A study has been made of the resistance of Oro and a derived crossbred, Orfed, to one race of Tilletia caries and three races of Tilletia foetida. Rapier and Dirk were used as the susceptible parents in crosses with Oro and Orfed respectively. Two methods were used in the genetic analysis of resistance to the four races. The frequency distribution of bunt infection in segregating F3 populations from the cross Oro X Rapier indicated that inheritance was not simple and this was confirmed by the fact that it was possible to select a number of strains exhibiting marked differential reactions to the four physiologic races. Some selections had an overall resistance greater than that of the Oro parent. In a backcross programme with Orfed as the donor parent and Dirk as the recurrent parent, it was possible to select strains with a resistance superior to that of Orfed. In both series of crosses, selections were secured which possessed a high resistance to races L.1 and L.14, and at the same time a high degree of susceptibility to races T.5 and L.3.

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