Race-specific expression of oat crown rust resistance conditioned by major and minor genes

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In the oat lines Pc 50–2 and Pc 50–4, identically resistant (infection type 0) to many crown rust isolates, an unusual difference in reaction to the Polish crown rust isolate 7–77P was found. Whereas Pc 50–4 was highly susceptible and severely affected, Pc 50–2 showed a reproducibly very low occurrence of resistant infection types (0; 1, 2). Genetic analyses of these lines to a rust isolate, avirulent to both lines, indicated that each of them contains a different major resistance gene. Furthermore, the crown rust resistance in Pc 50–2 was indicated to be influenced by a group of minor genes controlling the infection severity and the frequency of infection types when attacked with rust isolate 7–77P.