RESISTANCE TO BARLEY SCALD (RHYNCHOSPORIUM-SECALIS) IN WILD BARLEY GRASS (HORDEUM-GLAUCUM AND HORDEUM-LEPORINUM) POPULATIONS IN SOUTH-EASTERN AUSTRALIA

Plants from 22 wild barley grass populations, 10 Hordeum glaucum, 11 H ordeum leporinum, and one mixed population, were inoculated with seven isolates of Rhynchosporium secalis originally collected from H. lepor inum plants. There was substantial variability for resistance within a nd among populations from both Hordeum species, but H. glaucum was on average more resistant than H. leporinum. Individual populations often responded differentially to the R. secalis isolates, being resistant to some isolates and susceptible to others. Differential responses wer e more pronounced among H. glaucum populations. No consistent geograph ic correlations between level of resistance within a population and ge ographic location were found, indicating that large scale trends for r esistance do not exist in either H. glaucum or H. leporinum. The exist ence of widespread resistance variation in both wild barley grasses ma y create substantial selection pressures favouring tile emergence of v ariability for pathogenicity in R. secalis, which would complicate eff orts to breed for R. secalis resistance in cultivated barley.