POWDERY MILDEW RESISTANCE IN BARLEY LANDRACE MATERIAL .1. SCREENING FOR RESISTANCE

A total of 4,681 accessions of Hordeum vulgare landrace material from Ethiopia, East Mediterranean, Near East, Nepal and China were sown in the field and subjected to the natural powdery mildew epidemic in Denm ark. Apparently resistant accessions were selected. Selfed progeny fro m them were retested and reselected in subsequent years at four locati ons in Denmark. Finally, 16 promising donors of resistance were retain ed. They were characterized in the field and tested in the seedling st age for reaction to up to 72 different isolates of the powdery mildew fungus. The absence of the corresponding virulences in the Danish airb orne powdery mildew population was ascertained in five years. The resi stances in the 16 donors are apparently mutually different and from kn own sources of powdery mildew resistance in barley.