Abstract
Race 15B2-TLM of P. graminis f. sp. tritici produced significantly smaller colonies in seedlings of wheat accessions that rusted slowly, such as ''Thatcher'', than in seedlings of accessions that rusted rapidly, such as ''Prelude''. No significant differences in infectibility were noted in seedlings, but the rapidity with which uredia developed from flecks was significantly greater in seedlings of the fast-rusting accessions. Adult plants of slow-rusting wheats were significantly less receptive to the stem rust fungus than their fast-rusting counterparts.