GENETIC-STUDIES OF POWDERY MILDEW RESISTANCE IN COMMON OAT (AVENA-SATIVA L.) .1. CULTIVARS AND BREEDING LINES GROWN IN WESTERN-EUROPE AND NORTH-AMERICA

Common oat (Avena sativa L.) cultivars and breeding lines grown in Wes tern Europe and North America were tested against twelve Erysiphe gram inis f. sp. avenae mildew isolates collected in Germany and Denmark. T hese isolates were selected for their ability to produce differential response patterns permitting characterization of five oat mildew resis tance (OMR) groups. From a total of 259 cultivars and lines tested 173 accessions showed susceptible responses, 48 accessions were character ized by susceptible or intermediate responses and 38 accessions reveal ed isolate-specific resistance response patterns. Eight cultivars and lines had resistance patterns of OMR group 1, six cultivars of OMR gro up 2, and eleven cultivars of OMR group 3. Two cultivars, each possess ed resistance patterns corresponding to OMR groups 1 + 3 and 2 + 3 in combination, respectively. Three cultivars exhibited the response patt ern of OMR group 3 in association with an additional unknown resistanc e. Eight cultivars and lines showed a resistance response pattern not yet detected in the documented OMR groups.