Diploid Populations Research Articles

Effects of introgressions from Festuca pratensis on winter hardiness of Lolium perenne

Previous studies reported that some genotypes with introgressed Festuca chromosome segment(s) in Lolium genome showed enhanced winter hardiness compared to Lolium. The aim of this study was to search comprehensively for the Festuca pratensis chromosome regions affecting winter hardiness-related traits when introgressed into the Lolium perenne genome. Association between F. pratensis introgression and winter hardiness-related traits (fall and winter hardiness indexes, early-spring dry matter yield, and freezing tolerance) were screened in the diploid introgression populations (n = 203) that had some F. pratensis chromosome segments introgressed. Eighty-four intron markers corresponding to unique rice genes randomly distributed across the genome were used for genotyping. Winter hardiness of almost all plants in the introgression populations was lower than that of the F. pratensis and triploid hybrid parents, but the average was higher than that of L. perenne. A significant positive effect of F. pratensis introgression on early-spring dry matter yield was detected on chromosome 7. This quantitative trait locus (QTL) was confirmed by linkage analysis using a backcross population with F. pratensis introgression in the target region of chromosome 7. However, the contribution of the newly identified QTL was rather small (6.7–9.6%), suggesting that superior winter hardiness of F. pratensis compared to L. perenne is conferred by multiple small-effect QTLs. We also detected a previously unreported negative effect of Festuca introgression on winter hardiness. Newly obtained QTL information in this study would contribute to the design of Festuca/Lolium hybrid breeding.

A two-locus model of selection in autotetraploids: Chromosomal gametic disequilibrium and selection for an adaptive epistatic gene combination.

In this paper, we present a two-locus model of selection for an autotetraploid population. We also investigate a measure of disequilibrium that occurs between homologous chromosomes in the diploid gametes of autotetraploids, namely chromosomal gametic disequilibrium. We apply the model and measure of disequilibrium to compare how an adaptive epistatic gene combination is inherited and selected for in an autotetraploid versus diploid population. Autotetraploids are expected to have higher genomic mutation and recombination rates relative to diploids, due to a greater ploidy level. These two processes can work in opposition in terms of selection for adaptive epistatic gene combinations. While a higher genomic mutation rate can generate the alleles that confer an epistatic combination more quickly, a higher recombination rate is expected to break the combination down more quickly. We show that chromosomal gametic disequilibrium in autotetraploids can potentially compensate for less linkage disequilibrium in autotetraploids. We also explore how double reduction affects the inheritance of and selection for an epistatic gene combination. Over all, our analysis provides theoretical evidence that adaptive epistatic combinations can be selected for more efficiently in autotetraploids versus diploids. This may provide insight into empirical work that finds epistasis has a role in causing population differentiation between autotetraploid plant populations.

Aneuploidy Police Detect Chromosomal Imbalance Triggering Immune Crackdown!

Aneuploidy is ubiquitous in cancer and plays a pivotal, early role in tumor evolution. It must therefore be avoided, and two recent papers highlight the roles of p53, senescence, and the immune system in preventing the outgrowth of aneuploid clones in tissue culture. These mechanisms are likely to synergize to maintain diploid cell populations.

The Influence of Polyploidy on the Evolution of Yeast Grown in a Sub-Optimal Carbon Source.

Polyploidization events have occurred during the evolution of many fungi, plant, and animal species and are thought to contribute to speciation and tumorigenesis, however little is known about how ploidy level contributes to adaptation at the molecular level. Here we integrate whole genome sequencing, RNA expression analysis, and relative fitness of ∼100 evolved clones at three ploidy levels. Independent haploid, diploid, and tetraploid populations were grown in a low carbon environment for 250 generations. We demonstrate that the key adaptive mutation in the evolved clones is predicted by a gene expression signature of just five genes. All of the adaptive mutations identified encompass a narrow set of genes, however the tetraploid clones gain a broader spectrum of adaptive mutations than haploid or diploid clones. While many of the adaptive mutations occur in genes that encode proteins with known roles in glucose sensing and transport, we discover mutations in genes with no canonical role in carbon utilization (IPT1 and MOT3), as well as identify novel dominant mutations in glucose signal transducers thought to only accumulate recessive mutations in carbon limited environments (MTH1 and RGT1). We conclude that polyploid cells explore more genotypic and phenotypic space than lower ploidy cells. Our study provides strong evidence for the beneficial role of polyploidization events that occur during the evolution of many species and during tumorigenesis.

Abstract 2908: Single-cell genetic analysis of ductal carcinoma in situ with and without synchronous invasive breast cancer by multiplex FISH delineates specific patterns of tumor clonality and heterogeneity

Abstract We previously studied synchronous Ductal Carcinomas in Situ (DCIS) and Invasive Ductal Carcinomas (IDC) using a novel approach of multiplexing FISH probes that allows us to simultaneously assess the copy numbers of up to 20 loci within intact nuclei providing new insights into tumor clonality and heterogeneity. A high degree of chromosomal instability already in DCIS, and frequently, but not always, a direct clonal evolution from DCIS to IDC was detected. We now ask whether this degree of instability is also present in DCIS that did not progress to IDC and are therefore analyzing FFPE material from 20 patients with either low-grade and high-grade DCIS who did not present with invasive breast carcinoma during their follow-up (5-10 years), in addition to 10 patients who presented with synchronous IDC. The multiplex FISH assay used targets five oncogenes (COX2, MYC, CCND1, HER2, ZNF217) and three tumor suppressor genes (DBC2, CDH1, TP53) frequently altered in breast carcinomas. To date, we have analyzed two paired cases of synchronous DCIS and IDC, DCIS-IDC 3 and 4, and three cases of DCIS without IDC, OP-DCIS 1, 4 and 5. The paired cases exhibited very similar aberration patterns for synchronous DCIS and IDC indicating the invasive carcinoma is closely related to the DCIS lesion. Specifically, the major clones in DCIS 3 (low-grade) and IDC 3 showed a diploid tumor cell population with a gain of COX2, and losses of DBC2, MYC, TP53, and HER2. Of note, the only difference observed was a gain of ZNF217 in the DCIS which was not seen in the major clone of the invasive carcinoma. The other paired case, DCIS 4 (high-grade) and IDC 4, showed major clones of triploid tumor cell populations with gains of COX2, CCND1 and MYC and losses of DBC2, CDH1, TP53 and ZNF217. The three DCIS cases without synchronous or subsequent IDC exhibited varying degrees of aberration and complexity patterns in their clonal populations. Case OP-DCIS 1, a high-grade DCIS, revealed a tetraploid cell population which showed a major clone with an amplification of CCND1 and a MYC gain combined with losses of DBC2, CDH1, TP53 and HER2. A low-grade DCIS, OP-DCIS 4, exhibited a diploid cell population with a major clone showing loss of CDH1 as the only aberration. The third case OP-DCIS 5 (low-grade DCIS) exhibited a diploid cell population with one major clone showing losses of CDH1, MYC, DBC2, TP53, HER2 and CCND1. Our preliminary observations show a tendency of diploid lesions with a predominance of loss patterns for low-grade DCIS, while high-grade DCIS seem to reveal higher ploidy with more complex gain and loss patterns. However, also low-grade DCIS with mainly loss patterns progress to invasive cancers as seen in case DCIS-IDC3. We expect that the analysis of the remaining cases will further elucidate the dynamics of DCIS lesions which will hopefully help to assess and stratify progression risk in patients with DCIS. Citation Format: Irianna Marie Torres, Leanora Hernandez, Jausheng Tzeng, Russell Schwartz, Alejandro Schaffer, Edward Gertz, Stephen Brower, Miguel Sanchez, Gert Auer, Kerstin Heselmeyer-Haddad, Ried Thomas. Single-cell genetic analysis of ductal carcinoma in situ with and without synchronous invasive breast cancer by multiplex FISH delineates specific patterns of tumor clonality and heterogeneity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2908. doi:10.1158/1538-7445.AM2017-2908

On multilocus population genetic structure: II. Gametic disequilibrium dynamics under recombination–segregation pressure

A model of a random mating diploid population with non-overlapping generations is considered. The dynamics of the population-genetic structure (with respect to a set of autosomal loci) under the pressure of recombination and segregation is investigated. In discrete time, the model is described by difference equations with respect to the population genetic state (the vector of multilocus gamete frequencies). Transition from the state description in terms of gamete frequencies to the description in terms of the fixed reference state with independent combining of alleles in gametes and deviations from such independence (gametic disequilibria) is made. According to the first part of the communication, it is possible to select among gametic disequilibria the basis ones, and the others are decomposed into the basis disequilibria. Basis gametic disequilibria have a hierarchical organization, which is determined by the number of loci starting from which it becomes possible to find the existing disequilibrium. From this point of view, we characterize the known results on the convergence of the multilocus genetic structure to an equilibrium state with independent combining of alleles in gametes. Basis gametic disequilibria of the first level of hierarchy decay the fastest. They are observed only at investigation of the whole given set of studied loci simultaneously and they cannot be discovered on the subsets of smaller sizes. Gametic disequilibria of the second level of hierarchy have slower rates of decay. These disequilibria are observed starting from the subsets of loci one unit less in size, but they are invisible at a smaller quantity of loci, etc. The description is based on the use of the coordinate system developed by S. Karlin and U. Liberman in analysis of non-epistatic selection models, but considered from another angle of view. Justification of the results assumes that readers are familiar with the basics of linear algebra and, in particular, the properties of Kronecker multiplication.

Engineering heat tolerance in potato by temperature-dependent expression of a specific allele of HEAT-SHOCK COGNATE 70.

SummaryFor many commercial potato cultivars, tuber yield is optimal at average daytime temperatures in the range of 14–22 °C. Further rises in ambient temperature can reduce or completely inhibit potato tuber production, with damaging consequences for both producer and consumer. The aim of this study was to use a genetic screen based on a model tuberization assay to identify quantitative trait loci (QTL) associated with enhanced tuber yield. A candidate gene encoding HSc70 was identified within one of the three QTL intervals associated with elevated yield in a Phureja–Tuberosum hybrid diploid potato population (06H1). A particular HSc70 allelic variant was linked to elevated yield in the 06H1 progeny. Expression of this allelic variant was much higher than other alleles, particularly on exposure to moderately elevated temperature. Transient expression of this allele in Nicotiana benthamiana resulted in significantly enhanced tolerance to elevated temperature. An TA repeat element was present in the promoter of this allele, but not in other HSc70 alleles identified in the population. Expression of the HSc70 allelic variant under its native promoter in the potato cultivar Desiree resulted in enhanced HSc70 expression at elevated temperature. This was reflected in greater tolerance to heat stress as determined by improved yield under moderately elevated temperature in a model nodal cutting tuberization system and in plants grown from stem cuttings. Our results identify HSc70 expression level as a significant factor influencing yield stability under moderately elevated temperature and identify specific allelic variants of HSc70 for the induction of thermotolerance via conventional introgression or molecular breeding approaches.

Improved persistence of red clover ( Trifolium pratense L.) increases the protein supplied by red clover/grass swards grown over four harvest years

Abstract UK livestock agriculture can significantly reduce its protein imports by increasing the amount of forage based protein grown on-farm. Forage legumes such as red clover (Trifolium pratense L.) produce high dry matter yields of quality forage but currently available varieties lack persistence, particularly under grazing. To assess the impact of red clover persistence on protein yield, diploid red clover populations selected for improved persistence were compared with a range of commercially available varieties. All populations were grown over four harvest years in mixed swards with either perennial ryegrass (Lolium perenne L.) or perennial plus hybrid ryegrass (L. boucheanum Kunth). Red clover and total sward dry matter (DM) herbage yields were measured in Years 1–4, red clover plant survival in Years 3 and 4 and herbage protein (CP) yield and concentration in Years 2 and 4. In general, red clover DM yield in year 4 (3.4 t ha−1) was lower than in year 1 (13.9 t ha−1) but the red clover populations differed in the extent of this decline. Differences in the persistence of the red clover populations in terms of plant survival and yield were reflected in the contribution of red clover to the total sward yield in Year 4, which ranged from 61% for the highest yielding population, AberClaret, to 11% in the lowest yielding, Vivi. Increased red clover DM yield was reflected in a greater CP yield (protein weight per unit area), which ranged from 1.6 t ha−1 year−1 to 2.9 t ha−1 year−1 in Year 2 and from 1.1 t ha−1 year−1 to 1.9 t ha−1 year−1 in Year 4. CP concentration (protein weight per unit herbage weight) of all of the red clover populations was within a range considered suitable for ruminant production. The implication of these results for the future use of red clover in sustainable grassland systems is discussed.

On multilocus population genetic structure: I. Description of gametic disequilibrium architecture

A diploid population is analyzed with respect to the set of L autosomal loci. The attention is focused on the description of possible gametic disequilibria defined as deviations of the current population state from the reference state with the same allelic concentrations but with independent combination of alleles in gametes. The disequilibrum description is not based on any assumptions about microevolution factor pressures, generation overlapping, mating systems, etc. It is simply used to represent the current genetic structure of the population in terms of gametic disequilibria and allele concentrations. As the indicators of linkage disequilibrium, the basis vectors of subspaces of admissible deviations are chosen that were originally suggested as eigenvectors of a linearization matrix for the model of generalized nonepistatic selection in a series of papers by S. Karlin and U. Liberman. In the present paper, these characteristics are considered from a completely different, new point of view, namely, as the basis gametic disequilibria, and admissible deviations are decomposed into the basis ones. The disequilibrium hierarchical organization with respect to inducing marginal deviations from appropriate reference states on the locus subsets of different sizes is revealed. Each of the basis disequilibria is characterized by a set of loci K, the so-called deviation support. For a basis disequilibrium of a certain level of hierarchy, there is a threshold m (equal to the quantity of loci in K) for the number of loci which is necessary for that disequilibrium detection. Thus, it is required to analyze no less than m loci simultaneously to reveal the existing basis deviation from linkage equilibrium. The justification of the results is based on the use of linear algebra machinery, Kronecker multiplication, and linear subspace of admissible deviations. Properties of marginal deviations on various subsets of loci are considered in terms of gametic disequilibria.

Genetic differentiation in the polyploid complex of Suaeda corniculata (C.A. Mey.) Bunge in Eastern Siberia

Data on differentiation of the polyploid complex of Suaeda corniculata (C.A. Mey.) Bunge in East Siberia based on variability of morphological characteristics, karyological analysis, and genetic polymorphism in inter simple sequence repeat (ISSR) markers were given for the first time. It was established that the samples studied belonged to three cytotypes: diploids (2n = 2x = 18), tetraploids (2n = 4x = 36) and hexaploids (2n = 6x = 54). The analysis of variability of morphological characteristics by the method of principal coordinates showed division of the samples into three separate groups. On the basis of morphological and molecular-genetic methods, a genetically differentiated diploid population was revealed in Yakutia.

Combinatorial Ranking of Gene Sets to Predict Disease Relapse: The Retinoic Acid Pathway in Early Prostate Cancer.

Quantitative high-throughput data deposited in consortia such as International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA) present opportunities and challenges for computational analyses. We present a computational strategy to systematically rank and investigate a large number (210-220) of clinically testable gene sets, using combinatorial gene subset generation and disease-free survival (DFS) analyses. This approach integrates protein-protein interaction networks, gene expression, DNA methylation, and copy number data, in association with DFS profiles from patient clinical records. As a case study, we applied this pipeline to systematically analyze the role of ALDH1A2 in prostate cancer (PCa). We have previously found this gene to have multiple roles in disease and homeostasis, and here we investigate the role of the associated ALDH1A2 gene/protein networks in PCa, using our methodology in combination with PCa patient clinical profiles from ICGC and TCGA databases. Relationships between gene signatures and relapse were analyzed using Kaplan-Meier (KM) log-rank analysis and multivariable Cox regression. Relative expression versus pooled mean from diploid population was used for z-statistics calculation. Gene/protein interaction network analyses generated 11 core genes associated with ALDH1A2; combinatorial ranking of the power set of these core genes identified two gene sets (out of 211 - 1 = 2,047 combinations) with significant correlation with disease relapse (KM log rank p < 0.05). For the more significant of these two sets, referred to as the optimal gene set (OGS), patients have median survival 62.7 months with OGS alterations compared to >150 months without OGS alterations (p = 0.0248, hazard ratio = 2.213, 95% confidence interval = 1.1-4.098). Two genes comprising OGS (CYP26A1 and RDH10) are strongly associated with ALDH1A2 in the retinoic acid (RA) pathways, suggesting a major role of RA signaling in early PCa progression. Our pipeline complements human expertise in the search for prognostic biomarkers in large-scale datasets.

Adaptive photosynthetic and physiological responses to drought and rewatering in triploid Populus populations

Cuttings of Populus cathayana Rehd, originating from three triploid and one diploid populations with the same parents but different gamete origins, were used to examine physiological responses to drought stress and rewatering by exposure to three progressive water regimes. Progressive drought stress significantly decreased the leaf relative water content (RWC), photosynthesis, and chlorophyll fluorescence parameters, and increased the relative electrolyte leakage, malondialdehyde (MDA), free proline (Pro), and antioxidant enzymes, such as superoxide dismutase, peroxidase, and catalase, in the four populations evaluated. However, compared to the diploid population, triploid populations showed lower relative electrolyte leakage and MDA, higher RWC and Pro content, and more efficient photosynthesis and antioxidant systems under the same water regime. Our data indicated that triploid populations possessed more efficient protective mechanisms than that of diploid population with gradually increasing drought stress. Moreover, some triploid genotypes were less tolerant to water stress than that of diploids due to large intrapopulation overlap.

The Evolution of Vicia ramuliflora (Fabaceae) at Tetraploid and Diploid Levels Revealed with FISH and RAPD.

Vicia ramuliflora L. is a widely distributed species in Eurasia with high economic value. For past 200 years, it has evolved a tetraploid cytotype and new subspecies at the diploid level. Based on taxonomy, cytogeography and other lines of evidence, previous studies have provided valuable information about the evolution of V. ramuliflora ploidy level, but due to the limited resolution of traditional methods, important questions remain. In this study, fluorescence in situ hybridization (FISH) and random amplified polymorphic DNA (RAPD) were used to analyze the evolution of V. ramuliflora at the diploid and tetraploid levels. Our aim was to reveal the genomic constitution and parents of the tetraploid V. ramuliflora and the relationships among diploid V. ramuliflora populations. Our study showed that the tetraploid cytotype of V. ramuliflora at Changbai Mountains (M) has identical 18S and 5S rDNA distribution patterns with the diploid Hengdaohezi population (B) and the diploid Dailing population (H). However, UPGMA clustering, Neighbor-Joining clustering and principal coordinates analysis based on RAPD showed that the tetraploid cytotype (M) has more close relationships with Qianshan diploid population T. Based on our results and the fact that interspecific hybridization among Vicia species is very difficult, we think that the tetraploid V. ramuliflora is an autotetraploid and its genomic origin still needs further study. In addition, our study also found that Qianshan diploid population (T) had evolved distinct new traits compared with other diploid populations, which hints that V. ramuliflora evolved further at diploid level. We suggest that diploid population T be re-classified as a new subspecies.

Study on the Cytotaxonomy of Some Species of the Genus Festuca (Poaceae)

The karyological study of four species (11 populations) of the genus Festuca L. from different geographic origins is presented. Basic chromosome number in all populations was x = 7. A large variety of ploidy levels ranging from diploids to octoploids was obtained in different species and populations. Chromosomes of all populations were mostly metacentric (m) and sub-metacentric (sm). According to intrachromosomal asymmetry, F. rubra (8308) and F. pratensis (9623) had the most asymmetrical karyotypes and F. ovina (2127 and 2357) had the most symmetrical karyotype among all populations. While based on interchromosomal asymmetry, among diploid populations, F. pratensis (4363) and among hexaploid populations, F. arundinacea (3996) had the most asymmetrical karyotype. The results of analysis of variance revealed significant differences between the populations based on all karyotypic characteristics (p < 5%) except for A2. The results of cluster analysis showed that populations have been grouped in three clusters. Detailed karyotype analysis allows us to group different populations and interpret their relationships.

Distribution, karyomorphology, and morphology of Aspidistra subrotata (Asparagaceae) at different ploidy levels in limestone areas of Asia.

Aspidistra subrotata Y. Wan & C.C. Huang, 1987 is considered for the first time as a widespread polyploidy complex in the genus Aspidistra Ker Gawler, 1823 from limestone areas of Asia. The chromosome number of the tetraploid is 2n = 76 and the karyotype is formulated as 2n = 44 m + 8 sm + 24 st, while the chromosome number of the diploid is 2n = 38 and the karyotype formula 2n = 22 m + 4 sm + 12 st. In our studies, diploids occupy broader geographical and environmental niche spaces than tetraploids. Although the leaf-shape of Aspidistra subrotata varies quantitatively between and within diploid and/or tetraploid population(s), no obvious discontinuity in the width of leaf has been observed. The tetraploid plants may be distinguished from the diploid plants by their rigid petioles as well as thick deep green lamina. Aspidistra subrotata is therefore an interesting material to explore the formation and the evolutionary dynamics of a natural polyploid complex from limestone areas of the tropical regions.

Establishment of Proliferative Tetraploid Cells from Nontransformed Human Fibroblasts.

Polyploid (mostly tetraploid) cells are often observed in preneoplastic lesions of human tissues and their chromosomal instability has been considered to be responsible for carcinogenesis in such tissues. Although proliferative polyploid cells are requisite for analyzing chromosomal instability of polyploid cells, creating such cells from nontransformed human cells is rather challenging. Induction of tetraploidy by chemical agents usually results in a mixture of diploid and tetraploid populations, and most studies employed fluorescence-activated cell sorting or cloning by limiting dilution to separate tetraploid from diploid cells. However, these procedures are time-consuming and laborious. The present report describes a relatively simple protocol to induce proliferative tetraploid cells from normal human fibroblasts with minimum contamination by diploid cells. Briefly, the protocol is comprised of the following steps: arresting cells in mitosis by demecolcine (DC), collecting mitotic cells after shaking off, incubating collected cells with DC for an additional 3 days, and incubating cells in drug-free medium (They resume proliferation as tetraploid cells within several days). Depending on cell type, the collection of mitotic cells by shaking off might be omitted. This protocol provides a simple and feasible method to establish proliferative tetraploid cells from normal human fibroblasts. Tetraploid cells established by this method could be a useful model for studying chromosome instability and the oncogenic potential of polyploid human cells.

Seed Yield Components in Single Plants of Diverse Scandinavian Tetraploid Red Clover Populations (Trifolium pratense L.)

Satisfactory seed yield of red clover (Trifolium pratense L.) cultivars is crucial for the availability of seeds on the market. Many breeders and researchers have used seed yield components to measure, compare, and explain differences in seed yield between diploid and tetraploid red clover cultivars and populations; however, the relative importance of each component varies between studies. In 2011 and 2012, single‐plant trials with several tetraploid and one diploid red clover cultivar were established at the Norwegian plant breeding station at Bjørke. The goal was to study the impact of different seed‐yield components on the seed yield of tetraploid plants. Seed weight per flower head was the seed‐yield component that correlated best with the seed yield plant−1 (r = 0.91 and r = 0.68 in 2011 and 2012, respectively). Path coefficient analysis has also shown that the seed weight per flower head had the highest direct impact on seed yield plant−1 (direct path coefficients were 0.867 and 0.783 in 2011 and 2012, respectively). In comparison, the direct path coefficients for calculated number of flower heads, which was previously highlighted as the most important seed‐yield component, were lower and more variable (0.739 and 0.392 in 2011 and 2012, respectively). Since previously seed yield per flower head was also identified as the most important seed‐yield component in dense plant canopy, this component might have the potential to select for improved seed yield of new cultivars based on single plants. However, further studies are required to confirm this conclusion.

Characterization of Partial Resistance to Black Spot Disease of Rosa sp.

Black spot disease, caused by the fungus Diplocarpon rosae Wolf, is one of the most serious diseases of garden roses. Both complete (vertical) resistance conditioned by dominant Rdr genes and partial (horizontal) resistance conditioned by multiple genes have been described. The use of resistant rose cultivars would reduce the demand of agrochemical applications. The characterization of 16 genotypes for resistance to black spot using two laboratory assays, the detached leaf assay (DLA) and the whole plant inoculation (WPI) approach, indicated that these techniques were well correlated. Thus, either method could be used to assess the resistance of the plants to black spot. Fifteen diploid hybrid populations from 10 parents segregating for partial (horizontal) resistance to black spot derived from Rosa wichuraiana ‘Basye’s Thornless’ (RW) were assessed for black spot resistance by quantifying the percentage of the leaf area with symptoms (LAS) and lesion length (LL) measured by the diameter of the largest lesion per leaf in DLAs. The narrow-sense heritability of partial resistance to black spot as measured by LAS and LL data of DLA was estimated to be from 0.28 to 0.43 when calculated with a genetic variance analysis and from 0.74 to 0.86 when generated from offspring–midparent regression. This suggests that the development of rose cultivars with high levels of stable partial resistance to black spot is a feasible approach for the rose industry.

Survival of a recessive allele in a Mendelian diploid model.

In this paper we analyse the genetic evolution of a diploid hermaphroditic population, which is modelled by a three-type nonlinear birth-and-death process with competition and Mendelian reproduction. In a recent paper, Collet et al. (J Math Biol 67(3):569-607, 2013) have shown that, on the mutation time-scale, the process converges to the Trait-Substitution Sequence of adaptive dynamics, stepping from one homozygotic state to another with higher fitness. We prove that, under the assumption that a dominant allele is also the fittest one, the recessive allele survives for a time of order at least [Formula: see text], where K is the size of the population and [Formula: see text].

Invasion success in polyploids: the role of inbreeding in the contrasting colonization abilities of diploid versus tetraploid populations of Centaurea stoebe s.l.

Summary As a consequence of founder effects, inbreeding can hamper colonization success: First, in species with self‐incompatibility controlled by an S‐locus, inbreeding may decrease cross‐compatibility, mainly due to the sharing of identical S‐alleles between closely related mating partners. Secondly, inbreeding can reduce fitness of inbred relative to outbred offspring (i.e. inbreeding depression). Polyploids often show reduced inbreeding depression compared to diploids, which may contribute to the overrepresentation of polyploids among invasive species. This is the first study that tests how the effects of inbreeding differ between geocytotypes (i.e. ploidy levels within a given range). Our model organism, Centaurea stoebe, is strictly self‐incompatible and comprises three geocytotypes: diploids are more frequent than tetraploids in the native range, while only tetraploids occur in the invasive range. We conducted a breeding experiment (sib‐mating vs. outcrossing) with 14 native diploid, 13 native tetraploid and 15 invasive tetraploid populations. We recorded cross‐compatibility and estimated a cumulative index for offspring fitness. Since frequent inbreeding can result in purging of genetic load responsible for inbreeding depression, our analyses included a metric for within‐population relatedness, based on eight microsatellite markers, to assess the effect of purging. Inbreeding was found to reduce cross‐compatibility, which was similarly pronounced in diploids and tetraploids. It also caused inbreeding depression in cumulative fitness, which was significant in diploids but not in tetraploids. No evidence of purging was observed as inbred fitness was not affected by within‐population relatedness. Synthesis. Our results provide new insights into the contrasting invasion success of the cytotypes of C. stoebe. As the effects of cross‐compatibility and purging were comparable between cytotypes, both processes can be ruled out to affect the colonization success of diploids versus tetraploids. Our findings are consistent with the hypothesis that polyploidy increases the masking of recessive mutations, which maintains high fitness in inbred tetraploids and may thus facilitate colonization of new ranges. We highlight that reduced inbreeding depression may add to previously acknowledged advantages of polyploids in range expansions, a mechanism that may hitherto have been underestimated due to a lack of data on variation in inbreeding depression across geocytotypes.