Pseudoroegneria Stipifolia Research Articles

Waxy Gene-Orthologs in Wheat × Thinopyrum Amphidiploids

Starch, as the main component of grain in cereals, serves as the major source of calories in staple food and as a raw material for industry. As the technological and digestive properties of starch depend on its content, the management of its components, amylose and amylopectin, is of great importance. The starch properties of wheat grain can be attuned using allelic variations of genes, including granule-bound starch synthase I (GBSS I), or Wx. The tertiary gene pool, including wheatgrass (Thinopyrum) species, provides a wide spectrum of genes-orthologs that can be used to increase the allelic diversity of wheat genes by wide hybridization. Octaploid partial wheat–wheatgrass hybrids (amphidiploids, WWGHs) combine the complete genome of bread wheat (BBAADD), and a mixed genome from the chromosomes of intermediate wheatgrass (Thinopyrum intermedium, genomic composition JrJrJvsJvsStSt) and tall wheatgrass (Th. ponticum, JJJJJJJsJsJsJs). Thus, WWGHs may carry Wx genes not only of wheat (Wx-B1, Wx-A1 and Wx-D1) but also of wheatgrass origin. We aimed to assess the level of amylose in starch and investigate the polymorphism of Wx genes in 12 accessions of WWGHs. Additionally, we characterized orthologous Wx genes in the genomes of wild wheat-related species involved in the development of the studied WWGHs, Th. intermedium and Th. ponticum, as well as in the putative donors of their subgenomes, bessarabian wheatgrass (Th. bessarabicum, JbJb) and bluebunch wheatgrass (Pseudoroegneria stipifolia, St1St1St2St2). Although no significant differences in amylose content were found between different WWGH accessions, SDS-PAGE demonstrated that at least two WWGHs have an additional band. We sequenced the Wx gene-orthologs in Th. bessarabicum, P. stipifolia, Th. intermedium and Th. ponticum, and developed a WXTH marker that can discriminate the Thinopyrum Wx gene in the wheat background, and localized it to the 7E chromosome in Th. elongatum. Using the WXTH marker we revealed the allelic polymorphism of the Thinopyrum Wx gene in the studied WWGHs. The applicability of Thinopyrum Wx genes in wheat breeding and their effect on starch quality are discussed.

Development and Application of Transposable Element-Based Chromosomal Markers for the St Genome in Triticeae

The St genome, originating from Pseudoroegneria (Nevski) Á. Löve, plays an important role in Triticeae. In this study, the Pseudoroegneria stipifolia genome (2n = 2x = 14, StSt) was screened to identify sequences that could be used for FISH. A total of 163 effective clones were obtained from the genomic plasmid library which was constructed by DNase I digestion of P. stipifolia nuclear genomic DNA. Analysis of these clones identified 112 with characteristics of transposable elements (TEs), 13 with characteristics of tandem repetitive sequences, 8 with characteristics of mRNA sequences, and 30 unknown sequences. Fluorescent signals were detected for 11 of 41 TE sequences on P. stipifolia chromosomes after in situ hybridization and were divided into 4 types according to signal distribution patterns: over the whole St genome chromosomes, telomere to pericentromeric regions, centromere to pericentromeric regions, and terminal regions. The affinity between St and Y genomes was studied using the 11 TE probes in 3 StStYY species. Five TE probes showed no obvious difference between subgenomes, 2 probes displayed divergence only in 2 StStYY species, and 4 probes exhibited significant differences among 3 StStYY species. These results provide a preliminary understanding of the sequence composition of the St genome and enabled 11 novel TE probes to be developed and applied.

Plasticity in Triticeae centromere DNA sequences: a wheat × tall wheatgrass (decaploid) model.

Centromeres mediate chromosome attachment to microtubules and maintain the integrity of chromosomes for proper segregation of the sister chromatids during cell division. Advances in the assembly of Triticeae genome sequences combined with the capacity to recover hybrid species derived from very distantly related species provides potential experimental systems for linking retrotransposon amplification and repositioning of centromeres via non-mendelian inheritance in partial amphiploid breeds. The decaploid tall wheatgrass (Thinopyrum ponticum) is one of the most successfully used perennial species in wheat breeding for generating translocation lines with valuable agronomic traits. We found that wheat centromere retrotransposons CRW and Quinta widely occur within the tall wheatgrass genome. In addition, one of the genome donors to Th. ponticum, Pseudoroegneria stipifolia (StSt), has been shown to have Abigail and a satellite repeat, CentSt. We also found two other centromeric retrotransposons, Abia and CL135 in Th. ponticum by ChIP-seq. Examination of partial amphiploid lines that were generated in the 1970s demonstrated extensive modification in centromere sequences using CentSt, Abigail and Abia as probes. We also detected that St-genome chromosomes were more enriched with Abigail and CentSt, whereas E-genome chromosomes were enriched with CRW and Quinta in tall wheatgrass and its closer relatives. It can be concluded that bursts of transposition of retrotransposons and repositioning of centromeres via non-mendelian segregation are common in partial amphiploids derived from interspecific hybrids. Practically speaking, our study reveals that the existence of homologous centromere functional sequences in both a donor and its receptor can substantially contribute to the successful transfer of alien genes into crop species. OPEN RESEARCH BADGES: This article has earned an Open Data Badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The data is available at https://www.ncbi.nlm.nih.gov/sra/SRR9089557; https://www.ncbi.nlm.nih.gov/sra/SRR9089558; https://www.ncbi.nlm.nih.gov/sra/SRR9089559; https://www.ncbi.nlm.nih.gov/sra/SRR9089560; https://www.ncbi.nlm.nih.gov/sra/SRR9089561; https://www.ncbi.nlm.nih.gov/sra/SRR9089562; https://www.ncbi.nlm.nih.gov/sra/SRR9089563; https://www.ncbi.nlm.nih.gov/sra/SRR9089564; https://www.ncbi.nlm.nih.gov/nuccore/MK999394; https://www.ncbi.nlm.nih.gov/nuccore/MK999395; https://www.ncbi.nlm.nih.gov/nuccore/MK999396.

Polymorphism of ITS sequences in 35S rRNA genes in Elymus dahuricus aggregate species: two cryptic species?

Nuclear ribosomal internal transcribed spacer (ITS) sequences were sequenced for 23 species and subspecies of Elymus sensu lato collected in Russia. The Neighbor-Net analysis of ITS sequences suggested that there are four ribotypes called Core Northern St-rDNA, Core Southern St-rDNA, Northern dahuricus St-rDNA and Southern dahuricus St-rDNA. The Core Southern variant of St-rDNA is closely related to rDNA of diploid Pseudoroegneria stipifolia (PI 313960) and P. spicata (PI 547161). The Core Northern St-rDNA is closely related to rDNA of P. cognata (PI 531720), a diploid species of Kyrgyzstan carrying StY variant of the St genome. The Core Northern St-rDNA is widespread among the Elymus species of Siberia and the Far East, including Yakutia and Chukotka. The Core Southern St-ribotype is typical of southern Elymus and Pseudoroegneria of the South Caucasus, Primorye, Pakistan, and South Korea. The Northern dahuricus St-ribotype and Southern dahuricus St-ribotype are derivatives of the Core Northern and Core Southern St-ribotypes, correspondingly. Both of them were found in all four studied species of the E. dahuricus aggregate: E. dahuricus Turcz. ex Griseb., E. franchetii Kitag., E. excelsus Turcz. ex Griseb. and Himalayan E. tangutorum (Nevski) Hand.-Mazz. In other words, there are at least two population groups (two races) of the Elymus dahuricus aggregate species that consistently differ in their ITS-sequences in Siberia, the Far East and Northern China. Each contains all morphological forms, which taxonomists now attribute either to different species of E. dahuricus aggr. (E. dahuricus sensu stricto, E. franchetii, E. tangutorum, E. excelsus) or subspecies of Campeiostachys dahurica (Turcz. ex Griseb.) B.R. Baum, J.L. Yang et C.C. Yen. At the moment it is unknown if there are any morphological differences between plants carrying either Northern or Southern dahuricus rDNA. Probably, they are cryptic species, but it is certain that if differences in morphology between the two races exist, they are not associated with signs that are now considered taxonomically significant and are used to separate E. dahuricus s. s., E. franchetii, E. tangutorum, and E. excelsus.

High-throughput mining of E-genome-specific SNPs for characterizing Thinopyrum elongatum introgressions in common wheat.

Diploid Thinopyrum elongatum (EE, 2n=2x=14) and related polyploid species constitute an important gene pool for improving Triticeae grain and forage crops. However, the genomic and molecular marker resources are generally poor for these species. To aid the genetic, molecular, breeding and ecological studies involving Thinopyrum species, we developed a strategy for mining and validating E-genome-specific SNPs using Th. elongatum and common wheat (Triticum aestivum, AABBDD, 2n=6x=42) as experimental materials. By comparing the transcriptomes between Chinese Spring (CS, a common wheat variety) and the CS-Th. elongatum octoploid, 35,193 candidate SNPs between E genome genes and their common wheat orthologs were computed. Through comparative genomic analysis, these SNPs were putatively assigned to the seven individual E genome chromosomes. Among 420 randomly selected SNPs, 373 could be validated. Thus, approximately 89% of the mined SNPs may be authentic with respect to their polymorphism and chromosomal location. Using 14 such SNPs as molecular markers, complex E genome introgressions were reliably identified in 78 common wheat-Th. elongatum hybrids, and the structural feature of a novel recombinant chromosome formed by 6E and 7E was revealed. Finally, based on testing 33 SNPs assigned to chromosome 3E in multiple genotypes of Th. elongatum, Pseudoroegneria stipifolia (carrying the St genome related to E) and common wheat, we suggest that some of the SNP markers may also be applicable for genetic studies within and among the Thinopyrum species (populations) carrying E and/or St genomes in the future.

Phylogenetic relationships between Leymus and related diploid Triticeae species revealed by ISSR markers

To investigate the genetic diversity and phylogenetic relationships between polyploid Leymus and related diploid species of the Triticeae tribe, inter-simple sequence repeats (ISSR) markers was used to analyze 41 Leymus accessions representing 22 species and 2 subspecies, together with Pseudoroegneria stipifolia (St), Psathyrostachys fragilis (Ns), Australopyrum retrofractum (W), Hordeum bogdanii, H. chilense (H) and Lophopyrum elongatum (Ee). A total of 376 clear and reproducible DNA fragments were amplified by 29 ISSR primers, among which 368 (97.87%) fragments were found to be polymorphic. 8–18 polymorphic bands were amplified by each polymorphic primer, with an average of 12.69 bands. The data of 376 ISSR bands were used to generate Nei’s similarity coefficients and to construct a dendrogram by means of UPGMA. The similarity coefficients data suggested great genetic diversity in genus Leymus and related diploid Triticeae species, the genetic diversity among the different species more abundant than that of the different accessions. The dendrogram and principal coordinate analysis showed explicit interspecific relationships and demonstrated close phylogenetic relationships between Leymus species and Psathyrostachys.

Characterization of novel HMW-GS in two diploid species of Eremopyrum

Three HMW-GS and the respective ORFs from diploid species Eremopyrum distans and Eremopyrum triticeum were characterized. Compared to homologous proteins, they showed novel modifications in all domains. In the N-terminals, the y subunit from Er. triticeum (Xey) had 98 aa residues. A short G/IIFWGTS peptide deletion was responsible for the reduced number of aa residues. The end peptide in the y subunit from Er. distans (Fy) was IPTLLR. This unique structure was involved in a replacement between x types with IPA/TLLK/R and y types with R/TSSQTVQ. Both y subunits share the same short peptide LAAQLPAMCRL as x types in the C-terminals. Phylogenic relationships among orthologous genes from Triticeae species revealed that Fy and Xey were neither purely x type nor purely y type based on the N and C terminal residues. Divergence times indicated that Glu-Xe1 and Glu-F1 were separated from each other and that Glu-Xe1 separated from orthologous loci of wild wheat relatives earlier than Glu-F1. Based on the divergence times among Glu-F1, Glu-Xe1, Glu-O1, Glu-St1, and Glu-Ta1, it is possible that genome F separation from O, St, and Ta in species of Henrardia persica, Pseudoroegneria stipifolia, and Taeniatherum crinitum was more recent than the separation of F and Xe.

Evaluating Wheat Microsatellite Markers for the Use in Genetic Analysis ofThinopyrum, Dasypyrum,andPseudoroegneriaSpecies

A set of 42 SSRs of wheat were evaluated for their cross-amplification on the DNA ofThinopyrum ponticum, Thinopyrum intermedium, Thinopyrum elongatum, Thinopyrum bessarabicum, Pseudoroegneria stipifolia,andDasypyrum villosum.The number of the wheat SSR markers that amplified DNA fragments with determined size forTh. ponticumwas 33 (78.6%); forTh. intermedium,28 (66.7%); forTh. elongatum,24 (57.1%); forTh. bessarabicum,24 (57.1%); forP. stipifolia,26 (69.1%); and forD. villosum,29 (69.0%). Twenty-four primer pairs of wheat SSR markers were successfully amplified from all investigated species. The dataset can be used for phylogenetic studies of wild relatives of wheat, for the estimation of their diversity, and for the introgression of agronomically valuable genes into wheat genome.

Nucleotide divergence and genetic relationships of Pseudoroegneria species

Nucleotide variation in 8 diploid Pseudoroegneria species was characterized using two single copy nuclear genes, the second largest subunit of RNA polymerase II ( RPB2 ) and the translation elongation factor G ( EF-G ), and one chloroplast TrnD / T intergenic region. Among the Pseudoroegneria species studied, the estimates of nucleotide diversity ( π ) ranged from 0.04577 ( RPB2 ) and 0.00183 ( TrnD / T ) for Pseudoroegneria tauri to 0.10667 ( RPB2 ), 0.06174 ( EF-G ) and 0.03743 ( TrnD / T ) for Pseudoroegneria spicata . The highest nucleotide diversity of the RPB2 data set was found for P. spicata among the taxa analyzed. Our phylogenetic analyses separated the accessions of P. spicata into several groups, with 7 accessions of P. spicata forming a highly supported subclade (BS = 100%, PP = 1.00). The phylogenetic analysis also suggests that P. spicata , Pseudoroegneria gracillima and Pseudoroegneria stipifolia have a closer relationship than the other species within Pseudoroegneria . Pseudoroegneria libanotica and P. tauri were also found to exhibit a high level of sequence homology, however, only nuclear gene data ( RPB2 and EF-G ) clearly indicated the differentiation between the P. libanotica + P. tauri group with other St genome species. ► We characterized nucleotide variation in 8 diploid Pseudoroegneria species. ► The highest nucleotide diversity of the RPB2 was found for Pseudoroegneria spicata among the taxa analyzed. ► A close relationship among P. spicata , Pseudoroegneria gracillima and Pseudoroegneria stipifolia was revealed. ► Pseudoroegneria libanotica and Pseudoroegneria tauri were also found to exhibit a high level of sequence homology.

Isolation and characterization of a novel variant of HMW glutenin subunit gene from the St genome of Pseudoroegneria stipifolia

The x- and y-type high molecular weight (HMW) glutenin subunits are conserved seed storage proteins in wheat and related species. Here we describe investigations on the HMW glutenin subunits from several Pseudoroegneria accessions. The electrophoretic mobilities of the HMW glutenin subunits from Pd. stipifolia, Pd. tauri and Pd. strigosa were much faster than those of orthologous wheat subunits, indicating that their protein size may be smaller than that of wheat subunits. The coding sequence of the Glu-1St1 subunit (encoded by the Pseudoroegneria stipifolia accession PI325181) was isolated, and found to represent the native open reading frame (ORF) by in vitro expression. The deduced amino acid sequence of Glu-1St1 matched with that determined from the native subunit by mass spectrometric analysis. The domain organization in Glu-1St1 showed high similarity with that of typical HMW glutenin subunits. However, Glu-1St1 exhibited several distinct characteristics. First, the length of its repetitive domain was substantially smaller than that of conventional subunits, which explains its much faster electrophoretic mobility in SDS-PAGE. Second, although the N-terminal domain of Glu-1St1 resembled that of y-type subunit, its C-terminal domain was more similar to that of x-type subunit. Third, the N- and C-terminal domains of Glu-1St1 shared conserved features with those of barley D-hordein, but the repeat motifs and the organization of its repetitive domain were more similar to those of HMW glutenin subunits than to D-hordein. We conclude that Glu-1St1 is a novel variant of HMW glutenin subunits. The analysis of Glu-1St1 may provide new insight into the evolution of HMW glutenin subunits in Triticeae species.

Physical localization of the 18S-5.8S-26S rDNA and sequence analysis of ITS regions in Thinopyrum ponticum (Poaceae: Triticeae): implications for concerted evolution.

Fluorescence in situ hybridization was used in Thinopyrum ponticum, a decaploid species, and its related diploid species, to investigate the distribution of the 18S-5.8S-26S rDNA. The distribution of rDNA was similar in all three diploid species (Th. bessarabicum, Th. elongatum and Pseudoroegneria stipifolia). Two pairs of loci were observed in each somatic cell at metaphase and interphase. One pair was located near the terminal end and the other in the interstitial regions of the short arms of one pair of chromosomes. However, all of the major loci in Th. ponticum were located on the terminal end of the short arms of chromosomes, and one chromosome had only one major locus. The maximum number of major loci detected on metaphase spreads was 20, which was the sum of that of its progenitors. The interstitial loci that exist in the possible diploid genome donor species were probably 'lost' during the evolutionary process of the decaploid species. A number of minor loci were also detected on whole regions of two pairs of homologous chromosomes. These results suggested that the position of rDNA loci in the Triticeae might be changeable rather than fixed. Positional changes of 18S-5.8S-26S rDNA loci between Th. ponticum and its candidate genome donors indicate that it is almost impossible to find a genome in the polyploid species that is completely identical to that of its diploid donors. The possible evolutionary significance of the distribution of the rDNA is also discussed. Internal transcribed spacer (ITS) regions of nuclear DNA in Th. ponticum were investigated by PCR amplification and sequencing. The sequence data from five positive clones selected at random, together with restriction site analysis, indicated that the ITS repeated units are nearly homogeneous in this autoallodecapolypoid species. Combined with in situ hybridization results, the data led to the conclusion that the ITS region has experienced interlocus as well as intralocus concerted evolution. Phylogenetic analyses showed that the sequences from Th. ponticum have concerted to the E genome repeat type.

Genome analysis of Elytrigia pycnantha and Thinopyrum junceiforme and of their putative natural hybrid using the GISH technique.

Genomic in situ hybridization (GISH), using genomic DNA probes from Thinopyrum elongatum (Host) D.R. Dewey (E genome, 2n = 14), Th. bessarabicum (Savul. & Rayss) A. Love (J genome, 2n = 14), Pseudoroegneria stipifolia (Czern. ex Nevski) Love (S genome, 2n = 14), and Agropyron cristatum (L.) Gaertner (P genome, 2n = 14), was used to characterize the genome constitution of the polyploid species Elytrigia pycnantha (2n = 6x = 42) and Thinopyrum junceiforme (2n = 4x = 28) and of one hybrid population (2n = 5x = 35). GISH results indicated that E. pycnantha contains S, E, and P genomes; the first of these was closely related to the S genome of Ps. stipifolia, the second was closely related to to the E genome of Th. elongatum, and the third was specifically related to A. cristatum. The E and P genomes included 2 and 10 chromosomes, respectively, with S genome DNA sequences in the centromeric region. GISH analysis of Th. junceiforme showed the presence of two sets of the E genome, except for fewer than 10 chromosomes for which the telomeric regions were not identified. Based on these results, the genome formula SSPsPsEsEs is proposed for E. pycnantha and that of EEEE is proposed for Th. junceiforme. The genomic constitution of the pentaploid hybrid comprised one S genome (seven chromosomes), one P genome (seven chromosomes), and three E genomes (21 chromosomes). The E and P genomes both included mosaic chromosomes (chromosomes 1 and 5, respectively) with the centromere region closely related to S-genome DNA. On the basis of these data, the genome formula SPSESEE is suggested for this hybrid and it is also suggested that the two species E. pycnantha and Th. junceiforme are the parents of the pentaploid hybrid.

Genome Analysis of a Natural Hybrid with 2n= 63 Chromosomes in the Genus Elytrigia Desv. (Poaceae) Using the GISH Technique

Abstract: Genomic in situ hybridization (GISH), using genomic DNA probes from Thinopyrum elongatum (E genome, 2n= 14), Th. bessarabicum (J genome, 2n= 14), Pseudoroegneria stipifolia (S genome, 2n= 14), Agropyron cristatum (P genome, 2n= 28) and Critesion californicum (H genome, 2n= 14), was used to identify the genome constitution of a natural hybrid population morphologically close to Elytrigia pycnantha and with somatic chromosome number of 2n= 63. The GISH results indicated the presence of a chromosomal set more or less closely related to the E, P, S and H genomes. In particular, two sets of 14 chromosomes each showed close affinity to the E genome of Th. elongatum and to the P genome of A. cristatum. However, they included 2 and 10 mosaic chromosomes, respectively, with S genome specific sequences at their centromeric regions. Two additional sets (28 chromosomes) appeared to be very closely related to the S genome of Ps. stipifolia. The last genome involved (7 chromosomes) is related to the H genome of C. californicum but includes one chromosome with S genome‐specific sequences around the centromere and two other chromosomes with a short interstitial segment also containing S genome related sequences. On a basis of GISH analysis and literature data, it is hypothesized that the natural 9‐ploid hybrid belongs to the genus Elytrigia and results from fertilization of an unreduced gamete (n = 42) of E. pycnantha and a reduced gamete (n = 21) of E. repens. The genomic formula SSSSPSPSESESHS is proposed to describe its particular genomic and chromosomal composition.

Genome Characterization of MT‐2 Perennial and OK‐906 Annual Wheat × Intermediate Wheatgrass Hybrids

Montana‐2 (MT‐2; × Agrotriticum intermediodurum Khizhnyak) is a variable perennial F5:15 line derived from hybridization between durum wheat (Triticum turgidum L. var. durum, AABB) and Thinopyrum intermedium (Host) Barkw. & D.R. Dewey (StStEEEE). OK‐906 is a uniform annual line derived from hybridization between hexaploid wheat (Triticum aestivum L., AABBDD) and an unknown Thinopyrum sp. followed by backcrossing to wheat and several generations of selling and selection. We wished to characterize perennial (Thinopyrum) and annual (Triticum) chromosome content of MT‐2 and OK‐906 to determine how chromosome content corresponds to perenniality. When DNA of genomes ABD (T. aestivum) + Eb [Thinopyrum bessarubicum (Savul & Rayss) Löve] was used as the block and DNA of the genome St [Pseudoroegneria stipifolia (Czern. ex Nevski) A. Löve] was used as the probe, the average chromosome content amongl5 MT‐2 lines was 26.2 wheat + 9.4 St + 18.8 E + 1.5 St/E translocation = 55.9 chromosomes (8x). Variation for genomic content was found within as well as among MT‐2 lines, indicating that instability remains in the material. OK‐906 exhibited about 40 wheat + 6 St + 8 E + 2 St/E translocation = 56 chromosomes (8x), but some aneuploidy was present. Its chromosome content is similar to ‘Agrotana’, another wheat × Thinopyrum annual. Perenniality in MT‐2 may relate to its higher perennial chromosome dosage (about 30 of about 56 chromosomes) than OK‐906 or Agrotana (16 of 56 chromosomes). Alternatively, specific genes or chromosome segments may confer perenniality. Development of stable breeding populations from MT‐2 is improbable because of its variable chromosome constitution. However, individual lines could be useful for forage if they could be stabilized with improved seed yield.

Cytogenetics and Morphology of Elymus panormitanus var. Heterophyllus and Its Relationship to Elymus panormitanus var. Panormitanus (Poaceae: Triticeae)

Elymus panormitanus var. heterophyllus, PI-235086, was collected in Israel and became part of the National Plant Germplasm System as Elymus caninus L. in 1956. Bivalent pairing at metaphase I (MI) in E. panormitanus var. heterophyllus (2n = 42) was typical of other allohexaploids within the Triticeae. However, chromosome pairing analysis at MI of the tetraploid hybrids with Pseudoroegneria spicata (2n = 14, SS) and the pentaploid hybrids with Pseudoroegneria stipifolia (2n = 28, SSSS), Elymus lanceolatus (2n = 28, SSHH), E. panormitanus (2n = 28, SSYY), and Elymus nevski (2n = 28, SSYY) indicated that two of the three genomes of E. panormitanus var. heterophyllus were at least partially homologous to the S genome and confirmed the presence of a Y genome. Cluster analysis of 18 key characters separated E. panormitanus var. heterophyllus from E. panormitanus However, the continuous variation between the two taxa made taxonomic separation difficult unless the samples represented the two extremes. In this unique case, two taxa-E. panormitanus var. heterophyllus and E. panormitanus-were very close morphologically but different genomically. Elymus panormitanus var. heterophyllus is a hexaploid (SSSSYY; 2n = 42) and E. panormitanus is an allotetraploid (SSYY; 2n = 28).

Cytology and morphology of Pseudoroegneria deweyi (Poaceae: Triticeae): a new species from the foot hills of the Caucasus Mountains (Russia)

Cytological and morphological characteristics of a new species, Pseudoroegneria deweyi K. B. Jensen, from the Karachayevo-Cherkesskaya Avtonomnaya Oblast' Region of Russia are described. This species is cytologically stable, genomically similar to Pseudoroegneria tauri, highly fertile (cross-pollinating), and morphologically unique compared with most other species in the genus. Pseudoroegneria deweyi differs from other closely related species in the number of rachis nodes in the inflorescence. Pseudoroegneria stipifolia (2n = 2x = 14, SS) and Agropyron cristatum (2n = 2x = 14, PP) were used as male parents in crosses with P. deweyi. All three P. deweyi accessions studied were tetraploids (2n = 28) and behaved meiotically as allotetraploids with a mean chromosome association of 0.03 I + 13.30 II + 0.03 III + 0.26 IV per cell. In the hybrid P. deweyi × A. cristatum, average chromosome association was 5.92 I + 4.55 II + 1.83 III + 0.09 IV per cell, while the average chromosome association in P. deweyi × P. stipifolia was 4.98 I + 5.23 II + 1.73 III 0.04 IV per cell. Pseudoroegneria deweyi joins P. tauri as the only other known naturally occurring species with the genomic formula of SSPP. Cluster analysis of 21 morphological characters supports the inclusion of P. deweyi as part of the genus Pseudoroegneria rather than Agropyron. Key words: Agropyron, Pseudoroegneria, chromosome pairing, meiosis, Triticeae, new species.

Intergeneric Hybrids of Agropyron and Pseudoroegneria

Two intergeneric hybrids, Agropyron cristatum x Pseudoroegneria stipifolia (2n = 14) and A. desertorum x P. stipifolia (2n = 28), were produced by controlled pollination. Spike morphology of the hybrids was intermediate to that of the parents. Size differences between Agropyron (large) and Pseudoroegneria (small) mitotic chromosomes facilitated interpretation of chromosome pairing in the hybrids. Meiotic chromosome pairing in the diploid hybrids, x̄ = 3.09 II, was largely allosyndetic between homoeologous chromosomes of the S and the P genomes. Autosyndetic pairing prevailed in the tetraploid hybrids. Because the Agropyron chromosomes can pair with the Pseudoroegneria chromosomes, gene introgression between species in these two genera is possible.