The Aegilops ventricosa 2NvS segment in bread wheat: Cytology, genomics and breeding

Authors: GAO, LIANGLIANG - Kansas State University; KOO, DAL-HOE - Kansas State University; JULIANA, PHILOMIN - International Maize & Wheat Improvement Center (CIMMYT); RIFE, TREVOR - Kansas State University; SINGH, DALJIT - Kansas State University; DA SILVA, CRISTIANO - Kansas State University; LUX, THOMAS - Helmholtz Centre; Dorn, Kevin; CLINESMITH, MARSHALL - Kansas State University; SILVA, PAULA - Kansas State University; WANG, XU - Kansas State University; SPANNAGL, MANUEL - Helmholtz Centre; MONAT, CECILE - Leibniz Institute; FRIEBE, BERND - Kansas State University; STEUERNAGEL, BURKHARD - John Innes Center; MUEHLBAUER, GARY - University Of Minnesota; POZNIAK, CURTIS - University Of Saskatchewan; SINGH, RAVI - International Maize & Wheat Improvement Center (CIMMYT); STEIN, NILS - Leibniz Institute; MASCHER, MARTIN - Leibniz Institute; FRITZ, ALLAN - Kansas State University; POLAND, JESSE - Kansas State University; WALKOWIAK, SEAN - University Of Saskatchewan

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2020
Publication Date: 11/12/2020
Citation: Gao, L., Koo, D., Juliana, P., Rife, T., Singh, D., Da Silva, C., Lux, T., Dorn, K.M., Clinesmith, M., Silva, P., Wang, X., Spannagl, M., Monat, C., Friebe, B., Steuernagel, B., Muehlbauer, G., Pozniak, C., Singh, R., Stein, N., Mascher, M., Fritz, A., Poland, J., Walkowiak, S. 2020. The Aegilops ventricosa 2NvS segment in bread wheat: Cytology, genomics and breeding. Theoretical and Applied Genetics. 134:529-542. https://doi.org/10.1007/s00122-020-03712-y.
DOI: https://doi.org/10.1007/s00122-020-03712-y

Interpretive Summary: Bread wheat is susceptible to many diseases and pests that can cause significant reductions to yield, including wheat blast, root knot nematode, stripe rust, leaf rust, and stem rust fungus. Wheat breeders have utilized genes transferred from wild relatives of wheat to develop more resistant varieties. Since the 1990s, a segment of the genome of a wheat wild relative, Aegilops ventricosa, has been bred into wheat to confer resistance to wheat blast. The sequence and gene content of this important segment of the A. ventricosa genome, known as the 2NS translocation, has never been fully characterized. In this study, the 2NS segment was assembled by sequencing the genomes of two wheat varieties known to carry this genomic region from A.ventricosa. A full characterization of the genes in this region was carried out to discover several candidate genes underlying the wheat blast resistance. The abundance of this 2NS segment in breeding populations was also determined using high throughput genotyping and showed an increasing frequency of use of this segment in wheat breeding, along with a positive impact on wheat grain yield.

Technical Abstract: The Aegilops ventricosa 2NS translocation segment has been utilized in breeding disease resistant wheat crops since the early 1990s. This segment is known to possess several important resistance genes against multiple wheat diseases including root knot nematode, stripe rust, leaf rust, and stem rust fungus. More recently, this segment was associated with resistance to wheat blast, an emerging and devastating wheat disease in South America and Asia. To date, full characterization of the fragment, including its size, gene contents and its association with grain yield is lacking. Here we present a complete cytological and physical characterization of this agronomically important translocation in bread wheat. We de novo assembled the 2NS segment in two wheat varieties, ‘Jagger’ and ‘CDC Stanley’ and delineated the segment to be approximately 33Mb. A total of 535 high confidence genes were annotated within the 2NS region with >10% belonging to the nucleotide-binding leucine rich repeat (NLR) gene families. Identification of groups of NLR genes that are potentially 2N genome-specific and expressed in specific tissues can fast-track testing of candidate genes playing roles in various disease resistance. We also show the increasing frequency of 2NS among spring and winter wheat breeding programs over a history of two and a half decades, and the positive impact of 2NS on wheat grain yield based on historical datasets. The significance of the 2NS segment in wheat breeding due to multiple disease resistance and a positive impact on yield, highlights the importance of understanding and characterizing the wheat pan-genome for better insights into molecular breeding.