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.