LAUSR

Abstract. Powdery mildew caused by the fungus Blumeria graminis f. sp. hordei (Bgh) is a global disease of barley, and the wild subspecies Hordeum vulgare subsp. spontaneum (Hvs) is the closest relative of cultivated barley (H. vulgare subsp. vulgare). The responses to the pathogen of 363 Hvs accessions maintained by the International Center for Agricultural Research in the Dry Areas (ICARDA) gene bank were assessed. Thirty non-Israeli pathogen isolates representing the global pathogenic diversity were used for testing. Because of genetic heterogeneity within 146 accessions, the results from only 217 accessions are presented and discussed. Additional tests on 152 accessions with homogeneous responses in earlier tests were made by using six Israeli pathogen isolates. There were 154 resistance phenotypes among the set, 141 of which involved single accessions. The six most frequent phenotypes were recorded for 62 accessions, with the most frequent phenotype in 26 accessions that were resistant to all 30 non-Israeli Bgh isolates. The second most frequent phenotype, found in 16 accessions, was susceptible to all 30 non-Israeli isolates. The occurrence of specific resistance was high. The occurrence of specific resistance was high and for breeding barley cultivars the effective resistances can be combined with the resistance gene mlo. In such combinations, the mlo gene prevents rapid increase in the pathogen population from overcoming the given specific resistance, whereas the resistance gene will simultaneously prevent erosion of mlo resistance. A more effective method for achieving durable resistance is accumulation minor resistance genes that are also widely distributed in wild barley.