Detection of wheat-alien recombinant chromosomes using co-dominant DNA markers**

A study of homoeologous recombination along almost the complete genetic length of two homoeologous chromosomes in the Triticeae was conducted. Sears' phlb mutant was used to induce homoeologous pairing between chromosomes 7A of common wheat and 7Ai–l of Agropyron intermedium. 390 ph1b ph1b homozygous F₃ progeny were screened using six co-dominant DNA markers (RFLP loci). 63 of the progeny (16%) were putative recombinants, showing dissociation of RFLP markers within the arm(s). Progeny tests of self-fertile putative recombinants confirmed the dissociation phenotypes observed in the F₃ progeny. No recombination could be confirmed in 117 F₃ progeny plants having the Ph1– allele (control population). Frequencies and distribution of chiasmata along the chromosome arm 7AS were analysed using additional RFLP markers. The patterns of recombination between the two homoeologous chromosomes were found similar to those reported for homologous recombination between the same markers on short arms of group 7 chromosomes of Triticeae.     

Genesis of bivalent pairing in hexaploid clump Verbena

Both 6x Verbena aubletia (n=15) and 2x V. tenuisecta (n=5) form bivalents during meiosis, however, their 4x F₁ hybrid (V. aubletia × V. tenuisecta) shows almost complete homoeologous pairing involving on average 19.74 out of its 20 chromosomes. In 10% cells there are 4IV+2II indicating that essentially there may be 4 homoeologous sets of 5 chromosomes each in the F₁ hybrid. Evidently, V. aubletia is segmental allo-hexaploid involving 3 homoeologous genomes (A₁A₁ A₂A₂ A₃A₃). Whether its cytologically diploid behaviour is the result of a multivalent suppressor system or due to an acute property of preferential pairing, cannot be answered with certainty. In either case intergenomal homoeologies are totally suppressed resulting in bivalent pairing, meiotic isolation of the 3 genomes and institution of normal fertility.     

Transfer of Ph I genes promoting homoeologous pairing from Triticum speltoides to common wheat

Diploid-like chromosome pairing in polyploid wheat is controlled by several Ph (pairing homoeologous) genes with major and minor effects. Homoeologous pairing occurs in either the absence of these genes or their inhibition by genes from other species (Ph ^I genes). We transferred Ph ^I genes from Triticum speltoides (syn Aegilops speltoides) to T. aestivum, and on the basis of further analysis it appears that two duplicate and independent Ph ^I genes were transferred. Since Ph ^I genes are epistatic to the Ph genes of wheat, homoeologous pairing between the wheat and alien chromosomes occurs in the F₁ hybrids. Using the Ph ^I gene stock, we could demonstrate homoeologous pairing between the wheat and Haynaldia villosa chromosomes. Since homoeologous pairing occurs in F₁ hybrids and no cytogenetic manipulation is needed, the Ph ^I gene stock may be a versatile tool for effecting rapid and efficient alien genetic transfers to wheat.Contribution no. 93-435-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, KS 66506-5502, USA     

Electrophoretic evidence for homoeologous chromosome pairing in the apogamous fern species<Emphasis Type="Italic"> Dryopteris nipponensis</Emphasis> (Dryopteridaceae)

Segregation of genotypes through homoeologous chromosome pairing in the apogamous species Dryopteris nipponensis was tested by electrophoretic analysis. Of 284 progeny examined (250 gametophytes and 34 sporophytes), from the parental sporophyte with the Pgi-2 genotype abc, five showed different genotypes from that of the parent (three aac, one bbc and one bcc). This is the first evidence for genetic segregation in the progeny of apogamous fern species. Electronic Publication     

Chemical races in the red alga Laurencia nipponica (Rhodomelaceae, Ceramiales)

Genetic variation in the synthesis of halogenated secondary metabolites in the Japanese marine red alga Laurencia nipponica Yamada (Rhodomelaceae, Ceramiales) has been investigated in laboratory crossing experiments and chemical analyses, F₁ tetrasporophytes and F₁ gametophytes resulting from crosses within chemical races produced major metabolites characteristic of these races. F₁ tetrasporophytes derived from reciprocal interracial crosses produced: (i) both parental types of secondary metabolites; (ii) either of the parental types; or (iii) a further major compound in addition to both parental types or in addition to either of the parental types. The latter cases suggest that hybrid-specific products were formed by the combined enzymatic complements of the parents, as F₁ gametophytes derived from these interracial F₁ tetrasporophytes yielded one or other of their parental products in an approximate 1:1 ratio. The population structure was analyzed at localities in Hokkaido, where two of the chemical races occur sympatrically. At Usujiri (Minami-kayabe), where the prepacifenol race and the laureatin race were sym-patric, hybrid gametophytes (recombination type) were found in high frequency in addition to hybrid tetra sporophytes, which strongly suggests that a new, pre-pacifenol/laureatm race is beginning to be produced by natural hybridization and recombination. By contrast, at Oshoro Bay, where the laurencin race and the epi-lauraliene race grew together, the interracial hybrids were rare: only a few tetrasporophytes (probably F₁ generation) were found, suggesting that racial integrity may be retained by habitat segregation and/or the absence of recombination-type gametophytes.     

New hybrids between Agropyron and wheat

Summary Intergeneric hybrids of Triticum aestivum (2n=42,AABBDD) with Agropyron ciliare (2n= 28,SSYY), A. trachycaulum (2n=28,SSHH), A. yezoense (2n=28,SSYY) and A. scirpeum (2n=28) are reported for the first time. F₁ hybrids of T. aestivum were also produced with A. intermedium (2n=42,E₁E₁E₂E₂Z₁Z₁) and A. junceum (2n=14,JuJu). All wheat-Agropyron hybrids were obtained by embryo rescue technique. Cultivars and reciprocal crosses differed for seed set, seed development and F₁ plant production. The F₁ hybrids were sterile. Attempts to obtain amphiploids were unsuccessful. However, backcross derivatives were obtained with wheat as the recurrent parent.The level of chromosome pairing in A. trachycaulum x wheat, A. yezoense x wheat and wheat x A. junceum hybrids provided no evidence of homologous or homoeologous pairing. Mean pairing frequencies in A. ciliare x wheat, wheat x A. scirpeum and wheat x A. intermedium hybrids indicated homoeologous or autosyndetic pairing. Ph gene was more effective in regulating homoeologous pairing in A. yezoense x wheat hybrids than in A. ciliare x wheat hybrid. Chromosome pairing data of BC₁ derivatives indicated that either some of the wheat chromosomes were eliminated or Agropyron chromosomes caused reduced pairing of wheat homologues.Contribution No. 82-653-J, Department of Plant Pathology, Kansas State Agricultural Experiment Station, Manhattan, Kan, USA     

Induced Homoeologous Pairing for Transfer of Useful Variability for High Grain Fe and Zn from <Emphasis Type="Italic">Aegilops kotschyi</Emphasis> into Wheat

Biofortification of bread wheat by the transfer of useful variability of high grain Fe and Zn from Aegilops kotschyi through induced homoeologous pairing is the most feasible approach to alleviate micronutrient malnutrition worldwide. Deficiency of chromosome 5B in interspecific hybrids allows homoeologous pairing and recombination of chromosomes of wheat with those of the related species. The interspecific hybrid plants without 5B chromosome showed much higher chromosome pairing than did the plants with 5B. The F₁ plants without 5B chromosome were selected and repeatedly backcrossed with wheat cultivar PBW343. The chromosome number of BC₂F₁ plants ranged from 43 to 60 with several univalents and multivalents. Molecular markers and GISH analysis confirmed the introgression of U/S chromosomes of Ae. kotschyi and their fragments in wheat. The BC₂F₂ plants showed up to 125 % increase in Fe and 158 % increase in Zn compared to PBW343 with Lr24 and Yr36. Induced homoeologous pairing in the absence of 5B was found to be an effective approach for transfer of useful variability for enhanced grain Fe and Zn content for biofortification of wheat for high grain micronutrient content.     

C-banding in 6x-Triticale xSecale cereale L. hybrid cytogenetics

Summary The meiotic behaviour of F₁ hybrids of hexaploid Triticale that differed in their genotypic or chromosomic constitution, and diploid rye, was investigated. Meiotic analysis were done by Feulgen and C-banding staining methods. A differential desynaptic effect in the hybrids was detected and explained in terms of genetic differences in pairing regulators. The high homoeologous pairing (A-B wheat chromosomes and wheat-rye chromosomes) observed in the hybrids can be explained in terms of an inhibition of the effect of a single dose of thePh allele of the 5B chromosome produced by two doses of the 5R chromosome. The higher homoeologous pairing detected in the hybrid 188 x Canaleja could be the overall result of the balance between thePh diploidizing system (1 dose), the pairing promoter of the 5R chromosome (2 doses) and that of the 3D chromosome (1 dose coming from the parental line Triticale with the substitution 3R by 3D).     

Inheritance and tagging of gene regulating flowering time in the green manure crop <Emphasis Type="Italic">Sesbania rostrata</Emphasis> (Bremek. &; Obrem.)

This is the first report on genetic studies and molecular tagging of a gene regulating flowering time in the stem nodulating legume crop Sesbania rostrata (Bremek. & Obrem.). An F₂ segregating population was developed from a cross between Trombay Sesbania rostrata-1 (TSR-1, a radiation induced late flowering mutant) and S. rostrata. A phenotypic segregation ratio of 3 (normal flowering):1 (late flowering) in the F₂ generation indicated that the late flowering is governed as a monogenic recessive trait. A genotypic ratio of 1:2:1 in the F₂ generation, determined from phenotypic segregation patterns in 73 F₃ families, confirmed the monogenic inheritance of the late flowering trait. Inter Simple Sequence Repeat (ISSR) and Amplified Fragment Length Polymorphism (AFLP) marker techniques were evaluated for their applicability as genetic marker systems in this green manure crop. Using the F₂ segregating population, an ISSR marker (UBC 881₁₀₀₀) tightly linked to the trait was identified. Two linked AFLP markers GCTG₅₀₀ and CCAT₃₅₀ were also identified. They were found to be at a distance of 1.4 ± 0.034 cM and 8.0 ± 0.047 cM flanking the flowering locus respectively. The ISSR marker UBC 881₁₀₀₀ was converted into a Sequence Characterized Amplified Region (SCAR) marker. The single recessive mutation regulating the late flowering trait and the availability of tightly linked, flanking markers will help in identification and isolation of the gene controlling the flowering time trait.     

GISH reveals different levels of meiotic pairing with wheat for individual <Emphasis Type="Italic">Aegilops biuncialis</Emphasis> chromosomes

The Triticum aestivum — Aegilops biuncialis (2n=4x=28; U^bU^bM^bM^b) disomic addition lines 2M^b, 3M^b, 7M^b and 3U^b were crossed with the wheat cv. Chinese Spring ph1b mutant genotype in order to induce homoeologous pairing, with the final goal of introgressing Ae. biuncialis chromatin into cultivated wheat. Wheat-Aegilops homoeologous chromosome pairing was studied in metaphase I of meiosis in the F₁ hybrid lines. Using U and M genomic probes, genomic in situ hybridization (GISH) demonstrated the occurrence of wheat-Aegilops homoeologous pairing in the case of chromosomes 2M^b, 3M^b and 3U^b, but not in the case of 7M^b. The wheat-Aegilops pairing frequency decreased in the following order: 2M^b > 3M^b > 3U^b > 7M^b, which may reflect differences in the wheat-Aegilops homoeologous relationships between the examined Aegilops chromosomes. The selection of wheat-Aegilops homoeologous recombinations could be successful in later generations.     

Crossability of Brassica tournefortii and B. rapa, and morphology and cytology of their F1 hybrids

The crossability between Brassica tournefortii (TT, 2n = 20) and Brassica rapa (AA, 2n = 20) and the cytomorphology of their F₁ hybrids were studied. Hybrids between these two species were obtained only when B. tournefortii was involved as a female parent. The hybrid plants were intermediate for most of the morphological attributes and were found to be free from white rust under field conditions. The F₁ plants showed poor pollen fertility, although occasional seed set was achieved from open pollination. Self-pollination or backcrosses did not yield any seeds in these plants. The occurrence of chromosome association ranging from bivalents (0–7), trivalents (0–2) to a rare quadrivalent (0–1) in the dihaploid hybrids indicates pairing between the T and A genomes. The homoeologous pairing coupled with seed set in the F₁ plants offer an opportunity for interspecific gene transfers from B. tournefortii to B. rapa and vice-versa through interspecific hybridization. Received: 3 July 2000 / Accepted: 22 September 2000     

Development of Yellow Mosaic Virus (YMV) resistance linked DNA marker in <Emphasis Type="Italic">Vigna mungo</Emphasis> from populations segregating for YMV-reaction

Yellow mosaic virus, YMV, causes one of the most severe of biotic stresses in Vignas, an important group of pulse crops. The viral disease is transmitted through the white fly, Bemicia tabaci, and the yield of the plants is affected drastically. YMV-tolerant lines, generated from a single YMV-tolerant plant identified in the field within a large population of the susceptible cultivar T-9, were crossed with T-9, and F₁, F₂ and F₃ progenies raised. The different generations were phenotyped for YMV-reaction by forced inoculation using viruliferous white flies. A monogenic recessive control of YMV-tolerance was revealed from the F₂ segregation ratio of 3:1 (susceptible: tolerant), which was confirmed by the segregation ratio of the F₃ families. Of 24 pairs of resistance gene analog (RGA) primers screened, only one pair, RGA 1F-CG/RGA 1R, was found to be polymorphic among the parents. Selected F₂ individuals and F₃ families were genotyped with the polymorphic RGA primer pair and the polymorphism was found to be linked with YMV-reaction. This primer pair amplified a 445bp DNA fragment only from homozygous tolerant and the heterozygous lines. The 445bp marker band was sequenced and named 'VMYR1'. The predicted amino acid sequence showed highly significant homology with the NB-ARC domain present in several gene products involved in plant disease resistance, nematode cell death and human apoptotic signaling. To the best of our knowledge, this is the first report of YMV-resistance linked DNA marker development in any crop species using segregating populations. This YMV-resistance linked marker is of potential commercial importance in resistance breeding of plants.     

Regulation of homoeologous pairing in pentaploid wheat hybrids

Comparisons were made of levels of chromosome pairing in pentaploid hybrids between normal and ph _1b -and ph ₂ -mutant forms of Triticum aestivum ssp. vulgare cv. Chinese Spring each crossed with Triticum kotschyi and T. turgidum var. dicoccoides. Higher levels of multivalent formation in the ph _1b -kotschyi, compared with the ph _1b -dicoccoides pentaploid was attributed mainly to the absence of allelic buffering, by the Ph ₁ allele, in the Kotschyi pentaploid and its presence in the dicoccoides pentaploid. The higher level of homoeologous pairing in the ph ₂ -dicoccoides pentaploid compared with that of kotschyi was believed to be due to differential levels of homoe-and non-homoallelic buffering in the two pentaploids. The high level of homoeologous pairing caused by the ph ₂ -mutant in the dicoccoides pentaploid indicates a potential use of pairing promoters, free of homoallelic buffering, as a means of increasing thelevel of homoeologous pairing in wheat and in certain of its hybrids with alien species.     

RFLP marker analysis supports tetrasonic inheritance in Lotus corniculatus L.

Lotus corniculatus is a tetraploid (2n=4x=24) perennial forage legume and has been reported to have tetrasomic inheritance for several traits, although it has also been reported to show disomic inheritance. Molecular markers were used to clarify whether tetrasomic inheritance, disomic inheritance, or a combination of both, was found within an F₂ population arising from a cross between two diverse L. corniculatus accessions. The inheritance of ”tetra-allelic” RFLP markers (markers with four segregating bands) indicated that disomic inheritance could not account for the phenotypic F₂ classes observed, and that only tetrasomic inheritance would explain the observed results. Goodness of fit tests for ”tetra-allelic” and ”tri-allelic” (three segregating bands) RFLP marker data suggested support for chromosomal-type tetrasomic inheritance. RFLP genotypes interpreted from autoradiographic signal intensity provided additional support for tetrasomic inheritance and the occurrence of preferential pairing between parental chromosomes. Bivalent pairing was predominant in the two parental lines and their F₁ hybrid in cytological analyses. L. corniculatus has been classified as both an autotetraploid and an allotetraploid species. RFLP evidence of tetrasomic inheritance gives support for L. corniculatus being classified as an autotetraploid species. Even though bivalent pairing occurs, as seen in other autotetraploid species, pairing between any of the four homologous chromosomes is possible. Preferential pairing in the F₁ hybrid suggests that genome differentiation appears to be minimal between homologs within an accession, while genome differentiation is greater between homologs from different accessions of this genetically diverse species. Received: 16 November 1999 / Accepted: 14 July 2000     

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.     

Production and cytogenetic analysis of BC1, BC2, and BC3 progenies of an intergeneric hybrid between Triticum aestivum (L.) Thell. and tetraploid Agropyron cristatum (L.) Gaertn.

Summary Intergeneric hybrids between Triticum aestivum cv Chinese Spring and Agropyron cristatum 4x (2n= 5x=35, ABDPP genomes) with a high level of homoeologous meiotic pairing between the wheat chromosomes were backcrossed 3 times to wheat. Pollination of the F₁ hybrid with Chinese Spring resulted in 22 BC₁ seeds with an average seed set of 1.52%. Five BC₁ plants with 39–41 chromosomes were raised using embryo rescue techniques. Chromosome pairing in the BC₁ was characterized by a high frequency of multivalent associations, but in spite of this there was no evidence of homoeologous pairing between chromosomes of wheat and those of Agropyron. All of the plants were self sterile. The embryo rescue technique was again essential to produce 39 BC₂ plants with chromosome numbers ranging from 37 to 67. The phenomenon of meiotic non-reduction was also observed in the BC₃ progenies. In this generation male and female fertility greatly increased, and meiotic pairing was fairly regular. Some monosomic (2n=43) and double monosomic (2n=44) lines were produced. Analysis of these progenies should permit the extraction of the seven possible wheat-Agropyron disomic addition lines including those with the added chromosomes carrying the genes involved in meiotic non-reduction and in suppression of Ph activity.     

Development of novel PCR markers linked to the BYDV resistance gene <Emphasis Type="Italic">Bdv2</Emphasis> useful in wheat for marker-assisted selection

The distal segment of the long arm of the Thinopyrum intermedium chromosome 7Ai1 carries the barley yellow dwarf virus (BYDV) resistance gene Bdv2. This segment was transferred to the distal region of the long arm of wheat chromosome 7D in the Yw series of translocation lines by using the ph1b mutant to induce homoeologous pairing. To transfer Bdv2 to commercial varieties, we developed two resistance gene-analog polymorphism (RGAP) markers, Tgp-1₃₅₀ and Tgp-2₂₁₀, and one randomly amplified polymorphic DNA (RAPD) marker, OPD04₁₃₀₀. The diagnostic fragments of the RGAP marker Tgp-1₃₅₀ and the RAPD marker OPD04₁₃₀₀ were cloned, sequenced and converted into sequence-characterized amplified region (SCAR) markers, named SC-gp1 and SC-D04, respectively. SC-gp1 and SC-D04 were validated based on available translocation lines and segregating F₂ individuals. Our results indicated that the SCAR markers co-segregated with the BYDV resistance associated with Bdv2. Therefore, they can be used as a low-cost, high-throughput alternative to conventional phenotypic screening in wheat-breeding programs exploiting Bdv2. The marker-assisted selection for BYDV resistance was successfully performed in a wheat-breeding program.Electronic Supplementary Material Supplementary material is available for this article at     

Analysis of RFLP mapping inaccuracy in Brassica napus L.

 We identified sources of mapping inaccuracy during the construction of RFLP linkage maps from one F₂ population and two F₁ microspore-derived populations from the same cross of oilseed Brassica napus. The genetic maps were compared using a total of 145 RFLP marker loci including 82 loci common to all three populations. In the process, we identified a series of mapping events that could lead to ambigous conclusions. Superimposed restriction fragments could be mistaken as a single dominant restriction fragment in a F₂ population and, when analyzed as such, would yield inaccurate linkage information. Residual heterozygosity in parental lines resulted in complicated allelic assignment and yielded subsequent difficulties in linkage determination. Loose and spurious linkages occurred during mapping and were identified by comparing maps derived from different populations. LOD scores and χ² test of independence were compared for their capacity to detect loose linkages or generate spurious ones. Extreme segregation distortions towards the same parental allele also contributed to an additional source of spurious linkage. Small but significant segregation distortions resulted in reduced estimates of the recombination fraction. The use of the same ‘probe× enzyme’ combinations in doubled haploid populations allowed the identification of the correct allele assignment as well as loose and spurious linkages. A translocation between two homoeologous linkage groups was observed. The consequences of such a chromosomal event as a source of error in mapping applications are discussed. Received: 7 September 1996/Accepted: 25 October 1996     

Identification of a chromosome-specific probe that maps within the Ph1 deletions in common and durum wheat

 The Ph1 (pairing homoeologous) gene is the major factor that determines the diploid-like chromosome behavior of polyploid wheat. This gene, which is located on the long arm of chromosome 5B (5BL), suppresses homoeologous pairing at meiosis while allowing exclusive homologous pairing. In an effort to tag the specific chromosomal region where this gene is located, we have previously microdissected chromosome arm 5BL from bread wheat and produced a plasmid library by random PCR amplification and cloning. In this work we isolated from this library a 5BL-specific probe, WPG90, and mapped it within the interstitial deleted chromosome fragments carrying Ph1 in common and durum wheat. A PCR assay of Ph1 based on WPG90 was developed that allows an easy identification of homozygous genotypes deficient for this gene. Received: 19 June 1996 / Accepted: 18 October 1996     

INHERITANCE OF NUCLEAR 2C DNA CONTENT VARIATION IN INTRASPECIFIC AND INTERSPECIFIC HYBRIDS OF MICROSERIS (ASTERACEAE)

Nuclear DNA content varies over 20% within the diploid (2n = 18) species M. douglasii and M. bigelovii. Two different intraspecific crosses were made between M. douglasii biotypes which differed by about 10% in 2C nuclear DNA content. The F₂ progeny of one intraspecific cross showed no striking evidence of segregation for DNA content. The mean DNA contents of F₂ progeny from two sister hybrids from the second intraspecific cross were significantly different at the 1% level. An interspecific cross was made between biotypes of M. douglasii and M. bigelovii that differed by approximately 10% in DNA amount. The 12 F₁ progeny did not cluster around the parental midpoint, but instead encompassed nearly the entire range between the parental means. The five families of F₂ progeny studied each had a mean DNA content corresponding to that of the particular F₁ from which they were derived, indicating that the F₁ plants were not of identical DNA content. The results of this study suggest that DNA sequences which account for the DNA content differences among the plants are unstable and can undergo deletion or amplification in a hybrid. The altered DNA content may be heritably stable and show little or no segregation in the F₂ progeny.