Identification of winter habit bread wheat landraces in the national small grains collection with resistance to emerging stem rust pathogen variants

Authors: Gordon, Tyler; Jin, Yue; Gale, Sam; Rouse, Matthew - Matt; Stoxen, Samuel; WANYERA, RUTH - Kenya Agricultural And Livestock Research Organization; MACHARIA, GODWIN - Kenya Agricultural And Livestock Research Organization; RANDHAWA, MANDEEP - International Maize & Wheat Improvement Center (CIMMYT); BHAVANI, SRIDHAR - International Maize & Wheat Improvement Center (CIMMYT); Brown-Guedira, Gina; Marshall, David; Babiker, Ebrahiem; Bockelman, Harold; Bonman, John

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2021
Publication Date: 7/7/2021
Citation: Gordon, T.C., Jin, Y., Gale, S.W., Rouse, M.N., Stoxen, S.M., Wanyera, R., Macharia, G., Randhawa, M., Bhavani, S., Brown Guedira, G.L., Marshall, D.S., Babiker, E.M., Bockelman, H.E., Bonman, J.M. 2021. Identification of winter habit bread wheat landraces in the national small grains collection with resistance to emerging stem rust pathogen variants. Plant Disease. 105(12):3998-4005. https://doi.org/10.1094/PDIS-04-21-0743-RE.
DOI: https://doi.org/10.1094/PDIS-04-21-0743-RE

Interpretive Summary: Wheat stem rust caused by Puccinia graminis f. sp. tritici (Pgt) is a widespread and devastating disease of wheat. Emerging Pgt variants including Ug99 are rapidly overcoming major gene resistance deployed in wheat cultivars and threaten global wheat production. New sources of race-nonspecific resistance are urgently needed to address this threat. The National Small Grains Collection (NSGC) contains thousands of wheat landrace accessions that may harbor unique and broadly effective sources of resistance to emerging variants. In this study, 9,192 winter habit bread wheat landrace accessions were evaluated for their reaction to U.S. Pgt variants in a field nursery in St. Paul, MN. Accessions that were resistant in St. Paul were tested in a field nursery in Njoro, Kenya against emerging variants of Pgt including Ug99. Additionally, St. Paul resistant accessions were tested as seedlings with up to 13 Pgt variants, including Ug99, and 19 molecular markers linked with known stem rust resistance genes or genes associated with modern breeding practices. Forty-five accessions were identified that were resistant in both U.S. and Kenya field nurseries and lacked markers linked with known stem rust resistance genes. These 45 accessions with possible new sources of race-nonspecific resistance will be prioritized for further study.

Technical Abstract: Wheat stem rust caused by Puccinia graminis f. sp. tritici (Pgt) is a widespread and recurring threat to wheat production. Emerging Pgt variants are rapidly overcoming major gene resistance deployed in wheat cultivars and new sources of race-nonspecific resistance are urgently needed. The National Small Grains Collection (NSGC) contains thousands of wheat landrace accessions that may harbor unique and broadly effective sources of resistance to emerging Pgt variants. All NSGC available facultative and winter-habit bread wheat landraces were tested in a field nursery in St. Paul, MN against a bulk collection of six common U.S. Pgt races. Infection response, and severity data were collected on 9,192 landrace accessions at the soft-dough stage and resistant accessions were derived from single spikes. Derived accessions were tested in St. Paul a second time to confirm resistance and in a field nursery in Njoro, Kenya against emerging races of Pgt with virulence to many known resistance genes including Sr24, Sr31, Sr38, and SrTmp. Accessions resistant in the St. Paul field were also tested at the seedling stage with up to 13 Pgt races, including TTKSK and TKTTF, and 19 molecular markers linked with known stem rust resistance genes or genes associated with modern breeding practices. Forty-five accessions were resistant in both U.S. and Kenya field nurseries and lacked alleles linked with known stem rust resistance genes. Accessions with either moderate or strong resistance in the U.S. and Kenya field nurseries and with novel seedling resistance will be prioritized for further study.