Net Blotch: Seedlings of 21 differential barley genotypes and six six-row Nordic spring barleys were inoculated in the greenhouse with conidial suspensions of twenty single-spore isolates of Pyrenophora teres. Analysis of infection responses indicated that all isolates, taken from 11 sites in Finland, were pathogenic but differed in aggressiveness which appeared to be partly conditioned by the host barley from which the isolate derived; those from Arve (highly susceptible) being, on average, higher than those from Pohto (less susceptible). Genotypes CI9819 and CI7548 were highly resistant to all P. teres isolates, and all genotypes of the differential series were more resistant than the Nordic genotypes. The six Nordic genotypes were examined in the field, in small plots and in hill plots, during two seasons, where it was established that there were genotypic differences in quantitative resistance of adult plants. Genotypes H6221 and WW7977 were significantly more resistant than Arve, Agneta, Arttu and Pohto. This resistance also was demonstrated as differences in AUDPCs and terminal severities, and was reflected in differences in yield and some yield components.

Scald: Seedlings of a differential barley series containing a range of major resistance genes against Rhynchosporium secalis, and six six-row Nordic spring barleys were inoculated in the greenhouse with single-spore isolates deriving from three host barleys and four sites. Resistance also was monitored in the field on adult plants. All seedlings and adult plants of the differential series, with the exception of CI1179 as a seedling and CI7565 as an adult plant, showed resistance to all R. secalis isolates, which did however differ in aggressiveness. The Nordic genotypes were all susceptible to all isolates as adult plants and as seedlings, although differences in degree of susceptibility were apparent. In additional experiments, isolates of R. secalis from rye and couch grass were demonstrated not to be pathogenic on barley, and R. secalis isolates from Canadian barleys behaved similarly to those from Finland, with the exception of their being slightly less aggressive. Disease development and components of yield were assessed in the Nordic genotypes in the field over two years, as for the net blotch experiments. Results were not as unequivocal as for net blotch, but Arve was consistently susceptible; Verner and Pokko appeared the most resistant, and Loviisa, JO1599 and Pohto were intermediate.