E. B. Budashkina

Molecular Analysis of Leaf Rust-Resistant Introgression Lines Obtained by Crossing of Hexaploid Wheat Triticum aestivum with Tetraploid Wheat Triticum timopheevii

Twenty-four Triticum aestivum×T. timopheevii hybrid lines developed on the basis of five varieties of common wheat and resistant to leaf rust were analyzed by the use of microsatellite markers specific for hexaploid wheat T. aestivum. Investigation of intervarietal polymorphism of the markers showed that the number of alleles per locus ranged from 1 to 4, depending on the marker (2.5 on average). InT. timopheevii, amplification fragments are produced by 80, 55, and 30% of primers specific to the A, B, and D common wheat genomes, respectively. Microsatellite analysis revealed two major areas of introgression of the T. timopheevii genome: chromosomes of homoeological groups 2 and 5. Translocations were detected in the 2A and 2B chromosomes simultaneously in 11 lines of 24. The length of the translocated fragment in the 2B chromosome was virtually identical in all hybrid lines and did not depend on the parental wheat variety. In 15 lines developed on the basis of the Saratovskaya-29, Irtyshanka, and Tselinnaya-20, changes occurred in the telomeric region of the long arm of the 5A chromosome. Analysis with markers specific to the D genome suggested that introgressions of the T. timopheevii genome occurred in chromosomes of the D genome. However, the location of these markers on T. timopheevii chromosomes is unknown. Our data suggest that the genes for leaf rust resistance transferred from T. timopheevii to T. aestivum are located on chromosomes of homoeological group 2.

Genetic analysis and localization of loci controlling leaf rust resistance of Triticum aestivum × Triticum timopheevii introgression lines

Introgressive lines resulting from crossing common wheat Triticum aestivum with the tetraploid T. timopheevii are characterized by effective resistance to leaf rust caused by Puccinia triticina Eriks. Molecular analysis using 350 specific simple sequence repeat (SSR) markers determined localization of the T. timopheevii genome in chromosomes 1A, 2A, 2B, 5A, 5B, and 6B. A population of F2 offspring of crossing hybrid line 842-2 with common wheat cultivar Skala was obtained for mapping the loci controlling leaf rust resistance. Analysis of association of phenotypic and genotypic data by means of simple interval mapping (SIM) and composite interval mapping (CIM) has shown that the resistance of adult plants is determined by two loci in chromosomes 5B and 2A. The major locus QLr.icg-5B, transferred from T. timopheevii chromosome 5G mapped to the interval of microsatellite loci Xgwm408-Xgwm1257 controls 72% of the phenotypic variance of the trait. The other, minor locus QLr.icg-2A located to chromosome 2A at a distance of 10 cM from Xgwm312 accounts for 7% of the trait expression. Microsatellite markers located near these loci may be used for controlling the transfer of agronomically valuable loci when new lines and cultivars are created.

Intergenomic chromosome substitutions in wheat interspecific hybrids and their use in the development of a genetic nomenclature of Triticum timopheevii chromosomes.

The results of analysis of the genome formation in interspecific hybrids of Triticum aestivum with T. timopheevii are reviewed. The spectra of substitutions and rearrangements are shown to depend on the genotypes of the parental forms and on the direction of selection. The frequencies of substitutions of individual T. timopheevii chromosomes significantly vary and reflect the level of their divergence relative to the common wheat chromosomes. Some aspects of classification of the At- and G-genome chromosomes are discussed.

Microsatellite mapping of a leaf rust resistance gene transferred to common wheat from Triticum timopheevii

A leaf rust resistance gene transferred from the tetraploid wheat Triticum timopheevii (Zhuk.) Zhuk. (genomic composition: At At GG) into common wheat Triticum aestivum L. conditioned resistance at the seedling and adult plant stages in the introgression line ‘line 842-2’. To determine chromosome location and to map the resistance gene an F2 population from a cross between ‘line 842-2’ and susceptible wheat cultivar ‘Skala’ was developed and screened against leaf rust pathotype 77 (Puccinia triticina Erikss.). Microsatellite markers detected introgressions of the T. timopheevii genome on chromosomes 1A, 2A, 2B, 5B and 6B of ‘line 842-2’. Linkage analysis revealed an association between leaf rust resistance and microsatellite markers located on chromosome 5B. The markers Xgwm880 and Xgwm1257 were closely linked to the resistance gene with genetic distances of 7.7 cM and 10.4 cM, respectively. Infection type tests with three leaf rust isolates resulted in different patterns of infection types of ‘line 842-2’ and ‘Thatcher’ near-isogenic line with the Lr18 gene on chromosome 5B. The data corroborated the hypothesis of the diversity of the resistance coming from T. timopheevii. The resistance gene of the introgression ‘line 842-2’ seems to be different than Lr18 and therefore it was designated LrTt2.

Comparative cytological and molecular analysis of common wheat introgression lines containing genetic material of Triticum timopheevii Zhuk

A total of 40 introgression lines of common wheat (2 n = 42) Triticum aestivum L × T. timopheevii Zhuk., resistant to leaf rust and partly to powdery mildew, were examined. Based on cytological analysis of meiosis in pollen mother cells (PMC), hybrid lines were subdivided into two groups characterized by either stable or unstable meiosis. In cytologically stable lines, chromosome configuration at the MI stage of meiosis was mostly bivalent (21II) with small proportion of defect cells (almost 10%), which at most contained two univalents (20II + 2I). Cytologically unstable group was comprised of the lines, containing high proportions of cells with abnormal chromosome pairing in meiotic PMC, as well as the cells with multivalents, and the lines containing aneuploid plants. Localization of the T. timopheevii fragments performed with the use of SSR markers showed that the lines with unstable meiosis were characterized by higher numbers of introgressions compared to stable lines. The influence of certain chromosomes of T. timopheevii on chromosome pairing stability was also demonstrated. In cytologically unstable lines, the increased frequency of 2A substitutions along with the high frequency of introgression of T. timopheevii genetic material into chromosome 7A was observed. Multivalents were scored in all cases of introgression in chromosome 7A. It was suggested that the reason for the genome instability in hybrid forms lied in insufficient compensating ability of certain T. timopheevii chromosomes and/or their parts, involved into recombination processes.

A study of the storage proteins in the introgression lines of common wheat (Triticum aestivum L. × T. timopheevii Zhuk.) Resistant to brown leaf rust

Storage proteins, prolamins, were studied in ten introgression lines of common wheat bred with involvement of Triticum timopheevii (Tt) Zhuk. and five commercial hexaploid wheat cultivars. The lines are resistant to leaf rust. A comparative analysis of the storage proteins in the Triticum aestivum L. (Ta) introgression lines and the parental forms allowed us to (1) detect the active genes of prolamins on the chromosomes homeologous groups 1 and 6 in the introgression lines of T. aestivum and T. timopheevii; (2) clarify their origin; (3) identify the chromosome attribution of the products; (4) estimate the degree of introgression and postulate the introgression mechanisms; and (5) predict the bread-making quality of these introgression lines.

Wheat Microsatellites: The Prospects of Application for Gene Mapping and Analysis of the Reconstructed Genomes

Microsatellite markers Xgwmand Xgdmwere used to map the S1, S2, and S3genes of the induced sphaerococcoid mutants of Triticum aestivumL. and to analyze the introgressive lines of common wheat, obtained by crossing several common wheat cultivars to T. timopheeviiZhuk.; these lines carry the Lrgenes of resistance to leaf rust. All sphaerococcoid genes were linked to centromeric markers of the short and long arms of chromosomes of homoeologous group 3 of T. aestivum: the S1locus was located between the markers Xgdm72and Xgwm456; the S2gene, betweenXgwm845and Xgwm566; and the S3was located between Xgwm2and Xgwm720. The introgressive lines of common wheat carry the following substitutions from T. timopheevii, most of 2A and 2B and telomeric region of the 5AL chromosome in the line 821, the same introgression and also the completely substituted chromosome 4B in line 837, and the partially substituted chromosomes 2A and 2B in line 842. The introgression of the genomic material fromT. timopheeviiinto the chromosomes of homoeologous group 2 was the common trait of all three lines resistant to leaf rust. The authors discuss the feasibility of using microsatellite-derived data for analyzing nonmapped wheat species, linking new genes to wheat molecular genetic maps, and analyzing wheat genomes of diverse hybrid origins.

The study of agronomical traits determining the productivity of the Triticum aestivum/Triticum timopheevii introgression lines with resistance to fungal diseases

The development of resistant cultivars is one of the effective ways to protect common wheat T. aestivum L. from fungal pathogens. The gene pool of wild and cultivated wheat relatives is often used for widening the genetic diversity of the resistance genes. However, the alien genetic material introgressed into the wheat genome can contain genetic factors negatively affecting agronomically important traits. The T. aestivum/T. timopheevii introgression lines originating from different common wheat cultivars have characteristically good resistance to leaf rust and powdery mildew. A comparative assessment of these lines and the initial wheat varieties during four field seasons revealed the significant effect of environmental factors on the phenotypic differences between traits relevant to productivity. The averaged data obtained for individual introgression lines and for cross combinations revealed both positive and negative tendencies in the variations of the agronomical traits. The positive effects include a significant increase in the numbers of tillers and spikelets per spike of the lines originating from cv. Skala. A reduction in spike productivity was found in the groups of lines originating from cv. Tselinnaya 20 and cv. Novosibirskaya 67. However, no significant differences in the 1000-grain weight were found between most lines and the original wheat cultivars. The analysis of the data obtained showed no apparent correlation between the reduction of agronomic traits and the amount of alien genetic material introgressed into the common wheat genome. T. aestivum/T. timopheevii introgression lines can be used as a source of resistance genes without reducing the yield of wheat cultivars.

Molecular diversity of common wheat introgression lines (T. aestivum/T. timopheevii)

We investigated genetic diversity of T. aestivum/T. timopheevii introgression lines in relation to microsatellite loci and resistance to fungal diseases. The genotyping of hybrid lines and parental cultivars of common wheat with 143 Simple Sequence Repeat (SSR) markers revealed, respectively, 521 and 440 alleles or 3.24/2.73 alleles on average per microsatellite locus. A comparison of individual chromosomes with respect to the indices of genetic diversity revealed that chromosomes 4D and 5D show the lowest diversity for SSR loci, both in parents and hybrid lines, while chromosomes 5B and 6A presented the highest indices (0.62–0.68). Evaluation of SSR polymorphisms and indices in three genomes of introgression wheat lines revealed that chromosomes of genome B presented higher indices than genomes A and D (B > A > D), which may be the result of alien introgression in these chromosomes. A comparison of the results of the molecular and phytopathological tests indicates that despite the stringent selection for resistance to leaf rust during early generations, and a large number of subsequent selfing generations, the genetic diversity of introgression lines, with respect to microsatellite loci, is preserved, which is indicative of the stability of the alien genetic material transmitted to the common wheat genome.

A search for high-molecular-weight subunits of glutenin from Triticum timopheevi Zhuk. in the lines of common wheat (Triticum aestivum L. Triticum timopheevi Zhuk.)

The study is a continuation of investigation of prolamins in brown rust-resistant introgressive lines of common wheat, produced with participation of Triticum timopheeevi Zhuk. [1]. Two wheat lines with a substitution of the Glu-1 loci of T. timopheevi were identified. Line 684 had high-molecular-weight glutenin subunits encoded by 1Ax, as well as by 1Ay gene, which was silent in commercial lines. It was demonstrated that line 684 could serve as a source of the Glu-At1 locus. Line 186 carried the Glu-B1/Glu-G1 substitution. Comparative analysis of storage proteins from the introgression lines of common wheat Triticum aestivum L. with those from parental forms demonstrated polymorphism among the lines, resulted from natural varietal polymorphism, and introgression of the Glu-3 and Gli-1 loci from the genome of T. timopheevi.