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Abstract The centromere is the chromosome region where microtubules attach during cell division. In contrast to monocentric chromosomes with one centromere, holocentric species usually distribute hundreds of centromere units along the entire chromatid. We assembled the chromosome-scale reference genome and analyzed the holocentromere and (epi)genome organization of the lilioid Chionographis japonica. Remarkably, each of its holocentric chromatids consists of only 7 to 11 evenly spaced megabase-sized centromere-specific histone H3-positive units. These units contain satellite arrays of 23 and 28 bp-long monomers capable of forming palindromic structures. Like monocentric species, C. japonica forms clustered centromeres in chromocenters at interphase. In addition, the large-scale eu- and heterochromatin arrangement differs between C. japonica and other known holocentric species. Finally, using polymer simulations, we model the formation of prometaphase line-like holocentromeres from interphase centromere clusters. Our findings broaden the knowledge about centromere diversity, showing that holocentricity is not restricted to species with numerous and small centromere units.

Experiments were carried out to study the consequences of inoculating Rhododendron 'Nova Zembla' and 'Alfred' microcuttings and young plants with Serendipita indica (formerly Piriformospora indica), an endophytic fungus. The inoculation at the in vitro rooting stage decreased the in vitro root and shoot quality, but after planting microplants in a greenhouse in a non-fertilised peat substrate, the plants grew 33% taller, with 10% more leaves and with more abundant roots in comparison with the non-inoculated microplants. The young plants rooted in vitro, acclimated in a greenhouse in a peat substrate and inoculated with S. indica at the time of the transplantation to the pots displayed, after 15 months, an increase in the shoot lengths by 35% and 13%, depending on the cultivar, in the leaf number by 47% and in the chlorophyll content by 31% when compared with the non-inoculated plants. The beneficial effect of S. indica on the young Rhododendron plants indicates the possibility of its practical use in the nursery production of this plant.

Asparagus wild relatives could be a promising possibility to extent the genetic variability of garden asparagus and for new cultivars with favorable traits such as high yield stability, disease resistance and stress tolerance. In order to achieve an efficient use in breeding, a detailed cytogenetic characterization of the accessions is necessary. This study worked on 35 Asparagus accessions, including A. officinalis cultivars (‘Darlise’, ‘Ravel’ and ‘Steiners Violetta’) and Asparagus wild relatives, for which the number of chromosomes, their size, the nuclear DNA content, and the genomic distribution of 5S and 45S rDNA were analyzed. Different ploidy levels (diploid, triploid, tetraploid, pentaploid and hexaploid) were found. Furthermore, the size of the chromosomes of all diploid Asparagus accessions was determined which led to differences in the karyotypic formula. A. plocamoides harbors the smallest chromosome with 1.21 μm, whereas the largest chromosome with 5.43 μm was found in A. officinalis. In all accessions one 5S rDNA locus per genome was observed, while the number of 45S rDNA loci varied between one (A. albus, A. plumosus, A. stipularis) to four (A. setaceus). In most Asparagus accessions, the 5S and 45S rDNA signals were located on different chromosomes. In contrast, the genomes of A. africanus, A. plocamoides, A. sp. (a taxonomically unclassified Asparagus species from Asia) and A. verticillatus (diploid accessions) have one 5S and one 45S rDNA signal on the same chromosome. The measured 2C DNA content ranges from 1.43 pg (A. plocamoides, diploid) to 8.24 pg (A. amarus, hexaploid). Intraspecific variations for chromosome number, karyotypic formula, signal pattern with 5S and 45s rDNA probes and DNA content were observed. Interspecific variations were also recognized in the genus Asparagus.

Pelargonium is a versatile genus mainly from the Cape Region, South Africa. The genus is divided into four subgenera and 16 sections characterized by several groups of chromosomes sizes and numbers. The DNA content of species from all subgenera and sections of Pelargonium, except for the sections Subsucculentia and Campylia was estimated using flow cytometry. Nuclei of Pelargonium samples (leaf or petal tissue) and an internal plant standard (leaf tissue) were isolated together and stained with propidium iodide. The DNA content was estimated providing that the 2C peaks of sample and standard be in linearity in the flow cytometer histograms. In total, 96 Pelargonium accessions of 60 species (22 Pelargonium species for the first time) were analyzed. The 2C DNA content ranged from 0.84 pg (P. longifolium, section Hoarea) to 6.69 pg (P. schizopetalum, section Magnistipulacea) and the corresponding 1Cx DNA content from 0.42 pg (P. longifolium) to 1.72 pg (P. transvaalense. This demonstrates the high plasticity within the genus Pelargonium. Some species, such as P. peltatum accessions revealed a pronounced endopolyploidization in leaves but not in petals underlining the importance to choose the right tissue as sample for the flow cytometry analysis. The reported genome sizes are a step forward towards the characterization of the Pelargonium collection within the German Gene Bank for Ornamental Plants and a valuable base for future sequencing programs of the Pelargonium genomes.

Modern Pelargonium crispum hybrids (section Pelargonium) show low genetic and phenotypic variation due to the domestication effect. Species of the sections Cortusina, Ligularia, and Pelargonium are potential breeding partners at the diploid level (2n = 2x = 22). Five P. × crispum cultivars were used as seed parents and pollinated with one genotype of P. grandiflorum (section Pelargonium) and three genotypes of P. fulgidum (section Ligularia). In both combinations, embryo rescue was necessary. Embryos were rescued and cultured on Murashige & Skoog medium supplemented with phytohormones. After callus and adventitious shoot regeneration 15 viable interspecific hybrids were obtained from crossbreeding with P. grandiflorum and 11 intersectional hybrids from crossings with P. fulgidum, respectively. The hybrids were cultivated in the greenhouse until flowering. Their hybrid character was evident due to the intermediate morphological traits. Molecular investigations using dp-RAPD analysis confirmed this. Within the F1 population P. × crispum with P. grandiflorum three hybrids and after crossing with P. fulgidum one hybrid possessed larger flowers and fully developed anthers, respectively. Their ploidy level was confirmed as tetraploid using flow cytometry. Therefore, a spontaneous polyploidisation occurred during in vitro regeneration. The tetraploid F1 hybrids are fertile and could be used for further breeding.

Seven Pelargonium × crispum cultivars, four breeding clones and the species P. crispum were analysed by flow cytometry. Tomato ‘Stupické’ (2C value = 1.96 pg) and cauliflower ‘Korso’ (2C value = 1.31 pg) were used as inter­nal standards to estimate the DNA content of the samples. As expected, the 2C values of the investigated diploid and tetraploid genotypes discriminated significantly. Overall, the mean 2C values ranged from 0.97 to 2.18 pg DNA and formed three significantly different groups. The estimation of the DNA content of the cultivars and breeding clones was independent of the standard used with one exception; for P. crispum the estim­ated DNA contents differed significantly. The standards ‘Stupické’ and ‘Korso’ are equally appropriate for flow cyto­metric investigation of genotypes with 2C values < 1.8 pg like diploid genotypes of the section Pelargonium. Tomato ‘Stupické’ is a rather impractical standard for geno­types with 2C values of about 2 pg, due to the overlapping positions of the 2C values of sample and standard.

Caraway (Carum carvi) is a widespread and frequently used spice and medicinal plant with a long history of cultivation. However, due to ongoing climatic changes, the cultivation is becoming increasingly risky. To secure caraway cultivation in future, timely breeding efforts to develop adapted material are necessary. Analysis of genetic diversity can accompany this process, for instance, by revealing untapped gene pools. Here, we analyzed 137 accessions using genotyping by sequencing (GBS). Hence, we can report a broad overview of population structure and genetic diversity of caraway. Population structure was determined using a principal coordinate analysis, a Bayesian clustering analysis, phylogenetic trees and a neighbor network based on 13,155 SNPs. Genotypic data indicate a clear separation of accessions into two subpopulations, which correlates with the flowering type (annual vs. biennial). Four winter-annual accessions were closer related to biennial accessions. In an analysis of molecular variance, genetic variation between the two subpopulations was 7.84%. In addition, we estimated the genome size for 35 accessions by flow cytometry. An average genome size of 4.282 pg/2C (± 0.0096 S.E.) was estimated. Therefore, we suggest a significantly smaller genome size than stated in literature.

Für die Erweiterung der Zuchtmethodik bei Hydrangea macrophylla gelangten Methoden der induzierten Mutagenese und Polyploidisierung zur Anwendung. Für die Mutagenese wurden In-vitro-Nodienexplantate der Sorte Blaumeise mit Röntgenstrahlung mit den Dosen 5, 10, 15, 20 und 30 Gy behandelt. Die letale Dosis von 50% lag zwischen 20 und 30 Gy. Nach Gewächshausüberführung zeigten die bestrahlten Pflanzen veränderte Merkmale wie Wuchsdepressionen, deformierte Blütenstände und schwarze Stiele. Die Polyploidisierung wurde ebenfalls in vitro an Nodienexplantaten durchgeführt. Ausgangsmaterial waren die diploiden Sorten Adria und Libelle sowie die triploiden Sorten Blaumeise und Nachtigall. Kolchizin und Trifluralin dienten als chemische Agenzien zur Hemmung der Mitose. Nach Kolchizinbehandlung wurden nur vier Ploidiechimären gefunden. Trifluralin war weitaus effektiver. Bereits eine Konzentration von 0,001% Trifluralin induzierte die Bildung polyploidisierter Pflanzen. Hexaploide Pflanzen der Sorten Blaumeise und Nachtigall zeigten eine sehr starke Wuchsdepres­sion und Blattdeformierungen, die Blütenbildung war gestört. Dagegen waren tetraploide Pflanzen der Sorten Adria und Libelle attraktiv wie ihre diploiden Ausgangsformen. Die Flowzytometrie ermöglichte eine schnelle Feststellung des Ploidieniveaus und nach Fluoreszenz-in-situ-Hybridisierung mit Gensequenzen der 5S und 18/25S rDNA erfolgte die Bestimmung der Karyo­typen. Beide ribosomale Gensequenzen waren jeweils nur ein Mal im haploiden Genom auf unterschiedlichen Chromosomen lokalisiert. Die Bedeutung der Methoden Mutagenese und Polyploidisierung zur Schaffung von Prebreeding-Material wird diskutiert. Insbesondere der Einsatz von tetraploiden Hortensien im Zuchtprozess scheint ein aussichtsreicher Beitrag zur Erweiterung des bestehenden Sortenspektrums zu sein.