Development, identification, and utilization of wheat-tetraploid Thinopyrum elongatum 4EL translocation lines resistant to stripe rust.

KEY MESSAGE: The new stripe rust resistance gene Yr4EL in tetraploid Th. elongatum was identified and transferred into common wheat via 4EL translocation lines. Tetraploid Thinopyrum elongatum is a valuable genetic resource for improving the resistance of wheat to diseases such as stripe rust, powdery mildew, and Fusarium head blight. We previously reported that chromosome 4E of the 4E (4D) substitution line carries all-stage stripe rust resistance genes. To optimize the utility of these genes in wheat breeding programs, we developed translocation lines by inducing chromosomal structural changes through 60Co-γ irradiation and developing monosomic substitution lines. In total, 53 plants with different 4E chromosomal structural changes were identified. Three homozygous translocation lines (T4DS·4EL, T5AL·4EL, and T3BL·4EL) and an addition translocation line (T5DS·4EL) were confirmed by the genomic in situ hybridization (GISH), fluorescence in situ hybridization (FISH), FISH-painting, and wheat 55 K SNP array analyses. These four translocation lines, which contained chromosome arm 4EL, exhibited high stripe rust resistance. Thus, a resistance gene (tentatively named Yr4EL) was localized to the chromosome arm 4EL of tetraploid Th. elongatum. For the application of marker-assisted selection (MAS), 32 simple sequence repeat (SSR) markers were developed, showing specific amplification on the chromosome arm 4EL and co-segregation with Yr4EL. Furthermore, the 4DS·4EL line could be selected as a good pre-breeding line that better agronomic traits than other translocation lines. We transferred Yr4EL into three wheat cultivars SM482, CM42, and SM51, and their progenies were all resistant to stripe rust, which can be used in future wheat resistance breeding programs.

Development and Characterization of a Novel Wheat-Tetraploid Thinopyrum elongatum 6E (6D) Disomic Substitution Line with Stripe Rust Resistance at the Adult Stage.

Stripe rust, which is caused by Puccinia striiformis f. sp. tritici, is one of the most devastating foliar diseases of common wheat worldwide. Breeding new wheat varieties with durable resistance is the most effective way of controlling the disease. Tetraploid Thinopyrum elongatum (2n = 4x = 28, EEEE) carries a variety of genes conferring resistance to multiple diseases, including stripe rust, Fusarium head blight, and powdery mildew, which makes it a valuable tertiary genetic resource for enhancing wheat cultivar improvement. Here, a novel wheat-tetraploid Th. elongatum 6E (6D) disomic substitution line (K17-1065-4) was characterized using genomic in situ hybridization and fluorescence in situ hybridization chromosome painting analyses. The evaluation of disease responses revealed that K17-1065-4 is highly resistant to stripe rust at the adult stage. By analyzing the whole-genome sequence of diploid Th. elongatum, we detected 3382 specific SSR sequences on chromosome 6E. Sixty SSR markers were developed, and thirty-three of them can accurately trace chromosome 6E of tetraploid Th. elongatum, which were linked to the disease resistance gene(s) in the wheat genetic background. The molecular marker analysis indicated that 10 markers may be used to distinguish Th. elongatum from other wheat-related species. Thus, K17-1065-4 carrying the stripe rust resistance gene(s) is a novel germplasm useful for breeding disease-resistant wheat cultivars. The molecular markers developed in this study may facilitate the mapping of the stripe rust resistance gene on chromosome 6E of tetraploid Th. elongatum.

Development and Identification of a Novel Wheat-Thinopyrum scirpeum 4E (4D) Chromosomal Substitution Line with Stripe Rust and Powdery Mildew Resistance.

Stripe rust caused by Puccinia striiformis f. sp. tritici and powdery mildew caused by Blumeria graminis f. sp. tritici are devastating diseases of wheat worldwide. Exploration of new disease-resistant genes from cultivated wheat and wild relatives are the most effective means of reducing the amounts of fungicides applied to combat these diseases. Thinopyrum scirpeum (2n = 4x = 28, EEEE) is an important promising reservoir of useful genes, including stripe rust and powdery mildew resistance, and may be useful for increasing wheat disease resistance. Here, we characterize a novel wheat-Th. scirpeum disomic substitution line, K16-730-3, and chromosome-specific markers were developed that can be used to trace the Th. scirpeum chromosome or chromosome segments transferred into wheat. Genomic in situ hybridization and fluorescence in situ hybridization analyses indicated that K16-730-3 is a new 4E (4D) chromosomal substitution line. Evaluation of seedling and adult disease responses revealed that K16-730-3 is resistant to stripe rust and powdery mildew. In addition, no obvious difference in grain yield was observed between K16-730-3 and its wheat parents. Genotyping-by-sequencing analyses indicated that 74 PCR-based markers can accurately trace chromosome 4E, which were linked to the disease resistance genes in the wheat background. Further marker validation analyses revealed that 13 specific markers can distinguish between the E-genome chromosomes of Th. scirpeum and the chromosomes of other wheat-related species. The new substitution line K16-730-3 carrying the stripe rust and powdery mildew resistance genes will be useful as novel germplasm in breeding for disease resistance. The markers developed in this study can be used in marker-assisted selection for increasing disease resistance in wheat.

Molecular cytogenetic characterization of wheat-Elymus repens chromosomal translocation lines with resistance to Fusarium head blight and stripe rust.

BACKGROUND: Fusarium head blight (FHB) caused by the fungus Fusarium graminearum Schwabe and stripe rust caused by Puccinia striiformis f. sp. tritici are devastating diseases that affect wheat production worldwide. The use of disease-resistant genes and cultivars is the most effective means of reducing fungicide applications to combat these diseases. Elymus repens (2n = 6x = 42, StStStStHH) is a potentially useful germplasm of FHB and stripe rust resistance for wheat improvement. RESULTS: Here, we report the development and characterization of two wheat-E. repens lines derived from the progeny of common wheat-E. repens hybrids. Cytological studies indicated that the mean chromosome configuration of K15-1192-2 and K15-1194-2 at meiosis were 2n = 42 = 0.86 I + 17.46 II (ring) + 3.11 II (rod) and 2n = 42 = 2.45 I + 14.17 II (ring) + 5.50 II (rod) + 0.07 III, respectively. Genomic and fluorescence in situ hybridization karyotyping and simple sequence repeats markers revealed that K15-1192-2 was a wheat-E. repens 3D/?St double terminal chromosomal translocation line. Line K15-1194-2 was identified as harboring a pair of 7DS/?StL Robertsonian translocations and one 3D/?St double terminal translocational chromosome. Further analyses using specific expressed sequence tag-SSR markers confirmed that the wheat-E. repens translocations involved the 3St chromatin in both lines. Furthermore, compared with the wheat parent Chuannong16, K15-1192-2 and K15-1194-2 expressed high levels of resistance to FHB and stripe rust pathogens prevalent in China. CONCLUSIONS: Thus, this study has determined that the chromosome 3St of E. repens harbors gene(s) highly resistant to FHB and stripe rust, and chromatin of 3St introgressed into wheat chromosomes completely presented the resistance, indicating the feasibility of using these translocation lines as novel material for breeding resistant wheat cultivars and alien gene mining.