MOLECULAR MARKER ANALYSIS OF EUROPEAN SETOSPHAERIA-TURCICA POPULATIONS

Setosphaeria turcica is the causal agent of northern corn leaf blight, a foliar maize disease of worldwide economic importance. In Europe, i ts severity increases. To investigate the pathogen's population-geneti c structure in central Europe, a total of 80 isolates was sampled in G ermany, Switzerland, France, Austria, and Hungary and investigated wit h 52 random amplified polymorphic DNA (RAPD) markers. The mating type of the isolates was determined in testcrosses. Among the 73 isolates f rom maize there were 26 different RAPD haplotypes. All isolates with i dentical haplotype are considered clonemates. The haplotype shared by most members was represented by 22 isolates from Germany, Switzerland, and France, indicating high fitness and substantial migration. Only a single clone had members in both southeastern Austria and southwester n Switzerland, suggesting that the Alps constitute a major barrier for this pathogen. Several haplotypes differed by only one or two RAPD ba nds from the predominant haplotype and may have arisen by mutation. Fe w other clonal lineages were detected. The evolution of some haplotype s could not be explained by mutation alone. Sexual recombination may r arely occur. In population samples from Germany, Switzerland, and Fran ce, mating type MAT2 was predominating, while most isolates from Austr ia and Hungary had MAT1. Seven isolates from Johnson grass (Sorghum ha lepense), an alternative host of S. turcica, were clonemates and very different in RAPD haplotypes from all isolates collected from maize.