Identification of seedling resistance to stem rust in advanced wheat lines and varieties from Pakistan

Authors: REHMAN, MONSIF - International Maize & Wheat Improvement Center (CIMMYT); Gale, Sam; Brown-Guedira, Gina; Jin, Yue; Marshall, David; Whitcher, Lynda; Williamson, Sharon; Rouse, Matthew; AHMAD, JAVED - Ayub Agricultural Research Institute; AHMAD, GULZAR - Cereal Crops Research Institute; SHAH, IRFAN - Cereal Crops Research Institute; SIAL, MAHBOOB - Nuclear Institute For Agriculture And Biology; RAUF, YAHYA - International Maize & Wheat Improvement Center (CIMMYT); RATTU, ATIQ - Ayub Agricultural Research Institute; WARD, RICHARD - International Maize & Wheat Improvement Center (CIMMYT); NADEEM, MAJID - Ayub Agricultural Research Institute; ULLAH, GHULAM - International Maize & Wheat Improvement Center (CIMMYT); IMTIAZ, MUHAMMAD - International Maize & Wheat Improvement Center (CIMMYT)

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/16/2019
Publication Date: 3/18/2020
Citation: Rehman, M.U., Gale, S.W., Brown-Guedira, G.L., Jin, Y., Marshall, D.S., Whitcher, L.C., Williamson, S.M., Rouse, M.N., Ahmad, J., Ahmad, G., Shah, I., Sial, M., Rauf, Y., Rattu, A., Ward, R.W., Nadeem, M., Ullah, G., Imtiaz, M. 2020. Identification of seedling resistance to stem rust in advanced wheat lines and varieties from Pakistan. Crop Science. 60:804–811. https://doi.org/10.1002/csc2.20056.
DOI: https://doi.org/10.1002/csc2.20056

Interpretive Summary: Stem rust is a major disease of wheat worldwide and new stem rust pathogen races including TTKSK (also known as Ug99) and its variants pose a serious threat to wheat production. The effectiveness and protection of new varieties against stem rust can be increased by identifying and combining several types of stem rust resistance genes (Sr). In this study we screened a set of 707 advanced wheat breeding lines and cultivars against 11 races under glass house conditions. Resistance to several virulent races were identified from this germplasm. Screening against North American races showed that most of the tested genotypes were resistant. These genotypes were screened with DNA markers to predict the presence of specific stem rust genes Sr2, Sr9a, Sr24, Sr25, Sr31, Sr36, Sr38 and Sr57. The highest frequency of Sr genes was observed for Sr57 (199 genotypes) followed by Sr31 (177 genotypes). Except for genotypes carrying Sr25 and/or Sr24 genes, most genotypes were susceptible to race TTKSK. Since Ug99 is spreading and overcoming Sr genes worldwide, including Sr24 and Sr36, a strategy to pyramid multiple Sr genes in released cultivars should be pursued to achieve a durable control of stem rust. Information from this study will be highly useful for breeders to develop resistance to Ug99 and other important stem rust races using adapted germplasm as sources of resistance and Sr36, a strategy to pyramid multiple Sr genes in released cultivars should be pursued to achieve a durable control of stem rust. Information from this study will be highly useful for breeders to develop resistance to Ug99 and other important stem rust races using adapted germplasm as sources of resistance.

Technical Abstract: Stem rust is a major disease of wheat worldwide and new Puccinia graminis f. sp. tritici, (Pgt) races including TTKSK (also known as Ug99) and its variants pose a serious threat to wheat production. The effectiveness and protection of new varieties against Pgt races can be increased by identifying and combining several types of stem rust resistance genes (Sr). In this study we screened a set of 707 advanced wheat breeding lines and cultivars against 11 Pgt races under glass house conditions. Most of the genotypes were evaluated for the first time for seedling resistance to the tested Pgt races. Of the tested genotypes, entries 99, 513, 289 and 515 exhibited low infection type (IT<3) to races TTKSK, TRTTF, TTTTF and RRTTF, respectively. Screening against North American Pgt races (QFCSC, QTHJC, MCCFC, RCRSC, RKQQC, TPMKC and QCCSM) showed that most of the tested genotypes were resistant. These genotypes were screened with eight DNA markers to predict the presence of stem rust genes Sr2, Sr9a, Sr24, Sr25, Sr31, Sr36, Sr38 and Sr57. Stem rust gene Sr36 was absent from all the tested genotypes whereas Sr9a was postulated to be present in only four genotypes. The marker Sr2_ger93p predicted the presence of Sr2 in 40 wheat genotypes and marker barc71 suggested the presence of Sr24 in 12 genotypes. Sr25 was predicted in 13 genotypes while Sr38 was postulated in 54 wheat genotypes. The highest frequency of Sr genes was observed for Sr57 (199 genotypes) followed by Sr31 (177 genotypes). Except for genotypes carrying Sr25 and/or Sr24 genes, most genotypes were susceptible to Pgt race TTKSK. Since Ug99 is spreading and overcoming Sr genes worldwide, including Sr24 and Sr36, a strategy to pyramid multiple Sr genes in released cultivars should be pursued to achieve a durable control of stem rust. Also, the effectiveness of genotypes such as NRL0902, 11050, B-2(RF)-11 and CCRI-6, found in the current study and which feature other Sr genes against Ug99, warrants further investigation to identify the source of their resistance and use it in Pakistan wheat breeding programs.