DIFFERENTIAL REACTION OF BARLEY GENOTYPES TO RHYNCHOSPORIUM-SECALIS

Spring barley cultivars currently grown in Germany are all more or les s susceptible to Rhynchosporium secalis (Oudem.) J.J. Davis, but there are obvious differences in the degree of susceptibility under field c onditions. Small genotypic differences may be caused by both genetic a nd environmental effects, respectively. To minimize the influence of e nvironmental variation on disease expression, several inoculation meth ods were developed in the present study. In two experiments the effect iveness of the inoculation by spraying of single spore isolates was te sted in the glasshouse and in the field, respectively. High infection levels were achieved in the glasshouse. Despite the infection of barle y in the field, disease expression levels remained low due to unfavour able conditions. Another experiment showed the usefulness of infected straw applied in the autumn only for testing the seedling infection ty pe of spring barley cultivars against R. secalis. Seedling assay score s 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 re sistance/susceptibility of spring barley cultivars against leaf blotch .