Genetic diversity for random amplified polymorphic DNA (RAPD) markers in two Swedish populations of Pyrenophora teres

The genetic structure in two Swedish populations of Pyrenophora teres, caus al agent of net blotch of barley, is described. Each of the two populations consisted of 64 monoconidial isolates, hierarchically sampled in a farmers ' field of cv. Golf and a field of cv. Svani. The two fields were located i n western Sweden. 20 km apart. Isolates were obtained from infected barley leaves sampled at eight sites in each held. Three random amplified polymorp hic DNA (RAPD) primers, with a total of 19 reproducible loci, were used fro m the initial screening of 70 RAPD primers. The variation for the RAPD mark ers was large in both populations, resulting in mean gene diversities of 0. 182 and 0.216, respectively. The total gene diversity was 0.236 and 0.253, respectively, The differentiation among sampling sites was relatively high with coefficient of gene differentiation values of 0.219 and 0.180 for the two fields, but only 5.3% of the variation was due to differentiation betwe en the two populations. A phenogram based on genetic distances among sites also illustrates that the variation is distributed on a small scale. No cle ar differentiation between fields or among sites was revealed. A very low l evel of gametic disequilibrium was found. A raised level of disequilibrium in the P. teres cv. Svani population indicated an effect of asexual reprodu ction. The overall pattern of the genomic structure is that of a random mat ing sexual species.