Differential Reaction of Barley Genotypes to Rhynchosporium secalis

Spring barley cultivars currently grown in Germany are all more or less susceptible to Rhynchosporium secalis (Oudem.) J.J. Davis, but there are obvious differences in the degree of susceptibility under field conditions. Small genotypic differences may be caused by both genetic and environmental effects, respectively. To minimize the influence of environmental variation on disease expression, several inoculation methods were developed in the present study. In two experiments the effectiveness of the inoculation by spraying of single spore isolates was tested in the glasshouse and in the field, respectively. High infection levels were achieved in the glasshouse. Despite the infection of barley in the field, disease expression levels remained low due to unfavourable conditions. Another experiment showed the usefulness of infected straw applied in the autumn only for testing the seedling infection type of spring barley cultivars against R, secalis. Seedling assay scores and field infection levels were closely related (r = 0.796, P < 0.01; r = 0.911, P < 0.001). Therefore, both the spray infection technique in the glasshouse and the inoculation technique using infected straw in the field appear to be suitable to detect genetic differences in resistance/susceptibility of spring barley cultivars against leaf blotch.