Reaction of European spring barley varieties to a population of the net blotch fungus

About 320 European spring barley varieties and about 40 spring barley lines were tested in the field for reaction to a local population of the spot fo rm of the net blotch fungus Pyrenophora teres forma maculata with the imper fect stage Drechslera ter es. The European barley varieties showed a wide r ange of disease reactions, from nearly resistant to very susceptible. At le ast three groups of genetically related barley varieties could be distingui shed: (1) 'Agneta' and 'Clermont', (2) 'Nordal' and 'Arve', and (3) 'Tellus ', 'Pamina', 'Albert' and 'Birka'. The parentages of these three groups of barley are mutually distantly related and may thus constitute three differe nt sources of resistance to the pathogen population used. The range of dise ase reaction is similar in Varieties from different European countries but it differs among different breeding stations. The relatively high level of resistance is fairly uniformly distributed in contemporary barley varieties all over most of Western Europe. Over time, from about 1830-1982, the aver age level of resistance varied around 4.0 (scale value) (from 2.8 to 4.8). However, since about 1940 the variation in disease reaction has become much wider (from 1.8 to 6.9) for unknown reason(s).