Genome Of Th Research Articles

Characterization of novel wheat-Thinopyrum ponticum introgression lines derived from partial amphiploid AUS6770 for resistance to stripe rust

The wild decaploid species Thinopyrum ponticum (Podp.) Barkworth & D.R. Dewey is an important source of genes against biotic and abiotic stresses affecting wheat. The wheat–Th. ponticum partial amphiploid AUS6770 shows resistance to multiple diseases, including stripe rust, stem rust, and powdery mildew. Mitotic chromosomes of AUS6770 were characterized by non-denaturing-fluorescence in situ hybridization (ND-FISH), and the individual Th. ponticum chromosomes 1Ae to 7Ae were karyotypically distinguished by Oligo-FISH painting using bulked oligo pools based on wheat-barley collinear regions. A novel stripe rust resistant line A155, derived from AUS6770, was found to have 44 chromosomes, including a pair of 2Ae chromosomes and a pair of 6B-6Ae translocations. To detect plants with transfer of resistance genes from A155 to wheat chromosomes, 1770 plants were developed from F2–F5 progenies of A155 crossed with the susceptible wheat cultivar MY11 and characterized with ND-FISH using multiple probes. A high frequency of transmission of chromosome 2Ae was observed, and 31 types of 2Ae chromosomal aberrations were identified using ND-FISH. Ten chromosomal bins on the 2Ae chromosome were determined from the deletion and translocation lines based on genome-based PCR markers. In combination with the evaluation of disease resistance, the gene(s) for stripe rust resistance was located on the FL0.79–1.00 of 2AeS and covers the corresponding region of 0–58.26 Mb in the reference genome of Th. elongatum. The newly identified wheat-Th. ponticum 2Ae translocation lines can be exploited as potential germplasm in wheat breeding for stripe rust resistance

Functional analysis of the glutathione S-transferases from Thinopyrum and its derivatives on wheat Fusarium head blight resistance.

Functional analysis of the glutathione S-transferases from Thinopyrum and its derivatives on wheat Fusarium head blight resistance.

Cytogenetic Analysis and Molecular Marker Development for a New Wheat-Thinopyrum ponticum 1Js (1D) Disomic Substitution Line With Resistance to Stripe Rust and Powdery Mildew.

Thinopyrum ponticum (2n = 10x = 70), a member of the tertiary gene pool of wheat (Triticum aestivum L.), harbors many biotic and abiotic stress resistance genes. CH10A5, a novel disomic substitution line from a cross of T. aestivum cv. 7182 and Th. ponticum, was characterized by cytogenetic identification, in situ hybridization, molecular marker analysis, and morphological investigation of agronomic traits and disease resistance. Cytological observations showed that CH10A5 contained 42 chromosomes and formed 21 bivalents at meiotic metaphase I. Genome in situ hybridization (GISH) analysis indicated that two of its chromosomes came from the Js genome of Th. ponticum, and wheat 15K array mapping and fluorescence in situ hybridization (FISH) revealed that chromosome 1D was absent from CH10A5. Polymorphic analysis of molecular markers indicated that the pair of alien chromosomes belonged to homoeologous group one, designated as 1Js. Thus, CH10A5 was a wheat–Th. ponticum 1Js (1D) disomic substitution line. Field disease resistance trials demonstrated that the introduced Th. ponticum chromosome 1Js was probably responsible for resistance to both stripe rust and powdery mildew at the adult stage. Based on specific-locus amplified fragment sequencing (SLAF-seq), 507 STS molecular markers were developed to distinguish chromosome 1Js genetic material from that of wheat. Of these, 49 STS markers could be used to specifically identify the genetic material of Th. ponticum. CH10A5 will increase the resistance gene diversity of wheat breeding materials, and the markers developed here will permit further tracing of heterosomal chromosome fragments in the future.

Complete mitochondrial genome of the yellow-spotted grayling Thymallus flavomaculatus (Salmoniformes, Salmonidae)

The complete mitochondrial genome was sequenced in two individuals of yellow-spotted grayling Thymallus flavomaculatus. The genome sequences are 16,659 bp in size, and the gene arrangement, composition and size are very similar to the salmonid fish genomes published previously. The low level of sequence divergence detected between the genome of Th. flavomaculatus and the GenBank complete mitochondrial genomes of the Th. yaluensis (KJ866484) and Th. grubii (KF649073) may likely be due to recent divergence of the species and/or historical hybridization and interspecific replacement of mtDNA.

Microdissection and Chromosome Painting of the Alien Chromosome in an Addition Line of Wheat - Thinopyrum intermedium

In this study, chromosome painting was developed and used to identify alien chromosomes in TAi-27, a wheat - Thinopyrum intermedium addition line, and the chromosomes of the three different genomes of Th. Intermedium. The smallest alien chromosome of TAi-27 was microdissected and its DNA amplified by DOP-PCR was used as a probe to hybridize with metaphase chromosomes of TAi-27 and Th . intermedium . Results showed that hybridization signals were observed in all regions of a pair of the smallest alien chromosomes and the pericentromeric area of another pair of alien chromosomes in TAi-27, indicating that the probe from microdissected chromosome is species specific. In Th . intermedium , 14 chromosomes had wide and strong hybridization signals distributed mainly on the pericentromere area and 9 chromosomes with narrow and weak signals on the pericentromere area. The remaining chromosomes displayed a very weak or no signal. Sequential FISH/GISH on Th . intermedium chromosomes using the DNAs of microdissected chromosome, Pseudoroegneria spicata (St genome) and pDbH12 (a Js genome specific probe) as the probes indicated that the microdissected chromosome belonged to the St genome, three genomes (Js, J and St) in Th . intermedium could be distinguished, in which there is no hybridization signal on J genome that is similar to the genome of Th . bessarabicum . Our results showed that the smallest alien chromosomes may represent a truncated chromosome and the repetitive sequence distribution might be similar in different chromosomes within the St genome. However, the repetitive sequence distributions are different within the Js genome, within a single chromosome, and among different genomes in Th . intermedium . Our results suggested that chromosome painting could be feasible in some plants and useful in detecting chromosome variation and repetitive sequence distribution in different genomes of polyploidy plants, which is helpful for understanding the evolution of different genomes in polyploid plants.

Reaction of Wheat- Thinopyrum Progenies and Wheat Germplasm to Sharp Eyespot

The objectives of this study were to test the reactions of wheat-Thinopyrum derivatives, wheat (Triticum aestivum L.) cultivars and breeding lines to sharp eyespot (caused by Rhizoctonia cerealis Van der Hoeven) and to understand the relationship between Thinopyrum chromosomes and sharp eyespot resistance. Using field nursery tests, 321 common wheat accessions and 56 wheat-Thinopyrum derivatives were tested in Xuzhou and Nanjing, Jiangsu Province, China. In Xuzhou, none of the accessions was highly resistant, while 52 accessions (including 34 common wheat accessions) were moderately resistant. Six common wheat cultivars, i.e., Xiaonong 8506-1, Xiaoyan 81, Jizhi 4001, Nongda 195, Xuzhou 8913, and Jingdong 3066A-3, had the relative resistance index greater than 0.7. In Nanjing, all the common wheat entries were moderately or highly susceptible. Only five accessions of wheat-Thinopyrum progenies showed moderately resistant reaction. The chromosome addition, substitution, and translocation lines TA3513, TA3516, TA351, and TA3519 involving chromosome 4Ai#2 or 4Ai#2S of Th. intermedium and the chromosome substitution line SS767 involving the homoeologous group 4 chromosome of Th. ponticum had the disease indexes smaller than the susceptible controls Sumai 3 and Yangmai 158, as well the moderately resistant controls Annong 8455 and Ningmai 9. This indicated that the homoeologous group 4 chromosomes from Th. intermedium and Th. ponticum were most likely associated with the reduction of disease indexes. Genomic in situ hybridization using St genomic DNA from Pseudoroegneria strigos as a probe demonstrated that chromosome 4Ai#2 belongs to J s genome of Th. intermedium and the homoeologous group 4chromosome of Th. ponticum belongs to J genome. Although sharp eyespot and eyespot develop similar shapes of symptoms on the basal stems of wheat, the eyespot resistance genes Pch1 and Pch2 carried by the wheat cultivars Madsen and Cappelle-Desprez, respectively, were not effective against sharp eyespot.

A Compensating Wheat–Thinopyrum intermedium Robertsonian Translocation Conferring Resistance to Wheat Streak Mosaic Virus and Triticum Mosaic Virus

ABSTRACTWheat streak mosaic virus (WSMV), is a potentially devastating disease of common wheat (Triticum aestivum L.) in the Great Plains of North America. So far, two genes conferring resistance to WSMV have been named and used in cultivar improvement. Here we report a new source of resistance that was derived from a wheat–Thinopyrum intermedium (Host) Barkworth & D.R. Dewey ditelosomic addition line containing, in addition to the wheat chromosome complement, a pair of long arm telochromosomes from Th. intermedium previously believed to be of group‐4 origin. New molecular marker and genomic in situ hybridization analysis revealed that this telochromosome is homeologous to the group‐7 long arms and belongs to the S genome of Th. intermedium. Accordingly, this chromosome was designated as 7S#3L. One compensating Robertsonian translocation was obtained where the 7S#3L arm was translocated to the short arm of wheat chromosome 7B, resulting in the T7BS·7S#3L translocation chromosome. Homozygous T7BS·7S#3L lines were evaluated for their resistance to WSMV and Triticum mosaic virus (TriMV). The T7BS·7S#3L stock confers resistance to WSMV at 18 and 24°C. The T7BS·7S#3L stock also confers resistance to TriMV at 18°C but is not effective above 24°C. Based on chromosome position and effective resistance to WSMV at 24°C where both Wsm1 and Wsm2 are ineffective, the new gene in T7BS·7S#3L is designated as Wsm3.

Cloning of resistance gene analogs located on the alien chromosome in an addition line of wheat-Thinopyrum intermedium

Homology-based gene/gene-analog cloning method has been extensively applied in isolation of RGAs (resistance gene analogs) in various plant species. However, serious interference of sequences on homoeologous chromosomes in polyploidy species usually occurred when cloning RGAs in a specific chromosome. In this research, the techniques of chromosome microdissection combined with homology-based cloning were used to clone RGAs from a specific chromosome of Wheat-Thinopyrum alien addition line TAi-27, which was derived from common wheat and Thinopyrum intermedium with a pair of chromosomes from Th. intermedium. The alien chromosomes carry genes for resistance to BYDV. The alien chromosome in TAi-27 was isolated by a glass needle and digested with proteinase K. The DNA of the alien chromosome was amplified by two rounds of Sau3A linker adaptor-mediated PCR. RGAs were amplified by PCR with the degenerated primers designed based on conserved domains of published resistance genes (R genes) by using the alien chromosome DNA, genomic DNA and cDNA of Th. intermedium, TAi-27 and 3B-2 (a parent of TAi-27) as templates. A total of seven RGAs were obtained and sequenced. Of which, a constitutively expressed single-copy NBS-LRR type RGA ACR 3 was amplified from the dissected alien chromosome of TAi-27, TcDR 2 and TcDR 3 were from cDNA of Th. intermedium, AcDR 3 was from cDNA of TAi-27, FcDR 2 was from cDNA of 3B-2, AR 2 was from genomic DNA of TAi-27 and TR 2 was from genomic DNA of Th. intermedium. Sequence homology analyses showed that the above RGAs were highly homologous with known resistance genes or resistance gene analogs and belonged to NBS-LRR type of R genes. ACR 3 was recovered by PCR from genomic DNA and cDNA of Th. intermedium and TAi-27, but not from 3B-2. Southern hybridization using the digested genomic DNA of Th. intermedium, TAi-27 and 3B-2 as the template and ACR 3 as the probe showed that there is only one copy of ACR 3 in the genome of Th. intermedium and TAi-27, but it is absent in 3B-2. The ACR 3 could be used as a specific probe of the R gene on the alien chromosome of TAi-27. Results of Northern hybridization suggested that ACR 3 was constitutively expressed in Th. intermedium and TAi-27, but not 3B-2, and expressed higher in leaves than in roots. This research demonstrated a new way to clone RGAs located on a specific chromosome. The information reported here should be useful to understand the resistance mechanism of, and to clone resistant genes from, the alien chromosome in TAi-27.

Molecular characterization of a wheat – Thinopyrum ponticum partial amphiploid and its derivatives for resistance to leaf rust

Leaf rust (caused by Puccinia triticina Eriks.) occurs annually in most wheat-growing areas of the world. Thinopyrum ponticum (Podp.) Z.-W. Liu & R.-C. Wang has provided several leaf rust resistance genes to protect wheat from this fungal disease. Three chromosome substitution lines, Ji806, Ji807, and Ji859, and two chromosome addition lines, Ji791 and Ji924, with a winter growing habit were developed from crosses between wheat (Triticum aestivum L. em Thell.) and the wheat - Th. ponticum partial amphiploid line 693. These lines were resistant to leaf rust isolates from China. Sequence-tagged site (STS) analysis with the J09-STS marker, which is linked to the gene Lr24, revealed that the partial amphiploid line 693 and all of the substitution and addition lines carried gene Lr24. Genomic in situ hybridization (GISH) analysis was carried out on chromosome preparations using total genomic DNA from Pseudoroegneria strigosa (M. Bieb) A. Löve (St genome, 2n = 14) as a probe in the presence of total genomic DNA from T. aestivum 'Chinese Spring' wheat (ABD genomes, 2n = 42). The GISH analysis demonstrated that these lines had a pair of chromosomes displaying the typical pattern of a Js genome chromosome. This indicates that the chromosome that carries gene Lr24 belonged to the Js genome of Th. ponticum. In addition to 40 wheat chromosomes, eight Js and eight J genome chromosomes were also differentiated by GISH in the partial amphiploid line 693. Since most sources of Lr24 have a red grain color, the white-colored seeds in all of these substitution and addition lines, together with high protein content in some of the lines, make them very useful as a donor source for winter wheat breeding programs.

Inheritance of Blue Grain Colour and Its Association with J and J<sup>s</sup> Translocation Chromosomes in Wheat-Agrotana Hybrid Lines

Genomic in situ hybridization (GISH) using S genomic DNA as a probe was applied to study inheritance of blue seed color and characterize the chromosome constitution of blue-grained lines selected from derivatives of Chinese Spring (CS)×Agrotana, a multiple disease resistant wheat-Th. ponticum partial amphiploid line. The results showed that the expression of blue seed color in the CS-Agrotana advanced hybrid lines was always linked with a pair of translocation chromosomes derived from J and Js genomes of Th. ponticum. The blue-grained lines had 43–44 chromosomes, which included 2 J-Js+2 (or 1) Js-J alien translocation chromosomes, while the red-grained lines had 41–42 chromosomes, only carried 2 J-Js translocation chromosomes. This suggested that the Js-J translocation chromosomes might carry the major gene(s) that controlled the blue grain color. Since the J-Js translocation chromosomes were always present with the Js-J translocation chromosomes in blue-grained lines, it is possible that the blue grain color resulted from an interaction between the 2 translocations. Meiotic analyses of chromosome pairing in the blue-grained lines indicated that the 2 pairs of the alien translocation chromosomes did not pair each other, nor did they pair with the wheat chromosomes. The occurrence of 2 bivalents and no alien quadrivalents in the blue-grained lines with Js-J and J-Js translocation chromosomes, demonstrated that the 2 alien chromosome translocations were not reciprocal translocations. The J-Js translocation chromosomes present in the blue-grained lines were more stable at meiosis than the Js-J translocation chromosomes. The Js-J chromosomes were easily lost, resulting in an instability in grain color that could change from light blue to red. Our results determined the molecular cytogenetic characteristics and inheritance of the alien translocation chromosomes present in the blue-grained lines carrying resistance genes to common root rot. This study further confirmed that the chromosome translocations among the Js and J genome were responsible for blue grain color.

Breeding and molecular cytogenetic identification of wheat- Thinopyrum intermedium addition lines resistant to powdery mildew

Wheat-related species Th. intermedium was used to cross with common wheat Yannong 15. In the self progenies of the hybrid, two addition lines, II-1-7-1 and II-3-3-2, stable in cytology, were developed by cytology and powdery mildew resistance identification. Their chromosome number were 2n = 44 and formed 22 bivalents at PMC MI. In F1 of the two addition lines crossing with Yannong 15, there appeared about one univalent at PMC MI, respectively. Resistance identification in greenhouse and field using the No. 15 and mixed strains of E. gramnis f. sp. tritici showed that they were immune to powdery mildew. Chromosome number and resistance identification using the F2 single plants of the addition line crossing with Yannong 15 indicated that the resistant gene was located on the alien chromosomes. In situ hybridization using St and E genomic DNA as probe showed that the added chromosome in the two addition lines probably came from the E genome of Th. intermedium, which indicated that a pair of E genome chromosomes carried a new resistant gene to powdery mildew.

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.

Molecular cytogenetic evidence for a high level of chromosome pairing among different genomes in Triticum aestivum–Thinopyrum intermedium hybrids

Intergeneric hybrids (ABDJJsS genomes) were made between Triticum aestivum cv. Chinese Spring (CS) and Thinopyrum intermedium. Genomic in situ hybridization (GISH) using genomic DNA probes from Pseudoroegneria libanotica (Hackel) D.R. Dewey (genome S, 2n = 14) was used to study chromosome pairing among J, Js, S and wheat ABD genomes in the hybrids. It was shown that in the hexaploid (ABDJJsS) hybrids, high pairing occurred among wheat chromosomes and among Thinopyrum chromosomes. A closer relationship was observed among the three genomes of Th. intermedium than among the three genomes of T. aestivum. It was further discerned that S genome chromosomes paired with J- and Js-genome chromosomes at a high frequency. The frequency of heterologous pairing between S and J or S and Js chromosomes was higher than those between J and Js chromosomes, indicating that the S-genome was more closely related with these two genomes. Our results provided direct molecular cytogenetic evidence for the hypothesis that S-genome chromosomes are genetically similar to the J-genome chromosomes and, therefore, genetic exchange between these genomes is possible. The discovery of a close relationship among S, J and Js genomes provides valuable markers for molecular cytogenetic analyses using S-genomic DNA probes in monitoring the transfer of useful traits from Thinopyrum species into wheat.

Genome analysis of Thinopyrum intermedium and Thinopyrum ponticum using genomic in situ hybridization

Genomic in situ hybridization (GISH) using genomic DNA probes from Thinopyrum elongatum (Host) D.R. Dewey (genome E, 2n = 14), Thinopyrum bessarabicum (Savul. & Rayss) A. Löve (genome J, 2n = 14), and Pseudoroegneria strigosa (M. Bieb.) A. Löve (genome S, 2n = 14), was used to examine the genomic constitution of Thinopyrum intermedium (Host) Barkworth & D.R. Dewey (2n = 6x = 42) and Thinopyrum ponticum (Podp.) Barkworth & D.R. Dewey (2n = 10x = 70). Evidence from GISH indicated that hexaploid Th, intermedium contained the J, Js, and S genomes, in which the J genome was related to the E genome of Th. elongatum and the J genome of Th. bessarabicum. The S genome was homologous to the S genome of Ps. strigosa, while the Js genome referred to modified J- or E-type chromosomes distinguished by the presence of S genome specific sequences close to the centromere. Decaploid Th. ponticum had only the two basic genomes J and Js. The Js genome present in Th. intermedium and Th. ponticum was homologous with E or J genomes, but was quite distinct at centromeric regions, which can strongly hybridize with the S genome DNA probe. Based on GISH results, the genomic formula of Th. intermedium was redesignated JJsS and that of Th. ponticum was redesignated JJJJsJs. The finding of a close relationship among S, J, and Js genomes provides valuable markers for molecular cytogenetic analyses using S genome DNA probes to monitor the transfer of useful traits from Th. intermedium and Th. ponticum to wheat.

Direct evidence for high level of autosyndetic pairing in hybrids of Thinopyrum intermedium and Th. ponticum with Triticum aestivum

Genomic in situ hybridization (GISH) was used to distinguish autosyndetic from allosyndetic pairing in the hybrids of Thinopyrum intermedium and Th. ponticum with Triticum aestivum cv ‘Chinese Spring’ (CS). All hybrids showed high autosyndetic pairing frequencies among wheat chromosomes and among Thinopyrum chromosomes. The high autosyndetic pairing frequencies among wheat chromosomes in both hybrids suggested that Th. intermedium and Th. ponticum carry promoters for homoeologous chromosome pairing. The higher frequencies of autosyndetic pairing among Thinopyrum chromosomes than among wheat chromosomes in both hybrids indicated that the relationships among the three genomes of Th. intermedium and among the five genomes of Th. ponticum are closer than those among the three genomes of T. aestivum.

Molecular verification and characterization of BYDV-resistant germ plasms derived from hybrids of wheat with Thinopyrum ponticum and Th. intermedium

Twenty-five partial amphiploids (2n=8x=56), which were derived from hybrids of wheat (Triticum aestivum L.) with either Thinopyrum ponticum (Podpera) Liu & Wang, Th. intermedium (Host) Barkworth & D. Dewey, or Th. junceum (L.) A. Löve, were assayed for resistance to BYDV serotype PAV by slot-blot hybridization with viral cDNA of a partial coat protein gene. Three immune lines were found among seven partial amphiploids involving Th. ponticum. Seven highly resistant lines were found in ten partial amphiploids involving Th. intermedium. None of eight partial amphiploids or 13 addition lines of Chinese Spring - Th. junceum were resistant to BYDV. Genomic in situ hybridization demonstrated that all of the resistant partial amphiploids, except TAF46, carried an alien genome most closely related to St, whether it was derived from Th. ponticum or Th. intermedium. The two partial amphiploids carrying an intact E genome of Th. ponticum are very susceptible to BYDV-PAV. In TAF46, which contains three pairs of St- and four pairs of E-genome chromo somes, the gene for BYDV resistance has been located to a modified 7 St chromosome in the addition line L1. This indicates that BYDV resistance in perennial polyploid parents, i.e., Th. ponticum and Th. intermedium, of these partial amphiploids is probably controlled by a gene(s) located on the St-genome chromosome(s).

Genomic relationships in Thinopyrum

Substantial autosyndesis in the two F 1 hybrids obtained by crossing Triticum turgidum var. group durum Morris & Sears with Thinopyrum distichum (Thunb.) Love and Th . junceiforme (Love & Love) Love resulted in mean meiotic configurations of 14,12 I ; 4,8 II ; 0,38 III and 0,75 IV in the pollen mother cells (PMC’s) of the first hybrid, and 14,42 I ; 4,82 II ; 0,12 III and 0,19 IV in those of the second hybrid. These and other observations demonstrated that both the above tetraploid (2 n = 28) Thinopyrum species are segmental allopolyploids. The two intrageneric crosses of Th . distichum with Th . elongatum (Host) D.R. Dewey and Th . junceiforme provided the first direct cytological evidence linking the genomes of Th . distichum with the J genome, thus proving that this southern hemisphere species indeed belongs to the same genus as northern hemisphere species such as Th . elongatum and Th . junceiforme . The J e 1 genome of Th . elongatum appears to be as closely related to the two genomes of Th . distichum as it is to the genomes of Th . scirpeum (K. Presl) D.R. Dewey and Th . junceiforme , producing mean meiotic configurations of 2,91 I ; 4,36 II ; 2,96 III and 0,12 IV in the PMC’s of their triploid hybrid. On these grounds it is recommended that the two genomes of Th . distichum be designated J d 1 and J d 2 . The latter genomes appeared to be less closely related to the J 1 and J 2 genomes of Th . junceiforme than to J e 1 . New amphiploids were synthesized by treating the F 1 hybrids with colchicine. Fertile partial amphiploids AABBJ d 1 J d 2 were obtained by back-crossing the T . durum / Th . distichum amphiploids to T . durum . By applying the pivotal genome concept at the polyploid level the feasibility of producing new recombined genomes from the J d 1 , J d 2 and J e 1 genomes was demonstrated.