PATHOGENICITY OF RHYNCHOSPORIUM-SECALIS ISOLATES FROM NORWAY ON 30 CULTIVARS OF BARLEY

The pathogenic variability of the barley scald fungus, Rhynchosporium secalis, in central Norway was examined in 1994. The climate in this r egion is usually cold and wet during the growing season of spring barl ey. Leaf blotch is prevalent and causes significant yield losses. Fort y-two isolates of the fungus, from naturally infected spring barley in four counties, were differentiated into 32 pathotypes by the standard differential set for R. secalis. All pathotypes were complex and had virulence for nine to 22 differentials. The cultivar Osiris was resist ant to all isolates tested. The cultivars C.I.8162, Hudson, Atlas 46 a nd C.I.3515 were resistant to the majority of the isolates. Several di fferentials with various resistance genes were susceptible to up to 10 0% of the isolates. Isolates were derived from local cultivars with no known resistance genes, suggesting that R. secalis populations in cen tral Norway are characterized by it high degree of seemingly unnecessa ry pathogenicity. Because of the great variability and complexity of t he pathotypes, traditional breeding methods using single major genes a re not likely to be effective in central Norway.