Synthetic Wheat Accessions Research Articles

MORPHO-AGRONOMIC, CYTOGENETIC AND MOLECULAR CHARACTERIZATION OF SYNTHETIC WHEAT ACCESSIONS AS A POTENTIAL GERMPLASM FOR PLANT BREEDING

Synthetic hexaploid wheat (AABBDD) is produced by using the tetraploid Triticum turgidum var. durum (AABB) and the diploid Aegilops tauschii (DD) as parents. This cross has allowed genetic variability to be transferred from parental to other wheat hexaploid accessions, lines or cultivars. This transference may occur not only of variable disease resistance genes but also traits involving quality and tolerance to abiotic stresses. We evaluated and characterized the genetic diversity and stability of synthetic wheat accessions that can be used in breeding programs due to the presence of desirable characteristics. Fifty synthetic accessions were investigated regarding their morphological and agronomic characteristics, presence of micronuclei in tetrads and genetic similarity based on molecular markers. Four commercial cultivars were used as controls. Depending on their proposed use, some genotypes were characterised as suitable for breeding programs based on their morphological traits, genetic stability or genetic diversity, or because of a combination of these factors.

Genetic Analysis and Transfer of Favorable Exotic QTL Alleles for Grain Yield Across D Genome Using Two Advanced Backcross Wheat Populations.

Hexaploid wheat evolved through a spontaneous hybridization of tetraploid wheat (Triticum turgidum, AABB) with diploid wild grass (Aegilops tauschii, DD). Recent genome sequencing found alarmingly low genetic diversity and abundance of repeated sequences across D genome as compared to AB genomes. This characteristic feature of D genome often results in a low recombination rate and abrupt changes in chromosome, which are the major hurdles to utilize the genetic potential of D genome in wheat breeding. In the present study, we evaluated two advanced backcross populations designated as B22 (250 BC2F3:6 lines) and Z86 (150 BC2F3:6 lines) to test their yield potential and to enrich the D genome diversity simultaneously. The populations B22 and Z86 were derived by crossing winter wheat cultivars Batis and Zentos with synthetic hexaploid wheat accessions Syn022L and Syn086L, respectively. These populations were genotyped using SNP markers and phenotyped for yield traits in ten environments in Germany. Marker analysis identified lower recombination rate across D genome as compared to A and B genomes in both populations. Further, we compared the genotype data with the trait grain yield to identify favorable exotic introgressions from synthetic wheat accessions. QTL analysis identified seven and 13 favorable exotic QTL alleles associated with enhancement or at least stable grain yield in populations B22 and Z86, respectively. These favorable introgressions were located on all chromosomes from 1D to 7D. The strongest exotic QTL allele on chromosome 1D at SNP marker RAC875_c51493_471 resulted in a relative increase of 8.6% in grain yield as compared to cultivated allele. The identified exotic introgressions will help to refine useful exotic chromosome segments for their incorporation for improving yield and increasing D genome diversity among cultivated varieties.

Genetic stability in synthetic wheat accessions: cytogenetic evaluation as a support in breeding programs

ABSTRACT: Synthetic wheat is developed by crossing tetraploid species ( Triticum turgidum , AABB) with a diploid species ( Aegilops tauschii , DD), followed by chromosome duplication through the use of colchicine to restore the resultant sterile hybrid to a fertile hexaploid plant. The main importance of producing synthetically improved wheat is to increase their genetic variability and to incorporate genes that code for resistance to biotic and abiotic stressors. This study aimed to evaluate the presence of micronuclei (MN) and the meiotic index (MI) in the tetrad phase in synthetic wheat accessions and cultivars ( Triticum aestivum ) stored at the Germplasm Bank of Embrapa Trigo (Brazil), in order to identify and select genetically stable accessions for plant improvement. Five plants were collected by genotype, prior to anthesis, and the tissues were fixed in Carnoy solution. Cytological slides were prepared by the smash method, and the cells were dyed with 1% acetocarmine and observed under an optical microscope. Presence of MN was observed in all genotypes analyzed, and variability of genetic stability was reported in the two years of analysis. In 2014, the highest MI of synthetic wheat accessions was 96.86% and the lowest was 46.32%. In 2015, the highest MI was 96.60% and the lowest was 47.96%. Based on the results, some genotypes were considered meiotically stable and suitable for use in wheat breeding programs.

Meiotic Behavior of Wild, Synthetic and Cultivated Wheats

Wild relatives of bread wheat are potential sources of valuable genetic materials for wheat improvement. Genomic relationship and cross-ability between plant species can be deduced from chromosomal structure, size and behavior during meiotic division. In this study, the meiotic behavior of 21 wheat genotypes possessing the 3 ploidy levels of diploid, tetraploid and hexaploid and belonging to 3 wild, cultivated and synthetic growing statuses was investigated. The results indicated that the average number of ring bivalents at metaphase I ranged from 60 to 100% in the studied genotypes with the lowest rate belonging to the diploid wild relative wheat species. Four meiotic abnormalities including (1) precocious chromosome migration to the poles at metaphase I, (2) laggard chromosomes at anaphase I and telophase I, (3) chromosome stickiness and chromosome bridge at anaphase I and (4) formation of micronuclei at telophase I and in the tetrad cells were found in the studied genotypes. The highest meiotic abnormalities were found in synthetic wheat accessions. The average value of the meiotic index for the studied wheat genotypes was above 99%, revealing their normal meiotic behavior.

Identification, gene postulation and molecular tagging of a stripe rust resistance gene in synthetic wheat CI142

Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most serious diseases of wheat ( Triticum aestivum L.) worldwide. Of 94 Triticum durum/Aegilops tauschii synthetic wheat accessions tested, CI142 (Garza/Boy// Ae. squarrosa 271) was found to be resistant to 6 Chinese PST races. The resistance to stripe rust in CI142 was proven to be controlled by a single dominant gene, tentatively designated YrC142 . Gene postulation showed that the pathogenic specificity of CI142 is different from 21 other lines possessing known resistance genes, such as Yr10, Yr15, Yr24 , and Yr26 , located on chromosome 1B. Bulked segregant analysis (BSA) and F 2 segregation analysis of the CI142/Mingxian 169 cross were used to analyse the SSR markers linked to YrC142 . Five SSR markers were found to be closely associated with YrC142 in the order Xwmc419-YrC142-Xgwm273, Xbarc187-Xgwm18-Xwmc626 , in which the relative genetic distances of these SSR loci to the gene YrC142 were 5.4, 0.8, 0.8, 1.0, and 2.4 cM...