THE TRANSFER OF A POWDERY MILDEW RESISTANCE GENE FROM HORDEUM-BULBOSUM L TO BARLEY (HORDEUM-VULGARE L) CHROMOSOME-2(21)

Hordeum bulbosum L. is a source of disease resistance genes that would be worthwhile transferring to barley (H. vulgare L.). To achieve this objective, selfed seed from a tetraploid H. vulgar-e x H. bulbosum hy brid was irradiated. Subsequently, a powdery mildew-resistant selectio n of barley phenotype (81882/83) was identified among field-grown prog eny. Using molecular analyses, we have established that the H. bulbosu m DNA containing the powdery mildew resistance gene had been introgres sed into 81882/83 and is located on chromosome 2 (21). Resistant plant s have been backcrossed to barley to remove the adverse effects of a l inked factor conditioning triploid seed formation, but there remains a n association between powdery mildew resistance and non-pathogenic nec rotic leaf blotching. The dominant resistance gene is allelic to a gen e transferred from H. bulbosum by co-workers in Germany, but non-allel ic to all other known powdery mildew resistance genes in barley. We pr opose Mlhb as a gene symbol for this resistance.