Ploidy levels and reproductive behaviour in invasive Hieracium pilosella in Patagonia

Within a population of invasive Hieracium pilosella in Chilean Patagonia we found two ploidy levels, pentaploid and hexaploid. Each ploidy level was represented by one clone. Their reproductive system was apomictic (and thus replicating the maternal genome), with a low degree of residual sexuality. It is necessary to prevent the evolution of new biotypes via hybridisation with different clones of H. pilosella or other Hieracium species introduced into Patagonia

Hybridization within a Pilosella Population: a Morphometric Analysis

Abstract We traced hybridization processes taking place within a mixed population of Pilosella piloselloides subsp. bauhini and P. officinarum by means of a morphometric analysis of plants sampled in the field. Our results show that hybridization is frequent between the two taxa as well as between their two stabilized hybrids (P. brachiata and P. leptophyton). Plants utilizing three different modes of reproduction (sexual, facultatively apomictic and variable) participated in these hybridizations, Pilosella brachiata being the most important player. We identified several trends in progeny morphology, which evidently reflect different reproductive pathways, namely sexuality, apomixis and haploid parthenogenesis, occurring within the population under study. Introgression into sexual P. officinarum is commonplace

Prozesse innerhalb hybridisierender Pilosella-Populationen: P. aurantiaca und P. officinarum in Hagen (Nordrhein-Westfalen)

Pilosella aurantiaca – tetraploid, fakultativ apomiktisch und eingebürgert – und P. officinarum – tetraploid, sexuell und einheimisch – bilden bei Hagen, Nordrhein- Westfalen, einen Hybridschwarm aus tetraund hexaploiden Pflanzen. Der Hybridschwarm wurde 1990 auf einer inzwischen brach gefallenen Wiese gefunden. Seit 20 Jahren kommt hier fast unverändert ein breites Spektrum von Hybriden vor: P. aurantiaca angenäherte Morphotypen (entsprechen P. rubra), intermediäre Morphotypen (P. stoloniflora) und verschiedene P. officinarum angenäherte Morphotypen. Diese Population wurde hinsichtlich Ploidiegrad, Genomgröße, Fortpflanzungssystem, Chloroplasten- Haplotypen und Isoenzym-Phänotypen untersucht. Der zu P. rubra korrespondierende Morphotyp ist hexaploid mit variabler Fortpflanzung. Er produziert neben apomiktischen einen erheblichen Anteil sexueller und polyha - ploider Nachkommen. Die Struktur des Genotyps und der DNA-Gehalt macht eine wiederholte Entstehung aus unreduzierten Eizellen von P. aurantiaca und reduziertem Pollen von P. officinarum (2n + n-Hybridisierung) wahrscheinlich. Die damit koexistierenden Hybriden (P. stoloniflora) sind tetraploid und sexuell. Bei P. officinarum wurden zwei Chloroplasten-Haplotypen gefunden, wovon einer auch bei P. aurantiaca vorkommt. Das Vorkommen eines Chloroplasten-Haplotypen bei P. officinarum, der typisch für P. aurantiaca ist, macht Rückkreuzungen wahrscheinlich. Die unterschiedlichen Genomgrößen der wahrscheinlichen Elternarten spiegeln sich in den Genomgrößen der homoploiden (tetraploiden) Hybriden wider. Eine mehrfache Rückkreuzung mit P. officinarum, wie sie durch die Morphologie wahrscheinlich gemacht wird, wird durch Genomgröße und Chloroplasten-Haplotypen gestützt.Processes within hybridising Pilo - sella populations: P. aurantiaca and P. offi ci - narumin North Rhine-Westphalia (Germany). The hybridising population is comprised of two tetraploid morphologically distinct species, namely the introduced facultatively apomictic P. aurantiaca and the native sexual P. officinarum, and of their recent hybrids, both tetraploid and hexaploid. The hybrid swarm, first found in 1990, is growing on nutrient-poor fallow land, but the meadow was occasionally mown in the past. A wide spectrum of coexisting hybrid morphotypes has practically been unchanged over twenty years, involving the morphotypes (1) more close to P. aurantiaca (corresponding to P. rubra), (2) intermediate between parental species (P. stoloniflora) and (3) several different types more or less close to P. officinarum. Recently, the population structure was studied with respect to ploidy level, genome size, breeding system, chloroplast DNA haplotypes and isozyme phenotypes. The hybrid corresponding to P. rubra is hexaploid with a variable reproductive mode, producing a considerable amount of sexual/polyhaploid progeny in addition to true apomictic progeny. Its seed fertility is reduced. The genotype structure and DNA content in this hexaploid suggest a repeated origin via 2n + n hybridisation of P. aurantiaca (maternal parent) and P. officinarum. The other coexisting hybrids (P. stoloniflora) are tetraploid and sexual. Two chloroplast DNA haplotypes were found in P. officinarum at this locality, one of them shared with P. aurantiaca. The capture of a haplotype typical of P. aurantiaca by plants of P. officinarum supports backcrosses to P. officinarum. The different genome size (DNA content in the monoploid chromosome set) in the putative parental species, P. aurantiaca and P. officinarum, is reflected in their homoploid hybrids which have different proportions of parental genomes. Thus, a multistep hybridisation (backcrosses to P. officinarum) was suggested according to morphological characters of the tetraploid hybrids, this was supported using both the genome size data and haplotype structure

Small genomes and large seeds: chromosome numbers, genome size and seed mass in diploid Aesculus species (Sapindaceae)

Background and aimsAesculus L. (horse chestnut, buckeye) is a genus of 12-19 extant woody species native to the temperate Northern Hemisphere. This genus is known for unusually large seeds among angiosperms. While chromosome counts are available for many Aesculus species, only one has had its genome size measured. The aim of this study is to provide more genome size data and analyse the relationship between genome size and seed mass in this genus.MethodsChromosome numbers in root tip cuttings were confirmed for four species and reported for the first time for three additional species. Flow cytometric measurements of 2C nuclear DNA values were conducted on eight species, and mean seed mass values were estimated for the same taxa.Key resultsThe same chromosome number, 2 n = 40, was determined in all investigated taxa. Original measurements of 2C values for seven Aesculus species (eight taxa), added to just one reliable datum for A. hippocastanum , confirmed the notion that the genome size in this genus with relatively large seeds is surprisingly low, ranging from 0·955 pg 2C -1 in A. parviflora to 1·275 pg 2C -1 in A. glabra var. glabra.ConclusionsThe chromosome number of 2 n = 40 seems to be conclusively the universal 2 n number for non-hybrid species in this genus. Aesculus genome sizes are relatively small, not only within its own family, Sapindaceae, but also within woody angiosperms. The genome sizes seem to be distinct and non-overlapping among the four major Aesculus clades. These results provide an extra support for the most recent reconstruction of Aesculus phylogeny. The correlation between the 2C values and seed masses in examined Aesculus species is slightly negative and not significant. However, when the four major clades are treated separately, there is consistent positive association between larger genome size and larger seed mass within individual lineages