Observed segregation for reaction to stem rust in several oat crosses was on a monohybrid basis except in the cross Sac x Hajira-Joanette where segregation was observed to be on a three-factor basis. A mesothetic type of reaction to the composite of races 2 and 8 was observed in seedling plants classified as susceptible in two crosses, Mindo x Tama and Sac x Hajira-Joanette. Since no segregation was observed for reaction to race 2 in either of the two crosses, one factor pair for resistance to race 8 must be allelic to the one governing resistance to race 2 possessed by Tama and Hajira x Joanette.

Segregation for reaction to races 1 and 45 of crown rust was on a monogenic, digenic or trigenic basis in different crosses investigated. Five different factors for resistance to crown rust were identified in this study: A and B, complementary dominant factors which give the Bond type (type 0) of resistance of race 1; L, a simple dominant which gives the Landhafer type of resistance (type 0-1) to races 1 and 45; S, a simple dominant from Santa Fe which governs resistance (type 0) to races 1 and 45; and V, a simple dominant of the hypersensitive type (type 2) from Victoria which also governs resistance to races 1 and 45. The factor from Santa Fe (S) appears to be of great promise as a source of resistance to the relatively prevalent race 45. Many desirable agronomic progenies possessing resistance to races 1 and 45 from the cross of Santa Fe x Clinton have been selected for further testing. Very few selections have been made from Mindo x Landhafer for testing in F₄. The L factor does not appear to be too satisfactory under the conditions of this experiment for resistance in the mature plant stage.