Molecular cytogenetic identification of new wheat-rye 6R, 6RS, and 6RL addition lines with resistance to stripe rust and powdery mildew

Enrichment and Diversification of the Wheat Genome via Alien Introgression

Wheat, including durum and common wheat, respectively, is an allopolyploid with two or three homoeologous subgenomes originating from diploid wild ancestral species. The wheat genome's polyploid origin consisting of just three diploid ancestors has constrained its genetic variation, which has bottlenecked improvement. However, wheat has a large number of relatives, including cultivated crop species (e.g., barley and rye), wild grass species, and ancestral species. Moreover, each ancestor and relative has many other related subspecies that have evolved to inhabit specific geographic areas. Cumulatively, they represent an invaluable source of genetic diversity and variation available to enrich and diversify the wheat genome. The ancestral species share one or more homologous genomes with wheat, which can be utilized in breeding efforts through typical meiotic homologous recombination. Additionally, genome introgressions of distant relatives can be moved into wheat using chromosome engineering-based approaches that feature induced meiotic homoeologous recombination. Recent advances in genomics have dramatically improved the efficacy and throughput of chromosome engineering for alien introgressions, which has served to boost the genetic potential of the wheat genome in breeding efforts. Here, we report research strategies and progress made using alien introgressions toward the enrichment and diversification of the wheat genome in the genomics era.

Development of novel wheat-rye 6RS small fragment translocation lines with powdery mildew resistance and physical mapping of the resistance gene PmW6RS

KEY MESSAGE

Novel wheat-rye 6RS small fragment translocation lines with powdery mildew resistance were developed, and the resistance gene PmW6RS was physically mapped onto 6RS-0.58-0.66-bin corresponding to 18.38 Mb in Weining rye. Rye (Secale cereale L., RR) contains valuable genes for wheat improvement. However, most of the rye resistance genes have not been successfully used in wheat cultivars. Identification of new rye resistance genes and transfer of these genes to wheat by developing small fragment translocation lines will make these genes more usable for wheat breeding. In this study, a broad-spectrum powdery mildew resistance gene PmW6RS was localized on rye chromosome arm 6RS using a new set of wheat-rye disomic and telosomic addition lines. To further study and use PmW6RS, 164 wheat-rye 6RS translocation lines were developed by 60Coγ-ray irradiation. Seedling and adult stage powdery mildew resistance analysis showed that 106 of the translocation lines were resistant. A physical map of 6RS was constructed using the 6RS translocation and deletion lines, and PmW6RS was localized in the 6RS-0.58-0.66-bin, flanked by markers X6RS-3 and X6RS-10 corresponding to the physical interval of 50.23-68.61 Mb in Weining rye genome. A total of 23 resistance-related genes were annotated. Nine markers co-segregate with the 6RS-0.58-0.66-bin, which can be used to rapidly trace the 6RS fragment carrying PmW6RS. Small fragment translocation lines with powdery mildew resistance were backcrossed with wheat cultivars, and 39 agronomically acceptable homozygous 6RS small fragment translocation lines were obtained. In conclusion, this study not only provides novel gene source and germplasms for wheat resistance breeding, but also laid a solid foundation for cloning of PmW6RS.

Transfer of the Resistance to Multiple Diseases from a Triticum-Secale-Thinopyrum Trigeneric Hybrid to Ningmai 13 and Yangmai 23 Wheat Using Specific Molecular Markers and GISH

The middle to lower reaches of the Yangtze River are China's second largest area for wheat production; wheat disease is more serious there than in other areas because of the high humidity and warm weather. However, most cultivated varieties are susceptible to Fusarium head blight (FHB), powdery mildew, and stripe rust, and the lack of disease-resistant germplasm is an obstacle in wheat breeding. Rye and Thinopyrum elongatum, related species of wheat, carry many genes involved in disease resistance. In this study, a trigeneric hybrid, YZU21, with resistance to FHB, powdery mildew, and stripe rust was used to improve two major wheat cultivars, Ningmai 13 (NM13) and Yangmai 23 (YM23). Specific molecular markers and GISH were used to identify hybrid progenies. Five addition or substitution lines and one translocation line of the Triticum-Secale-Thinopyrum trigeneric hybrid were obtained and evaluated for agronomic traits and the resistance to multiple diseases. The results showed that the six trigeneric hybrid lines had desirable agronomic traits and improved resistance to FHB, powdery mildew, and stripe rust; they might be used as parents in wheat breeding for the resistance to multiple disease.