The stem rust resistance gene Rpg1 has conferred durable resistance in barley (Hordeum vulgare) to Puccinia graminis f. sp. tritici (wheat stem rust pathogen) for nearly 50 yr in the northern Great Plains. Detection of Rpg1 at the seedling stage can be difficult because most barley genotypes show mesothetic reactions to the stem rust pathogen. Genotypes with and without genes for stem rust resistance were inoculated with pathotypes Pgt-TPM, -MCC, and -HPH of P. g. tritici in the seedling stage. After 12 days of incubation at 25-28 C, infection types were assessed on plants. With pathotype TPM, differences between barley genotypes with and without resistance genes were not distinct, since similar infection types were frequently observed on genotypes in both groups (.)
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Brian J. Steffenson (1993) studied this question.