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Research has been conducted on natural population of wild emmer wheat Triticum dicoccoides. The role of the allele size constraints and genetic and clustering effects in simple sequence repeat diversity in this population has been investigated, and the details are reported.

Genome-wide mapping approaches in diverse populations are powerful tools to unravel the genetic architecture of complex traits. The main goals of our study were to investigate the potential and limits to unravel the genetic architecture and to identify the factors determining the accuracy of prediction of the genotypic variation of Fusarium head blight (FHB) resistance in wheat (Triticum aestivum L.) based on data collected with a diverse panel of 372 European varieties. The wheat lines were phenotyped in multi-location field trials for FHB resistance and genotyped with 782 simple sequence repeat (SSR) markers, and 9k and 90k single-nucleotide polymorphism (SNP) arrays. We applied genome-wide association mapping in combination with fivefold crossvalidations and observed surprisingly high accuracies of prediction for marker-assisted selection based on the detected quantitative trait loci (QTLs). Using a random sample of markers not selected for marker-trait associations revealed only a slight decrease in prediction accuracy compared with marker-based selection exploiting the QTL information. The same picture was confirmed in a simulation study, suggesting that relatedness is a main driver of the accuracy of prediction in marker-assisted selection of FHB resistance. When the accuracy of prediction of three genomic selection models was contrasted for the three marker data sets, no significant differences in accuracies among marker platforms and genomic selection models were observed. Marker density impacted the accuracy of prediction only marginally. Consequently, genomic selection of FHB resistance can be implemented most cost-efficiently based on low- to medium-density SNP arrays. [ABSTRACT FROM AUTHOR]

This study investigated allele size constraints and clustering, and genetic effects on microsatellite (simple sequence repeat, SSR) diversity at 28 loci comprising seven types of tandem repeated dinucleotide motifs in a natural population of wild emmer wheat, Triticum dicoccoides, from a shade vs sun microsite in Yehudiyya, northeast of the Sea of Galilee, Israel. It was found that allele distribution at SSR loci is clustered and constrained with lower or higher boundary. This may imply that SSR have functional significance and natural constraints. Genetic factors, involving genome, chromosome, motif, and locus significantly affected SSR diversity. Genome B appeared to have a larger average repeat number (ARN), but lower variance in repeat number (σ²ARN), and smaller number of alleles per locus than genome A. SSRs with compound motifs showed larger ARN than those with perfect motifs. The effects of replication slippage and recombinational effects (eg, unequal crossing over) on SSR diversity varied with SSR motifs. Ecological stresses (sun vs shade) may affect mutational mechanisms, influencing the level of SSR diversity by both processes. [ABSTRACT FROM AUTHOR]

The genetic diversity of common wheat hybrid lines Triticum aestivum/Triticum durum and Triticum aestivum/Triticum dicoccum (2n = 42, F(6-7)) using chromosome-specific microsatellite (SSR) markers and C-staining of chromosomes was studied. Cluster analysis of data obtained by 42 SSR markers indicated that the hybrid lines can be broken into three groups according to their origin. There were two cases of complete genetic similarity between lines 183(2)-2/184(1)-6 and-208-3/213-1, which were obtained using common wheat as the parental plants. In cross combinations, when the stabilization of the nuclear genome of hexaploid lines occurred against a background of the cytoplasmic genome of tetraploid wheats, there was a high level of divergence between sister lines, in some cases exceeding 50%. The evaluation of the degree of susceptibility of the lines to powdery mildew, leaf and stem rust, and septoria leafblotch was performed under different environmental conditions. It was shown that resistance to powdery mildew and leaf rust significantly depended on the region where assays were conducted. An evaluation of the field data showed that he lines 195-3, 196-1, and 221-1 with T. durum genetic material displayed complex resistance to fungal pathogens in Western Siberia and the Republic of Belarus. For lines 195-3 and 196-1, one shows a possible contribution of chromosomes 4B and 5B in the formation of complex resistance to diseases. Hybrid lines with complex resistance can be used to expand the genetic diversity of modern common wheat cultivars for genes of immunity.

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 short sequence repeat (SSR) markers was used to locate the T. timopheevii genome to 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 diversity 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 commercially valuable loci when new lines and cultivars are created.

Based on the cross (Triticum aestivum L. x Secale cereale L.) x T. aestivum L., wheat-rye substitution lines (2n = 42) were produced with karyotypes containing, instead of a pair of homologous wheat chromosomes, a homeologous pair of rye chromosomes. The chromosome composition of these lines was described by GISH and C-banding methods, and SSR analysis. The results of genomic in situ hybridization demonstrated that karyotype of these lines included one pair of rye chromosomes each and lacked wheat--rye translocations. C-banding and SSR markers were used to identify rye chromosomes and determine the wheat chromosomes at which the substitution occurred. The lines were designated 1R(1D), 2R(2D)2, 2R(2D)3, 3R(3B), 6R(6A)2. The chromosome composition of lines IR(1A), 2R(W)1, 5R(W), 5R(5A), and 6R(W)1, which were earlier obtained according to the same scheme for crossing, was characterized using methods of telocentric analysis, GISH, C-banding, and SSR analysis. These lines were identified as 1R(1A), 2R(2D)1, 5R(5D), 5R(5A), and 6R(6A)1, C-banding of chromosomes belonging to line 1R(1A) revealed the presence of two translocated chromosomes (3DS.3DL-del. and 4AL.W) during simultaneous amplification of SSR markers located on 3DL and 4AS arms. The "combined" long arm of the newly derived chromosome 4A is assumed to be formed from the long arm of chromosome 4AS itself and a deleted segment 3DL. All examined lines are cytologically stable, except for 3R(3B), which does not affect the stability of rye 3R chromosome transfer. Chromosome identification and classification of the lines will permit them to be models for genetic studies that can be used thereafter as promising "secondary gene pools" for the purpose of plant breeding.