Cytogenetical studies on artificial hybrids amongElymus sibiricus,E. dahuricus andAgropyron tsukushiense in the tribe Triticeae,Gramineae

To explore the cytogenetical relationships ofElymus andAgropyron of the tribe Triticeae, Gramineae, two species of AsiaticElymus, E. sibiricus (2n=28) andE. dahuricus (2n=42), and a JapaneseAgropyron, A. tsukushiense (2n=42) were crossed. Pentaploid and hexaploid F₁ hybrids were vigorous. All pollen grains were aborted and none of the hybrids produced seed. For the crossE. sibiricus × A. tsukushiense, the average chromosome pairing per cell at the MI of the PMCs in the F₁ was 16.38 univalents, 8.93 bivalents, 0.25 trivalents and 0.01 quadrivalents; for the crossE. dahuricus × A. tsukushiense, it was 4.41 univalents, 17.67 bivalents, 0.32 trivalents, 0.28 quadrivalents and 0.04 quinquevalents; and for the crossE. dahuricus × E. sibiricus, it was 17.11 univalents, 8.74 bivalents, 0.04 trivalents and 0.07 quadrivalents. From the present results, it is concluded thatE. sibiricus contains one genome andE. dahuricus contains two genomes, which are homologous to those ofA. tsukushiense, and that the third genome ofE. dahuricus might be partially homologous to the remaining genome ofA. tsukushiense. This conclusion is also supported by the cytogenetical analysis ofE. dahuricus × E. sibiricus. Contribution No. 27 from the Plant Germ-plasm Institute, Faculty of Agriculture, Kyoto University, Kyoto, Japan.     

Taxonomic studies of the genusPoa of Japan

With the aim of making clear the boundaries between species in thePoa acroleucahisauchii-nipponica aggregate, chromosomes and morphological features of 746 collections gathered from 125 localities in Japan were examined. For morphological observations, the voucher specimens of 95 collections whose chromosome numbers were reported previously (Tateoka, 1985) were also used. Tetraploids (2n=28) and hexaploids (2n=42), as well as a few pentaploids which were the hybrids between 4× and 6×, were found. By examining morphological features of these collections, two groups were recognized in tetraploids and one in hexaploids. The two tetraploid groups corresponded toPoa acroleuca Steud. andP. hisauchii Honda, and the hexaploid group toP. nipponica Koidz. It was confirmed that the hairiness on the internerve surface of lemma, ligule hairiness and the length ratio of anther/ lemma are the most important features for discriminating between these species; panicle shape, leaf shape and anther length are also helpful for the identification. The ambiguity of the boundaries between species which was hitherto present in the taxonomy of this species aggregate was unrelated to the creation of nature itself but was attributable to the insufficiency of our research work.     

Genomic relationships between species of theElymus semicostatus group andElymus sensu lato (Poaceae)

Meiotic pairing behaviour in 19 interspecificElymus hybrids is reported and discussed. The hybrids were made between four species belonging to theE. semicostatus group of sect.Goulardia, viz.,E. semicostatus, E. abolinii, E. fedtschenkoi, andE. panormitanus (all 2n = 28), andElymus species of seven different sections, viz., sect.Clinelymiopsis:E. caucasicus (2n = 28); sect.Elymus:E. sibiricus (2n = 28); sect.Goulardia:E. caninus (2n = 28),E. trachycaulus (2n = 28), andE. tsukushiensis (2n = 42); sect.Hyalolepis:E. batalinii (2n = 42); sect.Hystrix:E. hystrix (2n = 28); sect.Macrolepis:E. canadensis (2n = 28); and sect.Turczaninovia:E. dahuricus (2n = 42). Chromosomal pairing at meiotic metaphase I indicated that the species of theE. semicostatus group are genomically closer to the tetraploidE. caucasicus and the hexaploid species, regardless of sectional origin, than to the other tetraploid species of sectionGoulardia. Highest meiotic pairing was found in hybrids involvingE. caucasicus, E. tsukushiensis, andE. dahuricus. The presence of pairing regulating genes inE. abolinii is suspected.     

Morphology and cytology of intergeneric hybrids involvingLeymus multicaulis (Poaceae)

The morphology and meiotic behaviour of pollen mother cells were studied in hybrids involvingLeymus multicaulis (2n = 28) ×Psathyrostachys huashanica (2n = 14),L. multicaulis ×P. juncea (2n = 14), andL. secalinus (2n = 28) ×L. multicaulis. Chromosome pairing was almost identical in theL. multicaulis ×P. huashanica, andL. multicaulis ×P. juncea hybrids, in which it averaged 7.30 univalents + 6.69 bivalents + 0.096 trivalents and 7.48 univalents + 6.75 bivalents, respectively. The meiotic pairing in the two hybrids indicated that oneL. multicaulis genome was closely homologous with theP. huashanica andP. juncea genomes. BothP. huashanica andP. juncea are possibly donors of oneL. multicaulis genome. Chromosome pairing in theL. secalinus ×L. multicaulis hybrid averaged 4.49 univalents + 11.71 bivalents + 0.02 trivalents, indicating that the genomes ofL. multicaulis andL. secalinus are to some degree homologous. However, they are sufficiently differentiated to insure species distinctness.     

HYBRIDIZATION IN THE GENUS GLYCINE SUBGENUS GLYCINE WILLD. (LEGUMINOSAE,PAPILIONOIDEAE)

The genus Glycine is composed of two subgenera, Glycine and Soja. Soja includes the cultivated soybean, G. max, and its wild annual counterpart G. soja, while Glycine includes seven wild perennial species. Hybridization was carried out within and between wild perennial species of the subgenus Glycine. The success rate (pods set/flowers crossed) was 11% for intraspecific and 8% for interspecific crosses. A total of 220 F₁ hybrids was examined morphologically and cytologically where possible. Hybrids within G. canescens (2n = 40) and G. latifolia (2n = 40) were fertile as expected. Glycine clandestina (2n = 40) was morphologically separable into at least three groups, which produced fertile hybrids within each group. One cross between two groups gave vegetatively vigorous but sterile hybrids. The majority of crosses within G. tabacina (2n = 80) were fertile, except that extremely narrow-leaved forms gave sterile hybrids in combination with more usual forms. Sterility was also encountered in G. tomentella when aneuploids (2n = 78) from New South Wales, Australia, were crossed with tetraploids (2n = 80) from either Queensland, Australia, or Taiwan; crosses between the latter two populations resulted in seedling lethality. Cytological behavior of sterile hybrids followed a similar pattern, whether at the diploid or tetraploid level. The frequency of chromosome pairing was approximately half that expected if genomes showed full pairing homology. Bivalent disjunction at anaphase I was usually followed by precocious division of the majority of univalents. Telophase I and II were characterized by lagging chromosomes and micronuclei, so that resulting pollen was misshapen and sterile. Chromosome pairing data from sterile intraspecific hybrids at the tetraploid level may indicate a polyphyletic origin of tetraploids, whereby different diploid populations were involved in their formation. Similarly, chromosome pairing in sterile intraspecific diploid hybrids may indicate that the various diploid groups arose independently of one another. Both 40- and 80-chromosome forms are fully diploidized, however, and if they are of ancient origin, divergence since that time could have resulted in the chromosomal differentiation which becomes apparent when intraspecific hybridization is effected. Diploid (2n = 40) interspecific hybrids G. falcata × G. canescens, and G. falcata × G. tomentella grew poorly and did not reach flowering stage. Diploid (2n = 40) crosses between G. latifolia and G. tomentella produced inviable seedlings. Tetraploid (2n = 80) hybrids between G. tomentella and G. tabacina were vegetatively vigorous but sterile owing to low chromosome pairing at meiosis, indicating little pairing homology between the two species. Diploid hybrids between G. canescens and G. clandestina, however, showed almost complete chromosome pairing at diakinesis and partial fertility. Although morphologically distinct, these two species have not diverged sufficiently to prevent hybridization and possible gene exchange through recombination. Self compatibility, perennial growth habit, and geographic isolation have favored divergence among Glycine populations to the point that gene exchange appears no longer possible in many cases. Internal isolating mechanisms have been shown to operate at various levels of plant development from hybrid lethality at seedling stage, to failure of seed-set in sterile but vegetatively vigorous hybrids.     

Using DNA‐based techniques to identify hybrids among linear‐leaved Potamogeton plants collected in China

Abstract It is well known that interspecific hybrids occur in the genus Potamogeton. The linear‐leaved Potamogeton species commonly have highly variable morphological characteristics. Their hybrids often show similar vegetative characters to their parental species and their identification based solely on morphology is not always conclusive. In order to clarify whether there are any hybrids from the linear‐leaved Potamogeton plants collected in China, we used internal transcribed spacers (ITS) of nuclear ribosomal DNA and chloroplast rbcL gene sequences to identify the hybrids. Using ITS sequence additivity, we identified four hybrids, namely P. orientalis (P. pusillus×P. oxyphyllus), P. pusillus×P. berchtoldii, P. foliosus×P. octandrus, and P. cristatus×P. octandrus. The latter three hybrids should be considered as new hybrids in Potamogeton. The maternal parents of the four hybrids were confirmed using chloroplast rbcL gene sequences.     

NATURAL HYBRIDS BETWEEN ORYZOPSIS AND STIPA. III. ORYZOPSIS HYMENOIDES × STIPA PINETORUM

Johnson, B. Lennart. (U. California, Los Angeles.) Natural hybrids between Oryzopsis and Stipa. III. Oryzopsis hymenoides × Stipa pinetorum. Amer. Jour. Bot. 50(3): 228–234. Illus. 1963.—On the basis of morphological characters, the spontaneous hybrid Oryzopsis hymenoides × Stipa pinetorum is included in 0. bloomeri which consists of a number of sterile, natural hybrids between O. hymenoides (2n = 48) and various American species of Stipa (2n = 32-82). While intermediate between its parents in many attributes, the pinetorum hybrid is different from the other hybrids included in O. bloomeri with respect to lemma-hair length and other characters which are diagnostic for S. pinetorum (2n = 32). The hybrid has 2n = 40 chromosomes, but some plants of the hybrid and some of O. hymenoides had small supernumerary, somatic chromosomes. The parents formed only bivalents at meiosis. The hybrid showed some affinity among 14 chromosomes per sporocyte. This affinity is nearly as great as that shown by other Stiporyzopsis hybrids with 56 or 58 chromosomes, and is consistent with the earlier suggestion that bivalent formation in polyploid species of Stipa may be gene-controlled.     

Chromosome numbers and their taxonomic implications in the genusPoa of Japan

As part of the work leading to a taxonomic revision ofPoa of Japan, chromosome numbers of nearly all indigenous species of JapanesePoa, together with those of some putative interspecific hybrids, were examined. The following chromosome numbers were found:Poa annua, 2n=28;P. crassinervis, 2m=28;P. acroleuca, 2n=28;P. hisauchii, 2n=28;P. nipponica, 2n=28;P. crassinervis, 2n=28;P. acroleuca, 2n=35;P. tuberifera, 2n=28;P. fauriei, 2n=28;P. radula, 2n=42;P. hakusanensis, 2n=70;P. hayachinensis, 2n=42;P. malacantha var.shinanoana, 2n=63≈98;P. yatsugatakensis, 2n=ca. 71≈74, 77;P. sachalinensis, 2n=63, ca. 64, ca. 74;P. matsumurae, 2n=28;P. ogamontana, 2n=42;P. sphondylodes, 2n=28;P. viridula, 2n=42, 49, 56;P. nemoralis, 2n=70;P. glauca, 2n=42, 49, 56;P. eminens, 2n=42. It became clear that information obtained from chromosome counts is quite helpful in clarifying species boundaries in several species aggregates, such as thePoa acroleuca-hisauchii-nipponica aggregate. Results of the examination of morphological features of the voucher specimens in various species aggregates with taxonomic difficulties were reported, and the needs of some amendments for the species delimitation appearing in current floristic manuals were pointed out. A summary of chromosome counts so far made for JapanesePoa was tabulated. ThePoa flora of Japan characteristically lacked diploid plants.     

Experimental evidence on the affinities ofPapaver somniferum (Papaveraceae)

Results obtained from crossing experiments betweenP. somniferum subsp.somniferum (2n = 22) and subsp.setigerum (2n = 44),P. glaucum (2n = 14) andP. gracile (2n = 14) and from the observation of meiotic chromosome pairing in the various hybrids obtained do not provide straightforward evidence for the hypothesis thatP. somniferum originated as a triploid hybrid between taxa similar toP. glaucum andP. gracile (Kadereit 1986a, b).—On the one hand, the pattern of crossability found reflects the closer similarity of subsp.somniferum toP. glaucum and of subsp.setigerum toP. gracile, which was interpreted as segregation of parental characters, and the high frequency of 2n = 28 chromosomes among F₂-progeny from the hybrid subsp.somniferum × subsp.setigerum (2n = 33) might reveal n = 7 as the base number also ofP. somniferum. On the other hand, however, the general difficulty of obtaining hybrids, and the low incidence of bivalent formation in their meiosis, probably indicating a lack of chromosome homology between the different species, do not fit the above hypothesis.—These results are in marked contrast to the morphological similarity between the three species involved.     

Effect of pollen source and pollen ploidy on endosperm formation and seed set in pseudogamous apomictic Paspalum notatum

 It is generally accepted that most angiosperms require an accurate balance between maternal and paternal genome contribution for endosperm development. The endosperm balance number (EBN) hypothesis postulates that each species has an effective number which must be in a 2:1 maternal to paternal ratio for normal endosperm development and seed formation. The aim of this work was to investigate the effect of different sources and ploidy levels of pollen donors on endosperm formation and seed production of aposporous tetraploid (2n=4×=40) Paspalum notatum. Hand-emasculated spikelets of an apomictic 4× plant were dusted with pollen of 2×, 4×, 5×, 6× and 8× races of the same species; 3× and 4× races of a phylogenetically closely related species, P. cromyorrhizon; and 2× and 4× races of P. simplex, a species of a different subgenus. Experiments including self-pollination as well as emasculation without pollination were conducted for controls. Results indicated that apomictic 4×P. notatum is a pseudogamous species with effective fertilization of the two unreduced (2n) polar nuclei by a reduced (n) sperm. Endosperm development and seed production occurred independently of the species or the ploidy level of the pollen donor. However, seed germination rates were significantly lower than in the self-pollinated control when the pollen donor was 3×P. cromyorrhizon or 2× and 4×P. simplex. Aposporous embryo sacs in Paspalum contribute to endosperm formation with two unreduced (2n) polar nuclei, while the male contribution is the same as in sexual plants (n). Since sexual Paspalum plants fit the EBN hypothesis, the EBN insensitivity observed in apomictic plants might be a prerequisite for the spread of pseudogamous apomixis. The EBN insensitivity could have arisen as an imprinting consequence of a high maternal genome contribution. Received: 20 February 1998 / Revision accepted: 21 October 1998     

Variation and geographical distribution of ploidy levels inPennisetum sectionBrevivalvula (Poaceae) in Burkina Faso,Benin and southern Niger

Pennisetum sect.Brevivalvula is a species complex characterized by polyploidy and apomixis. Ploidy level was assessed by DAPI-flow cytometry for 304 plants of the section, originating from Burkina Faso, Benin and southern Niger. The results were confirmed for 54 plants based on chromosome counts. The samples show four euploidy levels (with x = 9) distributed among five species:P. hordeoides (2n = 36, 54),P. pedicellatum (2n = 36, 45, 54),P. polystachion (2n = 18, 36, 45, 54),P. setosum (2n = 54), andP. subangustum (2n = 18, 36, 54). The geographical distribution of these ploidy levels seems related to major vegetation zones present in Africa. Diploid populations ofP. polystachion andP. subangustum were found in the Banfora area, in Burkina Faso.     

Chromosome numbers and taxonomic implications in the fern genusAzolla (Azollaceae)

Investigation of chromosome numbers of allAzolla species, and for the first time of hybrids, has been undertaken. Removal of wax from the leaf surface proved invaluable in achieving clear cytological preparations and providing unambiguous chromosome numbers. In contrast to previous records, the speciesA. pinnata, A. filiculoides, A. filiculoides var.rubra, A. caroliniana, A. microphylla, andA. mexicana were found to be 2n=44, andA. nilotica to be 2n=52. Several triploids (2n=66) and one tetraploid (2n=88) were identified. No geographical pattern could be observed in the distribution of triploids which probably derive from the function of unreduced gametes. The chromosome number of hybrids occasionally deviates from the diploid chromosome number (2n=44). The small chromosome size limits karyotypic analysis and only differences in overall chromosome size can be observed. Taxonomic implications of chromosome numbers and sizes are discussed.     

Two new spontaneous hybrids of American hard pines from Pinus sect. Trifoliae (Pinaceae) found in the unique Russian Sochi Arboretum

In the 1990s, an extraordinarily abundant live collection of the genus Pinus, including 49 species, 4 subspecies, and 7 interspecific hybrids, found in the Sochi Arboretum in Russia on the northeast coast of the Black Sea, was taxonomically revised. Among these taxa, two previously unknown interspecific hybrids of American hard pine species from P. sect. Trifoliae had arisen spontaneously in culture. These are described here as the new hybrid species Pinus × transamericana (P. muricata × P. rigida) and Pinus × critchfieldii (P. patula × P. taeda). All known natural or artificial interspecific hybrids within P. sect. Trifoliae are listed, and hybridization between American hard pine species is discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chromosome numbers and pollen fertility in the Senecio nemorensis group (Compositae) in the Carpathians

New chromosome numbers for two species from the Senecio nemorensis group: S. dacicus (2n = 40) and S. ucranicus (2n = 40) have been ascertained. The counts for S. germanicus Wallr. subsp. germanicus (2n = 40), S. hercynicus Herborg subsp. hercynicus (2n = 40), S. ovatus (P. Gaertn. et al.) Willd. subsp. ovatus (2n = 40) occurring in the Carpathians are also reported. The study confirmed only the known tetraploid chromosome number for the taxa of this group. The pollen fertility ranged from 82.09 to 92.99% in all examined species and subspecies, including their hybrids.     

Recurrent hybridisation events between Primula vulgaris,P. veris and P. elatior (Primulaceae,Ericales) challenge the species boundaries: using molecular markers to re‐evaluate morphological identifications

Three Primula species, Primula vulgaris, P. veris and P. elatior, have been objects of fascination for gardeners and botanists over several centuries. The species are able to hybridise, and where they co‐occur, hybrids are commonly found. In Denmark, Møns Klint on the island of Møn and Købelev Skov on Lolland are examples of localities where all three species occur and where the hybrids P. × digenea, the hybrid between P. vulgaris and P. elatior, and P. × polyantha, the hybrid between P. veris and P. vulgaris, can also be found. To investigate relationships between the species and their hybrids, we sampled 168 specimens from 10 geographical locations and subjected them to genetic analysis. The samples were also identified based on morphological traits: primarily inflorescense structure, the size, shape, colour and markings of corolla and leaf basis, leaf blade texture and hairiness. After identifying species‐specific SNPs in the Internal Transcribed Spacer sequence, these were used to resolve species and hybrid boundaries and status through a cleaved amplified polymorphic sequence assay. Polymorphisms in the chloroplast trnL sequence were used as a high‐throughput marker and used to determine the maternal parent of hybrids. Ten simple sequence repeat markers were applied to obtain further insight into the genetic makeup of the accessions using structure and Introgress, providing information of genetic variability within and between populations. Our results indicated that backcrossing of P. × digenea hybrids with parental species has occurred, and that many of the P. × digenea sampled were later‐generation hybrids rather than F₁s. Analyses of P. × polyantha specimens show mostly the expected pattern for primary hybrids but indications of P. veris ancestry of a P. vulgaris plant was discovered. Our results further indicate that some of the specimens initially identified as P. elatior include P. vulgaris among their progenitors and thus challenge currently accepted species boundaries.     

Questions of procedure in moss cytotaxonomy: new data for some British species

Abstract

Cytological data for Gymnostomum aeruginosum (n = 13), Discelium nudum (n = 13) and Plagiomnium ellipticum (n = 6) supplement earlier records from Britain and elsewhere but those for Physcomitrium sphaericum (n = 26) are the first for the species. Chromosome counts continue to have a role to play in bryophyte cytotaxonomy as a means of identifying probable erroneous reports. It is considered, however, that karyotype definition in terms of Giemsa C-banding and cytogenetic studies related to chromosome behaviour have greater taxonomic potential.     

NATURAL HYBRIDS BETWEEN ORYZOPSIS AND STIPA. I. ORYZOPSIS HYMENOIDES × STIPA SPECIOSA

Johnson , B. Lennart . (U. California, Los Angeles.) Natural hybrids between Oryzopsis and Stipa. I. Oryzopsis hymenoides × S. speciosa. Amer. Jour. Bot. 47(9): 736–742. Illus. 1960.—Spontaneous, sterile hybrids between Oryzopsis hymenoides and Stipa speciosa heretofore have been referred to O. bloomeri, which species in an earlier paper was shown to consist of a series of hybrids between O. hymenoides and various species of Stipa. On many morphological characters (O. hymenoides × speciosa) is intermediate between its parents and similar to the other hybrids formerly classed as O. bloomeri. It is distinct from the other hybrids on characters which reflect S. speciosa, except with respect to indument of the awn which is recessive. Somatic chromosome counts are: O. enoides, 48; S. speciosa, 64; hybrid, 56. Both parents exhibit regular bivalents at meiosis. The hybrid shows only occasional bivalents and mostly asynchronous splitting or random distribution of univalents at metaphase I. Pollen abortion is complete. No evidence of natural amphiploidy or introgression was found.     

Meiotic pairing behaviour reveals differences in genomic constitution between Hystrix patula and other species of the genus Hystrix Moench (Poaceae, Triticeae)

Interspecific and intergeneric hybridizations were carried out to evaluate the genomic relationships among species of Hystrix Moench and to study the relationships between Hystrix species and Psathyrostachys huashanica Keng (2n=2x=14, Ns^h). Meiotic pairing in hybrids of Hystrix duthiei ssp. duthiei × P. huashanica (2n=3x=21), Hystrix duthiei ssp. longearistata × P. huashanica (2n=3x=21) and H. patula × P. huashanica (2n=3x=21) averaged 5.18, 5.11 and 0.29 bivalents per cell, while H. patula × H. duthiei ssp. longearistata (2n=4x=28) averaged 25.36 univalents and 1.32 bivalents per cell, respectively. The results indicate that (i) H. duthiei ssp. duthiei and H. duthiei ssp. longearistata have one set of Ns genome from Psathyrostachys; (ii) H. patula has no Ns genome; (iii) genomes of H. duthiei ssp. duthiei and H. duthiei ssp. longearistata are non-homologous to those of H. patula. The genomic relationships between H. patula and other Hystrix species are also discussed.     

A BIOSYSTEMATIC STUDY OF THE POLYGONUM HYDROPIPEROIDES (POLYGONACEAE) COMPLEX

The Polygonum hydropiperoides complex includes P. hydropiperoides Michx., P. opelousanum Riddell ex Small, P. setaceum Baldwin ex Ell., and P. hisutum Walter. Studies of morphology, cytology, and crossing compatibility were conducted with specimens from North Carolina, South Carolina, Georgia, and Florida. A multivariate cluster analysis using 212 specimens and 34 characters indicated that P. hirsutum and P. setaceum are each morphologically distinct while P. hydropiperoides and P. opelousanum are morphologically indistinct from one another. The chromosome counts of 2n = 20 for P. setaceum and P. hirsutum, and 2n = 40 for P. hydropiperoides and P. opelousanum are the first reported for the respective species. Experimental hybridizations produced the fertile hybrids P. hydropiperoides x opelousanum and P. setaceum × hirsutum. Results of these studies and population structure, habitat, and pollination studies suggest that P. hydropiperoides, P. setaceum, and P. hirsutum are each distinct species while P. opelousanum is indistinct and should be merged with P. hydropiperoides.