Partial Amphiploids Research Articles

Characterization of wheat-Thinopyrum partial amphiploids by meiotic analysis and genomic in situ hybridization

A combination of genomic in situ hybridization (GISH) and meiotic pairing analysis of wheat-Thinopyrum partial amphiploids was employed to identify the genomic constitution and relationships between partial amphiploids derived from wheat and wheatgrass crosses. On the basis of similarities in the meiotic behavior and GISH patterns, the alien chromosomes of two of eight partial amphiploids, TAF46 and 'Otrastayuskaya 38', were judged to originate from Th. intermedium, whereas Th. ponticum was one of the parents of the other six partial amphiploids; PWM706, PWM206, PWM209, PWMIII, OK7211542, and Ag-wheat hybrid. Each of these partial amphiploids was found to contain a synthetic alien genome composed of different combinations of St-, J-, or Js-genome chromosomes. For relatedness of partial amphiploid lines, meiotic analysis of F1 hybrids and GISH results were generally complementary, but the latter offered greater precision in identifying constituent genomes.

Breeding ofT. aestivum-Ag. intermedium translocation lines withT. timopheevii cytoplasm and characterization by GISH

A male-sterileT. aestivum-Ag. intermedium partial amphiploid with cytoplasm ofT. timopheevii as a female parent was crossed to common wheat. The hybrid was backcrossed to the male parent several times continually and setf-crossed at last. Two stable lines with common wheat phenotype, H96269-2 and H96278, have been obtained. The chromosome numbers of the two lines are all2n = 42 in somatic cetls. By inoculation test, the two lines show a high levet of resistance to yetlow rust. Through genomicin situ hybridization (GISH) withAg. intermedium total genomic DNA as a probe, it is demonstrated that the two stable lines are all small segmental translocation lines, and the translocated chromosome segments fromAg. intermedium are located on the short arm terminals of wheat chromosomes. Genetics analysis suggests that the yetlow rust resistance gene(s) are probably located on the translocated chromosome segments ofAg. intermedium.

Genomic in situ hybridization (GISH) analyses of Thinopyrum intermedium, its partial amphiploid Zhong 5, and disease-resistant derivatives in wheat

Genomic in situhybridization (GISH) to root-tip cells at mitotic metaphase, using genomic DNA probes from Thinopyrum intermedium and Pseudoroegneria strigosa, was used to examine the genomic constitution of Th. intermedium, the 56-chromosome partial amphiploid to wheat called Zhong 5 and disease-resistant derivatives of Zhong 5, in a wheat background. Evidence from GISH indicated that Th. intermedium contained seven pairs of St, seven JS and 21 J chromosomes; three pairs of Th. intermedium chromosomes with satellites in their short arms belonging to the St, J, J genomes and homoeologous groups 1, 1, and 5 respectively. GISH results using different materials and different probes showed that seven pairs of added Th. intermedium chromosomes in Zhong 5 included three pairs of St chromosomes, two pairs of JS chromosomes and two pairs of St-JS reciprocal tanslocation chromosomes. A pair of chromosomes, which substituted a pair of wheat chromosomes in Yi 4212 and in HG 295 and was added to 21 pairs of wheat chromosomes in the disomic additions Z1, Z2 and Z6, conferred BYDV-resistance and was identical to a pair of St-JS tanslocation chromosomes (StJS) in Zhong 5. The StJS chromosome had a special GISH signal pattern and could be easily distinguished from other added chromosomes in Zhong 5; it has not yet been possible to locate the BYDV-resistant gene(s) of this translocated chromosome either in the St chromosome portion belonging to homoeologous group 2 or in the JS chromosome portion whose homoeologous group relationship is still uncertain. Among 22 chromosome pairs in disomic addition line Z3, the added chromosome pair had satellites and belonged to the St genome and homoeologous group 1. Disomic addition line Z4 carried a pair of added chromosomes which was composed of a group-7 JS chromosome translocated with a wheat chromosome; this chromosome was different to 7 Ai-1, but was identical to 7 Ai-2. The leaf rust and stem rust resistance genes were located in the distal region of the long arm, whereas the stripe rust resistance gene(s) was located in the short arm or in the proximal region of the long arm of 7 Ai-2. A pair of JS-wheat translocation chromosomes, which originated from the WJS chromosomes in Z4, was added to the disomic addition line Z5; the added chromosomes of Z5 carried leaf and stem rust resistance but not stripe rust resistance; Z5 is a potentially useful source for rust resistance genes in wheat breeding and for cloning these novel rust-resistant genes. GISH analysis using the St genome as a probe has proved advantageous in identifying alien Th. intermedium in wheat.

Characterization of wheat-<i>Thinopyrum</i> partial amphiploids by meiotic analysis and genomic in situ hybridization

Characterization of wheat-<i>Thinopyrum</i> partial amphiploids by meiotic analysis and genomic in situ hybridization

Genomic in situ hybridization analysis of Thinopyrum chromatin in a wheat-Th. intermedium partial amphiploid and six derived chromosome addition lines

The genomic origin of alien chromosomes present in a wheat-Thinopyrum intermedium partial amphiploid TAF46 (2n = 8x = 56) and six derived chromosome addition lines were analyzed by genomic in situ hybridization (GISH) using S genomic DNA from Pseudoroegneria strigosa (2n = 2x = 14, SS) as a probe. The GISH analysis clearly showed that the chromosome complement of the partial amphiploid TAF46 consists of an entire wheat genome plus one synthetic genome consisting of a mixture of six S genome chromosomes and eight J (=E) genome chromosomes derived from Th. intermedium (2n = 6x = 42, JJJ(s)J(s)SS). There were no Js genome chromosomes present in TAF46. The J genome chromosomes present in TAF46 displayed a unique GISH hybridization pattern with the S genomic DNA probe, in which S genome DNA strongly hybridized at the terminal regions and weakly hybridized over the remaining parts of the chromosomes. This provides a diagnostic marker for distinguishing J genome chromosomes from Js or S genome or wheat ABD genome chromosomes. The genomic origin of the alien chromosomes present in the six derived chromosome addition lines were identified by their characteristic GISH hybridization patterns with S genomic DNA probe. GISH analysis showed that addition lines L1, L2, L3, and L5 carried one pair of J genome chromosomes, while addition lines L4 and L7 each carried one pair of S genome chromosomes. GISH patterns detected by the S genome probe on addition line of L1 were identical to those of the J genome chromosomes present in the partial amphiploid TAF46, suggesting that these chromosomes were not structurally altered when they were transferred from TAF46 to addition lines.

Genomic origins of Thinopyrum chromosomes specifying resistance to wheat streak mosaic virus and its vector, Aceria tosichella

The genomic origin of alien chromosomes carrying resistance to wheat streak mosaic virus (WSMV) and the wheat curl mite (WCM), Aceria tosichella Keifer, was evaluated in nine wheat-alien addition, substitution, or translocation lines, derived from hybrids of wheat with Thinopyrum ponticum (Podp.) Barkworth & D.R. Dewey (2n = 10x = 70), or with Th. intermedium (Host) Barkworth & D.R. Dewey (2n = 6x = 42). One of the four wheat × Th. ponticum lines was resistant to WSMV and WCM. The other three lines were resistant to WCM, but susceptible to WSMV. Five wheat × Th. intermedium lines were susceptible to WCM, but were highly resistant to WSMV. Genomic in situ hybridization (GISH) using different genomic DNA probes demonstrated that all WSMV- and WCM-resistant lines carried an alien chromosome(s) related to the Js genome in Th. ponticum and Th. intermedium. The Js alien chromosome(s) displayed a special GISH hybridization pattern with the S genomic DNA probe, in which S genome DNA hybridized strongly in the centromeric regions and occasionally in the terminal regions with no or a weak hybridization signal in the middle of the two arms of the chromosomes. The WCM-resistant wheat × Th. ponticum lines N/5.10.10 and 63-30-2-2-2-8-1 carried the same short arm of chromosome 6Js derived from the partial amphiploid Agrotana, while the WSMV-resistant wheat × Th. intermedium lines T-Ai, CI15092, CI17766, A29-13-3-1 and KS93WGRC27 all had the same alien chromosome or chromosome arm of 4Js from Th. intermedium. The Js genome present in Th. ponticum and Th. intermedium is an important source of WSMV and WCM resistance that can be transferred into wheat.Key words: wheat-Thinopyrum lines, WSMV- and WCM-resistance, genomic in situ hybridization, Js genome.

Genomic in situ hybridization analysis of <i>Thinopyrum</i> chromatin in a wheat - <i>Th. intermedium</i> partial amphiploid and six derived chromosome addition lines

Genomic in situ hybridization analysis of <i>Thinopyrum</i> chromatin in a wheat - <i>Th. intermedium</i> partial amphiploid and six derived chromosome addition lines

Molecular characterization of the genome composition of partial amphiploids derived from Triticum aestivum×Thinopyrum ponticum and T. aestivum×Th. intermedium as sources of resistance to wheat streak mosaic virus and its vector, Aceria tosichella

Wheat streak mosaic virus (WSMV), vectored by the wheat curl mite (WCM), is one of the most important viral diseases of wheat (Triticum aestivum) in the world. Genetic resistance to WSMV and the WCM does not exist in wheat. Resistance to WSMV and the WCM was evaluated in five different partial amphiploids namely Agrotana, OK7211542, ORRPX, Zhong 5 and TAF 46, which were derived from hybrids of wheat with decaploid Thinopyrum ponticum or with hexaploid Th. intermedium. Agrotana was shown to be immune to WSMV and the WCM; the other four partial amphiploids were susceptible to the WCM. Genomic in situ hybridization (GISH) using genomic DNA probes from Th. elongatum (EE, 2n=14), Th. bessarabicum (JJ, 2n=14), Pseudoroegneria strigosa (SS, 2n=14) and T. aestivum (AABBDD, 2n=42) demonstrated that three of the partial amphiploids, Agrotana, OK7211542 and ORRPX, have almost identical alien genome constitutions: all have 16 alien chromosomes, with 8 chromosomes being closely related to the Js genome and 8 chromosomes belonging to the E or J genomes and no evidence of any S-genome chromosomes. GISH confirmed that the alien genomes of Agrotana and OK7211542, like ORRPX, were all derived from Th. ponticum, and not from Th. intermedium. However, in contrast to Agrotana, ORRPX and OK7211542 were susceptible to the WCM and WSMV. The partial amphiploid Zhong 5 had a reconstituted alien genome composed of 4 S-and 4 Js-genome chromosomes of Th. intermedium with 6 translocated chromosomes between the S and Js genomes. This line was highly resistant to WSMV, but was susceptible to the WCM. TAF 46, which contained a synthetic genome consisting of 3 pairs of S-genome chromosomes and 4 pairs of E- or J-genome chromosomes in addition to the 21 pairs of wheat chromosomes, was susceptible to the WCM, but moderately resistant to WSMV. Agrotana offers great potential for transferring WSMV and WCM resistance into wheat.

Genomic constitution of a partial amphiploid OK7211542 used as a source of immunity to barley yellow dwarf virus for bread wheat

AbstractA combination of genomic in situ hybridization (GISH) and meiotic pairing analysis of crosses between a series of 2n= 56 partial amphiploids confirmed that the alien genome of the BYDV‐immune Agro‐tricum line OK7211542 is derived from Thinopyrum ponticum and not from Thinopyrum intermedium. The evidence from meiotic pairing analysis indicated that the chromosome constitution of OK7211542 is similar to another Agrotricum line, ORRPX, which was derived from a cross of wheat and Th. ponticum, but different from other Agrotricum lines, Zhong 5 and TAF 46 which were derived from the crosses between wheat and Th. intermedium. The GISH analysis confirmed that OK7211542 contained one complete set of 14 Th. ponticum chromosomes, in which no S chromosome was present in the alien genome. GISH also detected a small alien translocation attached to one of the wheat chromosomes, a result that was consistent with the pairing data.

Characterization of genomes and chromosomes in partial amphiploids of the hybrid Triticum aestivum × Thinopyrum ponticum by in situ hybridization, isozyme analysis, and RAPD

Genomic in situ hybridization (GISH) and Southern hybridization of genome-specific RAPD markers were used to demonstrate that the E genome (including Ee and Eb from Thinopyrum elongatum and Thinopyrum bessarabicum, respectively) and the St genome (from Pseudoroegneria species) were the two basic genomes in Thinopyrum ponticum. GISH also revealed that the centromeric region may be the critical area that discriminates the St genome from the E genome in Th. ponticum. Of the seven partial amphiploids isolated from backcrossed progenies of Triticum aestivum x Thinopyrum ponticum hybrids, two (lines 693 and 7631) have eight pairs of chromosomes from the Ee and (or) Eb genomes. Four partial amphiploids (lines 784, 68, 7430, and 40767-1) have an incomplete St genome, i.e., six pairs of chromosomes of St and one pair of chromosomes from Ee or Eb. In a heptaploid individual of the partial amphiploid 40767-2, there were four pairs of St chromosomes, one pair of St/1B Robertsonian translocation chromosomes, one pair of St/E translocation chromosomes, and one pair of Ee or Eb chromosomes. The isoelectric focusing of Est-5, Est-4, β-Amy-1, α-Amy-1, and α-Amy-2 and the RAPD data generated with 24 decamer primers on five partial amphiploids (lines 784, 693, 7631, 68, and 7430) indicated that lines 693 and 7631 had identical genomes from Th. ponticum. The partial amphiploid 784 probably had a set of chromosomes completely different from those of 693 and 7631. These results indicate that genome recombination usually occurred during the formation of new polyploid lines. Key words : Thinopyrum ponticum, wheat, partial amphiploid, GISH, isozyme, RAPD.

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).

N‐banded karyotype of Aegilops ovata and chromosomal constitution of its amphiploid with Triticum aestivum

AbstractThe N‐banded karyotype of an Aegilops ovata (2n = 4x = 28) accession was produced, and the chromosomal constitution of its partial amphiploid with bread wheat Triticum aestivum‘Chinese Spring’ was established. All A. ovata chromosomes showed specific N‐banding patterns and can easily be distinguished from each other. As a result of irregular meiotic behaviour of the chromosomes in the amphiploid, some structural rearrangements have probably occurred in most of the A. ovata chromosomes. The wheat chromosomes remained unmodified in their morphology and the N‐banding patterns.

Identification of a Potential Source of Complete Resistance to Soilborne Wheat Mosaic Virus in a Wheat‐Thinopyrum Intermedium Addition Line

AbstractSoilborne wheat mosaic virus (SBWMV) is a Furovirus transmitted by the plasmodiophoraceous fungus, Polymyxa graminis. Resistant cultivars of wheat (Triticum aestivum) to SBWMV have already been described. The resistance encountered mostly includes root infection without viral migration to foliage. In this study, the reaction of addition lines (L1, LIS, L2, L3, L4, L7), and the partial amphiploid derived from wheat (Vilmornn 27) and Thmopyrum intermedium has been evaluated. Lines L1. L3. L7. L1S and cultivar Vilmorin 27 are susceptible to SBWMV. Lines L4 and TAF 46 are root infected only. Chromosome 4Ag in L4 is thought to have an equivalent reaction to that one found in the mostly encountered resistance. Another type of resistance in a wheat line (1.2) with the added chromosome 3Agi of Th. intermedium has been characterized. In this line, L2, no SBWMV particles were detected on their roots by enzyme‐linked immunosorbent assays. Contrary to observations made on lines L1, LIS, L3, L4, L7, amphiploid TAF 46. and the wheat cultivars (Festival. Fandango, Vilmonn 27), no resting spores of P. graminis were found on roots of L2 2 months post inoculation. It is suggested that the disomic addition line L2 is immune to SBWMV.

Disomic Thinopyrum intermedium addition lines in wheat with barley yellow dwarf virus resistance and with rust resistances

Zhong 5 is a partial amphiploid (2n = 56) between Triticum aestivum (2n = 42) and Thinopyrum intermedium (2n = 42) carrying all the chromosomes of wheat and seven pairs of chromosomes from Th. intermedium. Following further backcrossing to wheat, six independent stable 2n = 44 lines were obtained representing 4 disomic chromosome addition lines. One chromosome confers barley yellow dwarf virus (BYDV) resistance, whereas two other chromosomes carry leaf and stem rust resistance; one of the latter also confers stripe rust resistance. Using RFLP and isozyme markers we have shown that the extra chromosome in the Zhong 5-derived BYDV resistant disomic addition lines (Z1, Z2, or Z6) belongs to the homoeologous group 2. It therefore carries a different locus to the BYDV resistant group 7 addition, L1, described previously. The leaf, stem, and stripe rust resistant line (Z4) carries an added group 7 chromosome. The line Z3 has neither BYDV nor rust resistance, is not a group 2 or group 7 addition, and is probably a group 1 addition. The line Z5 is leaf and stem rust resistant, is not stripe rust resistant, and its homoeology remains unknown.

Thinopyrum distichum addition lines: production, morphological and cytological characterisation of 11 disomic addition lines and stable addition-substitution line

Plants of the partial amphiploid Inia 66/Thinopyrum distichum (2n = 70)//Inia 66 (2n = 56) were used as male parents in crosses with the monosomic series in the common wheat cultivar Inia 66. The genome and homoeologous group of the monosomic used in the cross affected the distribution of chromosome number of the progeny plants in the F2 and F4. Meiosis in the pollen mother cells of the B1F7 partial amphiploids was not stable, and not different from that of the B1F1 in which univalents and multivalents were observed. Disomic addition lines were selected on the basis of morphology and meiotic stability in the F2, F4 and F5. Eleven of the fourteen possible wheat-Th. distichum disomic addition lines were identified using chromosome C-band pattern, as well as size and arm ratio, as genetic markers. Addition of T. distichum chromosome J (dll) produced a phenotype indicating homoeology with wheat group-2 chromosomes. Clear indications of homoeology based on morphological characteristics were not obtained in any of the other addition lines, probably due to the mixed homoeology of the Th. distichum chromosomes relative to wheat. The addition lines were all susceptible to leaf rust, unlike the germplasm-line Indis which carries a leaf rust resistance gene on a translocation segment derived from Th. distichum. Instability of meiotic pairing was observed in all addition lines. The stability, or not, of progeny chromosome counts did not reflect the level of chromosome pairing instability in the parental plants. SDS-PAGE for gliadin-type seed proteins revealed two addition lines which expressed seed storage proteins uncommon to Inia 66 but typical of Th. distichum.

Varying chromosome composition of 56-chromosome wheat × Thinopyrum intermedium partial amphiploids

Thinopyrum intermedium (2n = 42) is a source of many potentially useful genes for wheat improvement. Many partial amphiploids have been produced between Th. intermedium and Triticum aestivum that are fertile and stable. These partial amphiploids all have 56 chromosomes, including seven pairs of chromosomes from Th. intermedium. To explore the genomic composition of these lines, meiotic analysis was conducted on 32 hybrid combinations between eight different partial amphiploids. All but two of the chosen parents were distinguishable on the basis of perenniality, head morphology, and reactions to leaf, stripe, and stem rusts and to barley yellow dwarf virus. Chromosome pairing in the hybrids clearly indicated that all but two of the partial amphiploids differed in their composition of Thinopyrum chromosomes. The differences varied from one to five chromosomes. This confirms molecular evidence that the extra genome of the octoploid partial amphiploids is a variable synthetic genome combining chromosomes of the three Thinopyrum genomes E, J, and X. Though the extra synthetic genomes vary widely between different octoploids, they are nevertheless stable once formed. It is argued that the failure to establish these octoploid amphiploids as a new crop is a consequence of their differing chromosome complements, which makes it impractical to interbreed them.

Production and identification of three 4Ag(4D) substitution lines of Triticum aestivum — Agropyron: relative transmission rate of alien chromosomes

By crossing fertile nullisomics-4D of common wheat (nullisomics 72180 and 'Tianxuan' no. 15) with three octoploid Agrotriticum lines [partial amphiploids (2n=56) 78829 from the offsprings of wheat with Agropyron intermedium (=Thinopyrum intermedium, 2n=42) and 784 and 7631 from those of wheat with Ag. elongatum (Thinopyrum elongatum, 2n=70)], backcrossing the hybrid with 4D nullisomics as recurrent parent for one to two generations, and then selfing the BC individuals, we obtained three different alien substitution lines, 4Ei (4D), 4Ee(4D) blue grain, and 4Fe(4D) hairy leaf. The F1 hybrids of 784×78829 had the basic chromosome pairing configuration of 27″ + 2', indicating that 784 and 78829 differed by only one pair of chromosomes. This means that Ag. intermedium and Ag. elongatum have a genome (or genomes) in common. The formation of 22″ +12' in the F1 of 784×7631 suggested that there was only one pair of homologous chromosomes of Ag. elongatum in 784 and 7631. Because F1 plants of 7631×78829 generally formed 21″ +14' at metaphase I, the Agropyron genomes in the two octoploid Agrotriticums were presumed to differ from each other. Upon intercrossing the three alien substitution lines, we found that all of the pollen mother cells of the F1 plants had 20″ + 2' or more univalents at metaphase I. We concluded that the three Agropyron chromosomes were not homologous but belonged to the same homoeologous group. These results were confirmed by reciprocal crosses of the three octoploids. The relative transmission rates of 4Ee, 4Fe, 4Ei, 4R and 4D were calculated using blue grain and hairy leaf as genetic markers; these were 4D>4Ee>4Ei, 4Fe>4R. The four alien chromosomes could compensate for the 4D of bread wheat, the substitution lines being vigorous and fertile.

Karyological characterization of a partial amphiploid, Triticum turgidum L. var. durum × Agropyron intermedium (Host) P.B.

A Giemsa-C-banded karyotype of a partial amphiploid, Triticum turgidum L. var. durum cv. ‘Nodak’ × Agropyron intermedium (Host) P.B., called MT-2, was analyzed. MT-2 is a winterhardy grasslike octoploid germplasm which survived 5 winters in Montana, and its seed weight is 3 times that of A. intermedium seed. The MT-2 C-banding karyotype shows 6 chromosome pairs each of the A and B wheat genomes with 3A and 4B missing. Chromosomes 1B and 2B are involved in a reciprocal homozygous translocation (T1BS·2BS, T1BL·2BL) which was also confirmed by a nucleolus-associated quadrivalent in an MT-2 × durum wheat backcross. In addition to the wheat chromosomes, MT-2 consistently shows 16 A. intermedium chromosome pairs which are designated from A to P. These chromosomes show C-banding patterns similar to those reported earlier in the literature. A large amount of C-banding polymorphism and structural rearrangements in A. intermedium itself presently make a definite chromosome assignment to the homeologous groups of the Triticeae difficult. The data presented are crucial for further directed manipulation of this germplasm aimed at producing valuable chromosome additions and substitutions in wheat.

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.

Segregation in the pollen of F2 rye (Secale cereale) plants for induction of homoeologous chromosome pairing in hybrids with wheat (Triticum aestivum)

An attempt was made to determine the inheritance of the rye genes which induce high chiasma frequency in hybrids with wheat and to study if the ability of rye to induce partial amphiploidy in hybrids with wheat was heritable. Five to eight F2 pollen plants were derived from seeds taken from each of three F1 plants that had given high chiasma frequency in hybrids with 'Chinese Spring' wheat in earlier studies. Similarly, six to seven F2 pollen plants were derived from each of three F1 plants that had given partial amphiploids in hybrids with 'Chinese Spring' wheat in earlier studies. Chiasma frequency was studied in 127 hybrids with 'Chinese Spring' wheat. In the present study, significant differences in chiasma frequency were observed (i) among the 38 families represented by 127 plants, and (ii) between two groups of three sets each, one known for inducing high pairing and the other known for inducing partial amphiploidy associated with low pairing in wheat × F1 rye plants. Significant variation was also observed between families within sets (each originated from one F1 rye plant) suggesting that F2 rye plants derived from the same F1 plants also differed genetically for inducing heterogenetic (homoeologous) pairing in wheat × rye hybrids. One of the six sets particularly showed significantly higher pairing with a mean of 2.13 per cell (individual hybrids gave a chiasma frequency as high as a mean of 6.07 per cell) as against a range of 0.96 to 1.18 in the remaining five sets, suggesting accumulation of genes in F2 rye plants for inducing pairing in wheat × rye hybrids. It is expected that by intermating the segregating rye plants, it should be possible to accumulate genes and eventually to isolate homozygous lines inducing high pairing in hybrids with wheat. Contrary to expectation, no partial amphiploids were obtained in a study of 127 wheat × F2 rye hybrids, although three of the six F1 rye plants had earlier given partial amphiploids in wheat × F1 rye hybrids. Key words: intergeneric hybrids, wheat, rye, genetic control, chromosome pairing.