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Title: Dissection of the multigenic wheat stem rust resistance present in the Montenegrin spring wheat accession PI 362698

item Zurn, Jason
item Rouse, Matthew
item Chao, Shiaoman
item AOUN, MERIEM - North Dakota State University
item MACHARIA, GODWIN - Kenya Agricultural And Livestock Research Organization
item HIEBERT, COLIN - Agriculture And Agri-Food Canada
item PRETORIUS, ZACHARIAS - University Of The Free State
item Bonman, John
item ACEVEDO, MARICELIS - Cornell University

Submitted to: BMC Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2018
Publication Date: 1/22/2018
Citation: Zurn, J.D., Rouse, M.N., Chao, S., Aoun, M., Macharia, G., Hiebert, C.W., Pretorius, Z.A., Bonman, J.M., Acevedo, M. 2018. Dissection of the multigenic wheat stem rust resistance present in the Montenegrin spring wheat accession PI 362698. BMC Genomics. 19:67.

Interpretive Summary: A new race of the wheat stem rust pathogen emerged in Africa in 1999 that could cause disease on approximately 90% of global wheat varieties. Since 1999, this pathogen has constantly changed adapting to the resistant wheat varieties grown in Africa. To combat the looming threat posed by wheat stem rust, wheat varieties which have not been used in modern breeding are being evaluated to identify resistance. During a recent evaluation the highly resistant Montenegrin wheat varietiy PI 362698 was identified. Preliminary analysis of PI 362698 suggested multiple resistance genes were present in the variety. To identify which genes were responsible for resistance, a genetic maping experiment was conducted. Geneitc maping identified five regions associated with resistance that likely correspond to the resistance genes Sr5, Sr8a, Sr12, Sr15, and Sr16. Additionally, the resistance gene Sr57 is thought to be present based on diagnostic DNA testing. Interestingly, the broadly resistant Canadian variety 'Thatcher' is thought to have many of the same resistance genes. Future work is needed to determine why this combination of genes provides durable resistance.

Technical Abstract: Research to identify and characterize stem rust resistance genes in common wheat, Triticum aestivum, has been stimulated by the emergence of Ug99-lineage races of the wheat stem rust pathogen, Puccinia graminis f. sp. tritici (Pgt), in Eastern Africa. The Montenegrin spring wheat landrace PI 362698 was identified as a source of Pgt resistance. This accession exhibits resistance to multiple Ug99-lineage and North American Pgt races at seedling and adult-plant stages. A recombinant inbred population was developed by crossing the susceptible line LMPG-6 with a single plant selection of PI 362698. Quantitative trait locus (QTL) mapping using the Illumina iSelect 90K wheat assay identified five significant QTLs (a = 0.05) on chromosomes 2B, 3B, 6A, 6D, and 7A associated with Pgt resistance. The QTL on chromosome 3B was identified using both field data from Kenya (Ug99-lineage races) and seedling data from race MCCF. This QTL potentially corresponds to Sr12 or a new allele of Sr12. The multi-pathogen resistance gene Sr57 located on chromosome 7D is present in PI 362698 according to the diagnostic markers csLv34 and wMAS000003, however a significant QTL was not detected at this locus. The QTLs on chromosomes 2B, 6A, and 6D were identified during seedling trials and are thought to correspond to Sr16, Sr8a, and Sr5, respectively. The QTL identified on chromosome 7A was detected using MCCF seedling data and may be Sr15 or a potentially novel allele of recently detected Ug99 resistance QTLs. Interestingly, the combination of resistance QTLs found in PI 362698 is like the resistance gene combination present in the broadly resistant cultivar Thatcher. Additional, work will be needed to fully understand why these genes provide such durable resistance in combination.