Analysis of inheritance of morphological and biochemical characters introgressed into common wheat from Aegilops speltoides Tausch

Genetic control of some morphological traits and the gliadin composition were examined in plants of two lines of common wheat carrying genes introgressed from the wild diploid cereal Aegilops speltoides. Leaf hairiness was shown to be controlled by a single introgressed dominant gene that was not allelic to the known common wheat gene Hl1. Waxlessness of the whole plant is controlled by the introgressed from Ae. speltoides inhibitor gene allelic to gene W1 located on chromosome 2B. This gene was epistatic to the introgressed gene controlling spike waxlessness. The introgressed gene of spike color was shown to be allelic to Rg1 located on chromosome 1B of common wheat. However, the former gene proved to be linked to an allele of the Gli-B1 locus other than in wheat.     

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.     

Construction and study of leaf rust-resistant common wheat lines with translocations of <Emphasis Type="Italic">Aegilops speltoides</Emphasis> Tausch. Genetic material

Genotyping was performed for the leaf rust-resistant line 73/00i (Triticum aestivum × Aegilops speltoides). Fluorescence in situ hybridization (FISH) with probes Spelt1 and pSc119.2 in combination with microsatellite analysis were used to determine the locations and sizes of the Ae. speltoides genetic fragments integrated into the line genome. Translocations were identified in the long arms of chromosomes 5B and 6B and in the short arm of chromosome 1B. The Spelt1 and pSc119.2 molecular cytological markers made it possible to rapidly establish lines with single translocation in the long arms of chromosomes 5B and 6B. The line carrying the T5BS · 5BL-5SL translocation was highly resistant to leaf rust, and the lines carrying the T6BS · 6BL-6SL translocation displayed moderate resistance. The translocations differed in chromosomal location from known leaf resistance genes transferred into common wheat from Ae. speltoides. Hence, it was assumed that new genes were introduced into the common wheat genome from Ae. speltoides. The locus that determined high resistance to leaf rust and was transferred into the common wheat genome from the long arm of Ae. speltoides chromosome 5S by the T5BS · 5BL-5SL translocation was preliminarily designated as LrAsp5.     

Comparative genetic maps reveal extreme crossover localization in the Aegilops speltoides chromosomes

A total of 137 loci were mapped in Aegilops speltoides, the closest extant relative of the wheat B genome, using two F₂ mapping populations and a set of wheat-Ae. speltoides disomic addition (DA) lines. Comparisons of Ae. speltoides genetic maps with those of Triticum monococcum indicated that Ae. speltoides conserved the gross chromosome structure observed across the tribe Triticeae. A putative inversion involving the short arm of chromosome 2 was detected in Ae. speltoides. A translocation between chromosomes 2 and 6, present in the wheat B genome, was absent. The ligustica/aucheri spike dimorphism behaved as allelic variation at a single locus, which was mapped in the centromeric region of chromosome 3. The genetic length of each chromosome arm was about 50 cM, irrespective of its physical length. Compared to T. monococcum genetic maps, recombination was virtually eliminated from the proximal 50–100 cM and was localized in short distal regions, which were often expanded compared to the T. monococcum maps. The wheat B genome and the genome of Ae. longissima, a close relative of Ae. speltoides, do not show the extreme localization of crossovers observed in Ae. speltoides.     

Development of wheat lines carrying stem rust resistance gene <Emphasis Type="Italic">Sr39</Emphasis> with reduced <Emphasis Type="Italic">Aegilops speltoides</Emphasis> chromatin and simple PCR markers for marker-assisted selection

The use of major resistance genes is a cost-effective strategy for preventing stem rust epidemics in wheat crops. The stem rust resistance gene Sr39 provides resistance to all currently known pathotypes of Puccinia graminis f. sp. tritici (Pgt) including Ug99 (TTKSK) and was introgressed together with leaf rust resistance gene Lr35 conferring adult plant resistance to P. triticina (Pt), into wheat from Aegilops speltoides. It has not been used extensively in wheat breeding because of the presumed but as yet undocumented negative agronomic effects associated with Ae. speltoides chromatin. This investigation reports the production of a set of recombinants with shortened Ae. speltoides segments through induction of homoeologous recombination between the wheat and the Ae. speltoides chromosome. Simple PCR-based DNA markers were developed for resistant and susceptible genotypes (Sr39#22r and Sr39#50s) and validated across a set of recombinant lines and wheat cultivars. These markers will facilitate the pyramiding of ameliorated sources of Sr39 with other stem rust resistance genes that are effective against the Pgt pathotype TTKSK and its variants.     

Genetic analysis of the traits introgressed from <Emphasis Type="Italic">Aegilops speltoides</Emphasis> Tausch. to bread wheat and determined by chromosome 5A genes

A winter bread wheat accession from the Arsenal collection was genetically examined to study the results of introgression, which substantially changed the physiological and morphological traits of the original spring cultivar Rodina. Apart from its winter habit, the accession was characterized by awned speltoid spikes, suggesting introgression into chromosome 5A, which carries marker genes in the order Vrn-A1-Q-B1. Genetic analysis showed that the chromosome fragment introgressed from Aegilops speltoides recombined well with the homeologous region of bread wheat chromosome 5A in the region between the Vrn-A1 and Q genes. Recombination between the Vrn-A1 and B1 genes was not detected, and it was assumed that the order of the marker genes of chromosome 5A was inverted to produce Q-Vrn-A1-B1. When the winter introgression line was crossed with Triticum spelta L., an interaction of two dominant genes determining the spike character was for the first time detected in F₁, increasing the spike length and the number of spikelets, and followed with transgression in F₂. It was assumed that Ae. speltoides had a homeoallelic speltoid gene, which was designated as Q ^S .     

Hybrid and Monosomic Analyses of Smoky Coloration of the Ear in Common Wheat

The results of the hybrid and monosomic analyses of smoky ear coloration in the common wheat variety columbina are reported. The character has been found to be monogenic, and its gene has been located to chromosome 1DS. The smoky ear coloration is determined by an allele of gene Rg2 introgressed to wheat from Aegilops tauschii.__________Translated from Genetika, Vol. 41, No. 8, 2005, pp. 1147–1149.Original Russian Text Copyright © 2005 by Pshenichnikova, Bokarev, Shchukina.     

New 18S·26S ribosomal RNA gene loci: chromosomal landmarks for the evolution of polyploid wheats

Three new 18S·26S rRNA gene loci were identified in common wheat by sequential N-banding and in situ hybridization (ISH) analysis. Locus Nor-A7 is located at the terminal area of the long arm of 5A in both diploid and polyploid wheats. Locus Nor-B6 is located in N-band 1BL2.5 of the long arm of chromosome 1B in Triticum turgidum and Triticum aestivum. ISH sites, similar to Nor-B6, were also detected on the long arms of chromosomes 1G in Triticum timopheevii and 1S in Aegilops speltoides, but their locations on the chromosomes were different from that of Nor-B6, indicating possible chromosome rearrangements in 1GL and 1BL during evolution. The third new locus, Nor-D8, was only found on the short arm of chromosome 3D in the common wheat Wichita. The loss of rRNA gene locus Nor-A3 and gain of repetitive DNA sequence pSc119 on the terminal part of 5AS suggest a structural modification of 5AS. Comparative studies of the location of the 18S·26S rRNA gene loci in polyploid wheats and putative A and B (G) genome progenitor species support the idea that: (1) Triticum monococcum subsp. urartu is the donor of both the A and A^t genome of polyploid wheats. (2) Ae. speltoides is closer to the B and G genome of polyploid wheats than Aegilops longissima and is the most probable progenitor of these two genomes.     

Inheritance of Awnlessness in Tetraploid Wheat Species

Awn absence was shown to be inherited as a dominant character in the tetraploid wheat species Triticum dicoccum (Schrank) Schuebl. and T. durum Desf. but as a recessive one in T. aethiopicum Jakubz. The monogenic control of the character was demonstrated for all studied species. In accessions of emmer and durum wheat, the character is controlled by the dominant gene B1, located on chromosome 5A, and in Ethiopian wheat, by a recessive gene, which we designated asawn. The recessive awn gene was localized on chromosome 3B ofT. aethiopicum with the use of D-genome disomic substitution lines of cultivar Langdon.     

Homoeologous relationships of Aegilops speltoides chromosomes to bread wheat

 Homoeologous pairing at metaphase I was analysed in the standard-type, ph2b and ph1b hybrids of Triticum aestivum (AABBDD) and Aegilops speltoides (SS). Data from relative pairing affinities were used to predict homoeologous relationships of Ae. speltoides chromosomes to wheat. Chromosomes of both species, and their arms, were identified by C-banding. The Ae. speltoides genotype carried genes that induced a high level of homoeologous pairing in the three types of hybrids analyzed. All arms of the seven chromosomes of the S genome showed normal homoeologous pairing, which implies that no apparent chromosome rearrangements occurred in the evolution of Ae. speltoides relative to wheat. A pattern of preferential pairing of two types, A-D and B-S, confirmed that the S genome is very closely related to the B genome of wheat. Although this pairing pattern was also reported in hybrids of wheat with Ae. longissima and Ae. sharonensis, a different behaviour was found in group 5 chromosomes. In the hybrids of Ae. speltoides, chromosome 5B-5S pairing was much more frequent than 5D-5S, while these chromosome associations reached similar frequencies in the hybrids of Ae. longissima and Ae. sharonensis. These results are in agreement with the hypothesis that the B genome of wheat is derived from Ae. speltoides. Received: 8 January 1998 / Accepted: 4 February 1998     

Multiple genetic pathways for seed shattering in the grasses

Shattering is an essential seed dispersal mechanism in wild species. It is believed that independent mutations at orthologous loci led to convergent domestication of cereal crops. To investigate genetic relationships of Triticeae shattering genes with those of other grasses, we mapped spike-, barrel- (B-type), and wedge-type (W-type) spikelet disarticulation genes in wheat and its wild relatives. The Br1 gene for W-type disarticulation was mapped to a region delimited by Xpsr598 and Xpsr1196 on the short arm of chromosomes 3A in Triticum timopheevii and 3S in Aegilops speltoides. The spike- and W-type disarticulation genes are allelic at Br1 in Ae. speltoides. The B-type disarticulation gene, designated as Br2, was mapped to an interval of 4.4 cM between Xmwg2013 and Xpsr170 on the long arm of chromosome 3D in Aegilops tauschii, the D-genome donor of common wheat. Therefore, B- and W-type disarticulations are governed by two different orthologous loci on group-3 chromosomes. Based on map position, orthologs of Br1 and Br2 were not detected in barley, maize, rice, and sorghum, indicating multiple genetic pathways for shattering in grasses. The implications of the mapping results are discussed with regard to the evolution of polyploid wheat and domestication of cereals.Supplementary material is available in the online version of this article at     

Development of a molecular marker for the adult plant leaf rust resistance gene Lr35 in wheat

The objective of this work was to develop a marker for the adult plant leaf rust resistance gene Lr35. The Lr35 gene was originally introgressed into chromosome 2B from Triticum speltoides, a diploid relative of wheat. A segregating population of 96 F ₂ plants derived from a cross between the resistant line ThatcherLr35 and the susceptible variety Frisal was analysed. Out of 80 RFLP probes previously mapped on wheat chromosome 2B, 51 detected a polymorphism between the parents of the cross. Three of them were completely linked with the resistance gene Lr35. The co-segregating probe BCD260 was converted into a PCR-based sequence-tagged-site (STS) marker. A set of 48 different breeding lines derived from several European breeding programs was tested with the STS marker. None of these lines has a donor for Lr35 in its pedigree and all of them reacted negatively with the STS marker. As no leaf rust races virulent on Lr35 have been found in different areas of the world, the STS marker for the Lr35 resistance gene is of great value to support the introgression of this gene in combination with other leaf rust (Lr) genes into breeding material by marker-assisted selection. Received: 14 December 1998 / Accepted: 30 January 1999     

Molecular cytogenetic identification of a novel dwarf wheat line with introgressed <Emphasis Type="Italic">Thinopyrum ponticum</Emphasis> chromatin

Novel dwarfing germplasms and dwarfing genes are valuable for the wheat breeding. A novel semi-dwarf line, 31505-1, with reduced height compared with its common wheat parent, was derived from a cross between common wheat and Thinopyrum ponticum. Cytological studies demonstrated that 31505-1 contained 42 chromosomes and formed 21 bivalents at meiotic metaphase I. Genomic in situ hybridization (GISH) analysis showed that 31505-1 had no large Th. ponticum chromosome fragments. Fluorescence in situ hybridization (FISH) results revealed the absence of a pAs1 hybridization band on 2DL chromosome of 31505-1. Two SSR markers (Xwmc41 and Xcfd168) and two STS markers (Xmag4059 and Xmag3596), which were located on 2D chromosome, amplified unique bands of Th. Ponticum in 31505-1. These revealed presence of an introgressed Th. ponticum segment in 2DL chromosome of dwarf line 31505-1, although the alien segment could not be detected by GISH.     

The effect of B chromosomes on meiotic and pre-meiotic spindles and chromosome pairing in Triticum/Aegilops hybrids

Diploid populations of Aegilops mutica and Aegilops speltoides containing B chromosomes have been used as male parents in crosses with aneuploid genotypes of Triticum aestivum to investigate the effect of B chromosomes on meiotic homologous and homoeologous chromosome pairing. F₁ hybrids of T. aestivum/Ae. mutica and T. aestivum/Ae. speltoides segregated into four classes with regard to the degree of meiotic chromosome pairing, irrespective of the presence of B chromosomes. The B chromosomes do not introduce factors altering the level of pairing other than that due to the natural allelic and gene variation occurring in the diploids. Similarly no reduction in pairing of homologous chromosomes was observed in genotypes in which pairs of homologues co-existed with B chromosomes. However, a significant drop in chiasma frequency was observed in F₁ hybrids of T. aestivum × Ae. mutica with B chromosomes and T. aestivum × Ae. mutica nullisomic for wheat chromosome 5D with B chromosomes, in temperature regimes of 12° C. No asynapsis occurred in similar hybrids in the absence of Mutica B chromosomes at low temperatures. The low-temperature sensitive phase lies early in the pre-meiotic interphase. In this instance the Mutica B chromosomes are interacting with specific gene loci of the A chromosomes. Synaptic pairing has been observed between A and B chromosomes in Ae. mutica. A high frequency of pollen mother cells with twice the number of chromosomes was observed in hybrids in the presence of Mutica B chromosomes due to failure of spindle formation at the last pre-meiotic mitosis. Meiotic spindle irregularities occurred in hybrids containing Speltoides B chromosomes. Hybrids of Ae. speltoides + B's X Ae. mutica + B's displayed the mitotic and meiotic spindle abnormalities introduced by the presence of the B chromosomes of each parent.     

Molecular cytogenetic and genomic analyses reveal new insights into the origin of the wheat B genome

Key message

This work pinpointed the goatgrass chromosomal segment in the wheat B genome using modern cytogenetic and genomic technologies, and provided novel insights into the origin of the wheat B genome.

Abstract

Wheat is a typical allopolyploid with three homoeologous subgenomes (A, B, and D). The donors of the subgenomes A and D had been identified, but not for the subgenome B. The goatgrass Aegilops speltoides (genome SS) has been controversially considered a possible candidate for the donor of the wheat B genome. However, the relationship of the Ae. speltoides S genome with the wheat B genome remains largely obscure. The present study assessed the homology of the B and S genomes using an integrative cytogenetic and genomic approach, and revealed the contribution of Ae. speltoides to the origin of the wheat B genome. We discovered noticeable homology between wheat chromosome 1B and Ae. speltoides chromosome 1S, but not between other chromosomes in the B and S genomes. An Ae. speltoides-originated segment spanning a genomic region of approximately 10.46 Mb was detected on the long arm of wheat chromosome 1B (1BL). The Ae. speltoides-originated segment on 1BL was found to co-evolve with the rest of the B genome. Evidently, Ae. speltoides had been involved in the origin of the wheat B genome, but should not be considered an exclusive donor of this genome. The wheat B genome might have a polyphyletic origin with multiple ancestors involved, including Ae. speltoides. These novel findings will facilitate genome studies in wheat and other polyploids.

     

Identification of alien chromatin specifying resistance to wheat streak mosaic and greenbug in wheat germ plasm by C-banding and in situ hybridization

Summary The chromosome constitutions of eight wheat streak mosaic virus (WSMV)-resistant lines, three of which are also greenbug resistant, derived from wheat/ Agropyron intermedium/Aegilops speltoides crosses were analyzed by C-banding and in situ hybridization. All lines could be traced back to CI15092 in which chromosome 4A is substituted for by an Ag. intermedium chromosome designated 4Ai-2, and the derived lines carry either 4Ai-2 or a part of it. Two (CI17881, CI17886) were 4Ai-2 addition lines. CI17882 and CI17885 were 4Ai-2-(4D) substitution lines. CI17883 was a translocation substitution line with a pair of 6AL.4Ai-2S and a pair of 6AS.4Ai-2L chromosomes substituting for chromosome pairs 4D and 6A of wheat. CI17884 carried a 4DL.4Ai-2S translocation which substituted for chromosome 4D. CI17766 carried a 4AL.4Ai-2S translocation substituting for chromosome 4A. The results show that the 4Ai-2 chromosome is related to homoeologous group 4 and that the resistance gene(s) against WSMV is located on the short arm of 4Ai-2. In addition, CI17882, CI17884, and CI17885 contained Ae. speltoides chromosome 7S substituting for chromosome 7A of wheat. The greenbug resistance gene Gb5 was located on chromosome 7S.Contribution No. 90-515-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, Kan., USA     

Microsatellite mapping of <Emphasis Type="Italic">Ae. speltoides</Emphasis> and map-based comparative analysis of the S,G, and B genomes of Triticeae species

The first microsatellite linkage map of Ae. speltoides Tausch (2n = 2x = 14, SS), which is a wild species with a genome closely related to the B and G genomes of polyploid wheats, was developed based on two F₂ mapping populations using microsatellite (SSR) markers from Ae. speltoides, wheat genomic SSRs (g-SSRs) and EST-derived SSRs. A total of 144 different microsatellite loci were mapped in the Ae. speltoides genome. The transferability of the SSRs markers between the related S, B, and G genomes allowed possible integration of new markers into the T. timopheevii G genome chromosomal maps and map-based comparisons. Thirty-one new microsatellite loci assigned to the genetic framework of the T. timopheevii G genome maps were composed of wheat g-SSR (genomic SSR) markers. Most of the used Ae. speltoides SSRs were mapped onto chromosomes of the G genome supporting a close relationship between the G and S genomes. Comparative microsatellite mapping of the S, B, and G genomes demonstrated colinearity between the chromosomes within homoeologous groups, except for intergenomic T6A^tS.1G, T4AL.5AL.7BS translocations. A translocation between chromosomes 2 and 6 that is present in the T. aestivum B genome was found in neither Ae. speltoides nor in T. timopheevii. Although the marker order was generally conserved among the B, S, and G genomes, the total length of the Ae. speltoides chromosomal maps and the genetic distances between homoeologous loci located in the proximal regions of the S genome chromosomes were reduced compared with the B, and G genome chromosomes.     

Morphological characterization and inheritance of leaf hairiness in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) as analyzed by computer-aided phenotyping

Computer-aided image processing was used to study the morphology of leaf hairiness in the wheat cultivars Saratovskaya 29 and Golubka, as well as the introgressed line 102/00ⁱ of the cultivar Rodina carrying the gene for leaf hairiness introgressed from Aegilops speltoides. Morphological differences in leaf hairiness were detected and described in detail. The genetic control of hairiness was studied in two cultivars (Golubka and Saratovskaya 29) with similar hairiness patterns. Crossing these cultivars with the cultivar Rodina showed a monogenic inheritance in the cultivar Golubka and a digenic inheritance in the cultivar Saratovskaya 29, which has a denser hairiness. In the line 102/00ⁱ and the cultivar Golubka, the number of trichomes was positively correlated with their mean length. The cultivar Golubka was used as an example to study the effect of environmental conditions on the formation of hairiness. Plants of this cultivar were found to form more but shorter trichomes under field conditions.     

Genetics of growth habit (spring vs winter) in common wheat: confirmation of the existence of dominant gene Vrn4

The number of dominant Vrn genes in common wheat, Triticum aestivum L., is estimated. Data were obtained supporting Pugsley's and Gotoh's data on the presence of a dominant gene Vrn4 in near-isogenic line 'Triple Dirk F'. The presence of a dominant gene Vrn4 in line 'Gabo-2' of cultivar 'Gabo', which was used by Pugsley as a donor of the gene Vrn4 for the near-isogenic line 'Triple Dirk F', was also confirmed. The Vrn2 and Vrn4 relationship and their chromosomal location are discussed. It was demonstrated that the dominant Vrn8 gene which was introgressed from Triticum sphaerococcum to common wheat by Stelmakh and Avsenin is allelic to Vrn4. While genes Vrn6^sc and Vrn7^sc which were introgressed from rye, Secale cereale L., by the above-mentioned authors are not allelic to the genes Vrn1, Vrn2, Vrn3 and Vrn4.Communicated by J.W. Snape