Abstract
Race 21B of wheat leaf rust, Puccinia recondita Rob. ex Desm. f. sp. tritici Erikss., was found to have greater competitive ability than race 1A as cultured in mixtures on the wheat varieties Shinchunaga and Norin No.61 for 4 uredial generations. The superiority of race 21B was remarkable at low and moderate temperatures. The relative competitive ability of both races was found not to be influenced by the density of pustules on infected leaves. Pustules of race 21B grew faster than those of race 1A at low temperature. Under moderate and high temperatures race 21B was slightly faster than race 1A on the rust development.
