLs linked to P. infestans, four of these related to previous QTLs reported, and two novel QTLs (qrAUDPC-3 and qrAUDPC-8). Fifteen QTLs were linked to T. solanivora, being qIPC-6 and qOPA-6.1, and qIPC-10 and qIPC-10.1 stable in two different trials. This study is one of the first to identify QTLs for T. solanivora. As the population employed is a breeding population, results will contribute significantly to breeding programs to select resistant plant material, especially in countries where P. infestans and T. solanivora limit potato production.

Diploid and tetraploid cytotypes and subspecies of Odontarrhena tortuosa (Brassicaceae) in Pannonia: differences in morphology, ecology and genome size

Odontarrhena tortuosa is a herbaceous species occurring in steppe and rocky habitats of Eurasia. The present study is focused on the cytogeography and morphological variation of the species’ populations growing in the Pannonian basin (Central Europe), which represents the westernmost part of its distribution area. Flow cytometric analyses have revealed the existence of tetraploid populations, which are reported here for the first time for Central Europe. We analysed the morphological variation of 329 individuals from Slovakia, Hungary and Serbia by multivariate morphometric methods to evaluate morphological differences between two cytotypes (diploids and tetraploids), between the subspecies (O. tortuosa subsp. tortuosa and O. tortuosa subsp. heterophylla) and between populations growing in three regions differing in the type of substrate (rocks, sand dunes and sandy and rocky screes). Although we have not found any clear morphological differences between the cytotypes, we have confirmed several previously reported morphological differences between the two subspecies, which occur in regions differing in the type of substrate. Flow cytometric data also indicate certain differences in monoploid genome size between all groups of populations under comparison. Populations from Serbia differ from other populations of O. tortuosa subsp. tortuosa in morphology and genome size, but due to a lack of data on the genetic variation of the species we suggest no change in taxonomy. For the identification of the two subspecies, we present an updated determination key.

Quantitative trait loci conferring grain selenium nutrient in durum wheat × wild emmer wheat RIL population

The genetic and phenotypic basis of grain selenium concentration (GSeC) and yield per plant (GSeY) was studied in a tetraploid wheat population consisting of 152 F&lt;sub&gt;6&lt;/sub&gt; recombinant inbred lines (RILs) derived from a cross between Triticum dicoccoides (accession G18-16) and durum wheat cultivar Langdon (LDN) grown under three different environments over 2 years. Wide genetic variation was found among RILs for GSeC and GSeY. A total of 15 QTL effects on 9 chromosomes associated with GSeC and GSeY were detected, with a logarithm od the odds (LOD) score ranging from ca. 3.2 to 11.7, explaining 1.4% to 18.6% of the phenotypic variation. Higher GSeC and GSeY were conferred by the G18-16 allele at 10 loci and by the LDN allele at 5 loci. Seven QTLs showed interactions with environmental conditions. Five genomic regions harbouring QTLs for grain Se concentrations and yields were selected for further marker-assisted selection programs, facilitating the use of wild alleles for improvement of elite wheat cultivars.

Sexual, apomictic and mixed populations in Handroanthus ochraceus (Bignoniaceae) polyploid complex

Some tropical Bignoniaceae form sporophytic apomictic polyploid complexes are similar to better studied temperate plants. Handroanthus ochraceus is a widely distributed Neotropical savanna tree with both monoembryonic/self-sterile, and polyembryonic/apomictic and self-fertile populations, but lacking chromosome number and morphological comparative studies. We tested if monoembryonic/non-apomictic and polyembryonic/apomictic populations differed in ploidy and morphological features, as a basis to understand evolution and biogeography of these plants. Chromosome number and embryo number per seed were investigated, and uni- and multivariate analyses of flower and leaf morphology were done for five populations of H. ochraceus. We found two pure monoembryonic diploid (2n = 40), and one pure polyembryonic (62–94% of polyembryonic seeds) tetraploid population (2n = 80). One of the diploid populations presented only one individual with 3.2% polyembryonic seeds and was considered a non-apomictic population. Another population showed predominantly polyembryonic (27–66% of polyembryonic seeds) tetraploid individuals, but one diploid individual with 2% of polyembryonic seeds, and was considered a mixed apomictic and non-apomictic population. Morphological analyses confirmed breeding system clusters, and that stigma width, as well as pollen grain area, was consistently larger in polyembryonic populations. Polyploid plants showed larger cells, as well as larger organs and other distinctive features, which will be useful to identify apomictic populations and to future taxonomic discussions. The species can be considered an agamic complex with apomixis associated with neopolyploidy. This trend is also found in other tropical sporophytic apomictics, contrasting with the usual reports linking diploidy or paleopolyploidy to this kind of apomictics.

Genetic analyses for bioactive potential in tetraploid potato (Solanum tuberosum L.)

AbstractA total of four traits related to bioactive potential of the tetraploid potato were studied in a North Carolina II cross‐experiment. The objectives of this study were to estimate genetic parameters for target bioactive compounds in a tetraploid potato population, to determine phenotypic and genotypic correlations and to calculate combining ability effects of cultivars and breeding lines included in the crossing scheme. Total monomeric anthocyanins, phenolics, carotenoids and hydrophilic antioxidant capacity were measured by spectrophotometric methods. The sources of variation female (GCAf), male (GCAm) and their interaction (SCA) were significant for bioactive compounds and antioxidant capacity. Narrow‐sense heritability estimates (h2) were moderate for all the traits (0.413–0.657). Both phenotypic and genotypic correlations were highly significant for phenolic compounds and antioxidant capacity. As regards combining ability, positive and negative GCA and also SCA effects have been identified for bioactive compounds and antioxidant capacity. These results indicate that hybrid breeding lines can be obtained by choosing parents with significant GCA, whose bioactive potential can also be further enhanced if the crosses have a significant SCA.

Widening the Gene Pool of Sexual Tetraploid Bahiagrass: Generation and Reproductive Characterization of a Sexual Synthetic Tetraploid Population

The improvement of bahiagrass, Paspalum notatum Flüggé, has been inhibited by reduced levels of genetic diversity in sexual tetraploid germplasm. A few experimental sexual tetraploid genotypes (ESTGs) have been generated by chromosome doubling, but these plants typically exhibit low vigor. The objectives of this work were to generate and characterize the ploidy level, mode of reproduction, and fertility of a novel 308 individual sexual synthetic tetraploid population (SSTP) developed by intercrossing 29 sexual F1 hybrids originated by hybridizing several naturally occurring apomictic tetraploids from diverse origin with a few ESTGs. Ploidy levels were determined using flow cytometry, and reproductive modes were evaluated by a molecular assay with apospory‐linked markers and embryo sac observations. The tetraploid level and the sexual mode of reproduction remained stable after two cycles of recombination during the generation of the SSTP. Fertility was evaluated based on seed set under self‐ and open pollination during 3 yr. The SSTP exhibited in average 30.2 and 15.2% seed set under open and self‐pollination, respectively, showing a predominantly cross‐pollination behavior with variable levels of self‐fertility. There were no differences in terms of fertility between the SSTP and the ESTG. The novel tetraploid population behaves as sexual and cross‐pollinated, and it is expected to allow a more efficient genetic improvement under the proposed breeding approaches.