ABSTRACT 1998). Even though race-specific resistance has been Powdery mildew, caused by Blumeria graminis (DC.) E.O. Speer extensively used in wheat breeding programs, selection f. sp. tritici Em. Marchal (syn. Erysiphe graminis f. sp. tritici), is one pressure exerted by cultivars with race-specific resis-of the major diseases of wheat (Triticum aestivum L.) worldwide. tance genes results in the rapid build-up of pathotypes Race-specific resistance has been extensively used in wheat breeding with matching virulence genes. Subsequently, race-speprograms, even though it is ephemeral. Adult plant resistance (APR) to powdery mildew is more durable than race-specific resistance. The APR to powdery mildew in winter wheat cultivar Massey has remained effective since its release in 1981. A cross was made between Massey and a powdery mildew susceptible cultivar Becker. Powdery mildew severity on F-2 leaves (the second leaf below the flag leaf) of 180 F2:3 lines was rated under natural disease pressure in the field. Among 213 RFLP and 139 microsatellite markers surveyed, 88 (41%) cific resistance loses its effectiveness when confronted by pathotypes with matching virulence genes
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