[In Process Citation]
A complex cytophysiological study of the resistance of Aegilops speltoides K-389 and wheat-aegilops seedlings against Erysiphe graminis tritici was carried out. Ae. speltoides proved to be very resistant at the stage of pathogen penetration and endurant to the powdery mildew after infection. The wheat-aegilops lines had varying features of resistance against the powdery mildew but did not retain a sufficiently high resistance of Ae. speltoides at the stage of seedlings. Since the studied lines showed a high resistance in the field, their resistance appears to be determined by the genetic system of protection, predominantly at the adult stage. This should be taken into account when using Ae. Speltoides as a source of resistance by controlling the character of its expression not only at the adult state, but also at the stage of seedlings.