A cytogenetic study of Eriophyllum confertiflorum (Compositae,Helenieae)

Meiotic analyses of 176 plants from 130 populations of Eriophyllum confertiflorum var. confertiflorum showed that diploids (n = 8) and tetraploids were about equally frequent and that hexaploids and octoploids were rare. Supernumerary chromosomes were found in 14% of the individuals; other meiotic aberrations were uncommon. Eriophyllum confertiflorum var. tanacetiflorum is octoploid. Migration from southwest North America, tolerance of aridity, and spontaneous origin of polyploids may explain the nonrandom distribution of cytotypes in E. confertiflorum var. confertiflorum. Artificial intravarietal crosses of E. confertiflorum var. confertiflorum yielded vigorous, bivalent-forming progeny with mean pollen stainabilities of 41%-96% and 88%-90% at the diploid and tetraploid levels, respectively. Tetraploid x diploid crosses gave triploids in one case and tetraploids in another. The progenies of some artificial crosses between distant populations of E. confertiflorum var. confertiflorum had significantly lower rates of germination and pollen viability.     

A CYTOGEOGRAPHIC STUDY OF ERIOPHYLLUM LANATUM (COMPOSITAE,HELENIEAE)

Analysis of 368 plants derived from 239 natural populations showed that this taxonomically perplexing and wide-ranging species-complex consists of diploids (n = 8), tetraploids, hexaploids and octoploids. Microsporocytes were the source of most of the chromosome counts. Meiosis was basically regular. Multivalent formation was uncommon, but 11 % of all the plants examined had one or more full-sized extra chromosomes. The frequency of plants with extra chromosomes varied significantly among the taxa, from 0 (five varieties) to over 20 % (two varieties). Except in one instance, where one population yielded a diploid and a triploid, different ploidy levels were not found in the same population. The frequency of diploid, tetraploid, hexaploid and octoploid populations was, respectively, 71, 22, 4 and 2%. Variety obovatum appears to be exclusively diploid, and var. aphanactis exclusively tetraploid. Diploids and one or more polyploid levels occurred in the other taxa. No correlation was found between polyploidy and geological history, soils, topography or climate, nor were the polyploids more widely distributed than the diploids. Some of the polyploid populations seem to have been derived from inter-varietal hybridizations, but others do not. The complex has a “pillar” structure in which 10 diploid taxa support a three-level polyploid superstructure. The available evidence suggests that the major role of polyploidy here has been to stabilize the products of intra- and inter-varietal hybridizations.     

A new cytotype of Jacobaea vulgaris (Asteraceae): frequency,morphology and origin

Jacobaea vulgaris subsp. vulgaris (syn. Senecio jacobaea subsp. jacobaea) constitutes an intricate polyploid complex distributed in Europe. Four cytotypes have been reported in this species, three with euploid (diploid, tetraploid and octoploid; 2n=20, 40 and 80) and one with aneuploid (2n=32) chromosome numbers. Here we report that the diploid chromosome number (2n=20) reported from Bulgaria is due to misidentification with Jacobaea aquatica. On the other hand, we have discovered a new, hexaploid (2n=6x=60) cytotype within J. vulgaris subsp. vulgaris using flow cytometry. The new cytotype occurs within four sympatric populations of otherwise tetraploid and octoploid plants in Pannonia (one locality in the eastern Czech Republic and two localities in southwestern Slovakia) and in Podillya (one locality in western Ukraine). The frequency of hexaploid individuals within 76 studied populations is very low (only 10 of 693 analysed plants), and hexaploids probably represent hybrids between tetraploid and octoploid plants. Three mixed populations with hexaploid plants were subjected to detailed morphological and pollen fertility analyses. Multivariate morphometric analysis reveals partial separation of tetraploid and octoploid plants, whereas hexaploid individuals are similar in morphology to octoploids. In comparison with tetraploids, octoploids and hexaploids exhibit slightly longer ray florets, involucral bracts and tubular florets and more hairy outer achenes. Hexaploid plants display larger pollen grains and lower pollen fertility compared to tetraploids and octoploids.     

Effect of Sporophytic Heterozygosity on the Male Gametophyte of the Tetraploid Potato (Solanum tuberosum L.)

Quantitative variation for pollen stainability was examinedin both tetraploid x diploid and tetraploid x tetraploid familiesof potato (Solanum tuberosum L.). The diploid parents, whichwere highly heterozygous, produced first division restitution(FDR) 2n pollen. The families used were not affected by cytoplasmic-geneticmale sterility. Significant differences between families werefound. FDR 2n pollen producing diploid clones had progenieswith a significantly higher pollen stainability than those derivedfrom crosses between tetraploid parents. This was related tothe level of heterozygosity in the sporophyte. In FDR 2n pollen,80% of the heterozygosity and a large fraction of epistasispresent in the diploid parent was transmitted to its tetraploidprogeny. This is important for the production of open pollinated,true potato seed, because pollen stainability is significantlycorrelated with fruit set (r = 0·85).Copyright 1994,1999 Academic Press FDR 2n pollen, gametophytic heterozygosity, true potato seed     

Hybridization in the genera Vulpia and Festuca (Poaceae): meiotic behaviour of artificial hybrids

The course of meiosis, including an analysis of chromosome configurations, is described for five diploid × diploid Vulpia crosses, five tetraploid × diploid Vulpia crosses, one hexaploid × diploid Festuca × Vulpia cross, one tetraploid × hexaploid Vulpia × Festuca cross, and one hexaploid × hexaploid Vulpia × Festuca cross. In most cases there was 97.5% or more pollen sterility, but two heptaploid plants obtained (presumably by non-reduction) from a hexaploid × diploid cross had about 60% stainable pollen. In the diploid hybrids pairing was quite extensive, and in V. ligustica × V. geniculata it was more or less as in the parent species (mode 7 bivalents, with regular separation). In the triploid hybrids the modal situation was 7 bivalents + 7 univalents, but evidence concerning the genomes which were pairing was equivocal. Evidence from the crosses at higher ploidy levels shows that both homogenetic and heterogenetic pairing does occur, although the relative amounts are uncertain. The results in general support the current classsification of Vulpia , except that they suggest the removal of V. alopecuros from section Loretia.     

Phytogeographical studies ofCalamagrostis sachalinensis (Gramineae)

Chromosome numbers were determined on 223 collections ofCalamagrostis sachalinensis from 18 localities in Japan. The plants were found to be tetraploid (2n=28), hexaploid (2n=42) or octoploid (2n=56). A few collections were found to include one or two B-chromosomes. The tetraploid collections were made from central Honshu and Mt. Apoi in Hokkaido, while the hexaploids and the octoploids were detected in many localities. Pollen examination of these collections showed that the tetraploids with but one exception have good pollen and the hexaploids and the octoploids have no pollen or have bad pollen with stainability less than 10%. With the help of pollen examination of a number of herbarium specimens, the distribution of the tetraploids and that of the assemblage of the hexaploids and octoploids were delineated. Morphological studies indicated that the tetraploid, hexaploid and octoploid plants can not be separated in gross and spikelet morphology and that the tetraploids in central Honshu and those in Mt. Apoi are significantly different in leaf features. It was concluded thatC. sachalinensis represents an apo-amphimictic complex, which includes the following four races: 1) tetraploid, amphimictic, having thin leaf blades 5–10 mm broad and growing on the subalpine conifer forest belt and the conifer forest-alpine ecotone in the mountains of central Honshu; 2) tetraploid, amphimictic, having hard leaf blades 2–6 mm broad and growing on the stony, arid and exposed alpine belt on Mt. Apoi in Hokkaido; 3) hexaploid, mainly apomictic, the most variable ecologically, widely distributed; 4) octoploid, mainly apomictic, frequent in the upper montane to alpine belts, probably widely distributed.     

Hybridisation in the genera Vulpia and Festuca: the production of artificial F1 plants

The results of hybridisation experiments involving 24 strains of diploid, tetraploid and hexaploid Vulpia , representing nine species in three sections, and 22 strains of hexaploid and octoploid Festuca rubra agg., are presented, and the taxonomic implications discussed. 7848 pollinations produced 741 hybrid caryopses, from which 137 mature hybrid plants were raised (1.75% success rate) by embryo culture. Festuca x Festuca crosses were relatively easily achieved, and Festuca x Vulpia crosses were as successful as Vulpia x Vulpia crosses, indicating a close relationship between these two genera. Hybrids with F. rubra agg. were raised from females of species from all three sections of Vulpia. Within Vulpia , the most successful crosses involved V. geniculata, V. ligustica, V. fasciculata and V. pyramidata , whereas V. alopecuros was the least successful parent of all, producing only one mature hybrid from 2595 pollinations.     

Variation in DNA-ploidy Levels of Reynoutria Taxa in the Czech Republic

The genus Reynoutria is represented by four taxa in the Czech Republic: Reynoutria japonica var. japonica, R. japonica var. compacta, R. sachalinensis and R. xbohemica. By using flow cytometry, cytological variability within the genus is described based on 257 Reynoutria samples. The varieties of R. japonica are cytologically uniform, var. japonica is exclusively octoploid (2n = 8x = 88) and var. compacta occurs only as a tetraploid (2n = 4x = 44), but R. sachalinensis and R. xbohemica exhibit some variation in chromosome numbers. Reynoutria sachalinensis is predominantly tetraploid (2n = 4 x = 44), but also occurs occasionally as hexaploid and octoploid cytotypes. The most common ploidy level in R. xbohemica is hexaploid (2n = 6x = 66), but tetraploid and octoploid clones were also found. The four taxa occurring in the Czech Republic are described briefly and the possible origins of the cytotypes discussed.     

The basis of natural and artificial postzygotic hybridization barriers in Arabidopsis species

The success or failure of interspecific crosses is vital to evolution and to agriculture, but much remains to be learned about the nature of hybridization barriers. Several mechanisms have been proposed to explain postzygotic barriers, including negative interactions between diverged sequences, global genome rearrangements, and widespread epigenetic reprogramming. Another explanation is imbalance of paternally and maternally imprinted genes in the endosperm. Interspecific crosses between diploid Arabidopsis thaliana as the seed parent and tetraploid Arabidopsis arenosa as the pollen parent produced seeds that aborted with the same paternal excess endosperm phenotype seen in crosses between diploid and hexaploid A. thaliana. Doubling maternal ploidy restored seed viability and normal endosperm morphology. However, substituting a hypomethylated tetraploid A. thaliana seed parent reestablished the hybridization barrier by causing seed abortion and a lethal paternal excess phenotype. We conclude from these findings that the dominant cause of seed abortion in the diploid A. thaliana x tetraploid A. arenosa cross is parental genomic imbalance. Our results also demonstrate that manipulation of DNA methylation can be sufficient to erect hybridization barriers, offering a potential mechanism for speciation and a means of controlling gene flow between species.     

Evidence for autoploid evolution in the artemisia ludoviciana complex of the Pacific Northwest

TheArtemisia ludoviciana complex of the Northwest is considered to be an intervarietal autoploid complex on the basis of evidence obtained from cytogenetic analysis. The evidence includes the occurrence of chromosomal races within all but two of the inclusive taxa, the degree and constancy of multivalent formation in the polyploid races, and the high degree of homology among the genomes of the various taxa as demonstrated by the pairing relationships in the F₁ progeny. Both triploid and tetraploid progeny were produced in diploid-tetraploid crosses, and the tetraploid offspring were fully as fertile as the natural tetraploids. The triploids, on the other hand, produced very few viable pollen grains. The production of tetraploid offspring in interracial crosses could provide a mechanism for gene flow from the diploid to the tetraploid population. With the observation of both diploid and tetraploid populations ofA. douglasiana, in addition to the well-known hexaploid, a reasonable doubt is cast upon the putative amphidiploid origin of the hexaploid via hybridization betweenA. suksdorfii andA. ludoviciana.     

Chromosome counts in the genus Festuca L. section Festuca (Poaceae) in the Iberian Peninsula

Chromosome numbers have been counted in 102 populations belonging to 34 taxa of Festuca L. section Festuca from the Iberian Peninsula. Four of these taxa have been counted for the first time and another three for the first time from the Iberian Peninsula. Furthermore, the levels of ploidy for another three taxa have been obtained for new populations within their distribution area, and for another 18 taxa the ploidy levels have been confirmed. Five levels of ploidy have been established for this section: diploid, tetraploid, hexaploid, octoploid and decaploid. There are 17 diploid taxa, eight tetraploid, three octoploid, two octoploid and one decaploid. The three remaining taxa represent polyploid complexes (one tetra-hexa-octoploid and two hexa-octoploids).     

Breeding barriers at a diploid–hexaploid contact zone in <Emphasis Type="Italic">Aster amellus</Emphasis>

Polyploidization is an important mechanism of sympatric speciation, but few studies have addressed breeding barriers between polyploids and their diploid progenitors in the field, and the available data have been mainly obtained from diploid-tetraploid contact zones. In contrast to diploid-tetraploid complexes, hybridization between diploid and hexaploid individuals may lead to viable fertile tetraploid offspring, and thus the interactions between these ploidy levels can be more complex. We investigated the breeding barriers operating between diploid and hexaploid individuals of Aster amellus at a contact zone in Central Europe to understand the absence of hybrids (i.e., tetraploids) and mixed populations. Phenological segregation, assortative mating mediated by pollinators and crossing ability were assessed under natural and controlled conditions in diploid and hexaploid populations growing in close proximity. The results revealed low levels of reproductive isolation (RI) due to flowering phenology (RI = 11–45%) and pollinator behavior (RI = 17%), so that pollen transfer between diploids and hexaploids is possible. In contrast, almost complete reproductive isolation was observed due to a series of post-pollination barriers that significantly reduced the production of offspring from inter-cytotype crosses (RI = 99.9%), even though some tetraploids were detected in seeds and seedlings. We conclude that the absence of tetraploids at the contact zone is probably due to a combination of several factors, including spatial segregation, strong post-pollination barriers (such as gametic isolation, low viability of tetraploid seeds and/or inability of tetraploid plants to reach the flowering stage), and to a lesser extent, temporal and behavioral segregation. Future studies should explore the fitness of tetraploids and the effect of different traits on the reproductive success and fitness of each cytotype. This will enable a fuller understanding of the dynamics and mechanisms acting in contact zones.     

Unreduced gametes and neopolyploids in natural populations of Achillea borealis (Asteraceae)

Polyploidy is a major mechanism of speciation and adaptation, yet little is known about the origins of polyploids in natural species. I investigated gametic nonreduction and neopolyploid formation in natural tetraploid populations of Achillea borealis (Asteraceae), an autopolyploid complex consisting of tetraploid and hexaploid cytotypes. Cytological analyses of tetraploid populations revealed the occurrence of reduced (n=2x) as well as unreduced 'big' (2n=4x) and 'jumbo' (4n=8x) pollen grains, which were clearly distinguished by size. Production of unreduced pollen was monitored in two tetraploid populations in 1997 and 1998. Mean population-level frequencies of unreduced pollen ranged from 0.030 to 0.538%, with as few as one-third and as many as one-half of sampled plants producing unreduced grains. Eight individuals were found to produce >1% unreduced pollen, with highest observed frequencies of 7.0, 13.2 and 15.8%. Experimental crosses using high unreduced pollen producers as male parents generated viable seeds. However, the frequency of neohexaploids in the progeny of experimental crosses (0.388%) was similar to that observed in progeny of randomly selected, open-pollinated control parents (0.465%). These results suggest that unreduced eggs are the most likely source of new polyploids. In spite of the inefficiency of unreduced pollen in unilateral sexual polyploidization, the overall rate of neohexaploid formation (one in 233) was several orders of magnitude greater than estimates of genic mutation rates.     

Hybridization in the genera Vulpia and Festuca (Poaceae): the characteristics of artificial hybrids

The chromosome numbers and morphological characteristics, including life–form, vegetative and floral measurements and pollen fertility, of 70 artificial interspecific Vulpia hybrid plants and 49 artificial intergeneric Festuca rubra agg. x Vulpia hybrid plants are presented, together with comparable data from 60 artificial Festuca rubra agg. x Vulpia fasciculata plants produced by R. Cotton. The inheritance of various characters is summarized. It is concluded that most characters of the tetraploid Vulpia fasciculata are dominant over those of diploid species of Vulpia , but that most characters of the hexaploid Festuca rubra agg. are dominant over those of diploid and tetraploid species of Vulpia. In diploid x diploid Vulpia crosses the pubescent ovary tip is dominant to the glabrous state, but the inheritance of lemma pubescence is more complicated. The keeled lemmas of V. fasciculata and V. pyramidata are dominant to the rounded ones of other Vulpia species, but recessive to the rounded ones of F rubra agg. Bearing in mind such generalizations as these, the parentage of wild hybrids should be capable of correct interpretation. The significance of the results in our understanding of the origin of V. fasciculata is discussed.     

Further cytogenetical studies on diploid and polyploid species of Eryngium L. (Saniculoideae, Apiaceae) from Argentina

Meiotic studies are carried out in 7 species of Eryngium L. (Saniculoideae, Apiaceae), belonging to both sections Foetida and Panniculata. The chromosome number of E. dorae Norm. (n=8) (Foetida) is reported for the first time, while the gametic chromosome number of E. nudicaule Lam. (n=7) (Foetida) and E. eburneum Decne. (n=8), E. horridum Malme (n=8), E. megapotamicum Malme (n=16), E. mesopotamicum Pedersen (n=24), and E. pandanifolium Cham. et Schlechtd. (n=24) (all belonging to Panniculata) is confirmed in several natural populations. Whereas in section Foetida all species are diploids and two basic chromosome numbers are present (x=8 and x=7), in section Panniculata all species are x=8 but there are three different ploidy levels (diploid, tetraploid, hexaploid). This study reveals that meiosis in all species is normal, with regular bivalent formation in all studied cells. Furthermore, the pollen stainability is above 80% in all cases. These data, together with the previous karyotype analyses, will contribute to the clarification of the relationships between members of both sections, where different mechanisms of speciation have been postulated.     

Spontaneous tetraploidy in strawberry (Fragaria sp., Rosaceae)

A tetraploid (2n = 28) clone of Fragaria from SW Finland is described. The clone is true-breeding with respect to tetraploidy. The tetraploid strawberry shows RFLP similarity with F. vesca , a common species, and, to a lesser extent, with F. viridis , a southern species, whose nearest reported occurrence was about 80 km away during the 1940s. The following alternatives are considered as possible reasons for the tetraploidy: unreduced gametes in an interspecific hybrid or hybrid derivative; hybridization followed by induction of tetraploidy either by viruses, or by industrial pollutants, e.g. chlorophenols and their congener compounds in the soil. The original seed might also have been brought from abroad unintentionally with other seeds for field trials which have been conducted since 1928 in the vicinity. A hexaploid ( F. moschata )× diploid hybrid leads directly to tetraploidy and a tetraploid derivative from an octoploid ( F . × ananassa ) × diploid hybridization can be obtained but the current tetraploid has different morphology.     

Hybridization between Fagopyrum (Polygonaceae) species native to China

Thirty-eight crosses between seven Fagopyrum species native to China were studied. Following normal pollination, there were very low inter-group crossabilities (only 0 3%) between five species in the large-achene group and two species (E gracilipes and E pleioramosum) in the small-achene group, and high (15 50%) within the large-achene group, i.e. E esculentum, E tataricum, E zuogongense, E pilus and E megaspartanium. Crosses between various types of (lowers (homostyle, heterostyle etc.) suggested that the intraspecific incompatibility also occurs in interspecific crosses. The hybrid seeds obtained from interspecific crosses all withered or shrivelled and lacked activity. Only one hybrid plant was obtained, tetraploid E esculentum x tetraploid E zuogongense. The hybrid displayed anomalous behaviour at meiosis, pollen grain sterility and withering of achenes, confirming the genetic differences between E esculentum and E zuogongense. The results support the hypothesis that E megaspartanium and E pilus are the possible ancestors of cultivated buckwheat     

Morphological variation in populations of the Poa orinosa complex (Poaceae: Poeae) in northeastern China

We conducted a detailed study of the morphological and cytological variation in seven populations of the Poa orinosa complex along an ecological gradient in northeastern China. Three of the populations were at different elevations in wooded habitats; three were in habitats dominated by grasses other than Poa; and one was in a shrub–steppe habitat. Plants from two of the wooded sites were diploid; those from the third wooded site were primarily octoploid. Plants from two of the grassy sites were tetraploid; those from the third grassy site were hexaploid. The seventh population, located in a shrub–steppe habitat, was diploid. Twenty‐four morphological characters were scored on specimens from each site. Plants from the three wooded sites and the lowest grassy site differed from those from the other three sites in having longer culms, internodes and sheaths. The similarity of the tetraploid plants to the diploid plants suggested that they may be autotetraploids. Similarly, the morphological similarity of the octoploid population to the two diploid populations suggested that it too may be an autopolyploid. The morphological distinction of the hexaploid population suggests that it has incorporated a genome not present in the other populations.     

Plants recently discovered in Scotland

Summary

Saxifraga rosacea is recorded and Poa scotica described new to Scotland. The position of segregate taxa or breeding units within several species complexes is clarified within Scotland: (a) the hexaploid cytotype within the mostly tetraploid Campanula rotundifolia; (b) diploid Hedera helix and tetraploid H. hibernica;, (c) diploid and tetraploid Deschampsia cespitosa, D. alpina and D. parviflora; (d) octoploid sub-species scotica within usually hexaploid Festuca rubra; (e) an octoploid mountain Agrostis; (f) fertile hexaploid Potentilla anserina; (g) an approximately triploid aneuploid Vaccinium uliginosum ssp. microphyllum.     

Possible pathways of the gene flow inTaraxacum sect.Ruderalia

Reproductive behaviour and the pathways of gene flow among ploidy levels were studied experimentally inTaraxacum sect.Ruderalia. Diploid, triploid and tetraploid individuals were sampled from mixed diploid — polyploid natural populations. 136 experimental hybridizations between the plants of different ploidy levels were performed. Seeds resulting from these crosses, those obtained from isolated anthodia as well as from open pollinated anthodia (both from cultivated and wild plants) were subjected to the flow-cytometric seed screening (FCSS) to determine ploidy levels in the progeny and to infer breeding behaviour of maternal plants. Three possible pathways of the gene flow were studied: (A) fertilization of sexuals by pollen of apomicts, (B) B_III hybrid formation, (C) facultative apomixis. Diploid maternal plants when experimentally crossed with triploid pollen donors produced diploids and polyploid progeny, while when pollinated with a mixture of the pollen of diploids and triploids or insect pollinated, no polyploids were discovered. It seems that in the mixture with the pollen of diploids, the pollen of triploids is ineffective. Tetraploids produce hybrids much easier with diploid mothers and their role in wild populations requires further study. Triploid mothers, even those with subregular pollen did not show traces of facultative apomixis. B_III hybrids were present in the progeny of both triploids and tetraploids, in tetraploids in quite high percentages (up to 50% of the progeny in some crosses).