GENETIC-STRUCTURE OF THE SCALD PATHOGEN (RHYNCHOSPORIUM-SECALIS) IN SOUTH EAST AUSTRALIA - IMPLICATIONS FOR CONTROL STRATEGIES

A survey of electrophoretic variation in 89 isolates of Rhynchosporium secalis collected from cultivated and wild barley grass in Victoria, New South Wales and Tasmania detected an average of 2.5 alleles at eac h of 11 loci in 5 enzyme systems. At five loci, two alleles each occur red at frequencies exceeding 0.2. Comparison of the frequency of allel es at these loci showed little association with host or geographic ori gin, pathogenicity of the isolates or with the allelic state at other loci. Given that this pathogen reproduces asexually only, this lack of association confirms previous suggestions that some means of asexual recombination is important in this pathogen. Furthermore, the results suggest that the most effective means whereby long-term control over R . secalis will be achieved is through the use of both pathotype-specif ic and field resistance complemented by other strategies like the use of fungicides and possibly varietal mixtures.