Thermal Stability of Stem Rust Resistance in Oat Seedlings

Six of the identified genes for stem rust (Puccinia graminis Pers. f. sp. avenae Erikss. and Henn.) resistance in oats (Avena sativa L.) are divided into three categories of thermal sensitivity: resistance conferred by genes A and D is stable; that conferred by genes H and F 'breaks down' at intermediate temperatures; and that conferred by genes B and E breaks down at relatively low temperatures. Studies of oat lines carrying single or several resistance genes indicate that thermal sensitivity of the reactions conditioned by the genes conferring labile resistance is not affected by the presence of genes conferring stable resistance or by the rest of the host plant genotype. The critical temperature of breakdown varies with physiologic race.