RFLP-based maps of the homoeologous group-6 chromosomes of wheat and their application in the tagging of Pm12, a powdery mildew resistance gene transferred from Aegilops speltoides to wheat

Genetic maps of the homoeologous group-6 chromosomes of bread wheat, Triticum aestivum, have been constructed spanning 103 cM on 6A, 90 cM on 6B and 124 cM on 6D. These maps were transferred to a Chinese Spring (CS) x line #31 cross to locate a dominant powdery mildew resistance gene, Pm12, introgressed into line #31 from Aegilops speltoides. Pm12 was shown to lie on the short arm of translocation chromosome 6BS-6SS.6SL in line #31, but could not be mapped more precisely due to the lack of recombination between the 6S Ae. speltoides segment and chromosome 6B. Possible strategies to reduce the size of the alien segment, which probably encompasses the complete long arm and more than 82% of the short arm of chromosome 6B, are discussed.     

The Ph2 pairing homoeologous locus of wheat (Triticum aestivum): identification of candidate meiotic genes using a comparative genetics approach

Colinearity in gene content and order between rice and closely related grass species has emerged as a powerful tool for gene identification. Using a comparative genetics approach, we have identified the rice genomic region syntenous to the region deleted in the wheat chromosome pairing mutant ph2a, with a view to identifying genes at the Ph2 locus that control meiotic processes. Utilising markers known to reside within the region deleted in ph2a, and data from wheat, barley and rice genetic maps, markers delimiting the region deleted on wheat chromosome 3DS in the ph2a mutant were used to locate the syntenous region on the short arm of rice chromosome 1. A contig of rice genomic sequence was identified from publicly available sequence information and used in blast searches to identify wheat expressed sequence tags (ESTs) exhibiting significant similarity. Southern analysis using a subset of identified wheat ESTs confirmed a syntenous relationship between the rice and wheat genomic regions and defined precisely the extent of the deleted segment in the ph2a mutant. A 6.58-Mb rice contig generated from 60 overlapping rice chromosome 1 P1 artificial chromosome (PAC) clones spanning the syntenous rice region has enabled identification of 218 wheat ESTs putatively located in the region deleted in ph2a. What seems to be a terminal deletion on chromosome 3DS is estimated to be 80 Mb in length. Putative candidate genes that may contribute to the altered meiotic phenotype of ph2a are discussed.     

Chromosome substitutions of Triticum timopheevii in common wheat and some observations on the evolution of polyploid wheat species

Whether the two tetraploid wheat species, the well known Triticum turgidum L. (macaroni wheat, AABB genomes) and the obscure T. timopheevii Zhuk. (A^tA^tGG), have monophyletic or diphyletic origin from the same or different diploid species presents an interesting evolutionary problem. Moreover, T. timopheevii and its wild form T. araraticum are an important genetic resource for macaroni and bread-wheat improvement. To study these objectives, the substitution and genetic compensation abilities of individual T. timopheevii chromosomes for missing chromosomes of T. aestivum Chinese Spring (AABBDD) were analyzed. Chinese Spring aneuploids (nullisomic-tetrasomics) were crossed with a T. timopheevii x Aegilops tauschii amphiploid to isolate T. timopheevii chromosomes in a monosomic condition. The F₁ hybrids were backcrossed one to four times to Chinese Spring aneuploids without selection for the T. timopheevii chromosome of interest. While spontaneous substitutions involving all A^t- and G-genome chromosomes were identified, the targeted T. timopheevii chromosome was not always recovered. Lines with spontaneous substitutions from T. timopheevii were chosen for further backcrossing. Six T. timopheevii chromosome substitutions were isolated: 6A^t (6A), 2G (2B), 3G (3B), 4G (4B), 5G (5B) and 6G (6B). The substitution lines had normal morphology and fertility. The 6A^t of T. timopheevii was involved in a translocation with chromosome 1G, resulting in the transfer of the group-1 gliadin locus to 6A^t. Chromosome 2G substituted for 2B at a frequency higher than expected and may carry putative homoeoalleles of gametocidal genes present on group-2 chromosomes of several alien species. Our data indicate a common origin for tetraploid wheat species, but from separate hybridization events because of the presence of a different spectrum of intergenomic translocations.     

Molecular identification of powdery mildew resistance genes in common wheat (Triticum aestivum L.)

RFLP markers for the wheat powdery mildew resistance genes Pm1 and Pm2 were tagged by means of near-isogenic lines. The probe Whs178 is located 3 cM from the Pm1 gene. For the powdery mildew resistance gene Pm2, two markers were identified. The linkage between the Pm2 resistance locus and one of these two probes was estimated to be 3 cM with a F₂ population. Both markers can be used to detect the presence of the corresponding resistance gene in commercial cultivars. Bulked segregant analysis was applied to identify linkage disequillibrium between the resistance gene Pm18 and the abovementioned marker, which was linked to this locus at a distance of 4 cM. Furthermore, the RAPD marker OPH-11₁₉₀₀ (5-CTTCCGCAGT-3) was selected with pools created from a population segregating for the resistance of Trigo BR 34. The RAPD marker was mapped about 13 cM from this resistance locus.     

RELP markers linked to two Hessian fly-resistance genes in wheat (Triticum aestivum L.) from Triticum tauschii (coss.) Schmal

Summary Restriction fragment length polymorphism (RFLP) markers linked to genes controlling Hessian fly resistance from Triticum tauschii (Coss.) Schmal. were identified for two wheat (Triticum aestivum L.) germ plasm lines KS89WGRC3 (C3) and KS89WGRC6 (C6). Forty-six clones with loci on chromosomes of homoeologous group 3 and 28 clones on those of group 6 were surveyed for polymorphisms. Eleven and 12 clones detected T. tauschii loci in the two lines, respectively. Analysis of F₂ progenies indicated that the Hessian fly resistance gene H23 identified in C3 is linked to XksuH4 (6.9 cM) and XksuG48 (A) (15.6 cM), located on 6D. The resistance gene H24 in C6 is linked to XcnlBCD451 (5.9 cM), XcnlCD0482 (5.9 cM) and XksuG48 (B) (12.9 cM), located on 3DL.Paper No. 810 of the Cornell Plant Breeding Series     

Control of lectins in Triticum aestivum and Aegilops umbellulata by homoeologous group 1 chromosomes

Summary Each of the three genomes in hexaploid wheat controls the expression of a specific lectin in the embryo. The chromosomes which control their synthesis were determined using nullisomic-tetrasomic and inter-varietal chromosome substitution lines of Chinese Spring. All three wheat lectins were shown to be controlled by the homoeologous group 1 chromosomes. Using ditelosomic lines of Chinese Spring the lectin genes could be localized on the long arms of chromosomes 1A and 1D. Inter-specific addition and substitution lines of Aegilops umbellulata chromosomes to Chinese Spring indicated that chromosome 1U, which is homoeologous to the group 1 chromosomes of wheat, controls lectin synthesis.     

Dosage response of rye genes in a wheat background

Summary A series of hexaploid wheat lines containing zero, two or four doses of rye chromosome arm 1RS was used to investigate the response to changes in dosage by the rye genes when in a wheat background. The quantity of protein produced by the secalin protein genes contained on 1RS was directly related to the number of copies of 1RS present in the line. No response could be detected by representative wheat proteins suggesting that the increase in secalin protein observed was due to an increase in mRNA produced when four copies of the secalin gene was present. These results suggest that increasing the dosage of alien genes introgressed into wheat may be a useful tool for enhancing their expression.Mention of a trade name or proprietary product does not constitute a guarantee, warranty or recommendation of the product by the U.S. Department of Agriculture or the University of Missouri and does not imply its approval to the exclusion of other products that may be suitable.Contribution from the Missouri Agricultural Experiment Station. Journal Series No. 11,413     

Standard karyotype of Triticum umbellulatum and the characterization of derived chromosome addition and translocation lines in common wheat

A standard karyotype and a generalized idiogram of Triticum umbellulatum (syn. Aegilops umbellulata, 2n = 2x = 14) was established based on C-banding analysis of ten accessions of different geographic origin and individual T. umbellulatum chromosomes in T. aestivum — T. umbellulatum chromosome addition lines. Monosomic (MA) and disomic (DA) T. aestivum — T. umbellulatum chromosome addition lines (DA1U = B, DA2U = D, MA4U = F, DA5U = C, DA6U = A, DA7U = E = G) and telosomic addition lines (DA1US, DA1UL, DA2US, DA2UL, DA4UL, MA5US, (+ iso 5US), DA5UL, DA7US, DA7UL) were analyzed. Line H was established as a disomic addition line for the translocated wheat — T. umbellulatum chromosome T2DS·4US. Radiation-induced wheat — T. umbellulatum translocation lines resistant to leaf rust (Lr9) were identified as T40 = T6BL·6BS-6UL, T41 = T4BL·4BS-6UL, T44 = T2DS·2DL-6UL, T47 = Transfer = T6BS·6BL-6UL and T52 = T7BL·7BS-6UL. Breakpoints and sizes of the transferred T. umbellulatum segments in these translocations were determined by in situ hybridization analysis using total genomic T. umbellulatum DNA as a probeContribution no. 94-349-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, KS 66506-5502, USA     

The effect of ph mutations on homoeolgous pairing in hybrids of wheat with Triticum longissimum

Homoeologous pairing at metaphase-I was analyzed in wild-type, ph2b, and ph1b hybrids of wheat and a low-pairing type of T. longissimum in order to study the effect of ph mutations on the pairing of T. longissimum chromosomes with wheat chromosomes. Chromosomes of both species, and their arms, were identified by C-banding. The three types of hybrids, with low-, intermediate-, and high-pairing levels, respectively, exhibited a very similar pairing pattern which was characterized by the existence of two types, A-D and B-S¹, of preferential pairing. These results confirm that the S¹ genome of T. longissimum is closely related to the B genome of wheat. The possible use of ph1b and ph2b mutations in the transfer to wheat of genes from related species is discussed.     

Identification of C-banded chromosomes in meiosis of common wheat,Triticum aestivum L.

Summary The C-banding pattern of nine meiotic chromosomes of common wheat (Triticum aestivum L.) as described. In F₁s of crosses between monosomics of Chinese Spring and two Spanish wheat cultivars, univalent chromosomes were used to aid the recognition and analysis of the C-banding pattern for the individual chromosomes. The identification of one chromosome involved in one translocation in Chinese Spring x Pané 247 has been made through heterochromatin bands observed in the chromosomes involved in multivalents.     

Chromosome structure of Triticum longissimum relative to wheat

Homoeologous pairing at meiotic metaphase I was analyzed in T. longissimum x T. aestivum hybrids in order to reconfirm the homoeologous relationships of T. longissimum chromosomes to wheat. Hybrids between T. longissimum and Chinese Spring carrying the Ph1 gene or theph1b mutation, which showed low and high pairing levels, respectively, were used. Chromosome arms associated at metaphase I were identified by C-banding. The homoeology of chromosomes 1S ^l , 2S ^l , 3S ^l , 5S ^l and 6S ^l to wheat group 1,2, 3, 5, and 6 chromosomes, respectively, was confirmed. Chromsome arms 4S ^l S and 7S ^l S showed normal homoeologous relationships to wheat. The 4S ^l L arm carries a translocated segment from 7S ^l L relative to wheat. The 7S ^l L arm seldom paired, likely because this arm lost a relatively long segment and received a very short segment in the interchange with 4S ^l L. Available data suggest that translocation 4S ^l L/7S ^l L arose in the evolution of T. longissimum, which implies that this species was not the donor of the B genome of wheat.     

The meiotic pairing of nine wheat chromosomes

Summary The meiotic identification of nine pairs of chromosomes at metaphase I of meiosis of Triticum aestivum (B genome, 4A and 7A) has been achieved using a Giemsa C-banding technique. As a result, the analysis of the pairing of each chromosome arm in disomic and monosomic intervarietal hybrids between Chinese Spring and the Spanish cultivar Pané 247 could be carried out. Differences in the chiasmata frequencies per chromosome arm cannot be explained on the basis of relative arm lengths only. Possible effects of arm-to-arm heterochromatic differences on meiotic pairing are discussed.     

Dosage effects of chromosomes of homoeologous groups 1 and 6 upon bread-making quality in hexaploid wheat

Summary The endosperm storage proteins, glutenin and gliadin, are major determinants of bread-making quality in hexaploid wheat. Genes encoding them are located on chromosomes of homoeologous groups 1 and 6. Aneuploid lines of these groups in spring wheat cultivar Chinese Spring have been used to investigate the effect of varying the dosage of chromosomes and chromosome arms upon bread-making quality, where quality has been assessed using the SDS-sedimentation test. Differences between the group 1 chromosomes for quality were greater than those between the group 6 chromosomes. The chromosomes were ranked within homoeologous groups for their effect on quality as follows (>=better quality): 1D>1B>1A and 6A>6B=6D. The relationship of chromosome dosage with quality was principally linear for four of the chromosomes, but not for 6B and 6D. Increases in the dosage of 1B, 6A and, especially, 1D, were associated with significant improvements in quality, whereas increases in the dosage of 1A were associated with reductions in quality. The effects of 1A and 1D were such that the best genotype for quality was nullisomic 1A-tetrasomic 1D. For group 1, effects of the long arm appeared in general to be more important than effects of the short arm. For group 6, effects were found associated with the long arms as well as with the short arms, a surprising result in view of the absence of genes encoding storage proteins on the long arms. Significant interactions were found between chromosomes and genetic backgrounds, and between individual chromosomes. Analysis of trials grown over two years demonstrated that, although additive environmental differences over years and genotype x years interaction were present, they were relatively small in magnitude compared with purely genetic differences.     

The addition of Dasypyrum villosum (L.) Candargy chromosomes to durum wheat (Triticum durum Desf.)

Summary Six monosomic addition lines were produced in which different Dasypyrum villosum (L.) Candargy chromosomes were added to the chromosome complement of Triticum durum Desf. cv. Creso. Each added alien chromosome was found to have a specific effect on plant morphology and fertility. Transmission rate varied widely (from 7.5 to 27.7%) among the six univalent chromosomes. Different monotelosomic addition plants derived by a relatively high frequency of chromosome misdivision were isolated. The addition lines should be useful for studying Dasypyrum chromosome homoeology and the introduction of alien variation into durum and common wheats.Research supported by a grant from the Italian Research Council for Finalized Project IPRA. Sub-project Plant Breeding, Paper No. 1095     

Standard karyotype of Triticum searsii and its relationship with other S-genome species and common wheat

C-banding polymorphism was analyzed in 14 accessions of Triticum searsii from Israel, and a generalized idiogram of the species was established. One accession was homozygous for whole arm translocations T1S^sS·4S^sS and T1S^sL·4S^sL. C-banding analysis was also used to identify 7 T. aestivum cv Chinese Spring-T. searsii disomic chromosome addition lines, 14 ditelosomic chromosome addition lines, 21 disomic whole chromosome, and 31 ditelosomic chromosome substitution lines. The identity of these lines was further confirmed by meiotic pairing analysis. Sporophytic and gametophytic compensation tests were used to determine the homoeologous relationships of the T. searsii chromosomes. The results show that the T. searsii chromosomes do not compensate well for their wheat homoeologues. The C-banding patterns of T. searsii chromosomes are distinct from those of other S-genome species and from the B-genome chromosomes of wheat, indicating that T. searsii is not a direct B-genome donor species of T. turgidum and T. aestivum.Contribution No. 95-72-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, Kansas, USA     

Characterization of cytosolic phosphoglucoisomerase from immature wheat (Triticum aestivum L.) endosperm

Phosphoglucoisomerase from cytosol of immature wheat endosperm was purified 650-fold by ammonium sulphate fractionation, isopropyl alcohol precipitation, DEAE-cellulose chromatography and gel filtration through Sepharose CL-6B. The enzyme, with a molecular weight of about 130,000, exhibited maximum activity at pH 8.1. It showed typical hyperbolic kinetics with both fructose 6-P and glucose 6-P withK _m of 0.18 mM and 0.44mM respectively. On either side of the optimum pH, the enzyme had lower affinity for the substrates. Using glucose 6-P as the substrate, the equilibrium was reached at 27% fructose 6-P and 73% glucose 6-P with an equilibrium constant of 2.7. The ΔF calculated from the apparent equilibrium constant was +597 cal mol^-1. The activation energy calculated from the Arrhenius plot was 5500 cal mol^-1. The enzyme was completely inhibited by ribose 5-P, ribulose 5-P and 6-phosphogluconate, withK _i values of 0.17, 0.25 and 0.14 mM respectively. The probable role of the enzyme in starch biosynthesis is discussed.     

The chromosomal location of factors determining the presence of phenolic compounds in wheat (Triticum aestivum L.)

Summary Using thin-layer chromatography and nulli-tetrasomic and ditellosomic series of Triticum aestivum L. cv. Chinese Spring, it has been possible to relate the phenolic compounds found in adult plant leaves and 12 day-old seedling leaves with the chromosomes or chromosome arms 1 B, 2 BL, 3 BL, 5 A, 6 AL, 7 B and 7 DS.     

Molecular analysis of plants regenerated from embryogenic cultures of wheat (Triticum aestivum L.)

Total DNAs of plants regenerated from immature embryo-derived 2-month-old embryogenic calli of wheat (cultivars Florida 302, Chris, Pavon, RH770019) were probed with six maize mitochondrial genes (atpA, atp6, apt9, coxI, coxII, rrn18-rrn5), three hypervariable wheat mitochondrial clones (K, K3, X2), five random pearl millet mitochondrial clones (4A9, 4D1, 4D12, 4E1, 4E11) and the often-used wheat Nor locus probe (pTA71), in order to assess the molecular changes induced in vitro. In addition, protoplast-derived plants, and 24-month-old embryogenic and non-embryogenic calli and cell suspension cultures of Florida 302 were also analyzed. No variation was revealed by the wheat or millet mitochondrial clones. Qualitative variation was detected in the nonembryogenic suspension culture by three maize mitochondrial genes (coxI, rrn18-rrn5, atp6). A callus-specific 3.8-kb Hind III fragment was detected in all four cultivars after hybridization with the coxI gene. The organization of the Nor locus of the plants regenerated from Florida 302 and Chris was stable when compared to their respective control plants and calli. The Nor locus in regenerants of Pavon and RH, on the other hand, was found to be variable. However, Nor locus variability was not observed in 14 individual seed-derived control plants from either Pavon or RH sources. In Pavon, a 3.6-kb Taq I or a 5.6-kb Bam HI+ Eco RI fragment was lost after regeneration. In one of the RH regenerants, which lost a fragment, an additional fragment was observed.