Intergeneric hybridization and C-banding patterns inHordelymus (Triticeae,Poaceae)

Crosses ofHordelymus europaeus (2n = 4x = 28) with four genera in theTriticeae were attempted. Adult hybrids were obtained in combinations withHordeum bogdanii (2x),Hordeum depressum (4x), andSecale cereale (2x). The meiotic pairing was very low in the hybrids withH. bogdanii andSecale cereale (0.12 and 0.30 chiasmata/cell, respectively), whereas high pairing (9.90 chiasmata/cell) was found in hybrids withH. depressum due to autosyndetic pairing ofH. depressum chromosomes. The chromosome complement ofHordelymus europaeus comprised 16 metacentrics, 8 submetacentrics, and 4 SAT-chromosomes. The Giemsa C-banding patterns of the chromosomes were characterized by small to minute bands at no preferential positions. It is hypothesized thatHordelymus europaeus may genomically be closest related toTaeniatherum andPsathyrostachys spp.     

Interspecific hybridization and the analysis of meiotic chromosome pairing inDahlia (Asteraceae — Heliantheae) species with x = 16

The successful production of a large number of artificial hybrids betweenDahlia species based on x = 16 has allowed a detailed study of their genomic relationships. Chromosome behaviour in these artificial hybrids was extremely similar to that observed in parental species suggesting that there is a considerable degree of homology between the genomes of theseDahlia species. Using GISH it can be demonstrated that in these hybrids bivalent formation involved pairing only between parental genomes. The ability of GISH to differentiate between parental genomes in artificial hybrids was variable, indicating that molecular divergence of highly repeated sequences has accompanied the evolution of these species. However, the extent of chromosome pairing and chiasma formation in the hybrids does not reflect the differences that can be detected by GISH. Seyeral of the new hybrid combinations have resulted in horticulturally interesting plants.     

Biosystematic study of hexaploids Elymus tschimganicus and E. glaucissimus. II. Interspecific hybridization and genomic relationship.

To investigate genomic relationships of Elymus tschimganicus (Drobov) Tzvelev (2n = 6x = 42, S1S2Y genomes) and E. glaucissimus (M. Pop.) Tzvelev (2n = 6x = 42, S1S2Y genomes), interspecific hybridizations of the two target species were carried out with 27 other Elymus species containing the SH, SY, SYH, SYP, SYW, and SH1H2 genomes, respectively, collected from different geographic regions. Chromosome pairing behavior was analyzed at metaphase I in 27 hybrids representing 23 hybrid combinations, and overall genomic relationships of the two target species with the other Elymus taxa were estimated. The study concluded that (i) interspecific hybridization was principally easy to perform between the Elymus species, but no general pattern of crossability was obtained, and all hybrids were completely sterile, (ii) the two species have a similar meiotic pattern in their hybrids with the other Elymus species, and (iii) species containing the SY, SYP, and SYH genomes have a generally higher level of genomic homology to the target species than those possessing the SH genomes, and the South American hexaploid with the SH1H2 genomes has the lowest level of genomic homology to the two target taxa.     

Comparisons of the hybrids Hordeum chilensexH. vulgare,H. chilensexH. bulbosum,H. chilensexSecale cereale and the amphidiploid of H. chilensexH. vulgare

Summary Diploid hybrids between Hordeum chilense and three other species, namely H. vulgare, H. bulbosum and Secale cereale, are described together with the amphidiploid of H. chilensexH. vulgare. Both the diploid hybrid and the amphidiploid of H. chilensexH. vulgare were chromosomally unstable, H. chilensexH. bulbosum was less so, while H. chilensexS. cereale was stable. Differential amphiplasty was found in all combinations. No homoeologous pairing was found in the Hordeum hybrids but in H. chilensexS. cereale there was chromosome pairing both within the two genomes and between the genomes.     

披碱草属与大麦属系统关系的研究

禾本科中,披碱草属Elymus L.为多倍体属,约含150余种;大麦属Hordeum L.具二倍体和多倍体,约有40余种,该两属均广泛地分布于全球温带地区。该两属,尤其是披碱草属的系统分类较为困难。基于形态学的传统研究认为这两个属的系统关系较远,而细胞学研究的资料却表明,披碱草属的H染色体组起源于大麦属。笔者对来源不同的披碱草属和大麦属的物种进行了远缘杂交,并对其属间杂种F1的减数分裂中期I染色体配对行为进行了分析。结果表明,若以披碱草属作母本,该两属有相对较高的杂交亲合力,通过对杂种幼胚进行分割和离体培养,也能获得杂种F1植株。属间杂种植株的形态介于双亲之间,但更接近于披碱草属,杂种的生殖器官发育不健全,而且所有的杂种F1均完全不育。细胞学的观察结果表明,这两个属间的杂种F1通常具有较低的减数分裂中期I染色体配对数,但有较大的变异。通过笔者的工作及掌握的形态学和细胞学的资料分析认为：披碱草属和大麦属的亲缘关系较为复杂,不能一概而论。含H染色体组的披碱草属和大麦属物种有着较近的亲缘关系,但这两个属中所含的H染色体组已产生了程度不同的分化;不含H染色体组的披碱草属及大麦属的物种具有较远的亲缘关系。     

Interspecific hybridization with Hordeum depressum (Poaceae)

Hordeum depressum is a distinct, reproductively isolated, tetraploid species. The study of meiosis in hybrids with the closest congeneric relatives revealed intermediate to low pairing with most species. The exceptions are Hordeum brachyantherum ssp. californicum and H. arizonicum. H. depressum , probably share one highly similar genome with ssp. californicum and perhaps two with H. arizonicum . However, it is difficult to draw firm conclusions based only on meiotic figures, since the pairing may be disturbed by high autosyndetic pairing between the H. depressurn genomes.     

Genetic relationships in hibiscus sect. Furcaria

The eighteen species studied form an allopolyploid series (x=18). The morphology, crossing behavior, and geographical distribution of 6 diploid, 9 tetraploid, 2 octoploid, and 1 decaploid species were studied. From over 26,500 crosses, 19 hybrid combinations and several derived allopolyploids and three-species hybrids were obtained. Chromosome pairing in the hybrids showed that a minimum of 6 and a maximum of 14 well-differentiated genome groups exist in sect. Furcaia, at least two of which appear to be confined to the Old World. No evidence was found that New World genomes are represented in the Old World. The primary radiation of the diploid genomes probably occurred at about the same time as that of the diploid genomes of Gossypium, whereas the tetraploids and one of the octoploid species (H. furcatus Roxb., non Willd.) seem to be of later origin (late Pleistocene or Recent). Octoploid H. diversifolius Jacq., a circumtropical species, may be a relict of a much earlier round of polyploid evolution.     

Cytoplasmic and genomic effects on meiotic pairing in brassica hybrids and allotetraploids from pair crosses of three cultivated diploids

Interspecific hybridization and allopolyploidization contribute to the origin of many important crops. Synthetic Brassica is a widely used model for the study of genetic recombination and "fixed heterosis" in allopolyploids. To investigate the effects of the cytoplasm and genome combinations on meiotic recombination, we produced digenomic diploid and triploid hybrids and trigenomic triploid hybrids from the reciprocal crosses of three Brassica diploids (B. rapa, AA; B. nigra, BB; B. oleracea, CC). The chromosomes in the resultant hybrids were doubled to obtain three allotetraploids (B. juncea, AA.BB; B. napus, AA.CC; B. carinata, BB.CC). Intra- and intergenomic chromosome pairings in these hybrids were quantified using genomic in situ hybridization and BAC-FISH. The level of intra- and intergenomic pairings varied significantly, depending on the genome combinations and the cytoplasmic background and/or their interaction. The extent of intragenomic pairing was less than that of intergenomic pairing within each genome. The extent of pairing variations within the B genome was less than that within the A and C genomes, each of which had a similar extent of pairing. Synthetic allotetraploids exhibited nondiploidized meiotic behavior, and their chromosomal instabilities were correlated with the relationship of the genomes and cytoplasmic background. Our results highlight the specific roles of the cytoplasm and genome to the chromosomal behaviors of hybrids and allopolyploids.     

Meiosis and fertility of reciprocal triploid hybrids of Lolium multiflorum with Festuca pratensis

Diploid and tetraploid forms of Lolium multiflorum and Festuca pratensis were crossed under controlled conditions and after embryo rescue all four combinations of autoallotriploid hybrids were obtained. Male and female fertility and chromosome pairing at metaphase I of meiosis were studied in several plants from each hybrid combination. The hybrids with two genomes of L. multiflorum and one of F. pratensis (genomic formulae LmLmFp and FpLmLm) were male and female fertile while the hybrids with two genomes of F. pratensis and one of L. multiflorum had a reduced fertility (FpFpLm) or were completely sterile (LmFpFp). Chromosome pairing at metaphase I varied among hybrid combinations depending on their genomic composition. LmLmFp and FpLmLm hybrids had similar patterns of pairing (1.83I + 5.29II + 2.85III and 2.22I + 5.22II + 2.75III, respectively) but they differed from those of FpFpLm (3.65I + 4.65II + 2.68III) and especially from LmFpFp (4.78I + 5.87II + 1.49III). Conventional analysis of meiosis failed to explain the differences in chromosome behaviour and fertility/sterility levels between the autoallotriploid hybrids with two Lolium or two Festuca genomes.     

Interspecific hybridizations in the Elymus semicostatus group (Poaceae).

Meiotic pairing in 16 interspecific hybrids in the genus Elymus is reported. The hybrids were made among seven species in the Elymus semicostatus group, viz., E. semicostatus, E. validus (subgroup I), E. abolinii (subgroup II), E. fedtschenkoi, E. nevskii, E. praeruptus (subgroup III), and E. panormitanus (subgroup IV). All species are tetraploid (2n = 4x = 28) and possess the SY genomes. Meiotic pairing was distinctly higher in hybrids made within subgroups than between subgroups, but the genomes in E. panormitanus have differentiated from those in the other species. These results generally support the subdivision of the E. semicostatus group based on morphological data but also indicate that the subgroups are more distantly related than previously believed, and that the group may be nonmonophyletic.     

Interspecific hybrids between a transgenic rapeseed (Brassica napus) and related species: cytogenetical characterization and detection of the transgene.

In interspecific hybrids produced between a transgenic rapeseed, an allotetraploid species, resistant to herbicide, phosphinotricin, and five diploid related species, the risk for gene introgression in weed genomes was explored through cytogenetic and bar gene characterizations. Among the 75 hybrids studied, most had the expected triploid structure, with the exception of B. napus - B. oleracea amphidiploid plants and one B. napus - S. arvensis amphidiploid plant. In triploid hybrid plants, the reciprocal hybrids did not exhibit any difference in their meiotic behavior. The comparison of the percentage of chromosome pairing in the hybrids with that of haploid rapeseed permit to conclude that allosyndesis between AC genomes and related species genomes took place. This possibility of recombination was confirmed by the presence of multivalent associations in all the interspecific hybrids. Nevertheless, in B. napus - B. adpressa hybrids a control of chromosome pairing seemed to exist. The possibility of amphidiploid plant production directly obtained in the F1 generation increased the risk of gene dispersal. The B. napus - B. oleracea amphidiploid plant presented a meiotic behavior more regular than that of the B. napus - S. arvensis amphidiploid plant. Concerning the herbicide bar gene characterization, the presence of the gene detected by DNA amplification was correlated with herbicide resistance, except for two plants. Different hypotheses were proposed to explain these results. A classification of the diploid species was established regarding their gene dispersal risk based on the rate of allosyndesis between chromosomes of AC genomes of rapeseed and the genomes of the related species.     

Genome analysis of Elytrigia caespitosa, Lophopyrum nodosum, Pseudoroegneria geniculata ssp. scythica, and Thinopyrum intermedium (Triticeae: Gramineae).

To elucidate the genome constitutions of the tetraploid (2n = 4x = 28) species Elytrigia caespitosa, Lophopyrum nodosum, and Pseudoroegneria geniculata ssp. scythica and the hexaploid (2n = 6x = 42) Thinopyrum intermedium, meiotic pairing was studied in these species as well as 10 hybrids. Karyotype analysis with aceto-orcein stained root-tip cells was performed for the four species and the hybrids of T. bessarabicum with E. caespitosa, P. geniculata ssp. scythica, and T. intermedium. Karyotype analysis by Giemsa C-banding was carried out with the three tetraploid species and the two triploid hybrids involving T. bessarabicum. The species behaved as strict allopolyploids. All hybrids were male sterile with few stainable pollen grains. It is concluded from the results that the three tetraploid species have the genome formula JeJeSS and T. intermedium has the formula JeJeJeJeSS. The chromosomes of the Je and S genomes in these species had C-banding patterns differing from each other and from those of the extant diploid species. Based on these findings, the four species investigated should be placed in the same genus or the same section of a genus. However, new combinations are not proposed at this time pending future taxonomic investigation of the genome constitution of Elytrigia repens (L.) Nevski.     

Metaphase I bound arms frequency and genome analysis in wheat-Aegilops hybrids

Summary Meiotic associations of different wheat-Aegilops variabilis and wheat-Ae. kotschyi hybrid combinations with low and high homoeologous pairing were analyzed at metaphase I. Five types of pairing involving wheat and Aegilops genomes were identified by using C-banding. A genotype that seems to promote homoeologous pairing has been found in Ae. variabilis var. cylindrostachys. Its effect is detectable in the low pairing hybrids but not in the high ones. Pairing affinity has been analyzed on the basis of metaphase I associations in the low and high homoeologous pairing hybrids, and in bivalents and multivalents in the high pairing hybrids. The results indicate that the amount of bound arms of each type of identifiable association relative to the total associations formed (relative contribution) was not maintained, either between the different levels of pairing (low and high) or between different meiotic configurations (bivalents and multivalents). These findings seem to indicate that quantifications of genomic relationships based on the amount of chromosome pairing at metaphase I must be carefully done in this type of hybrid combinations.     

Cryptic homoeology analysis in species and hybrids of genus Zea

Cryptic intergenomic pairing of genus Zea was induced by the use of a diluted colchicine solution in order to elucidate the phylogenetic relations and differentiation of the homoeologous genomes. Results indicate that in species and hybrids with 2n = 20, there was chromosome pairing between the homoeologous A and B genomes with a maximum of 5IV, with the exception of Zea diploperennis and their interspecific hybrids where cryptic homoeologous chromosome pairing was not induced. In almost all 2n = 30 hybrids, observed cryptic pairing increased to a maximum of 10III although Z. mays × Z. mays with 2n = 30 did not show significant differences between treated and untreated materials. Pairing was also observed in species and hybrids with 2n = 40, in which a maximum of 10IV was observed, with the exception of Z. mays with 2n = 40 where treated and untreated cells did not differ significantly.     

A Biosystematic Study on Hybrids Between Psathyrostachys huashanica and Two Species of Roegneria

Intergeneric crosses were made betweem Psathyrostachys huashanica (2n=14, NN)and two Roegneria species, namely, R. ciliaris (2n=28, SSYY), and R. tsukushiensis (2n=42, SSHHYY). Two combinations of P. huashanica crossed with R. ciliaris and R. tsukushiensis produced adult hybrid plants. Although completely sterile, the hybrid plants developed rather vigorously, and were morphologically intermediate between the two parents.Two spikelets per node in part were observed in hybrids, which evidently came from P. huashanica. The chromosome configurations of R. ciliaris × P. huashanica and R. tsukushiensis × P. huashanica were 20.73 I+0.318 II, 24.80 I+1.578 II+0. 012 III, respectively. Polypolar division was found at anaphase I in meiosis of two hybrids. Abnormal meiosis in two hybrids was observed. The chromosome pairing indicates that there is only a little chromosome homoeology between “N” genome of P. huashanicaand “S”, “Y” or “H” genomes of R. ciliaris and R. tsukushiensis.     

Genomic constitutions of four Chinese endemic Elymus species: E. brevipes, E. yangii, E. anthosachnoides, and E. altissimus (Triticeae, Poaceae).

The objectives of this study were to determine the genomic constitution and to explore the genomic variation within four Chinese endemic Elymus species, i.e., E. brevipes (Keng) L?ve (2n = 4x = 28) and E. yangii B.R. Lu (2n = 4x = 28), E. anthosachnoides (Keng) L?ve (2n = 4x = 28), and E. altissimus (Keng) L?ve (2n = 4x = 28). Intraspecific crosses between different populations of the four Elymus species, as well as interspecific hybridizations among the four target species, and with six analyzer species containing well-known genomes, i.e., E. caninus (L.) L. (2n = 4x = 28, SH), E. sibiricus L. (2n = 4x = 28, SH), E. semicostatus (Lees ex Steud.) Melderis (2n = 4x = 28, SY), E. parviglumis (Keng) L?ve (2n = 4x = 28, SY), E. tsukushiensis Honda (2n = 6x = 42, SHY), and E. himalayanus (Nevski) Tzvelev (2n = 6x = 42, SHY), were achieved through the aid of embryo rescue. Chromosome pairing behaviors were studied in the parental species and their hybrids. Numerical analysis on chromosome pairing was made on the interspecific hybrids. With one exception, each meiotic configuration at metaphase I in the hybrids involving the target taxa and the analyzer species containing the "SH" genomes fit a 2:1:1 model with x-values ranging between 0.91 and 1.00; chromosome pairing in the hybrids involving analyzer parents with the "SY" genomes match a 2:2 model, with x-values between 0.97 and 0.99. All pentaploid hybrids with a genomic formula "SSYYH," except for two crosses having unexpected low c-values, had pairing patterns fitting the 2:2:1 model with x-values varying between 0.96 and 1.00. It is concluded based on hybridization, fertility, and chromosome pairing data that (i) the four target Elymus species are strictly allotetraploid taxa, (ii) they are closely related species, all comprised of the "SY" genomes, (iii) minor genomic structural rearrangements have occurred within the four Elymus species, and (iv) meiotic pairing regulator(s) exists in some of the Elymus taxa studied.     

Genome relationships in the genus Dasypyrum (Gramineae)

To elucidate the genome relationships in the genus Dasypyrum and the ancestry of tetraploid D. breviaristatum, two cytotypes of D. breviaristatum and D. villosum were reciprocally crossed with one another. Chromosome pairing at the first metaphase of meiosis and fertility were examined in the F1 hybrids and the parental plants. The mean pairing configuration and mean arm pairing frequency in D. villosum-D. breviaristatum (2x) hybrids were 11.12I + 1.44II per cell and 0.107, respectively, and they were almost completely sterile. In D. breviaristatum (4x)-D. breviaristatum (2x) hybrid, up to seven trivalents were formed, and the mean pairing configuration was 3.38I + 3.20II + 3.74III + 0.005IV per cell. The mean arm pairing frequency and relative affinity calculated in that F1 hybrid were 0.915 and 0.641, respectively. Seven bivalents and seven univalents were characteristically formed in D. villosum-D. breviaristatum (4x) hybrids. Based on the present results, we clearly concluded that the genome of diploid D. breviaristatum is distantly related to the genome V of D. villosum, and that these two species have different basic genomes. We, therefore, proposed the symbol Vb for the haploid genome of diploid cytotype of D. breviaristatum. Moreover, we concluded that tetraploid D. breviaristatum is an autotetraploid with doubled sets of the genomes homologous with that of diploid D. breviaristatum, and we proposed the genome constitution VbVb for the haploid genome set of tetraploid cytotype of D. breviaristatum. Furthermore, from the chromosome pairing in the F1 hybrids involving Moroccan and Greek accessions, it was suggested that complicated rearrangements of chromosome structure have occurred in tetraploid D. breviaristatum in its natural populations across the entire distribution area.     

Chromosomes and polyploidy in Lenophyllum (Crassulaceae)

Gametic chromosome numbers of 22, 32, 33, and 44 in five species of Lenophyllum suggest that they may be polyploids on a basic 11, but this number has not been found. Three species have 8-12 distinctively large chromosomes that do not pair with each other in their hybrids and probably belong to the same genome. In hybrids of many polyploid Mexican Crassulaceae preferential pairing occurs between corresponding chromosomes of their multiple genomes, which indicates that they are autopolyploids. However, little or no preferential pairing occurs between chromosomes of Lenophyllum in its hybrids, and its species appear to be allopolyploids. The putative parents are unknown.     

Synthesis and cytological characterization of trigeneric hybrids of durum wheat with and without Ph1.

Wild grasses in the tribe Triticeae, some in the primary or secondary gene pool of wheat, are excellent reservoirs of genes for superior agronomic traits, including resistance to various diseases. Thus, the diploid wheatgrasses Thinopyrum bessarabicum (Savul. and Rayss) A. Love (2n = 2x = 14; JJ genome) and Lophopyrum elongatum (Host) A. Love (2n = 2x = 14; EE genome) are important sources of genes for disease resistance, e.g., Fusarium head blight resistance that may be transferred to wheat. By crossing fertile amphidiploids (2n = 4x = 28; JJEE) developed from F1 hybrids of the 2 diploid species with appropriate genetic stocks of durum wheat, we synthesized trigeneric hybrids (2n = 4x = 28; ABJE) incorporating both the J and E genomes of the grass species with the durum genomes A and B. Trigeneric hybrids with and without the homoeologous-pairing suppressor gene, Ph1, were produced. In the absence of Ph1, the chances of genetic recombination between chromosomes of the 2 useful grass genomes (JE) and those of the durum genomes (AB) would be enhanced. Meiotic chromosome pairing was studied using both conventional staining and fluorescent genomic in situ hybridization (fl-GISH). As expected, the Ph1-intergeneric hybrids showed low chromosome pairing (23.86% of the complement), whereas the trigenerics with ph1b (49.49%) and those with their chromosome 5B replaced by 5D (49.09%) showed much higher pairing. The absence of Ph1 allowed pairing and, hence, genetic recombination between homoeologous chromosomes. Fl-GISH analysis afforded an excellent tool for studying the specificity of chromosome pairing: wheat with grass, wheat with wheat, or grass with grass. In the trigeneric hybrids that lacked chromosome 5B, and hence lacked the Ph1 gene, the wheat-grass pairing was elevated, i.e., 2.6 chiasmata per cell, a welcome feature from the breeding standpoint. Using Langdon 5D(5B) disomic substitution for making trigeneric hybrids should promote homoeologous pairing between durum and grass chromosomes and hence accelerate alien gene transfer into the durum genomes.     

Two new Tibetan species of Elymus (Poaceae: niticeae) and their genomic relationships

Two Elymus species, E. cacuminus (2n = 4x = 28) and E. retroflexus (2n = 2x = 28). native to western China are described as species new to science. In order to determine genomic constitutions of the two species, intergeneric and interspecific hybridizations were carried out between the two new species and Pseudoroegneria spicata (2n = 2x = 14, SS), and sixteen other Elymus species, fifteen tetraploids (2n = 4x = 28) and one hexaploid (2n = 6x = 42), containing the "SH", "SY", and "SYH" genomes. Chromosome pairing behaviour was studied in the two species and their hybrids. Generally low meiotic pairing was observed in the hybrids with S- and SH-genome species and high pairing in the hybrids with SY- and SYH-genome species. It is concluded from this study that (i) the two new species are strict allotetraploid (2n = 4x = 28) and self-pollinating taxa (inbreeders) in nature; (ii) they contain the "SY" genomes and; (iii) they have close genomic relationships with the SY-genome Elymus species from the same or geographically adjacent areas.