Characterization of Stem Rust Resistance in Wheat Cultivar Gage

Wheat (Triticum spp.) stem rust, caused by Puccinia graminis f. sp. tritici Eriks. and E. Henn. (Pgt), re-emerged as a devastating disease of wheat because of virulent race Ug99 (TTKSK). Many bread wheat (T. aestivum L.) cultivars grown in North America are susceptible to Ug99 or its derivative races that carry additional virulence. ‘Gage’ was released in 1963 mainly for its excellent field resistance to leaf rust (caused by Puccinia triticina Eriks) and stem rust. However, Gage's resistance has not been genetically characterized, which would facilitate its use in breeding programs. To better define the nature of the resistance in Gage, we created an F2 population and the corresponding F2:3 and F4:5 families from crosses between Gage and stem rust susceptible cultivar ‘Bill Brown’. Inheritance of resistance to Pgt race QFCSC and molecular marker analysis indicated that Sr2 and additional genes explain the stem rust resistance of Gage. Using seedling plant infection types from the F2, F2:3, and F4:5 families, we found that at least one dominant and, most likely, one recessive gene are involved in Gage's resistance. Seedling resistance genes acted independently of Sr2 since Sr2 is effective only at the adult plant stage.